A unified SoC balancing method with low-bandwidth distributed communication in island microgrid

Due to different initial state of charge (SoC) of distribution energy storage system (DESS) and mismatched line impedance, the SoC of DESS is unbalanced in microgrid. The conventional P-f droop, used to obtain accuracy load sharing, cannot balance the SoC. To overcome the drawback, this paper proposes a unified SoC based droop control method with distributed communication lines. In this scheme, the droop coefficient is changed by the correction information in real-time, which is obtained by the distributed control. Moreover, regardless of charging mode or discharging mode, the unified SoC balancing is able to be guaranteed. Meanwhile, load demand sharing is adjusted by this control method. The model of SoC based droop control is established, and the stability is verified through small signal analysis of the complete system. Finally, the effectiveness of SoC balancing and transient response are verified through simulations.