The Potential of SiC Cascode JFETs in Electric Vehicle Traction Inverters

The benefits of implementing silicon carbide (SiC) devices in electric vehicle (EV) powertrains have been widely reported in various studies. New generations of SiC devices including planar MOSFETs, trench MOSFETs, and more recently, cascode JFETs have been released by various manufacturers. SiC cascode devices comprise low-voltage silicon MOSFETs for gate driving and high-voltage depletion mode SiC JFETs for voltage blocking. These devices are particularly interesting, because they avoid the known reliability issues of SiC gate oxide traps resulting in threshold voltage drifts. In this article, an EV powertrain is simulated using experimental measurements of conduction and switching energies of various SiC devices including 650-V trench, 900-V planar, and 650-V cascode JFETs. Unlike in previous articles where losses are calculated using models based on datasheet parameters, here static and dynamic measurements on power devices at different currents and temperatures are used to calculate losses over simulated driving cycles. Field-stop IGBTs are also evaluated. The 3-phase, 2-level inverter model is electrothermal by accounting for the measured temperature dependence of the losses and uses accurate thermal networks derived from datasheets. The converter efficiency and the thermal performance are compared for each device technology. The results show that SiC cascode JFETs have great potential in EV powertrain applications.