ROLE OF TORQUE ANGLE IN INVERTER-FED INDUCTION MOTOR DRIVES

ABSTRACT

It is shown from the induction motor differential equations that changes in load torque, speed reference and torque angle are accompanied by a transient change in the speed of the air-gap mmf. The time constant associated with the torque angle change is different for a voltage source and a current source inverter-fed induction motor. This aspect throws light on the instability of current source inverter-fed induction motor on open loop operation. Evidently, the solution to overcome this instability is to use the torque angle for feedback control. It is proved that torque angle feedback alone is not sufficient for stabilization of the current source inverter-fed induction motor.