Unit commitment in a thermal generation system with multiple pumped-storage power stations

Abstract

A model is presented of the unit-commitment problem which takes into account generator maximum and minimum outputs, maximum loading and unloading rates, minimum shutdown times, and both on- and offline costs. This is formulated as a mixed-integer problem and solved by using a branch and bound method. The linear-programming problems that arise during the search procedure in the branch and bound algorithm are converted into capacitated transshipment problems which can be solved efficiently by a graphically-based solution procedure. Multiple pumped-storage power stations are then scheduled by a search procedure based on the principle that pumping can only take place if the resulting hydrogeneration reduces total production costs. This is applied iteratively to an initial thermal unit schedule until no further cost improvement occurs. Finally, the computational requirements of this method, both with and without pumped-storage stations, are shown to be less than those of other existing techniques and to be applicable to systems of realistic size.