Sensorless control of induction motor based on estimation of an electromotive force

Induction motor speed sensorless torque control, which allows operation at low and zero speed, optimizing both torque response and efficiency, is proposed. The produced torque is a continuous output variable of control. The magnitude and orientation angle of the rotor flux of the induction motor are determined by the output of the closed-loop rotor flux observer based on estimation of the extended electromotive force of a machine. A smooth transition into the field weakening region and the full utilization of the inverter current and voltage capability are thus made possible. The reference tracking performance of torque, speed, and rotor flux is demonstrated in a series of transient characteristics by simulation and experimental results.