Level-Shifted Pulse Width Modulation Based Battery State-of-Charge Balancing Method for Single-Phase Cascaded H-Bridge Multilevel Converters

Differences in electrochemical characteristics of batteries in cascaded H-bridge multilevel converter (CHB-MLC) based battery storage systems (BSSs) may cause variations in state-of-charges (SOCs) of batteries. As a result, capacity and efficiency of BSS decreases substantially. In this paper, a level-shifted pulse width modulation (LS-PWM) based battery SOC balancing method is proposed for grid-connected single-phase seven-level CHB-MLC based BSS. Sort and select method is employed along with LS-PWM and its feature of unequal power distribution to achieve SOC balancing. Moreover, a synchronous reference frame based bidirectional active-reactive power flow control is employed. Performance of the proposed SOC balancing method is tested and verified under unbalanced SOC conditions. It is confirmed that while active-reactive power flow is controlled, SOC balancing is achieved as well.