Control of tethered airfoils for a new class of wind energy generator

The paper investigates the control of tethered airfoils in order to devise a new class of wind generators able to overcome the main limitations of the present aeolian technology based on wind mills. A model taken from the literature is used to simulate the dynamic of a kite which can be controlled by suitably pulling two lines. Energy is generated by a cycle composed of two phases, indicated as the traction and the recovery one. The control unit has two electric drives which act as motors in pulling the lines for controlling the flight or for recovering the kite and as generators if the kite pulls the lines. In each phase, control is obtained by "fast" implementations of suitable NMPC designs. In the traction phase the control is designed such that the kite pulls the lines, maximizing the amount of generated energy. When the maximal length of the lines is reached, the control enters the recovery phase and 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. Simulation results are presented, related to a recently built small scale prototype