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Aiming at the defects of CAN bus real-time communication in substation automation system, this paper introduces the application mode of CAN bus in the substation integrated automation system and the defect solution. This paper mainly implements the construction manner of CAN bus distributed network system, in this construction, the protection measurement and control unit in Substation spacing layer can exchange information and data through the CAN bus network. In this way, a efficient data communication network has been built. This paper focuses on the modified design of the network controller on hardware and software, through the advanced design of the photoelectric isolation module and the overall design on the program code writing ideas. In the photoelectric isolation module, 89C52 is used as the micro controller, in this chip, the send and receive interrupt subroutine is built. Comprehensive the above design, the CAN network communication problems in the substation automation system is solved perfectly. Introduction With the development of computer technology and detection technology, computer automation technology has become increasingly mature, the more intelligent and networked operating form of unmanned substation has become a trend in the development of the substation [1]. In this trend, higher requirements has been put forward for the communication of substation automation system: a high degree of effectiveness and good real-time performance, the interference of communications in strong electromagnetic environment [2]. This requires us to use high-speed, reliable communications network, and the same time use the efficient communication protocol. For substation automation control systems, the hierarchical structure is shown in Figure.1: Processing layer Spacer layer Substation level Appropriate means of communication Fig.1. Ideal 35kV and under 35kV substation automation system structure The structure of the system is mainly composed of three layers: the processing layer, spacer layer and the substation level. The field intelligent control equipment and protective devices are in the spacer layer, the local monitoring host and necessary operation screen belong to substation layer. The spacer layer and the substation level contact to each other through certain means of communication. In connection of spacer and substation level, the used means of communication should ensure the data has a high degree of real-time and complete fully shared of data under the premise of the rapid transmission, and then achieve hierarchical distributed control of automatic control. The traditional RS232 and RS485 have obvious flaws in the transmission of ensuring the data reliable and real-time. For the traditional RS232, the communication mode of master-slave and the connection of point to point made it has a poor flexibility; for optimum performance of RS485, although improvements in flexibility, the number of nodes is limited, the network extremely inconvenient and poor real-time. Ethernet can achieve the automation control system, but erection International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 281 Ethernet and interface device are complexity and high cost. For substation automation systems with a limited amount of information communication, Ethernet does not have the cost performance advantage. In summary, the field CAN bus with multi-master communication mode can transmit large amounts of data, the bus can set a large number of nodes, high transmission speed and good real-time transmission, so it can take full advantage in the substation automation control systems. Design Brief of Substation Automation System Based CAN bus So far, CAN is the only international standard field bus, and its multi-master communication mode achieves sharing capabilities that any node in the network can send information to other nodes at any time initiatively, and regardless of master and slave [3]. In the selection of communication media, CAN bus can use fiber optic, twisted pair or fiber optic to communicate. In addition, the longest distance of CAN bus to communicate directly is up to 10km. Transfer rates is up to 1mbps (at this time the communication distance should be limited within 40 meters), in the case of a serious error, CAN node has a function to automatically turn off the output, so that the operation of other nodes on the bus can not be affected. Bus driver circuit determines the nodes number of CAN bus and it can be up to 110, when using the number of message identifier (29 bits) of extended frame, the nodes are basically unchecked. The adoption of Non-destructive arbitration technology in CAN bus makes that when there is a conflict caused by multiple nodes sending message simultaneously, the high priority node can uncontrolled transfer data preferentially and lower priority node will exit send data automatically [4]. Under heavy network load situations, such competition approach will greatly save arbitration time that the bus used when conflicting and then avoid the appearance of paralysis on the bus. For the structure of substation automation system, the field CAN bus has some advantages in achieving communication, such as good real-time performance, good communication reliability and network convenience, but the same time CAN bus has some technical difficulties on the problems of taking into account the communication distance and real-time communication. The following table shows the relationship between the communication distance and communication rate: Bit rate(kbps) 1000 500 250 125 100 50 20 Distance(m) 40 130 270 530 62 |
