Research of cogging torque in the brushless DC motor with fractional ratio of slots and poles

In the permanent-magnet motor, the cogging torque is rather concerned because it is often a principle source of vibration, noise and control difficulty. The simplified model for analyzing permanent-magnet motor with fractional ratio of slots and poles was presented, and the principle of removing cogging torque was explained clearly by mathematical analysis. The influence on cogging torque caused by non-uniform of rotor permanent-magnet can be analyzed by this model. The influence caused by amplitude and position errors of permanent-magnet magnetic motive force was analyzed, which was confirmed by experimental examples. Testing results are matched with analyses. The achievement of the research has utility purpose to improve the performance of brushless DC servomotor and reducing cogging torque. Moreover, practical effects have been got.