Design Considerations and Control Implementation for a Two-Tethered Kite-Based Airborne Wind Energy System

Emre Dikmen Control Engineer Kontra Engineering

Resitpasa Mah. Istanbul Technical University

KM Evl. No:2 A-2/1 Istanbul

Turkey emre@kontrapower.com

www.kontrapower.com

Design Considerations and Control Implementation for a Two-Tethered

Kite-Based Airborne Wind Energy System

Emre Dikmen1_{, Alper Dumanli}1,2_{, Caner Erdogan}1,2_{, Patrick Dreher}3 1_{Kontra Engineering}

2_{Istanbul Technical University} 3_{University of Applied Sciences Esslingen}

In order to build a kite-based wind energy prototype, which employs the phenomena of traction power conver-sion in a pumping cycle, we have applied the system lay-out and design for a small-scale prototype concept devel-oped in [1]. Several modifications at the mentioned sys-tem design have been made to allow us to test the con-cept according to energy generation via winding the teth-ers on a winch and to build it in a more cost efficient way via narrowing down the operating conditions and using low cost electronics. The assumed operation conditions are a maximum kite area of 6 m2 and maximum wind ve-locity of 6.5 m/s in an altitude range of about 20 m – 40 m. The aim of our work is to provide our design consider-ations for several disciplines (mechanics, electronics and controls) while building the prototype and to implement several control schemes in the future.

Instead of using a three-tethered leading edge inflatable kite, a two-tethered ram-air inflated kite is being used. In case of using a ram-air inflated kite, both tethers of the kite are responsible for load transmission and steer-ing of the kite. The used steersteer-ing mechanism, in which the first and second tethers are guided by pulleys, is al-ready known from the literature [1]. The actuation of the steering is carried out via a closed loop synchronous mo-tor and linear motion system combination. In addition to the already-known steering mechanism, both tethers

are winded on a winch for converting the components of traction power (which are linear velocity and force) into components of rotational power (which are torque and angular velocity). While one side of the winch transfers rotational motion to an alternator in only one direction, the other side is driven by an electric motor in only the opposite direction.

An encoder is mounted on the generator shaft and its measurement data will be used to measure the reeled out tether length in order to determine the kites position in combination with IMU sensor data. The kite is connected with an on-board IMU which provides measurement data for 3D accelerations and 3 orthogonal angular velocities. The communication is conducted by two wireless devices using “Zig- Bee” protocol. For the beginning, the control strategy developed in [1] in which a closed loop propor-tional controller which controls the velocity angle of the kite can be implemented on the built mechanism with the additions of reel-in and reel-out phase control strategy and experimental data [2].

References:

[1] Fagiano L., Zgraggen A. U., Morari M., Khammash M.: Automatic Crosswind Flight of Thetered Wings for Airborne Wind Energy: Mod-eling, Control Design and Experimental Results. IEEE Transactions on Control Systems Technology, Vol. 22, No. 4, pp. 1433–1447 (2014) [2] https://www.youtube.com/watch?v=L_9iKIZ2FSE. Accessed 1 June 2015