A Method to Estimate Torque and Stray Load Loss of Induction Motor without Torque Detector

This paper presents a new method to estimate the average torque of Induction Motor (IM) accurately from stator flux linkage and stator current vectors. To enhance the precision of torque estimation, this method entails taking additional losses, not only no-load iron and mechanical losses but also stray-load loss, into account. This paper also shows a new method to measure stray load loss indirectly using linearity of torque to rotor current. The proposed method can be performed without torque detector and is applicable to both sinusoidal and inverter drives. The proposed torque estimation is implemented on a squirrel-cage induction motor fed by sinusoidal, square and Pulse-Width-Modulation (PWM) drives. To verify the validity of the proposed method, the estimated torques are compared with measurement by torque detector.