Fault Detection And Isolation Based On Multi-objective Observer Design

In order to improve the safety in process of modern dynamic control systems,fault diagnosis technique has attracted many researchers' attention.Among the existing meth-ods,model-based fault diagnosis method has been researched the most deeply.Due to the unmodelled dynamic,perturbation of parameter and measurement noise,the exact mathematical model of the control system cannot be obtained,which will effect the fault detection result.In order to detect the fault from the unknown disturbance accurately,ro-bust fault detection and diagnosis has been one of the most important issues.Robust fault detection and diagnosis is different from the problem of robust state estimation.It requires that the residual generated by observer satisfies the disturbance robustness performance,meanwhile improves the fault sensitivity as much as possible.However,it is contradicto-ry between the disturbance robustness and fault sensitivity,the observer needs to make a trade off between the two performances.Thus,the observer is a kind of multi-objectives observer.This thesis focuses on fault detection and isolation based on multiple-objective observer design method.The main contributions of this thesis consist in the following aspects:The H_-/H_?residual generator in full frequency domain based on generalized output method is studied.In order to attenuate the effect of unknown disturbance to the residual,meanwhile maximum the fault sensitivity of the residual,H_-/H_?fault detection observer is one of the most used methods,in which the H_?norm and H_-index are used to measure the worst-case disturbance attenuation performance and fault sensitivity performance,re-spectively.It is required that the full-column rank condition of the fault distribution matrix in the measurement output equation in H_-index analysis.If only the actuator fault is con-sidered,the H_-index cannot be designed in full frequency domain.To deal with this problem,this thesis proposes an H_-/H_?residual generator based on generalized output method.First,an augmented system is generated by using the generalized output,the actuator fault is introduced into the measurement output of the augmented system,thus the H_-index can be designed.Then,an H_-/H_?residual generator is designed for the augmented system,an iterative algorithm is used in the observer design to reduce some conservatism.H_-/H_?residual generator design method in finite-frequency domain is investigated.In practice,for some system the H_-index is zero in full frequency but not zero in finite frequency.Moreover,faults usually emerge in the low frequency domain,thus it is signif-icant to study the fault detection method in finite frequency domain.The existing results of the observer design method in finite frequency exist some conservatism,in order to reduce some conservatism,this thesis proposes a novel method by introducing slack ma-trix.Moreover,it is proved that the proposed method has less conservatism theoretically.Besides,the finite frequency H_-/H_?residual generator is studied for Lipschitz nonlin-ear systems.Due to the Lipschitz nonlinear term,the generalized KYP lemma for linear systems cannot be used directly.This thesis provides the existing condition of finite fre-quency H_-/H_?residual generator for Lipschitz nonlinear systems the first time.Besides,the design conditions is transformed into LMIs.Integrated design of residual generation and residual evaluation based on H_-/L_?ob-server method is investigated.Due to the effect of the unknown disturbance,the residual is not zero at fault-free situation.Thus it is important to chose the residual evaluation function and threshold.One of the most used method is based on the H_?norm,which is suitable for the energy bounded signal.However,in practice,most signals are not ener-gy bounded but peak bounded.Therefore,this thesis proposes a disturbance attenuation method by using L_?norm for the system which is subjected by the peak bounded distur-bance.Furthermore,it is combined with H_-index and a finite frequency H_-/L_?observer is proposed.Besides,a dynamic threshold considering the initial condition of the estima-tion error vector is synthesized.This method is extended into Lipschitz nonlinear systems and discrete-time linear parameter varying systems,the design conditions of the observer is given.Unknown input H_-/H_?observer based fault detection and isolation method is s-tudied in this thesis.Most of the existing H_-/H_?observer design method only focuses on fault detection,little attention has been paid on fault isolation.In this thesis,a set of unknown input observes are first designed,the H_?disturbance attenuation performance is satisfied.Meanwhile,the residual generated by the ith observe is only decoupled with the ith actuator fault but sensitive to others.Then,the threshold is computed by zonotope method.The aim of this method is to recursively compute a zonotopic outer approxima-tion of the unknown disturbance by the center and the generator matrix.The zonotope is used to be the threshold.At last,fault detection and isolation is achieved by comparing the structural residual with the zonotopic threshold.