Dynamic self-organization and clustering in distributed networked systems for performance improvement

Exponential stability of networked control systems with network-induced random delaysIn this paper, the problem of exponential stability for the standard form of the state control, realized in a networked control system structure, is studied. To deal with the problem of stability analysis of the event-time-driven modes in the networked control systems the delayed-dependent exponential stability conditions are reformulated and proven. Based on the delay-time dependent Lyapunov-Krasovskii functional, exponential stability criteria are derived. These criteria are expressed as a set of linear matrix inequalities and their structure can be modified to use the bilinear inequality techniques.

This research addressed the issue of improving the quality of service for the control system of mobile radio networks. The analysis of the forecasting sphere concerning the methods of service quality of mobile radio networks for special purposes, in particular, forecasting the time of congestion of data transmission routes is carried out. It is found that these methods are used in wired and computer networks operating at the network and data link levels. The basic parameters of the protocols of the channel and network layers of mobile radio networks are highlighted. Forecasting methods are analyzed: temporal extrapolation, causality, expert, and the main disadvantages are indicated. A model of a control system for mobile radio networks with a forecasting subsystem is shown. The features of mobile radio networks, which form the requirements for routing methods, are described. A lot of requirements have been put forward for the model of a control system for mobile radio networks. The structure of a model of a control system for mobile radio networks with an improved forecasting subsystem is proposed. On the basis of genetic algorithms, the tasks that arise in the process of identification, training and forecasting in the forecasting subsystem are solved. The operation of the processes consists in building a base of rules aimed at identifying significant dependencies in a time series based on the use of a genetic algorithm. It is based on the use of evolutionary principles to find the optimal solution. Application of the proposed model will allow real-time identification and will significantly improve the quality of service for mobile radio networks. It will increase the speed and volume of data processed during training, improve the quality and reliability of predicting changes in data transmission routes

Driven by recent telecommunication demand, shared communication channels are more abundant today than ever before. These shared wired/wireless networks for communication are being exploited more and more in control systems to connect sensors, controllers and actuators resulting in so-called networked control systems (NCSs). NCSs replace the more traditional control systems where dedicated point-to-point (wired) connections are being used. The advantages of using NCS technology are inexpensive and easily modifiable communication links which allow control algorithms to be easily implemented in situations where dedicated connections are not possible (either economically or physically). However, the drawback is that the control system is susceptible to undesirable (possibly destabilizing) side-effects such as time-varying transmission intervals, time-varying delays, packet dropouts, quantization and a shared communication medium. These network-induced effects undermine fundamental assumptions on which traditional control theory is built and, therefore, it is essential to develop new techniques and tools that can be used to analyze and/or design control systems which communicate via a shared network. This thesis advances NCS analysis and design methodologies by contributing new theoretical developments, new software tools and new experimental validation results. The first new theoretical development is in the area of analyzing robust stability properties with respect to network-induced effects. A sum of squares (SOS) approach for a class of nonlinear NCSs incorporating bounded time-varying delays, bounded time-varying transmission intervals and a shared communication medium is developed. Mathematical models that describe these nonlinear NCSs are cast into suitable hybrid system formulations. Based on these hybrid system formulations, (families of) Lyapunov functions are constructed using SOS techniques. Amongst other benefits, it is shown that this technique improves the guaranteed robustness margins compared to existing work. The second new theoretical development concerns the design of networkaware decentralized controllers guaranteeing robust stability properties with respect to network-induced effects. We develop one of the first approaches based on semidefinite programming techniques to synthesize stabilizing decentralized observer-based output-feedback controllers for linear plants where the controllers, sensors and actuators are connected via a shared communication network subject to time-varying transmission intervals and delays. To effectively deal with the shared communication medium, a switched observer structure is adopted that switches based on the transmitted measured outputs and a switched controller structure is also adopted that switches based on the transmitted control inputs at each transmission time. By taking a discrete-time switched linear system perspective on modeling these decentralized NCSs, we are able to derive a general model that captures all these networked and decentralized control aspects. We provide linear matrix inequality (LMI)-based synthesis conditions which, if satisfied, provide stabilizing observer-based controllers that are both decentralized and robust to network effects. Regarding new software tools, the first prototype of a toolbox is developed to automate (robust) stability analysis (and controller design) for NCSs. Specifically, it is shown that the toolbox can be employed to efficiently verify if a linear time-invariant (LTI) plant and an LTI controller interconnected with a shared network are robust to certain network imperfections. The main intention of the toolbox is to make the available theory readily accessible to and applicable for the general control community. Additionally, the chosen software structure enables the incorporation of custom models or custom stability/performance analysis conditions in an easy manner, thereby allowing the control community to contribute and to further develop the toolbox. Finally, an experimental case study involving a wirelessly controlled inverted pendulum/cart system is investigated. In particular, the communication network itself is analyzed such that the network-induced effects can be characterized in terms of bounds on the transmission intervals and transmission delays. Based on these bounds, the prototype toolbox is applied to analyze the robustness regions for different performance specifications, which aid in tuning the controller to achieve more closed-loop robustness with respect to the network-induced effects. This leads to a validation of the developed theory in an experimental setting. In addition to the validation of the developed theory, many new insights into the network behavior are obtained and explained, thereby raising new interesting questions for future research on NCSs.

