Design of a minimum weight dual active bridge converter for an Airborne Wind Turbine system

The design procedure for a bidirectional DAB dc-dc converter, which provides a high dc voltage of 8kV to the tether of a 100 kW Airborne Wind Turbine (AWT) system, is presented. The maximum allowed weight of the dc-dc converter is 25 kg and, thus, the main challenge is the realization of a light-weight DAB converter. The investigated dc-dc converter is split up into 16 single DAB modules with a rated power of 6.25 kW and a dc port voltage of 2kV. Thus, a weight of less than 25 kg/16 = 1.56 kg needs to be achieved for a single DAB module. The design method used to obtain the minimum weight DAB converter, based on the evaluation of a power-to-weight ratio versus efficiency Pareto Front (γ-η-Pareto Front) is presented in this paper. For this purpose the transient voltages and currents of the employed SiC JFETs during switching are discussed in detail, since the respective measurement results allow for a prediction of the switching losses. Moreover, the calculated transformer is realized and experimental results are used to verify the weight, the losses, and the cooling system performance of the transformer. For a single DAB module a weight of m = 1.43 kg, an efficiency of η = 97%, and a power-to-weight ratio of γ = 4.4kW/kg results.