Application Analysis of Three Systems of Process Control in Power Plants

None of the three systems used for process control were developed for power plants, or, in the early days of their development, they were not the preferred control object for power plants. In the instructions for use of these systems, the power station is never used as the preferred scope of application, and some do not mention the power station at all. The strange thing is that these three control systems, especially DCS and PLC, have been widely used in power stations, and the effect is very good.

DCS or TDCS system

The distributed control system DCS and the distributed control system TDCS are monitoring technologies that integrate 4C (Communication, Computer, Control, CRT) technology. From the top to the bottom of the tree topology system, where communication is the key. The PID is in the interrupt station, and the interrupt station is connected to the computer and the field instrumentation and control device. It is a tree topology and a parallel continuous link structure, and there are also a large number of cables from the relay station in parallel to the field instrumentation. Analog signal, A/DD/A, mixed with microprocessor. A pair of instruments is connected to the I/O, and the control station is connected to the LAN. The DCS is a three-level structure of the control (engineering station), the operation (operator station), and the field instrument (site monitoring station). The disadvantage is that the cost is high, the products of each company cannot be interchanged, and they cannot interoperate. The large DCS system is different. Used for large-scale continuous process control, such as petrochemicals.

PLC system

From the development of switching control to sequential control and transportation processing, it is from the bottom up. Multi-function such as continuous PID control, PID is in the interrupt station. One PC can be used as the master station, and multiple PLCs of the same type are slave stations. It is also possible to have one PLC as the main station and multiple PLCs of the same type as slave stations to form a PLC network. This is more convenient than using a PC as the main station: when there is user programming, you do not need to know the communication protocol, just write it according to the format of the manual. The PLC grid can be used as a stand-alone DCS/TDCS or as a subsystem of DCS/TDCS. The large system is the same as DCS/TDCS, such as TDC3000, CENTUMCS, WDPFI, MOD300. It is mainly used for sequential control in industrial processes, and the new PLC also has closed-loop control function.

FCS system

The basic tasks are: essential (intrinsic) safety, dangerous areas, volatile processes, and very difficult environments to deal with. Fully digital, intelligent, and versatile to replace analog single-function instruments, meters, and control devices. Replace the scattered field instruments, control devices, PID and control center with two wires to replace the two wires of each instrument. The PID on the bus is equal to the instrument, instrument, and control device. Multivariable, multi-node, serial, and digital communication systems replace single-variable, single-point, parallel, and analog systems. It is interconnected, two-way, and open to replace one-way and closed. Replace the centralized control station with a decentralized virtual control station. It can be operated by the on-site computer, and can also be connected to the upper computer and connected to the upper computer of the same bus. LAN, and then communicate with the internet. Change traditional signal standards, communication standards and system standards into the enterprise management network.