Design of Polar Anisotropic Sintered NdFeB Ring-Type Permanent-Magnet for Brushless DC Motor

A Four polar anisotropic sintered NdFeB PM with high surface flux density was developed using dry pressing process with pulse magnetizing fields. In this paper, effects of filling density, magnetic field intensity, distribution of the cavity, and of the way of pre-magnetized powder for the high performance polar anisotropic sintered NdFeB PMs were studied. It can be seen that magnets produced by pre-magnetized powder process shows magnetic surface flux's maximum value that is 6,300 G due to pre-magnetized effects and that the back e.m.f. of Brushless motor, is 5.4 Vp/p per 1000 rpm, an increase about 35% above the conventional segment magnet.