Increased Common-mode Current and Power Losses in Medium Voltage Machines Enabled by 10 kV SiC MOSFETs

Increasing the operating voltage of the machine to medium voltage benefits high efficiency and cost-effectiveness. However, as a result hereof, the common-mode current and power loss introduced by common-mode capacitances become more pronounced compared to low voltage machines. By presenting a common-mode circuit model of the system as well as analysing the switching loss and current ripple caused by common-mode capacitances, this paper investigates the impacts of common-mode capacitances on a 4.16 kV machine and a medium voltage power stack enabled by 10 kV SiC MOSFETs. Theoretical and experimental results indicate that the common-mode capacitance causes additional power loss about 4.1 kW and at least 10% current ripple ratio. In addition, high common-mode capacitance in machine poses the design challenge on auxiliary circuit design for the machine drive.