A optimization Strategy to Balance sub-Module Capacity Voltage of MMC

Optimizing the sub-module control strategy of modular multi-level converter, especially considering the capacitor voltage fluctuation of sub-module, the second harmonic content of bridge arm circulation, the switching times of sub-module IGBT and the calculation amount of algorithm, a capacitor voltage control strategy of sub-module of modular multi-level converter is proposed. This paper expounds the contradiction between the voltage fluctuation of the sub-module capacitor, the switching times of the submodule IGBT and the computational complexity of the algorithm, then proves through theoretical analysis that there is also a non-linear relationship between the voltage fluctuation of the sub-module capacitor and the second harmonic content of the bridge arm circulating current. It is necessary to find an appropriate algorithm to achieve the optimal situation at the same time. Finally, the traditional control strategy, the control strategy proposed in other literature and the control strategy proposed in this paper are validated by dynamic model test. The experimental results show that the proposed strategy in this paper can be optimized in four aspects: voltage fluctuation of sub-module, second harmonic content in bridge arm circulation, switching times of sub-module IGBT and the computational complexity of the algorithm.