Low-speed performance of robust speed identification using instantaneous reactive power for tacholess vector control of induction motors

The authors have proposed a new approach to estimate induction motor speed from measured terminal voltages and currents for tacholess vector control. The proposed approach is based on observing the counter electromotive force vector or the instantaneous reactive power of the rotor flux. The described technique is robust to variations of motor parameters. It does not require any pure integration of sensed variables in principle, thus, achieving much wider bandwidth speed control than previous tacholess drives. The proposed method has been successfully implemented on high-speed (6 kW, 1 kHz) motor drive where the effectiveness has been verified. In consideration for wide applications, the authors apply this new technique to a general-purpose motor (7.5 kW, 60 Hz) drive in this paper with emphasis on performance at low speeds and zero primary frequency. The validity and robust performance are proved by simulation and experiment. Also, a high-precision detection method for the stator voltage at low speeds is proposed