Robust H∞ control for miniature unmanned aerial vehicles at hover by the finite frequency strategy

This study presents H-infinity control synthesis of a miniature unmanned aerial vehicle to improve its hovering capability in the presence of wind disturbances. By time-scale techniques, the six-degree-freedom flight system can be decoupled into subsystems in different time-scales: one including slow-varying translational dynamics and Euler angles, and another composed of fast-varying angular velocities. To avoid contradictions between subsystems, control specifications for subsystems are classified, respectively, in disjoint frequency ranges. Robust H controllers, applied directly to the original flight system, are formulated by composing the sub-controllers. To achieve desired handling and flying qualities, wind characteristics are considered, and a novel flexible strategy is then developed to ensure an adequate response in all flight modes under different weather conditions. The effectiveness and merits of the proposed methods are illustrated with a simulation example.