A comparative analysis of circulating current controllers for modular multilevel converters

The modular multilevel converter (MMC) is a highly efficient multilevel converter topology suitable for high and medium voltage applications. However, one of the negative traits of MMC is the existence of circulating current. The detrimental effects of circulating currents include distortion in arm voltages, converter power loss and high switching stresses on semiconductor devices. This paper aims to focus on different circulating current mitigation techniques and their comparative analysis. This paper also proposes a circulating current suppressing controller (CCSC) which depends upon the repetitive control (RC) to minimize the inner circulating current in an MMC. The proposed model is simulated in MATLAB/Simulink and the results are quite in proximity with theoretical analysis.