Development of a Bearingless PM Motor with Axial Magnetic Suspension Using Zero-Sequence Current

This paper proposes a one-axis actively positioned bearingless motor with 1 kW output power using a zero-sequence current. The axial suspension winding is connected between the neutral point of the motor windings and the midpoint of the capacitors in the DC link. The zero-sequence current flowing into the axial suspension winding produces active axial force, while the motor is driven by dq-axis currents. In the proposed bearingless motor, the flux of bias PMs for the axial magnetic suspension does not pass through the motor stator core, and therefore the motor design is not constrained from the bias flux. Additionally, the flux, which is produced by the zero-sequence current flowing into the motor winding, contributes to boost the axial force. To demonstrate the performance of both the motor and magnetic suspension, FEA and experiment were conducted. The rotor was successfully levitated and, the proposed bearingless motor system has a potential to achieve both stable magnetic suspension and 1 kW-output.