Title: KiteGen Project: Control as key technology for a quantum leap in wind energy generators
Author: Prof. Mario Milanese
Abstract: The talk presents some results on the control of tethered airfoils (kites) aimed to devise a new class of wind generators, indicated as KiteGen, able to overcome the main limitations of the present aeolian technology based on wind mills.
Two configurations are considered for energy generation, indicated as push-pull and carousel, respectively. The flight of the kite is controlled by means of a kite steering unit which pull the two lines which hold it by means of elctric drives able to act as motor as well as generators.
In the push-pull configuration, the kite steering unit is fixed with respect to the ground. Energy is generated by continuously repeating a cycle composed of two phases: the traction and the recovery ones. In the traction phase the control is designed such that the kite pulls the lines, so that a certain amount of energy is generated. When the maximal length of the lines is reached, the control enters into the recovery phase, where the kite is driven to a region where the lines can be pulled by the motors until the minimal length is reached, spending a small fraction of the energy generated in the traction phase and a new traction phase is undertaken. NMPC controllers are designed to maximize the energy generated in the traction phase and to minimize the energy spent in the recovery one.
In the carousel configuration, energy is generated by a cycle composed of two phases, indicated as the traction and the drag one. The kite control unit is placed on the arm of a vertical axis rotor, which is connected to an electric drive able to act as generator when the kite lines pull the rotor and as motor in dragging the kite against the wind flow. In each phase, control is obtained by NMPC designs. In the traction phase the control is designed such that the kite pulls the rotor arm, maximizing the amount of generated energy. When the kite is not able to generate energy any more, because flying against the wind, the control enters the drag phase and the kite is driven to a region where the energy spent to drag the rotor is a small fraction of the energy generated in the traction phase, until a new traction phase is undertaken. Simulation results are presented of the achievable power generation, using a model of the kite aerodynamic taken from M. Diehl.
Preliminary experimental results obtained from a sall scale prototype of the push-pull configuration are also presented.