Development of Slotless Single-Drive Bearingless Permanent Magnet Motor With Aerostatic Bearings for High-Speed Applications

For electrical motors, three translational (
x–y–z
) and two tilting (
θ_x–θ_y
) rotor motions must be restricted. Ball bearings are commonly used to restrict motion; however, they cannot be applied to high-speed motors with large
DN
(product of bearing diameter and speed) values. The rotor in this study has an aerostatic bearing support in radial (
x–y
) and tilting (
θ_x–θ_y
) motions. However, if an additional magnetic bearing or actuator is applied to the motor for axial motion control (
z
), the motor size and shaft length increases. To avoid this problem, a novel bearingless motor structure with a magnetically integrated bearing function is proposed in this paper. The structure combines the functions of both torque production (
θ_z
) and axial force generation (
z
) in one unit. It uses only a set of three-phase slotless windings and three-phase voltage source inverter. Such bearingless motors are referred to as single-drive bearingless motors. The
d
-axis and
q
-axis currents regulate the axial suspension force and torque, respectively. This paper presents the structure, operation principle, 3D-finite element calculation results, and experimental results. The fabricated prototype bearingless motor with a shaft diameter of 30 mm can actively control the axial motion of the rotor at 60,000 rpm, that is, with a
DN
value of 1,800,000.