Time-varying Network-induced Delays Research Articles

Decentralized Resilient Output-Feedback Control Design for Networked Control Systems Under Denial-of-Service

This article deals with the problem of decentralized resilient observer-based output-feedback control design for networked control systems (NCSs). The proposed scheme considers both network imperfections and security issues. It is assumed that the NCS is suffering from time-varying network-induced delays and time-varying transmission intervals. Moreover, data transmission is performed over a nonsecure network that suffers from a denial-of-service (DoS) attack. The DoS jamming attack has affected the network by the occurrence of consecutive packet dropouts, which result in attack-induced packet dropouts. Based on the fact that packet dropouts caused by DoS attacks naturally do not follow a specific statistical pattern, the attack-induced packet dropouts are modeled as an extension of time-varying intervals with no probability distribution. Sufficient conditions are provided to guarantee the uniformly globally exponential stability of the NCS in the form of linear matrix inequalities. Finally, the effectiveness and applicability of the proposed method are demonstrated by simulation results.

Relaxed stability analysis and sampled-data controller design for networked control systems with network-induced delays

This paper is devoted to the stability analysis and sampled-data controller design problem for networked control systems subject to network-induced delays. The objective is to provide relaxed conditions in terms of linear matrix inequalities. Indeed, reducing the conservatism of such conditions allows to maximize the admissible range of the network-induced delays. To do so, an augmented Lyapunov–Krasovskii functional is proposed, which involves a novel augmented state vector to include as much as possible the information from the time-varying network-induced delay into the stability conditions, together with the use of extended Wirtinger-based inequalities, an extended reciprocal convexity approach and the Finsler’s lemma. Then, declined from the proposed stability conditions, new relaxed delay-dependent conditions for the design of networked sampled-data controllers are proposed. These allow to obtain simultaneously the controller gains and the maximal allowable bound of the network-induced delays with regards to its lower bound. Three illustrative examples are provided to show the effectiveness of the proposed networked control systems stability and controller design conditions, as well as to highlight the so raised conservatism improvements regarding the previous relevant results from the literature.

Networked Motion Control for Smart EV With Multiple-Package Transmissions and Time-Varying Network-Induced Delays

This article aims to address the coupled problem of the multiple-package transmissions (MPT) and time-varying network-induced delays (TND) within the networked motion control systems of smart electric vehicles (EVs). The recent development of advance digital sensors, actuators, and controllers leverage the worldwide upgrade of transportation in terms of electrification and intellectualization. However, for smart EVs, this updating may challenge the in-vehicle network and then the vehicle control performance. In particular, the nonsynchronous MPT and the TND are the key issues in the vehicle's integrated motion control due to the absence of the synchronization mechanism and limitation of communication bandwidth. To deal with the effects of coupled MPT and TND, a hybrid schedule-control framework is developed, where a new MPT scheduler is developed with a flexible time-triggered schedule strategy with fractional-type basic period to eliminate the effect of the MPT and reorganize the TND to a bounded range of delay. Furthermore, an H∞-based linear quadratic regulator control approach is designed to deal with the uncertainties caused by the TND as well as guarantee the system's stability. The effectiveness of the proposed scheme is verified in three cases by the real-time hardware-in-the-loop bed tests.

Delay-Dependent Stability Improvement for Networked Control Systems: a Sampled Data Approach

This paper concerns the stability conditions and controller design for sampled-data networked control systems (NCSs) model subject to network communication delays, the main objective is to guarantee the maximum allowable upper bounds of network-induced time-varying delays that keep the NCSs stable. First, Lyapunov-Krasovskii functional with simple and double-integral terms is constructed considering both upper and lower bounds of network delay. Then, less conservative Linear Matrix Inequalities (LMIs) stability conditions are established using null terms to introduce free weighting matrices based on the Leibniz-Newton formula. Furthermore, Finsler's lemma is used for the relaxation of the obtained LMI's stability conditions using slack decision variables. It is also used to decouple Lyapunov-Krasovskii matrices from the system ones. The application of the proposed approach for different NCSs gives higher upper delay bounds compared with other methods.

