NonContact Monitoring of Stator Winding Temperature in Inverter-Fed Machines Using High-Frequency Switching Oscillations

Online monitoring of stator winding temperature is essential for ensuring the safe and reliable operation of inverter-fed machines. Conventional methods, such as NTC temperature sensors, are prone to inaccuracies due to installation deviations or sensor degradation, potentially leading to false derating, or protective shutdowns. To overcome these limitations, this article presents a novel approach for online temperature monitoring by utilizing self-excited high-frequency (HF) switching oscillations of the inverter. The study begins with an analysis of the temperature dependence of winding insulation capacitance, followed by the identification of the HF common-mode oscillation frequency as a robust indicator of insulation temperature. The proposed online monitoring method is experimentally validated on a 380 V/0.37 kW inverter-fed induction machine test bench. Results demonstrate that the method accurately tracks real-time stator winding temperature variations, exhibits strong robustness under various operating conditions, and achieves an average temperature measurement error of less than 1.97°C.