A fault-tolerant strategy of hybrid modular multilevel converter based on level adjusting method

With the advantage of DC fault ride-through and the reduced cost, a hybrid modular multilevel converter (HMMC) has become a promising topology for HVDC applications. However, the complicated configuration of HMMCs with a large number and different types of submodules (SM) increases the risk of submodule failure. This paper proposes a novel HMMC fault-tolerant strategy by adjusting the inserted SM number residing in the fault phases, analyzes voltage fluctuation of the SM capacitor, and designed an SM capacitor voltage controller in coordination with fault-tolerant strategy. Meanwhile, by utilizing the negative voltage output characteristic of FBSMs, this strategy can significantly improve the SM fault tolerance capability of the HMMC. Moreover, as compared to conventional fault-tolerant strategies, the proposed strategy requires fewer components and can be easily implemented. Finally, the effectiveness of the proposed fault-tolerant methods is demonstrated by MATLAB/Simulink under different fault conditions and MMC systems. (C) 2020 The Author(s). Published by Elsevier Ltd.