Improved flux estimation and stator-resistance adaptation scheme for sensorless control of induction motor

The speed-sensorless vector-controlled induction-motor drive is superior to the conventional vector-controlled induction-motor drive in terms of drive cost and reliability. In speed-sensorless control, one common practice is to estimate the flux position from the terminal voltage and current using a stator-voltage model. The accuracy of estimated flux position decides the performance of the vector-controlled drive. However, the performance is limited by the DCdrift problems that prohibit the use of open integration of the flux-producing voltage component for flux estimation. The paper proposes a flux-estimation method that gives the effect of open integration along with an inherent error-decaying mechanism to resolve the DC-drift problem. A stator-resistance-adaptation method is also incorporated in the flux estimator, which makes the flux-position estimation independent of resistive parameters of the motor. Using this fluxestimation algorithm, a rotor-flux-oriented speed-sensorless speed-control scheme of induction motor is proposed. The scheme is both simulated and experimentally verified.