A lightweight MMC topology with recombined half-bridge submodules for DC fault ride-through

The lightweight of modular multilevel converter (MMC) and the DC faults ride-through ability are main challenges for MMC-high voltage direct current (HVDC) transmission systems. By introducing the concept of time-division multiplexing, an arm multiplexing MMC (AM-MMC) topology with high utilization of submodules is presented to reduce the weight and volume of MMC. In order to block the DC side fault current, this paper proposes a novel submodule in AM-MMC, instead of using full-bridge submodules. The proposed recombined half-bridge submodules of AM-MMC (RHAM-MMC) contains four half-bridge submodules and an IGBT with reverse parallel diodes. The topology and operating principle of RHAM-MMC are introduced in detail. The time-division multiplexing of middle arms between upper and lower arms is achieved by introducing arm selection switches. Thus, a new type of arm switch and switching method is designed based on the switch state. The DC faults ride-through strategy is carried out based on its DC fault characteristic analysis. In addition, the economy analysis is conducted on the switching loss and operating loss of RHAM-MMC. Compared with the fault ride-through capability of other sub-modules (SMs), RHAM-MMC performs better in terms of investment cost and device losses. The simulation results based on MATLAB/Simulink reveal that RHAM-MMC can achieve the DC side fault ride-through and show effectiveness of the DC fault ride-through control strategy.