Comparative Analysis of Different Halbach Array Structures in the Design Optimization of an In-wheel Permanent Magnet Machine for Land Speed Racing

In this paper, three Halbach array structures are compared for the design of an in-wheel permanent magnet machine for land speed racing. A finite-element model (FEM) based multi-objective optimization is used to explore the potential of all three structures to achieve high torque-weight ratio, low torque ripple, and low losses. The comparison shows that the 3-segment structure has similar performances with the 4-segment structure and lower torque ripple. To better understand the optimization results, the winding function and mutual harmonics exclusion theory were used to analyze their performances. It was found that, although the magnetic potential of a 4-segment Halbach design could be more sinusoidal, the 3-segment design provides less torque ripple for a 24-slot 20-pole fractional slot concentrated winding machine due to mutual harmonics exclusion. The FEM optimization improved the flux distribution and torque performance of a 3-segment Halbach array by adjusting the magnet arc angle and finding an optimum magnetization direction.