MMC-MTDC transmission system with partially hybrid branches

This paper proposes a hybrid submodule modular multilevel converter (MMC) topology which is suitable for multi terminal direct current (MTDC) transmission systems. Each arm of the proposed MMC topology consists of a half-bridge submodule (HBSM) branch and two parallel full-bridge submodule (FBSM) branches. Comparing with the conventional MTDC transmission system, the proposed topology can selectively block the DC fault current and isolate the corresponding fault line without expensive DC circuit breakers (DCCBs). Thus, the influence range of the DC fault can be reduced and the reliability of the power supply can be improved as well. The corresponding modulation and voltage balancing strategies are developed for the proposed hybrid MMC topology. The feasibility of the proposed topology and control strategy is verified in the MATLAB/ Simulink simulation.