Applied bifurcation methods for efficient airborne wind energy generation

Airborne wind energy systems (AWES) are an emerging technology that harvests wind power at higher altitudes than conventional wind turbines do. This is done by tethering an unmanned aerial vehicle (UAV) to a ground station. The high wind pulls the UAV out, which drives the ground generator and generates electricity. AWES can benefit the UK's energy sector in a number of ways, including reduced carbon footprint, offshore and onshore use, and operation from remote areas. Therefore, investing into AWES can help create an alternative source of affordable renewable energy, which is of topical relevance to the UK. This will not only help address the ongoing energy price crisis, but also contribute to UK's effort toward net-zero by 2050.

To generate the most power, AWES must fly in intricate patterns whilst subjected to strong aerodynamic forces (relative to their sizes) pulling against the tether. This arrangement creates a complex system with delicate handling characteristics: a slight miscalculation could send the drone tumbling into the ground. Therefore, the flying characteristics and control system dictate AWES safety and efficiency. This means that improvements in these two areas will be essential for making AWES commercially viable. In many cases, however, a trade-off has to be made: either a complex controller is to be designed on a simplified AWES model, or that a simple controller is to be tested on a high-fidelity model. In the AWES community, there is currently no method to rapidly verify a complex model/controller pair. This has prevented many AWES prototypes from achieving full capacity in operation, leading to early termination of the project and hindering commercialisation.

This fellowship seeks to address this challenge through the use of bifurcation and continuation methods. This is a numerical technique that has been successfully used in aircraft dynamics studies to predict many dangerous behaviours including wing rock, spin, and deep stall. Bifurcation and continuation methods provide a 'map' of where these behaviours can be expected, and under what condition. This knowledge will provide the capability for rapid prototyping and testing of high-fidelity AWES models with complex control systems, thereby enabling new designs that maximises energy generation while minimising development time. By replacing existing computationally-expensive techniques with bifurcation methods, AWES can achieve significant cost savings and improved performance that will ultimately bring this technology closer to commercialisation.

This project is supported by the EPSRC (grant number EP/Y014545/1), along with in-kind contributions from the University Carlos III of Madrid (Spain) and Kitemill (Norway).