MATPOWER Manual

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MATPOWER-manual

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MATP WER
User’s Manual
Version 7.0b1
Ray D. Zimmerman Carlos E. Murillo-S´anchez
October 31, 2018
©2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018 Power Systems Engineering Research Center (PSerc)
All Rights Reserved
Contents
1 Introduction 10
1.1 Background ................................ 10
1.2 License and Terms of Use ........................ 11
1.3 Citing Matpower ............................ 12
1.4 Matpower Development ........................ 12
2 Getting Started 13
2.1 System Requirements ........................... 13
2.2 Getting Matpower ........................... 14
2.2.1 Versioned Releases ........................ 14
2.2.2 Current Development Version .................. 14
2.3 Installation ................................ 16
2.4 Running a Simulation ........................... 18
2.4.1 Preparing Case Input Data .................... 18
2.4.2 Solving the Case ......................... 18
2.4.3 Accessing the Results ....................... 19
2.4.4 Setting Options .......................... 20
2.5 Documentation .............................. 20
3 Modeling 23
3.1 Data Formats ............................... 23
3.2 Branches .................................. 23
3.3 Generators ................................. 25
3.4 Loads ................................... 25
3.5 Shunt Elements .............................. 26
3.6 Network Equations ............................ 26
3.7 DC Modeling ............................... 27
4 Power Flow 30
4.1 AC Power Flow .............................. 30
4.2 DC Power Flow .............................. 32
4.3 Distribution Power Flow ......................... 32
4.3.1 Radial Power Flow ........................ 33
4.3.2 Current Summation Method ................... 34
4.3.3 Power Summation Method .................... 35
4.3.4 Admittance Summation Method ................. 35
4.3.5 Handling PV Buses ........................ 37
4.4 runpf ................................... 38
4.5 Linear Shift Factors ............................ 39
5 Continuation Power Flow 43
5.1 Parameterization ............................. 44
5.2 Predictor .................................. 44
5.3 Corrector ................................. 45
5.4 Step Length Control ........................... 45
5.5 Event Detection and Location ...................... 46
5.6 runcpf ................................... 47
5.6.1 CPF Callback Functions ..................... 50
5.6.2 CPF Example ........................... 53
6 Optimal Power Flow 56
6.1 Standard AC OPF ............................ 56
6.1.1 Cartesian vs. Polar Coordinates for Voltage .......... 57
6.1.2 Current vs. Power for Nodal Balance Constraints ....... 58
6.2 Standard DC OPF ............................ 59
6.3 Extended OPF Formulation ....................... 60
6.3.1 User-defined Variables ...................... 61
6.3.2 User-defined Constraints ..................... 61
6.3.3 User-defined Costs ........................ 62
6.4 Standard Extensions ........................... 64
6.4.1 Piecewise Linear Costs ...................... 64
6.4.2 Dispatchable Loads ........................ 66
6.4.3 Generator Capability Curves ................... 68
6.4.4 Branch Angle Difference Limits ................. 69
6.5 Solvers ................................... 69
6.6 runopf ................................... 70
7 Extending the OPF 76
7.1 Direct Specification ............................ 76
7.1.1 User-defined Variables ...................... 76
7.1.2 User-defined Constraints ..................... 76
7.1.3 User-defined Costs ........................ 78
7.1.4 Additional Comments ...................... 79
7.2 Callback Functions ............................ 79
7.2.1 User-defined Variables ...................... 80
7.2.2 User-defined Costs ........................ 80
2
7.2.3 User-defined Constraints ..................... 81
7.3 Callback Stages and Example ...................... 82
7.3.1 ext2int Callback ......................... 83
7.3.2 formulation Callback ...................... 84
7.3.3 int2ext Callback ......................... 88
7.3.4 printpf Callback ......................... 91
7.3.5 savecase Callback ........................ 93
7.4 Registering the Callbacks ......................... 95
7.5 Summary ................................. 97
7.6 Example Extensions ........................... 97
7.6.1 Fixed Zonal Reserves ....................... 97
7.6.2 Interface Flow Limits ....................... 99
7.6.3 DC Transmission Lines ...................... 100
7.6.4 OPF Soft Limits ......................... 103
8 Unit De-commitment Algorithm 110
9 Miscellaneous Matpower Functions 112
9.1 Input/Output Functions ......................... 112
9.1.1 loadcase ............................. 112
9.1.2 savecase ............................. 112
9.1.3 cdf2mpc .............................. 113
9.1.4 psse2mpc ............................. 113
9.1.5 save2psse ............................. 114
9.2 System Information ............................ 114
9.2.1 case info ............................. 114
9.2.2 compare case ........................... 114
9.2.3 find islands ........................... 115
9.2.4 get losses ............................ 115
9.2.5 margcost ............................. 116
9.2.6 isload ............................... 116
9.2.7 loadshed ............................. 116
9.2.8 printpf .............................. 116
9.2.9 total load ............................ 117
9.2.10 totcost .............................. 117
9.3 Modifying a Case ............................. 117
9.3.1 extract islands ......................... 117
9.3.2 load2disp ............................. 118
3
9.3.3 modcost .............................. 118
9.3.4 scale load ............................ 118
9.3.5 apply changes .......................... 119
9.3.6 savechgtab ............................ 122
9.4 Conversion between External and Internal Numbering ......... 123
9.4.1 ext2int,int2ext ......................... 123
9.4.2 e2i data,i2e data ........................ 123
9.4.3 e2i field,i2e field ...................... 124
9.5 Forming Standard Power Systems Matrices ............... 125
9.5.1 makeB ............................... 125
9.5.2 makeBdc .............................. 125
9.5.3 makeJac .............................. 125
9.5.4 makeLODF ............................. 126
9.5.5 makePTDF ............................. 126
9.5.6 makeYbus ............................. 126
9.6 Miscellaneous ............................... 127
9.6.1 define constants ........................ 127
9.6.2 feval w path ........................... 127
9.6.3 have fcn ............................. 127
9.6.4 mpopt2qpopt ........................... 128
9.6.5 mpver ............................... 129
9.6.6 nested struct copy ....................... 129
10 Acknowledgments 130
Appendix A MIPS – Matpower Interior Point Solver 131
A.1 Example 1 ................................. 133
A.2 Example 2 ................................. 135
A.3 Quadratic Programming Solver ..................... 137
A.4 Primal-Dual Interior Point Algorithm .................. 138
A.4.1 Notation .............................. 138
A.4.2 Problem Formulation and Lagrangian .............. 139
A.4.3 First Order Optimality Conditions ............... 140
A.4.4 Newton Step ........................... 141
Appendix B Data File Format 144
Appendix C Matpower Options 150
C.1 Mapping of Old-Style Options to New-Style Options .......... 166
4
Appendix D Matpower Files and Functions 170
D.1 Directory Layout and Documentation Files ............... 170
D.2 Matpower Functions .......................... 172
D.3 Example Matpower Cases ....................... 184
D.4 Automated Test Suite .......................... 187
Appendix E Extras Directory 191
Appendix F “Smart Market” Code 193
F.1 Handling Supply Shortfall ........................ 195
F.2 Example .................................. 195
F.3 Smartmarket Files and Functions .................... 200
Appendix G Optional Packages 201
G.1 BPMPD MEX – MEX interface for BPMPD .............. 201
G.2 CLP – COIN-OR Linear Programming ................. 201
G.3 CPLEX – High-performance LP and QP Solvers ............ 202
G.4 GLPK – GNU Linear Programming Kit ................ 203
G.5 Gurobi – High-performance LP and QP Solvers ............ 203
G.6 Ipopt – Interior Point Optimizer .................... 204
G.7 KNITRO – Non-Linear Programming Solver .............. 205
G.8 MINOPF – AC OPF Solver Based on MINOS ............. 206
G.9 MOSEK – High-performance LP and QP Solvers ........... 206
G.10 Optimization Toolbox – LP, QP, NLP and MILP Solvers . . . . . . . 207
G.11 PARDISO – Parallel Sparse Direct and Multi-Recursive Iterative Lin-
ear Solvers ................................. 207
G.12 SDP PF – Applications of a Semidefinite Programming Relaxation of
the Power Flow Equations ........................ 208
G.13 TSPOPF – Three AC OPF Solvers by H. Wang ............ 208
Appendix H Release History 210
H.1 Pre 1.0 – released Jun 25, 1997 ..................... 210
H.2 Version 1.0 – released Sep 17, 1997 ................... 210
H.3 Version 1.0.1 – released Sep 19, 1997 .................. 210
H.4 Version 2.0 – released Dec 24, 1997 ................... 211
H.5 Version 3.0 – released Feb 14, 2005 ................... 212
H.6 Version 3.2 – released Sep 21, 2007 ................... 213
H.7 Version 4.0 – released Feb 7, 2011 .................... 215
H.8 Version 4.1 – released Dec 14, 2011 ................... 218
5
H.9 Version 5.0 – released Dec 17, 2014 ................... 219
H.10 Version 5.1 – released Mar 20, 2015 ................... 224
H.11 Version 6.0 – released Dec 16, 2016 ................... 227
H.12 Version 7.0 – beta 1 released released Oct 31, 2018 ........... 232
References 240
6
List of Figures
3-1 Branch Model ............................... 24
4-1 Oriented Ordering ............................ 33
4-2 Branch Representation: branch kbetween buses i(sending) and k
(receiving) and load demand and shunt admittances at both buses . . 34
5-1 Nose Curve of Voltage Magnitude at Bus 9 ............... 53
6-1 Relationship of wito rifor di= 1 (linear option) ............ 63
6-2 Relationship of wito rifor di= 2 (quadratic option) ......... 64
6-3 Constrained Cost Variable ........................ 65
6-4 Marginal Benefit or Bid Function .................... 66
6-5 Total Cost Function for Negative Injection ............... 67
6-6 Generator P-QCapability Curve .................... 68
7-1 Adding Constraints Across Subsets of Variables ............ 87
7-2 DC Line Model .............................. 101
7-3 Equivalent “Dummy” Generators .................... 101
7-4 Feasible Region for Branch Flow Violation Constraints ........ 104
List of Tables
4-1 Power Flow Results ............................ 39
4-2 Power Flow Options ........................... 40
4-3 Power Flow Output Options ....................... 41
5-1 Continuation Power Flow Results .................... 48
5-2 Continuation Power Flow Options .................... 49
5-3 Continuation Power Flow Callback Input Arguments ......... 51
5-4 Continuation Power Flow Callback Output Arguments ........ 52
5-5 Continuation Power Flow State ..................... 52
6-1 Optimal Power Flow Results ....................... 71
6-2 Optimal Power Flow Solver Options ................... 73
6-3 Other OPF Options ............................ 74
6-4 OPF Output Options ........................... 75
7-1 User-defined Nonlinear Constraint Specification ............ 78
7-2 Names Used by Implementation of OPF with Reserves ........ 83
7-3 Results for User-Defined Variables, Constraints and Costs ....... 89
7-4 Callback Functions ............................ 97
7-5 Input Data Structures for Fixed Zonal Reserves ............ 98
7-6 Output Data Structures for Fixed Zonal Reserves ........... 98
7
7-7 Input Data Structures for Interface Flow Limits ............ 99
7-8 Output Data Structures for Interface Flow Limits ........... 100
7-9 Soft Limit Formulation .......................... 105
7-10 Input Data Structures for OPF Soft Limits ............... 106
7-11 Default Soft Limit Values ........................ 107
7-12 Possible Hard-Limit Modifications .................... 107
7-13 Output Data Structures for OPF Soft Limits .............. 108
9-1 Columns of chgtab ............................ 120
9-2 Values for CT TABLE Column ....................... 120
9-3 Values for CT CHGTYPE Column ...................... 121
9-4 Values for CT COL Column ........................ 121
A-1 Input Arguments for mips ........................ 132
A-2 Output Arguments for mips ....................... 133
A-3 Options for mips ............................. 134
B-1 Bus Data (mpc.bus)............................ 145
B-2 Generator Data (mpc.gen)........................ 146
B-3 Branch Data (mpc.branch)........................ 147
B-4 Generator Cost Data (mpc.gencost)................... 148
B-5 DC Line Data (mpc.dcline)....................... 149
C-1 Top-Level Options ............................ 152
C-2 Power Flow Options ........................... 153
C-3 Continuation Power Flow Options .................... 154
C-4 OPF Solver Options ........................... 155
C-5 General OPF Options .......................... 156
C-6 Power Flow and OPF Output Options ................. 157
C-7 OPF Options for MIPS .......................... 158
C-8 OPF Options for CLP .......................... 158
C-9 OPF Options for CPLEX ........................ 159
C-10 OPF Options for fmincon ........................ 160
C-11 OPF Options for GLPK ......................... 160
C-12 OPF Options for Gurobi ......................... 161
C-13 OPF Options for Ipopt ......................... 161
C-14 OPF Options for KNITRO ........................ 162
C-15 OPF Options for MINOPF ........................ 163
C-16 OPF Options for MOSEK ........................ 164
C-17 OPF Options for PDIPM ......................... 165
C-18 OPF Options for TRALM ........................ 165
C-19 Old-Style to New-Style Option Mapping ................ 166
8
D-1 Matpower Directory Layout and Documentation Files . . . . . . . 171
D-2 Top-Level Simulation Functions ..................... 172
D-3 Input/Output Functions ......................... 172
D-4 Data Conversion Functions ........................ 173
D-5 Power Flow Functions .......................... 173
D-6 Continuation Power Flow Functions ................... 174
D-7 OPF and Wrapper Functions ...................... 175
D-8 OPF Model Objects ........................... 176
D-9 Deprecated @opt model Methods ..................... 177
D-10 OPF Solver Functions .......................... 177
D-11 Other OPF Functions ........................... 178
D-12 OPF User Callback Functions ...................... 179
D-13 Power Flow Derivative Functions .................... 179
D-14 NLP, LP & QP Solver Functions .................... 180
D-15 Matrix Building Functions ........................ 181
D-16 Utility Functions ............................. 182
D-17 Other Functions .............................. 183
D-18 Small Transmission System Test Cases ................. 184
D-19 Small Radial Distribution System Test Cases .............. 184
D-20 ACTIV Synthetic Grid Test Cases .................... 185
D-21 Polish System Test Cases ......................... 185
D-22 PEGASE European System Test Cases ................. 186
D-23 RTE French System Test Cases ..................... 186
D-24 Automated Test Functions from MP-Test ................ 187
D-25 MIPS Tests ................................ 187
D-26 Test Data ................................. 188
D-27 Miscellaneous Matpower Tests ..................... 189
D-28 Matpower OPF Tests ......................... 190
F-1 Auction Types .............................. 194
F-2 Generator Offers ............................. 196
F-3 Load Bids ................................. 196
F-4 Generator Sales .............................. 199
F-5 Load Purchases .............................. 199
F-6 Smartmarket Files and Functions .................... 200
9
MATP WER
1 Introduction
1.1 Background
Matpower [1] is a package of Matlab®M-files for solving power flow and optimal
power flow problems. It is intended as a simulation tool for researchers and educators
that is easy to use and modify. Matpower is designed to give the best performance
possible while keeping the code simple to understand and modify. The Matpower
website can be found at:
http://www.pserc.cornell.edu/matpower/
Matpower was initially developed by Ray D. Zimmerman, Carlos E. Murillo-
anchez and Deqiang Gan of PSerc1at Cornell University under the direction of
Robert J. Thomas. The initial need for Matlab-based power flow and optimal power
flow code was born out of the computational requirements of the PowerWeb project2.
Many others have contributed to Matpower over the years and it continues to be
developed and maintained under the direction of Ray Zimmerman.
Beginning with version 6, Matpower includes a framework for solving general-
ized steady-state electric power scheduling problems. This framework is known as
MOST, for Matpower Optimal Scheduling Tool [2,3].
MOST can be used to solve problems as simple as a deterministic, single pe-
riod economic dispatch problem with no transmission constraints or as complex as
a stochastic, security-constrained, combined unit-commitment and multiperiod op-
timal power flow problem with locational contingency and load-following reserves,
ramping costs and constraints, deferrable demands, lossy storage resources and un-
certain renewable generation.
MOST is documented separately from the main Matpower package in its own
manual, the MOST User’s Manual.
1http://pserc.org/
2http://www.pserc.cornell.edu/powerweb/
10
1.2 License and Terms of Use
Beginning with version 5.1, the code in Matpower is distributed under the 3-clause
BSD license3[5]. The full text of the license can be found in the LICENSE file at
the top level of the distribution or at http://www.pserc.cornell.edu/matpower/
LICENSE.txt and reads as follows.
Copyright (c) 1996-2016, Power Systems Engineering Research Center
(PSERC) and individual contributors (see AUTHORS file for details).
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. Neither the name of the copyright holder nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
3Versions 4.0 through 5.0 of Matpower were distributed under version 3.0 of the GNU General
Public License (GPL) [6] with an exception added to clarify our intention to allow Matpower to
interface with Matlab as well as any other Matlab code or MEX-files a user may have installed,
regardless of their licensing terms. The full text of the GPL can be found at http://www.gnu.
org/licenses/gpl-3.0.txt.Matpower versions prior to version 4 had their own license.
11
Please note that the Matpower case files distributed with Matpower are not
covered by the BSD license. In most cases, the data has either been included with
permission or has been converted from data available from a public source.
1.3 Citing Matpower
While not required by the terms of the license, we do request that publications derived
from the use of Matpower explicitly acknowledge that fact by citing reference [1].
R. D. Zimmerman, C. E. Murillo-S´anchez, and R. J. Thomas, “Matpower: Steady-
State Operations, Planning and Analysis Tools for Power Systems Research and Ed-
ucation,” Power Systems, IEEE Transactions on, vol. 26, no. 1, pp. 12–19, Feb. 2011.
DOI: 10.1109/TPWRS.2010.2051168
Similarly, we request that publications derived from the use of MOST explicitly
acknowledge that fact by citing both the main Matpower reference above and
reference [2]:
C. E. Murillo-S´anchez, R. D. Zimmerman, C. L. Anderson, and R. J. Thomas, “Secure
Planning and Operations of Systems with Stochastic Sources, Energy Storage and
Active Demand,” Smart Grid, IEEE Transactions on, vol. 4, no. 4, pp. 2220–2229,
Dec. 2013.
DOI: 10.1109/TSG.2013.2281001
1.4 Matpower Development
Following the release of Matpower 6.0, the Matpower project moved to an open
development paradigm, hosted on the Matpower GitHub project page:
https://github.com/MATPOWER/matpower
The Matpower GitHub project hosts the public Git code repository as well
as a public issue tracker for handling bug reports, patches, and other issues and
contributions. There are separate GitHub hosted repositories and issue trackers for
Matpower, MOST, MIPS and the testing framework used by all of them, MP-Test,
all available from https://github.com/MATPOWER/.
