Local Output Information Research Articles

Formation tracking of multiple rectangular agents based on fully distributed observer

In most existing studies, formation tracking algorithms are generally based on state feedback strategies and assume that agents are treated as points. However, in practical scenarios, directly obtaining the state of the target can often be challenging, and agents may have their own shapes. In this paper, we model agents as rectangles, allowing each agent to establish a safety zone to avoid collisions during formation. Based on these rectangular agents, we design formation tracking algorithms for a mobile target using only local output information. Specifically, two layers of control algorithms are designed for each agent. (1) Upper-level algorithm: two types of fully distributed mobile observers are constructed based on only a portion of the target’s output information. This is achieved by applying node-based adaptive coupling gains and edge-based adaptive gains to the consensus-based term in the state estimation algorithm, respectively. (2) Lower-level algorithm: a leader-following formation tracking algorithm is constructed. By cascading these two layers of algorithms, all agents track the target in formation at the same speed as the target. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed theoretical results.

Stealthy attacks against distributed state estimation of stochastic multi-agent systems under composite attack detection mechanisms

This paper is concerned with the security problem of distributed state estimation for stochastic multi-agent systems (MASs) under directed topology. First, in the absence of attacks, an optimal distributed filter is proposed to reconstruct the states of MASs by minimizing the mean square error, which makes full use of the measurable local output information and relative state estimates of agents. Moreover, instead of using a single detection mechanism to measure the stealthiness of attacks, based on the structure of the derived filter, a composite attack detection mechanism capable of simultaneously detecting anomalies in the sensor channels of the agents themselves and the network topologies between different agents is utilized in this paper. Then, from the perspective of potential adversaries, two stealthy attack strategies are established through a joint design of sensor and topology attacks, enabling attackers to fulfill diverse attack objectives while evading the given composite detection mechanisms. Finally, simulation results are provided to verify the availability of the designed filter and attack generation schemes.

Distributed Observer-Based Event-Triggered Load Frequency Control of Multiarea Power Systems Under Cyber Attacks

Information and communication technology tremendously facilitates the operation efficiency and economy of modern power systems in recent years. However, risks such as bandwidth constraints and malicious attacks threaten the secure load frequency control (LFC) of power systems. To mitigate such risks, this paper proposes distributed observer-based event-triggered LFC schemes for multi-area power systems under cyber attacks. Considering the practical situation that only local system output information may be available, distributed observer-based LFC schemes are designed. Meanwhile, to reduce the communication burden, an event-triggered mechanism is adopted to design control laws, where both static and dynamic event-triggered approaches are taken and the dynamic one is proved to be more economical in terms of control cost. Verifiable sufficient conditions are established to guarantee the stability of the closed-loop system in the presence of cyber attacks and the controller gains are explicitly derived. Finally, validation studies on a three-area interconnected power system are carried out to demonstrate the proposed control schemes. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —Load frequency is a crucial index for evaluating the quality of electric energy and thus LFC has brought considerable attention in the area of power systems control. Although many achievements have been made on the LFC of multi-area power systems, the risks such as bandwidth constraints and malicious attacks affect the normal operation of LFC due to the interconnection between different power systems. To deal with these risks, this paper focuses on designing event-triggered LFC to guarantee the stability of the frequency deviation while reducing the communication burden and mitigating cyber attacks. More importantly, the proposed event-triggered LFC is designed based on an observer and can be implemented in a distributed manner, which is relatively practical in real applications. The results presented in this paper aim to provide a helpful reference for stable and secure LFC design of multi-area power systems, such that the corresponding application research can be promoted.

