Optimum Split Ratio in Surface-Mounted Permanent Magnet Machines With Pieced Halbach Magnet Array

Abstract

The split ratio, defined as the outer radius ratio of the magnet to stator, has been investigated and optimized in surface-mounted permanent magnet (PM) machines having conventional/novel pieced Halbach magnet array. The air-gap magnetic field in PM machine with novel pieced Halbach magnet has been analytically obtained. The influences of split ratio and magnet arc length ratio on the torque density have been separately and analytically investigated for the machines with conventional pieced Halbach magnet array. In order to achieve the maximal torque density in the conventional pieced Halbach magnetized machines, the optimum split ratio and/or pole arc ratio have been obtained. In addition, the influences of one or both of the split ratio and magnetization angle on the torque density have been analytically investigated for the machines with novel pieced Halbach magnet array. In order to achieve the maximal torque density in the novel pieced Halbach magnetized machines, the optimum split ratio and/or magnetization angle have been determined. Finally, the linear analytical predictions have been compared with linear and nonlinear finite element analyses.