12
2 Getting Started
2.1 System Requirements
To use Matpower 7.0b1 you will need:
Matlab®version 7.3 (R2006b) or later4, or
GNU Octave version 4 or later5
See Section 2.1 in the MOST User’s Manual for any requirements specific to
MOST.
For the hardware requirements, please refer to the system requirements for the
version of Matlab6or Octave that you are using. If the Matlab Optimization
Toolbox is installed as well, Matpower enables an option to use it to solve optimal
power flow problems.
In this manual, references to Matlab usually apply to Octave as well. At the
time of writing, none of the optional MEX-based Matpower packages have been
built for Octave, but Octave does typically include GLPK.
4Matlab is available from The MathWorks, Inc. (http://www.mathworks.com/). Mat-
power 5 and Matpower 6 required Matlab 7 (R14), Matpower 4 required Matlab 6.5 (R13),
Matpower 3.2 required Matlab 6 (R12), Matpower 3.0 required Matlab 5 and Matpower 2.0
and earlier required only Matlab 4. Matlab is a registered trademark of The MathWorks, Inc.
5GNU Octave [4] is free software, available online at http://www.gnu.org/software/octave/.
Matpower 5 and Matpower 6 required Octave 3.4, Matpower 4 required Octave 3.2.
6http://www.mathworks.com/support/sysreq/previous_releases.html
13
2.2 Getting Matpower
You can either download an official versioned release or you can obtain the current
development version, which we also attempt to keep stable enough for everyday use.
The development version includes new features and bug fixes added since the last
versioned release.
2.2.1 Versioned Releases
Download the ZIP file of the latest official versioned release from the Mat-
power website7.
Go to the Matpower website.
Click the Download Now button.
2.2.2 Current Development Version
There are also two options for obtaining the most recent development version of
Matpower from the master branch on GitHub.
1. Clone the Matpower repository from GitHub.
From the command line:
git clone https://github.com/MATPOWER/matpower.git
Or, from the Matpower GitHub repository page8:
Click the green Clone or download button, then Open in Desk-
top.
Use this option if you want to be able to easily update to the current development
release, with the latest bug fixes and new features, using a simple git pull
command, or if you want to help with testing or development. This requires
that you have a Git client9(GUI or command-line) installed.
2. Download a zip file of the Matpower repository from GitHub.
Go to the Matpower GitHub repository page.
7http://www.pserc.cornell.edu/matpower/
8https://github.com/MATPOWER/matpower
9See https://git-scm.com/downloads for information on downloading Git clients.
14
Click the green Clone or download button, then Download ZIP.
Use this option if you need features or fixes introduced since the latest versioned
release, but you do not have access to or are not ready to begin using Git (but
don’t be afraid to give Git a try).10
See CONTRIBUTING.md for information on how to get a local copy of your own
Matpower fork, if you are interesting in contributing your own code or modifica-
tions.
10A good place to start is https://git-scm.com.
15
2.3 Installation
Installation and use of Matpower requires familiarity with the basic operation of
Matlab or Octave. Make sure you follow the installation instructions for the version
of Matpower you are installing. The process was simplified with an install script
following version 6.0.
Step 1: Get a copy of Matpower as described above.
Clone the repository or download and extract the ZIP file of the Mat-
power distribution and place the resulting directory in the location of
your choice and call it anything you like.11 We will use <MATPOWER>
as a placeholder to denote the path to this directory (the one containing
install matpower.m). The files in <MATPOWER>should not need to be
modified, so it is recommended that they be kept separate from your own
code.
Step 2: Run the installer.
Open Matlab or Octave and change to the <MATPOWER>directory.
Run the installer and follow the directions to add the required directories
to your Matlab or Octave path, by typing:
install matpower
Step 3: That’s it. There is no step 3.
But, if you chose not to have the installer run the test suite for you in step 2,
you can run it now to verify that Matpower is installed and functioning
properly, by typing:12
test matpower
The result should resemble the following, possibly including extra tests,
depending on the availablility of optional packages, solvers and extras.
11Do not place Matpower’s files in a directory named 'matlab'or 'optim'(both case-
insensitive), as these can cause Matlab’s built-in ver command to behave strangely in ways that
affect Matpower.
12The MOST test suite is run separately by typing test most. See the MOST User’s Manual for
details.
16
>> test_matpower
t_test_fcns.............ok
t_nested_struct_copy....ok
t_feval_w_path..........ok
t_mpoption..............ok
t_loadcase..............ok
t_ext2int2ext...........ok
t_jacobian..............ok
t_hessian...............ok
t_margcost..............ok
t_totcost...............ok
t_modcost...............ok
t_hasPQcap..............ok
t_mplinsolve............ok (6 of 44 skipped)
t_mips..................ok
t_mips_pardiso..........ok (60 of 60 skipped)
t_qps_matpower..........ok (288 of 360 skipped)
t_miqps_matpower........ok (240 of 240 skipped)
t_pf....................ok
t_pf_radial.............ok
t_cpf...................ok
t_islands...............ok
t_opf_model.............ok
t_opf_model_legacy......ok
t_opf_default...........ok
t_opf_mips..............ok (278 of 1296 skipped)
t_opf_dc_mips...........ok
t_opf_dc_mips_sc........ok
t_opf_userfcns..........ok
t_opf_softlims..........ok
t_runopf_w_res..........ok
t_dcline................ok
t_get_losses............ok
t_load2disp.............ok
t_makePTDF..............ok
t_makeLODF..............ok
t_printpf...............ok
t_vdep_load.............ok
t_total_load............ok
t_scale_load............ok
t_apply_changes.........ok
t_psse..................ok
t_off2case..............ok
t_auction_mips..........ok
t_runmarket.............ok
All tests successful (7961 passed, 872 skipped of 8833)
Elapsed time 29.39 seconds. 17
2.4 Running a Simulation
The primary functionality of Matpower is to solve power flow and optimal power
flow (OPF) problems. This involves (1) preparing the input data defining the all of
the relevant power system parameters, (2) invoking the function to run the simulation
and (3) viewing and accessing the results that are printed to the screen and/or saved
in output data structures or files.
2.4.1 Preparing Case Input Data
The input data for the case to be simulated are specified in a set of data matrices
packaged as the fields of a Matlab struct, referred to as a “Matpower case” struct
and conventionally denoted by the variable mpc. This struct is typically defined in a
case file, either a function M-file whose return value is the mpc struct or a MAT-file
that defines a variable named mpc when loaded13. The main simulation routines,
whose names begin with run (e.g. runpf,runopf), accept either a file name or a
Matpower case struct as an input.
Use loadcase to load the data from a case file into a struct if you want to make
modifications to the data before passing it to the simulation.
>> mpc = loadcase(casefilename);
See also savecase for writing a Matpower case struct to a case file.
The structure of the Matpower case data is described a bit further in Section 3.1
and the full details are documented in Appendix Band can be accessed at any time
via the command help caseformat. The Matpower distribution also includes many
example case files listed in Table D-18.
2.4.2 Solving the Case
The solver is invoked by calling one of the main simulation functions, such as runpf
or runopf, passing in a case file name or a case struct as the first argument. For
example, to run a simple Newton power flow with default options on the 9-bus system
defined in case9.m, at the Matlab prompt, type:
>> runpf('case9');
13This describes version 2 of the Matpower case format, which is used internally and is the
default. The version 1 format, now deprecated, but still accessible via the loadcase and savecase
functions, defines the data matrices as individual variables rather than fields of a struct, and some
do not include all of the columns defined in version 2.
18
If, on the other hand, you wanted to load the 30-bus system data from case30.m,
increase its real power demand at bus 2 to 30 MW, then run an AC optimal power
flow with default options, this could be accomplished as follows:
>> define_constants;
>> mpc = loadcase('case30');
>> mpc.bus(2, PD) = 30;
>> runopf(mpc);
The define constants in the first line is simply a convenience script that defines a
number of variables to serve as named column indices for the data matrices. In this
example, it allows us to access the “real power demand” column of the bus matrix
using the name PD without having to remember that it is the 3rd column.
Other top-level simulation functions are available for running DC versions of
power flow and OPF, for running an OPF with the option for Matpower to shut
down (decommit) expensive generators, etc. These functions are listed in Table D-2
in Appendix D.
2.4.3 Accessing the Results
By default, the results of the simulation are pretty-printed to the screen, displaying
a system summary, bus data, branch data and, for the OPF, binding constraint
information. The bus data includes the voltage, angle and total generation and load
at each bus. It also includes nodal prices in the case of the OPF. The branch data
shows the flows and losses in each branch. These pretty-printed results can be saved
to a file by providing a filename as the optional 3rd argument to the simulation
function.
The solution is also stored in a results struct available as an optional return value
from the simulation functions. This results struct is a superset of the Matpower
case struct mpc, with additional columns added to some of the existing data fields
and additional fields. The following example shows how simple it is, after running a
DC OPF on the 118-bus system in case118.m, to access the final objective function
value, the real power output of generator 6 and the power flow in branch 51.
>> define_constants;
>> results = rundcopf('case118');
>> final_objective = results.f;
>> gen6_output = results.gen(6, PG);
>> branch51_flow = results.branch(51, PF);
19
Full documentation for the content of the results struct can be found in Sec-
tions 4.4 and 6.6.
2.4.4 Setting Options
Matpower has many options for selecting among the available solution algorithms,
controlling the behavior of the algorithms and determining the details of the pretty-
printed output. These options are passed to the simulation routines as a Matpower
options struct. The fields of the struct have names that can be used to set the
corresponding value via the mpoption function. Calling mpoption with no arguments
returns the default options struct, the struct used if none is explicitly supplied.
Calling it with a set of name and value pairs modifies the default vector.
For example, the following code runs a power flow on the 300-bus example in
case300.m using the fast-decoupled (XB version) algorithm, with verbose printing of
the algorithm progress, but suppressing all of the pretty-printed output.
>> mpopt = mpoption('pf.alg', 'FDXB', 'verbose', 2, 'out.all', 0);
>> results = runpf('case300', mpopt);
To modify an existing options struct, for example, to turn the verbose option off
and re-run with the remaining options unchanged, simply pass the existing options
as the first argument to mpoption.
>> mpopt = mpoption(mpopt, 'verbose', 0);
>> results = runpf('case300', mpopt);
See Appendix Cor type:
>> help mpoption
for more information on Matpower’s options.
2.5 Documentation
There are four primary sources of documentation for Matpower. The first is
this manual, which gives an overview of Matpower’s capabilities and structure
and describes the modeling and formulations behind the code. It can be found in
your Matpower distribution at <MATPOWER>/docs/MATPOWER-manual.pdf and the
latest version is always available at: http://www.pserc.cornell.edu/matpower/
MATPOWER-manual.pdf.
20
Secondly, the MOST User’s Manual describes MOST and its problem formulation,
features, data formats and options. It is located at <MATPOWER>/docs/MOST-manual.pdf
in your Matpower distribution and the latest version is also available online at:
http://www.pserc.cornell.edu/matpower/MOST-manual.pdf.
The Matpower Online Function Reference is the third source of documen-
tation, allowing you to view not only the help text, but also the code itself for
each Matpower function directly from a web browser. It is available online at:
http://www.pserc.cornell.edu/matpower/docs/ref
Last, but certainly not least, is the built-in help command. As with Matlab’s
built-in functions and toolbox routines, you can type help followed by the name of
a command or M-file to get help on that particular function. Nearly all of Mat-
power’s M-files have such documentation and this should be considered the main
reference for the calling options for each individual function. See Appendix Dfor a
list of Matpower functions.
As an example, the help for runopf looks like:
21
>> help runopf
RUNOPF Runs an optimal power flow.
[RESULTS, SUCCESS] = RUNOPF(CASEDATA, MPOPT, FNAME, SOLVEDCASE)
Runs an optimal power flow (AC OPF by default), optionally returning
a RESULTS struct and SUCCESS flag.
Inputs (all are optional):
CASEDATA : either a MATPOWER case struct or a string containing
the name of the file with the case data (default is 'case9')
(see also CASEFORMAT and LOADCASE)
MPOPT : MATPOWER options struct to override default options
can be used to specify the solution algorithm, output options
termination tolerances, and more (see also MPOPTION).
FNAME : name of a file to which the pretty-printed output will
be appended
SOLVEDCASE : name of file to which the solved case will be saved
in MATPOWER case format (M-file will be assumed unless the
specified name ends with '.mat')
Outputs (all are optional):
RESULTS : results struct, with the following fields:
(all fields from the input MATPOWER case, i.e. bus, branch,
gen, etc., but with solved voltages, power flows, etc.)
order - info used in external <-> internal data conversion
et - elapsed time in seconds
success - success flag, 1 = succeeded, 0 = failed
(additional OPF fields, see OPF for details)
SUCCESS : the success flag can additionally be returned as
a second output argument
Calling syntax options:
results = runopf;
results = runopf(casedata);
results = runopf(casedata, mpopt);
results = runopf(casedata, mpopt, fname);
results = runopf(casedata, mpopt, fname, solvedcase);
[results, success] = runopf(...);
Alternatively, for compatibility with previous versions of MATPOWER,
some of the results can be returned as individual output arguments:
[baseMVA, bus, gen, gencost, branch, f, success, et] = runopf(...);
Example:
results = runopf('case30');
See also RUNDCOPF, RUNUOPF. 22
3 Modeling
Matpower employs all of the standard steady-state models typically used for power
flow analysis. The AC models are described first, then the simplified DC models. In-
ternally, the magnitudes of all values are expressed in per unit and angles of complex
quantities are expressed in radians. Internally, all off-line generators and branches
are removed before forming the models used to solve the power flow or optimal power
flow problem. All buses are numbered consecutively, beginning at 1, and generators
are reordered by bus number. Conversions to and from this internal indexing is done
by the functions ext2int and int2ext. The notation in this section, as well as Sec-
tions 4and 6, is based on this internal numbering, with all generators and branches
assumed to be in-service. Due to the strengths of the Matlab programming lan-
guage in handling matrices and vectors, the models and equations are presented here
in matrix and vector form.
3.1 Data Formats
The data files used by Matpower are Matlab M-files or MAT-files which define
and return a single Matlab struct. The M-file format is plain text that can be edited
using any standard text editor. The fields of the struct are baseMVA,bus,branch,gen
and optionally gencost, where baseMVA is a scalar and the rest are matrices. In the
matrices, each row corresponds to a single bus, branch, or generator. The columns
are similar to the columns in the standard IEEE CDF and PTI formats. The number
of rows in bus,branch and gen are nb,nland ng, respectively. If present, gencost
has either ngor 2ngrows, depending on whether it includes costs for reactive power
or just real power. Full details of the Matpower case format are documented
in Appendix Band can be accessed from the Matlab command line by typing
help caseformat.
3.2 Branches
All transmission lines14, transformers and phase shifters are modeled with a com-
mon branch model, consisting of a standard πtransmission line model, with series
impedance zs=rs+jxsand total charging susceptance bc, in series with an ideal
phase shifting transformer. The transformer, whose tap ratio has magnitude τand
14This does not include DC transmission lines. For more information the handling of DC trans-
mission lines in Matpower, see Section 7.6.3.
23
phase shift angle θshift, is located at the from end of the branch, as shown in Fig-
ure 3-1. The parameters rs,xs,bc,τand θshift are specified directly in columns BR R
(3), BR X (4), BR B (5), TAP (9) and SHIFT (10), respectively, of the corresponding row
of the branch matrix.15
The complex current injections ifand itat the from and to ends of the branch,
respectively, can be expressed in terms of the 2 ×2 branch admittance matrix Ybr
and the respective terminal voltages vfand vt
if
it=Ybr vf
vt.(3.1)
With the series admittance element in the πmodel denoted by ys= 1/zs, the branch
admittance matrix can be written
Ybr =ys+jbc
21
τ2ys1
τejθshift
ys1
τejθshift ys+jbc
2.(3.2)
Figure 3-1: Branch Model
If the four elements of this matrix for branch iare labeled as follows:
Yi
br =yi
ff yi
ft
yi
tf yi
tt (3.3)
then four nl×1 vectors Yff ,Yft,Ytf and Ytt can be constructed, where the i-th element
of each comes from the corresponding element of Yi
br. Furthermore, the nl×nbsparse
15A value of zero in the TAP column indicates that the branch is a transmission line and not a
transformer, i.e. mathematically equivalent to a transformer with tap ratio set to 1.
24
connection matrices Cfand Ctused in building the system admittance matrices can
be defined as follows. The (i, j)th element of Cfand the (i, k)th element of Ctare
equal to 1 for each branch i, where branch iconnects from bus jto bus k. All other
elements of Cfand Ctare zero.
3.3 Generators
A generator is modeled as a complex power injection at a specific bus. For generator i,
the injection is
si
g=pi
g+jqi
g.(3.4)
Let Sg=Pg+jQgbe the ng×1 vector of these generator injections. The MW and
MVAr equivalents (before conversion to p.u.) of pi
gand qi
gare specified in columns
PG (2) and QG (3), respectively of row iof the gen matrix. A sparse nb×nggenerator
connection matrix Cgcan be defined such that its (i, j)th element is 1 if generator j
is located at bus iand 0 otherwise. The nb×1 vector of all bus injections from
generators can then be expressed as
Sg,bus =Cg·Sg.(3.5)
A generator with a negative injection can also be used to model a dispatchable load.
3.4 Loads
Constant power loads are modeled as a specified quantity of real and reactive power
consumed at a bus. For bus i, the load is
si
d=pi
d+jqi
d(3.6)
and Sd=Pd+jQddenotes the nb×1 vector of complex loads at all buses. The
MW and MVAr equivalents (before conversion to p.u.) of pi
dand qi
dare specified in
columns PD (3) and QD (4), respectively of row iof the bus matrix. These fields can
also take on negative quantities to represent fixed (e.g. distributed) generation.
Constant impedance and constant current loads are not implemented directly,
but the constant impedance portions can be modeled as a shunt element described
below. Dispatchable loads are modeled as negative generators and appear as negative
values in Sg.
25
3.5 Shunt Elements
A shunt connected element such as a capacitor or inductor is modeled as a fixed
impedance to ground at a bus. The admittance of the shunt element at bus iis given
as
yi
sh =gi
sh +jbi
sh (3.7)
and Ysh =Gsh +jBsh denotes the nb×1 vector of shunt admittances at all buses.
