International audience

This article solves the fixed-time-synchronized (FTS) bipartite time-varying formation (BTVF) tracking control problem of networked Euler-Lagrange systems (NELSs) with disturbances, where all state elements of the NELSs can achieve BTVF at the same time. An improved hierarchical control strategy is proposed, comprising a distributed estimator layer and a local control layer. The former is responsible for estimating the desired position and velocity, while the latter employs a novel interval observer-based algebraic reconstruction mechanism to compensate for the unknown disturbance. Subsequently, a singularity-free FTS BTVF control protocol is established, leveraging a norm-normalized sign function-based switching sliding mode control technique. This protocol guarantees that, in the presence of a signed antagonistic interaction graph, all system states converge synchronously to equilibrium within a fixed time. Finally, comparisons and simulations are conducted to validate the feasibility, significance, and merits of the developed control scheme.Note to Practitioners—In practical applications, the performance of networked systems depends not only on when the system state converges, but also significantly on when and how each subsystem state element converges. Despite the superior convergence property of fixed-time control, its standalone application proves inadequate in scenarios where all state elements of the network systems are required to reach the desired values synchronously, as observed in coordinated transportation and formation, particularly in the domain of space attack and defense. In this article, the BTVF tracking control issue with FTS convergence of networked systems is studied for the first time. The design of non-singular and FTS coordination schemes is challenging in NELSs. In addition, the developed distributed strategy based on the hierarchical control technique is suitable for NELSs with unknown disturbances and antagonistic interaction graphs, and the use of the norm-normalized sign function-based switching sliding mode control method excludes the singular problem.

This article addresses both leaderless and leader-following consensus issues for Lipschitz nonlinear multi-agent systems. To begin with, the issues are discussed in view of leaderless scenarios. Firstly, a distributed dynamic event-triggered mechanism is introduced to mitigate continuous communication burdens among neighboring agents. This mechanism incorporates an open-loop estimation algorithm and an inner self-learning term into the triggering conditions. Secondly, to prevent Zeno behavior, a time/event hybrid mechanism is implemented. For each agent, based on the local state information at the current event-triggered instant and the recent event-triggered instant receiving from neighbors, open-loop state estimations are conducted. Then, by utilizing these open-loop state estimations, a distributed adaptive control protocol is developed within the framework of the hybrid dynamic event-triggered mechanism, including an updating mechanism for the coupling strength of each agent. The challenge posed by the Lipschitz nonlinearity is addressed by solving a Riccati equation. Additionally, the proposed method is improved to be suitable for leader-following multi-agent systems. Finally, simulation examples demonstrate the effectiveness of the proposed method.Note to Practitioners—The purpose of this paper is to introduce a hybrid dynamic event-triggered mechanism aimed at reducing the communication load in Lipschitz nonlinear multi-agent systems. By integrating a hybrid mechanism that combines both time-based and event-based triggers, the proposed scheme effectively minimizes unnecessary data exchanges among agents while naturally excluding the Zeno behavior. This is particularly advantageous in practical scenarios where bandwidth is limited or efficiency in data transmission is highly required in applications. The introduction of open-loop estimators ensures that continuous communication between two neighboring agents is not required. Furthermore, the introduction of an adaptive control protocol, which incorporates a projection algorithm for dynamically adjusting coupling gains, ensures that the interactions between agents remain within safe operational limits. The projection algorithm ensures that the adaptive gain remains within a prescribed range, thus preventing it from growing excessively and preserving system stability.

This paper addresses adaptive semi-global bipartite average tracking (SGBAT) for nonlinear multi-agent systems (MASs) with input saturation under two different low-gain feedback based control protocols via observer-based approach. A state observer and an average signal estimator (ASE) are designed for estimating actual states and obtaining auxiliary outputs. By using the estimated states and the auxiliary outputs, a continuous distributed control protocol is first proposed with adaptive gains. By constructing appropriate Lyapunov function, the adaptive SGBAT can be guaranteed for saturated nonlinear MASs by using low-gain feedback technique. Then, for reducing the communication load, an adaptive dynamic event-triggered control (DETC) protocol is developed with two dynamic event-triggered mechanisms (DETMs). Finally, for verifying the effectiveness of the two control protocols, an application simulation example of multiple satellite systems is displayed. Note to Practitioners—The control of nonlinear MASs with input saturation remains a significant challenge in engineering applications, such as formation of multiple satellite systems, synchronization of robot systems, etc. In practical systems, input saturation can lead to performance degradation if not properly addressed. Meanwhile, considering that actual system states are often unmeasured in these scenarios, further complexity arises. To solve the problem, this paper introduces an adaptive observer-based control protocol with a boundary layer function firstly. However, continuous communication between agents can lead to excessive communication overhead in systems with limited resources. To address this, an observer-based DETC protocol is further developed to reduce the communication load without sacrificing control performance. The proposed control schemes, which account for control inputs constrained by maximum and minimum values, are particularly applicable to scenarios like multiple satellite systems, where utilization rate of communication resources and tracking performance under input saturation are critical. The effectiveness of the control protocols is demonstrated through simulation, showcasing its potential for broader application in similar engineering challenges.

