The power transmission of magnetic gears, based upon the at-tractive force of magnets, does not involve direct
contact between the power transmission shafts. Thus, vibration or noise, due to friction, can be reduced. However,
magnets and iron cores, which are the main components of magnetic gears, generate cogging torque. This
increases torque ripples that are the cause of the noise and vibration of permanent-magnet (PM) machines. In
this study, a torque ripple reduction method, using the combination of number of poles and number of pole
pieces was proposed. This method uses the structural characteristics of magnetic gears only. This method was
suggested instead of the existing torque ripple reduction methods for PM machines to reduce the torque ripples
of magnetic gears. Furthermore, the correlation between the numbers of poles, pole pieces, and torque ripples
was analyzed. From this analysis, a design guideline that minimizes torque ripples in the initial design of
magnetic gears was proposed.