Evaluation of encoderless vector control techniques for induction motor drives

This paper describes the investigation of speed estimation techniques for vector controlled induction motor drives. Three model reference based schemes which provide speed estimates from stator voltage and current measurements are simulated. Rotor flux, reactive power and developed torque provide the model quantities. Results indicate that the scheme based upon reactive power is least susceptible to parameter variations during steady state operation, but is inherently difficult to stabilise during transient operation. The scheme based upon rotor flux can provide an identifier which is insensitive to parameter variations for transient operation, but suffers from greater steady state error