Structure of a permanent magnet motor used for electric vehicles to suppress the eddy current effect

A demagnetization fault in the permanent magnet (PM) may occur when the temperature exceeds the limit temperature of the PM material due to the limited heat dissipation of the rotor in PM motors in the driving system of electric vehicles. In addition, PM thermal stress arises as a result of the unbalanced axial temperature distribution of the motor. When the thermal stress exceeds the yield strength of PM, micro-deformation of the PM structure happens and affects the performance and structural reliability of the motor. In this study, the rotor structure of an 18 kW PM motor is improved, and an eddy current ring structure of stainless steel is proposed. First, the effects of eddy current rings with axial lengths of 2, 5, and 10 mm on the eddy current losses of PM are compared. Second, a three-dimensional, steady-state temperature model of the motor is established to analyze the effects of the eddy current rings with different axial lengths on rotor temperature when the motor is running at different speeds. Results show that the eddy current ring structure with 2 mm axial length has the best effect on reducing rotor temperature. Lastly, the simulation results are verified using the test results of the 18 kW PM motor.