IEEJ Transactions on Industry Applications
Online ISSN : 1348-8163
Print ISSN : 0913-6339
ISSN-L : 0913-6339
Cogging Torque Reduction in Permanent Magnet Brushless Motors
Kazuo Ohnishi
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2002 Volume 122 Issue 4 Pages 338-345

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Abstract

This paper studies properties and reducing techniques of cogging torque in brushless motors with surface permanent magnets and winding slots. Desirable combination between stator slots and magnet poles, and relation between the slots and added notches are shown. in order to minimize cogging torque, from the standpoint that cogging is mainly generated by fluctuation of 6th and 12th harmonic components in airgap magnetic energy lost by the stator slot openings.
Next, the proposed techniques are verified in the combination of poles and slots at typical 12 slots motors by using FEM simulation of two-dimensional model, and it is shown that bevelling of stator pole-tips reduces the cogging torque, especially in the motor with 12 slots and 10 poles.
Last, 6 slots and 4 poles motors with the added notches is calculated on the same 2D-FEM and it is shown that type B delivers better result in airgap magnetic flux distribution with rising part of quasi-sinusoidal waveform.

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