| Due to their simple structure, high efficiency and long life, brushless DC (BLDC) permanent magnet (PM) motors have wide applications in the automobiles, household appliances, medical equipments and other fields. Therefore, the investigation of performance of the BLDC PM motor is of significant importance.First, the structure and the operation principle of the BLDC PM motor have been presented, and the factors that affect the torque ripple have also been analyzed. Then, using a three dimensional finite element method (FEM), the three dimensional magnetic field of the motor has been obtained. Next, the performance parameters of the motor under the rated operating conditions have been derived, including the stator currents, electromagnetic torque, torque ripple, back electromotive force and cogging torque. Besides, the measured inductance values of the motor verified the validity of the calculation results.On the other hand, the cogging torque of the motor has been derived and analyzed using several methods. Eccentric circular arc and sinusoidal shape design of permanent magnet can effectively reduce the cogging torque of the motor. But the electromagnetic torque is also decreased. Using sinusoidal+ 3rd harmonic PM design, the electromagnetic torque can effectively increased about 15%. And, the number of the slope PM segments can reduce the cogging torque and the optimal slope angle can be obtained. In addition, the number and the shape of the stator or the rotor auxiliary slots has a great influence on the cogging torque. The even number of stator auxiliary slots or the odd number of the rotor auxiliary slots can significantly minimize the cogging torque and the auxiliary slots of rectangular shape can effectively reduce the cogging torque. Finally, it has been presented that different magnetization directions have different effects on the cogging torque. The cogging torque with the sinusoidal magnetization is remarkably less than the radial and parallel magnetization. |
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