Stable Operation Method for Speed Sensorless Induction Motor Drives at Zero Synchronous Speed With Estimated Speed Error Compensation

The methodologies applied to speed sensorless induction motor drives (SSIMD) can be divided into two categories. The first category makes use of the fundamental model of induction motor to establish speed and flux observers. However, the rotor speed is unobservable with these methods when synchronous speed is close to zero. The second category makes use of anisotropies of induction motor to observe rotor speed. However, the anisotropies of induction motor are too weak to extract rotor speed information. Consequently, the unstable problem of SSIMD at low synchronous speed (including zero synchronous speed) has not been solved yet by now. In this paper, a virtual voltage injection method is proposed to solve this problem. The voltage is only injected into observer. The observability of rotor speed based on proposed virtual voltage injection is analyzed. Because the injected voltage into observer results in estimated speed error, a compensation method is proposed then. The stability of the system with virtual voltage injection and corresponding compensation method is analyzed by the input-state-stability concept. Finally, the feasibility of the proposed method is verified by experiments.