Dominique Sauter

Fault-tolerant control in dynamic systems: application to a winding machine

The general fault-tolerant control method described in the article addresses actuator and sensor faults, which often affect highly automated systems. These faults correspond to a loss of actuator effectiveness or fault sensor measurements. After describing these faults, a fault estimation and compensation method was proposed. In addition to providing information to operators concerning the system operating conditions, the fault diagnosis module is especially important in fault-tolerant control systems where one needs to know exactly which element is faulty to react safely. The methods abilities to compensate for such faults are illustrated by applying it to a winding machine, which represents a subsystem of many industrial systems. The results show that once the fault is detected and isolated, it is easy to reduce its effect on the system, and process control is resumed with degraded performances close to nominal ones. Thus, stopping the system immediately can be avoided. However, the limits of this method are reached when there is the complete loss of an actuator. In this case, only a hardware redundancy is effective and could ensure performance reliability. The method proposed here assumes the availability of the state variables for measurement.

A Generic Strategy for Fault-Tolerance in Control Systems Distributed Over a Network

This paper provides a tutorial overview of a number of aspects and approaches to Control over the Network for Network Control Systems (NCS) that are likely to lead to good fault-tolerant control properties, subject to network faults. In order to analyze and derive the best strategies for fault tolerant NCS, it is initially assumed that the network communication bandwidth is infinite. This gives a simpler way to map the NCS structure in terms of computing nodes and control subsystems/components. Two Fault-tolerant NCS architectures have been described, analyzed and compared with view to demonstrating that the classical concepts of Fault-tolerant Control (FTC), namely of active and passive FTC can be related to equivalent (although more complex) concepts in NCS. The study confirms that the de-centralized approach to fault-tolerant control of NCS suffers from a difficult challenge as to how to compensate for fault effects occurring throughout the NCS. On the other hand, the distributed hierarchical structure, requires a coordination function which is able to manage (a) the local control task, (b) the compensation of faults, and (c) the network reconfiguration, if required, subject to significant network subsystem faults.

Fault Tolerant Control Design For Polytopic LPV Systems

Fault Tolerant Control Design For Polytopic LPV Systems This paper deals with a Fault Tolerant Control (FTC) strategy for polytopic Linear Parameter Varying (LPV) systems. The main contribution consists in the design of a Static Output Feedback (SOF) dedicated to such systems in the presence of multiple actuator faults/failures. The controllers are synthesized through Linear Matrix Inequalities (LMIs) in both fault-free and faulty cases in order to preserve the system closed-loop stability. Hence, this paper provides a new sufficient (but not necessary) condition for the solvability of the stabilizing output feedback control problem. An example illustrates the effectiveness and performances of the proposed FTC method.

Brief Robust fault detection in uncertain dynamic systems

The work reported in this paper focuses on the design of optimal filters for fault detection in uncertain dynamic systems. A design procedure dealing with interval type parameter uncertainties is proposed for residual generation via a frequency domain approach. Robustness enhancement is based on the design of optimal detection filters maximizing the effect of faults while minimizing the influence of disturbances. In this framework, in order to cope with parameter uncertainties, Kharitonov polynomials and Dasgupta geometry are introduced and an extension of previous results to worst case situation is proposed. An example is also included to illustrate the method efficiency.

Frequency-domain optimization for robust fault detection and isolation in dynamic systems

The paper deals with the design of optimal filters for fault detection and isolation (FDI) in dynamic systems. The proposed method, involving the generation of directional residuals derived from systems input-output description model, facilitates the enhancement of robustness even in cases where it is impossible to decouple fault effect from system perturbations. The proposed solution is based on the optimization of a performance index in the frequency domain. The resulting detection filter is capable of maximizing the effect of faults while minimizing the influence of disturbances.

Fault Isolation Filter for Networked Control System with Event-Triggered Sampling Scheme

In this paper, the sensor data is transmitted only when the absolute value of difference between the current sensor value and the previously transmitted one is greater than the given threshold value. Based on this send-on-delta scheme which is one of the event-triggered sampling strategies, a modified fault isolation filter for a discrete-time networked control system with multiple faults is then implemented by a particular form of the Kalman filter. The proposed fault isolation filter improves the resource utilization with graceful fault estimation performance degradation. An illustrative example is given to show the efficiency of the proposed method.

Robust Residual Generation Via Lmi

Abstract This paper presents a new approach that attempts to optimise two contradictory objectives: disturbance attenuation and fault sensitivity. The proposed method is applied to linear time-invariant systems subjected to unstructured perturbations and critical faults that involve a frequency change. This approach is based on H 2 estimation which allows optimising the attenuation of the worst-case effects of disturbances on the residual. To enhance the sensitivity of this residual to faults, a parametrisation of the initial observer is proposed. This parametrisation intends to improve the amplification of critical faults on residual with regard to disturbances attenuation.

Fault-tolerant control method for actuator and component faults

In this paper, a fault-tolerant control method is developed. This method makes possible the compensation of additive or multiplicative actuator and component faults. Its principle is based on the online estimation of a quantity which is equal to zero in the fault-free case and equal to the fault magnitude when a fault occurs on the system. Then, a new control law is added to the nominal one in order to compensate the fault effect on the system. The main advantage of this approach is that it is very easy to implement and it does not require a fault diagnosis module which reduce the computation time and avoid the problems caused by false alarms and delays in the fault detection and isolation. The performances of this method are tested in simulation on a pilot plant.

Actuator fault-tolerant control design: Demonstration on a three-tank-system

Fault-tolerant control or reconfigurable control systems are generally based on a nominal control law associated with a fault detection and isolation module. A general review of techniques dealing with this problem is given and a new fault-tolerant control approach is presented. This method is based on the on-line estimation of an eventual fault and the addition of a new control law to the nominal control law in order to reduce the fault effect once this fault is detected and isolated. The performances of this method depend on the time delay between the occurrence of the fault and its detection and isolation. A modified approach is then proposed in order to avoid the problems generated by delays, false alarms or non-detection inherent to diagnosis techniques. These methods are applied to a pilot plant and their performances are compared and discussed.

Design of an Active Fault Tolerant Control and Polytopic Unknown Input Observer for Systems described by a Multi-Model Representation

In this paper, an active Fault Tolerant Control (FTC) strategy is developed to systems described by multiple linear models to prevent the system deterioration by the synthesis of adapted controllers. First, a Polytopic Unknown Input Observer is synthesized for providing actuator fault estimation. The actuator fault estimation is used in a FTC scheme which schedules some predefined state feedback gains. These gains are performed through LMI both in fault-free and faulty cases in order to preserve the system performances over a wide operating range. For each separate actuator, a pole placement is designed by pole clustering. The effectiveness and performances of the method have been illustrated in simulation considering a hydraulic system: a three-tank system.