Scheduling units with multiple operating modes in unit commitment

The operating flexibility of certain types of generating units can be exploited to reduce the production cost of their system. These units have different operating modes where the operating parameters can differ greatly depending on which mode is operating at the time. Examples of such units are: combined cycle, fuel switching/blending, constant/variable pressure, overfire and dual boiler. A general modeling approach is described which can be used to model units with multiple operating modes. It is shown how Lagrangian relaxation can be used to schedule these units. Examples are given showing the benefit of using these methods to schedule a utility's system.