Hardware in the Loop Testing for Autonomous Airborne Wind Energy Systems

Damian Aregger University of Applied Sciences Northwestern Switzerland FHNW Institute of Aerosol and Sensor Technology

Klosterzelgstrasse 2 5210 Windisch

Switzerland damian.aregger@fhnw.ch

www.fhnw.ch

Hardware in the Loop Testing for Autonomous Airborne Wind Energy Systems

Roy S. Smith2_{, Rolf H. Luchsinger}3,4 1_{Institute of Aerosol and Sensor Technology, FHNW}

2_{Automatic Control Laboratory, ETH Zurich} 3_{Center for Synergetic Structures, Empa}

4_{TwingTec AG}

In the emerging field of airborne wind energy a crucial part of the system development is the validation of an-alytical results and simulation data. Often there exists a gap between theory and real life test data because of un-steady wind conditions or hardware constraints for exam-ple. At present, classic design and testing strategies for airborne wind energy system development include ana-lytical calculations, modelling, simulation, wind tunnel testing, tow testing or field testing. While the simula-tor approach allows for full system observability, it often lacks exact modelling of system constraints and dynam-ics. Typical problems encountered during field testing can be wind availability or limited repeatability of similar test conditions. A possible solution for those problems is the integration of real hardware subsystems into simula-tion, called hardware in the loop (HIL) testing. In a HIL simulation one splits the system into two parts, one sub-part is referred to as the system under test (SUT). This sub-part can be a controller or an actuator that exists in reality. The other subpart is referred to as the plant simulation. This part is a mathematical model of a dynamic system that interact with the SUT.

A ground generation based airborne wind energy sys-tem consists in general of three main components: The ground station, the tether and the kite. For the particular

experimental HIL setup a testing method including two ground stations was developed. The two ground stations are directly connected by means of two tethers. There-fore a physical force interaction between the two ground stations is possible. One ground station acts as the SUT whereas the other ground station acts as a kite emulator. Steering inputs to the ground station (SUT) result in cer-tain tether displacements. These tether movements are fed to the simulator, which in turns calculates the result-ing tether forces at every simulation time step. The sim-ulator uses the vortex lattice method combined with a tether dynamics model to calculate the virtual line force values [1]. These calculated forces are then translated into physical tether pulling forces by the second ground station. The physical line forces translate into line move-ments on the ground station (SUT) which closes the hard-ware loop.

The setup finally results in a weather independent labo-ratory test environment for extensive system testing. It is used from simple ground station parameter tuning to autonomous pumping cycle flight path strategy improve-ment.

References:

[1] Gohl F., Luchsinger R. H.: Simulation Based Wing Design for Kite Power. In: Airborne Wind Energy. Springer (2013)

WIND ENERGY 2.0