The Application Of SIEMENS PLC Redundant System In Coal Conveying Programmable Control System

In thermal power plant, the coal conveying system is a kind of auxiliary system with the features of large coverage, more facilities, quite incompact arrangement and most complex control. The requirements on reliability, stability, sensibility and performance and investment of coal conveying programmable control system are more and more from hardware to software, from self-control network to external interfaces and local facilities.The paper, based on renovation project of coal conveying programmable control system in Huaneng Weihai Power Plant, dissertates the concept, construction, control core, element selection, control method and design principle of coal conveying programmable control system. At present, the control core in coal conveying programmable control system is PLC system, which the CPU was redundantly configured with double host computers. The local station of the PLC system is linked with I/O stations through the communication network configured redundantly. Different PLC system has different configuration, communication and protocol, but all in high investment on CPU redundant structure.For SIEMENS S7-400 and S7-300series products, some CPUs can be redundantly configured through programming with software. Such system has the features of lower cost and reliability and the switching time of the redundant CPU completely meets the requirement of the coal conveying programmable control system. The communication between CPU and I/O is through PROFIBUS-DP. The detection on redundant switching between two CPUs is through PROFIBUS or Ethernet. The man-machine interface was linked with MPI or Ethernet. Based on SIEMENS STEP7, this paper describes the configuration of the redundant PLC system, meanwhile, concentrating on control technology and operation requirement of the coal conveying programmable control system , explains the programming principle and method, construction, function and steps, and gives an example of the PLC program in actual coal conveying programmable control system.This paper combines technical theory into actual project, describes the technical key point between coal conveying programmable control system and SIEMENS software redundant PLC system, gives theoretical evidence for the design and construction of the coal conveying programmable control system and finally discusses the method of operation and example project of SIEMENS software redundant PLC system.