A Nonintrusive Induction Motor Stator Resistance Estimation Method using a Soft-Starter

This paper presents a simulation and experimental study on the induction motor stator winding resistance (R_s) estimation using dc signal injection. The authors suggest that, for motors that are connected with soft-starters, R_s can be nonintrusively estimated by injecting dc components in the motor stator winding by adjusting the existing control strategies. A delay angle is introduced to the thyristor gate signals at the current zero-crossing to inject dc components in motor voltages and currents. The resultant torque pulsation is analyzed, and its correlation to the current and voltage frequency components is developed using sequence analysis theory. The proposed method has been verified by simulation and experimental results. The accuracy of stator resistance estimation is within 2% errors.