Characterization of an Axial Flux Machine With an Additively Manufactured Stator

Abstract

Axial flux machines (AFM) are promising alternatives to radial flux machines for applications that benefit from high torque density and a large diameter to axial length ratio, such as in-wheel traction motors. However, the 3D flux paths in AFM present unique challenges to manufacturing laminated stator cores. This paper positions metal additive manufacturing (AM) technology as a potential solution to manufacture unconventional electric machine components such as AFM stators by investigating novel lamination emulating geometric structures and material silicon composition as design handles. In this paper, techniques to additively manufacture soft magnetic components for rotating electric machines are reviewed, and the Hilbert pattern is identified as a promising candidate to reduce eddy-current losses in these components. To further reduce the eddy current losses, this paper investigates the use of 6.5% silicon steel, which has higher resistivity compared to conventional steel laminations. The results in this paper show that the Hilbert structure is effective in reducing the eddy current losses by 50% compared to a solid structure with 3% silicon steel, and using 6.5% silicon steel further reduces the eddy current losses by 24%. Finally, a candidate AFM stator is designed with the Hilbert pattern and fabricated additively using 6.5% silicon steel. This machine is characterized and experimentally compared with an identical axial flux machine that uses a laminated stator. The results demonstrate the potential of metal AM technology to fabricate electric machine components with eddy current losses comparable to ultra-thin gauge laminations at frequencies up to 200Hz and conventional 29Ga laminations up to 480Hz.