Proposed Control Protocol Research Articles

Fixed-Time Rigidity-Based Formation Maneuvering for Nonholonomic Multirobot Systems With Prescribed Performance.

This article presents rigidity-based formation maneuvering for a group of nonholonomic mobile robots subject to limited sensing capability, where the performance bounds are introduced to constrain the distance and angle errors. The time-varying and asymmetric performance constraints can prescribe the transient and steady-state performance of the closed-loop systems, which further specify collision avoidance and connectivity maintenance among neighboring robots and avoid the controller singularity issue. To satisfy the constraint requirements and fixed-time convergence, universal barrier Lyapunov functions are incorporated with control design such that angle errors are fixed-time stable and distance errors can converge to a small neighborhood around zero in fixed time. Under the proposed control protocol, all robots can track the desired time-varying velocity while generating and maintaining the predefined formation defined by a minimally and infinitesimally rigid graph. Simulation and experiment studies are carried out to illustrate the effectiveness of the proposed control protocol.

Fully distributed adaptive asymptotical consensus tracking control of uncertain high‐order nonlinear multi‐agent systems with event‐triggered communication

AbstractIn this article, the distributed adaptive asymptotical consensus tracking control is considered for a class of high‐order nonlinear multi‐agent systems with matched unknown parameters under the event‐triggered communication mechanism. The controllers, adaptive laws and triggering conditions are presented under directed topology with a spanning tree, relieving communication burden among the connected agents since continuous monitoring of in‐neighbors is no longer needed. To handle the cross‐coupling term associated with asymmetric Laplacian matrix and unknown parameters of all agents when the candidate Lyapunov function is defined in terms of local consensus errors, adaptive immersion and invariance control technique is adopted. Adaptive estimators are also designed to estimate the constants related to global information, with which the proposed control scheme is fully distributed. It is shown that all closed‐loop system signals are globally uniformly bounded and all agents can track the reference signal asymptotically while ruling out Zeno behavior though a subset of the agents cannot have direct access to the reference signal information. A numerical example is illustrated to show the effectiveness of the proposed control protocol.

Fixed time containment control of multi-agent system under multi-source mismatched disturbance

Aiming at the cooperative control problem of multi-agent system, the fixed-time containment control of general second-order multi-agent system under mismatched disturbances is studied. Firstly, the problem of multi-agent system fixed-time containment control in ideal state is analyzed, and a distributed control protocol based on variable structure control is proposed. Then, a nonlinear fixed-time disturbance observer is designed, aiming at the mismatched disturbance, and a fixed-time control protocol based on the nonlinear disturbance observer is proposed. Finally, the effectiveness of the proposed control protocol under switching topology and multi-source disturbance is verified by numerical simulation.

Hybrid protocols for leader–follower consensus of multi-agent systems with distributed delays

The primary focus of this paper is to investigate the leader–follower consensus problem of multi-agent systems (MASs) with discrete and distributed delays in complex domains. We propose a new hybrid consensus protocol that incorporates a continuous-time protocol based on the communication topology of follower agents, along with an event-triggered pinning impulsive control (ETPIC) protocol. Using the Lyapunov functional method in complex domains, we establish delay-dependent sufficient conditions for leader–follower consensus of delayed complex-valued MASs. Our results demonstrate that the proposed hybrid protocol can ensure leader–follower consensus even when the size of discrete and distributed delays exceeds the length of intervals between two consecutive triggering instants. Furthermore, we prove that the Zeno phenomenon can be excluded under the proposed control protocol. In particular, as a special case, we derive the leader–follower consensus result for delay-free complex-valued MASs based on a reduced hybrid control protocol. Two numerical examples are presented to validate the effectiveness of the proposed control scheme.

Prescribed-time leader-following consensus and containment control for second-order multiagent systems with only position measurements

The problems of prescribed-time leader-following consensus and prescribed-time containment control for double-integrator multiagent systems (MASs) with only position measurements are investigated in this paper. An observer-based prescribed-time control protocol is proposed, in which the two groups of observers for estimating the consensus errors of each follower both converge to zero within a specified time. Furthermore, the proposed controller only relies on its own observers and does not need to obtain the data from observers embedded in its neighbor nodes. The sufficient conditions for the MASs to achieve the defined prescribed-time consensus and to fulfill the goal of prescribed-time containment control are, respectively, given. The effectiveness of the proposed control protocol is further verified by computer simulations.

