Fixed Communication Topology Research Articles

Cooperative Adaptive Command Filtered Backstepping Control for EVs to UPS-Microgrid via Virtual Synchronous Generator.

Multiple batteries in uninterruptible power supply (UPS)-microgrid systems based on multiagents composed of multiple electric vehicles (EVs) can encounter state of charge (SoC) consistency problems. To solve this differential expansion and controller saturation problem, an adaptive command filter sliding-mode control strategy based on virtual synchronous generators (VSGs) and considering the power allocation principle is proposed. First, based on directed graph theory, an SoC consistency algorithm and power allocation strategy for multiple EVs were proposed, forming a dc power system with a fixed communication topology. Second, the rotor motion equation of synchronous generator (SG) is introduced into the inverter control algorithm to form the mathematical model of VSG. Third, a low-pass filter (LFP) was introduced in the voltage control process to simulate the excitation attenuation characteristics of the SG. Based on the above, a backstepping control strategy, including a command filter and sliding mode controller is proposed, which improves the operating stability of the system based on the system errors of angle, frequency, and power output. Finally, the UPS-microgrid system based on multiagents is simulated to demonstrate the stability of the system and the effectiveness of the proposed control strategy.

Event-triggered based adjustable containment control scheme design for multi-agent systems

The traditional containment control problem uses a mapping method with a fixed communication topology to generate a set of reference signals for followers, which may lead to a situation where the position of the reference signal cannot be adjusted and causes collisions. Therefore, based on backstepping theory, we propose a novel containment control scheme to address this problem, where the generated reference signals can be adjusted arbitrarily. In particular, it is important to point out that an estimator is designed to guide the follower if the reference signal is not available, so that the collision problem is avoided. In addition, the computational complexity of the controller is also reduced and the communication resources are saved by introducing the command filters and event-triggered mechanism. It is proved that the tracking errors of the closed multi-agent systems are uniformly and ultimately bounded through Lyapunov theory. Finally, experimental simulations verify that the proposed control scheme is reasonable and effective. Furthermore, the proposed scheme provides a more flexible solution for containment control studies, especially for collision avoidance research of multi-agents.

Communication-Topology-preserving Motion Planning: Enabling Static Routing in UAV Networks

Unmanned Aerial Vehicle (UAV) swarm offers extended coverage and is a vital solution for many applications. A key issue in UAV swarm control is to cover all targets while maintaining connectivity among UAVs, referred to as a multi-target coverage problem. With existing dynamic routing protocols, the flying ad hoc network suffers outdated and incorrect route information due to frequent topology changes. This might lead to failures of time-critical tasks. One mitigation solution is to keep the physical topology unchanged, thus maintaining a fixed communication topology and enabling static routing. However, keeping physical topology unchanged may sacrifice the coverage. In this article, we propose to maintain a fixed communication topology among UAVs, which allows certain changes in physical topology, so that to maximize the coverage. We develop a distributed motion planning algorithm for the online multi-target coverage problem with the constraint of keeping communication topology intact. As the communication topology needs to be timely updated when UAVs leave or arrive at the swarm, we further design a topology-management protocol. Experimental results from the ns-3 simulator show that under our algorithms, UAV swarms of different sizes achieve significantly improved delay and loss ratio, efficient coverage, and rapid topology update.

Relative controllability of nonlinear delayed multi-agent systems

Controllability of nonlinear delayed leader–follower multi-agent system with fixed communication topology is introduced. A solution of a semilinear time-delay control system and Gramian matrix for the linear part which has Kronecker delay perturbation of exponential matrix function are given. The assumptions and conditions under which the nonlinear delay multi-agent system can be controlled are determined thanks to control problem into fixed point problem. A comprehensive example to illustrate given theoretical contents is presented.

Nonlinear distributed filtering subject to censoring measurements under dynamic event-triggered communication mechanism: The state-saturated case

This paper studies the nonlinear distributed filtering problem for a class of discrete state-saturated systems with censoring measurements and multiplicative noises under the dynamic event-triggered communication mechanism (DETCM). The censoring measurements, which are characterized by the Tobit type I model, unavoidably arise in the measurement signals resulted from the sudden changes of circumstances or the repairs of components. Meanwhile, for the sake of reducing the communication cost and improving the data transmission efficiency, the DETCM is used to determine when the sensor has an opportunity to transmit the information to its adjacent nodes according to the fixed communication topology. The main purpose of the paper is to design a novel distributed filter under the DETCM for the underlying sensor networks, where a particular upper bound of the filtering error covariance is obtained by means of the mathematical induction approach and the matrix theory. Then, the proposed upper bound can be minimized via designing the suitable filter gain. Further, the boundedness of filtering error dynamics is proved based on some pre-set conditions. Finally, illustrative simulation experiments are provided to illustrate the effectiveness of the presented distributed filtering algorithm.

