Distributed Clock Synchronization Method Based On Ethernet POWERLINK And Its Application In Control System

With the rapid development of information network technology today, the traditional fieldbus techniques have been unable to meet the needs of industrial control systems. Industrial Ethernet is playing a more and more important role in industrial control network. Industrial Ethernet has a series of advantages like high communication rate, good openness, good real-time performance, low cost and resource sharing capability, which perfectly meet the requirements of communication in network control system. Ethernet POWERLINK is a typical real-time Industrial Ethernet, which is built on the standard Ethernet. Its real-time performance is impressive, the protocol is open source, and suitable for a variety of platforms, which gives it extensive application prospect in industrial control field. This paper analyses the structure, communication mechanism and performance of Ethernet POWERLINK protocol, and then a design of high performance process unit based on ARM and a real-time communication platform based on FPGA are presented, furthermore, an improvement strategy of clock synchronous method is proposed after analyzing the flaws of the protocol. Finally a design of gateway between Ethernet POWERLINK and TCP/IP network is presented, and the protocol is implemented in a new generation of distributed control system.The main content and innovation are as follows:1) The implementation of Ethernet POWERLINK network in a variety of platforms are discussed, mainly concentrating on the performance comparison in a Linux and FPGA environment. A design of high performance process unit based on ARM is presented, in which the driver module of general-purpose memory controller for Ethernet POWERLINK is implemented. Along with the unit, a design of real-time communication unit based on FPGA is presented too. Both parts composing the AP-PCP structure make the Ethernet POWERLINK node a perfect platform for high performance process and real-time communication.2) Two methods of clock synchronization for Ethernet POWERLINK are studied. After analysis of the cause for the clock synchronization deterioration, a method of reducing them is proposed. A Hub based on FPGA is also designed in the Ethernet POWERLINK network, which overcomes the shortage of inconsistence introduced by the packets back and forth. The study makes a significant improvement for the realization of high accuracy distributed clock synchronization network based on Ethernet POWERLINK.3) The cross communication function in Ethernet POWERLINK is studied and implemented. Also a design of gateway between Ethernet POWERLINK and TCP/IP network is presented, which solves the conflict between real-time and non-real-time data. Furthermore, the structure and characteristics of a new generation of distributed control system are introduced, in which the Ethernet POWERLINK protocol runs.