Flight Control Laws: Recent Advances in the Evaluation of their Robustness Properties

This paper reviews a set of robustness analysis tools developed by the authors during the last decade to evaluate the robustness properties of high-dimensional closed-loop plants subject to numerous time-invariant uncertainties. These tools are used to compute both upper and lower bounds on the robust stability margin, the worst-case H∞ performance level, as well as the traditional gain, phase, modulus and time-delay margins. The key idea is to solve the problem on just a coarse frequency grid and to perform a fast validation on the whole frequency range, which results in guaranteed but conservative bounds on the aforementioned quantities. Some heuristics are then applied to determine a set of worst-case parametric configurations  leading to over-optimistic bounds. A branch and bound scheme is finally implemented, so as to tighten these bounds with the desired accuracy, while still guaranteeing a reasonable computational complexity. The proposed algorithms are successfully assessed on a challenging real-world application: a flight control law validation problem.