Unknown Communication Delays Research Articles

Distributed cooperative control of mechatronic system driving multiple electrohydraulic actuators with uncertain nonlinearity and communication delay

AbstractBeing different from many centralized mechatronic systems, the distributed transmission mechanism has the significant advantage such that realize cooperative task only based on small amount neighbour nodes with low computational complexity. In this study, a distributed cooperative control is proposed for multiple electrohydraulic system (MEHS) to guarantee the follower electrohydraulic node tracking the leader motion, based on the approach of directed spanning tree. Firstly, the MEHS model is constructed as three‐orders isomorphic nonlinear dynamics. Then, a disturbance observer is adopted to estimate uncertain nonlinearities caused by hydraulic parametric uncertainties and unknown external loads in the MEHS. To address unknown communication delays in the network topology of MEHS, a quasi‐synchronous controller is designed via Lyapunov–Krasovskii technique to guarantee that the synchronous errors asymptotically converge to a zero neighbourhood. Finally, the effectiveness of the proposed distributed synchronous control is verified by simulation results under uncertain nonlinearities and different communication delays.

Synchronization for Linear Networked Systems Subject to Input and Communication Delays

This paper investigates the synchronization problem for generic linear multi-agent systems with known or unknown heterogeneous input and communication delays. We propose two protocols that consist of consensus-based internal controller states and decentralized controllers. This kind of distributed dynamic control methodology is able to circumvent the interactive nature of two delays by translating the synchronization problem of agents into the stability of a set of delay differential equations. We examine the synchronization problem for two distinct cases, namely, known delays and unknown delays. When the delays are known, the stability criteria are satisfied by the feasibility of an input-delay-dependent linear matrix inequality and a communication-delay-dependent coupling strength bound. The margin on the communication delay is dependent not only on the network topology but also on the system matrix, which does not have any eigenvalues with positive real parts. We also develop a distributed dynamic control protocol that can handle unknown input and communication delays, and the stability criteria are realized by using the feasibility of a linear matrix inequality and a positive coupling strength. Synchronization is guaranteed even if the unknown communication delays are arbitrarily large but bounded and the upper bound on the heterogeneous input delays is known. The proposed control methodology guarantees that inaccurate measurements of the actual states of a particular agent will not lead to an irretrievable failure of the mission.

H ∞ distributed frequency control with unknown communication delays and parametric uncertainties

<i>H</i> _∞ distributed frequency control with unknown communication delays and parametric uncertainties

Coordinated Time-Varying Low Gain Feedback Control of High-Speed Trains Under a Delayed Communication Network

The coordinated control problem for a multiple high-speed train (HST) system subject to unknown communication delays is systematically investigated in this paper. Taking into consideration the inertial lag of the servo motor, a third-order nonlinear control model is constructed to capture the dynamics of a train in real-world operations. By virtue of the backstepping linearization technique, the coordinated control of trains is formulated as a stabilization problem for a linear multiple-input multiple-output system with an unknown input delay. Distributed control laws with a time-varying low gain parameter are designed, besides solving the stabilization problem, to guarantee a fast convergency rate during the train status adjustment process. Numerical examples are provided to illustrate that the time-varying low gain parameter design achieves better control performance compared with the traditional constant low gain feedback design in terms of the convergency rate and the system overshot, and that the proposed control method is effective in train tracking distance adjustment.

Real-time neural control of all-terrain tracked robots with unknown dynamics and network communication delays

This work focuses on the design of an intelligent controller that is a considerably large challenge for cyber-physical systems. The proposed controller can deal with unknown dynamics, actuator saturation, unknown external and internal disturbances, unknown communication delays and packet losses. Such a controller is designed using a discrete-time approach based on inverse optimal control and a recurrent high-order neural network identifier. The applicability of the proposed scheme is shown through real-time results using a tracked robot platform controlled through a wireless network under different network scenarios.

Regulated State Synchronization of Homogeneous Discrete-Time Multi-Agent Systems via Partial State Coupling in Presence of Unknown Communication Delays

This paper studies regulated state synchronization for homogeneous discrete-time multi-agent systems (MAS) in the presence of unknown nonuniform communication delays. We consider partial state coupling, i.e., agents are coupled through part of their states. A low gain-based protocol is designed which only requires rough knowledge of the communication network, such that the state synchronization for MAS is achieved where the required synchronized trajectory is only given to some of the agents.

Consensus problem in multi-agent systems under delayed information

Abstract This paper studies the consensus problem of first-order multi-agent systems with unknown communication delay. Given unstable agent dynamics and directed network topology, consensus conditions upon two kinds of communication delays are provided. When the relative information is affected by delay, an allowable delay bound for consensus is obtained; if delay influences neighbors’ transmitted information, sufficient consensus condition admitting any large yet bounded delay is acquired. It is observed in particular that when the network topology is undirected, the delay is allowed to be time-varying. Finally, two numerical examples are carried out to demonstrate the effectiveness of the theoretical results.

