An Evaluation of Model-Based Stator Resistance Estimation for Induction Motor Stator Winding Temperature Monitoring

The feasibility of using an estimate of the stator resistance (Rs) as an indicator of stator winding temperature (Ts) is evaluated. The advantages of resistance-based temperature monitoring over conventional thermal model-based methods are presented. Since obtaining an accurate estimate of Rs is critical for this approach, an investigation of existing Rs estimation schemes, and an analysis showing the sensitivity of model-based Rs estimation due to the uncertainties in motor parameters and variables, are given. It is shown that Rs estimation is difficult during high-speed operation, because estimated Rs becomes sensitive to errors in motor electrical parameters and variables, as the input excitation frequency (speed) increases. A new Rs estimation scheme for the purpose of monitoring the temperature in steady state is proposed. Experimental results on a line-connected induction machine verify the validity of the proposed method and the analysis.