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At present, the decentralized control system has been applied to all aspects of industrial process control. Its control flexibility, diversity, and reliability have been proved by practice and have been recognized by people. However, the key to designing and selecting a successful distributed control system is to handle the redundancy configuration of the distributed control system. The rationality of redundant configuration directly affects the reliability of distributed control and project cost. Therefore, how to reasonably choose the redundancy configuration is the key to the configuration of a decentralized control system.
The word "redundancy" comes from the English "redundancy". The intention is to refer to the redundant control system, which refers to redundancy, redundancy, surplus, etc. It generally refers to the hot spare capacity or richness of the control system hardware performance or function. However, according to the international prevailing statement, if the master controller (process controller) of a decentralized control system is redundant, it means that the master controller has 1:1 online hot standby.
The redundancy of a decentralized control system can be broadly classified into three types of redundancy: hardware redundancy, performance redundancy, and function redundancy. The following analysis and discussion.
A. Hardware Redundancy of Distributed Control System Hardware redundancy mainly includes two parts. One part is to configure redundancy for the internal hardware of the system, including redundancy of communication network, redundancy of main controller or redundancy of I/O cards, and redundancy of external signals. For the general decentralized control system, the data communication highway and the main controller basically all use the 1:1 hot spare standard redundancy configuration; while the redundancy of the I/O card part is due to different manufacturers or restrictions on the project cost, There are different processing methods, such as adopting n + l standby mode, three taking two standby modes or 1:1 standby mode, and some use only channel standby or configuration optimization methods to ensure the reliability of the main signals, and some do not Redundant configuration.
Another part of the hardware redundancy is power configuration redundancy. General decentralized control system power redundancy uses two-way power, that is, dual power configuration redundancy. However, due to different manufacturers, the specific configuration is slightly different, such as the use of dual AC power supply (Figure 1) or all the way to 220VAC, another 220VDC or 110V DC power supply (Figure 2). 
The redundant configuration of the power supply must be designed in detail according to the different control objects and the characteristics of the decentralized control system itself, and cannot be generalized. The external power supply traditionally uses a single UPS as the upper power supply. If the engineering cost is allowed, dual 10O% UPS can also be used as a redundant standby power supply. The traditional single UPS power supply scheme is shown in Figure 3. 
Second, the performance of distributed control system Redundancy performance redundancy is mainly to the decentralized control system communication rate, storage capacity and other performance richness requirements, is to ensure that the control system in the task when the peak of information processing, operation, control to meet the decentralized control The basic requirements for the normal function of the system. Generally, the redundancy requirements of various performance indicators should be strictly controlled and reasonably considered in the engineering design to ensure that the peak operating conditions and the normal processing capacity of the decentralized control system are sufficient. Otherwise, the project cost will increase, affecting the cost and performance. Price ratio. In general, the main control indicators for the decentralized control system redundancy are as follows:
(1) Decentralized control system communication network load rate < 40%;
(2) The average load rate of the main controller of the decentralized control system is <40%, and the maximum load rate is ≯60%;
(3) The average memory capacity of the main controller is less than 40%;
(4) The power supply margin of the distributed control system is 30% to 40%;
(5) I/O points online hot standby >10%;
(6) I/O card slot standby >15%.
Third, the function of the decentralized control system The redundancy function mainly includes two aspects. On the one hand, the redundancy configuration for functional design; on the other hand, fault-tolerant technology is adopted for control technology software to implement fault-tolerant processing of system software and application software, achieve redundancy of system performance, and improve system reliability. For example, in the decentralized control system, the input and output signal and the analog signal are processed in three or two or three to process the calculation software, fault-tolerant redundancy of the input signal, such as disconnection or fault protection; the self-diagnosis function and expert used in the decentralized control system The redundant technologies such as analytical redundancy methods adopted by the system and CCS control; and the treatment of fire extinguishing judgment of the furnace flame signal, etc.
The function configuration of the main controller of the decentralized control system is the key to the successful application of the decentralized control system. Therefore, in the decentralized control system function design should pay attention to the use of redundant design, which can greatly improve the reliability of the decentralized control system to achieve a multiplier effect. The functional design is mainly to take advantage of the autonomous working capability of the redundant main controller of the decentralized control system. In the design, the functions are dispersed and the hazards are dispersed. This ensures that the entire controlled object does not affect the overall operation or safety due to a local system or equipment. . Its main characteristic is that different main controllers are selected according to the redundant arrangement characteristics of the main equipments of the controlled object. For example, A and B small steam turbine feed pumps, A, B, C, D, E, and F coal mills in the pulverizing system are controlled by different main controllers. In order to ensure the redundancy of the distributed control system and the reasonable redundant configuration and organic combination of the controlled object, the maximum redundancy of the entire controlled object and the control equipment is focused on, and the maximum reliability of the overall control is achieved.
IV. Conclusion In conclusion, in the design, manufacture and application of decentralized control systems, the redundancy and rationality are the key to decentralized control system technology problems. It is reflected in the redundancy of hardware, performance and function. , manufacturing, application of all aspects. The decentralized control system adopts redundant technology and reasonably considers its redundancy. The essence of the decentralized control system is to comprehensively consider the redundancy of the decentralized control system and the redundancy of the controllable object system, so that the decentralized control system can achieve a perfect unity and be finalized. Decentralized control system application engineering cost and reliability of distributed control system. Therefore, the redundancy and rationality analysis of the decentralized control system are the key technologies and core requirements for the design, manufacture, and application of decentralized control systems.
Analysis of Redundancy and Rationality of Distributed Control System
Abstract : According to the characteristics of distributed control system, this paper analyzes the redundancy configuration and rationality of distributed control system from three aspects: hardware, performance and function of distributed control system.