Effect of the number of poles on the acoustic noise from BLDC motors

The goal of this study is to examine the effect of the number of poles on the noise from BLDC motors. To this end, the number of slots was fixed to six and the number of the poles was set to four or eight before noise was measured. Motors having different numbers of poles showed clear differences in noise; cogging torque, torque ripple and normal local force were interpreted, analyzed and compared to determine the reason for the differences. To conduct precise comparisons of noise, efforts were made to prevent changes in other variables when constructing the four-pole and eight-pole motors. Noise measurements were conducted after going through the above preparation. The results show that the eight-pole motor produced a lower noise level than the four-pole motor. To determine the cause of the noise, the cogging torque, torque ripple and radial local force were calculated, which are representative noise sources in BLDC motors, and FFT was performed to analyze their frequency components (harmonics). The calculations were made using a finite element method with the Maxwell stress tensor.