Dynamical Modeling of Passively Levitated Electrodynamic Thrust Self-Bearing Machines

Abstract

Topologies of electrodynamic thrust bearings and axial flux permanent magnet machines exhibit a significant number of similarities. Starting from this observation, this paper introduces a new self-bearing motor combining, within a single armature winding and through the same permanent magnets, both the passive electrodynamic axial levitation and motor functions. The rotor axial stabilization being achieved through passively induced currents, no sensor, controller, and power electronics related to the bearing function are required. In addition, an electromechanical model describing both the axial and spin dynamics of such a motor is presented. This set of six equations depends on 12 parameters whose determination can be performed through static finite element simulations or quasi-static experimental measurements. The model is linearized allowing us to study the local stability of this passive self-bearing motor around an operation point characterized by the rotor spin speed, as well as the external force and torque. The dynamic and quasi-static behaviors as well as the stable spin speed ranges are analyzed through a case study. Finally, a first experimental investigation dedicated to the validation of the operation principle as well as the dynamical model is performed.