A new fuel cost model of thermal unit considering output ramp rate and its application to Economic Load Dispatch

ELD (Economic Load Dispatch) calculates how electric power demand should be dispatched over several thermal units to meet the load so as to optimize the total generation cost. Quadratic functions of output power have been used to describe the fuel cost of thermal unit in conventional ELD. However, in actual thermal power plants, the fuel flow rate is affected not only by the instantaneous output power itself but also its rate of change (ramp rate). The flow rate is bigger when the power output is increasing even if the output is the same. It means that we need to consider the ramp rate in the fuel cost model to improve its accuracy. Since the accurate fuel cost model provides a great economic effect in power system operation, we need to develop more accurate ELD method which considers the above mentioned effects of the output ramp rate. In this paper, firstly, we analyze how flow rate is influenced in actual thermal units by the output ramp rate using real data. Secondly, a new cost model and an ELD calculation algorithm are proposed which consider such effect. The validity of the proposal is confirmed by a simple numerical example.