Fast Switching SiC Cascode JFETs for EV Traction Inverters

This paper investigates the potential performance of high speed SiC cascode JFETs in EV traction inverters with high switching frequencies. Traction inverters implemented with SiC devices have shown improved energy conversion efficiency compared to IGBT based traction inverters however SiC MOSFETs suffer from unstable threshold voltage due to charge trapping at the SiC/SiO
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(due to high density of traps). Since SiC cascode JFETs combine low voltage silicon MOSFETs (at the input) with high speed/high-power density SiC JFETs (at the output), cascode JFETs combine the electrical gate oxide reliability of silicon devices with the power density of SiC. This paper simulates an EV driving cycle using experimental power loss measurements (at different currents and temperatures) of commercially available 650V SiC cascode JFETs and SiC MOSFETs. The inverter has been simulated at 10, 25 and 50 kHz to investigate the impact of increased switching frequency on device losses. The model is fully electrothermal since conduction and switching losses have been measured at different junction temperatures and used as inputs to the model. The results show the potential of superior performance of the SiC cascode JFET in terms of power loss and junction temperature swings. Furthermore, since higher switching frequencies might be desirable in future high-speed traction motors, the fast switching and low loss performance of SiC Cascode JFETs becomes more attractive.