Permanent Magnet Temperature Estimation in a Mass-Produced Traction Motor for an Electric Vehicle

Interior permanent magnet synchronous machine has been widely used in electric vehicles as a traction motor. The magnet temperature is an essential parameter in the permanent magnet motor. While several magnet temperature estimation methods exist for traction motors of electric vehicles, most of them have been developed and verified on low-power-capacity motors, which are operated at a relatively low speed and with a small current. Generally, the magnet temperature increases more rapidly in high speed and high current compared with low speed and low current. This study demonstrates that a reactive-energy-based method could estimate a mass-produced traction motor’s magnet temperature accurately. Furthermore, an indirect measurement method was developed for measuring the magnet temperature without requiring any modification in the motor structure. Finally, it was used to identify the relation between reactive energy and the magnet temperature in a traction motor. Additionally, implementing the reactive-energy-based estimation method was simplified by considering the configuration and estimation accuracy. The implemented method could estimate the magnet temperature in real time even in high-current (300 A) high-speed (6500 r/min, 2723 rad/s in electrical angular speed) operating conditions, regardless of extreme temperature variations. The maximum estimation error was less than 5 °C in an online estimation for 7020 s (1.95 h) in the presence of large variations in the speed and torque.