Application of Polar Anisotropic NdFeB Ring-Type Permanent Magnet to Brushless DC Motor

A four-pole polar anisotropic sintered NdFeB permanent magnet (PM) with high surface magnetic flux density is developed using a dry pressing process with pulse magnetizing fields. The effects of powder-filling density, magnetic field intensity, distribution in the cavity, and premagnetization of the powder on the magnet performance are investigated. Through an application of the developed PM to a brushless DC motor, it is shown that the premagnetization of the powder is very effective for increasing the surface magnetic flux density. Experimental results with a brushless DC motor adopting the developed PM shows that the surface magnetic flux density is increased up to 0.63 T, and the back emf at 1000 rpm measured 2.7 V, which is 41% higher than the conventional segment type PM