This article addresses the problem of identifying disconnected agents in multiagent systems via external estimators. Specifically, we employ external estimators with an appropriately designed decision rule to identify the disconnectedness (i.e., the status of being disconnected) between two arbitrarily chosen agents in formation-control multiagent systems. The design of the decision rule is inspired by the unit-root testing problem of autoregressive time series. To make the best possible decision, a best-effort procedure is also proposed. Then, by introducing the concept of connected components (or just components) in graph theory, and using the methods of consensus analysis and time-series analysis, we develop an analytical framework to show the theoretical performance of the designed decision rule. A particularly important result shown by our analysis is that the miss probability of the decision rule can converge to 0 as the number of data samples increases. Finally, simulation results validate the performance of the decision rule and the best-effort procedure, showing that they can perform well even in small samples.

This article explores a unified distributed cooperative control protocol, which is constructed to solve consensus seeking with desired convergence properties, two nonlinear functions included in the controller are designed to determine the control directions and performances, respectively. Some basic and intrinsic properties of these functions are initially analyzed and refined. By unified framework, we mean that different controller functions can be constructed through some necessary and common properties to achieve desired control requirements. Next, event-triggered and self-triggered control strategies based on finite/fixed-time convergence are explored under the proposed framework with three typical scenarios. Last, numerical simulations are provided to show the validity of the proposed control framework.

In this article, we investigate distributed consensus seeking with multiple convergence performance requirements for single-integrator multiagent systems under undirected graphs. A unified distributed control framework is proposed to ensure consensus or practical consensus as well as performance time requirements, which contains most existing complex protocol schemes as special cases. In the proposed framework, three functions with specific properties in the controller play different roles and can be freely designed to achieve desired convergence performances, which guarantee a high-level scalability for multiple control requirements in addition to convergence time. For highlighting the compatibility and flexibility of the proposed method, four typical scenarios are discussed to reach exponential, finite-time, fixed-time, and appointed-time consensus seeking, respectively. Finally, numerical simulations are carried out to verify the effectiveness of the theoretical analysis.

This work investigates the fixed-time distributed coordination control for multiple Euler-Lagrange systems and, in particular, addresses containment control with stationary/dynamic leaders as well as leaderless synchronization control. For the containment control scenario with stationary leaders, the subgraph associated with followers is directed. When dynamic leaders are involved, the information transfer between neighboring followers is bidirectional, for which a novel distributed estimator is developed. For the leaderless synchronization control scenario, the communication network among agents is unidirectional. Three fixed-time distributed control schemes are designed for the aforementioned three cases by applying the fixed-time stability theory. The convergence of the coordination control objectives can be achieved in a fixed time that does not depend on any initial conditions of agents' states, and the settling times are also explicitly derived. Finally, numerical simulations are presented to demonstrate the feasibility of the developed control strategies.

This article deals with the distributed$\mathcal {H}_{\infty }$robust control problem for linear multiagent systems perturbed by external disturbances and norm-bounded uncertain parameters over the Markovian randomly switching communication topologies. To tackle this problem, the distributed observer-based controller is proposed, which requires the relative information between neighbors and the absolute information of a subset of the nodes, and thus is intrinsically distributed. It is of great interest to see that the distributed$\mathcal {H}_{\infty }$robust control problem governed by such a controller can be converted to the stabilization with$\mathcal {H}_{\infty }$disturbance attenuation problems of some decoupled linear systems, whose dimensions equal those of a single node. Then, the$\mathcal {H}_{\infty }$stochastic robust performance region is defined to indicate the robustness of this controller against the variation of communication topologies. It is theoretically shown that the distributed observer-based controller yields bounded and connected robust performance region. Finally, the theoretical results are verified by conducting numerical simulations and experiments.

In this paper, the state estimation problem is investigated for a class of discrete nonlinear systems via sensor networks. A novel robust distributed extended Kalman filter, which can handle norm-bounded uncertainties in both the system model and its Taylor series expansion, is developed with ensured estimation performance. The filter is distributed in the sense that for each sensor, only its own measurements and its neighbors' information are utilized to optimize the upper bound of the estimation error covariance. Besides, a sufficient condition for the proposed algorithm is derived, which is simple and user-friendly since it depends on the property of the original nonlinear system instead of the estimation error covariance calculated at every step. Finally, the simulation results are presented to demonstrate the effectiveness of the filtering algorithm.

