A novel adaptive droop control strategy for SoC balance in PV-based DC microgrids

Battery energy storage systems (BESSs) are generally used as a buffer stage for photovoltaic (PV) power generation to tolerate the output power unpredictability in DC microgrids, in which the State-of-Charge (SoC) balance is a necessary and urgent issue to be solved. To this end, an integral feedforward sliding mode controller (SMC) is adopted to replace the traditionally proportional integral (PI) controller such that the voltage response speed of the converter in each BESS can be significantly enhanced. Further, a novel adaptive droop control strategy for SoC balance with three different working modes is proposed, in which all batteries can be cooperated through three different stages corresponding to their different SoC degrees. Compared with most existing SoC balancing approaches, the proposed SoC strategy can improve the transient performance for the BESSs and their robustness against the volatility of PV output powers. The effectiveness of the proposed SoC balancing strategy is verified through a simulation in a DC microgrid network consisting of several PV generators, batteries, and loads utilizing Simulink/SimPower Systems.