Bounded Communication Delays Research Articles

Privacy-preserving distributed frequency control for AC microgrids with constrained communication

Distributed control of AC microgrids is one of the most popular methods in the islanded operation mode. Whereas, most of the existing studies either do not consider the potential threat of privacy security or rely on the assumption of ideal communication networks. To this end, this paper presents a novel privacy-preserving distributed secondary frequency control strategy for the privacy protection problem of an islanded AC microgrid with constrained communication. The key contributions of this paper are threefold. (1) Different from the existing privacy-preserving approaches used in AC microgrids, a time-varying function is introduced to mask interactive information such that the frequency cannot be reconstructed by malicious attackers. (2) An event-triggered communication scheme is employed to cope with the constrained communication environment. (3) A privacy-preserving distributed event-triggered control strategy with communication delay is developed such that the frequency restoration and active power sharing of the microgrid are guaranteed. Moreover, the maximum communication delay that the proposed control can withstand is analyzed. Simulation results show the properties of the privacy preservation, the decrease of communication load, and the bounded communication delay allowed in the proposed control strategy.

Primal-Dual Fixed Point Algorithms Based on Adapted Metric for Distributed Optimization with Bounded Communication Delays

Primal-Dual Fixed Point Algorithms Based on Adapted Metric for Distributed Optimization with Bounded Communication Delays

Linear Convergence of distributed estimation with constraints and communication delays

Motivated by the multi-sensor estimation problem, we consider a distributed constraint parameter estimation problem on a directed graph. Our goal is to design a fast distributed algorithm to handle constraint parameter estimation problems, especially considering the communication delays when sensors interact on a directed graph. Based on the gradient-tracking algorithm and indirect projection method, the Projected Distributed Parameter Estimation Algorithm (PDPEA) is proposed, which can deal with the closed convex set constraint and use the historical information stored by the sensors to achieve fast and accurate mean gradient estimation. The analysis shows that the PDPEA converges to a global and consensual minimizer even under the influence of measurement noise, arbitrarily bounded communication delays, and directed information topologies. Under the assumption that the local cost function is strongly convex and smooth, we show that the algorithm converges at a linear rate for an appropriate choice of stepsize. Lastly, we demonstrate the effectiveness of the proposed algorithm by setting up a multi-sensor parameter estimation network.

Accurate consensus-based distributed secondary control with tolerance of communication delays for DC microgrids

Distributed secondary control is widely used in DC microgrids (MGs), which can achieve average voltage recovery and accurate power/current sharing among the distributed generators (DGs). In the distributed control architecture, a consensus-based average observer is usually desired to estimate the global average of the output voltage. However, the inevitable communication delay between DGs will cause the output average voltage to deviate from the rated. To tackle this problem, a novel dynamic average consensus observer based on bias compensation has been proposed in this paper, which can accurately converge to the average of the variables being tracked with tolerance of the bounded communication delay while getting rid of the harsh requirement for identical initial value of conventional distributed observer. Based on it, the proposed distributed secondary controller can ensure that the average output voltage converges to the rated without steady-state deviation and that the output currents are proportionally shared accurately. Instead of the conventional voltage and current dual secondary controller, the proposed secondary controller estimates the average of the voltage-current coupling variables and achieves the average voltage recovery and accurate current sharing simultaneously. Moreover, the communication delay margin is determined quantitatively. Finally, the performance of the proposed controller and the efficacy of the calculated communication delay margin is verified by real-time hardware-in-loop (HIL) tests.

Delay Robustness of Consensus Algorithms: Continuous-Time Theory

Consensus among autonomous agents is a key problem in multi-agent control. In this paper, we consider averaging consensus policies over time-varying graphs in presence of unknown but bounded communication delays. It is known that consensus is established (no matter how large the delays are) if the graph is periodically, or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">uniformly</i> quasi-strongly connected (UQSC). The UQSC condition is often believed to be the weakest sufficient condition under which consensus can be proved. We show that the UQSC condition can actually be substantially relaxed and replaced by a condition that we call <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">aperiodic</i> quasi-strong connectivity (AQSC), which, in some sense, proves to be very close to the necessary condition (the so-called integral connectivity). Under the assumption of reciprocity of interactions (e.g., for undirected or type-symmetric graphs), a necessary and sufficient condition for consensus in presence of bounded communication delays is established; the relevant results have been previously proved only in the undelayed case.

