Henrik Niemann

Fundamental problems in fault detection and identification

A number of different fundamental problems in fault detection and fault identification are formulated in this paper. The fundamental problems include exact, almost, generic and class-wise fault detection and identification. Necessary and sufficient conditions for the solvability of the fundamental problems are derived. These conditions are weaker than the ones found in the literature since we do not assume any particular structure for the residual generator. At the end of the paper, a time domain synthesis procedure based on state-space methods to construct appropriate residual generators is given. Copyright

Design of integrated systems for the control and detection of actuator/sensor faults

Considers control systems operating under potentially faulty conditions. Discusses the problem of designing a single unit which not only handles the required control action but also identifies faults occurring in actuators and sensors. In common practice, units for control and for diagnosis are designed separately. Attempts to identify situations in which this is a reasonable approach and cases in which the design of each unit should take the other into consideration. Presents a complete characterization for each case and gives systematic design procedures for both the integrated and non‐integrated design of control and diagnosis units. Shows how a combined module for control and diagnosis can be designed which is able to follow references and reject disturbances robustly, control the system so that undetected faults do not have disastrous effects, reduce the number of false alarms and identify which faults have occurred.

Norm based design of fault detectors

The design of fault detectors for fault detection and isolation (FDI) in dynamic systems is considered in this paper from a norm based point of view. An analysis of norm based threshold selection is given based on different formulations of FDI problems. Both the nominal FDI problem as well as the uncertain FDI problem will be considered. With reference to this analysis, a performance index based on norms of the involved transfer functions is given. A method for designing FDI filters which will minimize the performance index is also given.

Integration of Control and Fault Detection: Nominal and Robust Design 1

Abstract The integrated design of control and fault detection is studied. The result of the analysis is that it is possible to separate the design of the controller and the filter for fault detection in the case where the nominal model can be assumed to be fairly accurate. In the uncertain case, however, the design of the filter and the controller can not be separated when an optimal design is desired. For systems with Significant uncertainties, there turns out to be a fundamental trade-off between the performance in the control loop and the performance in the filter

An architecture for fault tolerant controllers

A general architecture for fault tolerant control is proposed. The architecture is based on the (primary) YJBK parameterization of all stabilizing compensators and uses the dual YJBK parameterization to quantify the performance of the fault tolerant system. The approach suggested can be applied for additive faults, parametric faults and for system structural changes. The modelling for each of these fault classes is described. The method allows for design of passive as well as for active fault handling. Also, the related design method can be fitted either to guarantee stability or to achieve graceful degradation in the sense of guaranteed degraded performance. A number of fault diagnosis problems, fault tolerant control problems, and feedback control with fault rejection problems are formulated/considered, mainly from a fault modelling point of view. The method is illustrated on a servo example including an additive fault and a parametric fault.

LTR design of discrete-time proportional-integral observers

Applies the proportional-integral (PI) observer in connection with loop-transfer recovery (LTR) design for discrete-time systems. Both the prediction and the filtering versions of the PI observer are considered. We show that a PI observer makes it possible to obtain time recovery, i.e., exact recovery for t/spl rarr//spl infin/, under mild conditions. Two systematic LTR design methods, one based on an extension of the linear quadratic Gaussian loop-transfer recovery (LQG/LTR) and the other based on linear matrix inequality (LMI), are derived for the discrete-time PI observer case, Explicit expressions for the recovery error when exact recovery is not achievable for all frequencies are also given.

Robust stability and performance of uncertain systems in state space

Robust performance analysis and state feedback design are considered for systems with time-varying parameter uncertainties. The notion of a strongly robust H/sub infinity / performance criterion is introduced, and its applications in robust performance analysis and synthesis for nominally linear systems with time-varying uncertainties are discussed and compared with the constant scaled small gain criterion. It is shown that most robust performance analysis and synthesis problems under this strongly robust H/sub infinity / performance criterion can be transformed into linear matrix inequality problems, and can be solved through finite-dimensional convex programming. The results are in general less conservative than those obtained using small-gain-type criteria.<<ETX>>

Reliable control using the primary and dual Youla parameterizations

Different aspects of modeling faults in dynamic systems are considered in connection with reliable control (RC). The fault models include models with additive faults, multiplicative faults and structural changes in the models due to faults in the systems. These descriptions are considered in connection with reliable control and feedback control with fault rejection. The main emphasis is on fault modeling. A number of fault diagnosis problems, reliable control problems, and feedback control with fault rejection problems are formulated/considered, again, mainly from a fault modeling point of view. Reliability is introduced by means of the (primary) Youla parameterization of all stabilizing controllers, where an additional loop is closed around a diagnostic signal. In order to quantify the level of reliability, the dual Youla parameterization is introduced which can be used to analyze how large faults can be tolerated without losing, e.g., stability.

Filter design for failure detection and isolation in the presence of modeling errors and disturbances

The design problem of filters for robust failure detection and isolation, (FDI) is addressed in this paper. The failure detection problem will be considered with respect to both modeling errors and disturbances. Both an approach based on failure detection observers as well as an approach based on a standard setup optimization is presented in this paper.

Fault detection for nonlinear systems - a standard problem approach

The paper describes a general method for designing (nonlinear) fault detection and isolation (FDI) systems for nonlinear processes. For a rich class of nonlinear systems, a nonlinear FDI system can be designed using convex optimization procedures. The proposed method is a natural extension of methods based on the extended Kalman filter.