Sensorless estimation for vector controlled induction motor drives

The desirability of eliminating mechanical shaft sensors for induction motor drives has led many manufacturers to introduce sensorless “vector” drives to their product range. Current generation sensorless drives are viewed as “medium performance” in that their speed holding and dynamic performance are superior to open-loop V-f drives but inferior to sensored vector drives. The paper reviews current methods and research which may expand the application of sensorless drives into areas which currently require shaft sensors. These applications include torque control, accurate speed holding and servos, multimotor applications requiring speed synchronisation and position control. The review considers PWM induction motor drives. Many of the methods are applicable to PM drives, which because of their inherent saliency and synchronism present a simpler engineering problem. It is assumed that the motor voltage and currents are known, either from direct line measurements alone or indirectly from knowledge of the switching patterns