Consensus robustness of multi-agent systems against heterogeneous asymmetric input saturations and asynchronous time-varying communication delays

This paper investigates the combined effect of input saturations and communication delays on the multi-agent consensus over a switching topology of weak connectivity. The input saturations are in a general form such that the saturation level of each agent is asymmetric and those of distinct agents are heterogeneous. Besides, the communication delays are time-varying and those in different channels are asynchronous. Both continuous- and discrete-time multi-agent systems are studied. For both the multi-agent systems over a switching digraph of uniform joint strong connectivity, it is demonstrated that the conventional distributed protocols, despite the simultaneous existence of the input saturations and communication delays, still guarantee the consensus results. It turns out that the consensus results are of great robustness against arbitrary heterogeneous asymmetric input saturations and arbitrary bounded communication delays. Simulations are carried out to verify this finding.

Formation Coordination Control of Leaderless Multi-AUV System with Double Independent Communication Topology and Nonconvex Control Input Constraints

In this paper, the formation coordination control of discrete-time distributed leaderless multiple autonomous underwater vehicle (AUV) system with double independent position–velocity communication topology and control inputs on a nonconvex set is studied. Firstly, the problem of formation coordination control of multi-AUV system is transformed into the problem of formation consensus of multi-AUV system, and the consistent state of leaderless multi-AUV system formation was defined. Secondly, considering the existence of bounded communication delay and nonconvex control input constraints for multi-AUV system formation under weak communication conditions, a formation consistent constraint controller algorithm for discrete-time leaderless multi-AUV system with double independent communication topology is proposed by introducing constraint operators. By using the properties of graph theory, random matrix and SIA matrix, and selecting appropriate controller parameters, the multi-AUV system formation can reach the defined consensus state. Furthermore, the unbounded communication delay of multi-AUV system formation is studied. Finally, the simulation results show that the proposed controller constraint algorithm is effective.

Distributed Localization of Multiagent Systems With Imperfect Channels Based on Iterative Learning

The real-time localization problem for a class of multiagent systems with imperfect channels under directed graphs is investigated in this article. A successive distributed localization estimation algorithm based on iterative learning is proposed to solve the localization problem of the agent with bounded communication delays. The barycentric coordinates are used to represent the relative position between agents. An estimator is proposed to inspect whether the received data packet is the latest through the iteration stamp on the packet. Meanwhile, an intermittent distributed localization algorithm is devised to handle with the random data loss of agents in real-time localization problem. The relationship between the convergence rate and the probability of the data loss is given in the sense of mathematical expectations. Both numerical simulation and Qbot-2e robot experiment are provided to verify the effectiveness and the feasibility of the aforementioned methods.

Synchronous and asynchronous resilient impulsive control for group consensus of second-order multi-agent systems with communication delays

This paper studies the resilient group consensus of continuous-time second-order multi-agent systems (MASs) with malicious agents. Adopting the idea that each normal agent ignores the most extreme values from neighbors, synchronous resilient impulsive algorithm based on sampled data is proposed for normal agents with bounded communication delays to achieve group consensus. Meanwhile, asynchronous resilient impulsive algorithm is also proposed for MASs where each agent has its own time clock. Sufficient topological conditions are obtained for solving resilient group consensus under synchronous and asynchronous settings, respectively. Numerical examples are provided to illustrate the effectiveness of the theoretical results.

