Security constrained unit commitment with continuous time-varying reserves

Abstract

This paper presents a security constrained unit commitment (SCUC) with continuous intra-hour time-varying reserves. The hourly formulation extends the power-based UC formulation and has reserves which vary continuously within the hour, as opposed to the traditional hourly energy-based SCUC that uses constant reserves within the hour. We show that the traditional hourly energy-based formulation cannot ensure N-1 security at all times, since this formulation is not able to take the power trajectories of units within the hour into account. This is remedied by an hourly power-based version which allows the formulation of contingency constraints to guarantee N-1 security at all times within the hour. The proposed formulation uses continuous time-varying reserves which lowers the cost for providing reserves and makes better use of units’ flexibility while still ensuring N-1 security. The energy-based and power-based formulations are evaluated using different versions of a 5-min security-constrained economic dispatch (SCED) based on real load data, thus simulating the real time operation of the system under different assumptions for reserve procurement. The results show that the power-based formulation increases security compared to the energy-based formulation, both if reserves are fixed to the values from the SCUC or co-optimized in real time by the SCED.