The term “distributed control system” was derived by translating the product name of a foreign company. Due to the numerous manufacturers and varying system designs, as well as the diverse functions and features of each system, the naming of these products also varies. In China, there are different names for the product, the most common ones being distributed control system (distributed control system, DCS), total distributed control system (total distributed control system, TDCS), and distributed computer control system (distributed computer control system, DCCS). [6]
The differences in names merely reflect variations in naming intentions and translations. Their fundamental nature of the system remains the same, and their intrinsic meanings are consistent. In the Chinese power industry, it is commonly referred to as a distributed control system. [6]
System Explanation
DCS usually adopts a hierarchical structure with multiple levels. Each level consists of several subsystems, and each subsystem achieves several specific limited goals, forming a pyramid structure. Reliability is the lifeblood of DCS development. To ensure the high reliability of DCS, there are mainly three measures: first, widely apply highly reliable hardware equipment and production processes; second, widely adopt redundancy technology; third, widely implement fault-tolerant technology, self-diagnosis of faults, and automatic processing technology in software design. Currently, the MTBF of most distributed control systems can reach tens of thousands or even hundreds of thousands of hours.
The distributed control system is a distribution of multiple physical resources and logical resources (multiple computers or processing units, multiple data sources, multiple instruction sources and programs), using a certain interconnection network or communication network to interconnect resources, having a high degree of local resource autonomy ability, mutual cooperation ability among resources, and overall coordination and control ability of resources. It can achieve dynamic management and allocation of distributed resources, parallel operation of distributed programs, and computer network control systems with decentralized functions. The meaning of the distributed control system is mainly reflected in “dispersion”, and the meaning of “dispersion” includes several aspects. [6]
Dispersed configuration
The locations of each controlled device are scattered, and the corresponding system control equipment is also configured in a dispersed manner. Multiple distributed control units based on microprocessors are respectively responsible for different control tasks. [6]
Function dispersion
The functions possessed by the distributed control system are not concentrated in a single central control unit. Instead, they are distributed among various decentralized control units. Moreover, the functions such as data acquisition, process control, operation display, monitoring operations, and self-tuning in the control system are also dispersed and relatively independent. [6]
Display dispersion
The display function of the decentralized control system can not only be centralized on the central operation station, but also be distributed to local operation stations. The central operation station has the ability to display all the information of any decentralized process point in the entire system, and can be displayed separately on different display terminals. The local operation station can not only display on-site information through the on-site control unit at any time, but also the third and fourth generation decentralized control systems can call information from other local operation stations or the central operation station at any local operation station for decentralized display. [6]
Database decentralization
Modern distributed control systems mostly employ distributed database systems. The field control units and control stations have local databases, which are shared by the entire system. [6]
Communication decentralization
The distributed control system adopts the communication technology of local area networks. Each process unit in the network has equal communication control rights, enabling decentralized communication. [6]
Power supply decentralization
The decentralized control system provides independent power supply devices for different control units, enabling the power supply of the system to be decentralized and enhancing the reliability of the system. [6]
Load distribution
In the distributed control system, the overall tasks are reasonably distributed to each control unit. One control unit only undertakes the control tasks of several local control loops or subsystems. The workload of the entire system is distributed, and the load of each control unit is basically uniform. [6]
Risk dispersion
The realization of “dispersion” means the dispersion of risks throughout the entire system.