High Temperature Design Optimization of DC/AC Power Converters Using SiC BJTs

Silicon Carbide (SiC) devices, with their superior properties, have made it possible to design converters with power densities that were previously unattainable with silicon (Si). Recently there have been several SiC based power converter designs that successfully utilize the device's higher breakdown voltage and faster switching speed. However, few designs have taken advantage of the ability of SiC devices to operate at higher temperatures. This is especially important from a design optimization standpoint since the higher the temperature the switching devices can operate at, the smaller the cooling component of the converter needs to be. To this end a design tool was created that optimizes the volume of a DC to 3-phase AC converter, whilst taking into account the temperature dependency of the switching devices. The tool selects the switching frequency, devices, passive components and heatsink that will minimise the overall volume of the converter. The tool was used to design a 5-kW rated converter that used high temperature SiC bipolar junction transistors (BJTs). Several converter designs were produced for maximum junction temperatures of 125, 150 and 175 degrees Celsius, all of which were prototyped and experimentally verified.