Seven-phase Axial And Radial Flux In-wheel Machine With Three Active Air Gaps

For in-wheel machine, outer rotor machines appear as a natural solution. Practically these machines are either radial-flux with one rotor or axial-flux with two rotors. The paper is proposing a machine with three outer rotors with two different polarities in order to reduce useless end-windings while keeping an acceptable thickness for the radial-flux rotor and high torque quality. This Hybrid Flux Permanent Magnet original structure (named HFPM) is possible thanks to the use of seven phases. The third rotor can be considered as an option of an initial double-rotor axial-flux machine in order to increase the torque density. First, the machine structure and the winding design are presented; then, based on 3D finite element method, comparison between the two machines, with two or three rotors, are provided in terms of torque densities and qualities.