The Research Of The Switching Control Algorithm For NCS With The Time Delay And Packet-drop

ABSTRACT: Networked control system (NCS) is consisted of sensors, controllers and actuators which are geographically distributed in different areas through the network, forming a fully distributed real-time and closed-loop feedback control system. The development trend of integration, distribution and intelligent of the nodes in NCS are fully reflected. However, due to the mechanism, the protocol of communication and the limited bandwidth shared by each node in the network, when the sensors, controllers and actuators exchange data through the network, multi-packet data transmission, data collision, congestion, and so on will be occurred frequently. It makes the time delay and packet-drop emerge inevitably. Therefore the performance of NCS will be declined because of the time delay and packet-drop even the stability will be lost, In order to overcome the bad effects caused by them, the scheme of compensate the delay and packet-drop is proposed in this paper.Firstly, the concept, composition and structure of NCS are introduced briefly and the characteristics and research situation are also introduced. Then a few problems such as the drive of nodes, time delay and packet-drop are brought out. Meanwhile, the target of the performance of NCS is described.Secondly, the reason of the time delay and packet-drop in NCS are mainly introduced. Meanwhile the results of previous studies about them are also described. Then the algorithm, model and current status both in domestic and international of switched control system are introduced. The trends of research and the former scholars’ studies are summarized in this paper.Thirdly, the concept of the switched control system is applied in the NCS and the concept the exponential stability theory, average dwell time and L~2gain are also concerned in this paper. The stability of the system is proved by using these theories. Moreover, a new switched model is built up to compensate time delay and packet-drop. According to the different time interval, the time delay is divided into many sections and different controllers are chosen. By this method, the performance of the system is improved.Fourthly, the model of packet-drop in NCS is studied specifically, and the definition of network switch rate is brought up. Then the state feedback system of NCS with time delay and packet-drop is modeled as an asynchronous switching system and the definition of the event rate of the state is brought out in a closed-loop system. Based on the model of NCS which is built up, the relationship between event rate and packet-drop rate is proposed and proved by the analysis of stability. Therefore, the two models(the time division switching model and the switch rate based model) are compared, and the similarities and differences about them are also analyzed. Moreover, the timing disorder is optimized for the model with time delay and packet-drop, which depended on the switch rate.Finally, the conclusions and the prospects of the paper are proposed.