Optimisation of a brushless motor excited by multi-polar permanent magnet array

The paper investigates the optimal multi-polar magnetization of an interior magnet brushless machine rotor comprising a permanent magnet (PM) array made up from discrete anisotropic arc segments. The particular case where the magnet array is constructed from two arc segments per pole is considered where the magnets are alternatively magnetised normal and tangential to the rotor surface. The influence of the relative magnetic air-gap and magnet thickness on the optimal PM array arrangement is analysed and it is shown the optimal arrangement is largely independent of the air-gap width. Both analytical and numerical approaches to the optimisation problem are presented, the latter using a two-dimensional (2D) parametric finite element model (FEM). The calculation results are compared to baseline radial and sinusoidal Halbach magnetisations of the rotor.