The parameters gi
sh and bi
sh are specified in columns GS (5) and BS (6), respectively,
of row iof the bus matrix as equivalent MW (consumed) and MVAr (injected) at a
nominal voltage magnitude of 1.0 p.u and angle of zero.
A shunt element can also be used to model a constant impedance load and, though
correctly, Matpower does not currently report these quantities as “load”.
3.6 Network Equations
For a network with nbbuses, all constant impedance elements of the model are
incorporated into a complex nb×nbbus admittance matrix Ybus that relates the
complex nodal current injections Ibus to the complex node voltages V:
Ibus =YbusV. (3.8)
Similarly, for a network with nlbranches, the nl×nbsystem branch admittance
matrices Yfand Ytrelate the bus voltages to the nl×1 vectors Ifand Itof branch
currents at the from and to ends of all branches, respectively:
If=YfV(3.9)
It=YtV. (3.10)
If [ ·] is used to denote an operator that takes an n×1 vector and creates the
corresponding n×ndiagonal matrix with the vector elements on the diagonal, these
system admittance matrices can be formed as follows:
Yf= [Yff ]Cf+ [Yf t]Ct(3.11)
Yt= [Ytf ]Cf+ [Ytt]Ct(3.12)
Ybus =Cf
TYf+Ct
TYt+ [Ysh].(3.13)
The current injections of (3.8)–(3.10) can be used to compute the corresponding
26
complex power injections as functions of the complex bus voltages V:
Sbus(V) = [V]I
bus = [V]Y
busV(3.14)
Sf(V) = [CfV]I
f= [CfV]Y
fV(3.15)
St(V) = [CtV]I
t= [CtV]Y
tV.(3.16)
The nodal bus injections are then matched to the injections from loads and generators
to form the AC nodal power balance equations, expressed as a function of the complex
bus voltages and generator injections in complex matrix form as
gS(V, Sg) = Sbus(V) + SdCgSg= 0.(3.17)
3.7 DC Modeling
The DC formulation [17] is based on the same parameters, but with the following
three additional simplifying assumptions.
Branches can be considered lossless. In particular, branch resistances rsand
charging capacitances bcare negligible:
ys=1
rs+jxs1
jxs
, bc0.(3.18)
All bus voltage magnitudes are close to 1 p.u.
viejθi.(3.19)
Voltage angle differences across branches are small enough that
sin(θfθtθshift)θfθtθshift.(3.20)
Substituting the first set of assumptions regarding branch parameters from (3.18),
the branch admittance matrix in (3.2) approximates to
Ybr 1
jxs1
τ21
τejθshift
1
τejθshift 1.(3.21)
Combining this and the second assumption with (3.1) yields the following approxi-
mation for if:
if1
jxs
(1
τ2ejθf1
τejθshift ejθt)
=1
jxsτ(1
τejθfej(θt+θshift)).(3.22)
27
The approximate real power flow is then derived as follows, first applying (3.19) and
(3.22), then extracting the real part and applying (3.20).
pf=<{sf}
=<vf·i
f
≈ <ejθf·j
xsτ(1
τejθfej(θt+θshift))
=<j
xsτ1
τej(θfθtθshift)
=<1
xsτsin(θfθtθshift) + j1
τcos(θfθtθshift)
1
xsτ(θfθtθshift) (3.23)
As expected, given the lossless assumption, a similar derivation for the power injec-
tion at the to end of the line leads to leads to pt=pf.
The relationship between the real power flows and voltage angles for an individual
branch ican then be summarized as
pf
pt=Bi
br θf
θt+Pi
shift (3.24)
where
Bi
br =bi11
1 1 ,
Pi
shift =θi
shiftbi1
1
and biis defined in terms of the series reactance xi
sand tap ratio τifor branch ias
bi=1
xi
sτi.
For a shunt element at bus i, the amount of complex power consumed is
si
sh =vi(yi
shvi)
ejθi(gi
sh jbi
sh)ejθi
=gi
sh jbi
sh.(3.25)
28
So the vector of real power consumed by shunt elements at all buses can be approx-
imated by
Psh Gsh.(3.26)
With a DC model, the linear network equations relate real power to bus voltage
angles, versus complex currents to complex bus voltages in the AC case. Let the
nl×1 vector Bff be constructed similar to Yff , where the i-th element is biand let
Pf,shift be the nl×1 vector whose i-th element is equal to θi
shiftbi. Then the nodal
real power injections can be expressed as a linear function of Θ, the nb×1 vector of
bus voltage angles
Pbus(Θ) = BbusΘ + Pbus,shift (3.27)
where
Pbus,shift = (CfCt)TPf,shift.(3.28)
Similarly, the branch flows at the from ends of each branch are linear functions of
the bus voltage angles
Pf(Θ) = BfΘ + Pf,shift (3.29)
and, due to the lossless assumption, the flows at the to ends are given by Pt=Pf.
The construction of the system Bmatrices is analogous to the system Ymatrices
for the AC model:
Bf= [Bff ] (CfCt) (3.30)
Bbus = (CfCt)TBf.(3.31)
The DC nodal power balance equations for the system can be expressed in matrix
form as
gP, Pg) = BbusΘ + Pbus,shift +Pd+Gsh CgPg= 0 (3.32)
29
4 Power Flow
The standard power flow or loadflow problem involves solving for the set of voltages
and flows in a network corresponding to a specified pattern of load and generation.
Matpower includes solvers for both AC and DC power flow problems, both of
which involve solving a set of equations of the form
g(x) = 0,(4.1)
constructed by expressing a subset of the nodal power balance equations as functions
of unknown voltage quantities.
All of Matpower’s solvers exploit the sparsity of the problem and, except for
Gauss-Seidel, scale well to very large systems. Currently, none of them include any
automatic updating of transformer taps or other techniques to attempt to satisfy
typical optimal power flow constraints, such as generator, voltage or branch flow
limits.
4.1 AC Power Flow
In Matpower, by convention, a single generator bus is typically chosen as a refer-
ence bus to serve the roles of both a voltage angle reference and a real power slack.
The voltage angle at the reference bus has a known value, but the real power gen-
eration at the slack bus is taken as unknown to avoid overspecifying the problem.
The remaining generator buses are typically classified as PV buses, with the values
of voltage magnitude and generator real power injection given. These are specified
in the VG (6) and PG (3) columns of the gen matrix, respectively. Since the loads Pd
and Qdare also given, all non-generator buses are classified as PQ buses, with real
and reactive injections fully specified, taken from the PD (3) and QD (4) columns of
the bus matrix. Let Iref ,IPV and IPQ denote the sets of bus indices of the reference
bus, PV buses and PQ buses, respectively. The bus type classification is specified in
the Matpower case file in the BUS TYPE column (2) of the bus matrix. Any isolated
buses must be identified as such in this column as well.
In the traditional formulation of the AC power flow problem, the power balance
equation in (3.17) is split into its real and reactive components, expressed as functions
of the voltage angles Θ and magnitudes Vmand generator injections Pgand Qg, where
the load injections are assumed constant and given:
gP, Vm, Pg) = Pbus, Vm) + PdCgPg= 0 (4.2)
gQ, Vm, Qg) = Qbus, Vm) + QdCgQg= 0.(4.3)
30
For the AC power flow problem, the function g(x) from (4.1) is formed by taking
the left-hand side of the real power balance equations (4.2) for all non-slack buses
and the reactive power balance equations (4.3) for all PQ buses and plugging in the
reference angle, the loads and the known generator injections and voltage magnitudes:
g(x) = "g{i}
P, Vm, Pg)
g{j}
Q, Vm, Qg)#i∈ IPV ∪ IPQ
j∈ IPQ.(4.4)
The vector xconsists of the remaining unknown voltage quantities, namely the volt-
age angles at all non-reference buses and the voltage magnitudes at PQ buses:
x=θ{i}
v{j}
mi /∈ Iref
j∈ IPQ.(4.5)
This yields a system of nonlinear equations with npv + 2npq equations and un-
knowns, where npv and npq are the number of PV and PQ buses, respectively. After
solving for x, the remaining real power balance equation can be used to compute
the generator real power injection at the slack bus. Similarly, the remaining npv + 1
reactive power balance equations yield the generator reactive power injections.
Matpower includes four different algorithms for solving the general AC power
flow problem.16 The default solver is based on a standard Newton’s method [8] using a
polar form and a full Jacobian updated at each iteration. Each Newton step involves
computing the mismatch g(x), forming the Jacobian based on the sensitivities of
these mismatches to changes in xand solving for an updated value of xby factorizing
this Jacobian. This method is described in detail in many textbooks.
Also included are solvers based on variations of the fast-decoupled method [9],
specifically, the XB and BX methods described in [10]. These solvers greatly reduce
the amount of computation per iteration, by updating the voltage magnitudes and
angles separately based on constant approximate Jacobians which are factored only
once at the beginning of the solution process. These per-iteration savings, however,
come at the cost of more iterations.
The fourth algorithm is the standard Gauss-Seidel method from Glimm and
Stagg [11]. It has numerous disadvantages relative to the Newton method and is
included primarily for academic interest.
By default, the AC power flow solvers simply solve the problem described above,
ignoring any generator limits, branch flow limits, voltage magnitude limits, etc. How-
ever, there is an option (pf.enforce q lims) that allows for the generator reactive
16Three more that are specific to radial networks typical of distribution systems are described in
Section 4.3.
31
power limits to be respected at the expense of the voltage setpoint. This is done
in a rather brute force fashion by adding an outer loop around the AC power flow
solution. If any generator has a violated reactive power limit, its reactive injection is
fixed at the limit, the corresponding bus is converted to a PQ bus and the power flow
is solved again. This procedure is repeated until there are no more violations. Note
that this option is based solely on the QMAX and QMIN parameters for the generator,
from columns 4 and 5 of the gen matrix, and does not take into account the trape-
zoidal generator capability curves described in Section 6.4.3 and specifed in columns
PC1QC2MAX (11–16). Note also that this option affects generators even if the bus
they are attached to is already of type PQ.
4.2 DC Power Flow
For the DC power flow problem [17], the vector xconsists of the set of voltage angles
at non-reference buses
x=θ{i},i /∈ Iref (4.6)
and (4.1) takes the form
BdcxPdc = 0 (4.7)
where Bdc is the (nb1) ×(nb1) matrix obtained by simply eliminating from Bbus
the row and column corresponding to the slack bus and reference angle, respectively.
Given that the generator injections Pgare specified at all but the slack bus, Pdc can
be formed directly from the non-slack rows of the last four terms of (3.32).
The voltage angles in xare computed by a direct solution of the set of linear
equations. The branch flows and slack bus generator injection are then calculated
directly from the bus voltage angles via (3.29) and the appropriate row in (3.32),
respectively.
4.3 Distribution Power Flow
Distribution systems are different from transmission systems in a number of respects,
such as the xs/rsbranch ratio, magnitudes of xsand rsand most importantly the
typically radial structure. Due to these differences, a number of power flow solu-
tion methods have been developed to account for the specific nature of distribution
systems and most widely used are the backward/forward sweep methods [12,13].
Matpower includes an additional three AC power flow methods that are specific
to radial networks.
32
4.3.1 Radial Power Flow
When solving radial distribution networks it is practical to number branches with
numbers that are equal to the receiving bus numbers. An example is given in Fig-
ure 4-1, where branches are drawn black. Furthermore, the oriented branch ordering
[14] offers a possibility for fast and efficient backward/forward sweeps. All branches
are always oriented from the sending bus to the receiving bus and the only re-
quirement is that the sending bus number should be smaller than the receiving bus
number. This means that i<kfor branch ik. The indices of the sending nodes of
branches are stored in vector Fsuch that i=fk.
Loop 1
Loop 2
011223
3
4477PV2
6
6
5PV1
5
Figure 4-1: Oriented Ordering
As usual, the supply bus (slack bus) is given index 1, meaning that branch indices
should go from 2 to nbwhich is the number of buses in the network. Introducing a
fictitious branch with index 1 and zero impedance, given with dashed black line in
Figure 4-1, the number of branches nlbecomes equal to the number of buses nb.
For the example of Figure 4-1 vector Fis the following
F=0123324T,
and it offers an easy way to follow the path between any bus and bus 0. If we
consider bus 4, the path to the slack bus consists of following branches: branch 4,
since considered bus is their receiving bus; branch 3, since f4= 3; branch 2, since
f3= 2; and branch 1, since f2= 1.
The representation of branch k, connecting buses iand k, is given in Figure 4-2,
where it is modeled with its serial impedance zk
s. At both ends there are load
demands si
dand sk
d, and shunt admittances yi
dand yk
dcomprised of admittances due
capacitance of all lines and shunt elements connected to buses iand k
yk
d=jXbk
lines +Xbk
shunt.
33
isk
fzk
ssk
tk
si
dyi
d
+
vi
sk
d
yk
d
+
vk
Figure 4-2: Branch Representation: branch kbetween buses i(sending) and k(re-
ceiving) and load demand and shunt admittances at both buses
4.3.2 Current Summation Method
The voltage calculation procedure with the Current Summation Method is performed
in 5 steps as follows [12,13].
1. Set all voltages to 1 p.u. (flat start). Set iteration count ν= 1.
2. Set branch current flow equal to the sum of current of the demand at receiving
end (sk
d) and the current drawn in the admittance (yk
d) connected to bus k
jk
b=sk
d
vk
+yk
d·vk, k = 1,2, . . . , nb.(4.8)
3. Backward sweep: Perform current summation, starting from the branch with
the biggest index and heading towards the branch whose index is equal to 1.
The current of branch kis added to the current of the branch whose index is
equal to i=fk.
ji
b,new =ji
b+jk
b, k =nl, nl1,...,2 (4.9)
4. Forward sweep: The receiving end bus voltages are calculated with known
branch currents and sending bus voltages.
vk=vizk
s·jk
b, k = 2,3, . . . , nl(4.10)
5. Compare voltages in iteration νwith the corresponding ones from iteration
ν1. If the maximum difference in magnitude is less than the specified toler-
ance
max
i=1...nbvν
ivν1
i< ε (4.11)
the procedure is finished. Otherwise go to step 2.
34
4.3.3 Power Summation Method
The voltage calculation procedure with the Power Summation Method is performed
in 5 steps as follows [14].
1. Set all voltages to 1 p.u. (flat start). Set iteration count ν= 1.
2. Set receiving end branch flow equal to the sum of the demand at receiving end
(sk
d) and the power drawn in the admittance (yk
d) connected to bus k
sk
t=sk
d+yk
d
v2
k
, k = 1,2, . . . , nb.(4.12)
3. Backward sweep: Calculate sending end branch power flows as a sum of re-
ceiving end branch power flows and branch losses via (4.13). Perform power
summation, starting from the branch with the biggest index and heading to-
wards the branch whose index is equal to 1. The sending power of branch kis
added to the receiving power of the branch whose index is equal to i=fkas
in (4.14).
sk
f=sk
t+zk
s·
sk
t
vk
2
k=nl, nl1,...,2 (4.13)
si
t,new =si
t+sk
fk=nl, nl1,...,2 (4.14)
4. Forward sweep: The receiving end bus voltages are calculated with known
sending powers and voltages.
vk=vizk
s· sk
f
vi!
k= 2,3, . . . , nl(4.15)
5. Compare voltages in iteration νwith the corresponding ones from iteration
ν1, using (4.11). If the maximum difference in magnitude is less than the
specified tolerance the procedure is finished. Otherwise go to step 2.
4.3.4 Admittance Summation Method
For each node, besides the known admittance yk
d, we define the admittance yk
eas the
driving point admittance of the part of the network fed by node k, including shunt
35
admittance yk
d. We also define an equivalent current generator jk
efor the part of the
network fed by node k. The current of this generator consists of all load currents fed
by node k. The process of calculation of bus voltages with the admittance summation
method consists of the following 5 steps [15].
1. Set all voltages to 1 p.u. (flat start). Set iteration count ν= 1. Set initial
values
yk
e=yk
d, k = 1,2, . . . , nb.(4.16)
2. For each node k, calculate equivalent admittance yk
e. Perform admittance sum-
mation, starting from the branch with the biggest index and heading towards
the branch whose index is equal to 1. The driving point admittance of branch k
is added to the driving point admittance of the branch whose index is equal to
i=fkas in (4.18).
dk
b=1
1 + zk
s·yk
e
k=nl, nl1,...,2 (4.17)
yi
e,new =yi
e+dk
b·yk
ek=nl, nl1,...,2 (4.18)
3. Backward sweep: For each node kcalculate equivalent current generator jk
e, first
set it equal to load current jk
dand perform current summation over equivalent
admittances using factor dk
bas in (4.17).
jk
e=jk
d=sk
d
vk
k=nl, nl1,...,2 (4.19)
ji
e,new =ji
e+dk
b·jk
ek=nl, nl1,...,2 (4.20)
4. Forward sweep: The receiving end bus voltages are calculated with known
equivalent current generators and sending bus voltages.
vk=dk
b·(vizk
s·jk
e)k= 2,3, . . . , nl(4.21)
5. Compare voltages in iteration νwith the corresponding ones from iteration
ν1, using (4.11). If the maximum difference in magnitude is less than the
specified tolerance the procedure is finished. Otherwise go to step 3.
36
4.3.5 Handling PV Buses
The methods explained in the previous three subsections are applicable to radial
networks without loops and PV buses. These methods can be used to solve the
power flow problem in weakly meshed networks if a compensation procedure based on
Thevenin equivalent impedance matrix is added [12,13]. In [14] a voltage correction
procedure is added to the process.
The list of branches is expanded by a set of npv fictitious links, corresponding to
the PV nodes. Each of these links starts at the slack bus and ends at a corresponding
PV bus, thus forming a loop in the network. A fictitious link going to bus kis
represented by a voltage generator with a voltage magnitude equal to the specified
voltage magnitude at bus k. Its phase angle is equal to the calculated phase angle
at bus k.
A loop impedance matrix Zlis formed for the loops made by the fictitious links
and it has the following properties
Element zmm
lis equal to the sum of branch impedances off all branches related
to loop m,
Element zmk
lis equal to the sum of branch impedances of mutual branches of
loops mand k.
As an illustration, in Figure 4-1 there a two PV generators at buses 5 and 7. The
fictitious links and loops orientation are drawn in red. The Thevenin matrix for this
case is
Zl=z2
b+z3
b+z5
bz2
b+z3
b
z2
b+z3
bz2
b+z3
b+z4
b+z7
b.
First column elements are equal to PV bus voltages when the current injection
at bus 5 is 1 p.u. and v1= 0. Bus voltages can be calculated with the current
summation method in a single iteration. By repeating the procedure for bus 7 one
can calculate the elements of second column.
