Design of SPM and IPM Rotors in Novel One-Axis Actively Positioned Single-Drive Bearingless Motor

This paper presents a novel one degree of freedom (1DOF) actively positioned bearingless motor. The advantages of the proposed bearingless motor are a compact axial length and high radial stiffness compared with conventional 1DOF bearingless motors. In the proposed bearingless motor, the single-drive bearingless motor concept has been adapted. Both torque and axial suspension force are regulated independently by only one three-phase inverter and one displacement sensor. Only axial direction z-axis is actively positioned. The other axes, radial movements x and y, and tilting movements theta(x) and theta(y), are passively stabilized. In this paper, principles of the active axial force and torque generations of the novel bearingless motor are presented. Moreover, the performances of the active axial force, passive stiffness and torque for surface permanent magnet (SPM) and interior permanent magnet (IPM) rotors are compared by 3D-FEM analysis. It is found that the proposed 1DOF bearingless motor can achieve high stiffness and short axial length.