Constrained Consensus in Nonlinear Multiagent Systems Under Switching Topologies

Regarding constrained consensus in nonlinear systems, most of the currently available results require fixed communication topologies. We investigate constrained consensus without such requirements for a type of strict-feedback system. To approach the discontinuous nature associated with topology switching and output constraints, we tailor a novel dynamic feedback system based on a transformed function to yield a desired output. This auxiliary dynamics enables us to develop a distributed control strategy for each agent utilizing minimal information from neighboring agents, namely, the neighbors’ output information. It is shown that consensus can be reached without constraint transgressions and that the boundedness of all signals in the closed-loop system is preserved. A simulation study validates the efficacy of the proposed strategy.

Distributed MIMO MFAC-based consensus tracking strategy for multiagent systems with fixed and switching topologies

In this research, the MIMO model-free-adaptive-control-based (MFAC-based) consensus tracking scheme for multiagent systems (MASs) has been proposed. The unknown system model of each agent is constructed by the compact form dynamic linearisation (CFDL) technique. The agents can receive the information from their neighbours, and only some agents, not all agents, can obtain the reference trajectory. Firstly, the distributed MIMO MFAC-based consensus tracking strategy for each follower agent with fixed communication topology is proposed. The proof of tracking convergence for this control strategy indicates that each agent can follow the reference trajectory. Then, we prove the MFAC-based consensus tracking scheme can be also applied to the MASs with switching topologies. Compared with prior work, the main features of this paper are that the dynamic models of agents are built only using real-time input/output data, and the MFAC-based consensus strategy can be utilised for MIMO MASs with switching topologies. Finally, two numerical simulations are provided to verify the merits and feasibility of the consensus strategy for MASs with fixed and switching topologies, respectively.

Global Consensus of High-Order Discrete-Time Multi-Agent Systems with Communication Delay and Saturation Constraint.

This article aimed to study the global consensus problem of high-order multi-agent systems with a saturation constraint and communication delay. Among them, all agents are described by discrete-time systems. Firstly, in order to compensate for the communication delay, a networked predictive control method is adopted and a predictive-based control protocol is designed. Secondly, for the neutrally stable agent model, leaderless and leader-following situations are considered and it is proven that, under a fixed communication topology, adopting the prediction-based control protocol makes the multi-agent systems with saturation constraint and communication delay achieve a global consensus. Finally, the results are illustrated via numerical simulation.

Distributed secondary control of islanded AC microgrids considering topology switching and plug-and-play operation

This paper proposes a distributed cooperative secondary voltage and frequency control scheme of a DG based islanded AC microgrid subjected to change in the topology of the microgrid communication network. The proposed control algorithm has been extended to take care of microgrid voltage and frequency profile in case of loss of communication of any DG in the network which facilitates plug-and-play operation of DGs. The centralized control schemes of an islanded microgrid pose multiple challenges in the case of maintaining microgrid voltage and frequency profile during fixed communication topology. The distributed controller gain in the proposed algorithm has been calculated using the linear quadratic regulator (LQR) principle. The adaptivity of the controller has also been introduced to consider the coupling gain dynamics among the DGs. An exhaustive Matlab simulation validates the effectiveness of the proposed distributed adaptive control design of the microgrid.

On Consensus-Optimality Trade-offs in Collaborative Deep Learning.

In distributed machine learning, where agents collaboratively learn from diverse private data sets, there is a fundamental tension between consensus and optimality. In this paper, we build on recent algorithmic progresses in distributed deep learning to explore various consensus-optimality trade-offs over a fixed communication topology. First, we propose the incremental consensus-based distributed stochastic gradient descent (i-CDSGD) algorithm, which involves multiple consensus steps (where each agent communicates information with its neighbors) within each SGD iteration. Second, we propose the generalized consensus-based distributed SGD (g-CDSGD) algorithm that enables us to navigate the full spectrum from complete consensus (all agents agree) to complete disagreement (each agent converges to individual model parameters). We analytically establish convergence of the proposed algorithms for strongly convex and nonconvex objective functions; we also analyze the momentum variants of the algorithms for the strongly convex case. We support our algorithms via numerical experiments, and demonstrate significant improvements over existing methods for collaborative deep learning.

