A study of cogging torque reduction methods in brushless dc motor

The cogging torque is undesirable effect in the brushless dc (BLDC) motor, causing vibration and audible noises. It arises from the rotor permanent magnet interacting with the steel teeth on the stator. Therefore, this paper studies the various reduction methods of cogging torque when designing a BLDC motor. These methods can be categorized according to three parts of motor structure, i.e., air gap length, rotor and stator parts. The finite element method magnetic (FEMM) is primarily used to analyze the cogging torque among these different reduction methods. In this paper, a 4-pole, 24-slot BLDC motor is focused with variations of air gap length, rotor, and stator parts in order to study its cogging torque reductions. Finally, the FEMM simulation results are presented to validate these reduction methods.