Influence of Solution Coding on Solving the Unit Commitment Problem with Metaheuristics

The unit commitment problem is an important scheduling problem in planning the operation of power generators, and it is a good example of the interest devoted by the Power Engineering sector, to this area of research. It is the on/off decision problem of selecting the power generating units to be in service within a given planning horizon (from 1 day to 2 weeks, generally split in periods of 1 hour) and for how long. The committed units must satisfy the forecasted system load and reserve requirements, at minimum operating cost, subject to a large set of other system, technological and environmental constraints. Due to important start-up and shut-down costs, the problem is in general very hard to solve, as it is not possible to perform a separate optimization for each time interval. Furthermore, given that the operating costs depend on the load assigned to each generator, the problem of committing units over the planning horizon is directly connected to the additional problem of (roughly) assigning the load demand to the on-line units (“pre-dispatch” problem). The final, actual assignment is done later, for a much shorter period (usually from 15 to 60 minutes).