Optimal state-of-charge balancing control for paralleled battery energy storage devices in islanded microgrid

The droop controlled battery energy storage device (BESD) becomes more and more commonplace to maintain the stability of the islanded power system. In discharging process, the state-of-charge (SOC) error between different BESDs could force some BESDs to cease operation earlier than expectation, which eliminates the system stability. An optimal SOC balancing control for parallel BESDs in islanded microgrid is proposed in this paper to effectively suppress the SOC error. The SOC of the battery is employed in the droop controller to adjust the output active power of BESD in real-time, and thus decline the SOC error among parallel BESDs. In addition, to achieve better performance of SOC balancing under the constraints of inverter's maximum output power and islanded microgrid's deviation frequency, the accelerating factor is optimized online based on the state of operation in order to diminish the final difference among SOCs. The effectiveness of the control scheme is validated by simulation and experiment results.