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Almost all of the available literature on secure state estimation focus on sensor attacks. Unlike the existing results, this study investigates the attack-resilient state estimation problem for continuous-time linear systems with sparse actuator attacks and process noises. It is assumed that, the attacker has limited resources and can only manipulate a certain number of actuators. Specifically, a novel switched observer is proposed with milder design conditions which are derived in terms of linear matrix (in)equalities. It is shown that, the observer not only provides an attack-resilient state estimation, but also guarantees that the resulting observer error system is with noise attenuation level which can be optimised. Finally, a simulation example of a linearised reduced-order aircraft system is provided to show the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper considers the cooperative fault-tolerant output regulation problem for linear multi-agent systems with actuator faults. It is assumed that the actuator faults are loss of effectiveness faults. A new lemma is introduced to ensure the transmission zero condition for the systems with actuator faults. Based on this lemma, the unique solution of the output regulation equations is achieved. Moreover, a distributed adaptive observer and a distributed state feedback controller with timevarying gains are designed to compensate the actuator faults. In addition, it is shown that the cooperative fault-tolerant output regulation problem can be solved under the proposed controller. Finally, a simulation example is presented to show the validity of the proposed controller. [ABSTRACT FROM AUTHOR]

In this study, the problem of fault detection (FD) observer design for discrete-time Lipschitz non-linear systems with finite-frequency specifications is investigated. The finite-frequency H∞ and H_ indices are introduced to measure the robustness to unknown disturbances and the sensitivity to faults, respectively. Based on the use of a reformulated Lipschitz property, the non-linear error dynamics are transformed into a linear parameter varying (LPV) system. A new lemma is proposed to characterise the system performances in finite-frequency domain. To reduce the conservativeness of the multi-objective problem, slack variable techniques are used to obtain the sufficient conditions for the design of FD observer which are derived in terms of linear matrix inequalities (LMIs). The proposed design method can provide less restrictive LMI conditions and achieve a better FD performance than the existing one in full frequency domain. Two numerical examples are given to show the effectiveness and superiority of the new results. [ABSTRACT FROM AUTHOR]

This study investigates the observer-based fault-tolerant control (FTC) problem for linear systems with multiple faults and external disturbances. Two novel types of FTC schemes are proposed, namely, the intermediate estimator-based parameter adjustment (IEBPA) FTC scheme, which deals with linear systems with matched disturbances and the intermediate estimatorbased (IEB) H∞ FTC scheme, which is applicable to linear systems with mismatched disturbances. For the case with matched disturbances, it is shown that the IEBPA FTC scheme ensures the states of the closed-loop system to be uniformly ultimately bounded with an explicit bound. For the case with mismatched disturbances, it is proved that the IEB H∞ FTC scheme guarantees the closed-loop to be robustly stable with a prescribed H∞ performance index. A simulation example is given to illustrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

The problem of fault estimation for a class of non-linear systems with Lipschitzian non-linearities and faults is studied. In most of the existing fault estimation methods, the coefficient matrix of the fault vector is required to be full column rank, which leads to that the corresponding estimation approaches are conservative and unsuitable commonly for systems with multiple faults or/and subject to disturbances. In this study, this restriction is relaxed. A novel fault estimation method is proposed, where a full-column-rank state variable substitution is introduced so as to meet the requirement of fault estimation. The designed estimation observer guarantees the asymptotic stability of the overall error system with a prescribed H8 performance. The states and faults can be estimated with good accuracy simultaneously. Then, the proposed estimation approach is further extended to solve the problem of fault estimation for non-linear systems with multiple faults or/and subject to disturbances. Finally, numerical examples illustrate the effectiveness and advantages of the proposed method. [ABSTRACT FROM AUTHOR]

This study presents a time-varying threshold-based fault detection (FD) method for a class of single-input singleoutput non-linear systems in strict-feedback form with unmeasurable states, unmatched non-linear fault functions and uncertainties. First, a residual generator with prescribed performance is designed in a framework of recursive technique. Then, the tight time-varying thresholds are computed by using the prescribed performance bound (PPB) and the FD scheme is presented. Furthermore, the fault detectability is analysed to characterise the sensitivity to the faults. It is shown that the residual signal satisfies the PPB and all the estimation errors are uniformly bounded before fault occurrence. Compared with the method without considering the PPB, the proposed time-varying thresholds improve the FD performance with fewer false alarms caused by overshoot during the transient process. Finally, a comparative simulation study illustrates the superiority of the proposed method. [ABSTRACT FROM AUTHOR]

