Modeling, Analysis And Control Of Networked Control Systems

Networked control systems(NCSs) are closed loop feedback systems constituted by real-time network.In NCSs,sensors,actuators and controllers are connected by means of a network or other shared medium,and information transmission among control system components is realized through a commonly shared network medium, which is the development and integration of control science,computer technology and network communication.Compared with the control system marked by traditional "point to point" direct link,there are several advantages for NCSs,which are given as follows,but not limited to less wire,less cost of installation,easy maintenance, higher flexibility and reliability,good fault detection ability,etc.However, some problems such as network-induced delay,packet dropout,multi-packet transmission and time-varying sampling period are usually arisen due to band-limited channels,so the use of a network may deteriorate the performance or cause instability. Consequently,associating the characteristic of NCSs,it has become a hot issue how to solve these problems in NCSs by utilizing existing control theories.Recently,a wide range of research has been reported dealing with problems related to modeling,stability analysis and design of controller of NCSs with network-induced delay and packet dropout.However,the problem how to efficiently utilize the finite communication resources and sufficiently share network bandwidth is still to be solved,which can guarantee stability of closed-loop system and maintain related good performance.On the basis of integration of related previous works, model formulation for NCSs with stochastic time delay and data dropout is proposed by utilizing the theory of Markov jump system,and static output feedback controller is designed in this dissertation.Furthermore,the model formulation for NCSs is proposed by virtue of periodically time-varying controller,which facilitates the share of information with the limited communication channel.Hence,the performance of system is improved.By using the dynamical scalar,the dynamical parameters can be switched,and the proposition of formulation of NCSs with quantized feedback controller can stabilize the model system and maintain good H_∞function.The main results obtained in this dissertation are summarized as follows:(1)Considering the limitation of bandwidth in the NCSs,a class of formulation methods for NCSs with stochastic delay and data packet dropout are proposed in terms of the theory of Markov jump systems,which is beneficial to saving the bandwidth,reducing congestion of network,shortening delay of data transmission. In the designed models,sensor node and controller node are time-driven,the actuator node is even-driven,and the sampled data were lumped together into single data packet.Since the state of NCSs can't be measured directly,the H_∞controller design is presented through static output feedback.By means of the LMI,the design of the H_∞optimal controller is formulated as a convex optimization problem.Compared with the existing results,the merits of the obtained results are simple and feasible.(2) The stabilization problem of NCSs is studied under conditions of restricted media access NCSs.Based on the theory of time-varying periodic system,the modeling of NCSs with multiple sensors,actuators and controllers are connected with a network is presented in this dissertation.Because of the limitation on bandwidth, only a portion of the sensors and actuators can receive the information delivered by the controller.However,the other sensors and actuators have to wait.Therefore, the performance of NCSs not only depends on the controller designed,but also depends on the media transmitted efficiently.In terms of the feasible solutions to LMI,a necessary and sufficient condition is derived via the usage of networks in the context of decentralized control,and the set of periodically time-varying(PTV) local controller can be derived.(3) The problem of controller design for NCSs via digital communication is addressed. The systems under consideration are stabilized via state feedback,where the effects of sampled signal,state quantization,network-induced delay and packet dropout are considered.The proposed delay-dependent stability criteria are formulated in the form of LMIs method,which ensures asymptotic stability and a prescribed H_∞performance level for NCSs with admissible uncertainties.Maximum allowable delay bound of NCSs is obtained by solving a convex optimization problem.At the same time,quantized feedback stability criterion of NCSs with nonlinear perturbation is proposed such that the closed-loop NCSs are stable.(4) The problem of the quantized dynamic output feedback controller design for NCSs is proposed.By using the quantized information of the system measurement output and the control input,a novel NCS model is described.This model covers many network-induced features,such as multi-rate sampled-data,quantized signal,time-varying delay and packet dropout.Based on Lyapunov-Krasovskii functions, a less conservative stabilization criterion for the existence of a dynamic output feedback controller is derived by introducing slack matrix variables.The quantized control strategy involves the updating values of the quantizer parametersμ_i(i=1,2) (μ_i(i=1,2) take on countable sets of values which dependent on the information of the system measurement outputs and the control inputs).Design of controller only needs the values of quantizers q_μ1(y_p(t)),q_μ2(y_c(t)) in the sample sequence t=s_i and t=σ_i(i=1,...,∞).In terms of the feasible solutions to LMI,maximum allowable delay bounds of time-varying delay are obtained.Compared with the existing results,the merits of the obtained results are less conservative.(5) The problem of the robust H_∞filtering for uncertain NCSs,where measurement quantization,signal transmission delays and data packet dropout are considered, is addressed.The signal transmission delays are assumed to have both an upper bound and a lower bound,which is more practical than existing results for NCSs.Based on Lyapunov-Krasovskii functions,a less conservative stability criterion is proposed such that the closed-loop NCS is asymptotically stable with an H_∞performance bound.The quantized control strategy involves the updating values of the quantizer parametersμ(μtake on countable sets of values which dependent on the information of the system measurement outputs).Design of filter only needs the value of quantizerq_μ(y_p(t)) in the sample sequence t=s_i(i=1,...,∞).The H_∞optimal filter is formulated as a convex optimization problem.Moreover,the resulting criterion is further extended to more general cases,where the parameter uncertainty of system matrices is assumed to be of the polytopie type.