A Robust Sensorless Sliding Mode Observer with Speed Estimate for the Flux Magnitude of the Induction Motor Drive

The paper presents a sensorless sliding mode observer for the flux magnitude of the induction motor (IM) drive. In order to implement a vector control scheme for the IM, the angle of the rotor flux and the flux magnitude are needed. To obtain them, it is typical to use a stationary frame flux observer - once the alpha, beta flux components have been estimated, they are used to compute the flux angle and the flux magnitude. However, in Indirect Field Orientation methods, such an observer is not used; then, a separate flux magnitude estimator is needed. The paper presents a flux observer that is based on a modified IM model in the rotating reference frame. This is constructed on the skeleton of a sensored observer - in order to make it sensorless, the observer is fed with a speed estimate. The paper shows that, with a certain gain design, the resulting sensorless observer is insensitive to the potential input speed inaccuracy. The observer yields an accurate flux magnitude without measuring the speed.