Accurate Distributed Secondary Control for DC Microgrids Considering Communication Delays: A Surplus Consensus-Based Approach

The state-of-the-art dynamic consensus-based microgrid (MG) secondary controls suffer from the communication delay effect. Specifically, the system could not converge to the desired operating points with time-delayed communications. Such deviations are hard to detect in a decentralized manner and could destabilize the system. This paper proposes an accurate distributed secondary controller for DC MGs based on the surplus consensus algorithm. The proposed controller achieves accurate proportional power sharing and average voltage regulation among distributed generators (DGs) with the presence of variable and bounded communication delays. A surplus consensus-based observer is developed. The developed observer is proved robust against variable and bounded communication delays; it tracks the average of a group of dynamic states with zero steady-state deviations, which cannot be done using the conventional dynamic consensus-based observer. The convergence speed of the developed observer is analyzed and a parameter design procedure is presented. Moreover, the delay-dependent stability analysis of DC MG operation with the proposed secondary controller is derived. The marginal delay that leads the system to instability is calculated. At last, the performance of the proposed secondary controller and the developed stability analysis are validated under various scenarios using MATLAB/Simulink.

Renaissance: A self-stabilizing distributed SDN control plane using in-band communications

By introducing programmability, automated verification, and innovative debugging tools, Software-Defined Networks (SDNs) are poised to meet the increasingly stringent dependability requirements of today's communication networks. However, the design of fault-tolerant SDNs remains an open challenge. This paper considers the design of dependable SDNs through the lenses of self-stabilization—a very strong notion of fault-tolerance. In particular, we develop algorithms for an in-band and distributed control plane for SDNs, called Renaissance, which tolerate a wide range of failures. Our self-stabilizing algorithms ensure that after the occurrence of arbitrary failures, (i) every non-faulty SDN controller can reach any switch (or another controller) within a bounded communication delay (in the presence of a bounded number of failures) and (ii) every switch is managed by a controller. We evaluate Renaissance through a rigorous worst-case analysis as well as a prototype implementation (based on OVS and Floodlight, and Mininet).

Primal-dual algorithms for multi-agent structured optimization over message-passing architectures with bounded communication delays

We consider algorithms for solving structured convex optimization problems over a network of agents with communication delays. It is assumed that each agent performs its local updates using possibly outdated information from its neighbours under the assumption that the delay with respect to each neighbour is bounded but otherwise arbitrary. The private objective of each agent is represented by the sum of two possibly nonsmooth functions one of which is composed with a linear mapping. The global optimization problem is the aggregate of local cost functions and a common Lipschitz-differentiable function. When the coupling between agents is represented only through the common function, the V\\~u-Condat primal-dual algorithm is studied. In the case when the linear maps introduce additional coupling between agents a new algorithm is developed. Moreover, a randomized variant of this algorithm is presented that allows the agents to wake up at random and independently from one another. The convergence of the proposed algorithms is established under strong convexity assumptions.

Rotating consensus for double-integrator multi-agent systems with communication delay

In this paper, the rotating consensus problem for the multi-agent systems of double-integrator dynamic is mainly considered with and without communication delay. A fully distributed control strategy is given on the more general complex plane. For the case without communication delay, we design a distributed control protocol with the help of local relative information and obtain the sufficient and necessary condition with the lower bounded control parameter for the directed communication topology. Furthermore, with taking communication delay into consideration, the sufficient and necessary condition with the upper bounded communication delay is obtained with the help of frequency domain analysis method. Compared with some existing results, the communication topology considered is a more general directed graph. Finally, some simulation examples are presented to clarify the correctness of our results.

Network-based gain-scheduled control for preview path tracking of autonomous electric vehicles subject to communication delays

The preview path tracking problem of autonomous electric vehicles with event-triggered transmission and bounded communication delays is addressed using polytope modelling and asynchronous gain-scheduled control methods. By finding a polytope with as few vertices as possible to wrap the curve composed of all time-varying parameters, a new polytope modelling method is proposed to describe the vehicle lateral dynamics, which can not only reduce the modelling complexity greatly but also keep the modelling accuracy. Based on the polytope system model, a network-based gain-scheduled controller that operates asynchronously with the polytope system is constructed, where the scheduling parameters are driven by transmitted longitudinal velocity. By computing the deviation bounds of scheduling parameters and utilising the deviation-bound-dependent method, an asynchronous gain-scheduled control design method is presented. The feasibility and advantages of the proposed methods are shown by numerical verification.

