针对模块化多电平变流器(Modular multilevel converter, MMC)冗余子模块在故障时存在耗尽的情况，提出了基频零序分量注入的故障容错控制方法。通过与中性点偏移相结合，保证即使出现冗余子模块耗尽，MMC仍能继续安全运行，解决剩余正常子模块承受应力不均衡问题，保障系统安全、可靠运行。同时，利于减少冗余备份量,并大幅度降低硬件成本和提高运行可靠性。经Matlab仿真验证了所提方法的正确性和有效性，为基于MMC的海上风电柔性直流输电变流器的可靠运行提供了一种有效的故障控制方案。%In order to fully implement the functionalities of modular multilevel converter (MMC), its fault-tolerant operation without redundant sub-modules (SMs) is comprehensively investigated. To avoid completely shut down the MMC system under SMs fault, a fundamental-frequency zero-sequence injection based neutral-shift method is adopted to enable the fail-safe energy transfer. This approach enhances both the reliability and availability of MMC while avoiding the undesired unbalanced stresses among the healthy SMs. Rigorous simulation studies are performed to demonstrate the validity and effectiveness of the proposed control methods. This work is supported by National Natural Science Foundation of China (No. 51377105) and National High Technology Research and Development program of China (863 Program) (No. 2011AA05A103).
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