Individual-Arm Modulation Strategy for Four-Arm Multiplexing MMC

As a state-of-the-art technology in flexible DC transmission, the modular multilevel converter (MMC) exhibits superior operational characteristics. However, its practicality is limited by issues such as large size, heavy weight, and high costs. Building on the arm multiplexing MMC (AM-MMC), this paper proposes a four-arm multiplexing MMC (FAM-MMC) by introducing an additional set of multiplexed arms and designs its circuit topology. Under the individual-arm modulation strategy, energy balancing calculations reveal that its optimal operating point exceeds 1, necessitating an overmodulation strategy. Accordingly, an individual-arm modulation strategy for FAM-MMC is developed. With an equivalent <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$N$</tex> of 36, the proposed FAM-MMC reduces the number of submodules required by 38.89% compared to conventional MMC, 18.52% compared to AM-MMC, and 8.33% compared to FAM-MMC using the advanced nearest level modulation (ANLM). This approach mitigates the fluctuation of submodule capacitor voltages, broadens capacitor selection criteria, effectively lowers converter costs, reduces size and weight, and further advances the goal of lightweight converter design.