A stabilization method for speed sensorless vector controlled induction motors at zero frequency operating condition with multirate adaptive observer

This paper proposes a stabilization method for speed sensorless vector controlled induction motors at zero frequency operating condition using a new configuration of the adaptive observer. In speed sensorless vector controlled induction motors, it has been pointed out that the speed identification system becomes unstable at zero frequency operating condition. This problem is caused by lack of the knowledge of the rotor side of induction motors, and the disturbance such as a parameter mismatch of the stator quantities at zero frequency operating condition. In this paper, a new configuration of the adaptive observer, which stabilizes speed sensorless vector control of induction motors without injecting a high frequency or an excitation signal, is proposed. Firstly, causes of unstable speed identification in the conventional speed sensorless vector control system are considered. Next, a configuration of the adaptive observer based on multirate control in order to stabilize the speed sensorless system at zero frequency operating condition is proposed. Finally, validity of the proposed method is shown by experimental results.