Analysis and Control of Three-Phase Modular Multilevel Converters Under the Single Arm Fault Condition

Modular multilevel converter (MMC) is an attractive topology for medium- and high-voltage applications due to the merits of high modularity, easy scalability, high-quality output voltage, and fault tolerance of submodules. This letter focuses on the control of a three-phase MMC under the single arm fault condition, which can further improve the fault tolerance ability of the MMC. According to three essential operating constraints of the MMC, this letter proposes a feasible arm voltage and current configuration method for the single arm failed MMC, which can guarantee its stable operation with reduced output power. Several operating limitations are also discussed. Experiment results based on a prototype with four half-bridge submodules per arm are presented to verify the proposed arm fault tolerance method.