Rare-Earth-Free Electric Machine Design for Traction Applications Considering Recycling Aspects
Rare earths are naturally occurring minerals with unique magnetic properties that are widely
used in electric propulsion systems. Because these minerals are expensive and in limited supply, alternative technologies must be developed to replace rare-earth-based magnets in electric motors. This problem has triggered a substantial endeavor to seek alternative solutions for application in propulsion systems, primarily focusing on non-rare earth magnets and machine topologies that do not rely on permanent magnets (PMs), all the while aiming to retain maximal performance and efficiency. Alternatives to rare earths will contribute to cost-effective electrified transportation, facilitating their widespread use and drastically reducing the amount of greenhouse gases released into the atmosphere. Therefore, it has become more important to consider less or rare-earth magnet-free machine designs.
This paper focuses on designing a new wound-field flux-switching machine (WFFSM) that considers recycling its components once the machine's end of life (EoL) is reached, and the machine is scrapped. WFFSMs possess effective thermal management capability, fault tolerance, and improved flux-weakening through variable flux operation. WFFSMs have both field and armature windings in the stator, eliminating permanent magnets in the rotor for a simple and robust machine design (Fig.1). Both windings are wound around the stator yoke instead of the stator pole. The design is suggested with toroidal field and armature windings, which simplifies the access of the copper at the EoL. Besides easier winding extraction toward a recycling process, this kind of stator is relatively easy to manufacture with a higher fill factor. It also provides better cooling because the stator winding is directly exposed to the stator housing with a cooling jacket.
The full paper quantifies the recycling potential of the metallic materials that make up WFFSM. The metals used to make the various parts of the WFFSM and the main recycling methods that allow their reuse are listed. The recycling potential is quantified by parts (stator and rotor) employing approximate equations obtained from the literature review and by materials (copper, aluminum, magnetic sheet, steel). The possibilities of energy-saving and the environmental advantages of dedicating efforts and resources for collecting, recycling, and reusing the materials in TW WFFSM for industrial applications are shown.