Research on Fault Control Strategy for Arm Switching Switch of AM-MMC Based on Independent Modulation and Zero-Sequence Voltage Injection

The arm multiplexing modular multilevel converter (AM-MMC) innovatively refines the topological structure of the traditional modular multilevel converter (MMC) based on the notion of “time-sharing multiplexing”. This topology reutilizes the intermediate arms through arm switching switch, effectively enhancing the utilization ratio of sub-modules and reducing the assembly quantity of submodules. Nevertheless, the frequent operation of the arm switching switch (ASS) within this topology is prone to inducing faults, resulting in the failure of the multiplexing function. In response to this problem, this paper initially conducts an in-depth analysis of the operational principle of AM-MMC and investigates the influence of the inability to switch the multiplexing mode normally on the system. On this basis, a novel control strategy based on independent modulation and zero-sequence voltage injection is proposed. This strategy employs the independent modulation approach to mitigate the shock when a fault occurs and injects zerosequence voltage after a fault, converting the three-phase symmetrical modulation wave into a two-phase asymmetrical modulation wave. This control strategy can effectively maintain the stable operation of the system during faults and ensure the normal switching of the multiplexing mode of the non-fault phases. This paper establishes a simulation based on this control strategy to verify the control effect when an arm multiplexing switch fault occurs in phase <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{B}$</tex>. The simulation results indicate that this strategy can guarantee the stable operation of the system under fault conditions and ensure the normal switching of the multiplexing mode of the non-fault phases, essentially achieving the expected objectives.