Demagnetization Analysis of Interior Permanent Magnet Synchronous Motors Under Realistic Vehicle Driving Conditions

Electric vehicles primarily use interior permanent magnet synchronous motors (IPMSMs) as traction motors. Although IPMSMs are powerful and efficient, their neodymium-based permanent magnets are susceptible to demagnetization under high-temperature conditions. Demagnetization weakens the motor and may compromise the overall performance of the vehicle. In severe cases, it may disable the motor entirely or cause accidents such as fires, thereby threatening the safety of the vehicle and its passengers. In addition, demagnetization characteristics can vary with driving conditions. Therefore, this study conducted a demagnetization analysis that considers the driving characteristics of a vehicle operating on the new European driving cycle (NEDC). Because analyzing data across the entire NEDC would be excessively time-consuming, only the starting and maximum-speed points, which are considered the worst-case conditions for demagnetization, were selected for analysis. A coupled electromagnetic and thermal analysis was performed for the selected points as well as the rated operating point to determine the convergence temperatures of the permanent magnets under ambient and high-temperature conditions. Based on the determined convergence temperature, the demagnetization rate, quantified by the reduction in the back electromotive force, was evaluated by varying the current magnitude and angle. Even at the rated operating point and maximum-speed point under high-temperature conditions, where a high current was applied, the demagnetization rate remained within 3%, and no irreversible demagnetization was observed. These findings provide practical insights for designing robust EV traction motors capable of withstanding worst-case thermal and loading conditions.