Design and Analysis of a Three-Speed Wound Bearingless Induction Motor

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.