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Capacitor Voltage Optimation Balance Control for Modular Multilevel Converter Based on Carrier Phase-shift Modulation

Modular Multilevel Converter (MMC) is a promising converter in the medium or high voltage application fields. However, once the capacitor voltage is not equal between different submodules, it is easy to cause inter-phase circulating current among the bridge arms, which may result in the imbalance of the three-phase currents. The traditional capacitance voltage balance strategy is often based on NLM modulation, which may cause higher switching frequency and large harmonics. In this paper, a new strategy for capacitance voltage submodule equalization based on carrier phase shift modulation is proposed. The energy distribution between the bridge arms and the voltage balance of each submodule are realized by setting the circulation suppression coefficient. Simulation results show that the inter-phase circulating current is suppressed, and the harmonics are reduced by using the proposed method.