A Sensorless Adaptive Stator Winding Temperature Estimator for Mains-Fed Induction Machines with Continuous-operation Periodic Duty Cycles

The thermal behavior of an induction machine is determined by various components with dissimilar thermal characteristics inside the machine. When a thermal model with a single thermal time constant is used to characterize the thermal dynamics of such a motor operated with periodic duty cycles, the magnitude of its thermal time constant needs to be adjusted according to the duty cycle to reflect the motor´s dominant thermal dynamics in that duration. Based on the analysis of the internal heating effects for a small to medium size mains-fed induction machine, a sensorless stator winding temperature estimator is proposed to compensate for the shift of the thermal time constant in a motor with continuous-operation periodic duty cycles. First, the rotor temperature is estimated from the voltage and current measurements and 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 a proportional integral observer is constructed to track the stator winding temperature. The experimental results are given to validate the proposed algorithm, and the overall scheme estimates the stator winding temperature efficiently without using any real temperature sensors