Regeneration characteristics of speed sensorless control method based on phase difference

A simple speed control method is needed for small induction motors. Previously, the authors have proposed a simple speed sensorless control method for small induction motors. In this method, the 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 remains constant. This paper presents the principle of this method and the experimental results including the regenerative regions with a 400 W induction motor.