A Combined Structure for Slip Power Control of Wound Rotor Induction Motors with Speed Sensorless Control

method combines the two conventional chopper and Kramer methods to control the slip power of the motor. The mentioned method acts in two modes، first the drive is forced to chopper control for starting up the motor and then the system switches to the Kramer control when motor passes the 80% of the reference speed. The combined converter eliminates the conventional resistor starters of the traditional Kramer converters and also provides speed sensorless control of the drive. Furthermore a sensorless control scheme is proposed which eliminates DC offset problem of some conventional methods. Simulation results show that the system reduces some drawbacks of the two conventional methods. Finally a low power laboratory set-up is constructed to show some dynamic behaviors of the combined method. In the laboratory set-up، a chopper controlled converter is designed and using a real-time control system، speed sensorless control and start-up process is successfully performed.