Vector control of induction motor without shaft encoder

A method of torque control in induction motor drives that requires not shaft encoder is presented. Both the torque control and the speed control are based on vector control. The proposed scheme of vector control is based on the self-control of rotor flux velocity, which is controlled with the torque-producing current and the rotor flux derived from the stator voltages and currents. An improved estimator of the rotor flux is proposed to reduce the influence of motor parameters, making it possible to calculate the rotor flux at standstill. Consequently, the proposed system can be controlled precisely over a wide speed and load range. These features are verified by theoretical examination, experimental results, and a practical application.<>