Multiple Time-varying Communication Delays Research Articles

Hierarchical Two-Layer Distributed Control Architecture for Voltage Regulation in Multiple Microgrids in the Presence of Time-Varying Delays

The Multiple Microgrids (MMGs) concept has been identified as a promising solution for the management of large-scale power grids in order to maximize the use of widespread renewable energies sources. However, its deployment in realistic operation scenarios is still an open issue due to the presence of non-ideal and unreliable communication systems that allow each component within the power network to share information about its state. Indeed, due to technological constraints, multiple time-varying communication delays consistently appear during data acquisition and the transmission process and their effects must be considered in the control design phase. To this aim, this paper addresses the voltage regulation control problem for MMGs systems in the presence of time-varying communication delays. To solve this problem, we propose a novel hierarchical two-layer distributed control architecture that accounts for the presence of communication latencies in the information exchange. More specifically, the upper control layer aims at guaranteeing a proper and economical reactive power dispatch among MMGs, while the lower control layer aims at ensuring voltage regulation of all electrical buses within each MG to the desired voltage set-point. By leveraging a proper Driver Generator Nodes Selection Algorithm, we first provide the best choice of generator nodes which, considering the upper layer control goal, speeds up the voltage synchronization process of all the buses within each MG to the voltage set-point computed by the upper-control layer. Then, the lower control layer, on the basis of this desired voltage value, drives the reactive power capability of each smart device within each MG and compensates for possible voltage deviations. Simulation analysis is carried out on the realistic case study of an MMGs system consisting of two identical IEEE 14-bus test systems and the numerical results disclose the effectiveness of the proposed control strategy, as well as its robustness with respect to load fluctuations.

Distributed leader-tracking adaptive control for high-order nonlinear Lipschitz multi-agent systems with multiple time-varying communication delays

This paper addresses the leader-tracking problem of high-order nonlinear Lipschitz agents sharing their state information through a delayed communication network. The multiple delays associated to each communication link are considered as time-varying functions. The problem is solved through a fully distributed adaptive protocol on the basis of a node-based local adaptation method that is independent of any global information and does not require any knowledge or estimation of the nonlinear agent dynamics. The stability of the closed-loop delayed Multi-Agent System (MAS) is proven to leverage the Lyapunov–Krasovskii approach combined with the Barbalat's Lemma. Stability conditions are expressed as a set of feasible Linear Matrix Inequalities (LMIs) derived via the free weighted matrices method. Exemplary numerical simulations confirm the effectiveness of the theoretical results.

Adaptive fuzzy finite-time control for spacecraft formation with communication delays and changing topologies

This paper aims to solve the finite time consensus control problem for spacecraft formation flying (SFF) while accounting for multiple time varying communication delays and changing topologies among SFF members. First, in the presence of model uncertainties and external disturbances, the coupled dynamics of relative position and attitude are derived based on the Lie group SE(3), in which the position and attitude tracking errors with respect to the virtual leader whose trajectory is computed offline are described by exponential coordinates. Then, a nonsingular fast terminal sliding mode (NFTSM) constructed by the exponential coordinates and velocity tracking errors is developed, based on which adaptive fuzzy NFTSM control schemes are proposed to guarantee that the ideal configurations of the SFF members with respect to the virtual leader can be achieved in finite time with high accuracy and all the aforementioned drawbacks can be overcome. The convergence and stability of the closed-loop system are proved theoretically by Lyapunov methods. Finally, numerical simulations are presented to validate the effectiveness and feasibility of the proposed controllers.

Average consensus in multi-agent systems with uncertain topologies and multiple time-varying delays

In this paper, we investigate average consensus problem in continuous-time multi-agent systems with uncertain topologies as well as multiple time-varying communication delays. The network of dynamic agents is directed and both fixed and switching topologies are considered. By using the linear matrix inequality method, we prove that all the nodes in the network can achieve average consensus asymptotically for appropriate delays and uncertainties if the network topology is weakly connected and balanced. Feasible linear matrix inequalities are established to determine the maximal allowable upper bounds of multiple delays. Numerical examples are presented to illustrate the availability of the theoretical results.

Average consensus seeking of high-order continuous-time multi-agent systems with multiple time-varying communication delays

The average consensus problem of high-order multi-agent systems with multiple time-varying communication delays is investigated in this paper. By using the idea of state decomposition, the condition for guaranteeing average consensus is converted into verifying the stability of zero equilibrium of disagreement system. Considering multiple time-varying communication delays, Lyapunov-Krasovskii approach in time-domain is employed to analyze the stability of zero equilibrium. With the help of Free-weighting Matrices (FWM) approach, the tolerant upper bounds on communication delays can be obtained through solving feasible linear matrix inequalities (LMIs). Delay-dependent stability criteria for both strongly-connected fixed and switching topologies are provided in the main results. Further, the conclusion is extended to the case of jointly-connected switching topologies. Numerical examples and simulation results are given to demonstrate the effectiveness and the benefit on reducing conservativeness of the proposed method.

Comments on "A Multichannel IOS Small Gain Theorem for Systems With Multiple Time-Varying Communication Delays

The small-gain condition presented by Polushin may be replaced by a strictly weaker one to obtain essentially the same result. The necessary minor modifications of the proof are given. Using essentially the same arguments, a global version of the result is also presented.

Cooperative Attitude Control of Multiple Rigid Bodies with Multiple Time-Varying Delays and Dynamically Changing Topologies

Cooperative attitude regulation and tracking problems are discussed in the presence of multiple time-varying communication delays and dynamically changing topologies. In the case of cooperative attitude regulation, we propose conditions to guarantee the stability of the closed-loop system when there exist multiple time-varying communication delays. In the case of cooperative attitude tracking, the result of uniformly ultimate boundedness of the closed-loop system is obtained when there exist both multiple time-varying communication delays and dynamically changing topologies. Simulation results are presented to validate the effectiveness of these conclusions.

A Multichannel IOS Small Gain Theorem for Systems With Multiple Time-Varying Communication Delays

A version of the input-to-output stability (IOS) small gain theorem is derived for interconnections where the subsystems communicate asynchronously over multiple channels, and the communication is subject to multiple time-varying possibly unbounded communication delays. It is shown that a ldquomulti-dimensionalrdquo version of the small gain condition guarantees the stability of the interconnection of IOS subsystems under certain mild assumptions imposed on communication process. The fulfillment of these assumptions does not depend on characteristics of the communication channels, but can always be guaranteed by implementation of certain features of the underlying communication protocol. This result is applicable to a wide range of dynamical systems whose parts communicate over networks, such as Internet-based teleoperators.

Projection-Based Force Reflection Algorithm for Stable Bilateral Teleoperation Over Networks

The problem of stable force-reflecting teleoperation is addressed, where the communication between the master and the slave is subject to multiple time-varying, discontinuous, and possibly unbounded communication delays. A new force reflection (FR) algorithm is proposed, which improves the stability of the system without decreasing its transparency. Based on the estimate of human forces provided by the high-gain input observer, the proposed algorithm restricts the reflected force in such a way that it eliminates the motion of the master induced by the FR signal without changing the human perception of the environmental force. It is shown that the proposed FR algorithm allows us to achieve stability of the system for an arbitrarily high FR gain and arbitrarily low damping and stiffness of the master manipulator. The stability analysis is based on the input-to-output stability small-gain theorem for systems with multiple time-varying communication delays.

Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays

In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results.