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A method of reducing ripple torque, i.e., the sum of cogging and commutation torques, in permanent-magnet motors without skewing is proposed. The ripple torque for a given range of stator current can be substantially reduced by shifting the pole pairs by half a slot pitch and by choosing the value of magnet width so as to minimize the second-order component of the cogging torque. The method is confirmed by the finite-element analysis of permanent-magnet motors with both radially magnetized and parallel-magnetized magnets. The optimal magnet width of the experimental motor is 6.18 slot pitches for the radially magnetized magnets and 5.80 slot pitches for parallel-magnetized magnets.>
Ishikawa et al. (Mon,) studied this question.
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