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Title: A New Approach to the Design of a Low Noise Permanent Magnet Machine

Authors: Zhentao Du and Thomas A Lipo

Abstract: Low torque ripple and high torque density are the two primary concerns in high performance electric machines. In particular, in submarine applications, the noise produced by the torque ripple of electric machines is highly undesirable, since it can lead to detection of the sub’s location. This paper proposes two surface permanent magnet machines with PMs that are specially shaped in the axial direction. The proposed designs are comprised of one with a sinusoidally shaped magnet and a second having a sinusoidally shaped magnet with an added third harmonic. The performance of the proposed designs are compared to a conventional surface PM machine, a conventional bread loaf surface PM machine, and a buried magnet V-shape IPM machine. The results show that the proposed design has 15% higher torque density than the sinusoidal shaped surface PM machine, while the torque ripple remains the same as the sinusoidal shaped surface PM machine (as small as 1%.). Both proposed designs are shown to be superior to the two conventional designs. In conclusion, using the third harmonic shaped PMs not only increases torque density but also minimizes torque ripple. Detailed results from a finite element study have verified the excellent performance of the proposed machines.