Flat singularities of chained systems, illustrated with an aircraft model

TL;DR

This paper studies flat differential control systems, introduces a new saddle Jacobi bound concept, and applies it to an aircraft model to identify flat outputs and analyze singularities, demonstrating robustness through simulations.

Contribution

It introduces the saddle Jacobi bound for flat systems and applies it to aircraft modeling, identifying flat outputs and analyzing singularities without differentiating initial equations.

Findings

Aircraft model is flat except in stalling conditions.

New flat outputs are derived for the aircraft model.

Feedback control using flat outputs is robust to perturbations.

Abstract

We consider flat differential control systems for which there exist flat outputs that are part of the state variables and study them using Jacobi bound. We introduce a notion of saddle Jacobi bound for an ordinary differential system of $n$ equations in $n+m$ variables. Systems with saddle Jacobi number equal to $0$ generalize various notions of chained and diagonal systems and form the widest class of systems admitting subsets of state variables as flat output, for which flat parametrization may be computed without differentiating the initial equations. We investigate apparent and intrinsic flat singularities of such systems. As an illustration, we consider the case of a simplified aircraft model, providing new flat outputs and showing that it is flat at all points except possibly in stalling conditions. Finally, we present numerical simulations showing that a feedback using those flat outputs is robust to perturbations and can also compensate model errors, when using a more realistic aerodynamic model.