Improved robust H ∞ stability analysis and stabilisation of uncertain and disturbed networked control systems with network-induced delay and packets dropout

This paper is concerned with stability analysis and stabilisation of uncertain Networked Control Systems (NCS) with network-induced delay and packet dropouts. This proposal aims at maximising the allowable upper bound of network-induced delay, together with the number of consecutive packet dropouts, from which uncertain and disturbed NCS plants are stable. A novel augmented Lyapunov–Krasovskii functionals (LKF), dependent on both the lower and upper bounds of the network-induced time-varying delay, is considered to derive the proposed delay-dependent LMI-based stability conditions. Relaxation of these conditions are obtained by exploiting simple and double integral Wirtinger's inequalities to introduce more degrees of freedom from the LKF terms than existing related conditions in the literature. Finally, numerical examples and simulation results are presented to illustrate the effectiveness and the conservatism improvement raised by this proposal compared to previous related results.

Robust Stability and Stabilization Conditions for Nonlinear Networked Control Systems With Network-Induced Delay via T–S Fuzzy Model

Robust stability and stabilization problems for a class of discrete-time nonlinear systems are studied in this article. The control signal is transmitted to the nonlinear systems through a lossy communication channel in which time-varying network-induced delay occurs. A Takagi–Sugeno (T–S) fuzzy model is used to represent the nonlinear systems. Using membership function boundary information, a novel membership-function-dependent (MFD) analysis approach is presented. Unlike most previous results, the proposed MFD analysis approach does not need to increase the number of slack variables to reduce conservatism. Combining auxiliary matrices and this approach, we propose some new fuzzy Lyapunov–Krasovskii functionals (FLKFs) that do not require the restrictions of positive definiteness imposed on Lyapunov matrices. Using the FLKF and MFD analysis approach, a sufficient condition in the form of linear matrix inequalities (LMIs) is developed to guarantee the stability of T–S fuzzy time-varying delay systems. Based on the results for stability, less conservative stabilization conditions are also derived. Finally, numerical examples show that less conservative results can be obtained by the proposed approach. The inverted pendulum system with state delay or network-induced delay is also studied to verify the effectiveness of the suggested approach.

Distributed predictor-based stabilization of interconnected systems with network induced delays

This paper presents sufficient stability conditions for distributed prediction-based control of interconnected systems subject to network-induced time-varying delay. Due to the flexibility of the proposed criteria, continuous-time, sampled-data control and output-feedback problems can be handled by the same framework. A detuning procedure is combined with a distributed LQR design in order to ensure the closed-loop stability for a given network-induced delay bound. If compared with related works, the proposed framework can be applied to obtain the time-varying delay bound derived from distinct combinations of distributed dead-time compensation strategies with stabilizing control laws. Two simulation case studies based on a benchmark problem and the level control of a irrigation canal are presented to illustrate the usefulness of the proposed framework.

Robust Distributed Secondary Voltage Restoration Control of AC Microgrids under Multiple Communication Delays

This paper focuses on the robust distributed secondary voltage restoration control of AC microgrids (MGs) under multiple communication delays and nonlinear model uncertainties. The problem is addressed in a multi-agent fashion where the generators’ local controllers play the role of cooperative agents communicating over a network and where electrical couplings among generators are interpreted as disturbances to be rejected. Communications are considered to be affected by heterogeneous network-induced time-varying delays with given upper-bounds and the MG is subjected to nonlinear model uncertainties and abrupt changes in the operating working condition. Robustness against uncertainties is achieved by means of an integral sliding mode control term embedded in the control protocol. Then, the global voltage restoration stability, despite the communication delays, is demonstrated through a Lyapunov-Krasovskii analysis. Given the delays’ bounds, and because the resulting stability conditions result in being non-convex with respect to the controller gain, then a relaxed linear matrix inequalities-based tuning criteria is developed to maximize the controller tuning, thus minimizing the restoration settling-time. By means of that, a criteria to estimate the maximal delay margin tolerated by the system is also provided. Finally, simulations on a faithful nonlinear MG model, showing the effectiveness of the proposed control strategy, are further discussed.

