Medium Voltage DC Transformer with Series-Connected Power Devices Based on Active Clamping Circuit

A DC transformer (DCT) that utilizes series-connected SiC MOSFETs is presented in this paper. To balance the voltages across the devices, an active clamping circuit, comprised of an auxiliary switch and a capacitor, is introduced. To increase power density and reduce assembly cost, 6 series-connected SiC MOSFETs along with their balancing circuit and gate drivers are packaged into a series-connected power device module. This module can function as a 7.2kV/50A power device. A DCT built with the modules is tested in both power flow direction and the series-connected SiC MOSET voltages are well balanced.