Control at low speed of an induction motor

The authors describe the design of a controller for a standard induction motor intended for application as a servo drive. The investigation was motivated by the fact that this type of motor is low in price as well as robust. The authors start with the fundamentals of an induction motor equipped with angular velocity control by means of a voltage source invertor. The fast control of torque and angular velocity necessitates the use of a dynamic flux controller. From the experiments performed it could be concluded that control of the motor by means of a standard voltage source invertor was not satisfactory since under quickly changing angular velocities the magnetic flux could not be kept at a constant level. It is shown that the control of torque and velocity in that case is too slow and also restricted, specially at the lower velocities, due to oscillations occurring in the flux