Circulating Current Elimination of Grid-Connected Modular Multilevel Converters

This paper presents an analytical dynamic model of a modular multilevel converter (MMC) in grid-connected operating mode. The proposed model is then efficiently used to design a circulating current controller. The proposed controller can accurately study the dynamic and steady-state performance of the converter through harmonic evaluations. Based on this configuration, the modulation is accomplished so that the stable performance of the converter in the network is obtained, which is considered as the foremost novelty of the proposed control method over existing control methods. In order to mitigate the circulating currents, the proposed controller inserts an estimated second harmonic component into modulation indices, which is considered as the second novelty of the proposed control method. The functionality and capability of the proposed control method are validated using detailed theoretical analysis and simulations with MATLAB/Simulink.