Adrian Gambier Senior Scientist
Fraunhofer Institute for Wind Energy and Energy System Technology IWES Division Wind Turbine and System
Technology Am Seedeich 45 27570 Bremerhaven Germany adrian.gambier@iwes.fraunhofer.de www.iwes.fraunhofer.de
Recovery Phase Analysis of a Pumping Kite Wind Generator
Adrian Gambier
Fraunhofer Institute for Wind Energy and Energy System Techology IWES The pumping cycle of a kite wind generator distinguishes
two phases [2]: the generation phase, in which the tether is reeled out from a drum due to the aerodynamic forced acting on the kite and the recovery phase, where the tether is reeled in back onto the drum. During the first phase, the energy is extracted from the wind and con-verted to electric energy by a generator, and in the second one, energy is consumed because the generator is used as motor to pull the kite back in.
Because pumping kite power is still an emergent technol-ogy, only few experimental setups are operational and therefore, it is difficult to accurately verify the achiev-able energy extraction. Several theoretical approaches have been proposed to approximate the mean value of the power extraction of a kite in the generation phase [1,4,6,7]. These approaches have been compared in [8] but have still not been verified experimentally.
On the other hand, experimental observations show that the efficiency of the pumping kite systems is strongly pendent on the effectiveness of the recovery phase. A de-tuned or suboptimal recovery phase leads very fast to a negative net power output. However, only few studies ex-ist on this topic [3,5,7]. In the present work, the recov-ery phase of the pumping kite wind generator is studied. For the recovery phase, three different approaches can be identified, which are called here fly to zenith (F2Z), pitch and pull (P&P) and free and pull (F&P). In the cur-rent work, only the first two techniques, F2Z and P&P, are studied.
The analysis focusses on the calculation of the mean
power that is required to return the kite to the initial posi-tion of the pumping cycle. The analysis is approached as a minmax optimisation problem (minimum energy con-sumption, maximum reel speed). This information is then used to obtain the net power extraction of the whole pumping cycle. It is also expected that the results can be used to support the dimensioning of the electrical ma-chine in order to obtain an optimal pumping cycle with maximum net power extraction.
References:
[1] Argatov I., Rautakorpi P., Silvennoinen R.: Estimation of the me-chanical energy output of the kite wind generator. Journal of Re-newable Energy, Vol. 34, pp. 1525–1532 (2009)
[2] Canale M., Fagiano L., Ippolito M., Milanese M.: Control of teth-ered airfoils for a new class of wind energy generator. Proceedings of the 45th IEEE Conference on Decision and Control, pp. 4020–4026, San Diego, December 2006
[3] Goela J. S., Vijaykumar R., Zimmermann R. H.: Performance characteristics of a kite-powered pump. Journal of Energy Re-source Technology, Vol. 108, pp. 188–193 (1986)
[4] Houska B.: Robustness and stability optimization of open-loop controlled power generating kites. M.Sc. Thesis, Heidelberg Univer-sity (2007)
[5] Houska B., Diehl M.: Optimal control for power generating kites. Proceedings of the 9th European Control Conference, pp. 3560– 3567, Kos, Greece, (2007)
[6] Lloyd M. L.: Crosswind kite power. Journal of Energy, Vol. 4, pp. 106–111 (1980)
[7] Luchsinger R.: Pumping cycle kite power. In: Airborne Wind En-ergy. Springer (2013)
[8] Sanno K., Rao K. V. S.: Estimation of wind power extraction from kites flying at high altitudes. Proceedings of the 2014 1st Interna-tional Conference on Non-ConvenInterna-tional Energy (ICONCE), pp. 193– 197, Kalyani, India, 16–17 January 2014
