Sensorless variable structure speed control of an induction motor

A field oriented, variable structure speed control scheme of an induction motor is presented. No mechanical transducers are employed. A sliding surface is defined in terms of the rotor flux producing component of the stator current. Once the sliding surface is reached, the rotor flux tends asymptotically to a constant value. The fems induced in the rotor an estimated and used to orient the controller. A derivative free estimator for the fems is derived. Simulation results are presented, showing very good transient and steady state behavior.