低频输电系统是一种结合传统的高压交流输电与高压直流输电且采用小于工频的低频的新型交流输电技术，该系统核心的功率变换器──模块化多电平矩阵变换器（modular multilevel matrix converter，M3C）是一种适用于高电压、大功率的新型AC/AC变换器拓扑结构，M3C的容错控制对于提高M3C系统可靠性具有重要意义，但目前其容错控制策略还存在问题。为此提出了一种最佳共模电压（common mode voltage，CMV）注入方法的容错控制策略，该方法能够在非冗余子模块失效后使M3C的输入和输出电压范围最大化。该方法通过实时计算基波参考电压与各桥臂分支最大可用电压之间的关系，可以动态调整注入的最优CMV，从而适应不同的故障情况。最后，在MATLAB/Simulink和RT-LAB两个平台进行实验，验证了在单桥臂和多桥臂分支故障情况下所提方法的正确性和有效性。

Low frequency transmission system is a new type of AC transmission technology that combines traditional high voltage AC transmission and high voltage DC transmission, and adopts low frequency below power frequency. The core power converter of the system, the modular multilevel matrix converter (M3C), is a new AC/AC converter topology suitable for high voltage and high power. The fault-tolerant control of M3C is of great significance for improving the reliability of M3C system, but there are still problems with its fault-tolerant control strategy at present. The fault-tolerant control strategy with an optimal common mode voltage (CMV) injection method is proposed in this paper, which is able to maximize the input and output voltage ranges of the M3C after the failure of the non-redundant submodules. By calculating the relationship between the fundamental reference voltage and the maximum available voltage of each bridge arm branch in real time, the method can dynamically adjust the optimal CMV for injection to adapt to different fault situations. Finally, experiments are conducted in both MATLAB/Simulink and RT-LAB platforms to verify the correctness and effectiveness of the method proposed in this paper under single and multiple bridge arm branches fault conditions.