Observer-based bipartite containment control of fractional multi-agent systems with mixed delays

This paper is concerned with observer-based bipartite containment control of nonlinear fractional multi-agent systems (FMASs) with distributed and input delays. First, a follower-based observer is designed by the local output information. On the basis of the state information observed, a delayed control protocol is proposed to achieve bipartite containment control on fixed signed directed network, several feasible conditions on devising observer and delayed controller are obtained with the help of signed graph theory, fractional Razumikhin method and matrix transformation. Secondly, the observer-based bipartite containment control on switching networks is furthered addressed by means of common Lyapunov function approach. Lastly, the effectiveness of presented conclusions is clarified through two simulation examples.

Distributed Output Feedback Funnel Control for Uncertain Nonlinear Multiagent Systems

Adaptive output-feedback consensus with funnel performance is studied for nonlinear uncertain multiagent systems (MASs). The nonlinear MASs contain unknown dynamics and only an output variable can be measured. The other states are not measured directly and are reconstructed via fuzzy state observers. The presence of output feedback makes the proposed design significantly different from the existing literature on control with funnel performance. In particular, appropriate adaptive laws must be defined to handle the presence of uncertain dynamics and local output information from a few neighboring nodes. Interestingly, with a suitable error transformation, it is shown that the proposed control law has a simpler structure than barrier function methods proposed in the literature to handle funnel-like performance. With respect to this point, simulation studies illustrate that the proposed method can dramatically reduce the control effort while satisfying transient and steady-state performance imposed by the funnel.

Decentralised H ∞ filtering of interconnected discrete-time systems

This paper studies the decentralised filtering problem for interconnected discrete-time systems. In the developed decentralised filter scheme, only local output information is available for each local filter. The dynamics of the original system and the dynamics of the proposed filter are expressed as an augmented system. The system matrices of the augmented system consist of matrix inversion terms, which are computationally expensive and even meet numerical stability problems. In order to avoid the matrix inversion computation, this paper derives novel computationally attractive sufficient conditions without inversion terms to guarantee the performance of the augmented system. Then, these conditions are transformed into linear matrix inequalities. The decentralised filter parameters can be obtained by solving linear matrix inequalities. Finally, two simulation examples are given to demonstrate the effectiveness and the advantages of the proposed approach.

Fully Distributed Anti-Windup Consensus Protocols for Linear MASs With Input Saturation: The Case With Directed Topology.

We aim to solve the consensus problem of linear multiagent systems (MASs) with input saturation under directed interaction graphs in this article, where only local output information of neighbors is available for each agent. By introducing the multilevel saturation feedback control approach, a fully distributed adaptive anti-windup protocol is proposed, where a local observer, a distributed observer, as well as an anti-windup observer are separately constructed for each agent to estimate consensus error, achieve consensus for a certain internal state, and provide anti-windup compensator, respectively. A dual protocol is further presented with the distributed observer designed based on the input matrix, which gives a thorough view on the connection between the distributed observer and the anti-windup observer, and provides the opportunity to reduce the order of the controller by designing the integrated distributed anti-windup observer. Then, three types of distributed anti-windup protocols are proposed based on the integrated distributed anti-windup observer, which requires different assumptions. Specifically, the first protocol needs two-hop relay information to generate the local observer to estimate consensus error; the second protocol designs the local observer with absolute output information to estimate the state instead; while the last protocol introduces certain assumption on transmission zero of agents' dynamics to design the unknown input observer to estimate consensus error. All of the protocols are validated by strictly theoretical proof, and are illustrated by performing simulation examples.

Distributed Fault Detection for Linear Time-Varying Multi-Agent Systems With Relative Output Information

This paper investigates the distributed fault detection problem for linear discrete time-varying heterogeneous multi-agent systems under relative output information. Due to the lack of absolute outputs, an augmented model is built by stacking all local relative output information. Then, the fault detection problem consisting of residual-generation and residual-evaluation is handled using the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> filtering framework. The residual-generation problem is actually a minimization problem of an indefinite quadratic form, and the Krein space-Kalman filtering theory is applied, which results in a low computational burden despite the time-varying characteristic. Using the Krein space theory, a necessary and sufficient condition for the minimum is derived, and a residual-generation algorithm is developed. Further, a residual-evaluation mechanism is designed by constructing an evaluation function and detecting faults by comparing it with a threshold. Finally, two illustrative examples are given to demonstrate the effectiveness of the proposed fault detection approach.