Stochastic H∞ Robust Decentralized Tracking Control of Large-Scale Team Formation UAV Network System With Time-Varying Delay and Packet Dropout Under Interconnected Couplings and Wiener Fluctuations

In this article, a robust decentralized tracking control scheme for a large-scale unmanned aerial vehicle (UAV) formation team networked control system (NCS) is proposed to overcome a non-scalable or even infeasible design problem due to high computational complexity by the centralized control. At the outset, wind external disturbance, intrinsic fluctuation, coupling from other UAV subsystems, time-varying network-induced delay and packet dropout are taken into account in the design procedure of large-scale team formation UAV network system. Moreover, an event-triggered mechanism is embedded in NCS to reduce the number of transmitted control signals to save the network traffic especially for a large-scale team formation network of UAVs. To effectively reduce the above uncertainties, a robust \textH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> decentralized tracking controller is proposed for the large-scale UAV team formation NCS which is constructed by virtual leader-follower tracking network of UAV subsystems. By the Takagi-Sugeno (T-S) fuzzy interpolation method, the \textH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> robust virtual leader-follower decentralized tracking control design problem of the large-scale UAV team formation NCS is transformed to an independent Hamilton-Jacobin inequality (HJI)-constrained optimization problem for each UAV, which is effectively solved by a linear matrix inequality (LMI)-constrained optimization problem. Finally, a large-scale UAV team formation example of 25 UAVs is proposed to validate the effectiveness of the proposed robust decentralized tracking controller of large-scale UAV team formation NCS.

Robust H∞ Pinning Synchronization for Complex Networks With Event-Triggered Communication Scheme

This paper investigates the issue of global robust ${H_\infty }$ pinning synchronization for a class of complex networks with sampled-data-based event-triggered communication via a pinning control approach. The complex network is subject to network-induced time-varying delays, parametric uncertainties and external disturbances. A directed and weighted communication topology is taken into account, and the phenomenon of uncertainties is reflected in both modelling and inner coupling matrices. In order to save communication resources, a new and practical event-triggered communication mechanism with an asynchronous sampling manner is developed, with which the Zeno behaviour can be absolutely avoided. Then, based on the presented event-triggered strategy, a pinning control protocol is proposed to reduce the frequency of controller updates and the computational burden. The problems on the minimal number and which of the nodes should be chosen are addressed. By Lyapunov stability theory, sufficient conditions are deduced to ensure the underlying network achieves global robust ${H_\infty }$ pinning synchronization. Finally, numerical examples are provided to verify the effectiveness of the new design techniques.

Robust stability and stabilization of networked control systems with stochastic time-varying network-induced delays

This paper investigates the robust stability analysis and state feedback controller design of networked control systems (NCSs). A stochastic network-induced delay in given interval with known lower and upper bounds is considered. Therefore, the NCS is modeled as linear system with probabilistic time-varying delay distribution. Then, the Lyapunov-Krasovskii functional (LKF) is formulated using probabilistic informations of both lower and upper bounds of the time-varying network-induced delay, and Wirtinger-based integral inequalities are used to estimate the accuracy of the resulting time derivatives and also to reduce conservatism by introducing some new cross terms. Afterwards, stability condition based on [Formula: see text] disturbance attenuation level is expressed in terms of a set of linear matrix inequalities (LMIs), and Finsler’s lemma is used to relax it by adding slack decision variables and decoupling the systems matrices from those of Lyapunov-Krasovskii. This procedure makes the state feedback controller design as simple as a variables change. Finally, a maximum allowable upper bound of the network-induced delay and state feedback controller gains are calculated by resolving the above relaxed LMIs’ convex optimization problem. Practical numerical examples are provided to validate the proposed approach; the results show that the negative effects of the unpredictable network-induced delays are compensated and the stability of NCSs with high disturbance attenuation level is guaranteed. A comparative study with other results in recent researches is also given and the superiority of the proposed method in terms of robustness and conservatism reduction is shown.

