Proposal of a One-DOF Actively Controlled Bearingless Motor Using Zero-Sequence Current

This paper proposes a one-DOF actively controlled bearingless motor with 1 kW output power using a three-phase four-wire inverter system equivalent to a three-phase inverter in terms of the number of power-switching devices. In the proposed system, the thrust suspension winding is connected between the neutral point of the Y-connected motor windings and the middle point of the two capacitors in the DC link. The zero-sequence current flowing into the thrust suspension winding generates active thrust force, while the motor is driven by dq-axis vector control. The flux of bias PMs for the thrust magnetic suspension is not flowing into the motor stator core, and the proposed motor design is superior to the conventional design. Additionally, the flux, which is generated by the zero-sequence current flowing into the motor winding, contributes to increasing the thrust force. To demonstrate the performance of both the motor and magnetic suspension, FEA was conducted. It was found that the proposed bearingless motor system has a potential to achieve both stable magnetic suspension and 1 kW-output.