Research And Application Of Ethernet In Networked Control System

With the development of information technology and control technology, profound revolution has happened to the traditional control system. The control system has gradually formed a networked and open structure. Networking, distributing and node-intelligentizing are going to be the new development direction. In the mean time, with the development of management and control integration technology, it is urgent to establish a unified and open communication network, and integrate the information network with the control network. In this way, it is easy to carry out centralized management, high-layer supervision and enterprise automation.Although field buses have provided a good solution for the networking of the equipment layer, it is difficult for them to integrate the management layer with the field control layer seamlessly. So people turn to Ethernet, which is used widely in high-layers of the enterprises, and want to extend it into the field equipment layer.However, the protocol CSMA/CD (Carrier Sense Multiple Access with Collision Detection) used in the MAC (Media Access Control) layer of Ethernet, makes the transmission delay of Ethernet uncertain, which becomes the main obstacle for adopting Ethernet in the field equipment layer. Except for the uncertainty, there are still many problems need to be resolved before applying Ethernet to the field environment, such as packet losses, stability of system, network security and so on.In the paper, the main researches aimed at the problems of Ethernet which is used in the field environment are described as follows.1. The paper analyses the real-time ability of Ethernet and factors that affect the ability. In the meantime, some measures are put forward to improve the real-time ability of Ethernet. Besides, it provides some primary methods to bus powered and security of the industrial control network.2. Based on model predictive control, a compensation algorithm is presented for Ethernet control systems with uncertain transmission delay. The algorithm is simulated using MATLAB software and the simulation results show that the control strategy is effective and feasible.3. According to the requirements of field equipments, the paper designs a hardware platform for Ethernet with the powerful embedded CPU ARM. The platform supplies some other functions as well, such as field data collection, control output and communication with CAN Bus. Then the paper transplants the real-time operating systemμC/OS-II to the platform, realizes the TCP/IP stack and builds an embedded Web Server. Besides, in order to build a whole experimental platform, the paper also designs two CAN bus nodes with MCU. They provide many functions, including data collection, man-machine interaction interfaces, step-motor control and so on.The paper is divided into six parts. The first part introduces the background, significance and actuality of the research. The second part analyses the industrial ethernet technology and puts forward some measures for important problems. The third part presents a compensation algorithm based on model predictive control for Ethernet control systems with uncertain transmission delay. The forth part introduces the design scheme of the hardware for the networked control system platform and the realization of the key drivers. The fifth part introduces the design and realization of the application software for the networked control system platform. The final part concludes the whole paper, and presents prospects for the future research.