Design, Analysis and Real-time Implementation of Networked Predictive Control Systems

This kind of control systems wherein the control loops are closed through a real time communication network can be called networked control systems. Networked control system is a new hot topic in the control engineering. The reduction of bandwidth necessitated by the communication network in a networked control system is a major concern. For this reason, a computation method of reducing the number of data packet exchanges between the sensor and the controller/actuator was explored. A novel model of controller and intelligent prtotocol were also designed for reducing the number of data packet exchanges which could make the networked control system stable.

Connecting a complex control system with various sensors, actuators, and controllers as a networked control system by a shared data network can effectively reduce complicated wiring connections. This system is also easy to install and maintain. The trend is to use networked control systems for time-sensitive applications, such as remote DC motor actuation control. The performance of a networked control system can be improved if the network can guarantee quality-of-service (QoS). Due to time-varying network traffic demands and disturbances, QoS requirements provided by a network may change. In this case, a network has to reallocate its resources and may not be able to provide QoS requirements to a networked control application as needed. Therefore, the application may have to gracefully degrade its performance and perform the task as best as possible with the provided network QoS. This paper proposes a novel approach for networked DC motor control systems using controller gain adaptation to compensate for the changes in QoS requirements. Numerical and experimental simulations, and prototyping, are presented to demonstrate the feasibility of the proposed adaptation scheme to handle network QoS variation in a control loop. The effective results show the promising future of the use of gain adaptation in networked control applications.

Networked control systems (NCS) consist of sensors, actuators and controllers the operations of which may be distributed over geographically disparate locations and co-ordinated by the exchange of information passed over a communication network. The communication network may be physically wired or not. The widespread applications of the Internet have been a major driving force for research and development of NCS. NCS have advantages in terms of cost reduction, system diagnosis and flexibility, minimizing wiring and making the addition and replacement of individual elements relatively simple; efficient data sharing makes taking globally intelligent control decisions easier with an NCS. The applications of NCS are very wide, from the large scale of factory automation and plant monitoring to the smaller but complicated networks of computers in modern cars, places and autonomous robots. Networked Control Systems presents the most recent results in stability and robustness analysis as well as new developments related to networked fuzzy and optimal control. Many of the chapters contain details of case-studies, experimental, simulation and/or other application-related work showing how the theories put forward can be implemented in real systems. The state-of-the art research reported in this volume by an international team of contributors will make Networked Control Systems an essential reference for researchers and postgraduate students in control, electrical, computer and mechanical engineering and computer science.

Networked control systems (NCSs), in which controllers and actuators are connected by communication networks, have been utilized in both industrial and consumer applications. In addition, sleep-based energy-efficient network interfaces have been developed for constructing a green networked society. The combination of the NCSs and energy-efficient network interfaces is a promising approach to reduce the power consumption of NCSs. However, sleeping of the network interface results in loss of data to be transmitted between a controller and an actuator. The sleep-induced data loss causes degradation of control performance. Moreover, NCSs originally include network delay for both forward and feedback paths, which also degrades control performance. This paper proposes a time-delay and data-loss compensation method using a modified communication disturbance observer (MCDOB) for NCSs with sleep-based energy-efficient interfaces. The proposed MCDOB can simultaneously compensate for not only the network delay but also sleep-induced data loss as a disturbance, whereas a conventional communication disturbance observer (CDOB) considers only network delay or network-induced data loss and cannot be directly introduced into the NCSs with sleep-based energy-efficient interfaces. Experimental results show that the proposed method with MCDOB outperforms the conventional method without the MCDOB in terms of integral square error (ISE) and communication rate, which indicates the power consumption of network interfaces.

