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Optimal Power Flow with Load Dispatch

Download the example files.

These examples show how Simulator’s Optimal Power Flow (OPF) may be used with dispatchable loads to relive transmission overloading. First, the OPF may be used with the minimum control change objective function. Here, the “cost” of changing a control (generator or load output) is the same for each MW of change in either direction. The OPF will seek to relieve transmission overloads with the minimum change from the initial operating point. Secondly, the OPF may be used with the minimum cost objective function. Here, generators have costs functions and loads have benefit functions. The OPF will seek to maximize total load benefit minus the total generation cost, subject to transmission constraints.

These examples are designed to run with the B7OPF.pwb file included with PowerWorld Simulator’s sample cases. This file, along with a one-line diagram and auxiliary files, are included with the example files.

For the example with minimum control change:

  1. Open the case (B7OPF.pwb) with PowerWorld Simulator.
  2. Load the auxiliary file B7OPFLoadDispatchMinControlChange.aux
  3. Solve the OPF.

Comments are provided in the auxiliary file, which may be viewed in any text editor, such as Windows Notepad. The auxiliary file makes the following changes:

  1. Sets the OPF objective function to minimum control change and globally enables load and generation controls with the OPF. (Generator controls are also needed to follow any changes in load.) These are options available in the LP OPF Dialog (Add Ons Ribbon -> OPF Options and Results…)
  2. Enables OPF load dispatch in each of the 3 areas in the case. This is the “Load MW Dispatch” field with the Area Records.
  3. Creates a single Super Area for the 3 areas and places it on OPF control.
  4. Increases the load at bus 5 to 200 MW to create an initial overload on the line between buses 2 and 5.
  5. Ensures that each load in the system is AGCable (“AGC” field with the Load Records). It also sets each load’s minimum MW value to zero and its maximum load value to the present value. In this way, each load may be curtailed, but not increased.
  6. Solves the power flow to get an initial operating point with the increased load at bus 5.

The OPF solution will then curtail the load at bus 5 and the generator at bus 2 by about 22 MW to relieve the overload.

For the example with minimum cost:

  1. Open the case (B7OPF.pwb) with PowerWorld Simulator. (You may also leave it open following the first example, with minimum control change.)
  2. Load the auxiliary file B7OPFLoadDispatchMinCost.aux
  3. Solve the OPF.

This auxiliary file is similar to the other, but has the following key differences:

  1. Sets the the OPF objective function to minimum cost.
  2. For each load, sets the “Benefit Model” field to “Piecewise Linear” and provides a benefit function with 5 break points. Each load exhibits decreasing marginal benefit at each break point.

The OPF solution decreases the loads at buses 5 and 7 to 160 MW. Both are dispatched at break points in the load benefit curves.

More details are available in our Market Modeling training course, with pertinent slides available here.

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January 5, 2015