Mechanical DC Breakers and Hybrid MMC-Based Coordinated Strategy for MMC-HVDC DC Fault Riding Through

The bipolar short-circuit fault, which is the most destructive dc side fault of modular multilevel converter (MMC)-high-voltage direct-current (HVDC) systems, and its riding through strategy is a current hotspot. Hybrid MMC (HMMC) is a promising topology for HVDC applications with the capability of dc fault isolation; however, it still suffers from the high cost. This article proposes a mechanical dc breakers and HMMC-based coordinated dc fault ride-through strategy that can reduce the ratio of the full-bridge submodules (FBSMs) in the HMMC and obviously cut the cost. To be specific, this strategy mainly depends on the FBSM’s negative output to suppress the fault current and eventually block it with the mechanical dc breakers. The impact on the performance of fault ride-through by the ratio of FBSMs in the HMMC is analyzed, and the superiority of the strategy proposed in this article has been proven with the analysis of conventional strategies. Finally, the effectiveness of the proposed strategy is validated with the RT-LAB experimental platform, and the optimal ratio range is obtained through the multiple groups of simulation experiments with different ratios of FBSMs in HMMC based on MATLAB/Simulink.