Applied Tracking Control for Kite Power Systems Claudius Jehle * and Roland Schmehl † Delft University of Technology, Delft, The Netherlands. This article presents a tracking controller applicable to tethered flying objects, such as kites for power generation or towing purposes. A kinematic framework is introduced employing definitions and terminology known from aerospace engineering, and is used for both modeling and control design. Derived from measurement data, an empirical steering law correlation is presented, establishing a highly reliable connection between the steering inputs and the kite’s yaw rate and thus providing an essential part of the cascaded controller. The target trajectory is projected onto a unit sphere centered at the tether anchor point, and based on geometrical considerations on curved surfaces, a tracking control law is derived, with the objective to reduce the kite’s spacial displacement smoothly to zero. The cascaded controller is implemented and integrated into the soft- and hardware framework of a 20kW technology demonstrator. Due to the lack of a suitable simulation environment its performance is assessed in various field tests employing a 25m 2 kite and the results are presented and discussed. The results on the one hand confirm that autonomous operation of the traction kite in periodic pumping cycles is feasible, yet on the other that the control performance is severely affected by time delays and actuator constraints. Nomenclature Latin symbols B Kite-fixed reference frame c 1 ,c 2 Fitting coefficients of empirical yawing correlation C Point on trajectory closest to kite position e χ Misalignment between commanded and actual flight direction; error of inner loop K P Proportional gain of inner loop controller K Position of kite projected onto unit sphere O Tether anchor point and origin of wind reference frame W p Roll velocity of kite (cf. ω) q Pitch velocity of kite (cf. ω) q K Kite’s azimuth and elevation angle tuple (ξ,η) r Yaw velocity of kite (cf. ω) S Local reference frame of tangent plane T S 2 S 2 Unit sphere around tether anchor point O t C Normalized course vector tangential to the target trajectory at closest point C t K Representation of course vector t C at the kite position K A T B Transformation matrix from reference frame B → A T K S 2 Tangent plane to S 2 at point K ∈ S 2 u S ,u P Relative steering/power setting v app Apparent wind velocity W Wind reference frame Greek symbols β Drift angle between of kite δ Geodesic distance between two points on unit sphere S 2 * Former graduate student at ASSET Institute, Delft; Now Lenaustr. 21, Berlin, Germany, c.jehle@jehle-rv.de. † Associate Professor, ASSET Institute, Kluyverweg 1, 2629HS, Delft, The Netherlands, r.schmehl@tudelft.nl. 1 of 22 American Institute of Aeronautics and Astronautics