Analysis And Identify Upper Bound Of Induced Delay Of Networked Control System

Computer technology, control and network communication are the three popular study and application field, and networked control system (NCS) is the combination of these three areas, it’s a new cutting-edge areas of research, has its particularity and complexity. It fully reflects the developmental tendency of control system networking, integrated, intelligent and distribution. With the development of science and technology, integration system of enterprise information increasing complexity and growth, network control is the external demand of the complex and remote control systems. Owing to it’s convenient wiring, easy to expand and maintenance, resources can be shared and a number of advantages. NCS is widely used in industrial, aerospace and other fields. NCS solves many problems in the control system, makes enterprise efficiency risen greatly, but the introduction of the net as a medium of information transfer create new problems to the control system. In addition to transmitting control information in the network, many data have nothing to do with control tasks also need to be transmitted, this led to data collision and packet loss, competition of network resources and congestion bring delay to network, the traditional control theory is no longer to describe the NCS objectively.This paper first introduces the definition, composition and development of NCS, describes the advantages of a networked control system compared to traditional control systems briefly, also pointes out basic problems in NCS, such as network-induced delay, packet loss, the stability of the system and so on..Then it makes a detailed introduction of the delay in the NCS. Because delay in network latency have much to do with the network’s types, the paper introduces three different net briefly and analyze its protocol, these three types net are PROFIBUS, CAN and Ethernet. Then we build model in short delay and long delay respectively, and analysis time sequence of each node in the network..Finally, we use the toolbox of Matlab/Truetime, built the model of the control system, simulated and analyzed the impact of different factors on the network-induced delay, These factors include network without interference and have varying degrees of interference, different network types (CSMA/CD, CSMA/AMP, Round Robin, Switched Ethernet). We use DC motor as controlled object and PID control algorithm. We verified the normality of the delay distributions and given a more reasonable upper bound network-induced delay through statistics and analysis delay data.