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An induction machine's thermal behavior is determined by various machine components with dissimilar thermal characteristics. When a model with a single thermal time constant is used to characterize the machine's thermal behavior under periodic duty cycles, the magnitude of the thermal time constant needs to be adjusted according to the duty cycles to reflect the machine's dominant thermal dynamics during that specific interval. Based on the analysis of the internal heating effects of a small- to medium-sized mains-fed induction machine, a sensorless stator winding temperature estimator is proposed to compensate for the shift in the thermal time constant for motors with continuous- operation periodic duty cycles. First, the rotor temperature is estimated from the voltage and current measurements and is used as an indicator of the motor's internal thermal operating condition. Then, a hybrid thermal model is employed to correlate the rotor temperature to the stator winding temperature. Finally, an observer is designed to take the estimated rotor temperature as a feedback signal into the hybrid thermal model. The correction provided by the feedback signal enables a reliable tracking of the stator winding temperature for motors with periodic duty cycles. The experimental results are given to validate the proposed method, and the overall scheme is shown to estimate the stator winding temperature efficiently without using any real temperature sensors.