A Bearingless Motor With Passive Electrodynamic Suspension in Axial Direction

This article presents a novel structure of a bearingless motor with integrated passive axial electrodynamic suspension. The simple initial structure has been improved in three steps. The structure was upgraded by including additional rings of permanent magnets and rotating back iron yokes in a double rotor structure that embraces the stator. Electrodynamic force generated in the final model was several times higher than that of the initial one. A prototype machine of the final structure was built. The suspension currents and axial electrodynamic forces were validated through an experiment under quasi-static condition, that is, constant rotational speed and fixed axial displacement. Theoretical equations for the axial electrodynamic force were derived. The force equation was compared to the finite-element analysis and experimental results.