State of charge balancing strategy for energy storage system in islanded DC microgrid based on micro-tuning virtual resistance

For the islanded DC microgrid, the energy storage system (ESS) can be employed to maintain the balance between the power generation and load consumption. In order to avoid the over-charging or over-discharging situation of the certain distributed energy storage unit (DESU), the accurate current sharing strategy considering unmatched line resistances is proposed to balance the state of charge (SoC) among DESUs. The micro tuning resistance is designed to eliminate the impact of line resistances on SoC balancing and achieves the accurate current sharing without affecting the bus voltage deviation. Then, the DESUs adaptively adjust the virtual resistance according to the SoC or depth of discharge (DoD) during charging and discharging to quickly balance the SoC. Additionally, the stability analysis based on the system characteristic equation is provided to theoretically guarantee the stability operation of the DC microgrid. Finally, the effectiveness of the proposed control strategy is proved by several comprehensive test cases based on real-time digital simulator (RTDS) platform.