Reset Event-Triggered Adaptive Fuzzy Consensus for Nonlinear Fractional-Order Multiagent Systems With Actuator Faults.

This article studies the problem of event-triggered adaptive fault-tolerant fuzzy output feedback consensus tracking control for nonlinear fractional-order multiagent systems with actuator failures under a directed graph. Considering the fact that the actual system works near the equilibrium point most of the time, a novel dynamic event-triggering strategy with the reset mechanism is proposed, where the dynamic threshold can be actively adjusted according to the preset conditions, so that the resource utilization can be further reduced. Based on an improved event-based consensus error, the state estimator about the derivative of reference trajectory and the adaptive law about the information of graph are constructed, which makes distributed consensus tracking control achieved without obtaining global information. Then, by introducing two adaptive compensating terms to deal with actuator failures and event-triggered measurement errors, it is shown in the sense of fractional-order stability criterion that tracking errors can converge to a compact set even if the fault parameters and modes are completely unknown. Finally, the correctness of the presented method is verified by a simulation example.

Cooperative Fault-Tolerant Output Regulation of Linear Heterogeneous Multiagent Systems via an Adaptive Dynamic Event-Triggered Mechanism.

This article considers the problem of cooperative fault-tolerant output regulation of linear heterogeneous multiagent systems with actuator faults where the exosystem matrix is known by part of the followers. An adaptive dynamic event-triggered scheme is proposed to avoid continuous communication between followers, removing the assumption that global information should be known for controller design. Different from the existing open-loop estimation method for obtaining intermittent communication, the approach proposed in this article does not require that the system matrices of all agents be the same and known a prior. Compared with the existing static or periodic event-triggered mechanism (ETM), by introducing dynamic variables, a more general form than an exponential function, the proposed adaptive dynamic event-triggered condition provides the potential to save energy and obtain better performance. It is demonstrated that the suggested event-triggered control (ETC) method performs cooperative fault-tolerant output regulation for all followers in a completely distributed way with intermittent communication while excluding Zeno behavior. Finally, a simulation example is carried out to illustrate the efficacy of the suggested strategy.

Distributed Fault-Tolerant Containment Control for Linear Heterogeneous Multiagent Systems: A Hierarchical Design Approach.

In this article, the problem of distributed hierarchical fault-tolerant containment control for heterogeneous linear multiagent systems (MASs) is investigated. In most of the existing distributed methods for MASs with system failures, each agent broadcasts its state, or output, or the estimation of state to neighbors. Once an agent is subjected system failures, faults affect the dynamics of other agents over the network, that is, the influence of faults on the agent will propagate with the network. In order to overcome this drawback, a fault-tolerant hierarchical containment control protocol is developed, which includes two layers: 1) the upper layer and 2) the lower layer. The upper layer consists of a virtual system and a cooperative controller to achieve a virtual containment objective. The lower layer consists of an actual system and a fault-tolerant controller to track the upper layer virtual system. Compared with the existing results, the phenomenon of fault propagation can be avoided by introducing the hierarchical design approach, that is, the fault of agent i only affects the dynamics of itself, and does not affect the dynamics of other agents through the network. It is shown that each follower converges asymptotically to a convex hull spanned by leaders with external input. Finally, the developed method is demonstrated by simulation results.

Robust Dynamic Actuator Failure Compensation Control of Nonlinear Systems via Cooperative Interaction Design.

This article studies fault-tolerant resilient control (FTRC) problems for uncertain Takagi-Sugeno fuzzy systems when subjected to additive actuator faults and/or malicious injections on control input signals. The effects of faults and malicious injections are modeled by unknown bounded signals. The signals are produced by any finite- L2 -gain dynamical system and a Lipschitz and derivable function with respect to states, so that the considered fault model contains some reported ones as special cases. By employing the available state and input data, a function, which is equivalent to a fictitious dynamical system comprising the information about compensation errors for unknown actuator faults, is presented. Then, based on the virtual system, a novel actuator failure compensator (AFC) with the structure of dynamic feedbacks is proposed, so that the compensation capability is improved via cooperative interaction designs between the virtual dynamical systems and closed-loop systems. Furthermore, through the equivalence class and Lyapunov theories, it is proved that the presented robust dynamic AFC-based fuzzy controller ensures the asymptotic convergence of system states to zero. Different from the existing FTRCs, good transient performance is guaranteed, even in the presence of unforeseen actuator faults. Two illustrative examples verify the effectiveness of the presented method.

