Stator-Flux-Linkage-Calculation-Based Torque Estimation of Induction Motors Considering Iron, Mechanical, and Stray Load Losses

Abstract

This article presents a method to estimate the average torque of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> -controlled induction motor (IM) accurately from stator flux linkage and stator current vectors. This method is based on stator flux linkage calculation by a dc-offset-less approximation integrator with error compensator considering not only no-load iron and mechanical losses but also stray load loss. Based on loss analysis, we point out the necessity of considering the iron loss, mechanical loss, and stray load loss caused by the fundamental wave power as additional losses in order to improve the torque estimation accuracy of the proposed method. This article also shows a new method to take the stray load loss into account using linearity of torque and rotor current. The proposed method can be performed without a torque meter and is applicable to both sinusoidal and inverter drives. The proposed torque estimation is implemented on two squirrel-cage IMs: a semiclosed rotor machine and a closed-slot rotor machine, fed by sinusoidal-, square-, and pulsewidth-modulation-wave drives. The result of the estimated torque is verified by comparing the estimated and measured torques.