Bipartite output synchronization of heterogeneous multiagent systems on signed digraphs

This paper studies the bipartite output synchronization problem of general linear heterogeneous multiagent systems on signed digraphs. We first show that, for heterogeneous multiagent systems, the bipartite output synchronization over the structurally balanced signed digraphs and the conventional output synchronization over the associated nonnegative digraphs are equivalent. Then, 3 different control protocols, using full‐state feedback, static output feedback, and dynamic output feedback are designed at each agent to solve the bipartite output synchronization problem based on solutions to the corresponding output regulator equations. Explicit local design procedures are proposed for all 3 control protocols. The compensators employed in these protocols incorporate only one copy of the virtual exosystem's dynamics, regardless of the dimensions of the outputs. This results in lower‐dimensional compensators and controllers and, hence, is more computationally tractable compared to the popular internal model principle‐based control protocols. Numerical simulations over 3 different signed communication digraphs validate the proposed control protocols.     

Controllability of multiagent systems based on path and cycle graphs

This paper studies the controllability of multiagent systems based on path and cycle graphs. For paths or cycles, sufficient and necessary conditions are presented for determining the locations of leaders under which the controllability can be realized. Specifically, the controllability of a path is shown to be determined by a set generated only from its odd factors, and the controllability of a cycle is determined by whether the distance between 2 leaders belongs to a set generated from its even (odd) factors when the number of its nodes is even (odd). For both graphs, the dimension of the controllable subspace is also derived. Moreover, the technique used in the derivation of the above results is further used to get sufficient and necessary conditions for several different types of graphs generated from path and cycle topologies. These types of graphs can be regarded as typical topologies in the study of multiagent controllability, and accordingly the obtained results have meaningful enlightenment for the research in this field.     

Controllability of heterogeneous multi-agent systems under directed and weighted topology

This paper considers the controllability problem for both continuous- and discrete-time linear heterogeneous multi-agent systems with directed and weighted communication topology. First, two kinds of neighbour-based control protocols based on the distributed protocol of first-order and second-order multi-agent systems are proposed, under which it is shown that a heterogeneous multi-agent system is controllable if the underlying communication topology is controllable. Then, under special leader selection, the result shows that the controllability of a heterogeneous multi-agent system is solely decided by its communication topology graph. Furthermore, some necessary and/or sufficient conditions are derived for controllability of communication topology from algebraic and graphical perspectives. Finally, simulation examples are presented to demonstrate the effectiveness of the theoretical results.     

Controllability of discrete‐time multiagent systems with switching topology

The current theoretical investigation on the controllability of switched multiagent systems mainly focuses on fixed connected topology or union graph without nonaccessible nodes. However, for discrete‐time multiagent systems with switching topology, it is still unknown whether the existing results are valid or not under the condition of arbitrary topology. Based on graph distance partitions and Wonham's geometric approach, we provide the lower and upper bounds for the dimension of controllable subspaces of discrete‐time multiagent systems. Unlike the existing results of controllability with switching topology, the proposed results have the advantage of being applicable to multiagent systems with arbitrary graphic topologies, union graph (strongly connected or not), and coupling weights. We also provide 2 algorithms for computing the lower and upper bounds for the dimension of controllable subspaces, respectively. Furthermore, as a remarkable application, we present how the proposed lower bound can be utilized for achieving the targeted controllability if the dimension of the controllable subspace of the switched system satisfies certain conditions.     

Controllability of multi‐agent systems under directed topology

In this paper, the controllability of multi‐agent systems is studied under leader‐follower framework, where the interconnection between agents is directed. The concept of leader‐follower connectedness is first introduced for directed graph to check controllability, and some graph‐theoretic conditions are derived for constructively designed topologies. Then, distance partition and almost equitable partition are employed to quantitatively study the controllable subspaces. Moreover, the relationship between the state invariance of multi‐agent systems and the existence of almost equitable partition is discussed. Copyright © 2017 John Wiley & Sons, Ltd.     

