This paper proposes a new full-order adaptive observer algorithm to overcome the instability of speed sensorless vector control system of induction motor at low speed, especially at extremely low speed. The algorithm consists of the improved feedback matrix algorithm and the improved speed adaptive law algorithm. By establishing an observer state error equation considering the non-linear voltage error of the inverter and the stator resistance voltage drop, a feedback matrix was designed to reduce the effect of inverter's nonlinear voltage error and stator resistance voltage drop on speed estimation. Meanwhile, this paper improves the traditional adaptive law. The basic idea is to add compensation amount equivalent to the non-linear voltage error, and the compensation amount is adaptive to the running speed and load to improve the motor speed estimation accuracy at low speed. Extensive experimental tests have been carried out to evaluate the performance of the proposed algorithm using a 2.2 kW induction motor experimental platform. The experimental results show that the algorithm presented in this paper can guarantee the stable operation of the motor under the rated-load and 180% rated-load at low, extremely low and 0 speed with good dynamic and static characteristics.
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