Modular multilevel converter (MMC) with reduced number of voltage sensors is conducive to the reduction of equipment cost and hardware complexity, however, usually resulting in the performance degradation. For example, when only one voltage sensor is equipped for the measurement of arm voltage, estimation of capacitor voltages may be not accurate enough, moreover, condition monitoring and fault diagnosis of submodules (SMs) are hard to implement. Thus, capacitor voltage estimation with capacitance self-updating based on grouping measurement (GM) is proposed in this article. By grouping and updating SM capacitance periodically, the accuracy of voltage estimation is greatly increased, meanwhile, severely aging or faulty capacitors can be detected, convenient for prompt replacement. Furthermore, GM-based fault diagnosis and fault disposal are proposed. Utilizing the measured and estimated group voltages, single or multiple SM open-circuit failures can be located in several sampling cycles and the isolating time of faulty SMs can be easily obtained even considering the time delay of bypass switch. Therefore, capacitor overvoltage and current distortion during SM failures are restrained effectively, which enhances the reliability and achieves seamless operation of MMC. Finally, the effectiveness of the proposed scheme is confirmed by simulation and experimental results.

中文翻译：

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模块化多电平转换器中具有电容自更新功能的组合电容器电压估计和故障诊断

减少电压传感器数量的模块化多电平转换器（MMC）有利于降低设备成本和硬件复杂性，但通常会导致性能下降。例如，当只有一个电压传感器测量臂电压时，电容电压的估计可能不够准确，而且子模块（SM）的状态监测和故障诊断很难实现。因此，本文提出了基于分组测量（GM）的具有电容自更新的电容器电压估计。通过定期对SM电容进行分组和更新，大大提高了电压估计的准确性，同时可以检测到严重老化或故障的电容器，便于及时更换。此外，提出了基于GM的故障诊断和故障处理。利用测量和估计的组电压，可以在几个采样周期内定位单个或多个 SM 开路故障，即使考虑旁路开关的时间延迟，也可以轻松获得故障 SM 的隔离时间。因此，有效抑制了SM故障期间的电容器过压和电流畸变，从而提高了可靠性并实现了MMC的无缝运行。最后，通过仿真和实验结果证实了所提出方案的有效性。有效抑制SM故障时的电容过压和电流畸变，提高可靠性，实现MMC无缝运行。最后，通过仿真和实验结果证实了所提出方案的有效性。有效抑制SM故障时的电容过压和电流畸变，提高可靠性，实现MMC无缝运行。最后，通过仿真和实验结果证实了所提出方案的有效性。