A 120°C ambient temperature forced air-cooled normally-off SiC JFET automotive inverter system

The degree of integration of power electronic converters in current hybrid electric vehicles can be increased by mitigation of special requirements of these converters, especially those regarding ambient air and cooling fluid temperature levels. Today, converters have their own cooling circuit or are placed far away from hot spots caused by the internal combustion engine and its peripheral components. In this paper, it is shown, how the use of SiC power semiconductors operated at a junction temperature of 250°C and active control electronics cooling employing a Peltier element can help to build an air-cooled inverter system for 120°C ambient temperature. First, a detailed analysis of the operating temperature ranges of power semiconductors, thermal interface materials, capacitors and control electronics is conducted. Then, concepts for deriving a converter design that takes the electrical, mechanical and thermal requirements of the components and their interaction into account are shown. The inverter and the active Peltier cooling of the control electronics are dimensioned. Finally, a hardware prototype with discrete power semiconductor devices and thus with a junction temperature limit of 175°C is shown to validate the theoretical considerations.