By breaking all links the network becomes radial [13] and the three backward/forward
sweep methods are applicable. Since all link are fictitious, only the injected reactive
power at their receiving bus mis determined [14] by the following equation
qm
pv = ∆dm
pv
v2
m
<{vm},(4.22)
which is practically an increment in reactive power injection of the corresponding
PV generator for the current iteration.
37
The incremental changes of the imaginary part of PV generator current ∆dm
pv can
be obtained by solving the matrix equation
={Zl} · Dpv = ∆Epv,(4.23)
where
em
pv =vm
g
|vm|1· <{vm}, m = 1,2, . . . , npv.(4.24)
In order to ensure 90phase difference between voltage and current at PV gen-
erators in [16] it was suggested to calculate the real part of PV generator current
as
cm
pv = ∆dm
pv ={vm}
<{vm}.(4.25)
In such a way the PV generator will inject purely reactive power, as it is supposed
to do. Its active power is added before as a negative load.
Before proceeding with the next iteration, the bus voltage corrections are cal-
culated. In order to do that, the radial network is solved by applying incremental
current changes ∆Ipv = ∆Cpv +jDpv at the PV buses as excitations and setting
v1= 0. After the backward/forward sweep is performed with the current summation
method, the voltage corrections at all buses are known. They are added to the latest
voltages in order to obtain the new bus voltages, which are used in the next iteration
[14].
4.4 runpf
In Matpower, a power flow is executed by calling runpf with a case struct or case
file name as the first argument (casedata). In addition to printing output to the
screen, which it does by default, runpf optionally returns the solution in a results
struct.
>> results = runpf(casedata);
The results struct is a superset of the input Matpower case struct mpc, with some
additional fields as well as additional columns in some of the existing data fields.
The solution values are stored as shown in Table 4-1.
Additional optional input arguments can be used to set options (mpopt) and
provide file names for saving the pretty printed output (fname) or the solved case
data (solvedcase).
38
Table 4-1: Power Flow Results
name description
results.success success flag, 1 = succeeded, 0 = failed
results.et computation time required for solution
results.iterations number of iterations required for solution
results.order see ext2int help for details on this field
results.bus(:, VM)bus voltage magnitudes
results.bus(:, VA) bus voltage angles
results.gen(:, PG) generator real power injections
results.gen(:, QG)generator reactive power injections
results.branch(:, PF) real power injected into “from” end of branch
results.branch(:, PT) real power injected into “to” end of branch
results.branch(:, QF)reactive power injected into “from” end of branch
results.branch(:, QT)reactive power injected into “to” end of branch
AC power flow only.
>> results = runpf(casedata, mpopt, fname, solvedcase);
The options that control the power flow simulation are listed in Table 4-2 and those
controlling the output printed to the screen in Table 4-3.
By default, runpf solves an AC power flow problem using a standard Newton’s
method solver. To run a DC power flow, the model option must be set to 'DC'. For
convenience, Matpower provides a function rundcpf which is simply a wrapper
that sets the model option to 'DC'before calling runpf.
Internally, the runpf function does a number of conversions to the problem data
before calling the appropriate solver routine for the selected power flow algorithm.
This external-to-internal format conversion is performed by the ext2int function,
described in more detail in Section 7.3.1, and includes the elimination of out-of-service
equipment, the consecutive renumbering of buses and the reordering of generators
by increasing bus number. All computations are done using this internal indexing.
When the simulation has completed, the data is converted back to external format
by int2ext before the results are printed and returned.
4.5 Linear Shift Factors
The DC power flow model can also be used to compute the sensitivities of branch
flows to changes in nodal real power injections, sometimes called injection shift factors
(ISF) or generation shift factors [17]. These nl×nbsensitivity matrices, also called
39
Table 4-2: Power Flow Options
name default description
model 'AC'AC vs. DC modeling for power flow and OPF formulation
'AC'– use AC formulation and corresponding alg options
'DC'– use DC formulation and corresponding alg options
pf.alg 'NR'AC power flow algorithm:
'NR'– Newtons’s method
'FDXB'– Fast-Decoupled (XB version)
'FDBX'– Fast-Decouple (BX version)
'GS'– Gauss-Seidel
'PQSUM'– Power Summation (radial networks only)
'ISUM'– Current Summation (radial networks only)
'YSUM'– Admittance Summation (radial networks only)
pf.tol 108termination tolerance on per unit P and Q dispatch
pf.nr.max it 10 maximum number of iterations for Newton’s method
pf.nr.lin solver '' linear solver option for mplinsolve for computing Newton update step
(see mplinsolve for complete list of all options)
'' – default to '\'for small systems, 'LU3'for larger ones
'\'– built-in backslash operator
'LU' explicit default LU decomposition and back substitution
'LU3' 3 output arg form of lu, Gilbert-Peierls algorithm with
approximate minimum degree (AMD) reordering
'LU4' 4 output arg form of lu, UMFPACK solver (same as
'LU')
'LU5' 5 output arg form of lu, UMFPACK solver w/row scaling
pf.fd.max it 30 maximum number of iterations for fast-decoupled method
pf.gs.max it 1000 maximum number of iterations for Gauss-Seidel method
pf.radial.max it 20 maximum number of iterations for radial power flow methods
pf.radial.vcorr 0 perform voltage correction procedure in distribution power flow
0 – do not perform voltage correction
1 – perform voltage correction
pf.enforce q lims 0 enforce gen reactive power limits at expense of |Vm|
0 – do not enforce limits
1 – enforce limits, simultaneous bus type conversion
2 – enforce limits, one-at-a-time bus type conversion
power transfer distribution factors or PTDFs, carry an implicit assumption about
the slack distribution. If His used to denote a PTDF matrix, then the element in
row iand column j,hij , represents the change in the real power flow in branch i
given a unit increase in the power injected at bus j,with the assumption that the
additional unit of power is extracted according to some specified slack distribution:
Pf=HPbus.(4.26)
40
Table 4-3: Power Flow Output Options
name default description
verbose 1 amount of progress info to be printed
0 – print no progress info
1 – print a little progress info
2 – print a lot of progress info
3 – print all progress info
out.all -1 controls pretty-printing of results
-1 – individual flags control what is printed
0 – do not print anything
1 – print everything
out.sys sum 1 print system summary (0 or 1)
out.area sum 0 print area summaries (0 or 1)
out.bus 1 print bus detail, includes per bus gen info (0 or 1)
out.branch 1 print branch detail (0 or 1)
out.gen 0 print generator detail (0 or 1)
out.force 0 print results even if success flag = 0 (0 or 1)
out.suppress detail -1 suppress all output but system summary
-1 – suppress details for large systems (>500 buses)
0 – do not suppress any output specified by other flags
1 – suppress all output except system summary section
Overrides individual flags, but (in the case of out.suppress detail) not out.all = 1.
This slack distribution can be expressed as an nb×1 vector wof non-negative
weights whose elements sum to 1. Each element specifies the proportion of the slack
taken up at each bus. For the special case of a single slack bus k,wis equal to the
vector ek. The corresponding PTDF matrix Hkcan be constructed by first creating
the nl×(nb1) matrix
e
Hk=e
Bf·B1
dc (4.27)
then inserting a column of zeros at column k. Here e
Bfand Bdc are obtained from Bf
and Bbus, respectively, by eliminating their reference bus columns and, in the case
of Bdc, removing row kcorresponding to the slack bus.
The PTDF matrix Hw, corresponding to a general slack distribution w, can be
obtained from any other PTDF, such as Hk, by subtracting Hk·wfrom each column,
equivalent to the following simple matrix multiplication:
Hw=Hk(Iw·1T).(4.28)
These same linear shift factors may also be used to compute sensitivities of branch
flows to branch outages, known as line outage distribution factors or LODFs [18].
41
Given a PTDF matrix Hw, the corresponding nl×nlLODF matrix Lcan be con-
structed as follows, where lij is the element in row iand column j, representing the
change in flow in branch i(as a fraction of the initial flow in branch j) for an outage
of branch j.
First, let Hrepresent the matrix of sensitivities of branch flows to branch endpoint
injections, found by multplying the PTDF matrix by the node-branch incidence
matrix:
H=Hw(CfCt)T.(4.29)
Here the individual elements hij represent the sensitivity of flow in branch iwith
respect to injections at branch jendpoints, corresponding to a simulated increase in
flow in branch j. Then lij can be expressed as
lij =
hij
1hjj
i6=j
1i=j.
(4.30)
Matpower includes functions for computing both the DC PTDF matrix and
the corresponding LODF matrix for either a single slack bus kor a general slack
distribution vector w. See the help for makePTDF and makeLODF and Sections 9.5.5
and 9.5.4, respectively, for details.
42
5 Continuation Power Flow
Continuation methods or branch tracing methods are used to trace a curve given an
initial point on the curve. These are also called predictor-corrector methods since
they involve the prediction of the next solution point and correcting the prediction
to get the next point on the curve.
Consider a system of nnonlinear equations g(x) = 0, x Rn. By adding a
continuation parameter λand one more equation to the system, xcan be traced by
varying λ. The resulting system f(x, λ) = 0 has n+ 1 dimensions. The additional
equation is a parameterized equation which identifies the location of the current
solution with respect to the previous or next solution.
The continuation process can be diagrammatically shown by (5.1).
xj, λjP redictor
(ˆxj+1,ˆ
λj+1)Corrector
xj+1, λj+1(5.1)
where, (xj, λj) represents the current solution at step j, (ˆxj+1,ˆ
λj+1) is the predicted
solution for the next step, and (xj+1, λj+1) is the next solution on the curve.
Continuation methods are employed in power systems to determine steady state
stability limits [19] in what is called a continuation power flow17. The limit is de-
termined from a nose curve where the nose represents the maximum power transfer
that the system can handle given a power transfer schedule. To determine the steady
state loading limit, the basic power flow equations
g(x) = P(x)Pinj
Q(x)Qinj = 0,(5.2)
are restructured as
f(x, λ) = g(x)λb = 0 (5.3)
where x, Vm) and bis a vector of power transfer given by
b=Pinj
target Pinj
base
Qinj
target Qinj
base .(5.4)
The effects of the variation of loading or generation can be investigated using the
continuation method by composing the bvector appropriately.
17Thanks to Shrirang Abhyankar, Rui Bo, and Alexander Flueck for contributions to Mat-
power’s continuation power flow feature.
43
5.1 Parameterization
The values of (x, λ) along the solution curve can parameterized in a number of ways
[20,21]. Parameterization is a mathematical way of identifying each solution so that
the next solution or previous solution can be quantified. Matpower includes three
parameterization scheme options to quantify this relationship, detailed below, where
σis the continuation step size parameter.
Natural parameterization simply uses λdirectly as the parameter, so the
new λis simply the previous value plus the step size.
pj(x, λ) = λλjσj= 0 (5.5)
Arc length parameterization results in the following relationship, where
the step size is equal to the 2-norm of the distance from one solution to the
next.
pj(x, λ) = X
i
(xixj
i)2+ (λλj)2(σj)2= 0 (5.6)
Pseudo arc length parameterization [23] is Matpower’s default pa-
rameterization scheme, where the next point (x, λ) on the solution curve is
constrained to lie in the hyperplane running through the predicted solution
(ˆxj+1,ˆ
λj+1) orthogonal to the tangent line from the previous corrected solution
(xj, λj). This relationship can be quantified by the function
pj(x, λ) = x
λxj
λjT
¯zjσj= 0,(5.7)
where ¯zjis the normalized tangent vector at (xj, λj) and σjis the continuation
step size parameter.
5.2 Predictor
The predictor is used to produce an estimate for the next solution. The better the
prediction, the faster is the convergence to the solution point. Matpower uses a
tangent predictor for estimating the curve to the next solution. The tangent vector
zj=dx j
Tat the current solution (xj, λj) is found by solving the linear
system fxfλ
pj1
xpj1
λzj=0
1.(5.8)
44
The matrix on the left-hand side is simply the standard power flow Jacobian with an
additional column and row added. The extra column fλis simply the negative of the
power transfer vector band the extra row, required to make the system non-singular
and define the magnitude of zj, is the derivative of the the parameterization function
at the previous solution point pj1.
The resulting tangent vector is then normalized
¯zj=zj
||zj||2
(5.9)
and used to compute the predicted approximation (ˆxj+1,ˆ
λj+1) to the next solution
(xj+1, λj+1) using ˆxj+1
ˆ
λj+1 =xj
λj+σj¯zj,(5.10)
where σjis the continuation step size.
5.3 Corrector
The corrector stage finds the next solution (xj+1, λj+1) by correcting the approxi-
mation estimated by the predictor (ˆxj+1,ˆ
λj+1). Newton’s method is used to find
the next solution by solving the n+ 1 dimensional system in (5.11), where one of
(5.5)–(5.7) has been added as an additional constraint to the parameterized power
flow equations of (5.3). f(x, λ)
pj(x, λ)= 0 (5.11)
5.4 Step Length Control
Step length control is a key element affecting the computational efficiency of a contin-
uation method. It affects the continuation method with two issues: (1) speed – how
fast the corrector converges to a specified accuracy, and (2) robustness – whether
the corrector converges to a true solution given a predicted point. Matpower’s
continuation power flow can optionally use adaptive steps, where the step size σis
adjusted by a scaling factor αwithin the limits specified.
σj+1 =αjσj, σmin σj+1 σmax (5.12)
This scaling factor αjfor step jis limited to a maximum of 2 and is calculated from
an error estimation between the predicted and corrected solutions γjas follows,
αj= 1 + βcpf cpf
γj1, αj2,(5.13)
45
where βcpf is a damping factor, cpf is a specified tolerance, and γjis given by
γj=
xj+1, λj+1ˆxj+1,ˆ
λj+1
.(5.14)
5.5 Event Detection and Location
A continuation power flow event is triggered when the value of one of the elements
of an event function changes sign from one continuation step to the next. The
event occurs at the point where the corresponding value of the event function passes
through zero. Matpower provides event functions to detect the location at which
the continuation power flow reaches the following:
a specified target λvalue
the nose point
the end of a full trace
a generator reactive power limit
a generator active power limit
a bus voltage magnitude limit
a branch flow limit
Each event function is registered with an event name, a flag indicating whether
or not the location of the event should be pinpointed, and if so, to within what
tolerance. For events that are to be located, when an event interval is detected, that
is, when an element of the event function value changes sign, Matpower adjusts
the continuation step size via a False Position or Regula Falsi method until it locates
the point of the zero-crossing to within the specified tolerance.
The detection of an event zero, or even an event interval, can be used to trigger
further actions. The CPF callback function capability was extended in Matpower
6.x to include the ability to handle events by including information about any event
intervals or zeros detected. For example, Matpower includes a callback that fixes
the reactive output of a generator and converts its bus from PV to PQ when the
corresponding event function indicates that its reactive power limit has been reached.
Another responds to the detection of the nose point by signaling the termination of
the continuation. In fact, continuation power flow termination for nose point, target
46
lambda or full trace modes are all based on CPF callback functions in conjunction
with event detection.
While Matpower does include a mechanism for supplying user defined callback
functions, it does not yet have a corresponding mechanism for user specified event
functions.
5.6 runcpf
In Matpower, a continuation power flow is executed by calling runcpf with two
Matpower cases (case structs or case file names) as the first two arguments,
basecasedata and targetcasedata, respectively. The first contains the base load-
ing/generation profile while the second contains the target loading/generation pro-
file. In addition to printing output to the screen, which it does by default, runcpf
optionally returns the solution in a results struct.
>> results = runcpf(basecasedata, targetcasedata);
Additional optional input arguments can be used to set options (mpopt) and
provide file names for saving the pretty printed output (fname) or the solved case
data (solvedcase).
>> results = runcpf(basecasedata, targetcasedata, mpopt, fname, solvedcase);
The results struct is a superset of the input Matpower case struct mpc, with
some additional fields as well as additional columns in some of the existing data
fields. In addition to the solution values included in the results for a simple power
flow, shown in Table 4-1 in Section 4.4, the following additional continuation power
flow solution values are stored in the cpf field as shown in Table 5-1.
The options that control the continuation power flow simulation are listed in
Table 5-2. All the power flow options for Newton’s method (tolerance, maximum
iterations) and for controlling the output on the screen (see Tables 4-2 and 4-3) are
also available with the continuation power flow.
47
Table 5-1: Continuation Power Flow Results
name description
results.cpf CPF output struct whose content depends on any user callback functions,
where default contains fields:
done msg string with message describing cause of continuation termination
events(eidx) a structure array of size ne, where neis the number of events located, with
fields:
kcontinuation step number at which event was located
name name of event
idx index(es) of critical elements in corresponding event function, e.g. index
of generator reaching VAr limit
msg descriptive text detailing the event
iterations nsteps, number of continuation steps performed
lam 1×nvector of λvalues from correction steps
lam hat 1×nvector of λvalues from prediction steps
max lam maximum value of λfound in results.cpf.lam
steps 1×nvector of step sizes for each continuation step performed
Vnb×nmatrix of complex bus voltages from correction steps
V hat nb×nmatrix of complex bus voltages from prediction steps
nis one more than the number of continuation steps, i.e. nsteps + 1, so the first element corresponds to the
starting point.
48
Table 5-2: Continuation Power Flow Options
name default description
cpf.parameterization 3 choice of parameterization
1 — natural
2 — arc length
3 — pseudo arc length
cpf.stop at 'NOSE'determines stopping criterion
'NOSE'— stop when nose point is reached
'FULL'— trace full nose curve
λstop — stop upon reaching target λvalue λstop
cpf.enforce p lims 0 enforce gen active power limits
0 — do not enforce limits
1 — enforce limits
cpf.enforce q lims 0 enforce gen reactive power limits at expense of Vm
0 — do not enforce limits
1 — enforce limits
cpf.enforce v lims 0 enforce bus voltage magnitude limits
0 — do not enforce limits
1 — enforce limits
cpf.enforce flow lims 0 enforce branch MVA flow limits
0 — do not enforce limits
1 — enforce limits
cpf.step 0.05 default value for continuation power flow step size σ
cpf.step min 104minimum allowed step size, σmin
cpf.step max 0.2 maximum allowed step size, σmax
cpf.adapt step 0 toggle adaptive step size feature
0 — adaptive step size disabled
1 — adaptive step size enabled
cpf.adapt step damping 0.7 damping factor βcpf from (5.13) for adaptive step sizing
cpf.adapt step tol 103tolerance cpf from (5.13) for adaptive step sizing
cpf.target lam tol 105tolerance for target lambda detection
cpf.nose tol 105tolerance for nose point detection (p.u.)
cpf.p lims tol 102tolerance for generator active power limit detection
(MW)
cpf.q lims tol 102tolerance for generator reactive power limit detection
(MVAr)
cpf.v lims tol 104tolerance for bus voltage magnitude limit detection (p.u)
cpf.flow lims tol 0.01 tolerance for branch flow limit detection (MVA)
cpf.plot.level 0 control plotting of nose curve
0 — do not plot nose curve
1 — plot when completed
2 — plot incrementally at each iteration
3 — same as 2, with pause at each iteration
cpf.plot.bus empty index of bus whose voltage is to be plotted
cpf.user callback empty string or cell array of strings with names of user callback
functions
See help cpf default callback for details. 49
5.6.1 CPF Callback Functions
Matpower’s continuation power flow provides a callback mechanism to give the
user access to the iteration process for executing custom code at each iteration,
for example, to implement custom incremental plotting of a PV nose curve or to
handle a detected event. This callback mechanism is used internally to handle de-
fault plotting functionality as well as to handle the standard CPF events. The
cpf default callback function, for example, is used to collect the λand Vresults
from each predictor and corrector iteration and optionally plot the PV nose curve.
