Impact of Ferromagnetic Yokes on Axial Flux Passively Levitated Self-Bearing Machines

Self-bearing machines have gained increasing interest over the past twenty years by bringing the benefits of magnetic suspension to high torque density systems. Among them, passively levitated machines have recently been investigated both at the theoretical and experimental levels, being nevertheless limited to ironless structures for the axial flux configuration. In this context, this paper introduces a rotor structure comprising a ferromagnetic yoke surrounding the armature winding. The scope of the existing electromechanical model is then enlarged to take into consideration the resulting variation of the inductance coefficients with the rotor axial position. Additional force and torque terms created by the motor current are highlighted. Finally, the proposed structure is compared to the classical ironless rotor, underlining that the former allows to increase the motor and suspension performance metrics.