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This paper focuses on fault-tolerant control for a battery-energy-storage system based on a multilevel cascade pulsewidth-modulation (PWM) converter with star configuration. During the occurrence of a single-converter-cell or single-battery-unit fault, the fault-tolerant control enables continuous operation and maintains state-of-charge balancing of the remaining healthy battery units. This enhances both system reliability and availability. A 200-V, 10-kW, 3.6-kW·h laboratory system combining a three-phase cascade PWM converter with nine nickel-metal-hydride battery units is designed, constructed, and tested to verify the validity and effectiveness of the proposed fault-tolerant control.