Optimal generation scheduling with ramping costs

In this paper, a decomposition method is proposed which relates the unit ramping process to the cost of fatigue effect in the generation scheduling of thermal systems. The objective of this optimization problem is to minimize the system operation cost, which includes the fuel cost for generating the required electrical energy and starting up decommitted units, as well as the rotor depreciation during ramping processes such as starting up, shutting down, loading, and unloading. According to the unit fatigue index curves provided by generator manufacturers, fixed unit ramping-rate limits, which have been used by previous studies, do not reflect the physical changes of generator rotors during the ramping processes due to the fatigue effect. Even though the use of properly pre-selected ramp-rate limits can guarantee a conservative generation schedule, it fails to provide the flexibility of choosing appropriate ramping rates for minimizing the system operation cost. Since ramping rates do not change linearly with ramping costs, we have to know the ramping duration beforehand in order to select the proper ramping. This is the most difficult aspect of incorporating ramping costs into the generation scheduling procedure since the ramping costs vary with the generation schedule. By introducing ramping costs, the unit on/off states can be determined more economically by the proposed method.<<ETX>>