Reserve Formulations for Power-Based Unit Commitment with N-1 Security

This paper presents power-based unit commitment (UC) formulations with N-l security constraints. Two different formulations are proposed, one with constant reserves within the hour and one with time-varying reserves. The formulations are compared to a conventional energy-based UC formulation using different examples. We show that the energy-based formulation does not ensure N-l security at all times within the hour, since it does not account for the power profile of units. In contrast, the proposed power-based formulations guarantee N-l security within the whole hour for a piecewise linear demand profile. The formulations are also evaluated using a 5-min economic dispatch based on a real load profile, simulating the real-time operation of the power system, showing that the power-based formulations also provide increased security in this case. Compared to using a power-based formulation with constant reserves, using time-varying reserves decreases the reserve cost while ensuring a similar level of security.