Publications, papers published in April 1999/communications publiées en avril 1999

Bibliography

1

J.-F. Magni.
Multimodel eigenstructure assignment in flight-control design.
Aerospace Science and Technology (special issue "Flifht control law design"), 3(3):141-151, April 1999.
This paper presents a control design approach based on eigenstructure assignment by dynamic feedback. The proposed method permits the designer to handle simultaneously robustness against real parameter variations (from a multimodel point of view) and the use of structured gain including, as a special case, scheduled gains. Furthermore, given a feedback gain, it is possible to re-design it by eigenstructure assignment by re-assigning its leading eigenstructure. This technique has two advantages. First, it can be viewed as an efficient controller order reduction, second, the design methodology can be initialized, for example, by H_infinity or mu-synthesis which makes it possible to combine the advantages of techniques of different nature.The proposed method alternates multimodel design and mu-analysis but apart from these natural iterations, only algebraic computation is involved.

2

C. Döll, G. Ferreres, and J.-F. Magni.
-tools for flight control robustness assessment.
Aerospace Science and Technology, 3(3):177-189, April 1999.
The aim of this paper is to emphasize the usefulness of the framework for the analysis of the robustness properties of flight control systems. Model uncertainties may correspond, either to parametric uncertainties (e.g. in the aerodynamic model or in the value of the trim point) or to neglected high frequency dynamics (e.g.in the actuators or sensors). We especially show that several classical problems (computation of a phase or delay margin, non-linear analysis of a PIO effect, computation of a frequency domain overshoot)can be extended to an uncertain aircraft model. A flexible model of the aircraft can be moreover taken into account.
Le but de cet article est de mettre en valeur la -analyse pour caractériser la robustesse et les performances des systËmes de pilotage. Les incertitudes de modèle correspondent, soit aux incertitudes paramètriques (induites par le modèle aérodynamique ou le point d'équilibre), soit aux dynamiques négligées aux hautes fréquences dues aux actionneurs ou capteurs). Plus précisément, on montre que plusieurs problèmes classiques (tels que le calcul d'une marge de phase ou de retard, l'analyse non-linéaire du phénomène de pompage piloté, le calcul du dépassement dans le domaine fréquentiel) peuvent être étendus à un modèle d'avion incertain. En outre, un modèle flexible d'avion peut aussi pris en compte.

3

J.-M. Biannic and P. Apkarian.
Missile autopilot design via a modified LPV synthesis technique.
Aerospace science and Technology (special Issue : Flight Control Law Design), 3(3):153-160, April 1999.
Robust control via Linear Time-Invariant LTI Hinfini or mu techniques has been extensively studied in the past few years. In this area, the theory is now quite mature. However, its limitation to linear time-invariant systems often remains a weakness which may give rise to well-founded criticisms. This has enforced the need for an extension of standard Hinfini synthesis techniques to the class of Linear Parameter-Varying (LPV) plants. Many references are now available in the literature on this topic and several variants have been proposed to improve the original approach. The major improvement consists in incorporating knowledge on the rate of variation of the parameters. This constraint is of high practical interest and is naturally expected to relax significantly the conservatism of the original approach. Unfortunately, it often leads to computationnaly expensive algorithms. In this paper, we propose a very simple approach which consists in applying the original method to a modified LPV system. Thus, the attractive numerical properties of the initial algorithm are preserved. In return, the proposed method suffers from the lack of rigorous theoretical justification. This remains yet a minor drawback if we consider the practical interest of the method which is demonstrated on a realistic example, namely an autopilot design.