Displacement sensorless control of a bearingless induction motor based on hybrid flux estimation

To address the problems of bulk-size, high cost for traditional mechanical displacement sensors in a bearingless induction motor (BL-IM), a displacement sensorless control strategy based on hybrid flux estimation for the BL-IM is proposed. By analyzing the merits and shortcomings of the voltage-type and the current-type flux estimator, a hybrid flux estimation model composed of two kinds of flux estimators is designed using the complementary characteristics of the two estimation models in high- and low-speed applications, and the velocity correlation function is used to achieve dynamic smooth switching between two models in the medium-speed zone. Secondly, the radial displacement of the rotor is calculated according to the mathematical model of the BL-IM, so as to realize the self-detection of the rotor displacement. Then, the vector control displacement sensorless system of the BL-IM is established. Finally, the simulation and experimental study are carried out on an experimental prototype designed by our research group. The simulation and experimental results show that the flux estimator has good estimation accuracy, and the sensorless control system of the BL-IM based on flux estimation not only has good self-detection ability of rotor radial displacement, but also has good speed characteristic and suspension properties.