A Complete Common-Mode Voltage Reduction Method for MMC with Output Current and Voltage Fluctuation Optimization

Common mode voltage (CMV) has attracted much attention in high power applications as it can cause problems such as leakage current in non-isolated inverters. As a solution, modular multilevel converter (MMC) has been widely used in medium and high voltage applications due to its naturally low CMV feature, and additional CMV mitigation methods have been proposed for MMC. However, there is always a trade-off between the CMV and the THD of the output current in the existing methods. This paper proposes a novel complete common-mode voltage reduction (CCR) method based on the nearest level modulation scheme, which can minimize the CMV and reduce the THD of the output current at the same time. Moreover, the proposed method is simple and easy to implement, and it can suppress the capacitor voltage fluctuation, thus contributing to a lower demand for the capacitance. Finally, the simulation results verify the effectiveness of the proposed method.