Event-Triggered H-Infinity Control for Continuous-Time Singular Networked Cascade Control Systems With State Delay

This paper is concerned with the problems of modeling, stabilization, and H control for continuous-time singular networked cascade control systems (SNCCSs) with state delay and event-triggered control. An event-triggered scheme is firstly introduced to this system for utilizing the network bandwidth resources efficiently. Considering the effects of both time-varying network-induced delay and event-triggered control, a singular networked cascade control system (SNCCS) model is established. By constructing a suitable Lyapunov-Krasovskii functional, sufficient condition of admissibility for this system is proposed, and the co-design method of event-triggered parameter, primary state feedback controller and secondary state feedback controller are also derived. Furthermore, H ∞ control is concerned for SNCCS via linear matrix inequality (LMI) technique. Finally, a simulation example considering a heating furnace with the structure of SNCCS and event-triggered control is given to illustrate the effectiveness of the proposed method, where it can be seen this method is superior to the existing one with periodic control.

Event-triggered Hꝏ control for NCS with time-delay and packet losses

Abstract This paper is concerned with the discrete event-triggered dynamic output-feedback ${H}_{\infty }$ control problem for the uncertain networked control system, where the time-varying sampling, network-induced delay and packet losses are taken into account simultaneously. The random packet losses are described via the Bernoulli distribution. And then, the closed-loop system is modelled as an augmented time-delay system with interval time-varying delay. By using the Lyapunov stability theory and the augmented state space method, the sufficient conditions for the asymptotic stability of the closed-loop system are proposed in the form of linear matrix inequalities. At the same time, the design method of the ${H}_{\infty }$ controller is created. Finally, a numerical example is employed to illustrate the effectiveness of the proposed method.

Distributed Cooperative Secondary Control for Islanded Microgrid With Markov Time-Varying Delays

The network-induced delays have a great impact on microgrid performance and stability. In this paper, we proposed a distributed cooperative secondary control with stochastic Markov time-varying network-induced delays, by which both output voltage/frequency restoration and active power sharing can be obtained. A new small-signal model of the microgrid control system is developed, and a small-signal model-based information Kalman observer is introduced to acquire the estimated state vector. Then, the global closed-loop stochastic system accommodated by the Markov time-varying network-induced delays of the microgrid is derived, and the corresponding global stability theorem is introduced. Finally, the simulation of a microgrid test system is presented to verify the control performance. The results show that our approach has accurate regulations on voltage/frequency restoration and active power sharing in terms of load variations, plug-and-play capability, and network-induced delays. In addition, the control gain parameters and network-induced delays effects on the microgrid secondary control are also verified.

Dynamic surface control for discrete-time strict-feedback systems with network-induced time-varying delays and packets loss

In this paper, a dynamic surface control (DSC) strategy for discrete-time strict-feedback multiple-input-multiple-output systems is proposed. State variables are estimated by Luenberger observer using latest outputs received in controller. The control signals, bearing the same time-stamps as the target system, are constructed based on DSC methodologies. The control mechanism also considers the network-induced time-varying delays, packet drops and disorder; these parameters are systematically stacked into the network and transmitted into an actuator where the control function is performed. In order to establish all the design parameters, a simplified methodology of utilising linear matrix inequality and homotopy algorithm is proposed. The simulation results prove that the proposed method is effective.

