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Suppression of Capacitor Voltage fluctuation by AuxiliaryApproximation for MMC
The capacitor voltage balancing of the submodule is the most important part of the (MMC )control of the modularized multilevel converter(MMC). It has large number of submodules that applied high voltage grade engineering. The switching loss caused by frequent switching is considerable. Therefore, a strategy of grouping and setting the upper and lower limit voltage balancing control strategy is proposed.Even if the level is constant, the sub modules beyond the limiting voltage should be switched for balancing capacitance voltage. In order to reduce switching loss, the ability to maintain the original state of the submodule is increased by grouping. To make the output DC voltage approach the reference value, the compensation module PC is introduced. It can support DC voltage and suppress circulation effectively. Finally, the MMC-HVDC model is built in MATLAB/Simulink. Simulation and experimental results show the effectiveness of the proposed control strategy.