Output consensus for heterogeneous multiagent systems with Markovian switching network topologies

This paper investigates the output consensus problem of heterogeneous continuous‐time multiagent systems under randomly switching communication topologies. The switching mechanism is governed by a time‐homogeneous Markov process, whose states correspond to all possible communication topologies among agents. A novel dynamic consensus controller is proposed. The controller gains are designed based on the information of the expectation graph and the solutions to regulator equations. Furthermore, a necessary and sufficient condition is presented for output consensus of the controlled multiagent system in mean square sense. Finally, a simulation example is provided to corroborate the effectiveness of the proposed controller.     

Target controllability of multiagent systems under fixed and switching topologies

In this article, the target controllability of multiagent systems under fixed and switching topologies is investigated, respectively. In the fixed topology setting, some necessary and/or sufficient algebraic and graph‐theoretic conditions are proposed, and the target controllable subspace is quantitatively studied by virtue of almost equitable graph vertex partitions. In the switching topology setting, based on the concepts of the invariant subspace and the target controllable state set, some necessary and sufficient algebraic conditions are obtained. Moreover, the target controllability is studied from the union graph perspective. The results show that when the union graph of all the possible topologies is target controllable, the multiagent system would be target controllable even if each of its subsystems is not. Numerical simulations are provided finally to verify the effectiveness of the theoretical results.     

Robust consensus of heterogeneous multiagent systems with switching topologies: A time-delay case

The robust leader-following consensus of heterogeneous multiagent systems under switching communication topologies is investigated in this paper. Especially, the input delay is considered in each follower. In order to access the information of leader through time-varying communication, a type of distributed dynamic compensator is proposed for every follower firstly, which get rid of the dependence on the global spectrum information and is proved that it can be viewed as a asymptotic observer of the leader. Then combined with the internal model principle, two types of distributed control law are proposed based on the compensator. By applying the truncated predictor feedback scheme to synthesize the closed-loop systems, it is proved that the consensus can be achieved by both of the control laws despite the existence of the input delay and the plant parameters perturbations. Finally, numerical simulations are illustrated to demonstrate the results.     

Event‐triggered output consensus for heterogeneous multiagent systems with fixed and switching directed topologies

This paper studies the event‐triggered output consensus problem of heterogeneous linear multiagent systems characterized via fixed and switching directed graphs. With proper state‐dependent triggering functions, two new event‐triggered output consensus control schemes are proposed for each agent to achieve consensus. Notably, under the proposed control protocols, continuous communication among agents is not required in both controllers updating and triggering threshold detection, which means being completely continuous communication free. The communication instances are reduced significantly, and the periodic or high‐frequency communication is restrained. It is also ensured that events cannot be triggered infinitely in finite time (ie, the Zeno behavior is elegantly avoided). Meanwhile, the simulation examples are given to illustrate the theoretical analysis.     

Differential graphical games for H∞ control of linear heterogeneous multiagent systems

Differential graphical games have been introduced in the literature to solve state synchronization problem for linear homogeneous agents. When the agents are heterogeneous, the previous notion of graphical games cannot be used anymore and a new definition is required. In this paper, we define a novel concept of differential graphical games for linear heterogeneous agents subject to external unmodeled disturbances, which contain the previously introduced graphical game for homogeneous agents as a special case. Using our new formulation, we can solve both the output regulation and H_∞ output regulation problems. Our graphical game framework yields coupled Hamilton‐Jacobi‐Bellman equations, which are, in general, impossible to solve analytically. Therefore, we propose a new actor‐critic algorithm to solve these coupled equations numerically in real time. Moreover, we find an explicit upper bound for the overall ‐gain of the output synchronization error with respect to disturbance. We demonstrate our developments by a simulation example.     

Output sign‐consensus of heterogeneous multiagent systems over fixed and switching signed graphs

This paper investigates output sign‐consensus of multiagent systems over directed signed graphs. In signed graphs, the sign of each edge stands for either hostile interaction (associated with positive sign) or antagonistic interactions (associated with negative sign) among agents. Agent dynamics are heterogeneous, allowing coexistence of distinct agent dynamics in one group. Heterogeneity in this paper also implies that the states of different agents may have different dimensions, but their outputs should have the same dimension. Distributed control laws are designed for both fixed and switching graph topologies. For fixed topology, the graph is assumed to be eventually positive. For switching topology, the graph needs to be jointly eventually positive, which extends the well‐known concept of joint connectivity by taking dwell time into consideration.     

