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Abstract-This paper introduces the monitor system of lowvoltage power distribution based on MODBUS communication protocol. The system adopts master-slave structure. Slave stations which are used to collect data and control are made of many PLCs and intelligent electric power monitoring instruments. Master station communicates with the slave stations by RS485 line of communication based on MODBUS communication protocol and manages data.
Index Terms-PLC, MODBUS Communication Protocol, low-voltage power distribution
I. INTRODUCTION
Along with the complication of industrial production method and the unceasing enhancement of function request, more and more high request is brought forward to the power distribution system. Besides satisfying the traditional capacity and the reliability, some new requests such as the data acquisition, the long-distance control, the failure detection and so on have been put forward. Monitor system of low-voltage power distribution based on MODBUS communication protocol adopts masterslave structure[1][2][3]. Slave stations are made of many PLCs and intelligent power monitoring instruments, which are used to collect the electrical parameter information of low-voltage system and the switch state information of power distribution, and so on. Master station is the human machine interface of the whole monitor system, which is used to monitor and control the equipments, and realizes the information centralized management.
II. THE WHOLE DESIGN OF THE SYSTEM
This system adopts formidable function Industrial Personal Computer(IPC) to be the master station, and adopts SIMATIC Company S7-200 series CPU224 model PLC and SOCOMEC Company DIRIS AP A40 intelligent electric power monitoring instrument to be the slave station. The slave station connects with the low-voltage power distribution cabinet, according to the request of RTU pattern based on MODBUS communication protocol. The master station connects with the slave stations by RS485 corresponding line to compose the low-voltage power distribution supervisory system. Its hardware connection is shown in Fig1.
III. MODBUS COMMUNICATION PROTOCOL
MODBUS communication protocol is developed by MODICON Corporation, which is mainly used to make the protocol about correspondence rule between the single master station and lots of slave stations. It stipulates that the data transmission takes the frame as one unit, and takes the message as one frame. The message is made of the transmission address, the control information, the transmission data and the verification information. It is a data unit...