The optimal consensus problem of asynchronous sampling single-integrator and double-integrator multiagent systems is solved by distributed model predictive control (MPC) algorithms proposed in this article. In each predictive horizon, the finite-time linear-quadratic performance is minimized distributively by the control input with consensus state optimization. The MPC technique is then utilized to extend the optimal control sequence to the case of an infinite horizon. Conditions depending only on each agent's weighting scalar and sampling step are derived to guarantee the stability of the closed-loop system. Numerical examples of rendezvous control of multirobot systems illustrate the efficiency of the proposed algorithm.

The minimal real part of all the nonzero eigenvalues of Laplacian matrix, also known as the dominant convergence rate, characterizes the consensus performance of multiagent systems on a directed graph. The effect of adding the second reverse edge to a directed chain graph on the dominant convergence rate is investigated. According to the relative positions of the two reverse edges, three cases are discussed, respectively. It is revealed that the dominant convergence rate of the whole network is determined only by the ranges and the relative positions of the reverse edges. Moreover, the consensus performance will not get better with the new reverse edge being added, and it decreases as the reverse range increases. Finally, the theoretical results are illustrated by some numerical examples.

This article considers the rendezvous problem of a group of heterogeneous second-order agents subject to information transmission delays. A major challenge to construct a fully distributed rendezvous protocol is to deal with these delays, which are assumed to be nonuniform and time-varying. Inspired by the fact that a large enough damping coefficient can improve the robustness of a second-order agent against external disturbance, we overcome the above challenge by studying the impact of the damping coefficient on the rendezvous problem. To theoretically analyze the impact, one type of static rendezvous protocol is first proposed and employed. It is interesting to find that agents can reach rendezvous under the static protocol if the damping coefficient is large enough, even though the duration of the time-delay is uncertain. This fact indicates that a large damping coefficient can make the static protocol be robust to the uncertainty of time-delay, which is consistent with the common sense. Then, we apply this impact to deal with the uncertainty introduced by the nonuniform time-varying information delays. To fully apply this impact, we adopt an adaptive approach to making the damping coefficient automatically adapt with the changes of the time-delay. Hence, two classes of fully distributed and adaptive rendezvous protocols are designed, which do not need the global information of the entire communication graph or the value of these time-delays at all. The difference between two classes of protocols is whether it can realize low-frequency learning or not. Finally, some numerical simulations are performed on multiple robots to illustrate the analytical results.

In this paper, we develop some new event-triggered algorithms for achieving distributed consensus for a multiagent system that guarantees fully Zeno-free triggerings for all the agents. In the proposed framework, each agent updates its control input only at its own triggering instants by using local measurements (i.e., relative states) with respect to neighboring agents, and such local measurements can be done in a local coordinate frame. For all agents, a positive Lpsignal function is embedded in the event detector functions, which aims to avoid the possible comparison of an event error term to a zero threshold that may happen in a zero-crossing scenario. We further propose a Zeno-free self-triggered algorithm to achieve multiagent consensus, which enables discrete-time measurements and thus avoids continuous measurements between the neighboring agents. We also show that the proposed event-based consensus algorithms guarantee less frequent triggered events in a bounded time interval compared to the conventional algorithm without Lpsignals. Simulations and comparisons are provided to validate the performance and effectiveness of the proposed event-based consensus schemes.

This paper investigates an event-based tracking problem of networked second-order systems with unknown inertias and switching networks, where the leader's trajectory is dynamic and is available to only a subset of followers. Besides, the followers have only local interactions. A new class of distributed event-triggered control protocols with and without velocity measurements are designed to guarantee the tracking performance. Furthermore, it is strictly proved that the proposed algorithms guarantee a fully Zeno-free triggering for all the agents. Finally, simulation results are provided to demonstrate the effectiveness of the proposed theoretical results.

This paper considers the consensus control problem of heterogeneous linear multiagent systems. A distributed proportional-integral (PI) protocol is presented to ensure consensus of heterogeneous linear multiagent systems with directed communication graphs. Sufficient conditions for the choice of control parameters are derived. For the case that the agents are subject to the external time-varying but bounded disturbances, the proposed distributed PI protocol can assure uniformly ultimate boundedness of the consensus error. The effectiveness of the results is illustrated both theoretically and numerically.

