Electrical design and winding selection for a bearingless Axial-Force/Torque Motor

The Axial-Force/Torque Motor is a completely new type of bearingless drive. The presented Lorentz-force type actuator features a compact and integrated design using a very specific permanent magnet excitation system together with concentric non-overlapping air gap windings. The end-windings of the bent air-core coils, shaped in circumferential rotor direction, provide active axial magnetic suspension forces. No additional (bearing) coils are thus necessary for stable axial levitation. The four remaining degrees of freedom of the rotor are stabilized by passive magnetic ring bearings. This article provides a comprehensive overview of the complex practical design process of single-phase Axial-Force/Torque Motors. The electrical design and especially the winding selection is a very crucial part of the motor design. Levitation force and drive torque specifications must both be fulfilled concurrently at rated rotor speed using only one common winding system, while respecting several electrical, thermal and mechanical boundaries likewise. Provided, that the air gap winding is designed properly, a sophisticated (closed-loop) drive control strategy permits the autonomous manipulation of both control variables, drive torque and levitation force. As conclusion of this article, a short presentation of the experimental setup highlights possible fields of application for the proposed drive concept.