Secure group consensus of nonlinear multi‐agent systems with multiple attacks under periodic event‐triggered control

SummaryIn this paper, the secure group consensus is investigated via periodic event‐triggered output feedback control for nonlinear multi‐agent systems subject to multiple attacks, where replay attacks and denial‐of‐service attacks are considered simultaneously. To avoid uninterrupted communication between agents, a novel fixed/switching continuous‐discrete compensator is first put forward by introducing a discrete‐time triggering mechanism in relative output signals. Then, with the help of the gain control technique, a compensator‐based periodic event‐triggered secure control protocol is established, which includes a triggering mechanism and an output feedback controller that both are discrete‐time. Particularly, Zeno behavior and continuous monitoring of the triggering function are naturally avoided compared with existing event‐triggered control protocols. Further, by combining the Lyapunov‐Krasovskii functional approach with switching topology theory, the secure group consensus is successfully achieved under the designed secure control protocol, meanwhile, the negative effect of multiple attacks on the system is compensated. Finally, two simulation examples are applied to verify the effectiveness of proposed control protocols.

Adaptive dynamic event-triggered cluster consensus for second-order delayed MASs with input saturation

In this paper, the cluster consensus problem of second-order multi-agent systems (SOMASs) is investigated in which cooperative-competitive interactions among agents, input time delay, and input saturation are involved simultaneously. A novel adaptive dynamic event-triggered control (ETC) protocol is first designed to realize cluster consensus. Since the constant in static trigger condition is replaced by a dynamic parameter, the new control scheme can reduce the trigger times and save energy consumption. Then, switching topology problem of heterogeneous multi-agent systems (MASs) is also discussed based on the dynamic ETC strategy. Some sufficient conditions for achieving the cluster consensus of SOMASs are proposed by utilizing the Lyapunov stability theory and algebraic graph theory. Especially, to solve the saturation problem, Lagrange mean value theorem is adopted. Moreover, it is also proved that no Zeno behavior occurs under the proposed control protocol. Finally, two examples justify the significance of our theoretical results.

Formation Control of Nonlinear Multi-Agent Systems with Nested Input Saturation

A decentralized robust control protocol addressing leader-follower formation control of unknown nonlinear input-constrained multi-agent systems with adaptive performance specifications is proposed in this paper. The performance characteristics predefined by the user are adaptively modified in order to comply with the actuation constraints of the agents regarding both the magnitude and the rate of the control signals, ensuring closed-loop stability. The proposed control protocol is characterized by easy gain tuning and low structural complexity which simplifies the integration to real systems. A thorough experiment involving a system of multiple quadrotors was conducted to clarify and verify the theoretical findings.

Observer-based impulsive consensus control of nonlinear multi-agent systems under denial-of-service attacks

This paper is concerned with the distributed impulsive consensus problem for nonlinear multi-agent systems (MASs) subject to denial-of-service (DoS) attacks, where the information of agent states is not fully available in the impulsive control design. To reconstruct the states of MASs and guarantee secure average consensus, a novel observer-based impulsive secure control protocol is put forward, and some sufficient conditions are derived by means of linear matrix inequality (LMI) technique and Lyapunov method. It should be pointed out that both the proposed state observer and control protocol adjust the state value abruptly at some discrete instants in an impulsive manner. Moreover, the considered asynchronous DoS attack model can allow jam each channel independently, under which the decay rates of different attack modes are estimated. Finally, two simulation examples, including a practical control system, verify the effectiveness of the proposed consensus algorithm.

Distributed time-varying optimization control protocol for multi-agent systems via finite-time consensus approach

This paper addresses a distributed time-varying optimization problem with inequality constraints based on multi-agent systems over switching communication graphs. To reduce the influence of time-varying inequality constraints, an exact penalty method and smoothing technique are employed. Then, a Hessian-based distributed control protocol is presented to seek the time-varying optimal solution of the distributed time-varying optimization problem by virtue of only local information and interaction. It is shown that all agents not only achieve finite-time consensus but also track the time-varying global optimal target eventually. Compared with the existing distributed optimization protocols, the proposed control protocol is suitable for more general distributed time-varying optimization problems and enjoys high-efficiency convergence. Finally, numerical examples and experiment on moving target tracking of Unmanned Aircraft Vehicle (UAV) are performed to illustrate the effectiveness of the proposed control protocol.

