Comparison Criteria and Stability Analysis of Electrodynamic Thrust Bearings

Electrodynamic bearings can ensure contactless levitation of rotors at room temperature solely relying on passive phenomena. Recently, two models describing the axial quasistatic and dynamic behaviours of a wide variety of electrodynamic thrust bearings (EDTBs) have been derived. However, although these models enable to study EDTB topologies in terms of stiffness and rotational losses, criteria allowing us to objectively compare their intrinsic qualities still lack. The present paper thus introduces four comparison criteria related to the axial stiffness, the bearing energy efficiency and the external damping required to stabilise the thrust bearing regardless of the spin speed. To this end, an analytical stability analysis is first performed on the basis of these dynamic models. This notably leads to static and dynamic conditions that ensure the stability at a specific speed. Finally, three topologies are compared on the basis of the comparison criteria in the framework of a case study.