A Study Of Robust Control Application To Networked Control Systems

With the rapid developments of computer, network and communication technology, the naissance of intelligentized sensor, actuator and drive device consists of the substance foundation of networked control systems (NCS). The reliability and open issues of NCS have been solved by the sustained developments and successful applications of high speed Ethernet and fieldbus control technology, which promote the extensive applications of NCS. NCS incarnates enough the development tendency of control systems i.e. network, integration, decentralization, intelligence. However, with the impact of network circumstance, many issues emerged inevitably, such as network-induced transmission delay, multi-channel transmission brought by the limited bandwidth, data packet dropouts for the failed communication, the asynchronous clock among network nodes etc. These problems not only depress the performance of normally designed control systems, but also destroy the system stability. So, we consider the main problems of network-induced delay, data packet dropout and external disturbance in NCS. Basing on the quality of service of control networks, surrounding the performance index of NCS, we study the issues of modeling, stability analysis, robust control, non-fragile guaranteed cost optimal control, H∞optimal control for NCS. The main achievements are listed as follows:The problem of robust and non-fragile guaranteed cost controller design for NCS with network-induced delay less than or equals to one sampling period is studied. Aiming at the discrete model of closed-loop NCS, the uncertainty caused by loop time-delay is transformed into the matrix parameter uncertainty of the equation of the controlled plant. Thus, by using the Lyapunov theory and linear matrix inequality (LMI) approach, sufficient conditions about the existence of the non-fragile state feedback controller with two classes of control gain perturbations, and the controller design method is presented. Furthermore, the design problem of the suboptimal guaranteed cost controller is turned into a convex optimization problem with linear matrix inequalities constraints.The problem of robust H∞control for a class of networked control systems with short transmission delay and limited external disturbance is investigated. There are two parts. (1) The state feedback NCS with control input constraints and uncertain delay less than or equals to one sampling period is modeled as a linear time-variant discrete system. Basing on the model built, we development the condition of robust stability and the design method of robust H∞control law for the system. (2) In practical control systems, the state of NCS can't always be measured. So we derive the sufficient condition and robust H∞controller design method of asymptotic stability of dynamical output feedback NCS.For a class of linear time-invariant normal controlled plant with network-induced delay more than one sampling period, we study the problem of modeling and robust H∞controller design. By using the Lyapunov theory and LMI approach, the sufficient condition of network induce delay-independent asymptotic stability is derived. Then, the methods of H∞controller design and obtaining maximum allowable delay bound are also presented. For a class of linear time-invariant normal controlled plant with network-induced delay and date packet dropout, the problem of modeling, exponential stability and controller design for NCS. For the given date packet dropout rate, the networked control systems can be modeled as an asynchronous dynamical system constrained by two configuration event rates. Based on the theory of asynchronous dynamical system, the sufficient condition of exponential stability for NCS is derived. Meanwhile, the dynamical output feedback controller can be solved by a set of linear matrix inequalities.