Winch Control of Tethered Kites

Mani Kakavand PhD Researcher Semnan University School of Mechanics

Across Sookan Park Damghan Rd. Semnan, 19111-35131 Iran manikakavand@gmail.com english.semnan.ac.ir

Semnan University

Winch Control of Tethered Kites

Mani Kakavand Semnan University Winch control has an important role in both efficiency

and safety of AWE systems with tethered wings. In this research, a force control scheme is presented that guar-antees the convergence of reel-out speed to its optimal value, upon which maximum mechanical work is gener-ated. Besides, it can keep tether’s force within certain lim-its. The lower bound is imposed to make sure the wing stays aloft and controllable, and the upper bound pre-vents the system from force overload. Reel-out speed can take the optimal value only within those boundaries. The controller’s ability to prevent the force from violating the lower and upper bounds can have an impact on the ca-pacity factor of the system; enabling it to operate in tur-bulent wind environment.

Having an asynchronous generator as winch, the con-troller commands the synchronous speed to the gener-ator that causes it to rotate at the optimal speed. The winch controller’s performance is assessed in a simula-tion environment, in which the wing is represented as a point-mass and the winch is modeled as presented refer-ence [1]. The wing flies along a figure-of-eight path. Since tether’s dynamics is important in evaluating winch’s per-formance in simulation environment, a dynamic model of cable with varying length is used. This model consists of elastic rod elements and takes into account the effect of mass transfer. The quasi-steady model introduced in reference [2] is the basis for generating the optimal syn-chronous speed.                                                        

Simulation results of a tethered wing with area of 9 m2_{, completing} each figure-of-eight in 24 seconds on average, and a 20 kW winch. The initial and final tether length are 600 and 860 m, respectively. (a) - Tether’s force remains 2 to 3 kN (the cyan strip) as the wind speed (measured at kites altitude) changes randomly. The limits are selected for illustration purposes only. Wind speed derivation takes its maximal value of 1.8 m/s2_{at 34 s.}

(b) - Reel-out speed takes its optimal value while tether’s force is within 2 to 3 kN. The small gap between the optimal value and reel-out speed is due to errors in parameter estimation.

References:

[1] Fechner, Uwe, et al. "Dynamic Model of a Pumping Kite Power System." Renewable Energy 83 (2015): 705-716

[2] Schmehl R., Noom M., van der Vlugt R.: Traction Power Genera-tion with Tethered Wings. In: Airborne Wind Energy. Springer (2013)