Transient response of speed sensorless control method based on phase difference [for induction motors]

A simple speed control scheme is needed for small induction motors. Here, the authors proposed a simple method in which the motor's load torque is estimated from the phase difference between the stator current and the stator voltage, and the drive frequency is calculated from the estimated torque. As a result, the average speed of the induction motor is kept constant. This paper presents the principle of this method and the transient responses of torque fluctuations and speed commands with a 90 W induction motor.