Identification of sensorless rotor temperature estimation technique for Permanent Magnet Synchronous Motor

Reversible demagnetization effects due to temperature increase is a common problem in rare-earth magnets widely used in Permanent Magnets Synchronous Machines (PMSM). Variation of the magnetization level of the magnets leads to different saturation levels in the steel stator core of the machine. The paper proposes a simple method to detect magnetization variation by an intermittent injection of a voltage pulse in the d-axis of the motor, while the q-current is kept zero. The slope of the resulted d-current response reflects a given saturation level which is distinctive for a given magnet temperature. Since this is a strongly non-linear relationship, a look-up-table (LUT) for the motor is required. The paper proposes a procedure where the identification of the LUT without measuring directly the rotor temperature can be achieved at standstill.