ABSTRACT
The techniques for the speed or position estimation of the rotor are called in literature sensorless or encoderless. The main advantages of sensorless-controlled drives are the reduced hardware complexity, the lower cost, the reduced size of the drive machine, the elimination of the sensor cables, the better noise immunity, the increased reliability, and the lower maintenance requirements. As far as sensorless control based on high-frequency voltage carrier injection is concerned, the amplitude of the carrier voltage is the cause of the excitation, while the corresponding current harmonic content is the effect. Various rotor speed and slip speed open-loop estimators can be obtained by rewriting the stator and rotor equations of the Induction Machine. There are basically two forms of implementation of an estimator: open loop and closed loop, the distinction between the two being whether or not a correction term, involving an estimation error term, is exploited to adjust on-line the response of the estimator.
