Stabilization And Filtering Of Networked Control Systems

In a networked control system (NCS), plant and controller are typically connected via a communication network which may be shared with other applications. The main advantages of NCSs are low cost, reduced weight, simple installation and maintenance, and high reliability. Consequently, NCSs have been applied in a broad range of areas such as mobile sensor networks, manufacturing systems, teleportation of robots, aircraft systems, etc. however,the usage of the network may lead to some new problems, such as network delay, data packet loss, signal quantization, etc. In this paper, the analysis and design of networked control systems with network delay and (or) packet dropout are considered. The main contents are as follows:Stabilizability and detectability of NCSs with random packet dropout are investigated, where the network packet-loss is modeled as an i.i.d. Bernoulli process. Two commonly used modes compensating for signal-loss—using a zero signal and using the latest available signal are compared. First NCSs with the"zero signal"mode is considered. Several necessary and sufficient conditions for stabilizablity are established. A notion of stabilizable degree is proposed, which help to further analyze the relationship between network transmission probability and stabilizability of the networked control systems. Due to the duality between stabilizability and detectability, the above results and notions about the stabilizability can readily be extended to solve the detectabiliy. For the SISO systems, an explicit formula for the least required transmission probability for the purpose of stabilizing or detecting a networked control system is derived. The result shows that the least required transmission probabilities are equal each other when stabilizing or detecting a networked control system. And it is merely dependent on the unstable poles of the system. It is theoretically validated that the least required transmission probability is strictly positive interrelated with the degree of instability of the system. That is, the more the degree of instability of a system is, the more the required transmission probability will be. Then a necessary condition for stabilizablity of NCSs with the"latest available signal"mode is proposed. It is theoretically proved that the"latest available signal"mode can not better compensate the effect of loss data than the"zero signal"one. In addition, optimizing location of state-observer based controller in the network is considered. When the controller is located the optimal node, by selecting appropriate controller parameter, the closed-loop system can be stable with maximum loss probability of the network. The efficiency of the proposed results is illustrated with some simulation examples.The stability of the discrete-time networked control systems is analyzed when there are both network delay and packet loss in the network. A new delay-dependent stability criterion is proposed. Compared with the some existing results, the advantage of the proposed stability condition lies in its less conservativeness. Differently to pervious methods, by utilizing the properties of convex function, the differences of the delay and its upper and lower bound need not simultaneously be enlarged as the differences of its upper and lower bound. Thus the conservativeness of the result is reduced. Both theoretical proof and example show the advantage of the proposed stability criterion. Based on the stability criterion, the design method of the state-feedback controller is provided. Moreover, the CCL algorithm has been improved. Simulation example is given to show that the proposed design method of controller is also less conservativeness than the existing ones.A new networked predictive control method is proposed for the discrete-time networked control systems, which simultaneously contain network delay and packet loss. Compared with the existing methods, the proposed method has the following merits. The proposed method can more efficiently compensate the effect of network delay and packet dropout. Thus the stabilizability condition of closed-loop systems is very easily satisfied. Moreover, by the proposed method, the state-feedback controller and state predictor can be separately designed, so the networked predictive controller can easily be design to guarantee the stability of closed-loop system. By theoretical analysis and simulation example, the advantages of the proposed method are verified.The H∞filtering in the networked control systems is considered. Under this case, the measured signals of the system are transmitted to the filter through the network, which are inevitably subjected to the effect of the network delay. The network delays are assumed to satisafy an i.i.d. Bernoulli process. A new form of the filtering error system is proposed, which translates the delay system into a delay-free system. Therefore, Lyapunov-Krasovskii is not required when the H∞filtering performance is analyzed so that the conservativeness of result of performance analysis is reduced. Moreover, the proposed H∞performance criterion is theoretically proved that it is less conservative than the existing one. Based on this performance criterion, a new parametric design method of the filter is proposed. It also is proved that it is less conservative than the existing one. In addition, by introducing some slack variables, an improved filter design is presented and its efficiency is illustrated by an example.