Torque and Power Capabilities of Coreless Axial Flux Machines with Surface PMs and Halbach Array Rotors

This paper investigates employing a Halbach PM rotor array to increase torque and power density within coreless axial flux permanent magnet (AFPM) machines. Analytical and 2/3-dimensional finite element analysis (FEA) methods are developed to study torque and power capabilities within an example double-rotor, single-stator coreless AFPM machine with a PCB stator. Compared to a surface PM topology of the same mass and volume, employing a Halbach array increases torque density by as much as 30% through increased airgap flux density amplitude. Multiple parametric studies are performed to explore methods of increasing torque and power density while employing Halbach arrays combined with enhanced cooling methods and coil transposition to minimize associated losses. A design procedure is also developed that relies on the advantages of coreless AFPM machines controlled by ultra-high-frequency SiC-based drive systems to maximize potential torque gain.