Matthias Gramlich

University of Freiburg

Thursday, February 18, 2021, 12:00

online

Abstract

In this thesis, high-altitude wind turbines have been investigated with respect to their electrical harvestable power, and the question has been pursued whether and to what extent it is possible to integrate a generator model into the awebox. This should help to advance this new type of renewable energy faster, in order to finally displace the fossil energy sources from the market due to the cheap green electricity
generated by AWEs and thus to stop the climate catastrophe. In an airborne wind energy systems, kites flying periodic trajectories transmit force down a tether to a winch, where the mechanical rotational energy can be harvested. Thus, it is possible to harvest mechanical rotational energy. This has been converted into electrical energy by this bachelor thesis. Specifically, the existing optimal control problem from the simulation program awebox - which previously only optimized the mechanical power - can now also optimize the electrical power. For this purpose a permanent magnet synchronous machine has been implemented. The model of the permanent magnet synchronous machine has been transformed into a rotating coordinate system with the dq-transformation, in order to simplify the model. Furthermore, the mechanical ordinary differential equations have been implemented outside the equation of motion of the Lagrange formalism and this system has been additionally extended by a gear. The moment of inertia of the gearbox depends, among other things, on the transmission ratio. The built-up system has been examined in detail using a single kite as an example to work out physical and logical errors. In order to be able to make further statements, especially with regard to differences between mechanically and electrically optimized systems, these have been examined with regard to their angular velocity and the moment caused by the tether. The results of this is that the ranges of values of these variables differ in part greatly. A comparison of the performance under different wind conditions has also been carried out. These show that the mechanical performance of the electrically optimized systems approaches the mechanical performance of the mechanically optimized systems. The electrical performance, however, has a low efficiency due to the high currents and thus also the high power loss.