The arm multiplexing modular multilevel converter (AM-MMC) possesses lower cost, smaller volume and higher efficiency compared with modular multilevel converter (MMC). However, it faces the challenge of fixed operating modulation index. Therefore, additional control strategies are required to achieve the energy balance under the wide-voltage range operation of the converter. This paper proposed a novel compact single-arm multiplexing multilevel converter (SMMC), which consists of commutation switch stacks and multiplexed arms. Simultaneously, a multiple degrees of freedom method is proposed to address the energy balance of the multiplexed arms, which is composed by commutation angle regulation and the third-order harmonic injection. Furthermore, to explore the performance of the SMMC, mathematical model and control strategy of the SMMC are provided. Compare with AM-MMC, the number of submodules (SMs) is reduced by 52%. Finally, the topology and proposed control strategy are verified by the simulation results.

The 50% submodule utilization of the modular multilevel converters (MMC) results in a large size and weight. This problem becomes more serious when the requirement of DC fault ride-through (FRT) is met, for the half-bridge submodules (HBSMs) need to be substituted by full-bridge submodules (FBSMs) with double IGBTs. This paper proposes a compact topology named hybrid arm-multiplexing MMC (HAM-MMC). By introducing arm selection switches composed of series connected IGBTs, the phase leg of the conventional two-arm structure is divided into upper, middle, and lower arms, respectively configured with HBSMs, FBSMs, and HBSMs. The middle arm can be multiplexed according to modulation demands, thus saving 25% submodules by increasing utilization. The structure and switching principle of arm selection switches are elaborated, and an improved capacitor voltage balancing scheme is presented. The negative level output capability of FBSMs in the middle arm can work in conjunction with the arm selection switches to reduce the DC voltage and ride through DC faults. The simulation results show that the proposed MMC has similar DC FRT ability to traditional hybrid MMC, with a 50% reduction in the number of FBSMs.

This paper proposes a half-wave alternate multilevel converter (HAMC)., based on the idea of alternate arm multiplexing and time-division multiplexing. Compared with MMC, the submodules number of the HAMC can be reduced to 25%, which significantly achieves the lightweight goal. Through the cooperation of the DC side director switches and the AC side selection switches, HAMC operates alternately in two multiplexing modes, which can realize the full-cycle utilization of the multiplexing arm and be the lightweight nature. A modified modulation method applied to the HAMC is presented to achieve the capacitor voltage balancing. Then, its operation losses and comparison with other typical multilevel converters are analyzed. The simulation results based on Matlab/Simulink verify the feasibility of the HAMC topology and the effectiveness of its control strategy.