SOC Balancing Control Strategy Based on Piecewise Adaptive Droop Coefficient Algorithm for Multi-energy Storage Units in DC Microgrid

In order to achieve the state of charge (SOC) balancing among multiple energy storage units in an islanded DC microgrid, the SOC balancing control strategy of multi-energy storage based on a piecewise adaptive droop coefficient algorithm is proposed. The proposed algorithm dynamically adjusts the droop coefficient according to the lithium battery SOC deviation. When the SOC deviation is large, the droop coefficient is adjusted so that the lithium battery that has a high (low) SOC when discharging (charging) is discharged (charged) with the maximum power. Simultaneously, another lithium battery is controlled to make up the remaining power, so the SOC balancing is accelerated. When the SOC deviation is small, the droop coefficient is optimized based on the different line impedance and the real capacity to realize the SOC balancing control. The voltage automatic recovery control is adopted to realize the non-difference of bus voltage and stabilize the bus voltage and improve the power supply quality. Finally, simulation is implemented in MATLAB/Simulink for verification. The simulation results show that the proposed control strategy can rapidly balance the SOC of multiple energy storage units and maintain the stability of the bus voltage.