An Improved Multilayer State of Charge Balancing Control Strategy for the Cascaded H-Bridge-Based Battery Energy Storage System

To improve the state of charge (SoC) balancing speed of each battery pack, a multilayer SoC balancing strategy is proposed for the cascaded H-bridge (CHB)-based battery energy storage system (BESS). Firstly, the negative-sequence current is injected for inter-phase SoC balancing control, and its real-time injection component is analyzed based on instantaneous power analysis. Then, the modulation wave of each H-bridge cell is adjusted for the inner-phase SoC balancing control of each battery pack. Compared with the conventional zero-sequence voltage-based SoC balancing control method, the modulation margin for inner-phase SoC balancing control is increased, and the SoC balancing speed is greatly improved. Finally, verification results indicate that the proposed multilayer SoC balancing control strategy can effectively balance the SoC of each battery pack in the CHB-based BESS.