Time-varying Communication Delays Research Articles

Adaptive control for position and force tracking of uncertain teleoperation with actuators saturation and asymmetric varying time delays

Abstract This paper presents a new bounded force feedback control law to improve transparency in nonlinear bilateral teleoperation systems in the presence of three problems in practical applications of teleoperation systems such as input saturation, asymmetric time varying communication delays with no restriction on their rates of variation and parametric uncertainties, simultaneously. The proposed controller is a nonlinear-proportional plus nonlinear damping (nP + nD) controller with the addition of a nonlinear adaptive term and nonlinear function of the environment force on the slave side and nonlinear function of the human force and force error on the master side. Using a novel Lyapunov–Krasovskii functional, the asymptotic stability and position and force tracking performance of the teleoperation system are established under specific conditions on the controller parameters, actuator saturation characteristics and maximum allowable time delay. The validity of the theoretical results is corroborated by the simulation results.

Self-Triggered Min–Max DMPC for Asynchronous Multiagent Systems With Communication Delays

This article studies the formation stabilization problem of asynchronous nonlinear multiagent systems (MAS) subject to parametric uncertainties, external disturbances, and bounded time-varying communication delays. A self-triggered min–max distributed model predictive control (DMPC) approach is proposed to address this problem. At triggering instants, each agent solves a local min–max optimization problem based on local system states and predicted states of neighbors, determines its next triggering instant, and broadcasts its predicted state trajectory to the neighbors. As a result, the communication load is greatly alleviated while retaining robustness and comparable control performance compared to periodic DMPC algorithms. In order to handle time-varying delays, a novel consistency constraint is incorporated into each local optimization problem to restrict the deviation between the newest predicted states and previously broadcasted predicted states. Consequently, each agent can utilize previously predicted states of its neighbors to achieve cooperation in the presence of the asynchronous communication and time-varying delays. The proposed algorithm’s recursive feasibility and MAS’s closed-loop stability at triggering instants are proven. Finally, numerical simulations are conducted to verify the theoretical results.

Connectivity Preserving Formation Stabilization in an Obstacle-Cluttered Environment in the Presence of Time-Varying Communication Delays

This technical article addresses the formation stabilization problem for multiagent systems (MASs) composed of dynamical agents moving within an obstacle-cluttered environment and sharing information via nonideal wireless communication networks. A novel distributed cooperative navigation function based control strategy is proposed, which drives the MAS to a desired formation without any collision while counteracting the presence of unavoidable communication impairments originated by the wireless network. By recasting the formation stabilization problem into a consensus one and by combining the Lyapunov stability theory with Halanay’s lemma, uniformly ultimately bounded stability of the whole delayed closed-loop system is proved. In the special case of an obstacle-free environment, our approach guarantees exponential stability of the closed-loop networked system. The stability analysis also provides an estimation of the delay upper bound and allows to evaluate the stability margins with respect to the latencies that can be observed in practical application scenarios. Theoretical derivations are verified through nontrivial simulations.

Exponential bipartite tracking consensus in cooperative-antagonistic nonlinear Multi-Agent Systems with multiple communication time-varying delays

This article deals with the bipartite tracking consensus problem for high-order nonlinear Multi-Agent Systems (MASs) with cooperative–antagonistic agents interacting via a directed non-ideal communication network. For a more realistic interaction scenario, a different time-varying delay is associated to each communication link connecting a couple of agents, whose actual value is determined by the current wireless channel condition. In this context, we propose a novel distributed delayed bipartite tracking consensus control strategy which ensures the exponential stability of the whole networked control system. The theoretical analysis, carried out via Lyapunov theory and Halanay’s Lemma, provides the control gains tuning rule and an estimation of the maximum admissible delay upper bound. Numerical simulations corroborate the theoretical derivations.

Improved model‐free adaptive predictive control‐based cooperative driving control for connected and automated vehicles subject to time‐varying communication delays and packet losses at signal‐free intersections

The cover image is based on the Research Article Improved model-free adaptive predictive control-based cooperative driving control for connected and automated vehicles subject to time-varying communication delays and packet losses at signal-free intersections by Jie Yu et al., https://doi.org/10.1049/itr2.12222.

