Reliability of Modular Multilevel Converters Considering Physics of Failure in MVDC Applications

In medium-voltage DC (MVDC) systems, the failure of one converter can potentially lead to a network-wide outage. The design of modular multilevel converters (MMCs) for MVDC applications involves a lower number of sub-modules (SMs) compared to high-voltage DC (HVDC) systems, increasing the impact of a faulty SM on overall converter operation. By implementing mission profiles of MVDC network scenarios, this work investigates converter reliability with the consideration of physics of failure (PoF) in MMCs. It is demonstrated that the uniform thermal distribution within one SM topology and fewer components in a converter typically yield high reliability for the overall MMC. Moreover, the diverse thermal cycles introduced by different mission profiles can lead to significant differences in MMC reliability across multiple scenarios in MVDC systems. This paper aims to provide a comprehensive evaluation of converter reliability based on PoF, identify high-reliability options for SM topologies, and investigate the effect of mission profiles on the reliability of MMCs in MVDC applications.