This paper addresses the secure bipartite consensus control problem for multi-agent systems under denial-of-service (DoS) attacks. A class of aperiodic time-sequence-based DoS attacks is considered, and its impact on both undirected and directed network topologies is analyzed. The stability analysis is conducted using a Lyapunov function approach combined with an iterative method. To reduce energy consumption and prevent Zeno behavior, a hybrid dynamic event-triggered mechanism is introduced. This mechanism incorporates an improved dynamic event-triggering condition, which determines when each agent updates its control signal and transmits its currently triggered state to neighboring agents. The proposed approach integrates this mechanism with the developed distributed control protocol and to ensure bipartite consensus even in the presence of DoS attacks. The effectiveness of the method is demonstrated through two simulation examples.

This article investigates the secure control problem for a class of Lipschitz nonlinear descriptor multiagent systems (MASs) with unknown inputs under Denial-of-Service (DoS) attacks. In order to address the presence of unknown state variables and external disturbances in both the state and output equations, a local unknown input observer (UIO) is developed for each follower agent. The proposed UIO is capable of simultaneously estimating the system state, measurement noise and unknown inputs through an interval observer. With regards to DoS attacks, we consider two types: those that maintain connectivity and those that paralyze it by disrupting the structure of the information communication topology graph. By utilizing the proposed UIO, a distributed compensation controller is designed to achieve asymptotic consensus for leader-following MASs under DoS attacks. Additionally, a comprehensive stability analysis of the closed-loop system is provided, taking into account switching systems. Finally, two simulation examples are presented to validate the effectiveness of the proposed UIO-based distributed secure control scheme.

In this article, the human-in-the-loop leader-follower consensus control problem is addressed for multiagent systems (MASs) with unknown external disturbances. A human operator is deployed to monitor the MASs' team by transmitting an execution signal to a nonautonomous leader in response to any hazard detected, with the control input of the leader unknown to all followers. For each follower, a full-order observer, in which the observer error dynamic system decouples the unknown disturbance input, is designed for asymptotic state estimation. Then, an interval observer is constructed for the consensus error dynamic system, where the unknown disturbances and control inputs of its neighbors and its disturbance are treated as unknown inputs (UIs). To process the UIs, a new asymptotic algebraic UI reconstruction (UIR) scheme is proposed based on the interval observer, and one of the significant features of the UIR is the capacity to decouple the control input of the follower. The subsequent human-in-the-loop asymptotic convergence consensus protocol is developed by applying an observer-based distributed control strategy. Finally, the proposed control scheme is validated through two simulation examples.

In this article, a leader-follower asymptotic consensus control strategy is developed for a class of linear multiagent systems (MASs) with unknown external disturbances and measurement noises. First, the preconditions, the minimum phase condition (MPC) and observer matching condition (OMC), are discussed in detail, and an equivalent result under these two preconditions is given. In this way, the corresponding results from Corless and Tu (1998) are improved. Meanwhile, a reduced-order observer is designed for a constructed augmented system to estimate the system states and noises of each agent. Next, with the help of a traditional interval observer, a novel unknown disturbance reconstruction method is developed, and the reconstruction can converge to the unknown disturbance asymptotically and decouple from the control input. The subsequent asymptotic consensus is accomplished by utilizing an observer-based control scheme, with its design satisfying the so-called separation principle. Finally, two simulation examples are given to verify the effectiveness and show the advantages of the proposed methods.

This article addresses the issues of the bipartite time-varying formation (BTVF) control for multiagent systems (MASs) on signed digraphs. All the designs are performed under the assumptions that the leader and followers suffer from external disturbances, the control input signal of the leader is unreachable to any follower, and the state variables of the followers are unmeasurable. To begin with, an unknown input observer (UIO) is designed for each follower using a traditional interval observer to obtain the state estimates. To realize the BTVF tracking, a distributed consensus error dynamic system is constructed. Furthermore, a distributed unknown input reconstruction method is developed to estimate the multiple disturbances in the consensus error system. Then, an event-triggered BTVF control protocol is proposed which allows two antagonistic time-varying formations to be formed, while excluding Zeno behavior. A simulation of a group of wheeled robots is used to demonstrate the performance of the proposed methods.

