Analytical Methods for Characterizing Frequency Dynamics in Islanded Microgrids with Gensets and Energy Storage

Microgrids with increased penetration of renewables experience serious challenges due to large frequency excursions under power system disturbances. An energy storage system (ESS) can provide frequency regulation, but the effectiveness depends on whether it is configured for grid-forming or grid-following mode of operation. For this purpose, two critical parameters are studied for frequency regulation in distribution systems: (i) the initial rate-of-change-of-frequency (ROCOF), and (ii) the minimum value of frequency, also known as frequency nadir, following a load change. The aim of this work is to identify analytical methods for accurately calculating the frequency parameters like ROCOF and frequency nadir. Reduced-order models are developed to determine the frequency deviation against power system disturbances. The results are verified against simulation models validated by testing at the CERTS Microgrid test bed.