Study And Application Of Communication For PLC-based Hydro-turbine Governors

Owing to the characteristics of high reliability, standardization, series, application widely and new technology, Programmable Logic Controller (PLC) is used in hydro-turbine governor widely. And PLC-based governor has become the leading product of hydro-turbine governor in our country currently. With the development of computer network technology and field bus technology, the communication between the PLC-based governor that located in the level of local control device and the monitoring and control system is more and more convenient and efficient. Considering the multiformity of manufacturer who produces the monitoring and control system and the local control unit (LCU), which adopts different field bus, it is necessary making it clear that if PLC corresponds with the field bus, and that if the communication protocol is consistent. Combined with the engineering object——hydro-turbine governor control system of ZheJiang Beixi grade 2 hydropower station, aiming at the fact that the communication protocol of the PLC-based governor is not in accord with that of the monitoring and control system, this paper proposes a method that realizes communication between the PLC-based governor and the monitoring and control system by protocol conversion programming with C language, and developed the communication protocol convertor successfully. This paper is made up of 6 sections. In chapter 1, the domestic and overseas development of hydro-turbine governor and the general situation of microprocessor-based governor are introduced. The characteristics of programmable logic controller and the advantages of application in hydro-turbine governor system are described later. In chapter 2, it makes an introduction on the base of computer communication and the technology of field bus, and Open System Interconnect Reference Model and Field Bus Model are discussed in detail. In chapter 3, it makes a detail description on MODBUS communication protocol and MITSUBISHI MELSEC communication protocol. Analyzing and comparing these two kinds of protocols, it proves the feasibility of protocol conversion. In chapter 4, it describes the structure of communication system, and makes an introduction on the hardware structure and software design. In chapter 5, a test and local operational experiment for the protocol convertor is carried on and the experiment result is analyzed. Finally, it summarizes and makes expectation in chapter 6.