Non-invasive torque estimation for broken bar detection in induction motors

Rotor asymmetries lead to perturbations of air-gap flux patterns in induction machines. These perturbations in flux components affect a number of components including currents and electromagnetic torque. The supervision of these signals enables early detection of such faults and assists in fault diagnosis. This paper studies the detection of rotor imperfections by spectral analysis of the electromagnetic torque, computed by two stator flux estimators using only noninvasive sensors such as current and voltage sensors. In a first approach, the Extended Luenberger Observer (ELO) is used to estimate stator flux components as well mechanical velocity. A second approach uses a nonlinear High Gain Observer (HGO) for the same purposes. Experimental results and comparison show the significant potential of these methods in detecting these types of faults.