Base Failure Rate Calculation for Submodules in Modular Multilevel Converters for MVDC Applications

In the application of modular multilevel converter (MMC) for medium-voltage DC (MVDC) systems, the small number of sub-modules (SMs) lead to reduced reliability in the overall converter. For the multiple SM topologies that have been developed for MMC, a methodology is proposed for the evaluation of SM failure rate. Considering the failure modes of SM components, structure redundancy, and classification of SM faults, this approach provides a comprehensive comparison of SM failure rate and identifies the high-reliability options for SM topologies. With the calculation of SM failure rate, the utilization of different types of IGBT modules, proportion of failure schemes in IGBT, and arm reliability in MMC are further analysed.