Daniel Alazard

Exact observer-based structures for arbitrary compensators

In this paper, some new techniques for determining the observer-based or LQG form of any compensator with arbitrary order are discussed. The practical appeal of such techniques is that they allow for a simplified implementation and reduced memory storage of general controllers and offer additional flexibility for handling gain-scheduling and input saturation constraints as compensateor states become meaningful variables. The derived observers-based controllers are input-output equivalent to the original controller but with an explicit separated estimation/control structure. Such structures involve both static control and estimation gains with an extra Youla parameter that can be either static or dynamic. The proposed techniques are applicable both in continuous-and discrete-time, to full-order controllers, that is, controllers whose order controllers whose orders are greater or smaller, respectively. Necessary conditions to apply this general controller equivalence principle are derived. The interest and practicality of such techniques are then investigated with regards to the LQG implementation of Hinfinty and u controllers, classes of controllers that does not generally enjoy ease of implementation.

Robust H Design for Lateral Flight Control of Highly Flexible Aircraft

A lateral flight control design for a flexible aircraft is presented. It is based on a standard two-input two-output problem formalism and H2 synthesis. The proposed approach consists of two steps. The first step deals with the synthesis of a dynamic output feedback satisfying modal specifications on the rigid modes, stability requirements on the structure and performance robustness with respect to the various loading cases. The originality in the synthesis setup we propose lies in the fact that it combines eigenstructure assignment,H2 frequency domain synthesis and parametric robustness design. The second step uses a recent theoretical result to transform a given compensator into an linear quadratic gaussian (LQG) compensator involving a judiciously selected on-board model. The two degree of freedom compensator thus obtained allows time domain specifications in response to the pilot’s commands to be met satisfactorily.We provide a detailed discussion of the approach together with the aircraft models used and corresponding closed-loop analysis.

Launcher attitude control: discrete-time robust design and gain-scheduling

In this paper, a robust multi-objective design for the control of a launcher during atmospheric flight is investigated. This approach is based on the Cross Standard Form formulation which allows to incorporate the various specifications of the launcher problem in a streamlined manner. An important feature of this approach is that a non-conventional LQG/LTR approach, required to satisfy time-domain specifications, can be embedded into a more general standard problem in order to account for frequency-domain robustness constraints. The specific form of this standard problem is also very interesting for gain scheduling.

Controller Design via Nonsmooth Multi-Directional Search

Abstract We propose an algorithm which combines multi-directional search (MDS) with nonsmooth techniques such as bundling to solve several difficult synthesis problems in automatic control. Applications include static and fixed-order output feedback controller design, simultaneous stabilization, H2/H ∞ synthesis to cite just a few. We show in which way direct search techniques may be safeguarded by nonsmooth oracles in order to maintain convergence certificates in the presence of nonsmoothness. Our numerical testing includes numerous benchmark examples. For instance, our algorithm needs 0.41 seconds to compute a static output feedback stabilizing controller for the Boeing 767 flutter benchmark problem (E.J. Davison, 1990), a system with 55 states.

A Robust Multi-Objective Synthesis Applied to Launcher Attitude Control

Abstract We present in this paper an application of a multi-objective to the control of launcher during the atmospheric flight and at the maximal aerodynamic pressure point. This approach is based on the Cross Standard Form. The goal of this new method is to design control laws with high performances and robustness and to handle various kind of specification.Two principal methods encountered in the literature to solve this problem are either the LQG or H 2 control and the H ∞ method. The interest of our approach is that a non conventional LQG/LTR approach, required to satisfy the performance specification, can be integrated in a more general standard problem.

H2 optimal and frequency limited approximation methods for large-scale LTI dynamical systems

Model order reduction over a bounded frequency range is more adapted than the standard H2 approximation whenever the entire frequential behaviour of the large-scale model is not needed or not accurately known. However most of the methods that enable to reduce a model on a limited frequency range are based on the use of weights. Yet their determination is often an issue for engineers. That is why, in this paper, two weight-free model approximation algorithms are proposed. They are based on recent algorithms that achieve local H2 optimal model reduction (see Gugercin (2007), Van Dooren et al. (2008) and Gugercin et al. (2008)). The proposed algorithms efficiency are validated both on a standard benchmark and on an industrial use case.

Avionics/Control co-design for large flexible space structures

In this paper, a multi-model H1 synthesis scheme for fixed-structure controller design is developed and applied to the attitude control of a highly flexible earth-observation satellite. The particularity of the proposed approach is that the decision variables optimized by the fixed-structure Hinfinity solver include the structured controller parameters but also some parameters which characterize the avionics. Furthermore the proposed control scheme can be very easily adapted to a new configuration of sensors and thus can handle gyro or gyroless configurations. This way, various avionics configurations can be easily evaluated. The avionics characteristics for a given configuration and the control law can be simultaneously optimized avoiding time-consuming iterations between the definition of avionics and the design of the controller on the basis of the current avionics. The approach is applied on a earth observation satellite for two different study cases. The first one aims to design an improved controller in order to meet the nominal requirements with a poor avionics. The second ones aims to find a controller and an improved avionics to meet very challenging requirements.

Cross standard form: a solution to improve a given controller with H 2 or H ∞ specifications

This paper introduces in cross standard form (CSF) as a solution to the inverse optimal control problem. That is, the CSF is a canonical standard problem whose unique H ∞ or H 2 optimal controller is a given controller. From the control design point of view, the general idea is to apply the CSF to a given controller in order to set up a standard problem which can be completed to handle frequency domain H 2 or H ∞ specification. The analytical formulation of the CSF proposed in this paper can be applied to reduced-, full- or augmented-order compensators or two-degree of freedom compensations. Numerical and academic examples are given.

Design of a flight control architecture using a non-convex bundle method

We design a feedback control architecture for longitudinal flight of an aircraft. The multi-level architecture includes the flight control loop to govern the short-term dynamics of the aircraft, and the autopilot to control the long-term modes. Using