Fault Tolerant Modulation Method of Modular Multilevel DC/DC Converter for BESS Under Module Fault Conditions

The inductor current ripple performance of battery energy storage system based on modular multilevel DC/DC converter will degrade when module fault occurs. This paper proposes a phase shifting algorithm through harmonic model in phasor diagram to suppress the ripple under module fault condition in multilevel BESS with unbalanced module parameters. By adjusting only part of the modules’ phase-shifted angle, whereas keeping others unchanged, a closed polygon of harmonic vectors can be reconstructed, which represents the output harmonic elimination. Experimental result on a five-module MDC is presented to verify the feasibility and effectivity of proposed method.