The prototype for a CPF callback function is
function [nx, cx, done, rollback, evnts, cb_data, results] = ...
cpf_user_callback(k, nx, cx, px, done, rollback, evnts, ...
cb_data, cb_args, results)
and the input and output arguments are described in Tables 5-3 through 5-5 and in
the help for cpf default callback. Each registered CPF callback function is called in
three different contexts, distinguished by the value of the first argument kas follows:
1. initial – called with k= 0, without results input/output arguments, after base
power flow, before first CPF step.
2. iterations – called with k>0, without results input/output arguments, at
each iteration, after predictor-corrector step
3. final – called with k<0, with results input/output arguments, after exiting
predictor-corrector loop, inputs identical to last iteration call, except knegated
The user can define their own callback functions which take the same form and
are called in the same contexts as cpf default callback. User callback functions are
specified via the Matpower option cpf.user callback. This option can be a string
containing the name of the callback function, or a struct with the following fields,
where all but the first are optional:
fcn - string with name of callback function
priority - numerical value specifying callback priority,18 default = 20
args - arbitrary value (any type) passed to the callback as cb args each time
it is invoked
Multiple user callbacks can be registered by assigning a cell array of such strings
and/or structs to the cpf.user callback option.
18See cpf register callback for details.
50
Table 5-3: Continuation Power Flow Callback Input Arguments
name description
kcontinuation step iteration count
nx next CPF state*
, corresponding to proposed next step
cx current CPF state*
, corresponding to most recent successful step
px previous CPF state*
, corresponding to last successful step prior to cx
done struct, with flag to indicate CPF termination and reason, with fields:
.flag termination flag, 1 terminate, 0 continue
.msg string containing reason for termination
rollback scalar flag to indicate that the current step should be rolled back and
retried with a different step size, etc.
evnts struct array listing any events detected for this step
cb data struct containing static data§
, with the following fields (all based on internal
indexing):
.mpc base Matpower case struct of base case
.mpc target Matpower case struct of target case
.Sbusb handle of function returning nb×1 vector of complex base case bus injec-
tions in p.u. and derivatives w.r.t. |V|
.Sbust handle of function returning nb×1 vector of complex target case bus
injections in p.u. and derivatives w.r.t. |V|
.Ybus bus admittance matrix
.Yf branch admittance matrix, “from” end of branches
.Yt branch admittance matrix, “to” end of branches
.pv list of indices of PV buses
.pq list of indices of PQ buses
.ref list of indices of reference buses
.idx pmax vector of gen indices of gens at PMAX
.mpopt Matpower options struct
cb args arbitrary data structure containing user-provided callback arguments
results initial value of output struct to be assigned to cpf field of results struct
returned by runcpf
*See Table 5-5 for details of the CPF state.
See cpf detect events for details of the evnts field.
§Please note that any callback that modifies the underlying problem is responsible to update the contents of
cb data accordingly. E.g. converting a bus from PV to PQ requires updates to mpc base,mpc target,Sbusb,
Sbust,pv,pq, and possibly ref. So, cb data should only be thought of as static for a fixed base and target
case pair.
51
Table 5-4: Continuation Power Flow Callback Output Arguments
name description
All are updated versions of the corresponding input arguments, see Table 5-3 for more details.
nx next CPF state*
, user state (cb field) should be updated here if rollback
is false
cx current CPF state*
, may contain updated this step or this parm values
to be used if rollback is true
done callback may have requested termination and set the msg field
rollback callback can request a rollback step, even if it was not indicated by an
event function
evnts msg field for a given event may be updated
cb data this data should only be modified if the underlying problem has been
changed (e.g. generator limit reached), in which case it should always
be followed by a step of zero length, i.e. set nx.this step to 0§
results updated version of results input argument to be assigned to cpf field of
results struct returned by runcpf
*See Table 5-5 for details of the CPF state.
In this case, the callback should also modify the step size or parameterization to be used for the re-try, by
setting the this step or this parm fields in cx.
See cpf detect events for details of the evnts field.
§It is the job of any callback modifying cb data to ensure that all data in cb data is kept consistent.
Table 5-5: Continuation Power Flow State
name description
lam hat value of λafter predictor step
V hat vector of complex bus voltages after predictor step
lam value of λafter corrector step
Vvector of complex bus voltages after corrector step
znormalized tangent predictor, ¯z
default step default step size
default parm default parameterization*
this step step size for this step only
this parm parameterization*for this step only
step current step size
parm current parameterization*
events event log
cb user state for callbacks, a user-defined struct containing any information
a callback function would like to pass from one invokation to the next
ef cell array of event function values
*Corresponding to the cpf.parameterization option in Table 5-2.
Replaces cb state from Matpower 5.
52
5.6.2 CPF Example
The following is an example of running a continuation power flow using a version of
the 9-bus system, looking at increasing all loads by a factor of 2.5. This example
plots the nose curve shown in Figure 5-1.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Voltage at Bus 9
λ
Voltage Magnitude
Figure 5-1: Nose Curve of Voltage Magnitude at Bus 9
53
define_constants;
mpopt = mpoption('out.all', 0, 'verbose', 2);
mpopt = mpoption(mpopt, 'cpf.stop_at', 'FULL', 'cpf.step', 0.2);
mpopt = mpoption(mpopt, 'cpf.plot.level', 2);
mpcb = loadcase(t_case9_pfv2); % load base case
mpct = mpcb; % set up target case with
mpct.gen(:, [PG QG]) = mpcb.gen(:, [PG QG]) * 2.5; % increased generation
mpct.bus(:, [PD QD]) = mpcb.bus(:, [PD QD]) * 2.5; % and increased load
results = runcpf(mpcb, mpct, mpopt);
This should result in something like the following output to the screen.
MATPOWER Version 7.0b1, 31-Oct-2018 -- AC Continuation Power Flow
step 0 : lambda = 0.000, 4 Newton steps
step 1 : stepsize = 0.2 lambda = 0.181 2 corrector Newton steps
step 2 : stepsize = 0.2 lambda = 0.359 2 corrector Newton steps
step 3 : stepsize = 0.2 lambda = 0.530 2 corrector Newton steps
step 4 : stepsize = 0.2 lambda = 0.693 3 corrector Newton steps
step 5 : stepsize = 0.2 lambda = 0.839 3 corrector Newton steps
step 6 : stepsize = 0.2 lambda = 0.952 3 corrector Newton steps
step 7 : stepsize = 0.2 lambda = 0.988 3 corrector Newton steps
step 8 : stepsize = 0.2 lambda = 0.899 3 corrector Newton steps
step 9 : stepsize = 0.2 lambda = 0.776 3 corrector Newton steps
step 10 : stepsize = 0.2 lambda = 0.654 3 corrector Newton steps
step 11 : stepsize = 0.2 lambda = 0.533 2 corrector Newton steps
step 12 : stepsize = 0.2 lambda = 0.413 2 corrector Newton steps
step 13 : stepsize = 0.2 lambda = 0.294 2 corrector Newton steps
step 14 : stepsize = 0.2 lambda = 0.176 2 corrector Newton steps
step 15 : stepsize = 0.2 lambda = 0.060 2 corrector Newton steps
step 16a : stepsize = 0.2 lambda = -0.054 2 corrector Newton steps ^ ROLLBACK
step 16 : stepsize = 0.0604 lambda = 0.000 3 corrector Newton steps
CPF TERMINATION: Traced full continuation curve in 16 continuation steps
The results of the continuation power flow are then found in the cpf field of the
returned results struct.
54
>> results.cpf
ans =
V_hat: [9x17 double]
lam_hat: [1x17 double]
V: [9x17 double]
lam: [1x17 double]
steps: [1x17 double]
iterations: 16
max_lam: 0.9876
events: [1x1 struct]
done_msg: 'Traced full continuation curve in 16 continuation steps'
55
6 Optimal Power Flow
Matpower includes code to solve both AC and DC versions of the optimal power
flow problem. The standard version of each takes the following form:
min
xf(x) (6.1)
subject to
g(x) = 0 (6.2)
h(x)0 (6.3)
xmin xxmax .(6.4)
In both cases, the objective function f(x) consists of the polynomial cost of gener-
ator injections, the equality constraints g(x) are the power balance equations, the
inequality constraints h(x) are the branch flow limits, and the xmin and xmax bounds
include reference bus angles, voltage magnitudes (for AC) and generator injections.
6.1 Standard AC OPF
The optimization vector xfor the standard AC OPF problem consists of the nb×1
vectors of voltage angles Θ and magnitudes Vmand the ng×1 vectors of generator
real and reactive power injections Pgand Qg.
x=
Θ
Vm
Pg
Qg
(6.5)
The objective function f(x) in (6.1) is simply a summation of individual polynomial
cost functions fi
Pand fi
Qof real and reactive power injections, respectively, for each
generator:
f(Pg, Qg) =
ng
X
i=1
fi
P(pi
g) + fi
Q(qi
g).(6.6)
The equality constraints in (6.2) are simply the full set of 2 ·nbnonlinear real and
reactive power balance equations from (4.2) and (4.3).
gP, Vm, Pg) = Pbus, Vm) + PdCgPg= 0 (6.7)
gQ, Vm, Qg) = Qbus, Vm) + QdCgQg= 0 (6.8)
56
The inequality constraints (6.3) consist of two sets of nlbranch flow limits as non-
linear functions of the bus voltage angles and magnitudes, one for the from end and
one for the to end of each branch:
hf, Vm) = |Ff, Vm)| − Fmax 0 (6.9)
ht, Vm) = |Ft, Vm)| − Fmax 0.(6.10)
The flows are typically apparent power flows expressed in MVA, but can be real power
or current flows, yielding the following three possible forms for the flow constraints:
Ff, Vm) =
Sf, Vm),apparent power
Pf, Vm),real power
If, Vm),current
(6.11)
where Ifis defined in (3.9), Sfin (3.15), Pf=<{Sf}and the vector of flow limits
Fmax has the appropriate units for the type of constraint. It is likewise for Ft, Vm).
The values used by Matpower’s OPF for the flow limits Fmax are specified in the
RATE A column (6) of the branch matrix,19 and the selection of flow constraint type
in (6.11) is determined by the opf.flow lim option.
The variable limits (6.4) include an equality constraint on any reference bus angle
and upper and lower limits on all bus voltage magnitudes and real and reactive
generator injections:
θref
iθiθref
i, i ∈ Iref (6.12)
vi,min
mvi
mvi,max
m, i = 1 . . . nb(6.13)
pi,min
gpi
gpi,max
g, i = 1 . . . ng(6.14)
qi,min
gqi
gqi,max
g, i = 1 . . . ng.(6.15)
The voltage reference angle θref
iand voltage magnitude bounds vi,max
mand vi,min
mare
specified in columns VA (9), VMAX (12) and VMIN (13), respectively, of row iof the bus
matrix. Similarly, the generator bounds qi,max
g,qi,min
g,pi,max
gand pi,min
gare specfied in
columns QMAX (4), QMIN (5), PMAX (9) and PMIN (10), respectively, of row iof the gen
matrix.
6.1.1 Cartesian vs. Polar Coordinates for Voltage
Another variation of the standard AC OPF problem represents the bus voltages
in cartesian, rather than polar, coordinates. That is, instead of Θ and Vm, the
19Setting the RATE A column (6) of branch to zero is the preferred way to indicate a completely
unconstrained line.
57
optimization vector xincludes the real and imaginary parts of the complex voltage,
denoted respectively by Uand W, where V=U+jW .
x=
U
W
Pg
Qg
(6.16)
The objective function remains unchanged, but the nodal power balance con-
straints (6.7) and (6.8) and branch flow constraints (6.9) and (6.10) are implemented
as functions of Uand W.
gP(U, W, Pg) = Pbus(U, W ) + PdCgPg= 0 (6.17)
gQ(U, W, Qg) = Qbus(U, W ) + QdCgQg= 0 (6.18)
hf(U, W ) = |Ff(U, W )| − Fmax 0 (6.19)
ht(U, W ) = |Ft(U, W )| − Fmax 0.(6.20)
In this formulation, the voltage angle reference constraint (6.12) and voltage mag-
nitude limits (6.13) cannot be simply applied as bounds on optimization variables.
These constrained quantities also become functions of Uand W.
θref
iθi(ui, wi)θref
i, i ∈ Iref (6.21)
vi,min
mvi
m(ui, wi)vi,max
m, i = 1 . . . nb(6.22)
In Matpower setting the opf.v cartesian option to 1 (0 by default) selects the
cartesian representation for voltages when running an AC OPF.20
6.1.2 Current vs. Power for Nodal Balance Constraints
Another variation of the standard AC OPF problem uses current balance constraints
in place of the power balance constraints (6.7)–(6.8) or (6.17)–(6.18). If we let M
and Nrepresent the real and imaginary parts, respectively, of the current, we can
express the current balance functions for the polar form as
gM, Vm, Pg, Qg) = <{Ibus, Vm)+[V]1(SdCgSg)}= 0 (6.23)
gN, Vm, Pg, Qg) = ={Ibus, Vm)+[V]1(SdCgSg)}= 0 (6.24)
20This option only applies to solvers based on MIPS,fmincon,Ipopt and KNITRO.
58
and for the cartesian form as
gM(U, W, Pg, Qg) = <{Ibus(U, W )+[V]1(SdCgSg)}= 0 (6.25)
gN(U, W, Pg, Qg) = ={Ibus(U, W )+[V]1(SdCgSg)}= 0 (6.26)
where Sd=Pd+jQd,Sg=Pg+jQgand [V]1is a diagonal matrix whose i-th
diagonal entry is 1/v
i, that is 1
vi
mejθior 1/(uijwi).
In this formulation, which can be selected by setting the opf.current balance
option to 1,21 the objective function and other constraints are not affected. This
option can be used in conjuntion with either the polar or cartesian representation of
bus voltages.
6.2 Standard DC OPF
When using DC network modeling assumptions and limiting polynomial costs to
second order, the standard OPF problem above can be simplified to a quadratic
program, with linear constraints and a quadratic cost function. In this case, the
voltage magnitudes and reactive powers are eliminated from the problem completely
and real power flows are modeled as linear functions of the voltage angles. The
optimization variable is
x=Θ
Pg(6.27)
and the overall problem reduces to the following form.
min
Θ,Pg
ng
X
i=1
fi
P(pi
g) (6.28)
subject to
gP, Pg) = BbusΘ + Pbus,shift +Pd+Gsh CgPg= 0 (6.29)
hf(Θ) = BfΘ + Pf,shift Fmax 0 (6.30)
ht(Θ) = BfΘPf,shift Fmax 0 (6.31)
θref
iθiθref
i, i ∈ Iref (6.32)
pi,min
gpi
gpi,max
g, i = 1 . . . ng(6.33)
21This option only applies to solvers based on MIPS,fmincon,Ipopt and KNITRO.
59
6.3 Extended OPF Formulation
Matpower employs an extensible OPF structure to allow the user to modify or
augment the problem formulation without rewriting the portions that are shared
with the standard OPF formulation described above. The standard formulation is
modified by introducing additional variables, user-defined costs, and/or user-defined
constraints. The full extended formulation can be written as follows:
min
ˆxf(x) + fu(ˆx) (6.34)
subject to
ˆg(ˆx) = 0 (6.35)
ˆ
h(ˆx)0 (6.36)
ˆxmin ˆxˆxmax (6.37)
lAˆxu(6.38)
The first difference to note is that the optimization variable xfrom the standard
OPF formulation has been augmented with additional variables zto form a new
optimization variable ˆx, and likewise with the lower and upper bounds.
ˆx=x
zˆxmin =xmin
zmin ˆxmax =xmax
zmax (6.39)
Second, there is an additional user-defined cost term fu(ˆx) in the objective function.
This cost consists of three pieces that will be described in more detail below.
fu(ˆx) = fq(ˆx) + fnln(ˆx) + flegacy(ˆx) (6.40)
Third, the nonlinear constraints gand hare augmented with user defined additions
guand huto give ˆgand ˆ
h.
ˆg(ˆx) = g(x)
gu(ˆx),ˆ
h(ˆx) = h(x)
hu(ˆx)(6.41)
And finally, a new set of linear constraints are included in (6.38).
Up through version 6.0 of Matpower, the OPF extensions were handled via op-
tional input parameters that define any additional variables,22 linear constraints,23
22Parameters zmin and zmax in (6.39).
23Parameters A,l,uin (6.38).
60
and costs of the pre-specified form defined by flegacy.24 This preserved the ability to
use solvers that employ pre-compiled MEX files to compute all of the costs and con-
straints. This is referred to as Matpower’s legacy extended OPF formulation [24].
For the AC OPF, subsequent versions also include the general nonlinear con-
straints guand hu, and the quadratic and general nonlinear costs fqand fnln. The
new quadratic cost terms can be handled by all of Matpower’s AC OPF solvers,
but the general nonlinear costs and constraints require a solver that uses Matlab
code to implement the function, gradient and Hessian evaluations.25
Section 7describes the mechanisms available to the user for taking advantage of
the extensible formulation described here.
6.3.1 User-defined Variables
The creation of additional user-defined zvariables can be done explicitly or implicitly
based on the difference between the number of columns in Aand the dimension of
the standard OPF optimization variable x. The optional vectors zmin and zmax are
available to impose lower and upper bounds on z, respectively.
6.3.2 User-defined Constraints
Linear Constraints – The user-defined linear constraints (6.38) are general
linear restrictions involving all of the optimization variables and are specified
via matrix Aand lower and upper bound vectors land u. These parameters
can be used to create equality constraints (li=ui) or inequality constraints
that are bounded below (ui=), bounded above (li=) or bounded on
both sides.
