Control of Microgrids with Distributed Energy Storage Operating in Islanded Mode

For microgrids with multiple distributed energy storage units (ESU) operating in islanded mode, it is important to maintain desirable frequency and voltage performance while avoiding over degradation of certain ESU. In this paper, a control strategy with State-of-Charge (SoC) balancing capability and improved dynamic performance is proposed. The washout-filter based power sharing gets rid of secondary control needed for voltage and frequency deviation due to conventional droop control. The SoC balancing is realized by adjusting the power reference instead of modifying the droop slope, so desirable frequency performance can be maintained. The transient virtual resistance (TVR) can increase damping of the system without introducing voltage deviation in steady state. Parameters of the washout filter, TVR and SoC balancing control are tuned based on small-signal analysis of the reduced model of microgrids. The proposed control strategy is verified with Matlab/Simulink simulation.