Supervisory Control of Networked Discrete Event Systems With Timing Structure

In this article, we study the supervisory control problem of networked discrete event systems with timing structure assuming bounded communication delays and intermittent loss of observations. The communication between the plant and the supervisor is through a network that can have several channels, and so communication delays may change the order of event observations by the supervisor. We assume a priori knowledge of the minimal activation time of the plant transitions and the maximum communication delays, and propose an equivalent untimed model that takes into account all possible observation delays and also loss of observations. Based on this model, we formulate a networked supervisory control problem and show that it can be converted into an equivalent range control problem. We also address implementation, and, to this end, we present a representation for networked supervisors that is able to deal with possible loss of synchronization between event occurrence and its observation.

Networked opacity for finite state machine with bounded communication delays

Networked finite state machines consider the delay factor in real-time communication networks, and the security has become an important research topic in cyber-physical systems (CPSs). In this brief paper, we explore the networked opacity of finite state machine with bounded communication delays. Firstly, the networked opacity is proposed from the perspective of security state reachability, and by use of the Boolean matrix semi-tensor product (STP), we introduce the reachability matrix with respect to all feasible events to give the current dynamics with bounded communication delays. Subsequently, based on the algebraic equation, we continue to discuss the corresponding current estimate of possible reachable states, which can be calculated by a matrix approach. Then, a more simple and effective verification criterion of networked opacity is derived by some matrix manipulations. Finally, a typical example is provided to validate the impact of communication delay on the opacity of CPSs, and our results contribute to deeply understanding the information security in the area of CPSs.

Consensus of discrete-time multi-agent systems with multiplicative uncertainties and delays

This paper studies the consensus problem of discrete-time single-integrator multi-agent systems with multiplicative uncertainties and bounded communication delays in switching networks. Some sufficient conditions for non-stochastic consensus are obtained by adopting the constant-gain protocol. For the case that the uncertainty is exponentially decaying (i.e. is with ), it is proved for any bounded delays, the consensus can be achieved if the switching topology is uniformly rooted. For the case that the uncertainty is polynomially decaying (i.e. is with ), under a precondition that the system state is bounded, a similar conclusion is also obtained. The convergence rate of the consensus protocol is quantified in terms of the decay rate of uncertainties. Simulation results are given to verify the correctness of the conclusion.

Model predictive position tracking control for motion system with random communication delay

This study focuses on position tracking control for the networked predictive motion control system with random communication delay. First, the output feedback controller is designed by networked predictive control law to actively compensate the time delay induced by the random channels of the motion control system. A closed-loop model is established for the networked predictive motion control system with random bounded communication delay, modelled by a Markov chain. Then, the sufficient conditions of stability for the networked predictive motion control system are provided, by constructing the Lyapunov–Krasovskii functional, followed by the theoretical proof. Furthermore, the output feedback controller is constructed and the linear matrix inequality method is applied to obtain the designed controller gain. Last, the simulation and experimental results are presented to prove the effectiveness of the proposed method.

Multiagent Containment Control With Nonconvex States Constraints, Nonuniform Time Delays, and Switching Directed Networks.

This brief studies the constrained containment control problem of continuous-time multiagent systems with nonconvex states constraints, nonuniform time delays, and switching directed networks. A distributed containment control algorithm consisting of nonlinear projection, nonlinear constraints, and communication delays is proposed. Based on the model transformation technique, convex analysis method, and the Lyapunov function, we prove that all agents finally converge into the convex hull formed by the given stationary points with arbitrarily bounded communication delays and arbitrarily switching networks as long as each agent jointly has at least one path from the given points to itself. Finally, a numerical example is included to show the effectiveness of theoretical results.

Sampled‐data based resilient consensus of heterogeneous multiagent systems

SummaryThis article studies consensus of a group of heterogeneous agents with first‐order and second‐order integrator dynamics in presence of malicious agents. We employ the algorithm where each normal agent ignores large and small relative state values of its neighbors to mitigate the effects of malicious agents. Assuming that the maximum number of malicious agents in the neighborhood of each agent is known, sufficient topological condition is obtained to guarantee resilient consensus in directed networks. The result is further extended to heterogeneous multiagent systems with bounded communication delays. Moreover, impulsive control strategy is introduced in the update schemes and sufficient condition in terms of graph robustness is provided for resilient consensus. Numerical examples are provided to illustrate the effectiveness of the theoretical results.