Tight Formulation of Transition Ramping of Combined Cycle Units

In recent years, combined-cycle units (CCUs) have been operated as providers of flexibility to facilitate increasing shares of renewables. Consequently, optimization models have been proposed to determine the configuration of CCUs. However, most of the existing models assume that any transition between configurations finishes in a single interval. This assumption is often violated in reality, as a transition might last up to a few hours during which the CCU has limited dispatchability. In this paper, we propose a mixed-integer programming formulation that represents the transition ramping of CCUs. We show the tightness and compactness of the proposed model. Numerical studies are performed on an illustrative test system and a MISO system.