Cogging torque of brushless DC motors due to the interaction between unevenly magnetized permanent magnet and teeth chamfering

This research investigates the characteristics of the cogging torque in brushless DC motors due to the interaction between unevenly magnetized permanent magnet (PM) and teeth shape. The excitation frequencies of cogging torque are the harmonics of the least common multiple of the poles and slots in the brush less DC motors with the ideally magnetized PM. However, uneven magnetization of PM additionally generates the harmonics of slot number whose magnitudes are affected not only by the uneven magnetization of PM but also by the teeth shape. Effective reduction of cogging torque can be accomplished by investigating the interaction between unevenly magnetized PM and teeth shape.