Weight optimization of a machine for airborne wind turbines

This paper details the weight optimization of the electrical machine required for an Airborne Wind Turbine (AWT) system. Presented investigations include the analysis of the power-to-weight ratio versus efficiency limits, γ-η Pareto fronts, of radial and axial flux machine topologies, by making use of analytical models, describing the electromagnetic and thermal behaviour. A direct search method is employed rather than a cost function minimization algorithm, as the analytical models allow the evaluation of the whole design space in a computationally efficient manner. The results reveal that the best performance in this case is achieved with a radial flux machine with an internal rotor where the magnets are arranged in a Halbach configuration. Including the weight of electromagnetically inactive parts, such as bearings, shaft and housing, a power-to-weight ratio of γ ≈ 6.2 kW/kg (2.8 kW/lb), at an efficiency of η ≈ 96 %, and a rated speed of 3200 r/min is achieved.