On bipartite consensus of linear MASs with input saturation over directed signed graphs: Fully distributed adaptive approach

This paper studies the bipartite consensus problem with input saturation for general linear represents multi-agent systems (MASs) with signed digraphs. Based on relative state information among neighbour agents, distributed adaptive protocols and a compensation observer are proposed, wherein both leaderless bipartite consensus and tracking bipartite consensus problems are addressed. For the case only relative output information is available, observer-based distributed adaptive protocols are also designed, where for each agent, a local observer is given to estimate signed consensus error and a distributed observer is presented to achieve bipartite consensus and generate control input and a compensation observer is designed to handle input saturation. Simulation illustrations are given to explain the feasibility. The control protocols presented in this article depend on only local relative state or output information, without any eigenvalue information of Laplacian matrices associated with signed digraphs, which can be practically used for each agent in a fully distributed way.

Fully Distributed Adaptive NN-Based Consensus Protocol for Nonlinear MASs: An Attack-Free Approach.

This article works on the consensus problem of nonlinear multiagent systems (MASs) under directed graphs. Based on the local output information of neighboring agents, fully distributed adaptive attack-free protocols are designed, where speaking of attack-free protocol, we mean that the observer information transmission via communication channel is forbidden during the whole course. First, the fixed-time observer is introduced to estimate both the local state and the consensus error based on the local output and the relative output measurement among neighboring agents. Then, an observer-based protocol is generated by the consensus error estimation, where the adaptive gains are designed to estimate the unknown neural network constant weight matrix and the upper bound of the residual error vector. Furthermore, the fully distributed adaptive attack-free consensus protocol is proposed by introducing an extra adaptive gain to estimate the communication connectivity information. The proposed protocols are in essence attack-free since no observer information exchange among agents is undertaken during the whole process. Moreover, such a design structure takes the advantage of releasing communication burden.

Observer-Based Bipartite Containment Control for Singular Multi-Agent Systems Over Signed Digraphs

This paper aims at solving the bipartite containment problem for linear singular multi-agent systems (MASs) with multiple dynamic leaders over general signed digraphs, where each leader can be autonomous or dynamically evolving via interactions with its neighboring leaders. To this end, we first establish some properties for the Laplacian matrices of signed digraphs. Then, three distributed observer-based bipartite containment protocols are proposed using different local output information. Multi-step algorithms for constructing the corresponding proposed protocols are also given. It is shown that under the proposed control protocols, bipartite containment can be achieved for any admissible initial states provided that the underlying signed digraph is weakly connected. Compared to the existing related works, the major contribution of present work is that the developed results are applicable for arbitrary weakly connected signed digraphs, no matter whether they are sign-symmetric or sign-asymmetric and whether they are structurally balanced or unbalanced. Two numerical examples are finally given to demonstrate the validity of our results.

Decentralized Adaptive Tracking of Interconnected Nonlinear Systems by Corrupted Output Feedback

A decentralized adaptive resilient output-feedback stabilization strategy is presented for a class of uncertain interconnected nonlinear systems with unknown time-varying measurement sensitivities. In the concerned problem, the main difficulty is to achieve the decentralization of interconnected output nonlinearities unmatched to the control input by using only local output information corrupted by measurement sensitivity, namely the exact output information cannot be used to design the decentralized output-feedback control scheme. Thus, a decentralized output-feedback stabilizer design using only the corrupted output of each subsystem is developed where the adaptive control technique is employed to compensate for the effects of unknown measurement sensitivities. The stability of the resulting decentralized control scheme is analyzed based on the Lyapunov stability theorem.

