Modeling and Operation of a Bearingless Fixed-Pole Rotor Induction Motor

The rotor currents are induced by both suspension force winding magnetic field and torque winding magnetic field in the traditional bearingless induction motors (BIMs). Due to the currents induced by the suspension force winding, there are errors in the generation of radial suspension forces. To address such problems, a novel BIM with fixed-pole rotor, called bearingless fixed-pole rotor induction (BFPRI) motor is proposed. The structure of BFPRI motor is first analyzed and the mathematical models of radial suspension forces are deduced. Based on the finite element analysis, the induced currents and radial suspension forces are also investigated and compared with the traditional BIM. Finally, the prototype motor is built and experimental research is carried out. In this novel motor, only the torque winding magnetic field induces currents in the rotor, which makes the precision of radial suspension forces higher and thereby reduces the complexity of BIM control system. The effectiveness of the proposed BFPRI motor is validated by both simulation and experiments.