Cascaded H-bridge multilevel power conversion system of energy storage (CHB-PCS) generally has the issue of battery state of charge (SOC) imbalance among phases. To address this issue, the traditional zero-sequence voltage injection method has been commonly used, but it has slow speed and overmodulation problems when the extent of imbalance is high. Concerning this problem, this study analyzed the influencing factors of the injected zero-sequence voltage, studied the relationship between balance coefficient (Λ) and general vector (ΔSOCg), and proposed a zero-sequence voltage injection balance strategy based on self-adaptive balance coefficient. The proposed self-adaptive balance control strategy is able to regulate the coefficients during the balancing process and accelerate the balancing process without causing over-modulation, thus ensuring the safe and stable operation of the system. A simulation of CHB-PCS was built in MATLAB/SIMULINK, which verified the feasibility and effectiveness of the proposed control strategy.

cascaded H-bridge; power conversion system; SOC-balancing control; zero-sequence voltage injection.