Frequency-constrained unit commitment under uncertain PFR of energy storage systems

Abstract

By increasing the penetration of low-inertia renewable energy systems (RESs) in the power systems, the grid frequency stability becomes even more challenging. It is necessary to emulate the inertia or primary frequency response (PFR) of RESs with power electronic converters (PECs) to have more accurate model. Therefore, frequency constrained unit commitments (FCUCs) are developed based on fully reliable RESs or energy storage systems (ESSs) contribution in frequency control. As, PEC-based resources are not guaranteed to work perfectly in an outage, any sensor, control, or drive system malfunction results in false detection or response. Consequently, if the FCUC relies on the fast, and perfect inertia response of RESs, the frequency may exceed from its standard ranges in the presence of malfunction. To avoid frequency instability, the imperfect PEC-based resource contribution is accounted, here. Thus, the malfunctioned units are removed from the frequency ancillary services. As malfunctioned units are unknown, a distributionally robust optimization is utilized. This paper extracts a robust FCUC model considering the uncertain PFR of PEC-based ESSs. The model proficiency is analyzed under IEEE RTS96 system. It is concluded that the proposed method prevents frequency instability by spending 6.38 % more cost than the FCUC model with perfect operation of converters. In addition, merits of the proposed model get more significance in higher penetration of malfunctioned units.