The Short-Run Security-Constrained Economic Dispatch

Abstract: In liberalized electricity markets, the outputs of controllable units (both generatorsand demands) must be defined at regular time intervals ("dispatch intervals"). Nowadays,balancing services are procured and dispatched not in the most efficient waypartly due to long dispatch intervals. The dispatch interval in most European countriesis one hour. The shortest dispatch interval is five minutes and is used in theAustralian National Electricity Market (NEM). During the dispatch interval, demandand wind power capacity uctuates a lot. To keep the supply-demand balance in thesystem, some generators participate in frequency control. This action increases thesystem operation cost.By reducing the dispatch interval to short periods of time over which physical limitsof the power system are fully respected, balance services could be dispatched in amore efficient way. This improves the overall economic efficiency of the system.This work derives the mathematical model for short-run economic dispatch. For thismodeling, three stages are considered: (1) initial steady state in which the systemmight be exposed to a change, (2) the transition period which models the transitioncost after the change happened and before the system goes to another steady stateequilibrium, and finally (3) the final steady state equilibrium which models the systemcost when the change in the system has been handled by the exible generating units.These three stages are modeled in a single optimization problem. The developedoptimization problem is a linear programming problem. The developed formulationfor the short-run economic dispatch is modeled in GAMS platform. Two applicationsof the proposed model are discussed: (1) power system security, and (2) real-timebalancing market. In the first application, analysis of the optimal dispatch of nodaloperating reserves to provide sufficient exibility to survive a set of credible contingenciesis performed. In the second application, an algorithm for the dispatch ofbalancing services in the real-time balancing market is proposed . These two applicationsof the proposed short-run economic dispatch are tested on a simple six-busexample system and IEEE twenty-four-bus example system. The optimal dispatch isfound and conclusions are drawn. The numerical results of the proposed model showpromising results.