To ensure stable suspension of rotor for bearingless motor, the rotor displacement information as a feedback signal must be obtained accurately. Traditional mechanical sensors increase system cost and volume and are sensitive to environment. When the motor starts at low speed, the signal-to-noise ratio of flux linkage is so low that the rotor displacement information is difficult to be extracted. In this paper, for bearingless permanent magnet vernier motor (BPMVM) with dual-purpose-no-voltage (DPNV) winding, a specific radial displacement observer based on high-frequency voltage injection is proposed. Due to particularity of DPNV winding structure, after injecting high-frequency signal into the torque voltage, the difference between induced high-frequency voltages in symmetrical windings can be computed. High-frequency bias voltage whose amplitude is linear with radial displacement is included in the difference, and the radial displacement observer can be consequently designed. A major feature of the proposed observer is that there is no theoretical error in different steady and dynamic conditions. The topology of DPNV winding and mathematical model considering rotor eccentricity are analyzed in detail. The proposed radial displacement sensorless control method is validated on a BPMVM prototype, proving that it is robust to radial and tangential disturbance.

Bearingless permanent magnet (PM) vernier motor (BPMVM), dual purpose no voltage (DPNV) winding, sensorless control, high-frequency voltage injection, mathematical model considering rotor eccentricity, radial displacement observer.