Aiming at the influence on the actual speed caused by the suspension winding′s rotor induced current of a squirrel-cage bearingless induction motor (SBIM), a novel three-speed wound bearingless induction motor (WBIM) is designed based on establishing the stator–rotor equivalent circuit, deriving the exciting current-suspension slip ratio equation and analyzing the magnetic field distribution with odd pole pairs and dipole pairs. The stator is embedded with a fixed four pole winding and a 2/6 pole-changing winding, while the rotor is wound with series–parallel windings connecting at a slip ratio ring. By changing the connection method of the stator coils, adjusting the three-phase voltage source, and controlling the short circuit of the rotor winding central point, it can realize that the rotor only induces the torque winding′s magnetic field under three speeds. Combining with the finite-element analysis, the induced current, air gap magnetic density, suspension force, and electromagnetic torque of the traditional SBIM and the new WBIM are quantitatively compared. Finally, an experimental platform is built for further verification. The results show that the designed three-speed WBIM can not only effectively suppress the induced current of the suspension winding and reduce its influence on the motor torque and speed, but also makes the motor has a better start-up and steady-state performance.

In a fixed pole bearingless induction motor (FPBIM), the influence of the suspension winding is neglected in the traditional mathematical model, leading to the inaccurate speed estimation of speed sensorless control. Aiming at this problem, this article proposes an improved mathematical model. First, considering the influence of the suspension winding, the resistance matrix and inductance matrix are extended based on the traditional natural coordinate model and the FPBIM's natural coordinate model (in the a-b-c stationary frame) is established. Second, through the rotation transformation by an extended transformation matrix, the FPBIM's two-phase stationary coordinate model (in the α–β stationary frame) is obtained and the flux linkage equations are extracted from it. Finally, to verify the effectiveness and feasibility of this improved mathematical model, it is applied to the speed sensorless control based on model reference adaptive system. The simulations and experiments show that the FPBIM improved mathematical model gets more accurate speed estimation and better rotation performance under no-load, load, load disturbance and displacement disturbance, while the suspension performance is not affected.

To enhance the working efficiency of a bearingless induction motor with the specific pole, an accurate modeling method considering the iron loss is proposed, and the optimal rotor flux-oriented control strategy is studied in this article. First, the mutual inductance expressions with rotor eccentricity of the torque winding and suspension winding are deduced and verified theoretically. In addition, the two windings are converted into the same circuit and the composed mutual inductance is discussed. Second, the accurate equivalent circuit model on the d -, q -axis considering the iron loss is established, and the optimal rotor flux is figured out. Third, by theoretical deduction, the rotor flux expression is directly turned into the function of the equivalent composed winding current, and the parameter identification method based on the simplified flux-current model is proposed to enhance the control accuracy. Further, the delayed field weakening strategy is introduced in the control system to suppress the rotor vibration. Finally, an experimental platform is built to validate the practicality. Theoretical analysis and experimental results indicate that the adopted optimal rotor flux control both improves the motor efficiency and achieves an excellent levitation performance.

To improve the quality of starting torque and suspension force, a composite cage rotor bearingless induction motor (CCR-BIM) is designed, which adopts a composite cage rotor structure that combines an inner rotor and an outer rotor. First, the overall structure of the CCR-BIM is designed, the composite cage rotor of the CCR-BIM is specially designed and analyzed for the induction principle, and the mathematical model of suspension force and torque is deduced. Second, the initial structural parameters are determined, and motor qualities, such as starting torque quality and suspension force quality, are compared and analyzed between the proposed motor and BIM using a finite element model (FEM). Third, based on the response surface model (RSM), a multi-objective improved NSGA-II is constructed, and the three optimization objectives of starting torque, suspension force, and suspension force pulsation are optimized. Finally, the results of the experimental setup prove that the starting torque increases by 6.98%, the suspension force increases by 5.45%, and the suspension force pulsation decreases by 18.54%. The effectiveness of the proposed motor and the correctness of the multi-objective optimization strategy are verified.