Dynamic output-feedback-based [formula omitted] design for networked control systems with multipath packet dropouts

This paper concerns the problem of the model, stability and controller design for networked control system (NCS) with time-varying delay and dropped out packet. For the NCS with time-varying delay and data packet dropout, four new control methods of dynamical state feedback control, dynamical state feedback proportional-integral (PI) control, state feedback proportional-derivative (PD) control and dynamical state feedback PD control are presented. The NCS with time-varying delay and data packet dropout based on the four control methods is modeled as an asynchronous dynamical system (ADS) constrained by event rates. Furthermore, based on the ADS theory, principle of Lyapunov stability and method of linear matrix inequality, both the semi-negative definite matrix conditions of exponential stability and the controller design for NCS are given. Finally, numerical example illustrates the feasibility of the results.

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.

The problem of stabilization of networked control systems (NCSs) with time-varying transmission delays is investigated. The time-varying delays lie in any two adjoining sampling instants of the plant. A technique is proposed for designing stabilizing controllers by converting NCSs with time-varying transmission delays into parameter uncertain systems with constant input delay, then the theory of robust stabilization of delay systems can be applied to solving this problem. Sufficient condition on stabilization of such NCSs is developed in terms of linear matrix inequality.

The presence of a communication network in a control loop induces many imperfections such as varying transmission delays, varying sampling/transmission intervals, packet loss, communication constraints and quantization effects, which can degrade the control performance significantly and even lead to instability. Various techniques have been proposed in the literature for stability analysis and controller design for these so-called networked control systems. The aim of this chapter is to survey the main research lines in a comprehensive manner.

Network-induced delays and packet dropouts are relevant issues that can degrade networked control systems' performance and may even lead to instability. This paper concerns the establishment of a stability criterion for networked control systems (NCSs) consisting of an LTI process and a dynamic feedback controller. Conditions for stability are provided in terms of Linear Matrix Inequalities (LMIs), whose solution yields network-induced delay upper bounds. Numerical examples and a simulation ratify the theoretical results.

This paper is concerned with the problem of designing a robust observer-based controller for discrete-time networked systems with limited information. An improved networked control system model is proposed and the effects of random packet dropout, time-varying delay, and quantization are considered simultaneously. Based on the obtained model, a stability criterion is developed by constructing an appropriate Lyapunov-Krasovskii functional and sufficient conditions for the existence of a dynamic quantized output feedback controller which are given in terms of linear matrix inequalities (LMIs) such that the augmented error system is stochastically stable with an performance level. An example is presented to illustrate the effectiveness of the proposed method.

Input-to-state stability for networked control system with predictive scheme

Improved stability and stabilization design for networked control systems using new quadruple-integral functionals

The last two decades have witnessed a great deal of interests in sensor/actuator networks (SANs), or, generally, networked control systems (NCSs). Compared to conventional system architectures, NCSs have numerous advantages such as reduced systemwiring, being easier for design, diagnosis, and maintenance, lower cost, and increased flexibility, reliability, and safety. As a result, NCSs have been widely applied to many areas, for example, automobiles, aircrafts, and spacecrafts, autonomous vehicles, transportation systems, power systems, remote monitoring and data acquisition systems, chemical processes, and many manufacturing plants. Research on NCSs has heretofore focused mainly on several basic communication constraints that can cause performance degradation or stability loss, such as network-induced delays, packet dropouts, data corruptions or disordering, and data rate limitation and quantization effects. Medium access constraint is another important issue worthy of intensive investigation, which refers to the fact that the network cannot accommodate all the nodes (sensors, actuators, subsystems, etc.) simultaneously at any time. There are other open issues awaiting investigation, too. As a special type of NCSs, sensor/actuators networks typically have a large number of devices advanced in sensing, communicational, computational, and mobility capabilities, demanding nontrivial energy. In addition, the batteries powering these devices have limited capacity and cannot be replaced or recharged conveniently. As a consequence, many interesting and challenging issues are open, for example, localization, coverage and routing of mobile sensor/actuator networks, and so forth. The special issue focuses on the state-of-the-art research and development in the analysis and design for networked control systems as well as the theoretical and technological advances in sensor and actuator networks. The intention of this special issue was to provide for researchers a forum to share their latest research results on filtering, estimation, control, and other aspects in sensor/actuator networks and networked control systems and for readers an opportunity to have an overview of the latest achievements about some interesting issues this field has been encountering. In the next section, we give a brief description of the papers in this special issue.

Recent technological advances have enabled distributed control systems to be implemented via networks. This allows feedback control loops to be closed over a shared communication channel. Network-induced delays are inevitable, however, when transmitting digital data between control devices. This paper analyzes the stability of such networked control systems (NCS). We first review some previous work on this topic, offering some improvements. We analyze the influence of the sampling rate and network delay on system stability. We further study the stability of NCS using a hybrid system stability analysis technique.

Event-triggered controller design of nonlinear discrete-time networked control systems in T-S fuzzy model

The problem of stabilization of networked control systems (NCSs) with data packet dropout is studied. Sufficient conditions are presented on the stability and stabilization of the NCSs with packet dropout. The novelty of this work lies in that NCSs with arbitrary but finite data packet dropout are modelled as switched linear systems, and this enables us to apply the result of switched systems to the analysis and synthesis of such NCSs. The admissible upper bound of the dropped packets can be determined by a set of linear matrix inequalities (LMIs) which guarantee the stability of the NCSs. Stabilizing controllers (via state feedback and static output feedback) can be constructed by solving a set of LMIs. Also, for an NCS with a convergence rate constraint, similar results are obtained. Examples are worked out to illustrate the effectiveness of the proposed method

This paper is concerned with quantitative analysis and synthesis for continuous-time networked control systems (NCSs) with packet dropouts and interval time-varying sampling period. A new packet dropout separation method is proposed to separate packet dropouts from the sum of network-induced delay and packet dropouts, and an interval time-varying sampling period approach is presented to model the variation of sampling period. Then, a novel packet dropout decomposition based Lyapunov functional is constructed, and the quantitative relationships between packet dropout probability and stability and stabilization of NCSs are established. A numerical example is given to illustrate the merits and effectiveness of the proposed methods.

The controller design techniques for Networked Control Systems (NCSs) with uncertain, time-varying network induced delay and data packet dropout is studied. A state predictor is used to predict current plant states, predicted states is used to construct control law. Combined with the state predictor, the NCS with long time delay and data packet dropout is modelled as asynchronous dynamical system with event rate constraints. Based on the model, sufficient conditions of exponential stability for NCS are given in the form of matrix inequalities. Through the feasible solution of the matrix inequalities the control law can be obtained. A numerical example demonstrates the effectiveness of the proposed method.

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