Traditional modular multilevel converter (MMC) systems are often characterized by low submodule utilization, leading to high component costs and a large physical footprint, which limits their applicability in converter stations. To address these limitations and reduce the overall weight and size of the converter, this paper proposes a three-phase arm multiplexing series MMC (AM-SMMC) topology suitable for voltage-source converter high-voltage direct current (VSC-HVDC) stations. The proposed topology builds on the principles of three-phase leg cascading and arm time-division multiplexing (TDM). By reorganizing the arm structure of the conventional series MMC (S-MMC) into upper, multiplexed, and lower arms and incorporating arm switching devices to enable multiplexing of the intermediate arm, the number of required submodules is significantly reduced. Furthermore, a zero-voltage switching modulation strategy is developed specifically for the AM-SMMC to fulfill the modulation requirements for connverter stations in VSC-HVDC transmission applications. Simulation results obtained from MATLAB/Simulink validate the feasibility of the AM-SMMC architecture and the effectiveness of the proposed modulation strategy. Compared to the conventional S-MMC, the AM-SMMC achieves a 25% reduction in submodule capacitance while maintaining the same number of IGBT switches, thereby reducing both the manufacturing cost and physical volume of the converter station.
Yu et al. (Fri,) studied this question.