On Sensor Fusion for Airborne Wind Energy Systems

A study on filtering aspects of airborne wind energy generators is presented. This class of renewable energy systems aim to convert the aerodynamic forces generated by tethered wings, flying in closed paths transverse to the wind flow, into electricity. The accurate reconstruction of the wing's position, velocity, and heading is of fundamental importance for the automatic control of these kinds of systems. The difficulty of the estimation problem arises from the nonlinear dynamics, wide speed range, large accelerations, and fast changes of direction that the wing experiences during operation. It is shown that the overall nonlinear system has a specific structure allowing its partitioning into subsystems, hence leading to a series of simpler filtering problems. Different sensor setups are then considered, and the related sensor fusion algorithms are presented. The results of experimental tests carried out with a small-scale prototype and wings of different sizes are discussed. The designed filtering algorithms rely purely on kinematic laws, hence they are independent of features such as wing area, aerodynamic efficiency, mass, and so on. Therefore, the presented results are representative for systems with larger size and different wing design, different number of tethers and/or rigid wings also.