Network control system (NCS) is a kind of distributed control system, which is widely used in industrial control process. The communication network is used to exchange information and control signals among various physical components of subsystems. The transmission of data and information on the communication network to achieve system control will lead to the inevitable delay of information transmission time, which will reduce the performance and even make the system unstable. Reducing network traffic is one of the most effective methods to reduce the impact of network control system delay on system performance. This paper discusses the adjustable deadband as a method to reduce network traffic in networked control systems, and proposes a modeling method of networked control systems with random delay and communication constraints based on quasi T-S fuzzy model. Based on robust fault-tolerant control theory and information scheduling theory, the integrity design of this kind of networked control system is analyzed. After detailed theoretical analysis, simulation results are given to further verify the proposed scheme.

Due to major advancements in the area of networking over the past decade, a new paradigm of control systems has emerged, namely networked control systems. Such systems differ from classical control systems in that their control loops are closed around communication networks. Thus, the need for new stability and performance guarantees arises. In this paper, we aim to shed some light on the major advancements and inherent problems in networked control systems.

Networked control systems offer significant advantages in terms of reliability, commissioning and maintenance, especially for complex systems. They must be able to withstand delays and data corruption caused by the underlying communication network. Existing results in networked control systems provide varying degrees of robustness. However, cost is also an important factor for real world implementations, which further restricts the bandwidth of the underlying network and complexity of the communication protocol. In this paper we introduce a networked control system method, WMBPNCS, that we have previously proposed, and implement a control system using IEEE 802.15.4 (ZigBee) as its communication protocol, in an attempt to overcome these problems. We find through simulations that performance of our implementation is acceptable even under large amounts of random network delay and data loss.

In this paper, a novel approach for networked control system (NCS) task scheduling is proposed. The proposed neural-genetic method utilizes the information about the quality of service (QoS) over the communication network and enables online reconfigurable scheduling on distributed environment. In this way the NCS's bandwidth can be shared properly among different parallel control tasks. For NCS, two significant factors of QoS that affect validity of scheduling results are the packet loss and delay, which occurred in the communication among tasks. By adopting a Elman neural network based prediction model, the one-step ahead packet loss and time delay are obtained. The knowledge about the predict QoS factors, combined with the task execution features and the resources available in the system, are used as an entry to improve the decisions of the proposed scheduling algorithm. Such algorithm uses genetic algorithm techniques to find out the appropriate task scheduling scheme to adapt changes of application and communication circumstance. The proposed neural-genetic approach is evaluated through simulation by using a model parameterized with the features obtained from a real scenario of Ethernet based control system. The simulation results clearly show the effectiveness of the proposed approach in solving the task scheduling problems in NCS.

In this paper, the robust H∞ control problem is developed for a class of linear time-varying networked control system (NCS) with uncertainties and external disturbance. In network, the network-induced delay and packet dropouts are simultaneously considered. Firstly, a discrete-time switched system model is established based on the signals transmission delay in network. Then, a time-varying H∞ controller is designed. Such the controller can vary according to delay in network. Furthermore, by constructing delay-dependent Lyapunov-Krasovskii functional, a sufficient condition is given to guarantee that the closed-loop system is stochastically stable with an H∞ disturbance attenuation level in terms of nonlinear matrix inequalities. In order to solve the controller gain, the cone complementarity linearization (CCL) algorithm is employed. Finally, a networked DC motor control system is analyzed to illustrate the effectiveness of the proposed method.

Networked control systems (NCS) are in existence for quite some time. The network-induced delays and packet drops; and their effect on control system's performance has been a burning topic for last one decade. Dependability in context of NCS has not got much attention. While it is an important aspect of NCS intended to be used in critical application. The paper reviews the present state of developments in NCS and presents open problems pertaining to dependability of NCS. Solutions to these problems may increase the presence of NCS by many folds and in many fields.

The problem is studied of achieving a specified formation among a group of mobile autonomous agents by distributed control. If convergence to a point is feasible, then more general formations are achievable too, so the focus is on convergence to a point (the agreement problem). Three formation strategies are studied and convergence is proved under certain conditions. Also, motivated by the question of whether collisions occur, formation evolution is studied.