Robust Distributed Nash Equilibrium Seeking for Games Under Attacks and Communication Delays

In this article, a noncooperative game in which the engaged players are of double integrator-type dynamics, is investigated. The dynamics of the players are considered to be subject to unknown time-varying disturbances and unmodeled terms. Besides, the communication topology among the players suffers from attacks and time-varying communication delays. To find a Nash equilibrium for such games, a distributed robust Nash equilibrium seeking algorithm is proposed. By utilizing average dwell-time and time-ratio constraints to tackle the attacks, the closed-loop system is modeled as a hybrid system with memory. To analyze the stability of the distributed switched algorithm, a Lyapunov functional is constructed, by which we show the uniform global asymptotic stability of the equilibrium. Finally, an example is given to illustrate our results.

Distributed robust secondary control of islanded microgrid with stochastic time-varying delays and external disturbances

In the islanded microgrid (MG) with multiple distributed generation units (DGs), the stochastic time-varying communication delays and external disturbances have a great impact on its operation. In this paper, we propose a distributed secondary robust control to realize the robust stability of voltage and frequency. First, a small-signal model is built for a single DG unit, and then the global closed-loop state-space model for MG is derived. Afterward, a new Lyapunov–Krasovskii functional is introduced to analyze the robust stability of the MG. According to the proposed stability theorem, a controller design method optimizing the robust performance of the MG system is presented. Lastly, we verify the correctness of the robust stability theorem and the validity of the controller design method by simulation.

Distributed Adaptive Fault-Tolerant Control for Heterogeneous Multiagent Systems With Time-Varying Communication Delays

This article considers the distributed adaptive fault-tolerant control problem for heterogeneous linear multiagent systems with actuator faults and nonuniform time-varying communication delays. First, novel distributed switching observers are proposed to estimate the system matrix and the state of the exosystem. The observers allow each agent to share its information with its underlying neighbors only at sampled instants of time, thus making a distinct difference from the existing results that require the exosystem matrix to be accessible to all agents at every continuous instant of time. Second, a sufficient condition is derived such that the observer error systems are exponentially stable under the influence of communication delays among interacting agents. Third, new distributed adaptive fault-tolerant controllers, which promise fewer adaptive parameters, are presented to compensate for the actuator faults. It is shown that the developed controllers are capable to effectively and efficiently solve the cooperative fault-tolerant output regulation problem with reduced computational complexity. Finally, three illustrative examples, including an inverted pendulum system, an electronic double-integrator circuit system, and an AC microgrid system, are presented to show the validity and efficiency of the developed method.

Neurodynamic algorithms for constrained distributed convex optimization over fixed or switching topology with time-varying communication delay

Neurodynamic algorithms for constrained distributed convex optimization over fixed or switching topology with time-varying communication delay

Adaptive neural network control for flexible telerobotic systems with communication constraints

This paper investigates the synchronous control problem for a class of flexible telerobotic systems subject to system uncertainties and communication constraints. In view of the asymmetric time-varying communication delays, an adaptive time-delay estimator is designed to reduce the impacts of delays on the system. Moreover, by combining the neural networks and parameter adaptive method, the uncertainties of system dynamics are estimated and compensated. Based on these efforts, a new adaptive compensation control protocol is proposed. Additionally, input quantization in network control induced chattering phenomenon and unknown parameters is also dealt with by the adaptive compensation method. A useful characteristic of this paper is that the “complexity explosion” problem caused by the backstepping technique is circumvented effectively. Finally, sufficient conditions are derived for the synchronous control of the master-slave flexible telerobotic system under Lyapunov stability theory. A numerical example of flexible-joint robotic system is provided to illustrate the effectiveness of the proposed control schemes.

Event-Triggered Consensus of Multiagent Systems With Time-Varying Communication Delay

In this article, the consensus problem of linear multiagent systems (MASs) is investigated, where an event-triggered mechanism combined with sampler is introduced to rationally utilize the network bandwidth and the communication energy. Different from most existing results on the event-triggered consensus of MASs, a time-varying communication delay (CD) with a more general form is constructed in this article. With the help of a new class of Lyapunov functional and advanced inequalities, some novel criteria for achieving the asymptotic consensus of the considered MASs under different CD cases are obtained. For demonstrating the superiority of the proposed method from the conservatism and the practicability, a compared example and an application of spacecraft formation flying are proposed, respectively.