Velocity tracking control of nodes for the nonlinear complex dynamical networks associated with outgoing links subsystem

In general, a complex dynamical network (CDN) can be viewed as a combination of a nodes subsystem(NS) and an outgoing links subsystem (OLS), both of which are coupled with each other. In this paper, a velocity tracking control protocol is used to achieve the velocity tracking control of nodes for the nonlinear CDN with the help of OLS. Firstly, the models of NS and OLS for the CDN are established, and three assumptions for CDN and the definition of the outgoing links vector are given. Further, the control objectives of this article are given. The appropriate control protocol and the scheduled auxiliary targets (SAT) are synthesized to realize the velocity tracking control of nodes for the nonlinear CDN. Finally, a numerical simulation comparison experiment is bench tested to validate the effectiveness of the proposed control protocol and the SAT.

Fixed-time containment control for nonlinear multi-agent systems via dynamic event-triggered mechanism over directed graphs

This paper focus on a dynamic event-triggered mechanism to solve fixed-time containment control problems for nonlinear multi-agent systems (MASs) with uncertain disturbances over directed graphs. An event-triggered algorithm based on dynamic variables is proposed to achieve the fixed-time containment control of MASs, which can effectively reduce the number of event-triggered instants. By modifying the auxiliary variables and reconstructing the dynamic variables, the effect of input time-delays in MASs is successfully eliminated. It is noteworthy that only the auxiliary variables are modified while the structure of the dynamic variables is not changed, which further indicates that the designed dynamic event-triggered algorithm is also suitable for solving multi-agent systems with input time-delays. In addition, the setting time associated with the time-delays is also computed and the Zeno behavior is successfully avoided by computing the minimum time interval between event triggering as non-negative. Finally, simulation results are given to verify the effectiveness of proposed control protocol.

Distributed adaptive time‐varying formation of multi‐UAV systems under undirected graph

AbstractIn this paper, a fully distributed control protocol is presented based on adaptive technology to solve the time‐varying formation problem of multi‐unmanned aerial vehicle (UAV) systems, where the coupling weights between neighbouring UAVs can be adjusted through adaptive method. Firstly, the proposed control protocol eliminates the need for global information on the interaction topology of multi‐UAV systems, the calculation of Laplacian matrix eigenvalues is avoided and reduces the computational complexity of the system. Secondly, an algorithm with two steps is proposed to determine the distributed adaptive control gain matrices, where the feasibility condition of time‐varying formation of multi‐UAV systems is given. Then, the closed‐loop stability of multi‐UAV systems is proved through Lyapunov theory. Finally, numerical simulation is conducted to verify the effectiveness of the theoretical results.

Group consensus of multi‐agent systems with reference states via pinning control

AbstractThis article investigates the group consensus via pinning control for continuous‐time first‐order and second‐order multi‐agent systems (MASs) with reference states. For the group consensus of first‐order MASs, the dependence between the agent's state and the control input is considered. For second‐order MASs, group consensus control without the velocity information of agents is considered. Instead, the virtual velocity estimation controller is designed. Meanwhile, for the designed control protocols, not only under fixed topology, but also under switching topology are considered. It is demonstrated that group consensus could be obtained under the proposed control protocols by using graph theory and stability theory. Finally, a series of numerical examples are provided to verify the control performance of the propounded control protocols.

Fixed-time sliding mode-based consensus of multi-agent systems with mismatched disturbances

This paper investigates the fixed-time consensus of second-order multi-agent systems subject to matched and mismatched disturbances. The derivatives of disturbances are assumed to be bounded. A novel integral sliding mode-based observer is presented by utilizing the super-twisting algorithm to estimate the agent states. The estimations can achieve the convergence to the leader in a fixed time. Furthermore, the corresponding fixed-time controller is developed to make the agents converge to the estimated states. As the estimated states converge to the leader, the agents will track the leader states with the help of estimated states. In addition, the overall convergence of multi-agent systems is non-monotonic due to the disturbances. It is theoretically shown that the proposed control approach can maintain a bounded convergence and get the consensus of multi-agent systems in a fixed time. Some simulations are presented to verify the effectiveness of the proposed control protocol.