Reliable asynchronous control for delayed multi-agent systems with stochastic faults and switching topologies

The issue of exponential consensus for delayed multi-agent systems (MASs) with stochastic faults and switching topologies is addressed in this work. In contrast with the existing relative works on MASs with a fixed communication topology, the topological graph is governed by an uncertain Markov chain, where the restrictions on transition rates (TRs) of Markov switching topologies are loose, which may be partially known or completely unknown. Moreover, a reliable asynchronous control protocol with the stochastic failure behaviour of the actuator on account of the relative information of neighbouring agents is devised. Relaxation of criterions with respect to the consensus of delayed MASs based on the Lyapunov methodology, Wirtinger's inequality and an improved reciprocally convex combination strategy are derived. An unmanned aerial vehicle (UAV) is presented to demonstrate the superiority and applicability of the proposed method.

Data-Driven Terminal Iterative Learning Consensus for Nonlinear Multiagent Systems With Output Saturation.

This article considers the problem of finite-time consensus for nonlinear multiagent systems (MASs), where the nonlinear dynamics are completely unknown and the output saturation exists. First, the mapping relationship between the output of each agent at the terminal time and the control input is established along the iteration domain. By using the terminal iterative learning control method, two novel distributed data-driven consensus protocols are proposed depending on the input and output saturated data of agents and its neighbors. Then, the convergence conditions independent of agents' dynamics are developed for the MASs with fixed communication topology. It is shown that the proposed data-driven protocol can guarantee the system to achieve two different finite-time consensus objectives. Meanwhile, the design is also extended to the case of switching topologies. Finally, the effectiveness of the data-driven protocol is validated by a simulation example.

Relative controllability of delay multi‐agent systems

SummaryThis article considers the controllability of delayed linear and nonlinear multi‐agent systems, respectively, with leader‐follower architecture and fixed communication topology. For the linear multi‐agent systems, a relative protocol is designed to realize the interactions among agents and explicit solutions of the controlled agreement system are constructed in two cases, respectively, involving two kinds of delayed exponential matrix functions and the properties of the Kronecker product. Further Gramian and rank criteria for relative controllability are established, respectively. For the nonlinear ones, the control problem is transformed into the existence of fixed points which is tackled viaKrasnoselskii's fixed point theorem. Numerical examples of linear and nonlinear systems are given to verify the theoretical results.

Open-loop and closed-loop Dα-type iterative learning control for fractional-order linear multi-agent systems with state-delays

This study focuses on implementing consensus tracking using both open-loop and closed-loop Dα-type iterative learning control (ILC) schemes, for fractional-order multi-agent systems (FOMASs) with state-delays. The desired trajectory is constructed by introducing a virtual leader, and the fixed communication topology is considered and only a subset of followers can access the desired trajectory. For each control scheme, one controller is designed for one agent individually. According to the tracking error between the agent and the virtual leader, and the tracking errors between the agent and neighboring agents during the last iteration (for open-loop scheme) or the current running (for closed-loop scheme), each controller continuously corrects the last control law by a combination of communication weights in the topology to obtain the ideal control law. Through the rigorous analysis, sufficient conditions for both control schemes are established to ensure that all agents can achieve the asymptotically consistent output along the iteration axis within a finite-time interval. Sufficient numerical simulation results demonstrate the effectiveness of the control schemes, and provide some meaningful comparison results.

Distributed guidance-based formation control of marine vehicles under switching topology

Because of the limited and unreliable communication topology in complex marine environment, the formation control of marine vehicles under switching topology is investigated in this paper, whereas the most previous works for marine formation focused on the fixed communication topology. In order to simplify the formation control design, a novel distributed guidance system, rather than the traditional distributed control system, is established based on leader-follower strategy only using a portion of communication links. To address the problem of input saturation of marine vehicle, the model predictive control is therefore employed to design the marine formation controller; furthermore, the predictive mechanism allows model predictive control to prevent the constraint violation in advance, which brings advantages against the large inertia of ship motion. Both formation tracking control and formation regulation control are studied herein. For application of formation tracking control of marine vehicles, i.e., the time-varying reference signal, the formation control can be realized under switching topology with the condition that the communication topology contains a directed spanning tree. For application of formation regulation control of marine vehicles, i.e., the constant reference signal, the formation control can be realized under switching topology with a relative milder condition that the union of communication topology contains a directed spanning tree. Multiple simulations are included to show the effectiveness of the presented distributed guidance-based MPC formation controllers.