Nonlinear Constraints – The user-defined general nonlinear constraints take
the form
gj
u(x)=0 j∈ Gu(6.42)
hj
u(x)0j∈ Hu,(6.43)
where Guand Huare sets of indices for user-defined equality and inequality
constraint sets, respectively.
Each of these constraint sets is defined by two M-file functions, similar to those
required by MIPS, one that computes the constraint values and their gradients
(Jacobian), and the other that computes Hessian values.
24Parameters H,C,N, ˆr,k,d,min (6.48)–(6.51).
25At the time of this writing, this includes solvers based on MIPS,fmincon,Ipopt and KNITRO.
61
6.3.3 User-defined Costs
The user-defined cost function fuconsists of three terms for three different types of
costs: quadratic, general nonlinear, and legacy. Each term is a simple summation
over all of the cost sets of that type.
fq(ˆx) = Pjfj
q(ˆx) (6.44)
fnln(ˆx) = Pjfj
nln(ˆx) (6.45)
flegacy(ˆx) = Pjfj
legacy(ˆx) (6.46)
Quadratic Costs for a cost set jare specified by parameters Qj,cjand kj
that define a quadratic function of the optimization variable ˆx.
fj
q(ˆx) = ˆxTQjˆx+cj
Tˆx+kj(6.47)
General Nonlinear Costs for a cost set jconsist of a cost function fj
nln(ˆx)
provided in the form of a function handle to an M-file function that evaluates
the cost and its gradients and Hessian for a given value of ˆx.
Legacy Costs fj
legacy(ˆx) are specified in terms of parameters Hj,Cj,Nj, ˆrj,
kj,djand mj. For simplicity of presentation, we will drop the jsubscript for
the rest of this discussion. All of the parameters are nw×1 vectors except the
symmetric nw×nwmatrix Hand the nw×nˆxmatrix N. The legacy user cost
function takes the form
flegacy(ˆx) = 1
2wTHw +CTw(6.48)
where wis defined in several steps as follows. First, a new vector uis created
by applying a linear transformation Nand shift ˆrto the full set of optimization
variables
u=Nˆxˆr, (6.49)
then a scaled function with a “dead zone” is applied to each element of uto
produce the corresponding element of w.
wi=
mifdi(ui+ki), ui<ki
0,kiuiki
mifdi(uiki), ui> ki
(6.50)
62
Here kispecifies the size of the “dead zone”, miis a simple scale factor and fdiis
a pre-defined scalar function selected by the value of di. Currently, Matpower
implements only linear and quadratic options:
fdi(α) = α, if di= 1
α2,if di= 2 (6.51)
as illustrated in Figure 6-1 and Figure 6-2, respectively.
wi
mi
ri
ˆri
ki
ki
Figure 6-1: Relationship of wito rifor di= 1 (linear option)
This form for flegacy provides the flexibility to handle a wide range of costs, from
simple linear functions of the optimization variables to scaled quadratic penal-
ties on quantities, such as voltages, lying outside a desired range, to functions
of linear combinations of variables, inspired by the requirements of price coor-
dination terms found in the decomposition of large loosely coupled problems
encountered in our own research.
Some limitations are imposed on the parameters in the case of the DC OPF
since Matpower uses a generic quadratic programming (QP) solver for the
optimization. In particular, ki= 0 and di= 1 for all i, so the “dead zone” is
not considered and only the linear option is available for fdi. As a result, for
the DC case (6.50) simplifies to wi=miui.
63
wi
ri
ˆri
ki
ki
Figure 6-2: Relationship of wito rifor di= 2 (quadratic option)
6.4 Standard Extensions
In addition to making this extensible OPF structure available to end users, Mat-
power also takes advantage of it internally to implement several additional capa-
bilities.
6.4.1 Piecewise Linear Costs
The standard OPF formulation in (6.1)–(6.4) does not directly handle the non-
smooth piecewise linear cost functions that typically arise from discrete bids and
offers in electricity markets. When such cost functions are convex, however, they
can be modeled using a constrained cost variable (CCV) method. The piecewise lin-
ear cost function c(x) is replaced by a helper variable yand a set of linear constraints
that form a convex “basin” requiring the cost variable yto lie in the epigraph of the
function c(x).
Figure 6-3 illustrates a convex n-segment piecewise linear cost function
c(x) =
m1(xx1) + c1, x x1
m2(xx2) + c2, x1< x x2
.
.
..
.
.
mn(xxn) + cn, xn1< x
(6.52)
defined by a sequence of points (xj, cj), j= 0 . . . n, where mjdenotes the slope of
64
x
x0
x1
x2
c
c0
c1
c2
y
cn
xn
Figure 6-3: Constrained Cost Variable
the j-th segment
mj=cjcj1
xjxj1
, j = 1 . . . n (6.53)
and x0< x1<··· < xnand m1m2≤ ··· < mn.
The “basin” corresponding to this cost function is formed by the following n
constraints on the helper cost variable y:
ymj(xxj) + cj, j = 1 . . . n. (6.54)
The cost term added to the objective function in place of c(x) is simply the variable y.
Matpower uses this CCV approach internally to automatically generate the
appropriate helper variable, cost term and corresponding set of constraints for any
piecewise linear costs on real or reactive generation. All of Matpower’s OPF
solvers, for both AC and DC OPF problems, use the CCV approach with the ex-
ception of two that are part of the optional TSPOPF package [25], namely the
step-controlled primal/dual interior point method (SCPDIPM) and the trust region
based augmented Lagrangian method (TRALM), both of which use a cost smoothing
technique instead [26].
Note that Matpower (in opf setup) automatically converts any single-segment
piecewise linear costs into polynomial (linear) form to avoid unnecessarily creating
extra variables and constraints. It is this modified cost, rather than the original
piecewise linear equivalent, that is returned in the gencost field of the results struct.
65
6.4.2 Dispatchable Loads
A simple approach to dispatchable or price-sensitive loads is to model them as nega-
tive real power injections with associated negative costs. This is done by specifying
a generator with a negative output, ranging from a minimum injection equal to the
negative of the largest possible load to a maximum injection of zero.
Consider the example of a price-sensitive load whose marginal benefit function is
shown in Figure 6-4. The demand pdof this load will be zero for prices above λ1,p1
for prices between λ1and λ2, and p1+p2for prices below λ2.
λ(marginal benefit)
$/MW
MW
λ1
λ2
p1
p2
p(load)
Figure 6-4: Marginal Benefit or Bid Function
This corresponds to a negative generator with the piecewise linear cost curve
shown in Figure 6-5. Note that this approach assumes that the demand blocks can
be partially dispatched or “split”. Requiring blocks to be accepted or rejected in
their entirety would pose a mixed-integer problem that is beyond the scope of the
current Matpower implementation.
It should be noted that, with this definition of dispatchable loads as negative
generators, if the negative cost corresponds to a benefit for consumption, minimizing
the cost f(x) of generation is equivalent to maximizing social welfare.
With an AC network model, there is also the question of reactive dispatch for
such loads. Typically the reactive injection for a generator is allowed to take on any
value within its defined limits. Since this is not normal load behavior, the model used
66
MW
2
1
p1
p2
$
p(injection)
c(total cost)
1p1
2p2
Figure 6-5: Total Cost Function for Negative Injection
in Matpower assumes that dispatchable loads maintain a constant power factor.
When formulating the AC OPF problem, Matpower will automatically generate
an additional equality constraint to enforce a constant power factor for any “negative
generator” being used to model a dispatchable load.
The power factor, which can be lagging or leading, is determined by the ratio of
reactive to active power for the load and is specified by the active and reactive limits
defining the nominal load in the gen matrix. For all dispatchable loads, the value
in the PMIN column is negative and defines the nominal active power of the load.
And PMAX is zero, allowing the load to be fully curtailed depending on the price.
The reactive limits, QMIN and QMAX, depend on whether the power flow is lagging
or leading. One defines the nominal reactive load and the other must be zero to
allow the load to be fully curtailed. The values of PG and QG must be defined to be
consistent with the nominal power factor.
Lagging Power Factor – The reactive injection is negative, meaning that
reactive power is consumed by the load. Hence, QMIN is negative, QMAX is zero,
and PG and QG must be set so that QG is equal to PG * QMIN/PMIN.
Leading Power Factor – The reactive injection is positive, that is, reactive
power is produced by the load. Hence, QMAX is positive, QMIN is zero, and PG
and QG must be set so that QG is equal to PG * QMAX/PMIN.
67
6.4.3 Generator Capability Curves
The typical AC OPF formulation includes box constraints on a generator’s real and
reactive injections, specified as simple lower and upper bounds on p(pmin and pmax)
and q(qmin and qmax). On the other hand, the true P-Qcapability curves of phys-
ical generators usually involve some tradeoff between real and reactive capability,
so that it is not possible to produce the maximum real output and the maximum
(or minimum) reactive output simultaneously. To approximate this tradeoff, Mat-
power includes the ability to add an upper and lower sloped portion to the standard
box constraints as illustrated in Figure 6-6, where the shaded portion represents the
feasible operating region for the unit.
qmax
1
qmax
2
qmin
2
qmin
1
qmin
qmax
pmax
pmin
p1
p2
q
p
Figure 6-6: Generator P-QCapability Curve
The two sloped portions are constructed from the lines passing through the two
pairs of points defined by the six parameters p1,qmin
1,qmax
1,p2,qmin
2, and qmax
2.
If these six parameters are specified for a given generator in columns PC1QC2MAX
(11–16), Matpower automatically constructs the corresponding additional linear
inequality constraints on pand qfor that unit.
68
If one of the sloped portions of the capability constraints is binding for genera-
tor k, the corresponding shadow price is decomposed into the corresponding µPmax
and µQmin or µQmax components and added to the respective column (MU PMAX,MU QMIN
or MU QMAX) in the kth row of gen.
6.4.4 Branch Angle Difference Limits
The difference between the bus voltage angle θfat the from end of a branch and
the angle θtat the to end can be bounded above and below to act as a proxy for a
transient stability limit, for example. If these limits are provided in columns ANGMIN
(12) and ANGMAX (13) of the branch matrix, Matpower creates the corresponding
constraints on the voltage angle variables.26
6.5 Solvers
Early versions of Matpower relied on Matlab’s Optimization Toolbox [27] to
provide the NLP and QP solvers needed to solve the AC and DC OPF problems,
respectively. While they worked reasonably well for very small systems, they did not
scale well to larger networks. Eventually, optional packages with additional solvers
were added to improve performance, typically relying on Matlab extension (MEX)
files implemented in Fortran or C and pre-compiled for each machine architecture.
Some of these MEX files are distributed as optional packages due to differences in
terms of use. For DC optimal power flow, there is a MEX build [28] of the high
performance interior point BPMPD solver [29] for LP/QP problems. For the AC
OPF problem, the MINOPF [30] and TSPOPF [25] packages provide solvers suitable
for much larger systems. The former is based on MINOS [31] and the latter includes
the primal-dual interior point and trust region based augmented Lagrangian methods
described in [26]. Matpower version 4 and later also includes the option to use
the open-source Ipopt solver27 for solving both AC and DC OPFs, based on the
Matlab MEX interface to Ipopt28. It also includes the option to use CPLEX29 or
MOSEK30 for DC OPFs. Matpower 4.1 added the option to use KNITRO [32]31
26The voltage angle difference for branch kis taken to be unbounded below if branch(k, ANGMIN)
is less than or equal to 360 and unbounded above if branch(k, ANGMAX) is greater than or equal
to 360. If both parameters are zero, the voltage angle difference is unconstrained.
27Available from http://www.coin-or.org/projects/Ipopt.xml.
28See https://projects.coin-or.org/Ipopt/wiki/MatlabInterface.
29See http://www.ibm.com/software/integration/optimization/cplex-optimizer/.
30See http://www.mosek.com/.
31See http://www.ziena.com/.
69
for AC OPFs and the Gurobi Optimizer [33]32 for DC OPFs and Matpower 5
added GLPK [34] and 5.1 added CLP [35]. See Appendix Gfor more details on
these optional packages.
Beginnning with version 4, Matpower also includes its own primal-dual interior
point method implemented in pure-Matlab code, derived from the MEX implemen-
tation of the algorithms described in [26]. This solver is called MIPS (Matpower
Interior Point Solver) and is described in more detail in Appendix A. If no optional
packages are installed, MIPS will be used by default for both the AC OPF and
as the QP solver used by the DC OPF. The AC OPF solver also employs a unique
technique for efficiently forming the required Hessians via a few simple matrix opera-
tions [3638]. This solver has application to general nonlinear optimization problems
outside of Matpower and can be called directly as mips. There is also a conve-
nience wrapper function called qps mips making it trivial to set up and solve LP and
QP problems, with an interface similar to quadprog from the Matlab Optimization
Toolbox.
6.6 runopf
In Matpower, an optimal power flow is executed by calling runopf with a case
struct or case file name as the first argument (casedata). In addition to printing
output to the screen, which it does by default, runopf optionally returns the solution
in a results struct.
>> results = runopf(casedata);
The results struct is a superset of the input Matpower case struct mpc, with
some additional fields as well as additional columns in some of the existing data
fields. In addition to the solution values included in the results for a simple power
flow, shown in Table 4-1 in Section 4.4, the following additional optimal power flow
solution values are stored as shown in Table 6-1.
32See http://www.gurobi.com/.
70
Table 6-1: Optimal Power Flow Results
name description
results.f final objective function value
results.x final value of optimization variables (internal order)
results.om OPF model object
results.bus(:, LAM P) Lagrange multiplier on real power mismatch
results.bus(:, LAM Q) Lagrange multiplier on reactive power mismatch
results.bus(:, MU VMAX) Kuhn-Tucker multiplier on upper voltage limit
results.bus(:, MU VMIN) Kuhn-Tucker multiplier on lower voltage limit
results.gen(:, MU PMAX) Kuhn-Tucker multiplier on upper Pglimit
results.gen(:, MU PMIN) Kuhn-Tucker multiplier on lower Pglimit
results.gen(:, MU QMAX) Kuhn-Tucker multiplier on upper Qglimit
results.gen(:, MU QMIN) Kuhn-Tucker multiplier on lower Qglimit
results.branch(:, MU SF) Kuhn-Tucker multiplier on flow limit at “from” bus
results.branch(:, MU ST) Kuhn-Tucker multiplier on flow limit at “to” bus
results.mu shadow prices of constraints
results.g (optional) constraint values
results.dg (optional) constraint 1st derivatives
results.raw raw solver output in form returned by MINOS, and more
results.var.val final value of optimization variables, by named subset
results.var.mu shadow prices on variable bounds, by named subset
results.nle shadow prices on nonlinear equality constraints, by named subset
results.nli shadow prices on nonlinear inequality constraints, by named subset
results.lin shadow prices on linear constraints, by named subset
results.cost final value of user-defined costs, by named subset
See help for opf model and opt model for more details.
See help for opf for more details.
71
Additional optional input arguments can be used to set options (mpopt) and
provide file names for saving the pretty printed output (fname) or the solved case
data (solvedcase).
>> results = runopf(casedata, mpopt, fname, solvedcase);
Some of the main options that control the optimal power flow simulation are listed
in Tables 6-2 and 6-3. There are many other options that can be used to control the
termination criteria and other behavior of the individual solvers. See Appendix C
or the mpoption help for details. As with runpf the output printed to the screen can
be controlled by the options in Table 4-3, but there are additional output options
for the OPF, related to the display of binding constraints that are listed Table 6-4,
along with an option that can be used to force the AC OPF to return information
about the constraint values and Jacobian and the objective function gradient and
Hessian.
For OPF problems, the preferred way to eliminate the flow limit on a branch is
to set the RATE A column (6) of the corresponding row in the branch matrix to zero.
This indicates a completely unconstrained flow (as opposed to zero flow).
By default, runopf solves an AC optimal power flow problem using a primal dual
interior point method. To run a DC OPF, the model option must be set to 'DC'. For
convenience, Matpower provides a function rundcopf which is simply a wrapper
that sets the model to 'DC'before calling runopf.
Internally, the runopf function does a number of conversions to the problem
data before calling the appropriate solver routine for the selected OPF algorithm.
This external-to-internal format conversion is performed by the ext2int function,
described in more detail in Section 7.3.1, and includes the elimination of out-of-service
equipment, the consecutive renumbering of buses and the reordering of generators
by increasing bus number. All computations are done using this internal indexing.
When the simulation has completed, the data is converted back to external format
by int2ext before the results are printed and returned. In addition, both ext2int
and int2ext can be customized via user-supplied callback routines to convert data
needed by user-supplied variables, constraints or costs into internal indexing.
72
Table 6-2: Optimal Power Flow Solver Options
name default description
opf.ac.solver 'DEFAULT'AC optimal power flow solver:
'DEFAULT'– choose default solver, i.e. 'MIPS'
'MIPS'– MIPS, Matpower Interior Point Solver,
primal/dual interior point method
'FMINCON'Matlab Optimization Toolbox, fmincon
'IPOPT'Ipopt*
'KNITRO'– KNITRO*
'MINOPF'– MINOPF*
, MINOS-based solver
'PDIPM'– PDIPM*
, primal/dual interior point method
'SDPOPF'– SDPOPF*
, solver based on semidefinite relax-
ation
'TRALM'– TRALM*
, trust region based augmented Lan-
grangian method
opf.dc.solver 'DEFAULT'DC optimal power flow solver:
'DEFAULT' choose default solver based on availability
in the following order: 'GUROBI','CPLEX',
'MOSEK','OT','GLPK'(linear costs only),
'BPMPD','MIPS'
'MIPS'– MIPS, Matpower Interior Point Solver,
primal/dual interior point method
'BPMPD'– BPMPD*
'CLP'– CLP*
'CPLEX'– CPLEX*
'GLPK'– GLPK*(no quadratic costs)
'GUROBI'– Gurobi*
'IPOPT'Ipopt*
'MOSEK'– MOSEK*
'OT'Matlab Opt Toolbox, quadprog,linprog
*Requires the installation of an optional package. See Appendix Gfor details on the corresponding package.
For MIPS-sc, the step-controlled version of this solver, the mips.step control option must be set to 1.
For SC-PDIPM, the step-controlled version of this solver, the pdipm.step control option must be set to 1.
