Over Temperature Protection During Hill-hold and Low-Speed Conditions for Electric Vehicle Traction Inverter

The thermal characterization and control of the semiconductor devices in an electric vehicle traction inverter is crucial for achieving optimal performance in a safe and reliable manner during hill-hold and low-speed conditions. This paper presents a comprehensive electrothermal traction drive model to analyze power module temperature characteristics during hill-hold and low-speed operating conditions. Furthermore, this paper proposes an optimal thermal control methodology to maintain junction temperatures under the maximum limitations while minimizing the torque derating requirement. The semiconductor temperature effects with respect to rotor position at stand-still are analyzed and an innovative vehicle displacement solution is provided to reduce the maximum junction temperature across the three-phases of the inverter. Furthermore, a variable switching frequency strategy is proposed to maintain peak junction temperatures below the maximum limitations using the analysis of temperature oscillations in the power module at low fundamental frequencies.