Discrete-time event-triggered H-infinity stabilization for networked cascade control systems with uncertain delay

This paper is concerned with the problem of discrete-time event-triggered H∞ control for networked cascade control systems (NCCSs) with time-varying network-induced delay. First of all, an event-triggered scheme is introduced to this system for reducing the unnecessary waste of limited network bandwidth resources. Considering the effect of time-varying delay, a new mathematical model for this system is constructed. In this paper, based on the model and Lyapunov functional method, the co-design method of event-triggered parameter, state feedback primary controller and secondary controller with H∞ performance is derived via linear matrix inequality technique. To illustrate the effectiveness of the proposed method, a simulation example considering a main steam temperature cascade control system is given. The proposed method emphasizes the application in the corresponding industrial control systems, it can be found that this method is superior to the one in some existing references, and the provided example demonstrates the effectiveness of the co-design method in the networked cascade control systems with event-triggered scheme.

Event-based reduced-order fuzzy filtering for networked control systems with time-varying delays

This paper investigates the event-based reduced-order fuzzy filtering problem for nonlinear networked control systems with network-induced time-varying delays. A novel fuzzy filter design approach is proposed to analyze the fuzzy systems under a reduced-order scheme. The problem of mismatched membership functions is presented in the fuzzy filtering to simplify implementation complexity and increase design flexibility of the designed reduced-order filter. In addition, the integrands of the Lyapunov–Krasovskii functional are dependent of membership functions and the existence conditions of the fuzzy filtering are given by utilizing a linearization approach. Compared with the existing reduced-order filter design approaches, the time-derivatives of membership functions are considered in the analysis process for reducing the conservativeness of obtaining the maximum delay bounds. Finally, a simulation result is given to show the effectiveness and advantages of the analysis scheme.

Periodic Event-Triggered Sampling and Dual-Rate Control for a Wireless Networked Control System With Applications to UAVs

In this paper, periodic event-triggered sampling and dual-rate control techniques are integrated in a wireless networked control system (WNCS), where time-varying network-induced delays and packet disorder are present. Compared to the conventional time-triggered sampling paradigm, the control solution is able to considerably reduce network utilization (number of transmissions), while retaining a satisfactory control performance. Stability for the proposed WNCS is ensured using linear matrix inequalities. Simulation results show the main benefits of the control approach, which are experimentally validated by means of an unmanned-aerial-vehicle-based test-bed platform.

The Research of Network-induced Delay Measurement Methods in Wireless Networked Control Systems based on Zigbee Network

The large and random network-induced delay in ZigBee wireless network seriously reduce the performance of wireless networked control systems (WiNCS) based on ZigBee network, due to unreliable communication, limited bandwidth, as well as high bit error rate of ZigBee network. Compared with other methods, such as converting time-varying network-induced delay into a fixed value, assuming network-induced delay under a certain statistical law, real-time measurement and compensation of random network-induced delay can effectively improve the performance of WiNCS. In order to obtain the network-induced delay of WiNCS based on ZigBee network on-line, this paper deeply analyzes the composition of delay, provides three delay measurement methods, clock synchronization method, confirm mechanism method and online estimation method, and designs a WiNCS network data transmission experimental platform. Then measurement precision of this measurement methods are analyzed by experiments that based on the experimental platform. The experiments show that, these measurement methods achieve very high measurement precision by taking compensation measures.

Adaptive Neural Tracking Control for an Uncertain State Constrained Robotic Manipulator With Unknown Time-Varying Delays

This paper presents an adaptive neural control strategy for an ${n}$ -link rigid robotic manipulator with both state constraints and unknown time-varying delayed states. The design difficulties cause by the state constraints and unknown network-induced time-varying delays which appear in the ${n}$ -link rigid robot simultaneously. In order to overcome these difficulties, the novel Barrier Lyapunov functions and an iterative backstepping technique are employed to guarantee constraint satisfaction of the position of the robot, the opportune Lyapunov-Krasovskii functionals and separation techniques are utilized to eliminate the effect of unknown functions with time-varying delayed states in communication channels. As the universal approximator, the neural networks are used to estimate the unknown functions of systems. By using the Lyapunov analysis, we can achieve that all the closed-loop signals are semiglobal uniformly ultimately bound, the tracking errors converge to a small set about zero and the good tracking performances of the system output. The feasibility of the proposed control algorithm can be demonstrated by providing simulation results.