Velocity and Input Constrained Coordination of Second-Order Multi-Agent Systems With Relative Output Information

In this work, we consider the coordination control of second-order multi-agent systems subject to both velocity and input constraints with only relative output information. First, the leaderless consensus problem is considered where a nonlinear distributed controller is proposed which achieves asymptotic consensus of the agents using only local velocity and relative output information. Then, generalization to the leader-following formation control with known leader's input is studied. For the case of unknown leader's input, a finite-time observer-based controller is proposed using sliding mode control ideas. Finally, the collision avoidance requirement for the leader-following formation control is handled by employing control barrier functions. Necessary modifications to the nominal formation controllers are obtained by properly formulating some quadratic problems and the velocity and input constraints are met during the entire operation. Several simulation examples are provided to illustrate the developed controllers and the effectiveness of the collision avoidance strategy.

Distributed Deception Attack Detection in Platoon-Based Connected Vehicle Systems

This article investigates the distributed sensor deception attack and estimation for a class of platoon-based connected vehicles. In these systems, the information of each vehicle's position and its relative distances with respect to its neighbours plays a crucial role to achieve the desired group performance. When getting deception attacks on such important information, it will result in severe consequences including collision. In order to detect and estimate deception attacks, a longitudinal dynamic model of vehicle platoons with modelling uncertainties, measurement noises and piece-wise constant deception attacks on sensors is first presented. With the consideration of the practical issue that a local vehicle is not able to access to global information, a distributed Kalman filter is proposed to estimate the state information using local output information. Based on the residuals obtained by the distributed Kalman filter, a modified generalized likelihood ratio (GLR) algorithm is proposed to detect and estimate the sensor deception attacks. Finally, simulations with the help of standard Carsim software are provided to verify the effectiveness of the proposed algorithm. Fair comparisons between the proposed method and the standard $\chi ^2$ detector are also presented in order to provide insights for engineering practitioners.

Fully Distributed Low-Complexity Control for Nonlinear Strict-Feedback Multiagent Systems With Unknown Dead-Zone Inputs

In this paper, the distributed control problem of nonlinear strict-feedback multiagent systems is addressed under directed and time-invariant communication graphs. With the utilization of the prescribed performance control methodology, a control algorithm is proposed to ensure predefined bounds of overshoot, convergence rates, and steady-state values of the neighborhood synchronization errors in the presence of unknown dead-zone inputs. The algorithm is fully distributed in the sense that the control input for each agent is independent of any global information of the communication graph and is solely based on local relative output information from its neighborhood set. The approximating structures, e.g., neural networks or fuzzy systems, and the command filters that are typically incorporated to avoid the need for analytical derivatives in the backstepping design are not employed here, resulting in a low-complexity design. Simulation results are included to verify the algorithm.

On Consensus of Multiagent Systems With Input Saturation: Fully Distributed Adaptive Antiwindup Protocol Design Approach

Input saturation is a quite common phenomenon when implementing a controller. Failing to deal with the effect of input saturation may cause failure of the control tasks. This article develops fully distributed adaptive protocol design approaches for consensus of multiagent systems subject to input saturation with local output information. By introducing an extra internal state as the antiwindup compensator for each agent, two types of fully distributed adaptive protocols are presented, namely, edge-based distributed adaptive antiwindup protocol and node-based distributed adaptive antiwindup protocol. For the case with absolute output information, to further reduce the order of the protocols, the local observer as well as the integrated distributed antiwindup observer are designed, based on which a fully distributed edge-based adaptive antiwindup protocol is presented. Such an integrated observer suitable for the node-based protocol is also proposed, and the corresponding fully distributed node-based adaptive antiwindup protocol is then given. The discussions on the difference among the protocols designed in this article are also elaborated. The main feature of the presented protocols is that an extra term is introduced in the controller as the compensator, which plays a fundamental role in effectively tackling input saturation. The protocols given in this article depend only on local output information of each agent, without any use of eigenvalue information of the Laplacian matrix associated with communication topologies, and thus, are all fully distributed.

