A Fault-Tolerant Method Based on a Modified Selective Harmonic Mitigation Technique for Modular Multilevel Converter

This article deals with the postfault operation of a modular multilevel converter (MMC) with multiple submodules failures. A selective harmonic mitigation (SHM)-based fault-tolerant method is proposed where the modulation references of MMC phase arms are modified under postfault conditions to achieve the maximum possible balanced line-to-line voltages using unbalanced phase voltages. In addition to mitigating the low-order harmonics, a set of constraints is defined in SHM equations so that overmodulation is avoided after modification of modulation references. The suggested method optimizes the MMC capacity to provide the highest attainable line-to-line voltages with a suitable harmonic profile under postfault conditions. Furthermore, the proposed method reduces the peak value of common mode voltage (CMV) and high-frequency components of CMV. This function decreases the CMVs adverse impact on the converter and the load. Comparative simulation and experimental results are provided to validate the feasibility and effectiveness of the proposed method.