Consensus in discrete-time one-sided Lipschitz nonlinear multi-agent systems with time-varying communication delay

This paper discusses consensus in discrete-time nonlinear multi-agent systems with time-varying delay in a directed communication topology. Since each agent can obtain information only from its neighbouring agents, for the purpose of analysis, a consensus protocol is proposed that considers the relative position information between the leader and followers and between neighbouring followers under time-varying communication delay. This nonlinear problem is solved by employing nonlinear behaviour based on the one-sided Lipschitz method. By constructing an appropriate Lyapunov-Krasovskii function, the consensus criterion for the leader-following problem is established in terms of the linear matrix inequality (LMI) framework. Furthermore, the solution of gain matrix is addressed by utilizing the cone complementarity linearization (CCL) algorithm. The results of a numerical simulation indicate that this method can be used to effectively solve this problem.

Distributed Double-Layer Control for Coordination of Multiplatoons Approaching Road Restriction in the Presence of IoV Communication Delays

Internet of Vehicle (IoV) has become a hot topic in the last years due to its significant benefits in transportation systems in terms of quality, costs, and traffic management capability. Indeed, accurate and real-time information acquisition and diffusion are required to reach an efficient traffic management system according to the smart city paradigm. In this context, this article provides a novel IoV-based distributed double layer control architecture to address the coordination control problem of connected autonomous vehicles (CAVs) multiple platoons negotiating the access to a road section restriction in the presence of heterogeneous communication time-varying delays. To this aim, leveraging the IoV paradigm and the equivalent virtual formation concept, we propose a novel distributed diffusive longitudinal protocol and a distributed lateral potential-function-based control strategy, where both of them are able to cope with communication delays and ensuring the multiplatoon coordination in finite time, i.e., before accessing the road section restrictions, so to avoid vehicles collisions. The finite-time stability of both the cooperative controllers is analytically proved by exploiting the Lyapunov–Krasovskii theory and the derived delay-dependent stability conditions, expressed as a set of linear matrix inequalities (LMIs), allows the proper tuning of the controllers gains. Numerical analysis confirms the theoretical derivation and discloses the effectiveness and the robustness of the proposed cooperative multiplatoon control in ensuring the safe crossing of the road section restriction in finite time.

Containment Control of Double-Integrator Multi-Agent Systems With Time-Varying Delays

This article mainly considers the containment control problem of multi-agent systems (MASs), where the time-varying communication delays are taken into consideration and the multiple leaders are stationary or dynamic. Specially, when leaders are stationary, the communication delays among agents are nonuniform, which is rarely considered in existing papers. Furthermore, when leaders are dynamic, we derive the sufficient conditions for the case with uniform time-varying communication delays. In both cases, all followers are included into the convex hull spanned by leaders with proposed control protocol, in which we get the sufficient conditions by using Lyapunov-Krasovskii functional. At last, the effectiveness is verified by simulations.

Predictive Consensus for Networked Multi-Agent Systems With Switching Topology, Input Delay and Time-Varying Communication Delays

This brief investigates the consensus for networked delayed multi-agent systems with switching topologies and time-varying communication delays. Novel consensus protocol that uses (pseudo) predictive scheme is proposed to synchronize the states of agents. Sufficient consensus conditions are derived, and the results show that the state consensus can be guaranteed if the graphs contain a joint spanning tree as frequently as the system evolves and no eigenvalues of system matrix exist outside the unit circle. Numerical examples illustrate the theoretic results.

Mean-Square Consensus of Heterogeneous Multi-Agent Systems With Time-Varying Communication Delays and Intermittent Observations

This brief studies the consensus problem for heterogeneous multi-agent systems subject to time-varying communication delays, intermittent observations and system noises. An internal reference model for switching and directed communication topologies is constructed to generate a common signal for all agents. Different from existing literatures that design observer to estimate each agent’s state, the optimal estimator in this brief is derived based on the intermittent observations. A sufficient condition is given for the mean-square consensus of the closed loop control systems. A simulation example is provided to illustrate the effectiveness of the proposed algorithm.

