针对模块化多电平换流器型高压直流输电（modular multilevel converter-high voltage direct current，MMC-HVDC）系统，提出了一种创新的换流器桥臂保护方法。首先，分析了在换流器单桥臂接地以及单相桥臂间接地情况下电流的流通路径，构建了等值电路，并推导了换流器闭锁前后桥臂电流的表达式。基于此，剖析了故障后三相桥臂电流之和的独有特征，提出了通过检测三相桥臂和电流的基频分量是否为零来区分桥臂内部故障与外部故障的保护策略。鉴于现有桥臂保护方法无法有效应对换流器单相桥臂间短路的问题，进一步研究了此类短路情况下的特性，发现故障相上、下桥臂电流仅包含基频分量而不含直流分量，从而制定了相应的动作判据。将三相桥臂和电流保护与单相桥臂间短路保护判据进行，能够全面识别换流器桥臂上发生的各种故障，丰富和完善了换流器桥臂的保护原理。最终，通过在MATLAB/SimulinK中搭建双极MMC-HVDC系统仿真模型验证了所提出保护方法的有效性和可靠性。

An innovative converter bridge arm protection method is proposed for the modular multilevel converter - high voltage direct current （MMC-HVDC） system. Firstly, the current flow paths are analyzed when the single bridge arm of the converter is grounded and when the single-phase bridge arm is indirectly grounded. An equivalent circuit is constructed, and the expressions of the bridge arm current before and after the converter is locked are derived. Based on this, the unique characteristics of the sum of the three-phase bridge arm currents after a fault are analyzed, and a protection strategy is proposed to distinguish internal faults from external faults of the bridge arm by detecting whether the fundamental frequency components of the three-phase bridge arm and the current are zero. Given that the existing bridge arm protection methods cannot effectively deal with the short-circuit problem between single-phase bridge arms of the converter, the characteristics under such short-circuit conditions are further studied. It is found that the currents of the upper and lower bridge arms of the faulty phase only contain the fundamental frequency component and don’t contain the DC component, and thus the corresponding action criteria are formulated. By outputting the short-circuit protection criterion between the three-phase bridge arm and current protection and the single-phase bridge arm through or gate, various faults occurring on the converter bridge arm can be comprehensively identified, enriching and improving the protection principle of the converter bridge arm. Finally, by building the simulation model of the bipolar MMC-HVDC system in MATLAB/Simulink, the effectiveness and reliability of the proposed protection method are verified.