Adaptive Speed Sensorless Induction Motor Drive for Very Low Speed and Zero Stator Frequency Operation

This article proposes a control method to achieve the goal of very low speed and zero stator frequency operation for a speed sensorless vector-controlled induction motor drive. The speed estimation is first formulated using a closed-loop reduced-order rotor flux observer and an adaptive speed estimator. The aim is to reduce the computational complexity of the sensorless control algorithms and to shorten the execution time. It is further improved by a phase shift technique and by an injection of a low-frequency signal. Experimental results are presented to show the validity of the proposed approach in such driving modes as zero stator frequency, reversible speed, and zero rotor speed control.