Reliable cooperative control and plug-and-play operation for networked heterogeneous systems under cyber-physical attacks.

This paper considers a reliable cooperative control and plug-and-play operation problem in networked heterogeneous systems (NHSs), and focuses on the scenario subjected to physical attack-induced actuator failures/uncertainties and Denial-of-Service (DoS) attacks on communication channels between physical nodes. To solve it, a new self-feedback control with an adaptive integral sliding-mode compensator is developed. The new one configures each heterogeneous system under the malicious actuator failures/uncertainties to be passivity-short (PS). The PS index quantifies the impact of each attacked heterogeneous dynamics on their networked operations. Furthermore, based on cloud networks, a novel network-level distributed control is proposed. It improves robustness of the systems against DoS with no frequency and duration constraints. And then, a technical condition is presented with the aid of the impact equivalence principle. Under the condition, the self-feedback and network-level controls designed separately but performed together ensure the leader-follower consensus and plug-and-play operation of the attacked NHSs. Finally, the effectiveness of the proposed method is verified by flight control systems.

Fault detection for non-Gaussian stochastic distribution fuzzy systems by an event-triggered mechanism.

This paper studies an event-triggered fault detection (FD) problem for non-Gaussian stochastic distribution fuzzy systems. Different from other systems, the available information of the stochastic distribution systems is the measurable output probability density functions (PDFs) rather than the output itself. This increases the difficulty of the event-triggered-based observer synthesis. To overcome the difficulty, a new event-triggered observer approach based on the information of the output PDFs is proposed. First, a B-spline model is employed to approximate the output PDFs. Second, a novel event-triggered scheme (ETS) is designed to save the limited communication source. Then, a finite-frequency H_∕L∞ fault detection observer is constructed such that the effect of the PDFs approximation error on the residual signal can be attenuated and the FD performance can be increased. Finally, two examples are presented to demonstrate the effectiveness of the proposed method.

Reliable Control Policy of Cyber-Physical Systems Against a Class of Frequency-Constrained Sensor and Actuator Attacks.

This paper is concerned with reliable control problems of cyber-physical systems against a class of frequency-constrained sensor and actuator attacks. We consider a continuous-time linear physical system equipped with an observer-based abnormal detector, and it is assumed that control signals and partial sensor outputs transmitted via network layers are vulnerable to cyber attacks. With the use of detection mechanisms of the abnormal monitor, an upper bound of the worst stealthy attacks is obtained, which is composed of the information of the detector's threshold, the attack's structure, and frequency characteristic. By exploiting the bound information, a novel attack compensator, which can stabilize the system with a nearly desired system performance, is proposed for a situation where an attack may occur without triggering an alarm. Finally, the effectiveness of the proposed control policy is verified by a numerical example.

Robust Adaptive Fuzzy Control of a Class of Uncertain Nonlinear Systems With Unstable Dynamics and Mismatched Disturbances.

This paper studies the robust stabilization problem for a class of uncertain nonlinear systems with unstable zero dynamics. The considered zero dynamic is not assumed to be input-to-state practically stable and contains nonlinear uncertainties and mismatched external disturbances. A new robust adaptive fuzzy control method is developed by combining theory with backstepping technique. First, an ideal virtual control function is designed, which can guarantee the zero dynamic asymptotically stable with a suboptimal performance. Then, based on some non-negative functions and backstepping design, the actual controller is constructed for the overall system, which ensures that the tracking error for the ideal virtual control signal converges to a priori accuracy regardless of external disturbances. In this design, an auxiliary signal is introduced to overcome the difficulties from the unavailable virtual reference signal. By exploiting the implicit function theorem, the proposed design technique is directly applied to a special case, where the zero dynamic is partially linear. A two inverted pendulums is used to illustrate the application and effectiveness of the proposed design method.

A New Sensor Fault Isolation Method for T-S Fuzzy Systems.

This paper is concerned with the fault isolation problem for T-S fuzzy systems with sensor faults. With the help of a set theoretic description of T-S fuzzy models, a new fault isolation scheme is proposed. It consists of a set of fuzzy observers and each of them corresponds to a specified sensor, where the antecedent and consequent parts of the observer are independent on the sensor output. Different from the existing approaches, the premise variables, which do not depend on the specified sensor output but depend on the other sensor outputs, are used in the proposed observer, which has the potential to lead to a better fault isolation performance. In the end, an example is given to show the effectiveness of the fault isolation method.

