Fault-tolerant operation of the modular multilevel converter in an energy storage system based on split batteries

This paper proposes a new control structure to operate a split-battery energy storage system (sBESS) based on the modular multilevel converter (MMC) in case of multiple module faults. Energy can be shifted independently between the arms to achieve an equal power draw from all batteries and an equalization of their state-of-charge, even in case of fault. Because this operating mode requires the converter to drive additional balancing currents through its arms, this has an influence on the design, which is discussed in detail. Comprehensive simulation results demonstrate the effectiveness of the proposed approach and confirm the design considerations.