shaped rotor requires some form of banding on the circumference of the disc, so it is arguably about as prone to disintegration at high rpm as the surface PM construction, but it is undeniably less effective than burying the magnets, as in the IPM construction. Furthermore, the push and pull of the magnetic fields from the stator poles exert torsional, or wave-like twisting, forces on the axial-flux rotor, and resisting these forces is not the strong suit of a disc shape. Consequently, the parts of the rotor that hold the field magnets in place must have a very high strength-toweight ratio, which basically means using exotic (read: expensive!) materials like woven carbon fiber composite. The combination of exotic construction materials and rare earth magnets in the rotor is the reason that the axial-flux configuration is one of the most expensive types being considered for EV use, and there doesn’t seem to be much that can be done to lower its cost in the future. For a more in-depth explanation of the axial-flux PMSM construction, see my article in the May/June 2020 issue of Charged. For those wondering if there is an axial-flux analog to the ACIM; well, it’s theoretically possible, but doesn’t really offer any compelling advantages over its conventional radial-flux counterpart. Another alternative motor construction that leverages the existing VFD ecosystem is the Interior Permanent Magnet-Synchronous Reluctance Motor
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