Improvement of lower side speed control characteristics of an induction motor without a speed sensor

Various methods for the improvement of speed control performance in the low speed region of an induction motor without a speed sensor are proposed. However, most of those methods seem to have various problems for practical use. In this paper, a speed estimation method with new primary resistance identification is proposed. The better performance of speed control in the very low frequency range under full-load conditions is possible without a deterioration of speed and torque control response by the proposed method. Speed reversal operations at acceleration over 30r/min/sec through zero frequency have also been achieved under full load condition.