Determination of an optimum fictitious air gap and rotor disk thickness for a coreless AFPMM

Abstract

This article presents the research on the optimum distance (fictitious air gap) between permanent magnets of the coreless axial flux permanent magnet machine with a double rotor and single stator. Magnetic flux density of the permanent magnets follows the mean flux path between the opposite magnets. The size of the leakage flux depends on the axial distance between the magnets, the distance between adjacent magnets and the back iron of the rotor disks. If the fictitious air gap (clearance between opposite permanent magnets) is too large, the flux path will close through the adjacent magnet and not the opposite one. The article presents the finite element analysis of the magnetic flux density between the permanent magnets mounted on the rotor disks where the fictitious air gap thickness was set as a variable to determine the maximum clearance. Connection between bending (pull) forces of rotor disks and fictitious air gap thickness is also presented with the mechanical stress analysis of rotor disks.