Design of a stator flux sliding mode observer for direct torque control of sensorless induction machine

One of the most important issues in implementing the direct torque control of induction motor drives is to obtain accurate information about stator flux level and position for the entire speed range. Among the advanced observation methods, the variable structure observer is the closest to the principal DTC characteristics, which are simplicity and robustness. This paper presents a design approach for a stator flux sliding mode observer that matches these characteristics without speed sensing or estimating. The design strategy considers the nonlinear induction motor dynamic system as a linear system subjected to bounded uncertainties due mainly to both speed and stator resistance variations