Observability Analysis for Speed Sensorless Induction Motor Drives With and Without Virtual Voltage Injection.

For speed sensorless induction motor drives, the unobservable problem of rotor speed at low synchronous speed has not been solved yet. To obtain a unified observable condition, the local weak observability concept is used in this paper. Based on the result of analysis, virtual voltage injection method is proposed. With this method, the states of induction motor, including rotor speed, are locally weakly observable at zero synchronous. The stability of proposed method is proved by Lyapunov's stability theorem. Finally, the feasibility of proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]