Research On The Robust Controller Design For Networked Control Systems

In the networked control system, the unavoidable time delay and data dropout whichmake the performance of the control system reduce, even cause the system unstable. In thepractical industrial control, because of the changes in the work condition or environment,components of the control system aging and some physical dates changing, the dynamicperformance of the controlled object is hard to be described by the accuracy math model andthis is the uncertainty in the design of the network control. It has important meaning to designrobust controller for the system due to the time delay and uncertainty.The research background and the structure of the network control system and the currentresearch situation of the analyses and design for the time delay and data dropout areintroduced in this paper. Based on the robust control theory and prediction control theory,the application of the control and prediction of the robust are researched in the networkcontrol system. Then the major research work is expanded on the basis of it.A design method of a suboptimum robust controller is presented. It turns the time-lag ofthe network system and uncertainty which is caused by the modeling mechanism into theuncertainty matrix which meets the given constraint condition. The uncertainty that is causedby the unknown turbulence of the external environment equals to the unknown but boundedenergy function matrix. It meets the upper boundary value of the uncertainty matrix under thisconstraint condition. And it also meets boundary value of the energy function matrix that hasa given performance index, All above can be considered as uncertain factors which can havebad impacts on the system when designing the controller. Based on Lyapunov function andlinear matrix inequality (LMI), a sufficient condition for networked control system subject tothe asymptotic stability and H∞performance is derived, and a robust controller is designed,which neither sets a limitation to whether the time delay exceeds a sampling period, nor needsto meet a certain type of random distribution.A new design method of robust controller based on state estimation is put forward. Inorder to solve the time delay which causes data transmission delay and data lose, it adds thestate estimation device which adopts single-exponential smoothing model as the predictionmodel of the control system and it conduces state estimation at every sampling instant. Whenthe time delay of data transmission between sensor and controller is larger than a samplingcycle, the state variable of estimation will be used as the input of the controller, otherwise the practical state variable will be adopted. In order to achieve the prompt driving of thecontroller under the above conditions, the controller adopts compound driving method withregard to the clock driving and the event driving. The design of the robust controller based onstate estimation can be achieved combining Lyapunov function and theory of linear matrixinequality. The designe method improves the control precision of the networked controlsystems.