Dispatch with Three-Segment Piecewise Linear Incremental Heat Rate Function
Given: two generating units with incremental heat rate (IHR) curves specified as three connected line segments (four points as shown in Figure 3.30).

Both units are running. Calculate the optimum schedule (i.e., the unit megawatt output for each unit) for various total megawatt values to be supplied by the units. Find the schedule for these total megawatt values:

300 MW, 500 MW, 700 MW, 840 MW

Notes: Piecewise linear increment cost curves are quite common in digital computer executions of economic dispatch. The problem is best solved by using a "search" technique. In such a technique, the incremental cost is given a value and the units are scheduled to meet this incremental cost. The megawatt outputs for the units are added together and compared to the desired total. Depending on the difference, and whether the resulting total is above or below the desired total, a new value of incremental cost is "tried."

This is repeated until the incremental cost is found that gives the correct desired value. The trick is to search in an efficient manner so that the number of iterations is minimized.