Output feedback fuzzy controller design with local nonlinear feedback laws for discrete-time nonlinear systems.

This paper considers the output feedback control problem for nonlinear discrete-time systems, which are represented by a type of fuzzy systems with local nonlinear models. By using the estimations of the states and nonlinear functions in local models, sufficient conditions for designing observer-based controllers are given for discrete-time nonlinear systems. First, a separation property, i.e., the controller and the observer can be independently designed, is proved for the class of fuzzy systems. Second, a two-step procedure with cone complementarity linearization algorithms is also developed for solving the H( ∞) dynamic output feedback (DOF) control problem. Moreover, for the case where the nonlinear functions in local submodels are measurable, a convex condition for designing H(∞) controllers is given by a new DOF control scheme. In contrast to the existing methods, the new methods can design output feedback controllers with fewer fuzzy rules as well as less computational burden, which is helpful for controller designs and implementations. Lastly, numerical examples are given to illustrate the effectiveness of the proposed methods.

Switching fuzzy dynamic output feedback H(infinity) control for nonlinear systems.

This paper studies the problem of dynamic output feedback H (infinity) control for nonlinear systems, which are described by Takagi-Sugeno fuzzy parts with measurable premise variables and uncertainty parts. The uncertainties are parameter dependent, unknown, and time varying but bounded. A switching fuzzy dynamic output feedback control scheme is proposed, which depends on the measurable premise variables and the bounds of the unknown parameters of the considered system, where the switching mechanism is introduced to handle the unknown parameters. A two-step linear-matrix-inequality-based optimization procedure is developed to design switching fuzzy H (infinity) controllers. An example is given to illustrate the effectiveness of the proposed design method.

Control synthesis of continuous-time T-S fuzzy systems with local nonlinear models.

This paper is concerned with the problem of designing fuzzy controllers for a class of nonlinear dynamic systems. The considered nonlinear systems are described by T-S fuzzy models with nonlinear local models, and the fuzzy models have fewer fuzzy rules than conventional T-S fuzzy models with local linear models. A new fuzzy control scheme with local nonlinear feedbacks is proposed, and the corresponding control synthesis conditions are given in terms of solutions to a set of linear matrix inequalities (LMIs). In contrast to the existing methods for fuzzy control synthesis, the new proposed control design method is based on fewer fuzzy rules and less computational burden. Moreover, the local nonlinear feedback laws in the new fuzzy controllers are also helpful in achieving good control effects. Numerical examples are given to illustrate the effectiveness of the proposed method.

H(infinity) filtering for fuzzy singularly perturbed systems.

This paper considers the problem of designing H(infinity) filters for fuzzy singularly perturbed systems with the consideration of improving the bound of singular-perturbation parameter epsilon. First, a linear-matrix-inequality (LMI)-based approach is presented for simultaneously designing the bound of the singularly perturbed parameter epsilon, and H(infinity) filters for a fuzzy singularly perturbed system. When the bound of singularly perturbed parameter epsilon is not under consideration, the result reduces to an LMI-based design method for H(infinity) filtering of fuzzy singularly perturbed systems. Furthermore, a method is given for evaluating the upper bound of singularly perturbed parameter subject to the constraint that the considered system is to be with a prescribed H(infinity) performance bound, and the upper bound can be obtained by solving a generalized eigenvalue problem. Finally, numerical examples are given to illustrate the effectiveness of the proposed methods.

Dynamic output feedback control synthesis for continuous-time T-S fuzzy systems via a switched fuzzy control scheme.

This correspondence paper is concerned with the problem of designing switched dynamic output feedback H(infinity) controllers for continuous-time Takagi-Sugeno (T-S) fuzzy systems. A new type of dynamic output feedback controllers, namely, switched dynamic parallel distributed compensation (SDPDC) controllers, is proposed, which are switched by basing on the values of membership functions. A new method for designing SDPDC controllers for guaranteeing stabilities and H(infinity) performances of closed-loop nonlinear systems is presented, where the design conditions are given in terms of the solvability of a set of linear matrix inequalities. It is shown that the new method provides better or at least the same results of the existing design methods via a pure DPDC scheme. A numerical example is given to illustrate the effectiveness of the proposed method.