Mechanism Of Network-induced Delay And State Prediction Control Of The Networked Control System

Networked control systems (NCSs) are distributed feedback control systems whose sensors, actuators, and control units are connected through communication networks. This type of system has the advantage of greater flexibility with respect to traditional control systems. Also, it allows for reduced wiring, as well as a lower installation cost. It also permits greater agility in diagnosis and maintenance procedures. NCSs are the collaboration of three engineering fields, computer engineering, communication engineering (either wired or wireless) and control engineering, and become a novel interdisciplinary research front as the development direction of modern industry. Therefor, some problem such as time delay, data package loss, may accur in the network transmission, which can make the analysis to NCS a difficult task. Because the classical control theory can not be directly applied to NCSs'controller design.Firstly, the media access mechanism, the delay mechanism and charactersitcs and real-time property of several tapical fieldbuses are studied with comparison according to the composition of the network induced delay. The primary factors that affect the forming of the delay in different protocols are discussed via analyzing the worst-case response time and statistical properties of the delay in the network. On the basis above, the mathematical models in three kinds of delay conditions, short delay without data package loss, short delay with data package loss and long delay, of NCS are built. Then, the influence of the network induced delay and the node driven modes to the control performance of NCS is discussed. And, it is pointed that the time driven mode increases the delay, but gives a way to compensate the delay with package loss by using advanced control arithmetics.Whereafter, a delay compensation arithmetic based on time-stamp (TS-DCA) is studied to reduce or eliminate the influence of the network transmission to the control computing. In the short delay condition, a state prediction control method that model the state of the plant in the controller and use time driven mode in actuator is propsed to improve the TS-DCA which need accurate model and can only compensate the delay between sensor and controller. Also, the necessary and sufficient conditions for this kind of NCS's stability are derivated.Furthemore, the maximum sampling interval in the state prediction based networked control system is studied, as foreward channel connect with backward channel using network. The aim is to reduce the network bandwidth in condition of keeping the system in statbility. Modeling, stability analysis, control and simulating of the state prediction based networked control system in the case of state feedback, output feedback and discrete time, are studied. Also, the effect of state estimation error and delay to the maximum communication interval is analyzed.Finally, the approach to realizing measurement and compensation of the delay between controller and actuator by setting buffer at the actuator is proposed. The GPC arithmetic is utilized to achieve delay compensation and optimal control of NCS. Simulation results show the validity of the proposed controller design method.