Cogging torque

Slots of the stator of the permanent magnet electric machine interact with the rotor magnets, and this results in the pulsations on the torque vs position plot. This effect is called a cogging torque, and it affects the motor operation, especially at lower speeds.
Cogging torque effects are more prominent when the ratio of the number of stator slots to the number or rotor poles is an integer.

Cogging torque plot in PM generator with 12 poles on the rotor and 48 slots in the stator.

Cogging torque may be analyzed in QuickField: Cogging torque in wind turbine generator.

Additional links on this subject: Cogging_torque from Wikipedia, the free encyclopedia.

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