Effect of Wind Variations on Tether Load Transfer from Kite to Winch

Solenn Le Pense Simulation & Controls Engineer

KPS

103 West Regent Street Glasgow

G2 2DQ United Kingdom

solenn.lepense@kps.energy www.kps.energy

Effect of Wind Variations on Tether Load Transfer from Kite to Winch

KPS Ltd

Key to the development of optimized Airborne Wind En-ergy systems are the use of simulators, providing a devel-opment and test platform for subsystems design and con-trol systems. Most of the existing simulators idealize the tether as a rigid or elastic link in between kite and winch [1], as a chain of rigid rods [2], or as a chain of elastic ele-ments neglecting dynamic effects. Studies that do use a more complex tether model tend to focus on control sys-tems and do not look in details at subsyssys-tems-induced loads and the performance of the full system [3-4]. Some energy is dissipated along the tether due to damp-ing and drag effects. Given the length of the tether and the temporal and spatial wind variations, it is expected that the tether tension signal originating at the kite will be modified while travelling down the tether, and the line tension signal seen at the winch will be different. This can have significant implications on the loads that have to be considered to design the system components, in order to optimize power production, limit excessive loads on com-ponents, and consider components lifecycle.

The KPS simulator consists of a modular Simulink envi-ronment that can be adapted to look at specific prob-lems. In this study, we use a model comprising a dynamic winch connected to a lumped mass tether model placed in a 3D turbulent wind field. The tether model is made of point masses connected by spring-damper elements,

includes drag forces on point masses, and models reel-in and reel-out by adding and substracting mass points. The kite trajectory is fully specified as a history of kite coordi-nates.

This study will give some insight into the effect of tether dynamics and energy dissipation on winch loading for specified kite trajectories, which will help assessing the importance of considering those effects. This will ulti-mately feed into tether and winch design requirements in a view to optimize Airborne Wind Energy systems per-formance and durability.

References:

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83(May), 705ś716 (2015)