Nonfragile observer-based event-triggered fuzzy tracking control for fast-sampling singularly perturbed systems with dual-layer switching mechanism and cyber-attacks

This paper investigates the problem of nonfragile observer-based tracking control for a class of fuzzy fast-sampling singularly perturbed systems (SPSs) with sensor saturation, which subject to event-triggered scheme and random cyber-attacks. The switching topology of the fast-sampling SPSs is dominated by a dual-layer switching mechanism, in this case, the Markov process in the underlying system is nonhomogeneous and its time-varying transition probabilities (TPs) are governed by a persistent dwell-time switching signal. First, in order to avoid asynchronous phenomenon of premise variable between the fuzzy fast-sampling SPSs and the fuzzy controller under network environments, the non-parallel distributed compensation (non-PDC) technique is applied to improve the design flexibility and reduce the conservativeness of the results. Furthermore, a novel fuzzy tracking control design scheme is proposed, in which integrating the fuzzy nonfragile observer and reference model signal into the synthetic design of the tracking controller can be expected to reduce the tracking error. Second, by constructing a well-designed time-delay and mode-dependent Lyapunov function, some sufficient conditions are derived such that the closed-loop system is mean-square exponential stable and with extended dissipative tracking performance. Finally, the effectiveness and applicability of the proposed control protocol are illustrated by two simulation examples.

Impulsive consensus tracking for leader-following multi-AUV system with sampled information

In this paper, impulsive consensus tracking for a leader-following multiple autonomous underwater vehicles (multi-AUV) system with sampled information is studied. Two novel impulsive consensus protocols are proposed to address both the multi-AUV system recovery problem with the static leader and the formation tracking problem with the dynamic leader. It is worth noting that the proposed control protocols do not require continuous information exchange between AUVs. For the static leader case, each AUV only needs to exchange position information with its neighbors at sampling instants. For the dynamic leader case, only partial follower AUVs can obtain position information of the leader AUV at sampling instants. By using the stability theory of impulsive systems and algebraic graph theory, sufficient conditions to guarantee the leader-following consensus of the multi-AUV system are obtained. Furthermore, both the proposed algorithms can save the bandwidth of underwater acoustic communication and improve the robustness of the system. Finally, two numerical simulations are provided to demonstrate the effectiveness of the proposed theoretical analysis.

Sampled-Data Output Feedback Leader-Following Scaled Consensus for Uncertain Nonlinear Multiagent Systems With Communication Delays and Noises

Communication delays and noises are common in practical problems. When they exist in the nonlinear multiagent system, this article addresses the leader-following scaled consensus problem. In the concerned system, nonlinearities can contain uncertainty and essential time-varying characteristic, and the output information is only available at sampling instants. In this article, we propose a class of time-varying gains to design the delay-dependent observer and control protocol, where a newly defined variable is used to cope with unknown noises. Under the output feedback control protocol, followers can asymptotically track the leader by assigned ratios. Different from existing works, the sampling period, communication delays, and noises are not restricted to a fixed upper bound. Two simulation examples are eventually presented to show the effectiveness of the proposed control protocol. Some future works can extend to general nonlinear systems with communication noises, and different time-varying delays.

Periodic Intermittent Adaptive Control with Saturation for Pinning Quasi-Consensus of Heterogeneous Multi-Agent Systems with External Disturbances.

A periodic intermittent adaptive control method with saturation is proposed to pin the quasi-consensus of nonlinear heterogeneous multi-agent systems with external disturbances in this paper. A new periodic intermittent adaptive control protocol with saturation is designed to control the internal coupling between the follower agents and the feedback gain between the leader and the follower. In particular, we use the saturation adaptive law: when the quasi-consensus error converges to a certain range, the adaptive coupling edge weight and the adaptive feedback gain will not be updated. Furthermore, we propose three saturated adaptive pinning control protocols. The quasi-consensus is achieved through its own pinning as long as the agents remain connected to each other. Using the Lyapunov function method and inequality technique, the convergence range of the quasi-consensus error of a heterogeneous multi-agent system is obtained. Finally, the rationality of the proposed control protocol is verified through numerical simulation. Theoretical derivation and simulation results show that the novel proposed periodic intermittent adaptive control method with saturation can successfully be used to achieve the pinning of quasi-consensus of nonlinear heterogeneous multi-agent systems.

Consensus tracking and vibration control for multiple single-link flexible manipulators with input signal quantization

This study examines consensus tracking and vibration control of a multiagent system consisting of multiple single-link flexible manipulators with input signal quantization. The dynamics of each flexible manipulator are described by fourth-order partial differential equations (PDEs). A logarithmic quantizer with changeable parameters is adopted to quantize control inputs, and adaptive laws are designed to compensate for the effect caused by quantization. A distributed adaptive boundary control protocol is proposed based on the PDE model to ensure all manipulators track the desired angular position and eliminate vibrations without knowledge of quantizer parameters. The proposed control protocol is proven to ensure the uniformly bounded stability of the closed-loop system. Simulations are carried out under three cases to illustrate the effectiveness of the designed strategy.