A low-cost MMC submodule topology with fast DC fault handling capability

Abstract

With the continuous development of new energy technologies and the widespread application of high voltage direct current transmission technology, the use of modular multilevel converters (MMC) has significantly increased. Traditional MMCs, composed of half-bridge submodules, lack fault handling capabilities, and cannot block fault currents on the DC side, thus compromising the stability of transmission systems. Therefore, this study proposes a low-cost improved MMC submodule topology based on the dual-bidirectional switch submodule (DBSSM) and provides an analysis and description of its structure and operating principles. The proposed DBSSM structure can output five voltage levels: 0, ± Uc, and ±2 Uc. Compared to the full-bridge submodule topology, which achieves the same effect, the DBSSM reduces the number of IGBTs by half, significantly lowering hardware costs. A simulation model with a DC side voltage of 80 kV was built using MATLAB/Simulink to verify this topology. In the 80 kV scenario, the proposed DBSSM achieved DC fault ride-through within 3 ms, doubling the speed compared to the full-bridge submodule. Finally, hardware-in-the-loop testing was performed using the dSPACE1202 and relevant hardware circuits, confirming the feasibility of the proposed structure.