Sensorless Induction Machine Observer in Presence of Nonlinear Magnetic Characteristic

We are considering the problem of state estimation in induction motors. Generally, the motor observer design has been dealt based on standard models that neglect the saturation effect of the magnetic characteristic. As a matter of fact, magnetic saturation cannot be ignored especially when considering (speed, torque) control strategies that involve large flux variations. Such large flux variations are necessary to meet optimal operation conditions in presence of wide range load torque change. On the other hand, it is well known that the use of mechanical (speed, torque) sensors entails reliability issues. In this paper a new observer design is developed for induction machine based on a model that accounts for the nonlinear feature of the magnetic circuit. The observer provides estimates of the mechanical and magnetic variables using only stator currents and voltages measurements. The observer convergence is formally analyzed and illustrated by simulation.