Distributed Adaptive Observer-Based Control for Output Consensus of Heterogeneous MASs With Input Saturation Constraint

Without assuming that the global connectivity information of the interaction graph is available to any agent, fully distributed saturated controller design for output consensus of heterogeneous multi-agent systems (MASs) under directed leader-follower communication topologies is addressed in this paper. The main difficulty of the problem lies in the coupling of the nonlinearities caused by the input saturation and the adaptive feedback control. To decouple these two types of nonlinearities, a distributed adaptive observer is first designed for each follower to realize asymptotical estimation of leader’s state, where the adaptive coupling gain is embedded to estimate the graph connectivity, and then an extra tracking error observer is introduced to tackle input saturation constraint. The controller is then constructed based upon these two observers, which is fully distributed with only the information of the distributed adaptive observer transmitted between neighboring agents and the local output information of each agent involved. To reduce the order of the controller, an in-depth analysis of the proposed controller is conducted, and the novel controller is designed by removing the tracking error observer and modifying the multi-level saturation control parameters for each follower. Furthermore, to remove the limitation of using absolute output information of each agent, novel controller is proposed with tracking error estimation designed in a distributed manner, which can achieve output consensus tracking for heterogeneous non-introspective MASs with undirected subgraph among followers.

Distributed Time-Varying Formation Control for Linear Swarm Systems With Switching Topologies Using an Adaptive Output-Feedback Approach

Fully distributed time-varying formation (TVF) control problems are addressed in this paper using an adaptive output-feedback approach for general linear swarm systems with fixed and switching topologies. In contrast to the earlier results on formation control problems, the general linear swarm system can achieve the predefined TVF using only local output information and independent of the Laplacian matrix associated with the communication topologies. The implementation cost of calculating the global information and requiring full state information is avoided when achieving the desired TVF. First, a node-based TVF control protocol is constructed via dynamic output feedback for the case with fixed communication topology, where adaptive-based coupling weights are introduced to eliminate the dependence on the global information about the topology. Then an algorithm is presented to determine the gain matrices in the node-based adaptive TVF control protocol, and a feasible formation constraint is provided. The stability of the algorithm is proved based on the Lyapunov theory. Furthermore, under the case of switching communication topologies, an edge-based TVF control protocol is constructed with dynamic output feedback and an adaptive law for adjusting the coupling weights among agents. A sufficient condition is derived using the common Lyapunov theory for general linear swarm systems to achieve the predefined TVF satisfying the feasible formation constraint. Two numerical examples are presented to illustrate the theoretical results.

Decentralized control for linear systems with multiple input channels

In this paper, we consider the decentralized optimal control problem for linear discrete-time systems with multiple input channels.First, under centralized control, the optimal feedback gains are given in terms of two algebraic Riccati equations. A reduced order observeris then designed using only the local input and output information. By selecting an appropriate initial value for the observer,we derive an observer-based decentralized optimal controller where the feedback gain is the same as that obtained in the centralized optimal control problem. Last but not least, we study the optimal control problem ofnon-homogeneous multi-agent systems as an application. A suboptimal decentralized controller is obtained and the difference between the suboptimal cost and the optimal one is given.

Fully Distributed Event-Triggered Protocols for Linear Multiagent Networks

This paper considers the distributed event-triggered consensus problem for general linear multi-agent networks. Both the leaderless and leader-follower consensus problems are considered. Based on the local sampled state or local output information, distributed adaptive event-triggered protocols are designed, which can ensure that consensus of the agents is achieved and the Zeno behavior is excluded by showing that the interval between any two triggering events is lower bounded by a strictly positive value. Compared to the previous related works, our main contribution is that the proposed adaptive event-based protocols are fully distributed and scalable, which do not rely on any global information of the network graph and are independent of the network's scale. In these event-based protocols, continuous communications are not required for either control laws updating or triggering functions monitoring.