Influence of Circulating Current Control on the Performance of Modular Multilevel Converter

The circulating current affects various aspects of MMC performance, such as safe operation area(SOA) of the switching devices, power losses and the selected submodule capacitance. Firstly, the causes of the second circulating current are analyzed theoretically. The influence of circulating current control is included by considering the effects of the second-harmonic component on reference voltages based on the analytical analysis. This paper studies relationship among different performance indicators of MMC. Then the curves of circulation control on MMC performance index is drawn by MATLAB. According to the curves, the circulation control optimization method to improve each performance index of MMC converter is proposed.