Performance analysis of permanent magnet brushless DC motor

The authors propose to reduce the torque ripple of brushless low power motor with neodymium-iron-boron (Nd-Fe-B) segmented magnets. They have voluntarily been chosen to have one slot per pole and per phase which is an unfavourable condition. Three techniques are studied. The first one consists in defining the influence of the winding. The second is a classical one. It is the skewing of the magnets or of the slots. The third is very original and consists in introducing a magnetic ring in the air-gap, this kind of ring, but not magnetic is generally recommended to maintain the magnets in case of high speed. This last technique is very interesting. It permits one to obtain a better torque quality with a small average value decrease. A finite elements method has been used to obtain these results