This paper details the design, the implementation, and the experimental verification of a minimum weight input series output parallel (ISOP) structured Dual Active Bridge (DAB) converter for an Airborne Wind Turbine (AWT) system. The main power components of the DAB converter, in particular the bridge circuits, the actively cooled high frequency (HF) transformer and inductor, and the cooling system, which largely contribute to the total system weight, are designed and realized based on multi-objective considerations, i.e. with respect to weight and efficiency. Furthermore, the design includes all necessary considerations to realize a fully functional prototype, i.e. it also considers the auxiliary supply, the control for stable operation of the system, which also comprises an input filter, over the specified operating range, and the startup and shut down procedure. These considerations show the complex interactions of the various system parts and reveal that a comprehensive conceptualization is necessary to arrive at a reliable minimum weight design. Experimental results validate the proposed design procedure for a realized lightweight DAB hardware prototype with a rated power of 6.25 kW. The prototype weighs 1.46 kg, i.e. features a power to weight ratio of 4.28 kW/kg (1.94 kW/lb), and achieves a maximum full-load efficiency of 97.5 %.

This Paper details the weight optimization of forced convection cooling systems, composed of fan and extruded fin heat sink, required for a dc-dc converter of an airborne wind turbine (AWT) system. The presented investigations detail the optimization of the heat sink's fins with respect to minimum weight and the selection of a suitable fan for minimum overall system weight. A new analytical cooling system model is introduced, the calculated results are compared to the results determined with a preexisting analytical model and Finite Element Model (FEM) simulations. The comparison to experimental results demonstrate the accuracy improvements achieved with the proposed methods. Compared to commercially available products a weight reduction of 52 % is achieved with the proposed optimization procedure for the required heat sink system with Rth,S-a = 1 K/W.

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