Air inlet/outlet arrangement for rotor cooling application of axial flux PM machines

Highlights: • Secondary cooling technique for axial flux permanent magnet machine is proposed. • A novel rotor cooling method to cools both machine's rotors. • Computational Fluid Dynamics (CFD) based study on the inlet and outlet of rotor cooling arrangement. • Implementation of rotor cooling on Yokeless and Segmented Armature (YASA) machines. - Abstract: The maximum power and torque of a Permanent Magnet (PM) machine may be limited by its magnets' temperature. An operational temperature above the magnets' threshold may cause demagnetization, particularly under abnormal conditions. For Axial Flux Permanent Magnet (AFPM) machines, the PMs are mounted on its rotor, therefore, one way to regulate the PM temperature is via an appropriate rotor cooling method. Selective designs of air inlet and outlet arrangement have been studied by the Computational Fluid Dynamics (CFD) analysis to assess and compare their flow and cooling capabilities. The new cooling designs were then implemented on a Yokeless and Segmented Armature (YASA) machine for flow experimental validation. Additionally, the cooling performance after the design implementation is analysed via CFD. This paper's proposed cooling method is expected to lead to lower magnet temperatures, thus increased reliability, output power and efficiency.