Improved stator flux and stator resistance estimators for sensor-less control induction motor drives

Induction motor drives are widely used in adjustable speed applications. The use of speed sensors (encoders) for speed control introduces difficulties in drives operation and degrades the reliability especially in hostile environments, and makes the system more expensive to maintain and replace. This increases the demand for speed sensor-less induction motor drive schemes where the speed is estimated through various estimation schemes and algorithms. One such method of speed estimation is through the estimation of stator flux of the machine. But the major drawback of this method is its dependence on stator resistance for flux estimation; the stator resistance of an induction motor varies with operating conditions such as loading and temperature. An improved stator flux estimation technique with online stator resistance estimation is proposed in this paper. Stator flux estimator discussed in the paper is based on closed loop offset compensation algorithm and the stator resistance is estimated online using the variables measured from the motor terminals. The proposed schemes for stator flux estimation and stator resistance estimation for speed sensor-less vector controlled induction motor drive are validated through extensive simulation on a Matlab-Simulink platform.