Evaluation of various slip estimation techniques for an induction machine operating under field-oriented control conditions

Six published methods of rotor slip estimation for sensorless speed control were evaluated using simulated data. Only two of these showed signs of being usable. Both are based on the steady-state machine model and produce a fair slip accuracy for a machine running under perfect field alignment conditions. It was not determined whether the other four techniques were unsuccessful because they require a closed-loop speed controller, were presented incorrectly in the literature, or contain fundamental deficiencies. On the basis of these evaluations, a new technique was developed, and both measured and predicted results are presented to show that it works well. Moreover, this new technique has many features that make it theoretically and practically more attractive than most existing techniques.>