Design and Analysis of a Variable Arc Permanent Magnet Array for Spherical Motor

This paper presents the design and analysis of a variable arc magnet array comprising two segments per pole for permanent magnet (PM) spherical motor. The harmonic model for radial air-gap flux density distribution is solved by magnetic scalar potential equation using spherical harmonic series and validated by finite-element method. After the influence of magnet array parameters on the fundamental harmonics amplitude and higher harmonic content of the air-gap flux density is analyzed, the optimization of four-pole magnet array is performed in which the higher harmonics of the radial air-gap flux density are minimized. The final design is compared with iron-cored classical array and air-cored equal arc Halbach array, and the result shows that for a given relative volume of magnetic material the proposed variable arc magnet array produces lower higher harmonic content than the other two arrays.