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This research investigates the characteristics of cogging torque in brushless DC motors due to the interaction between the uneven magnetization of a permanent magnet and the shape of the teeth. The excitation frequencies of the cogging torque are the harmonics of the least common multiple of the poles and slots in ideal brushless DC motors. However, this research numerically and experimentally illustrates that the uneven magnetization of a permanent magnet also generates the harmonics of slot number. Magnitudes of cogging torque are affected not only by the uneven magnetization of a permanent magnet but also by the shape of the teeth. The cogging torque can be effectively reduced by determining optimal teeth curvature once the range of uneven magnetization of permanent magnet in a brushless DC motor is identified.
Date of Publication: July 2011