Induction Motor Temperature Estimation Based on High-Frequency Model of Rotor Bar

This paper analyzes a high-frequency (HF) voltage injection-based rotor winding temperature estimation method for current-regulated squirrel-cage induction motors. We develop a theoretical HF model of the rotor bar and then first provide analysis of relevant HF model-based estimation aspects, such as dependency of the rotor leakage inductance on the temperature and the relationship between the rotor resistance and the rotor leakage inductance. The paper also includes an analysis of magnetic saturation to improve the estimation accuracy as well as analysis of the phase delay effect resulting from the drive which significantly affects the HF signal precision. Then, a specialized offline commissioning scheme is proposed to compensate the effect of the phase delay and the magnetic saturation. The estimation technique and sensitivity analysis are verified by means of experiments performed on an inverter-fed 1.5 kW induction motor.