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A Surface-Mounted Permanent-Magnet Motor With Sinusoidal Pulsewidth-Modulation-Shaped Magnets

This paper proposes a design of a surface-mounted permanent magnet (SPM) motor with a magnet surface of a sinusoidal pulsewidth-modulation (SPWM) shape. The fundamental harmonic of the flux density distribution over the SPWM-shaped magnet surface is sinusoidal, which makes the back electromotive force induced in the phase winding close to sinusoidal. Slots can be cut easily into the magnet to form an SPWM-shaped surface, and less rare-earth magnet material is used if the SPWM-shaped permanent magnet (PM) is sintered or bonded in the molds. The optimal SPWM magnet shape on the SPM motor for an electric scooter is designed by maximizing the output torque and efficiency and minimizing the magnet volume and is verified by the finite-element analysis. Prototype motors are fabricated with magnets of various shapes, with or without an SPWM surface. The amount of rare-earth magnet material used in the motor with the SPWM-shaped PMs is 9.4%–13.2% less than that without the SPWM-shaped PMs, while the maximum torque is reduced by only 3%–5.4%.