Input-constrained optimal output synchronization of heterogeneous multiagent systems via observer-based model-free reinforcement learning

This paper presents a new formulation of input-constrained optimal output synchronization problem and proposes an observer-based distributed optimal control protocol for discrete-time heterogeneous multiagent systems with input constraints via model-free reinforcement learning. First, distributed adaptive observers are designed for all agents to estimate the leader's trajectory without requiring its dynamics knowledge. Subsequently, the optimal control input associated with the optimal value function is derived based on the solution to the tracking Hamilton-Jacobi-Bellman equation, which is always difficult to solve analytically. To this end, motivated by reinforcement learning technique, a model-free Q-learning policy iteration algorithm is proposed, and the actor-critic neural network structure is implemented to iteratively find the optimal tracking control input without knowing system dynamics. Moreover, inputs of all agents are constrained in the permitted bounds by inserting a nonquadratic function into the performance function, where input constraints are encoded into the optimization problem. Finally, a numerical simulation example is provided to illustrate the effectiveness of the proposed theoretical results.     

Distributed containment control for nonlinear multiagent systems in pure‐feedback form

In this paper, the problem of distributed containment control for pure‐feedback nonlinear multiagent systems under a directed graph topology is investigated. The dynamics of each agent are molded by high‐order nonaffine pure‐feedback form. Neural networks are employed to identify unknown nonlinear functions, and dynamic surface control technique is used to avoid the problem of explosion of complexity inherent in backstepping design procedure. The Frobenius norm of the ideal neural network weighting matrices is estimated, which is helpful to reduce the number of the adaptive tuning law and alleviate the networked communication burden. The proposed distributed containment controllers guarantee that all signals in the closed‐loop systems are cooperatively semiglobally uniformly ultimately bounded, and the outputs of followers are driven into a convex hull spanned by the multiple dynamic leaders. Finally, the effectiveness of the developed method is demonstrated by simulation examples.     

Fully distributed bipartite output consensus of heterogeneous linear multiagent systems based on event‐triggered transmission mechanism

This study investigates the fully distributed bipartite output consensus issue of heterogeneous linear multiagent systems (HLMASs) based on event‐triggered transmission mechanism. Both the cooperative interaction and the antagonistic interaction between neighbor agents are considered. A fully distributed bipartite compensator consisting of time‐varying coupling gain and dynamic event‐triggered mechanism is first proposed to estimate the leader's states. Different from the existing schemes, the proposed compensator is independent of any global information of the network topology, is capable of achieving intermittent communication between neighbors, and is applicable for the signed communication topology. Then the distributed output feedback control protocol is developed such that the fully distributed bipartite event‐triggered output consensus problem can be achieved. Moreover, we extend the results in HLMASs without external disturbances to HLMASs with disturbances, which is more challenging in three cases (a) the disturbances are not available for measurement, (b) the disturbances suffered by each agent are heterogeneous, and (c) the disturbances are not required to be stable or bounded. It is proven that the proposed controllers fulfill the exclusion of Zeno behavior in two consensus problems. Finally, two examples are provided to illustrate the feasibility of the theoretical results.     

异构多无人机网络化协同控制系统的可控性

研究具有Leader-Follower结构和分布式通信拓扑的异构多无人机网络化分布式协同控制系统的可控性问题. 基于同构网络的受控一致性思想建立了异构多飞行器网络控制系统的动态模型; 并针对该动态模型的不同形式, 基于代数图论和传统的控制理论, 分别得到了异构多无人机网络化协同控制系统的可控性条件, 尤其是可控性与该网络化系统中通信拓扑之间的关系; 然后分析且提出了改善系统可控性的可行性方法. 最后仿真结果验证了本文相关结论的正确性.     