This study addresses the cooperative fault-tolerant tracking control problem for a class of multi-agent systems subject to mismatched parameter uncertainties, external disturbances and actuator faults including loss of effectiveness, outage and stuck. The communication network is undirected connected graph with a fixed topology. It is assumed that the actuator efficiency factors, the upper bounds of the unparametrisable time-varying stuck faults and disturbance, are unknown. Different from the traditional centralised fault-tolerant tracking control problem, only part of the follower nodes can obtain the information of leader directly. On the basis of the local state information of neighbouring agents, a novel cooperative fault-tolerant tracking control scheme by using adaptive mechanism is proposed. By introducing the estimates of controller parameters driven by neighbourhood tracking errors, it is shown that not only the actuator faults in the follower nodes can be compensated, but also the global tracking objective can be achieved. Furthermore, it is proved that all closedloop signals are bounded and all follower nodes asymptotically tracking to the leader can be achieved in the presence of actuator faults, external disturbances and mismatched parameter uncertainties. Finally, a numerical example is given to show the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

In this study, a direct adaptive control scheme is developed to solve the robust fault-tolerant control problem for linear systems with mismatched parameter uncertainties, disturbances and actuator faults including loss of effectiveness, outage and stuck. Although the unparameterisable time-varying stuck faults and the upper bounds of disturbances are unknown, the adaptive laws are proposed to estimate the unknown controller parameters online. Then, by using the information from the adaptive mechanism, a class of robust adaptive state feedback controllers are constructed for automatically compensating the actuator faults, external disturbances and mismatched parameter uncertainties. Moreover, on the basis of Lyapunov stability theory, it is proved that the resulting adaptive closed-loop system can be guaranteed to be asymptotically stable in the presence of actuator faults, disturbances and mismatched parameter uncertainties. Finally, simulation results are presented to illustrate the efficiency of the proposed fault-tolerant design approach. [ABSTRACT FROM AUTHOR]

This study studies the robust fault-tolerant control problem for uncertain linear systems via sliding-mode output feedback. It is assumed that measured output and compensator state signals are quantised before transmission. By employing the matrix full-rank factorisation technique with a flexible design parameter, a sufficient condition for the existence of a linear sliding surface and a compensator in the augmented space is given. Then the non-linear discontinuous vector gain of the sliding-mode controller is designed based on a static adjustment law of the quantisation parameters. It is shown that the proposed sliding-mode fault-tolerant strategy guarantees that the closed-loop system is asymptotically stable in the presence of quantisation errors and actuator faults including outage. Compared with the existing results, the derived results lead to less conservativeness and much wider scope of applicability. Finally, the effectiveness of the proposed design method is illustrated via a B747-100/200 aircraft model. [ABSTRACT FROM AUTHOR]

This study deals with the fault diagnosis (FD) problem for affine non-linear systems with single output. Under a well-defined persistent excitation condition including m time delays, m parallel coupled adaptive high-gain FD observers have been designed in some existing literature based on Lyapunov function approach. By employing Lyapunov-Krasovskiii functional approach, this study presents an alternative algorithm to design a simplified FD observer with global exponential convergence, which drastically reduces the complexity of the existing FD systems. A simulation example about a single-link robot arm is provided to illustrate the proposed theoretical results. [ABSTRACT FROM AUTHOR]

This study is concerned with the fault detection (FD) problem for a switched linear parameter-varying system, which is modelled by some different operating points of flight envelope. FD filters are designed such that the estimation errors between the residual signals and the faults are minimised for disturbances, faults and time-varying parameters. By the aid of the parameter-dependent multiple Lyapunov functions method, sufficient conditions for the solvability of this problem are formulated by linear matrix inequalities, furthermore, the filter gains are characterised in terms of a convex optimisation problem. A simulation on the longitudinal motion of Highly Maneuverable Aircraft Technology vehicle is given to demonstrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]