Event-Triggered Zero-Gradient-Sum Distributed Algorithm for Convex Optimization with Time-Varying Communication Delays and Switching Directed Topologies

Nowadays, distributed optimization algorithms are widely used in various complex networks. In order to expand the theory of distributed optimization algorithms in the direction of directed graph, the distributed convex optimization problem with time-varying delays and switching topologies in the case of directed graph topology is studied. The event-triggered communication mechanism is adopted, that is, the communication between agents is determined by the trigger conditions, and the information exchange is carried out only when the conditions are met. Compared with continuous communication, this greatly saves network resources and reduces communication cost. Using Lyapunov-Krasovskii function method and inequality analysis, a new sufficient condition is proposed to ensure that the agent state finally reaches the optimal state. The upper bound of the maximum allowable delay is given. In addition, Zeno behavior will be proved not to exist during the operation of the algorithm. Finally, a simulation example is given to illustrate the correctness of the results in this paper.

Towards Cyber–Physical Systems Robust to Communication Delays: A Differential Game Approach

Collaboration between interconnected cyber-physical systems is becoming increasingly pervasive. Time-delays in communication channels between such systems are known to induce catastrophic failure modes, like high frequency oscillations in robotic manipulators in bilateral teleoperation or string instability in platoons of autonomous vehicles. This paper considers nonlinear time-delay systems representing coupled robotic agents, and proposes controllers that are robust to time-varying communication delays. We introduce approximations that allow the delays to be considered as implicit control inputs themselves, and formulate the problem as a zero-sum differential game between the stabilizing controllers and the delays acting adversarially. The ensuing optimal control law is finally compared to known results from Lyapunov-Krasovskii based approaches via numerical experiments.

Adaptive LFC Incorporating Modified Virtual Rotor to Regulate Frequency and Tie-Line Power Flow in Multi-Area Microgrids

This research investigates a new coordination strategy for both isolated single-area and interconnected multi-area microgrids (MGs) using a modified virtual rotor-based derivative technique supported with Jaya optimizer based on balloon effect modulation (BE). Accordingly, the main concept of BE is to assist the classic Jaya to be more sensitive and trackable in the event of disturbances, as well as to provide optimum integral gain value on the secondary frequency controller adaptively for both suggested MGs. The proposed modified virtual rotor mechanism is consisting of virtual inertia and virtual damping that are added as a tertiary controller within proposed MGs considering full participation of the inverter-based energy storage systems. The proposed virtual rotor mechanism is consisting of virtual inertia and virtual damping that are added as a tertiary controller within proposed MGs to emulate the reduction in system inertia and the enhanced damping properties. Several nonlinearities were proposed in this work such as a dead band of governor, generation rate constraints, and communication time-delay are considered within the dynamic model of the suggested MGs. In addition, the proposed design of multi-area MGs takes the interval time-varying communication delays into account for stability conditions. In this study, A comparative study using unimodal (i.e., Sphere) and multimodal (i.e., Rastrigin) benchmark test functions are conducted to validate the proposed direct adaptive Jaya-based BE. Furthermore, Wilcoxon’s rank-signed non-parametric statistical test using a pairwise comparison was performed at a 5 % risk level to judge whether the proposed algorithm output varies from those of the other algorithms in a statistically significant manner. Thence, the superiority and effectiveness of the proposed method have also been verified against a variety of other metaheuristics optimization techniques, including classic electro-search, particle swarm, multi-objective seagull, and Jaya optimizers. In addition, an operative performance is assessed against the conventional integral controller, coefficient diagram method, and classic Jaya with/without virtual inertia. The final findings emphasize the superiority of the proposed direct adaptive Jaya-based BE supported by a modified virtual rotor and state better performance and stability compared to existing controllers.

Impulsive average-consensus of multi-agent systems with time-delays

In this paper, the impulsive average-consensus problem of first-order multi-agent systems with dynamically changing topologies is investigated. Continuous-time dynamics and impulsive protocols are both subjected to effects from nonuniform time-varying communication delays. By utilizing Razumikhin techniques and time-varying Lyapunov function method, some impulse-delay-dependent sufficient criteria for the average-consensus of multi-agent systems are derived. In addition, the discrete-time connection digraph is designed in terms of linear matrix inequalities for given impulsive sequences and some programming skills are used to make the discrete-time topology meet the needs of the actual environment. Numerical simulations are given to illustrate the effectiveness and validity of the theoretical results.