Effect of Inverter Output dv/dt with Respect to Gate Resistance and Loss Comparison with dv/dt Filters for SiC MOSFET based High Speed Machine Drive Applications

Fast switching characteristic of wide band gap (WBG) devices enables high frequency switching of power devices and thereby, facilitates high fundamental frequency operation of a machine. However, with the switching transition times being in orders of tens of nanoseconds, a high dv/dt is observed across the switching device. The high dv/dt experienced by the switches, and consequently by the machine, can degrade winding insulations or bearings over a period of time. It is therefore imperative to maintain dv/dt below recommended values depending on the machine insulation. The dv/dt across the devices can be adjusted by using higher values of gate resistance. However, this introduces additional switching losses on the device. Using different dv/dt filtering techniques can also help to control the dv/dt on the machine terminals. These techniques do not increase the switching losses on the device. However, the filter circuits introduce losses in the circuit and additional costs. In this paper, an analysis based on the impact of gate resistance on the dv/dt across the machine, and the corresponding losses is carried out. In addition, a comparision is performed on the basis of efficiency between these two techniques. A SiC MOSFET based 3-phase inverter (CREE-CCS020M12CM2) is used for the analysis.