Principle of a Novel Single-Drive Bearingless Motor With Cylindrical Radial Gap

In this paper, a novel single-drive bearingless motor with cylindrical radial air-gap is proposed. The single-drive bearingless motor has only one set of three-phase windings. It generates both torque and axial suspension force independently with only one three-phase inverter and one displacement sensor. Therefore, this single-drive bearingless motor has the advantages of low cost and small size. Only axial direction $\boldsymbol{z}$-axis is actively positioned. The other axes, radial movements $\boldsymbol{x}$ and $\boldsymbol{y}$, and tilting movements $\boldsymbol{\theta}_{\boldsymbol {x}}$ and $\boldsymbol {\theta}_{\boldsymbol{y}}$, are passively stable. In the proposed motor, the rotor is a cylindrical permanent magnet magnetized in a radial parallel direction. The stator consists of six C-shaped cores and one set of three-phase windings. The principles of the suspension force and torque generations by the $\boldsymbol{d}$- and $\boldsymbol{q}$-axis currents, respectively, are shown. The proposed machine was fabricated and tested only to confirm the principles. In the experiments, start-up was successfully achieved. In an acceleration test up to 3600 r/min, stable magnetic suspension and speed regulation by the $\boldsymbol{d}$- and $\boldsymbol{q}$-axis current regulations were confirmed.