Rotor Thermal Estimation and Active Protection Strategy for Reliable Operation of WRSM

Wound rotor synchronous motor (WRSM) have attracted considerable attention as high-efficiency alternatives to rare-earth permanent-magnet motors. However, the structural limitations in managing the thermal behavior of the rotor field winding restrict its practical performance. Here, a sensorless rotor temperature estimation method based on the field current and voltage offset characteristics and a control strategy that dynamically switches the field current operating map according to the estimated temperature are proposed. In the baseline operation, a lookup table (LUT) constructed for minimum-copper-loss control is adopted. When the estimated rotor temperature exceeded a critical threshold, the system transitioned to the use of a thermal protection map that reduced the field current, thereby ensuring a thermal margin with slight efficiency reduction. The proposed strategy effectively prevents rotor overheating, extends the duration of continuous rated operation, and enables stable high-output performance under various load conditions. Furthermore, by leveraging the controllability of the field current, the map-switching mechanism reflects the trade-offs between efficiency and thermal characteristics, making it suitable for real-world applications.