The problem of distributed formation control for multiple quadrotor aircraft in the form of leader-follower structure is considered in this paper. Based on a nonsmooth backstepping design, a novel consensus formation control algorithm is proposed and utilized. First, for the position control subsystem, based on the linear quadratic regulator optimal design method, a formation control law for multiple quadrotor aircraft is designed such that the positions of all the quadrotor aircraft converge to the desired formation pattern. The designed formation control law for position systems will generate the desired attitude for the attitude control systems. Second, for the attitude control subsystem described by unit quaternion, by employing the technique of finite-time control and switch control, a global bounded finite-time attitude tracking controller is designed such that the desired attitude can be tracked by the multiple quadrotor aircraft in finite time. Finally, numerical example is performed to demonstrate that all quadrotor aircraft converge to the desired formation pattern in the 3-D-space.

This paper presents some necessary and sufficient conditions for the synchronization of second-order interconnected networks, where fixed inner-linked connections with information communication exist. First, a novel derivation of the conditions for a second-order polynomial with complex coefficients to be Hurwitz is provided. Based on this, a sufficient and necessary condition is proposed for the synchronization of the coupled complex network. Next, the design method of the synchronization protocol is constructively given, where the upper and lower bounds of the control gains are obtained through the properties of the polynomial. In addition, we consider some special cases where the second-order model is a double integrator, or general multiagent model without fixed interactions. Finally, the simulation result is given to verify the theoretical analysis.

Over the last decades, distributed output regulation problems have received much consideration due to its extensively applications in real world practices. Traditionally, it is assumed that each node obtains the same signal. However, an important observation is that each agent possesses different measurement due to the observability or configuration of the systems. To solve the output regulation problem in this case, we proposed a cooperative output regulation network, where each agent obtains a part of system output measurement on states of plant and exosystem. Distributed state observers and disturbance observers are designed in order to fuse the observed data. Different from traditional literatures, our design shows that even none of the agents can locally reconstruct the state of exosystem, it is still possible to design a networked system to track the reference signal properly. Conditions that guarantee the existence of parameters are given in the cases, where the network topologies are fixed and time-varying, respectively. The simulation results verify our method very effectively.

This paper studies the distributed containment control problem of multiple rigid bodies with event-triggered controllers. An event-triggered cooperative strategy is proposed based on combinational measurements. In this framework, each agent is triggered only at its own triggering instants, which reduces the frequency of controller updates in practice. It is shown that the triggering time sequence of each agent is Zero-free. Finally, a modified event-triggered condition is designed to avoid continuous combinational measurements between neighboring agents. It is also shown that no agents will exhibit Zeno triggering in this case.

In this paper, the problem of attitude synchronization for flexible spacecraft system with actuator faults is investigated. The spacecraft formation is studied in a leader-following architecture and the reference attitude is represented by a virtual leader. A distributed unit quaternion-based synchronization control law is proposed for flexible spacecraft with loss of actuator effectiveness fault. To damp out the induced oscillations of the spacecraft's flexible appendages, an adaptive parameter is introduced. Numerical simulations are presented to demonstrate the effectiveness of the proposed method.

This paper addresses the distributed consensus tracking problem for a class of multi-agent systems with Lipschitz-type node dynamics in the presence of a single leader. The main contribution in the present work is to solve the consensus tracking problem without the over-idealized assumption that the communication topology among dynamic agents is strongly connected and fixed. A distributed protocol based only on the relative states between neighboring agents is designed. Then, by using tools from nonnegative matrix analysis and switching systems theory, it is theoretically shown that consensus tracking in a closed-loop multi-agent network with a switching directed topology can be achieved if there always exists a directed path from the leader to each follower, with the control parameters suitably selected.

This paper is concerned with reduced-orderinfinfiltering of stochastic systems. Based on linear matrix inequality (LMI) technique, a new design method is proposed for the reduced-order filtering of stochastic linear systems. The method is derived from decomposing the key matrix in LMIs which determines the order of designed filters. Different from the existing methods, the proposed method first minimizes the upper bound of the key matrix and then eliminates its near-zero eigenvalues, which results in a simpler, more direct and reliable design procedure. The method is applicable to both continuous and discrete time stochastic systems. Its effectiveness is illustrated by an example

This paper is concerned with reduced-order H/sub 2/ and H/sub /spl infin// multirate filter bank design. Parameter-dependent Lyapunov function (PDLF) based linear matrix inequality (LMI) conditions are presented for the design of reduced-order synthesis filters. By the introduction of two new slack variables in PDLF, the constraint on the Lyapunov matrix is converted to the constraint on the new slack variables. This renders a less conservative design method for reduced-order multirate filter bank. The effectiveness of the proposed method is illustrated by an example.