Grid Forming Hybrid Energy Storage System for Flexible Frequency Regulation in Islanded AC Microgrids

Due to the widespread adoption of renewable energy sources like photovoltaic and wind power, the inertia of power grid systems has experienced a significant reduction. Consequently, the AC microgrid will experience increased frequency fluctuations and a larger frequency nadir, which may endanger the dynamic performance of the grid. In order to increase the inertia, the energy storage systems have been widely used. Based on the equivalent inertia model of the virtual synchronous machine, this paper designed a grid forming hybrid energy storage system (HESS) which consists of a supercapacitor (SC) and a battery, allocating low-frequency response of load power disturbance to battery and high-frequency response to SC, thereby increasing the inertia and providing flexible frequency regulation of the AC microgrid. In order to evaluate the effectiveness of frequency regulation provided by the HESS, simulation results are offered. According to the simulation results, the designed HESS can improve the frequency nadir of the AC microgrid and achieve reasonable power allocation.