Circulating Currents and Losses Analysis of an MMC with Using SVM-based Common Mode Voltage Reduction Strategy for a Wind Turbine Application

In wind turbine applications, the common mode voltage induced bearing currents lead to the frequent failures in wind turbines. Thus, it would be beneficial to reduce the common mode voltage in the system to reduce the bearing currents. In this study, a space vector modulation based strategy which aims to achieve low common mode voltage for a wind turbine application using modular multilevel converters is investigated. The impact between the common mode voltage reduction strategy, the circulating currents, the submodule capacitor voltages, and the converter losses are studied as well. It is found that the common mode voltage reduction can be affected by the circulating current control to some extent, however, the target of reducing the common mode voltage can still be achieved. The results show that the peak-to-peak amplitude of the common mode voltage can be decreased by 40% along with the circulating current control in the converter. On the other hand, the total losses inside the converter increase by 82% when using the common mode voltage reduction strategy, and this should be justified from a long-term perspective when considering the life-cycle cost of the system.