Adaptive mean-square consensus of heterogeneous multiagent systems with stochastic switching topologies

The leader–following consensus of linear heterogeneous multiagent systems is investigated in this paper. To comply with the most practical scenario, the communicating topologies among agents are assumed to switch stochastically and driven by a continuous-time discrete-state Markov process, whose state space corresponds to all the possible topologies. A novel distributed adaptive compensator is designed for the followers to reconstruct the exogenous signals without knowing the Laplacian matrix who is regarded as a global information, and sufficient conditions are given to ensure the compensator converges to the dynamic of the leader asymptotically in the mean square sense. Then, based on the compensator, we solved the consensus problem both by distributed state and measurement output feedback control schemes under output regulation framework, which allow followers to have nonidentical state dimensions. Finally, the theoretical results are demonstrated by a numerical example.     

Regulated state synchronization of homogeneous multiagent systems with partial‐state coupling via low‐gain adaptive protocol

This paper studies regulated state synchronization for continuous‐time homogeneous multiagent systems with weakly unstable agents where the reference trajectory is given by a so‐called exosystem. The agents share part of their state over a communication network. We assume that the communication topology is completely unknown and directed. An algebraic Riccati equation–based low‐gain adaptive nonlinear dynamic protocol design is presented to achieve the regulated state synchronizations. Utilizing the adaptive control, our nonlinear dynamic protocol is universal and does not depend on any information about the communication topology or the number of agents.     

Adaptive‐impulsive consensus of multiagent systems

This paper studies the leader‐following consensus problem of multiagent nonlinear systems with uncertain parameters and control gain error. On the basis of the theory of impulsive differential equations, the adaptive control technique, and the Lyapunov stability theory, some novel adaptive‐impulsive consensus conditions are given to realize the consensus of a class of multiagent nonlinear systems. Compared with the existing investigations on the impulsive consensus of multiagent systems, the proposed impulsive control protocol with uncertain parameters and control gain error is more rigorous and effective in practical systems. Four numerical simulations are verified to confirm the effectiveness of the proposed methods.     

Distributed output‐feedback finite‐time tracking control of nonaffine nonlinear leader‐follower multiagent systems

The distributed output‐feedback tracking control for a class of networked multiagents in nonaffine pure‐feedback form is investigated in this article. By introducing a low‐pass filter and some auxiliary variables, we first transform the nonaffine system into the affine form. Then, the finite‐time observer is designed to estimate the states of the newly derived affine system. By applying the fraction dynamic surface control approach and the neural network‐based approximation technique, the distributed output‐feedback control laws are proposed and it is proved that the tracking errors converge to an arbitrarily small bound around zero in finite time. Finally, some simulation examples are provided to confirm the effectiveness of the developed method.     

Distributed adaptive formation tracking for heterogeneous multiagent systems with multiple nonidentical leaders and without well‐informed follower

This paper studies the time‐varying output formation tracking (OFT) problems for linear heterogeneous multiagent systems with multiple leaders, where both the followers and the leaders can have nonidentical dynamics and dimensions. The existing results on formation tracking with multiple leaders depend on the assumption that each follower is well‐informed or uninformed, where the well‐informed follower has all the leaders as its neighbor. To remove this assumption, a novel OFT approach is presented using a distributed observer scheme. Firstly, based on the local estimation and the interaction with neighboring followers, a fully distributed observer is designed for each follower to estimate the dynamical matrices and the states of multiple leaders without requiring the well‐informed follower assumption. The convergence of the distributed observer is proved by using Lyapunov theory. Then, an adaptive algorithm is proposed to solve the regulator equations in finite time based on the estimation of the leaders' dynamical matrices. Furthermore, the desired time‐varying output formation of each follower is generated by a local active exosystem. A time‐varying OFT protocol is presented using the estimated states of multiple leaders, the online solutions of the regulator equations, and the desired formation vector generated by the local exosystem. It is proved that the outputs of the followers can not only realize the expected formation shape but also track the predefined convex combination of multiple leaders. Finally, a simulation example is given to verify the theoretical results.