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

This paper deals with the post-fault operation of a modular multilevel converter (MMC) with multiple submodules (SMs) failures. A selective harmonic mitigation (SHM) based fault-tolerant method is proposed where the modulation references of MMC phase arms are modified in post-fault 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 are defined in SHM equations so that over-modification 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 in post-fault conditions. Furthermore, the proposed method reduces the peak value of common mode voltage (PCMV) and high-frequency components of common mode voltage (HF-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.