Use of a Hybrid Storage System for Frequency Regulation Services from a Photovoltaic Plant: Emulating Synchronous Generator Dynamics

The gradual decommissioning of grid-forming synchronous generators and the increasing penetration of grid-following renewable energy sources such as photovoltaics (PVs), undermine the reliable operation of the grid. In this sense, even small power imbalances can cause significant frequency deviations. To address such issues, the employment of standalone battery storage systems is usually proposed to alleviate the power imbalances by releasing/absorbing energy when needed. However, a standalone battery suffers from quick lifetime fading and it cannot effectively provide multiple grid services simultaneously. To this end, this study presents a controller for a hybrid storage system that consists of a power-type superconducting magnetic energy storage (SMES) and an energy-type battery. The hybrid storage system is AC-coupled and provides frequency regulation services on behalf of the PV plant without any modification on its inverter. Through proper control, SMES handles the short-term power fluctuations emulating the inertial properties of a synchronous generator, while battery cope with long-term demands imitating the primary frequency response of the generator. Thus, the distinct features of both SMES and battery are effectively exploited, ensuring minimal stress on battery. To evaluate the proposed method during grid frequency events, simulation results are presented.