Taha Boukhobza

Sliding mode observer for triangular input form

This paper discusses the problem of designing an observer for nonlinear systems. In Drakunov and Utkin (1995) a new concept of sliding observers was introduced, where the key point is that the equivalent control concept is extensively used. Moreover, in Boukhobza, Djemai, and Barbot (1996) we use a classical sliding mode observer in order to design an observer for the largest class with the so-called output injection form. Here, our purpose is to discuss the observer design for a system in a triangular input observer form. For a system in a triangular input observer form there is no problem of singular input. The second purpose of this paper is to show how to use the anti-peaking sliding method in the case of successive equivalent vectors.

Brief paper: State and input observability for structured linear systems: A graph-theoretic approach

This paper deals with the state and input observability analysis for structured linear systems with unknown inputs. The proposed method is based on a graph-theoretic approach and assumes only the knowledge of the systems structure. Using a particular decomposition of the systems into two subsystems, we express, in simple graphic terms, necessary and sufficient conditions for the generic state and input observability. These conditions are easy to check because they are based on comparison of integers and on finding particular subgraphs in a digraph. Therefore, our approach is suited to study large-scale systems.

Robustness against unknown Networked induced Delays of Observer based FDI

Abstract In this paper, we are concerned by the problem of Fault diagnosis in Networked Control Systems (NCS). The effect of unknown networked induced delays on conventional observed based residual generator is studied. It is shown that the detection performances may be reduced due to the sensitivity of the residuals to the delays. With the assumption that the network delays belong to a given bounded set , in order to enhance the robustness of fault detection an adaptive evaluation procedure of the residuals is proposed. The detection thresholds which depend on the maximum influence of the network delays are estimated using an optimization approach.

Brief paper: Observability analysis for structured bilinear systems: A graph-theoretic approach

This paper is devoted to the generic observability analysis for structured bilinear systems using a graph-theoretic approach. On the basis of a digraph representation, we express in graphic terms the necessary and sufficient conditions for the generic observability of structured bilinear systems. These conditions have an intuitive interpretation and are easy to check by hand for small systems and by means of well-known combinatorial techniques for large-scale systems.

Brief paper: State and input observability recovering by additional sensor implementation: A graph-theoretic approach

This paper deals with the problem of additional sensor location in order to recover the state and input observability for structured linear systems. The proposed method is based on a graph-theoretic approach and assumes only the knowledge of the systems structure. It allows one to provide the minimal number of the required sensors and either their pertinent location or a necessary and sufficient condition which allows one to check if a sensor location is adequate or not. We obtain a sensor placement procedure based on classical and well-known graph theory algorithms, which have polynomial complexity orders.

DECENTRALIZED AND AUTONOMOUS DESIGN FOR FDI/FTC OF NETWORKED CONTROL SYSTEMS

Abstract In this paper, the fault tolerant control problem is addressed in a networked framework. An isolation filter together with a fault compensation mechanism are proposed for FDI/FTC. Several design procedures are studied. First, in the centralized architecture, the inputs and outputs information used for FDI & FTC are collected and processed in a central node. Considering that sub-systems exchange information over the network, a decentralized architecture is then proposed for FDI/FTC. The autonomous capability of the decentralized design is also considered. But, whatever the design architecture is, fault detectability and isolability, are dependant on the available information. A method based on system structural analysis is then proposed, to provide fault detectability and fault isolability conditions, thus making possible fault tolerant control. Finally, we give an algorithm which allows to distribute a system into subsystems such that the problem of autonomous FDI is solvable for each of these subsystems.

Nonlinear Sliding Observer for Systems in Output and Output Derivative Injection Form

Abstract Necessary and sufficient conditions to obtain output and outputs derivative injection form are given. From this form, a sliding observer design is presented. The paper starts and ends with examples illustrating the proposed method.

Brief paper: Observability of switching structured linear systems with unknown input. A graph-theoretic approach

This paper deals with the observability of the discrete mode, the internal state and the input of switching structured linear systems with unknown input. The proposed method, based on a graph-theoretic approach, assumes only the knowledge of the systems structure. We express, in graphical terms, necessary and sufficient conditions for the generic observability of the discrete mode, the continuous internal state and the input of a switching structured linear system. These conditions can be implemented by classical graph theory algorithms based on finding particular paths and cycles in a digraph.

Brief paper: Observability analysis and sensor location study for structured linear systems in descriptor form with unknown inputs

This paper deals with the state and input right-hand side observability and the sensor location problem to ensure this property for structured linear systems in the descriptor form. The proposed method is based on a graph-theoretic approach. It is applicable to a large class of descriptor systems including regular and nonregular systems even if they are underdetermined, overdetermined or square. After defining a bipartite graph which represents such systems, we deduce some graphic necessary and sufficient conditions to achieve the right-hand side observability of the state and the input. Next, we propose a sensor placement procedure to recover this property. More precisely, we provide the minimal number of the sensors required and either their pertinent location or a necessary and sufficient condition to check if a given sensor configuration is adequate or not to ensure state and input right-hand side observability. Our approach uses algorithms with polynomial complexity orders and assumes only the knowledge of the systems structure and so is suited for large scale systems.

Partial state and input observability recovering by additional sensor implementation: a graph-theoretic approach

This article deals with the problem of additional sensor location in order to recover the observability of any given part of the state and unknown input for structured linear systems. The proposed method is based on a graph-theoretic approach and assumes only the knowledge of the systems structure. We first provide graphical and necessary sufficient conditions for the generic observability of any given part of the state and input. Then, we study the number and location of additional sensors in order to satisfy the latter conditions. On the one hand, we provide necessary requirements to be satisfied by these additional sensors. On the other hand, we give other sufficient simple conditions allowing us to add a number, which is guaranteed to be minimal, of sensors to ensure the observability of any given part of the state and unknown input.