73
Table 6-3: Other OPF Options
name default description
opf.current balance 0 use current, as opposed to power, balance formulation for
AC OPF, 0 or 1
opf.v cartesian 0 use cartesian, as opposed to polar, representation for volt-
ages for AC OPF, 0 or 1
opf.violation 5×106constraint violation tolerance
opf.use vg 0 respect generator voltage setpoint, 0 or 1
0 – use voltage magnitude limits specified in bus, ig-
nore VG in gen
1 – replace voltage magnitude limits specified in bus
by VG in corresponding gen
opf.flow lim 'S'quantity to limit for branch flow constraints
'S'– apparent power flow (limit in MVA)
'P'– active power flow (limit in MW)
'I' current magnitude (limit in MVA at 1 p.u.
voltage)
'2'– same as 'P', but implemented using square
of active flow, rather than simple max
opf.ignore angle lim 0 ignore angle difference limits for branches
0 – include angle difference limits, if specified
1 – ignore angle difference limits even if specified
opf.softlims.default 1 behavior of OPF soft limits for which parameters are not
explicitly provided
0 do not include softlims if not explicitly specified
1 include softlims with default values if not ex-
plicitly specified
opf.init from mpc*-1 specify whether to use the current state in Matpower
case to initialize OPF
-1 – Matpower decides based on solver/algorithm
0 – ignore current state in Matpower case
1 – use current state in Matpower case
opf.start 0 strategy for initializing OPF starting point
0 – default, Matpower decides based on solver,
(currently identical to 1)
1 – ignore current state in Matpower case
2 – use current state in Matpower case
3 – solve power flow and use resulting state
opf.return raw der 0 for AC OPF, return constraint and derivative info in
results.raw (in fields g,dg,df,d2f)
*Deprecated. Use opf.start instead.
Using a value between 0 and 1 results in the limits being determined by the corresponding weighted average of
the 2 options.
Only applies to fmincon,Ipopt, KNITRO and MIPS solvers, which use an interior point estimate; others use
current state in Matpower case, as with opf.start = 2.
74
Table 6-4: OPF Output Options
name default description
out.lim.all -1 controls constraint info output
-1 – individual flags control what is printed
0 – do not print any constraint info
1 – print only binding constraint info
2 – print all constraint info
out.lim.v 1 control output of voltage limit info
0 – do not print
1 – print binding constraints only
2 – print all constraints
out.lim.line 1 control output of line flow limit info
out.lim.pg 1 control output of gen active power limit info
out.lim.qg 1 control output of gen reactive power limit info
Overrides individual flags.
Takes values of 0, 1 or 2 as for out.lim.v.
75
7 Extending the OPF
The extended OPF formulation described in Section 6.3 allows the user to modify the
standard OPF formulation to include additional variables, costs and/or constraints.
There are two primary mechanisms available for the user to accomplish this. The first
is by directly constructing the full parameters for the addional costs or constraints
and supplying them either as fields in the case struct or directly as arguments to
the opf function. The second, and more powerful, method is via a set of callback
functions that customize the OPF at various stages of the execution. Matpower
includes several examples of using the latter method, for example to add a fixed zonal
reserve requirement, to implement interface flow limits, dispatchable DC transmission
lines, or branch flow soft limits.
7.1 Direct Specification
This section describes the additional fields that can be added to mpc (the Matpower
case struct) or, alternatively, the input parameters that can be passed directly to the
opf function. The former is the preferred approach, as it allows the normal use of
runopf and related functions.
7.1.1 User-defined Variables
In the case of direct specification, additional variables are created implicitly based on
the difference between the number of columns in Aand the number nxof standard
OPF variables. If Ahas more columns than xhas elements, the extra columns are
assumed to correspond to a new zvariable. The initial value and lower and upper
bounds for zcan also be specified in the optional fields or arguments, z0,zl and zu,
respectively.
7.1.2 User-defined Constraints
Linear Constraints can be added by specifying the A,land uparameters of
(6.38) directly as fields or arguments of the same names, A,land u, respectively,
where Ais sparse.
Nonlinear Constraints for a constraint set j, that is, gj
u(x) or hj
u(x) from
(6.42) or (6.43), are implemented by defining two M-file functions, similar to
76
those required by MIPS. The first is a function to compute the constraint values
and their gradients (Jacobian),33 with calling syntax:
[g, dg] = my constraint fcn(x, <p1>, <p2>, ...)
Here <p1> and <p2> represent arbitrary optional input parameters that remain
constant for all calls to the function. The second is a function to compute the
Hessian of the corresponding term in the Lagrangian function, that is the term
corresponding to λTgj
u(x) or µThj
u(x). This function has the following calling
syntax:
d2G = my constraint hess(x, lambda, <p1>, <p2>, ...)
Once again this is similar to the form of the Hessian evaluation function ex-
pected by MIPS.34
In order to add a set of user-defined nonlinear constraints to the formula-
tion through direct specification, an entry must be added to the optional
user constraints.nle (nonlinear equality) or user constraints.nli (nonlin-
ear inequality) fields of the Matpower case struct. These fields are cell ar-
rays, in which each element (also a cell array) specifies a constraint set of the
corresponding kind. The format is as follows, where the details are described
in Table 7-1.
mpc.user_constraints.nle = {
{name, N, g_fcn, hess_fcn, varsets, params},
...
};
There is an example in the OPF testing code (e.g. t opf mips) near the end,
that implements a nonlinear relationship between three different generator out-
puts by adding the following line.
33The differences between this function and the one required by MIPS is that (1) this one repre-
sents a single set of equality constraints or inequality constraints, not both, (2) it returns in dg the
m×nJacobian (for mconstraints and nvariables), whereas MIPS expects the n×mtranspose,
(3) this function allows arbitrary additional parameters, and (4) xcan be a cell array of sub-vectors
of optimization variable ˆx(see varsets in Table 7-1).
34The differences between this function and the one required by MIPS is that (1) this one returns
the Hessian of a single term of the Lagrangian, not of the full Lagrangian, (2) the lambda argument
is a simple vector of multipliers (λor µ) corresponding just to this set of constraints, not a struct
containing the full λand µvectors, in fields eqnonlin and ineqnonlin, respectively, and (3) this
function allows arbitrary additional parameters, and (4) xcan be a cell array of sub-vectors of
optimization variable ˆx(see varsets in Table 7-1).
77
Table 7-1: User-defined Nonlinear Constraint Specification
name description
name string with name of constraint set, used to label multipliers in results struct
Nnumber of constraints, i.e. dimension of gj
u(x) (or hj
u(x) as the case may be)
g fcn string containing name of function to evaluate constraint and gradients (Jacobian)
hess fcn string containing name of function to evaluate Hessian of corresponding term of
Lagrangian
varsets cell array of variable set names, specifying sub-vectors of optimization vector ˆxto
be passed as inputs in x
params cell array of optional, arbitrary parameters to pass to each call to the constraint and
Hessian evaluation functions
If varsets is empty, xwill be the full optimization vector ˆx, otherwise it will be a cell array of sub-vectors of ˆxfor
the specified variable sets. Valid names include 'Va','Vm','Pg', and 'Qg'. It can include others depending on
the OPF extensions in use. See the variable names displayed by results.om for a complete list for your problem.
mpc.user_constraints.nle = {
{'Pg_usr', 1, 'opf_nle_fcn1', 'opf_nle_hess1', {'Pg'}, {}}
};
This adds a single constraint named 'Pg usr'as a function of the vector of
generator active injections (xwill be {Pg}, where Pg is a sub-vector of the
optimization vector ˆxcontaining only the generator active injections). The
constraints and gradients are evaluated by a function named 'opf nle fcn1'
and the Hessian of the corresponding term of the Lagrangian by a function
named 'opf nle hess1', neither of which expect any additional parameters.
7.1.3 User-defined Costs
Quadratic Costs by direct specification are not currently supported.
General Nonlinear Costs by direct specification are not currently supported.
Legacy Costs – To add legacy costs directly, the parameters H,C,N, ˆr,k,
dand mof (6.48)–(6.51) described in Section 6.3.3 are specified as fields or
arguments H,Cw,Nand fparm, respectively, where fparm is the nw×4 matrix
fparm =dˆr k m .(7.1)
When specifying additional costs, Nand Cw are required, while Hand fparm are
optional. The default value for His a zero matrix, and the default for fparm is
78
such that dand mare all ones and ˆrand kare all zeros, resulting in simple
linear cost, with no shift or “dead-zone”. Nand Hshould be specified as sparse
matrices.
7.1.4 Additional Comments
For a simple formulation extension to be used for a small number of OPF cases, this
method has the advantage of being direct and straightforward. While Matpower
does include code to eliminate the columns of Aand Ncorresponding to Vmand Qg
when running a DC OPF35, as well as code to reorder and eliminate columns appro-
priately when converting from external to internal data formats, this mechanism still
requires the user to take special care in preparing the Aand Nmatrices to ensure
that the columns match the ordering of the elements of the optimization vectors x
and z. All extra constraints and variables must be incorporated into a single set of
parameters that are constructed before calling the OPF. The bookkeeping needed to
access the resulting variables and shadow prices on constraints and variable bounds
must be handled manually by the user outside of the OPF, along with any pro-
cessing of additional input data and processing, printing or saving of the additional
result data. Making further modifications to a formulation that already includes
user-supplied costs, constraints or variables, requires that both sets be incorporated
into a new single consistent set of parameters.
7.2 Callback Functions
The second method, based on defining a set of callback functions, offers several
distinct advantages, especially for more complex scenarios or for adding a feature
for others to use, such as the zonal reserve requirement or the interface flow limits
mentioned previously. This approach makes it possible to:
define and access variable/constraint/cost sets as individual named blocks
define constraints, costs only in terms of variables directly involved
pre-process input data and/or post-process result data
print and save new result data
simultaneously use multiple, independently developed extensions (e.g. zonal
reserve requirements and interface flow limits)
35Only if they contain all zeros.
79
With this approach the OPF formulation is modified in the formulation callback,
which is described and illustrated below in Section 7.3.2. The modifications to the
formulation are handled by adding variables, costs and/or constraints to the OPF
Model object (om) using one of the add * methods. Please see the documentation for
each of these methods for more details.
7.2.1 User-defined Variables
Additional variables are added using the add var method.
om.add_var('myV', N, myV0, myV_min, myV_max);
Here myV is the name of the variable set, Nthe number of variables being added (i.e.
this is an N×1 vector being appended to the current optimization variable ˆx), and
myV0,myV min,myV max are vectors of initial values, lower bounds and upper bounds,
respectively.
7.2.2 User-defined Costs
Quadratic Costs are added using the add quad cost method.
om.add_quad_cost('myQcost', Q, c, k, varsets);
Here myQcost is the name of the cost set, Q,cand kare the Qj,cjand kj
parameters from (6.47), respectively, and var sets is an optional cell array of
variable set names. If var sets is provided, the dimensions of Qand cwill
correspond, not to the full optimization vector ˆx, but to the subvector formed
by stacking only the variable sets specified in var sets.
General Nonlinear Costs are added using the add nln cost method.
om.add_nln_cost('myNonlinCost', 1, fcn, varsets);
Here myNonlinCost is the name of the cost set, fcn is a function handle and
var sets is an optional cell array of variable set names. The function handle
fcn must point to a function that implements the fj
nln(ˆx) function from (6.46),
returning the value of the function, along with its gradient and Hessian. This
function has a format similar to that required by MIPS for its cost function.
If var sets is provided, instead of the full optimization vector ˆx, the xpassed
to the function fcn will be a cell array of sub-vectors of ˆxcorresponding to the
specified variable sets.
80
Legacy Costs are added using the add legacy cost method.
om.add_legacy_cost('myLegacyCost', cp, varsets);
Here myLegacyCost is the name of the cost set, cp is a struct containing the cost
parameters H,C,N, ˆr,k,dand mfrom (6.48)–(6.51) in fields H,Cw,N,rh,kk,
dd and mm, respectively, and var sets is an optional cell array of variable set
names. If var sets is provided, the number of columns in Nwill correspond,
not to the full optimization vector ˆx, but to the subvector formed by stacking
only the variable sets specified in var sets.
7.2.3 User-defined Constraints
Linear Constraints are added using the add lin constraint method.
om.lin_constraint('myLinCons', A, l, u, varsets);
Here myLinCons is the name of the constraint set, A,land ucorrespond to
additional rows to add to the A,land uparameters in (6.38), respectively, and
var sets is an optional cell array of variable set names. If var sets is provided,
the number of columns in Awill correspond, not to the full optimization vector
ˆx, but to the subvector formed by stacking only the variable sets specified in
var sets.
Nonlinear Constraints are added using the add nln constraint method.
om.nln_constraint('myNonlinCons', N, iseq, fcn, hess, varsets);
Here myNonlinCons is the name of the constraint set, Nis the number of con-
straints being added, iseq is a true or false value indicating whether this is a set
of equality (or else inequality) constraints, fcn and hess are function handles
and var sets is an optional cell array of variable set names. The function han-
dle fcn must point to a function that implements the corresponding constraint
function gj
u(x) or hj
u(x) and its gradients, and hess to one that evaluates the
corresponding term in the Hessian of the Lagrangian function. This function
has a format similar to that required by MIPS for its cost function. See more
details in Section 7.1.2.
If var sets is provided, instead of the full optimization vector ˆx, the xpassed
to the function fcn will be a cell array of sub-vectors of ˆxcorresponding to the
specified variable sets.
81
7.3 Callback Stages and Example
Matpower defines five stages in the execution of a simulation where custom code
can be inserted to alter the behavior or data before proceeding to the next stage.
This custom code is defined as a set of “callback” functions that are registered via
add userfcn for Matpower to call automatically at one of the five stages. Each
stage has a name and, by convention, the name of a user-defined callback func-
tion ends with the name of the corresponding stage. For example, a callback for
the formulation stage that modifies the OPF problem formulation to add reserve
requirements could be registered with the following line of code.
mpc = add_userfcn(mpc, 'formulation', @userfcn_reserves_formulation);
The sections below will describe each stage and the input and output arguments
for the corresponding callback function, which vary depending on the stage. An
example that employs additional variables, constraints and costs will be used for
illustration.
Consider the problem of jointly optimizing the allocation of both energy and
reserves, where the reserve requirements are defined as a set of nrz fixed zonal MW
quantities. Let Zkbe the set of generators in zone kand Rkbe the MW reserve
requirement for zone k. A new set of variables rare introduced representing the
reserves provided by each generator. The value ri, for generator i, must be non-
negative and is limited above by a user-provided upper bound rmax
i(e.g. a reserve
offer quantity) as well as the physical ramp rate ∆i.
0rimin(rmax
i,i), i = 1 . . . ng(7.2)
If the vector ccontains the marginal cost of reserves for each generator, the user
defined cost term from (6.34) is simply
fu(ˆx) = cTr. (7.3)
There are two additional sets of constraints needed. The first ensures that, for
each generator, the total amount of energy plus reserve provided does not exceed the
capacity of the unit.
pi
g+ripi,max
g, i = 1 . . . ng(7.4)
The second requires that the sum of the reserve allocated within each zone kmeets
the stated requirements.
X
iZk
riRk, k = 1 . . . nrz (7.5)
82
Table 7-2: Names Used by Implementation of OPF with Reserves
name description
mpc Matpower case struct
reserves additional field in mpc containing input parameters for zonal reserves in
the following sub-fields:
cost ng×1 vector of reserve costs, cfrom (7.3)
qty ng×1 vector of reserve quantity upper bounds, ith element is rmax
i
zones nrz ×ngmatrix of reserve zone definitions
zones(k,j) =1 if gen jbelongs to reserve zone k(jZk)
0 otherwise (j /Zk)
req nrz ×1 vector of zonal reserve requirements, kth element is Rkfrom (7.5)
om OPF model object, already includes standard OPF setup
results OPF results struct, superset of mpc with additional fields for output data
ng ng, number of generators
Rname for new reserve variable block, ith element is ri
Pg plus R name for new capacity limit constraint set (7.4)
Rreq name for new reserve requirement constraint set (7.5)
Table 7-2 describes some of the variables and names that are used in the example
callback function listings in the sections below.
7.3.1 ext2int Callback
Before doing any simulation of a case, Matpower performs some data conversion
on the case struct in order to achieve a consistent internal structure, by calling the
following.
mpc = ext2int(mpc, mpopt);
All isolated buses, out-of-service generators and branches are removed, along with
any generators or branches connected to isolated buses. The buses are renumbered
consecutively, beginning at 1, and the in-service generators are sorted by increasing
bus number. All of the related indexing information and the original data matrices
are stored in an order field in the case struct to be used later by int2ext to perform
the reverse conversions when the simulation is complete.
The first stage callback is invoked from within the ext2int function immediately
after the case data has been converted. Inputs are a Matpower case struct (mpc)
freshly converted to internal indexing, a Matpower options struct mpopt,36 and
36The mpopt may be empty if ext2int() is called manually without providing it.
83
any (optional) args value supplied when the callback was registered via add userfcn.
Output is the (presumably updated) mpc. This is typically used to reorder any input
arguments that may be needed in internal ordering by the formulation stage. The
example shows how e2i field can also be used, with a case struct that has already
been converted to internal indexing, to convert other data structures by passing in
2 or 3 extra parameters in addition to the case struct. In this case, it automatically
converts the input data in the qty,cost and zones fields of mpc.reserves to be
consistent with the internal generator ordering, where off-line generators have been
eliminated and the on-line generators are sorted in order of increasing bus number.
Notice that it is the second dimension (columns) of mpc.reserves.zones that is being
re-ordered. See the on-line help for e2i field and e2i data for more details on what
all they can do.
function mpc = userfcn_reserves_ext2int(mpc, mpopt, args)
mpc = e2i_field(mpc, {'reserves', 'qty'}, 'gen');
mpc = e2i_field(mpc, {'reserves', 'cost'}, 'gen');
mpc = e2i_field(mpc, {'reserves', 'zones'}, 'gen', 2);
This stage is also a good place to check the consistency of any additional input
data required by the extension and throw an error if something is missing or not as
expected.
7.3.2 formulation Callback
This stage is called at the end of opf setup after the OPF Model (om) object has been
initialized with the standard OPF formulation, but before calling the solver. This
is the ideal place for modifying the problem formulation with additional variables,
constraints and costs, using the add var,add lin constraint,add nln constraint,
add quad cost,add nln cost and add legacy cost methods of the OPF Model ob-
ject.37 Inputs are the om object, the Matpower options struct mpopt and any
(optional) args supplied when the callback was registered via add userfcn. Output
is the updated om object.
The om object contains both the original Matpower case data as well as all of
the indexing data for the variables and constraints of the standard OPF formulation.
