Longitudinal Flight Control for a Novel Airborne Wind Energy System: Robust MIMO Control Design Techniques

This paper deals with the longitudinal flight control for a novel Airborne Wind Energy (AWE) system: the EAGLE System. It is a tethered lighter-than-air flyer wind turbine composed of a blimp, several aerodynamic airfoils (wings) with specific aerodynamic control surfaces (ailerons, elevator, rudder), a counter-rotating aerodynamic rotor for the wind turbine (four identical sections, symmetrically arranged, with three blades each), an electrical synchronous generator attached to the counter-rotating rotors, and a tether to secure the airship and to transmit the generated power. Additional information can be found in US Patent, Provisional Application No. 61/387,432 developed by the authors. The designed system proposed here supports a 2.5 kW generator and flies at approximately 100 meters. The mathematical model developed for the AWE system incorporates a hybrid blimp-airfoil design, modeled using a hybrid Cartesian-polar coordinate system to capture the dynamics of both the airship and the tether, and includes the effect of the counter-rotating aerodynamic rotor of the wind turbine, as well as the aerodynamic control surfaces. This paper presents the design of a robust Multi-Input Multi-Output (MIMO) controller for the 3×3 longitudinal flight dynamics of the tethered airborne wind energy system. The control system is designed by applying sequential MIMO robust Quantitative Feedback Theory (QFT) techniques.