Structured μ-synthesis of robust attitude control laws for quad-tilt-wing unmanned aerial vehicle

The problem of designing the longitudinal flight controller for a quad-tilt-wing unmanned aerial vehicle to achieve robust performance under constraints on the controller structure is considered. An approach based on μ-synthesis is proposed, in which a nonparametric inverse multiplicative uncertainty description is employed to account for the uncertainties of the aircraft attitude dynamics at each operating condition, with specific reference to variations in the number of unstable modes. The resulting μ-synthesis problem with a frequency-dependent weighting function, the structure of which is defined a priori, is reformulated as a structured H∞ problem and solved by means of available MATLAB software. Simulation results are presented in order to show the effectiveness of the approach.