Unit commitment with flexible generating units

In today´s volatile environment of restructured power markets, and with the passage of more stringent Clean Air Act Amendment of 1990, competitive generation units must have the ability for operating under flexible conditions to respond to various market driving forces. Among generating units with flexible operating conditions, those with fuel switching and fuel-blending capabilities, as well as combined cycle units, are commonly considered for responding to volatile market environments. For a detailed modeling of flexible operating conditions, we consider fuel types and limitations along with operating constraints such as unit configuration, min up/down time, ramping, generating capacity, and start-up characteristics, which could make unit commitment (UC) calculations even more cumbersome. In this paper, we consider network constraints in security-constrained unit commitment (SCUC). The SCUC problem is decomposed into two coordinated problems, based on Benders decomposition, which include a master problem for optimizing UC and a subproblem for minimizing network violations. We apply Lagrangian relaxation to UC for modeling various types of generation units. Several numerical examples demonstrate the impact of flexible generating units on power system operation and the potential impact of volatile fuel prices and network constraints on the performance of these units.