Effect of Rotor Geometry on Rotor Air Cooling of a Ventilated Axial-Flux Permanent Magnet Machine

High heat losses are generated in the rotors of Axial-flux Permanent Magnet (AFPM) machines due to their high power density. Therefore, they require intensive cooling to maintain safe continuous and peak power operation. For ventilated-type machines, air cooling is the predominant cooling method that keeps the rotor magnets temperature below critical limits. Integration of air-cooling features such as protruding magnets, rotor vents, and rotor integrated fan blades into machines has been widely investigated. These features improve the overall cooling of the machine and eliminate the reliance on external cooling devices. This study investigates different rotor geometries, including either a single or a combination of the mentioned features, and assesses their thermal performance and cooling efficiency considering associated windage losses. From the simulated cases, it was found that rotors with geometrical features that allow though-flow ventilation to directly cool the magnets are more efficient compared to others that rely on indirect cooling.