Rendezvous with connectivity preservation of mobile agents subject to uniform time-delays

This paper investigates the problem of rendezvous with connectivity preservation for a group of mobile agents subject to both unknown input delay and unknown communication delay. We propose a new potential function and design a potential function based distributed control law. To tackle unknown time-delays, we introduce a control gain in the control law and develop an energy functional to characterize the energy of the whole system. By analyzing the energy change, the control gain is designed. It is shown that as long as the communication network is connected at the initial time, the proposed control law can make all agents reach the same location and maintain connectivity of the communication network for all time. Meanwhile, it can accommodate arbitrarily bounded uniform constant input delay and communication delay.

Consensus of linear multi‐agent systems subject to communication delays and switching networks

SummaryIn this paper, the consensus problem for linear multi‐agent systems subject to nonuniform time‐varying communication delays and jointly connected switching networks is investigated. Two cases, known communication delay and unknown communication delay, are considered, respectively. For each case, both distributed dynamic state feedback control law and distributed dynamic output feedback control law are proposed. By establishing some technical lemmas, it is shown that the proposed distributed control laws can solve the consensus problem, respectively. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Consensus for networked multi-agent systems with unknown communication delays

The problem of consensus for linear discrete-time networked multi-agent systems with directed topologies and communication delays is investigated in this paper. The communication delays are assumed to be constant but unknown. A consensus protocol is designed to compensate for the unknown delays based on the networked predictive control scheme. A sufficient condition for the consensus of multi-agent systems is derived. Finally, a numerical example is given to illustrate that the consensus protocol proposed in this paper is effective.

A sliding-mode controller for dual-user teleoperation with unknown constant time delays

SUMMARYIn this paper, a control methodology is proposed for dual-user teleoperation system in the presence of unknown constant communication time delay. To satisfy dual-user system-desired objectives, three impedance characteristics are defined as the desired closed-loop system. In order to satisfy the desired impedance characteristics, a sliding-mode-based impedance controller is applied. The proposed controller affords unknown communication delay, an issue that is disregarded in the previous studies performed on dual-user systems. The nonlinear gain of the controller is achieved independent of time delay caused by communication channels. Therefore, the necessity of measurement or estimation of the time delay is relaxed. In addition, the stability analysis is presented for the closed-loop system using the passivity theory. The validity of the proposed controller scheme is demonstrated via experimental results performed on a dual-user system in the presence of unknown communication delay. In addition, due to lack of availability of forces corresponding to the operators’ hand that are required in the proposed controller, a Kalman Filter-based Force Observer (KFFO) is proposed.

High-order consensus of heterogeneous multi-agent systems with unknown communication delays

This paper studies the high-order consensus problem for heterogeneous multi-agent systems with unknown communication delays. A necessary and sufficient condition is given for the existence of a high-order consensus solution to heterogeneous multi-agent systems. The condition shows that, for systems with diverse communication delays, high-order consensus does not require the self-delay of each agent to be equal to the corresponding communication delay. When the communication delays are unknown, a simple adaptive adjustment algorithm is presented for on-line adjusting self-delays.

Robust Adaptive Coordinated Attitude Control Problem with Unknown Communication Delays and Uncertainties

We address the robust adaptive coordinated attitude control problem (CACP) for formation spacecraft with model and disturbance uncertainties, and with unknown constant time delays existing in the information exchanged channels. Here, spacecraft attitude is described via quaternion, and the local relative attitude is obtained in non-convex space, i.e., on the nonlinear manifold-Lie Group. Unlike in existing designs, where constant delays must be explicit and bounded, our novel laws, by injecting a nonlinear term, solve the CACP with disturbances and unknown/large constant communication delays. To overcome model uncertainties, the adaptive method is adopted. The closed-loop systems are investigated based on the Lyapunov-Krasovskii theory and Barbalat Lemma, and a spacecraft formation is conducted to demonstrate the effectiveness of theoretical results.

Construction of Logically Correct Communication Protocols without Over-Specification

For a communication protocol, it is particularly important to specify exactly the constraints, which must be respected by the participating entities for their succesful cooperation. A method is suggested for construction of logically correct communication protocols without over-specification. The method applies to any system topology and any type of communication channels, under the assumption of network fairness. For illustration, specific construction heuristics are provided for systems with an optional to-pology and reliable, unbounded FIFO channels with unknown communication delays, ranging from zero to any finite amount of time.

Construction of logically correct communication protocols without over-specification

For a communication protocol, it is particularly important to specify exactly the constraints, which must be respected by the participating entities for their succesful cooperation. A method is suggested for construction of logically correct communication protocols without over-specification. The method applies to any system topology and any type of communication channels, under the assumption of network fairness. For illustration, specific construction heuristics are provided for systems with an optional topology and reliable, unbounded FIFO channels with unknown communication delays, ranging from zero to any finite amount of time.