State-of-charge balancing control strategy of battery energy storage system based on modular multilevel converter

This paper proposed a novel battery energy storage system based on modular multilevel converter (MMC), which has several merits compared with two-level and cascaded multilevel battery energy storage systems. The proposed system can manage the state-of-charges (SOCs) of all batteries to be equal to avoid the overcharge or over discharge of single battery stack as traditional. Besides, the inherent power exchange characteristics using circulating current could increase the control flexibility for SOC balancing, and improve output waveform quality, maximize storage capacity and reduce internal losses. The key issues regarding injected dc current control, SOC balancing control and circulating current control are discussed in this paper. Finally, the proposed system were verified through Matlab/Simulink simulation and a scaled down experiment prototype.