Analysis And Control Of Networked Systems Based On Stochastic Switching Approach

Feedback control systems wherein the control loops are connected with a real-time network are called networked control systems (NCSs). The primary advantages of NCSs are low cost, reduced system wiring, simple installation and maintenances, high efficiency and shared information. As a result, NCSs have been widely applied to many complicated control systems, such as industrial automation, intelligent traffic, robot, aviation and aerospace fields, airplane manufacture. However, the insertion of the communication network in feedback control loop makes the analysis and design of NCSs complicate because it introduces some problems existing in network into control systems such as limited communication band width, network-induced delay, data packets dropout, disorder of data packets and clock asynchronous. These problems lead to control signal can not be executed immediately. As a result, performances of control systems become badly or even control system become instable. Because these problems do not exist or can be ignored in traditional feedback control systems, methods of control design and analysis based on traditional control theory is hardly applied into NCSs directly. So control strategies adapting for network environment should be found based on new ideas, new methods and new conceptions. Therefore, analysis and synthesis of NCSs have become one of the most important issues in control theories reasearch, and also have received considerable attention and interest by researchers in recent years.In the dissertation, some essential issues of NCSs are discussed from the point of view on control theory and arithmetic. Modeling, stability analysis, fault tolerant and control problems of NCSs are investigated based on time-delay system theory, jump linear system theory, Lyapunov stability theory combined with linear matrix inequalities (LMIs) techniques, V-K iterations, free weighting matrices approach and greedy algorithm. Some new results are given as to these basic problems based on analysis and synthesis of NCSs.As to problem of time varying delay existing in NCSs, a time-varying model including certain system and uncertain system are constructed firstly, and then stability and stabilization of these systems are discussed based on time-delay system theory, cone convex optimization theory and free weighting matrices approach. Conditions of time-dependent stability and stabilization with less conservative are given in the form of linear matrix inequalities.Based on discrete time Markov jump linear system theory, stability and controller designed are considered when time-induced delay, packet dropout and disorder of data packets exist in NCSs at the same time. An intelligent stochastic switching controller which can self-adjust adapted for different network load is proposed to stabilize NCSs. Compared normal feedback gain controller, stochastic switching controller not only has larger stability scope but better dynamic stability performances.A new switch model switched according to probability is proposed to discuss problem of stochastic fault about actuator. Using V-K iterations, mode-dependent and mode-independent fault tolerant controller are designed under some stochastic disturbances such as stochastic actuator fault and the maximum redundancy degree of system is given.As to the multirate essences of NCSs, a new multirate method is proposed to stabilize NCSs combined with time-induced delay, packet dropout and disorder of data packets. The advantage of this method is that, a unitized model which can describe short time delay and long time delay is constructed. Based on this unitized model, stability and stabilization of NCSs are discussed. Sufficient condition of mean square stability of NCSs is given when transition matrix is known. From simulation example we know, multirate controller has stronger robust performance compared with single controller under the same conditions.Based on analysis of data coming from test in internet and normal method developed from general NCSs, a unitized method which can deal with time varying part of time delay less than one sampling period or more than one sampling period but bounded is proposed . Finally from simulation we know, compared normal controller, controller designed with this method has strong robust performances.Consider the character of multi-signal transimisson and different statistic rules of every class of signal in wireless sensor network, a new model which can describe wireless sensor networked control systems accurately is constructed firstly. A static output feedback controller is designed through weighted mean method, and then stability and stabilization of wireless sensor network are disscussed using jump linear systems. Numerical examples and simulations show that the methods are effective.Finally, a summary has been done for all discussions in the dissertation. The research works in further study are presented.