Design of a second-order sliding mode MRAS speed estimator for the induction motor drive

The paper presents a speed estimation method for the induction motor (IM) drive. The speed is obtained using the Model Reference Adaptive System (MRAS) principle and is based on a second order sliding mode (SM) observer. First, the stationary frame fluxes of the IM are obtained using a Voltage Model Observer - this is based on the stator equations (which do not depend on speed) and serves as the reference model. The adjustable model re-estimates the fluxes and is made to match the reference model by adapting the speed - specifically, the speed estimate is a second order sliding mode term. The method is relatively simple and is not computationally intensive. The paper shows the implementation by first order sliding mode and also by second-order sliding mode. The speed estimate is obtained by filtering a switching term. The speed estimate is accurate and robust; when the second-order SM approach is used, it is obtained using minimal filtering only.