Research Of Communication Network In Power Quality Monitoring And Control System

With the further development of the national economy, the demand to improve power quality is greatly needed. In the whole power quality monitoring and control system, all the controlling command, data transmission and information exchange among workstation, front-end computer and monitor and control equipment of power quality are implemented by digital communication, which needs well real-time performance and reliability. Moreover, communication network and network transmission protocols are the key factors that decide the reliability of communication system and the high speed of information transmission.The paper studies the communication between monitor and control equipment of power quality and front-end computer in the power quality monitoring and control system, then design the dual-network communication module and the CDT protocol Program.First, the thesis inquired into the power quality monitoring and control system in the applied present condition of the communication network and protocol, discussing to study the necessity of the exhibition thesis, introducing the fundamental mode of information transmission: serial communication. Then according to the characteristics of the ISO/ OSI seven layer reference models aim at the power energy metrical LAN to carry on the analysis, and fieldbus technology and it carried on the introduction in the application in the power quality monitoring and control system, among them, the point introduced the of the RS-485 and CAN,and put forward "CAN+ High speed RS-485" fieldbus communication system. After the point is to take CDT protocol as an example, discussing the telecontrol protocol.Then carry on the design to the test and control subnetwork of the power quality monitoring and control system. We combine the RS-485 to deliver the distance far and deliver the quick advantage of speed with CAN, the redundant dual of the formation" CAN+ High speed RS-485" install. Not only can raise the speed and extension the distance, but also can complete the hot-reserved function. Thus, make the function of the test and control subnetwork good. Carried on the detailed introduction to the design of hardware circuit of the dual immediately. The node of CAN mainly is responsible for the CAN net communication, among them adopting the SJA1000 to be the controller of CAN, the PCA82C250 is the transceiver of CAN;The high speed RS-485 design part is the standard of the physics layer with the RS-485, joining of HDLC protocol in the data link layer, choose the MT8952B HDLC as protocol controller, and adopt the chip of MAX483 to be the transceiver.Finally, use the Visual C++ to design the software of test and control subnetwork. Because the openness of the power quality monitoring and control system is one of the important index signs of function, hence this paper use the CDT protocol that enacted by Ministry of Electric. Use the MSComm carried out the concrete process of the serial communication part of the test and control subnetwork, and communication with the CDT protocol standard, adopting a kind of quickly simple CRC algorithm. This procedure adopted the object-oriented method in design process, each function modules can transplant other platforms or software very expediently, also can enlarge other protocol procedures according to the demand.