Ramp-based scheduling vs. energy-block scheduling in day-ahead market

Abstract

Although unit commitment (UC) based on energy blocks is the most common way to schedule the generators in current power systems, it has been reported that it may not be capable of guaranteeing feasible schedules. In particular, when the instantaneous power trajectories are not modeled explicitly, the solution of the energy-block based UC may include violations of ramp constraints of thermal units, which will typically be managed by an inefficient use of the operating reserves procured. In order to cope with these drawbacks, a new ramp-based UC formulation has been proposed recently in the literature, where it simultaneously schedules ramp and energy. However, this approach has only been tested with academic study cases. In order to assess the applicability of such ramp-based UC, this paper presents a comprehensive comparison between the two scheduling approaches applied to a realistic system. The ERCOT system has been selected as a good representative of a large system, where the generation mix is mainly thermal with a remarkable presence of renewable generation. The numerical results obtained provide strong evidence about the benefits of the ramp-based UC with respect to the energy-block approach.