Leader-following consensus of discrete-time multi-AUV recovery system with time-varying delay

This paper is concerned with the leader-following consensus of discrete-time multi-AUV recovery systems with time-varying delay. During the recycling process, the mothership is regarded as a leader, and AUVs are regarded as followers. The multi-AUV recovery problem is transformed into the leader-following coordinated control problem. A new leader-following consensus control protocol with time-varying delay for discrete-time multi-AUV recovery systems is proposed by modeling directed fixed communication topology. New stability criteria are established to guarantee the consensus of the multi-AUV recovery system based on suitable Lyapunov-Krosovskii functional and a set of linear matrix inequalities. Therefore, the controller gains are derived. Finally, simulation results are provided to illustrate the effectiveness of theoretical results.

Limited-Budget Formation Control for High-Order Linear Swarm Systems with Fix Topologies

This paper discusses limited-budget time-varying formation design and analysis problems for a high-order linear swarm system with a fixed communication topology. Firstly, the communication topology among agents is modeled as an undirected and connected graph, and a new formation control protocol with an energy integral term is proposed to realize formation control and to guarantee the practical energy assumption is less than the limited energy budget. Then, by the matrix inequality tool, sufficient conditions for limited-budget formation design and analysis are proposed, respectively, which are scalable and checkable since they are independent of the number of agents of a swarm system and can be transformed into linear matrix inequality constraints. Moreover, an explicit expression of the formation center function is given, which contains the formation function part and the cooperative state part and is not associated with the derivatives of the formation functions. Finally, a numerical simulation is shown to demonstrate the effectiveness of theoretical results.

Leader-following consensus of second-order multi-agent systems with time-varying delays and arbitrary weights

Using Lyapunov first method instead of traditional Lyapunov second method, this paper focuses on studying the consensus tracking control problem of multi-agent systems (MASs) with time-varying delays and arbitrary adjacent weights under fixed topology and switching topology, respectively. We first give four equivalent criteria for MASs with fixed communication topology, where the positive stability of matrix [Formula: see text] ( L is the Laplacian matrix of [Formula: see text], B is the leader’s adjacency matrix) not only plays a key role as usual but also becomes an urgent and more complicated problem due to the introduction of negative weights in MASs. Second, for MASs with switching communication topology if the average dwell time of switching topology, the total activation time of stable subsystems and the upper bound of time delay satisfy some conditions, then MASs with all stable subsystems (partially stable subsystems) can achieve consensus tracking. Finally, simulations are given to demonstrate the effectiveness of our theoretical results.

Necessary and Sufficient Conditions for Leader-Following Bipartite Consensus With Measurement Noise

This paper considers leader-following bipartite consensus of single-integrator multiagent systems in the presence of measurement noise. To attenuate the noise, a time-varying consensus gain ${q}$ ( ${t}$ ) is introduced into the stochastic approximation-type protocol. Necessary and sufficient conditions for ensuring a strong mean square leader-following bipartite consensus are given. In particular, in the absence of measurement noise, the convergence speed of error dynamics is dependent on the eigenvalues of Laplacian and the rate of ${\int ^{{t}}_{0}{q}({s})\text {d}{s}}$ approaching infinity. By appropriately choosing ${q}$ ( ${t}$ ), the speed of leader-following bipartite consensus convergence can be improved in a fixed communication topology. It is proven that conditions for the signed digraph to be structurally balanced and having a spanning tree are necessary and sufficient to ensure leader-following bipartite consensus, regardless of measurement noise.

Structural Controllability of a Consensus Network With Multiple Leaders

This paper examines the structural controllability for a group of agents, called followers , connected to each other based on the consensus law under commands of multiple leaders , which are agents with superior capabilities, over a fixed communication topology. It is proved that the graph-theoretic sufficient and necessary condition for the set of followers to be structurally controllable under the leaders’ commands is leader–follower connectivity of the associated graph topology. This shrinks to graph connectivity for the case of solo leader. In the approach, we explicitly put into account the dependence among the entries of the system matrices for a consensus network using the linear parameterization technique.