37It is perfectly legitimate to register more than one callback per stage, such as when enabling
multiple independent OPF extensions. In this case, the callbacks are executed in the order they
were registered with add userfcn. E.g. when the second and subsequent formulation callbacks
are invoked, the om object will reflect any modifications performed by earlier formulation callbacks.
84
See the on-line help for opf model and opt model for more details on the OPF model
object and the methods available for manipulating and accessing it.
In the example code, a new variable block named Rwith ngelements and the
limits from (7.2) is added to the model via the add var method. Similarly, two linear
constraint blocks named Pg plus R and Rreq, implementing (7.4) and (7.5), respec-
tively, are added via the add lin constraint method. And finally, the add quad cost
method is used to add to the model a quadratic (actually linear) cost block corre-
sponding to (7.3).
Notice that the last argument to add lin constraint and add quad cost allows
the constraints and costs to be defined only in terms of the relevant parts of the
optimization variable ˆx. For example, the Amatrix for the Pg plus R constraint
contains only columns corresponding to real power generation (Pg) and reserves (R)
and need not bother with voltages, reactive power injections, etc. As illustrated in
Figure 7-1, this allows the same code to be used with both the AC OPF, where
ˆxincludes Vmand Qg, and the DC OPF where it does not. This code is also
independent of any additional variables that may have been added by Matpower
(e.g. yvariables from Matpower’s CCV handling of piece-wise linear costs) or by
the user via previous formulation callbacks. Matpower will place the constraint
and cost matrix blocks in the appropriate place when it constructs the aggregated
constraint and cost matrices at run-time. This is an important feature that enables
independently developed Matpower OPF extensions to work together.
85
function om = userfcn_reserves_formulation(om, mpopt, args)
%% initialize some things
define_constants;
mpc = om.get_mpc();
r = mpc.reserves;
ng = size(mpc.gen, 1); %% number of on-line gens
%% variable bounds
Rmin = zeros(ng, 1); %% bound below by 0
Rmax = r.qty; %% bound above by stated max reserve qty ...
k = find(mpc.gen(:, RAMP_10) > 0 & mpc.gen(:, RAMP_10) < Rmax);
Rmax(k) = mpc.gen(k, RAMP_10); %% ... and ramp rate
Rmax = Rmax / mpc.baseMVA;
%% constraints
I = speye(ng); %% identity matrix
Ar = [I I];
Pmax = mpc.gen(:, PMAX) / mpc.baseMVA;
lreq = r.req / mpc.baseMVA;
%% cost
Cw = r.cost * mpc.baseMVA; %% per unit cost coefficients
%% add them to the model
om.add_var('R', ng, [], Rmin, Rmax);
om.add_lin_constraint('Pg_plus_R', Ar, [], Pmax, {'Pg', 'R'});
om.add_lin_constraint('Rreq', r.zones, lreq, [], {'R'});
om.add_quad_cost('Rcost', [], Cw, 0, {'R'});
86
Va
A = 0A10 00 A2
A = 0A1 0A2
Ar = A1 A2
Va PgVm yQg R
Pg y R
AC OPF
DC OPF
Figure 7-1: Adding Constraints Across Subsets of Variables
87
7.3.3 int2ext Callback
After the simulation is complete and before the results are printed or saved, Mat-
power converts the case data in the results struct back to external indexing by
calling the following.
results = int2ext(results, mpopt);
This conversion essentially undoes everything that was done by ext2int. Generators
are restored to their original ordering, buses to their original numbering and all
out-of-service or isolated generators, branches and buses are restored.
This callback is invoked from int2ext immediately before the resulting case is
converted from internal back to external indexing. At this point, the simulation has
been completed and the results struct, a superset of the original Matpower case
struct passed to the OPF, contains all of the results. This results struct is passed to
the callback, along with the Matpower options struct mpopt,38 and any (optional)
args supplied when the callback was registered via add userfcn. The output of the
callback is the updated results struct. This is typically used to convert any results
to external indexing and populate any corresponding fields in the results struct.
The results struct contains, in addition to the standard OPF results, solution
information related to all of the user-defined variables, constraints and costs. Ta-
ble 7-3 summarizes where the various data is found. Each of the fields listed in
the table is actually a struct whose fields correspond to the named sets created by
add var,add lin constraint,add nln constraint,add quad cost,add nln cost and
add legacy cost.
In the example code below, the callback function begins by converting the reserves
input data in the resulting case (qty,cost and zones fields of results.reserves) back
to external indexing via calls to i2e field. See the help for i2e field and i2e data
for more details on how they can be used.
38The mpopt may be empty if int2ext() is called manually without providing it.
88
Table 7-3: Results for User-Defined Variables, Constraints and Costs
name description
results.var.val final value of user-defined variables
results.var.mu.l shadow price on lower limit of user-defined variables
results.var.mu.u shadow price on upper limit of user-defined variables
results.lin.mu.l shadow price on lower (left-hand) limit of linear constraints
results.lin.mu.u shadow price on upper (right-hand) limit of linear constraints
results.nle.lambda shadow price on nonlinear equality constraints
results.nli.mu shadow price on nonlinear inequality constraints
results.cost final value of legacy user costs
results.nlc final value of general nonlinear costs
results.qdc final value of quadratic costs
89
Then the reserves results of interest are extracted from the appropriate sub-fields
of results.var,results.lin and results.cost, converted from per unit to per MW
where necessary, and stored with external indexing for the end user in the chosen
fields of the results struct.
function results = userfcn_reserves_int2ext(results, mpopt, args)
%%----- convert stuff back to external indexing -----
%% convert all reserve parameters (zones, costs, qty, rgens)
results = i2e_field(results, {'reserves', 'qty'}, 'gen');
results = i2e_field(results, {'reserves', 'cost'}, 'gen');
results = i2e_field(results, {'reserves', 'zones'}, 'gen', 2);
r = results.reserves;
ng = size(results.gen, 1); %% number of on-line gens (internal)
ng0 = size(results.order.ext.gen, 1); %% number of gens (external)
%%----- results post-processing -----
%% get the results (per gen reserves, multipliers) with internal gen indexing
%% and convert from p.u. to per MW units
[R0, Rl, Ru] = results.om.params_var('R');
R = results.var.val.R * results.baseMVA;
Rmin = Rl * results.baseMVA;
Rmax = Ru * results.baseMVA;
mu_l = results.var.mu.l.R / results.baseMVA;
mu_u = results.var.mu.u.R / results.baseMVA;
mu_Pmax = results.lin.mu.u.Pg_plus_R / results.baseMVA;
%% store in results in results struct
z = zeros(ng0, 1);
results.reserves.R = i2e_data(results, R, z, 'gen');
results.reserves.Rmin = i2e_data(results, Rmin, z, 'gen');
results.reserves.Rmax = i2e_data(results, Rmax, z, 'gen');
results.reserves.mu.l = i2e_data(results, mu_l, z, 'gen');
results.reserves.mu.u = i2e_data(results, mu_u, z, 'gen');
results.reserves.mu.Pmax = i2e_data(results, mu_Pmax, z, 'gen');
results.reserves.prc = z;
for k = 1:ng0
iz = find(r.zones(:, k));
results.reserves.prc(k) = sum(results.lin.mu.l.Rreq(iz)) / results.baseMVA;
end
results.reserves.totalcost = results.cost.Rcost;
90
7.3.4 printpf Callback
The pretty-printing of the standard OPF output is done via a call to printpf after
the case has been converted back to external indexing. This callback is invoked from
within printpf after the pretty-printing of the standard OPF output. Inputs are
the results struct, the file descriptor to write to, a Matpower options struct, and
any (optional) args supplied via add userfcn. Output is the results struct. This is
typically used for any additional pretty-printing of results.
In this example, the out.all flag in the options struct is checked before printing
anything. If it is non-zero, the reserve quantities and prices for each unit are printed
first, followed by the per-zone summaries. An additional table with reserve limit
shadow prices might also be included.
91
function results = userfcn_reserves_printpf(results, fd, mpopt, args)
%% define named indices into data matrices
[GEN_BUS, PG, QG, QMAX, QMIN, VG, MBASE, GEN_STATUS, PMAX, PMIN, ...
MU_PMAX, MU_PMIN, MU_QMAX, MU_QMIN, PC1, PC2, QC1MIN, QC1MAX, ...
QC2MIN, QC2MAX, RAMP_AGC, RAMP_10, RAMP_30, RAMP_Q, APF] = idx_gen;
%%----- print results -----
r = results.reserves;
ng = length(r.R);
nrz = size(r.req, 1);
if mpopt.out.all ~= 0
fprintf(fd, '\n=======================================================');
fprintf(fd, '\n| Reserves |');
fprintf(fd, '\n=======================================================');
fprintf(fd, '\n Gen Bus Status Reserves Price');
fprintf(fd, '\n # # (MW) ($/MW)');
fprintf(fd, '\n---- ----- ------ -------- --------');
for k = 1:ng
fprintf(fd, '\n%3d %6d %2d ', k, results.gen(k, GEN_BUS), ...
results.gen(k, GEN_STATUS));
if results.gen(k, GEN_STATUS) > 0 && abs(results.reserves.R(k)) > 1e-6
fprintf(fd, '%10.2f', results.reserves.R(k));
else
fprintf(fd, ' - ');
end
fprintf(fd, '%10.2f ', results.reserves.prc(k));
end
fprintf(fd, '\n --------');
fprintf(fd, '\n Total:%10.2f Total Cost: $%.2f', ...
sum(results.reserves.R(r.igr)), results.reserves.totalcost);
fprintf(fd, '\n');
fprintf(fd, '\nZone Reserves Price ');
fprintf(fd, '\n # (MW) ($/MW) ');
fprintf(fd, '\n---- -------- --------');
for k = 1:nrz
iz = find(r.zones(k, :)); %% gens in zone k
fprintf(fd, '\n%3d%10.2f%10.2f', k, sum(results.reserves.R(iz)), ...
results.lin.mu.l.Rreq(k) / results.baseMVA);
end
fprintf(fd, '\n');
%% print binding reserve limit multipliers ...
end
92
7.3.5 savecase Callback
The savecase is used to save a Matpower case struct to an M-file, for example,
to save the results of an OPF run. The savecase callback is invoked from savecase
after printing all of the other data to the file. Inputs are the case struct, the file
descriptor to write to, the variable prefix (typically 'mpc.') and any (optional) args
supplied via add userfcn. Output is the case struct. The purpose of this callback is
to write any non-standard case struct fields to the case file.
In this example, the zones,req,cost and qty fields of mpc.reserves are written
to the M-file. This ensures that a case with reserve data, if it is loaded via loadcase,
possibly run, then saved via savecase, will not lose the data in the reserves field.
This callback could also include the saving of the output fields if present. The
contributed serialize function39 can be very useful for this purpose.
39http://www.mathworks.com/matlabcentral/fileexchange/1206
93
function mpc = userfcn_reserves_savecase(mpc, fd, prefix, args)
%
% mpc = userfcn_reserves_savecase(mpc, fd, mpopt, args)
%
% This is the 'savecase' stage userfcn callback that prints the M-file
% code to save the 'reserves' field in the case file. It expects a
% MATPOWER case struct (mpc), a file descriptor and variable prefix
% (usually 'mpc.'). The optional args are not currently used.
r = mpc.reserves;
fprintf(fd, '\n%%%%----- Reserve Data -----%%%%\n');
fprintf(fd, '%%%% reserve zones, element i, j is 1 iff gen j is in zone i\n');
fprintf(fd, '%sreserves.zones = [\n', prefix);
template = '';
for i = 1:size(r.zones, 2)
template = [template, '\t%d'];
end
template = [template, ';\n'];
fprintf(fd, template, r.zones.');
fprintf(fd, '];\n');
fprintf(fd, '\n%%%% reserve requirements for each zone in MW\n');
fprintf(fd, '%sreserves.req = [\t%g', prefix, r.req(1));
if length(r.req) > 1
fprintf(fd, ';\t%g', r.req(2:end));
end
fprintf(fd, '\t];\n');
fprintf(fd, '\n%%%% reserve costs in $/MW for each gen\n');
fprintf(fd, '%sreserves.cost = [\t%g', prefix, r.cost(1));
if length(r.cost) > 1
fprintf(fd, ';\t%g', r.cost(2:end));
end
fprintf(fd, '\t];\n');
if isfield(r, 'qty')
fprintf(fd, '\n%%%% max reserve quantities for each gen\n');
fprintf(fd, '%sreserves.qty = [\t%g', prefix, r.qty(1));
if length(r.qty) > 1
fprintf(fd, ';\t%g', r.qty(2:end));
end
fprintf(fd, '\t];\n');
end
%% save output fields for solved case ...
94
7.4 Registering the Callbacks
As seen in the fixed zonal reserve example, adding a single extension to the standard
OPF formulation is often best accomplished by a set of callback functions. A typical
use case might be to run a given case with and without the reserve requirements
active, so a simple method for enabling and disabling the whole set of callbacks as a
single unit is needed.
The recommended method is to define all of the callbacks in a single file containing
a “toggle” function that registers or removes all of the callbacks depending on whether
the value of the second argument is 'on'or 'off'. The state of the registration of any
callbacks is stored directly in the mpc struct. In our example, the toggle reserves.m
file contains the toggle reserves function as well as the five callback functions.
95
function mpc = toggle_reserves(mpc, on_off)
%TOGGLE_RESERVES Enable, disable or check status of fixed reserve requirements.
% MPC = TOGGLE_RESERVES(MPC, 'on')
% MPC = TOGGLE_RESERVES(MPC, 'off')
% T_F = TOGGLE_RESERVES(MPC, 'status')
if strcmp(upper(on_off), 'ON')
% <code to check for required 'reserves' fields in mpc>
%% add callback functions
mpc = add_userfcn(mpc, 'ext2int', @userfcn_reserves_ext2int);
mpc = add_userfcn(mpc, 'formulation', @userfcn_reserves_formulation);
mpc = add_userfcn(mpc, 'int2ext', @userfcn_reserves_int2ext);
mpc = add_userfcn(mpc, 'printpf', @userfcn_reserves_printpf);
mpc = add_userfcn(mpc, 'savecase', @userfcn_reserves_savecase);
mpc.userfcn.status.dcline = 1;
elseif strcmp(upper(on_off), 'OFF')
mpc = remove_userfcn(mpc, 'savecase', @userfcn_reserves_savecase);
mpc = remove_userfcn(mpc, 'printpf', @userfcn_reserves_printpf);
mpc = remove_userfcn(mpc, 'int2ext', @userfcn_reserves_int2ext);
mpc = remove_userfcn(mpc, 'formulation', @userfcn_reserves_formulation);
mpc = remove_userfcn(mpc, 'ext2int', @userfcn_reserves_ext2int);
mpc.userfcn.status.dcline = 0;
elseif strcmp(upper(on_off), 'STATUS')
if isfield(mpc, 'userfcn') && isfield(mpc.userfcn, 'status') && ...
isfield(mpc.userfcn.status, 'dcline')
mpc = mpc.userfcn.status.dcline;
else
mpc = 0;
end
else
error('toggle_dcline: 2nd argument must be ''on'', ''off'' or ''status''');
end
Running a case that includes the fixed reserves requirements is as simple as
loading the case, turning on reserves and running it.
mpc = loadcase('t_case30_userfcns');
mpc = toggle_reserves(mpc, 'on');
results = runopf(mpc);
96
7.5 Summary
The five callback stages currently defined by Matpower are summarized in Ta-
ble 7-4.
Table 7-4: Callback Functions
name invoked . . . typical use
ext2int . . . from ext2int immediately after
case data is converted from external
to internal indexing.
Check consistency of input data, con-
vert to internal indexing.
formulation . . . from opf after OPF Model (om)
object is initialized with standard
OPF formulation.
Modify OPF formulation, by adding
user-defined variables, constraints,
costs.
int2ext . . . from int2ext immediately before
case data is converted from internal
back to external indexing.
Convert data back to external index-
ing, populate any additional fields in
the results struct.
printpf . . . from printpf after pretty-printing
the standard OPF output.
Pretty-print any results not included
in standard OPF.
savecase . . . from savecase after printing all of
the other case data to the file.
Write non-standard case struct fields
to the case file.
7.6 Example Extensions
Matpower includes three OPF extensions implementing via callbacks, respectively,
the co-optimization of energy and reserves, interface flow limits and dispatchable DC
transmission lines.
7.6.1 Fixed Zonal Reserves
This extension is a more complete version of the example of fixed zonal reserve
requirements used for illustration above in Sections 7.3 and 7.4. The details of
the extensions to the standard OPF problem are given in equations (7.2)–(7.5) and
a description of the relevant input and output data structures is summarized in
Tables 7-5 and 7-6, respectively.
The code for implementing the callbacks can be found in toggle reserves. A
wrapper around runopf that turns on this extension before running the OPF is
97
Table 7-5: Input Data Structures for Fixed Zonal Reserves
name description
mpc Matpower case struct
reserves additional field in mpc containing input parameters for zonal reserves in the
following sub-fields:
cost (ngor ngr)×1 vector of reserve costs in $/MW, cfrom (7.3)
qty (ngor ngr)×1 vector of reserve quantity upper bounds in MW, ith element is
rmax
i
zones nrz ×ngmatrix of reserve zone definitions
zones(k,j) =1 if gen jbelongs to reserve zone k(jZk)
0 otherwise (j /Zk)
req nrz ×1 vector of zonal reserve requirements in MW, kth element is Rkfrom (7.5)
Here ngr is the number of generators belonging to at least one reserve zone.
Table 7-6: Output Data Structures for Fixed Zonal Reserves
name description
results OPF results struct, superset of mpc with additional fields for output data
reserves zonal reserve data, with results in the following sub-fields:
Rreserve allocation ri, in MW
Rmin lower bound of riin MW from (7.2), i.e. all zeros
Rmax upper bound of riin MW from (7.2), i.e. min(rmax
i,i)
mu shadow prices on constraints in $/MW
lshadow price on lower bound of riin (7.2)
ushadow price on upper bound of riin (7.2)
Pmax shadow price on capacity constraint (7.4)
prc reserve price in $/MW, computed for unit ias the sum of the shadow prices of
constraints kin (7.5) in which unit iparticipates (k|iZk)
All zonal reserve result sub-fields are ng×1 vectors, where the values are set to zero for units not participating
in the provision of reserves.
provided in runopf w res, allowing you to run a case with an appropriate reserves
field, such as t case30 userfcns, as follows.
results = runopf_w_res('t_case30_userfcns');
See help runopf w res and help toggle reserves for more information. Exam-
ples of using this extension and a case file defining the necessary input data can be
found in t opf userfcns and t case30 userfcns, respectively. Additional tests for
runopf w res are included in t runopf w res.
98