Post-assembly impulse magnetization of brushless DC motors equipped with rare-earth magnets

The magnetization of fully dense and bonded forms of rare-earth magnets poses considerable problems due to their high magnetizing field requirements. The authors present a general methodology for the design of post-assembly magnetizing fixtures, albeit applied to radial-field topologies of brushless DC motor. The design details are established in three stages, the first of which estimates the peak MMF requirement, the second deduces the optimal disposition and number of conductors, and the third involves a detailed simulation of the complete impulse magnetization process. This latter step is based on the simultaneous time-stepped solution of the nonlinear differential equation governing the capacitor discharge magnetizer/fixture circuit and the transient diffusion equation governing the electromagnetic field with due account of heating of the fixture