Affine nonlinear systems are special kinds of nonlinear systems, and they can represent many practical systems. Dealing with affine nonlinear system based on T–S fuzzy model has drawn much attention in the literature recently. In this article, a robust control method is proposed for affine nonlinear system with disturbance based on T–S fuzzy model. First, an optimization T–S fuzzy model is constructed focusing on optimizing the parameters of the weight functions by using differential evolution algorithm. Second, in order to reconstruct the disturbance, an interval observer is designed for the affine nonlinear system, and then a novelty disturbance reconstruction method based on the interval observer is developed. The disturbance reconstruction value can asymptotically approach the actual disturbance value, and furthermore, it decouples the control input. Third, by taking the optimization T–S fuzzy model as design model and by introducing the reconstruction of disturbance into controller, a feedback robust controller with disturbance compensation is designed to stabilize the affine nonlinear system. Finally, a simulation example of the crane model is given and some comparisons are provided to verify the effectiveness and show the advantages of the proposed method.

This article deals with the fault detection and isolation problems for a class of uncertain discrete-time Takagi-Sugeno (T-S) fuzzy system based on the combination of the H-infinity observer and the zonotope method (ZM). For fault detection (FD) purpose, first, a Luenberger-like H-infinity observer, which is robust to disturbance in a sense of H-infinity performance index is designed under the assumption of the feasibility of an linear matrix inequality. Second, the ZM is applied to the H-infinity observer error dynamic system such that the interval state estimation can be calculated iteratively if the system suffers from neither actuator nor sensor faults. Third, a residual is constructed and its interval estimation is also given, and furthermore, based on the residual interval estimation, an FD scheme is developed. After this, we discuss the fault isolation issue in the similar way to alarm the appearance of the exact type fault: actuator or sensor fault. It is the ZM is applied onto the Luenberger-like observer, the fault detection and isolation performances are improved greatly. Finally, a numerical simulation example is given and some comparisons are also made to the existing results to verify the effectiveness and to show the advantages of proposed method.

This paper examines the problem of observer-based sliding mode control designs for a class of descriptor Takagi-Sugeno fuzzy systems with time delay and uncertainties. Specifically, based on the detailed discussions on the existence conditions, a reduced-order robust observer is designed first where the influences of the uncertainties are totally removed. Second, by choosing appropriate coordinate transformations and matrix decompositions, an actual and a virtual sliding mode variables are constructed, and an observer-based sliding mode controller is developed to handle the uncertainties such that the virtual sliding mode surface can be reached and maintained in a finite time, whereas the actual sliding mode variable approaches to zeros asymptotically. And then, we prove that the system asymptotic stability can be guaranteed after the virtual sliding mode surface has been reached or the actual sliding mode variable approached to zero. In addition, the existence conditions for both the observer and the sliding mode controller are given in strict linear matrix inequality forms. Finally, a simulation example is given to demonstrate the effectiveness of the proposed method.

This correspondence paper is concerned with observer design problems for a class of unknown input switched descriptor systems under average dwell time switching signals. The switched descriptor system under consideration is first transformed into a general switched linear system, and then a switched reduced-order observer that can asymptotically estimate the system state without suffering the influence from the unknown inputs is developed. Besides, a high-order sliding mode observer is introduced to obtain the estimations of the output derivatives by using the system measured outputs. On the basis of estimations of the states and output derivatives, an unknown input reconstructing method is provided. Finally, two examples are presented to verify the effectiveness of the proposed approaches.

The problem of actuator fault estimation and fault-tolerant control for a class of uncertain nonlinear systems using Takagi-Sugeno fuzzy models is investigated. A design procedure for nonfragile proportional-integral (PI) observer is proposed to estimate the states of the nonlinear system and reconstruct the abrupt (modeled as step-like faults) and incipient fault signals. Subsequently, a nonfragile fault-tolerant controller is constructed, which is informed by the PI observer. Sufficient conditions of the existence of the PI observer and the fault-tolerant controller are provided in the form of linear matrix inequalities. The proposed fault-tolerant control architecture is tested on two numerical examples.

In this paper, iterative codeword-averaged density evolution (DE) formulas for low-density parity-check (LDPC) codes are developed for joint source-channel asymmetric Slepian-Wolf (ASW) coding of two correlated binary nonuniform memoryless sources with parity based approach. In order to be compatible with the parity based approach, a new ensemble definition of irregular codes being able to distinguish the degree distributions of the edges incident to information variable nodes and the edges incident to parity-checking variable nodes is introduced. Extensive simulations demonstrate the effectiveness of the proposed DE for joint source-channel ASW coding with parity based approach.