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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.

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 Pg limit
results.gen(:, MU_PMIN) Kuhn-Tucker multiplier on lower Pg limit
results.gen(:, MU_QMAX) Kuhn-Tucker multiplier on upper Q g limit
results.gen(:, MU_QMIN) Kuhn-Tucker multiplier on lower Qg limit
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.

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.

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' –

Artelys Knitro*

'MINOPF' –

MINOPF*,MINOS-based solver

'PDIPM' –

PDIPM*,primal/dual interior point method‡

'SDPOPF' –

SDPOPF*, solver based on semidefinite relaxation

'TRALM' –

TRALM*, trust region based augmented Langrangian 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 G for 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.

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 voltages for AC OPF, 0 or 1

opf.violation 5× 10−6

constraint violation tolerance

opf.use_vg 0

respect generator voltage setpoint, 0 or 1†

0 –

use voltage magnitude limits specified in bus, ignore 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, i.e. kA⋅VbasekV )

'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 explicitly 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, Artelys Knitro and MIPS solvers, which use an interior point estimate; others use current state in Matpower case, as with opf.start = 2.

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.

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 and the consecutive renumbering of buses. 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.

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