Fast Frequency Regulation in Islanded Microgrid Using Model-Based Load Estimation

Islanded microgrids have low inertia due to large penetration of non-inertial inverter based power sources. Such systems are prone to instability due to a higher rate of change of frequency (RoCoF) and large peak frequency deviation in case of a sudden load change or generation loss. This paper proposes a novel fast frequency control method for an islanded microgrid comprised of both inverter based distributed generators (DGs) and synchronous generators (SGs). The frequency controller estimates the power imbalance during the transient and compensates for it through a battery energy storage system (BESS). For the estimation of the power imbalance, an approximated linear model of the microgrid is developed considering multiple SGs operating in parallel. To transfer the compensated power from BESS to SGs, and also to maintain the state of charge (SoC) of the BESS, a SoC balancing control method is presented which is implemented by controlling the biased frequency of the SGs. The performance of the proposed frequency control method is verified using Typhoon real-time hardware-in-the-loop simulator.