Shared Redundancy Strategy to Improve the Reliability and Fault-Tolerant Capability of Modular Multilevel Converter

Utilizing redundant submodules is a well-known strategy to improve the reliability and fault-tolerant capability of the modular multilevel converter (MMC). Redundancy-based fault-tolerant strategy makes it possible to restore the full performance of the converter in the postfault condition. The main drawback of this strategy is the high cost. In this configuration, each redundant submodule (RSM) can only be utilized in a specific arm and it cannot be used in other arms. This limitation leads to inefficient utilization of the RSMs in conventional MMC. This article proposes a shared redundancy strategy which allows RSMs to be used either in upper or lower arms. The derived reliability models in various case studies illustrate that the proposed strategy significantly improves the reliability and useful lifetime of MMC. To investigate the effectiveness of the proposed strategy, simulation and experimental results are provided.