Joseph-Julien Yamé

Fault Diagnosis of Networked Control Systems

Fault Diagnosis of Networked Control Systems Networked Control Systems (NCSs) deal with feedback control systems with loops closed via data communication networks. Control over a network has many advantages compared with traditionally controlled systems, such as a lower implementation cost, reduced wiring, simpler installation and maintenance and higher reliability. Nevertheless, the network-induced delay, packet dropout, asynchronous behavior and other specificities of networks will degrade the performance of closed-loop systems. In this context, it is necessary to develop a new theory for systems that operate in a distributed and asynchronous environment. Research on Fault Detection and Isolation (FDI) for NCSs has received increasing attention in recent years. This paper reviews the state of the art in this topic.

Model-free reconfiguration mechanism for fault tolerance

Model-free reconfiguration mechanism for fault tolerance The problem of fault tolerant control is studied from the behavioral point of view. In this mathematical framework, the concept of interconnection among the variables describing the system is a key point. The problem is that the behavior we intend to control is not known. Therefore, we are interested in designing a fault accommodation scheme for an unknown behavior through an appropriate behavioral interconnection. Here we deal simply with the trajectories that are generated by the system in real time. These trajectories determine the behavior of a system in various (faulty/healthy) modes. Based on the desired interconnected behavior, only the trajectories that obey certain laws are selected. These laws, representing the desired behavior, can indeed be achieved by a regular interconnection. Thus, when the trajectories do not belong to a certain desired behavior, it is considered to be due to the occurrence of a fault in the system. The vantage point is that the fault tolerant control problem now becomes completely a model-free scheme. Moreover, no explicit fault diagnosis module is required in our approach. The proposed fault tolerance mechanism is illustrated on an aircraft during the landing phase.

On implementing on-line designed controller for smooth interconnection in the behavioral framework

Abstract In the behavioral setting, a controller is designed using the behavior of the plant, and the given desired behavior. Further, the synthesized controller makes an interconnection with the plant such that the interconnected system satisfies the desired behavior. However, at the time of interconnection it might not be possible. Here, first we design an on-line controller using the real-time measurements generated by the plant, and the given desired behavior. Secondly, we show a way to implement this on-line designed controller such that at the time of interconnection, the closed-loop satisfies the desired behavior. The novelty of the demonstrated approach lies in the fact that we do not have any a priori information about the plant in real-time.

Distributed state estimation and model predictive control: Application to fault tolerant control

In this paper, a distributed and networked control system architecture based on unsupervised and independent Model Predictive Control/Kalman-Filter (MPC/KF) schemes, is proposed. Interconnected subsystems, possibly located at different sites, exchange information via the communication network. For the partial local state measurement, the key component for realistic Distributed Model Control (DMPC) formulation is the state estimations. These state estimations are provided by Kalman filters. In this distributed framework, MPC and KF algorithms may require information from other sub-controllers to achieve their task in a cooperative way. The given distributed and cooperative control system architecture may be suitable for Fault Tolerant Control (FTC) in a network of distributed subsystems. This insight gained the design of such architecture is used to implement FTC under actuator faults.

Active Fault-Tolerant Control Systems: A Behavioral System Theoretic Perspective

The book introduces novel algorithms for designing fault-tolerant control (FTC) systems using the behavioral system theoretic approach, and presents a demonstration of successful novel FTC mechanisms on several benchmark examples. The authors also discuss a new transient management scheme, which is an essential requirement for the implementation of active FTC systems, and two data-driven methodologies that are broadly classified as active FTC systems: the projection-based approach and the online-redesign approach. These algorithms do not require much a priori information about the plant in real-time, and in addition this novel implementation of active FTC systems circumvents various weaknesses induced by using a diagnostic module in real-time. The book provides graduate students taking masters and doctoral courses in mathematics, control, and electrical engineering an excellent stepping-stone for their research. It also appeals to practitioners interested to apply innovative fail-safe control techniques.

A real-time model-free reconfiguration mechanism for fault-tolerance: Application to a hydraulic process

In this note, we present a real-time model-free reconfiguration mechanism to achieve fault-tolerant control (FTC) and we show the feasibility of this technique with a simple hydraulic plant subject to actuators faults. The main feature of the reconfiguration technique is that it relies solely on the data generated by the actual plant and on the (control) specifications given by a performance functional. The resulting FTC system does not embed any on-line model-based fault detection and isolation (FDI) algorithms, and therefore such closed-loop system gets rid off the drawbacks of FDI-based fault-tolerant controllers.

On stabilization and spectrum assignment in periodically time-varying continuous-time systems

This note discusses the stabilization and spectrum assignment problems in linear periodically time-varying (LPTV) continuous-time systems with sampled state or output feedback. The hybrid nature of the overall feedback system in this case imposes some carefulness in handling classical concepts related to purely LPTV continuous-time systems, In particular, this note points out the fact that the stabilization of such systems by periodic feedback gains with sampled state or output does not imply the relocation of the original characteristic exponents of the LPTV systems. It is also shown that the concept of monodromy matrix as extended to LPTV hybrid systems has not all the features of a true monodromy matrix.

Trajectory-based real-time control of an electrical circuit against unknown faults

Abstract This paper presents a trajectory-based online control reconfiguration mechanism against unknown fault occurring in an electric circuit. First, we demonstrate the modeling of an electric circuit by taking the time-trajectory viewpoint, where no a priori input–output partition has been made. The uniqueness of this viewpoint lies in the fact that it deals only with variables that describe the system without any dedicated (external or internal -type) representation. Subsequently, we illustrate a novel real-time fault-tolerant control (FTC) strategy based on this trajectory standpoint, which does not require an explicit model-based fault diagnosis unit. Instead, the controller is reconfigured directly based on the trajectories generated by the system in real-time, and the given control specifications. In this way, we efficiently excrete the shortcomings that are often seen in model-based fault-tolerant systems. The proposed FTC method is effectively demonstrated on an RLC circuit.

A note on the canonical controller in the behavioral system-theoretic approach

This paper aims at gaining some insights into the structure of the canonical controller introduced by A.J. Van der Schaft in the behavioral approach to system theory. One of the striking feature of this controller is its nice property of achieving exactly the specified behavior when interconnected to a plant for which it has been designed. We carry out a study of this controller by instantiating its general behavioral equation in the classical single-input/single output unity-feedback configuration. In doing so, insights into the action of the controller are obtained and reveal that the canonical controller, in that setting, acts essentially as a “plant-inverting” controller. We give also an independant result which shows how any controller which achieves a specification can be designed with experimental plant input/output data without an explicit knowledge of the behavioral equations of the controlled plant. Such a result might be of certain importance for some classes of dynamical plants and also for dealing with real-time (online) fault-tolerant controller design.

A real-time projection-based approach for fault accommodation in NREL's 5MW Wind Turbine systems

This paper presents a real-time mechanism to tolerate faults occurring in a Wind Turbine system such that it can generate the rated power at anytime. This mechanism lies under the taxonomy of Active Fault-Tolerant Control (AFTC) system, namely projection-based approach. In the proposed approach, we do not use any a priori information about the model of the plant in real-time. In fact, we use the online measurements generated by the plant. Based on the given control objectives, and the observed measurements, the controller is re-configured such that the turbine can generate the rated power even under faulty conditions. Secondly, no use of an explicit fault-diagnosis module is seen in this approach. The benchmark model for the Wind Turbine is a FAST coded simulator designed by the U.S. National Renewable Energy Laboratorys (NREL) National Wind Turbine Center.