Self-air-cooling Design and Optimization for an Outer-rotor PMSG in External Still Air

For hybrid-electric unmanned aerial vehicles (UAVs), the stable power supply from the onboard permanent magnet synchronous generator (PMSG) is critical. Overheating in the confined compartment can directly lead to power interruption and system failure. Therefore, proactively improving the thermal management is not only a key technical prerequisite for ensuring flight reliability and mission success, but also enhances the machine's efficiency and the overall power density of the system. Targeting the stringent spatial constraints in UAV applications, novel self-air-cooling heat dissipation topologies are investigated and highlighted on the rotor sidewall for compact outer-rotor generators. A systematic optimization framework, centered on a multi-objective genetic algorithm, is developed to Pareto-optimize the fin geometries, balancing thermal performance against aerodynamic penalty. The proposed topologies are innovatively deployed on the rotor sidewall, uniquely combining the structural space of an outer-rotor machine with self-air-cooling to generate directed airflow of varying patterns that directly enhance the cooling efficiency of the stator. The parameters of the designed self-air-cooled heat dissipation topologies are optimized via a multi-objective genetic algorithm. A temperature rise test under windless conditions shows that the proposed self-air-cooled structure reduces the stator temperature of the generator by 37.1 °C at 5000 r/min, confirming the effectiveness and engineering feasibility for practical applications..