A SoC control strategy based on wireless droop control for energy storage systems in ac islanded microgrid

Abstract

Due to the fact that the line impedances in microgrid and initial value of State-of-Charge(SoC) are different, SoC of energy storage systems (ESS) in microgrid is unbalance and exists the phenomenon of overcharge and overdischarge of the ESS. At the same time, the conventional droop control used for balancing the output power of the inverters lead to voltage deviation in the ac island microgrid. In order to overcome these issues and prolong the service life of ESS, a wireless droop control strategy is presented in this paper. This method achieves SoC balancing by shifting droop characteristic curve according to SoC of each ESS. In order to prevent overcharge and overdischarge of ESS, ESS will operates in power control mode (PCM) when SoC reaches the maximum charge and the minimum discharge limit. A voltage compensation term is added to the proposed droop control method to restore the voltage deviation. Different cases are studied by simulation and experiment to validate the effectiveness of the proposed approach.