Discussion on the Principles and Techniques of Distributing Control System Master Controller Function Distribution

The large-scale thermal power plant adopts a mature and reliable decentralized control system to achieve a high level of automatic control and has entered the mature period of application. General advanced 300 MW or more units can achieve single-machine single-person normal operation, full-automatic process control, and programmatic accident handling. Practice has proved that large-scale unit automation technology can not only reduce the labor intensity of the operating personnel, more importantly, it ensures the safe, economical and efficient operation of the unit. The correct and reasonable application of the decentralized control system is crucial to the function allocation of the main controller. Therefore, to obtain a plant automation system with high automation level and high reliability, a reliable and mature decentralized control system must first be established. However, for the success of decentralized control system application, there must be successful distribution and application of the main controller function. This article combines the engineering practice of two 600MW units in the third phase of Zouxian Power Plant, discusses the principles and techniques for the function allocation of the main controller of the decentralized control system.
First, the decentralized control system The main controller function distribution hardware requirements and basic conditions There are currently thousands of decentralized control systems in the world, but there are about 10 manufacturers in China are widely used products, generally, experts recommend There are six approved foreign manufacturers:
Westinghouse (US) WDPF, Ovation
BaileyContr01s (US) Network90, INFl90
Foxboro (USA) Spectrum, I/ASeries
Siemens (Tec) TELEPERM, PCS
Leeds & Northrup (US) MAXl000
Hatachi (Japan) Hiacs-3000
Due to the rapid development of the information industry, especially the development of computer chip technology, computer technology and automation technology, these manufacturers have also launched their replacement products. However, no matter how the decentralized control system develops, its basic topology is generally divided into two types: one is a highway type and the other is a ring network type. From the network level, it can be divided into single-layer network or multi-layer network. Therefore, the basic level of a decentralized control system is:

● Example: DPU Redundant Structure of Westinghouse Distributed Control System

According to different manufacturers, the main controller is also called the distributed processing unit DPU, multi-function controller MFP, control module, main control module, main control board, main processor and so on. It is the core component of decentralized control. All decentralized system functions are implemented by different coordination of its function allocation. It cooperates with other main controllers, and a pair of redundant main controllers are used for mutual backup. The task does not have to depend on the network. Each pair of DPUs forms a whole system through the network and realizes information communication and function coordination. Therefore, how to apply a field control system, the function allocation and configuration configuration of the main controller will be crucial.
Although the principle of each decentralized control system is basically the same, the specific structure is still very different, and the function and characteristics of the main controller itself have some differences. Some main controllers are limited by the structure of the decentralized control system itself or the limitation of manufacturing technology, and their function strength, size, and application range are also different. Some are dedicated main controllers, such as dedicated main controllers for data acquisition, main controllers for sequence control, and main controllers for automatic adjustment. However, with the development of decentralized control technology, the number of such decentralized systems is decreasing, and the main controller is developing towards full functionality. Therefore, the function allocation of dedicated main controllers will not be described in detail herein.
The full-featured main controller, ie, the main controller in the distributed system, has the same structure and characteristics, and can realize any combination of functions or multi-functions required by the automatic control system. The application of the dedicated function is no longer enhanced but the task. Integration can achieve many functions such as DAS, SCS, CCS, and ETS, while giving designers greater autonomy. This article mainly describes the principle and skills of the main controller of this type of distributed control system.
How to choose a reliable and mature decentralized control system is a very complicated task, and it is not included in the content of this article. Here only the most basic hardware requirements and basic conditions that affect the allocation of the main controller, namely the physical environment, are proposed as follows: Principle requirements:
● The decentralized control system must have a sufficiently strong communication rate to support the basic communication assurance necessary for all master controllers to complete field missions.
● The main controller in a decentralized control system must be fully functional and its hardware configuration must be reliable and redundant. Redundancy includes hardware redundancy and performance redundancy.
● The number of master controllers must meet the requirements of on-site implementation tasks, and there is redundancy, and all technical indicators are within the control range.
● The level and communication method of the decentralized control system should be concise and reliable, and there should be no bottleneck in communication. The comprehensive communication of the multi-layer network should have sufficient speed and reliability.
● The redundancy configuration of the decentralized control system is reasonable and reliable, and the performance-cost ratio is reasonable. Similarly, "redundancy" includes physical configuration redundancy and performance configuration redundancy. Physical configuration redundancy: such as redundant power supply configuration (dual power supply), redundant configuration of main controller (1:1 hot standby), and redundant configuration of important I/O (triple taking two or three taking). Performance redundancy: such as redundancy of power supply capacity, redundant configuration of highway communication speed, memory redundancy of main controller, CPU speed redundancy of main controller, redundancy of main controller load rate, redundancy of communication rate, etc. .
For example, in the procurement of the Zouxian Phase III decentralized control system, the proposed hardware requirements and basic conditions are as follows:
● The load rate of the communication network of the decentralized control system is less than 40%;
● Availability of decentralized control systems >99.9%;
● CRT data refresh time is less than ls;
● DCS system manual operation response time <2s;
● CRT screen response time <1s;
● The main controller load rate is <40%:
● The average memory occupancy of the main controller is actually 43.24% (factory test):
● The main controller redundant configuration;
● Distributed control system power supplies are redundantly configured, and all the way to AC, all the way to DC and so on.
Practice has proved that the above provisions on the hardware requirements and basic conditions of the decentralized system are indispensable for ensuring the distribution of the functions of the main controller. It is the material basis for the rational allocation of the main controller and discusses the decentralized controller function. Prerequisites and prerequisites for distribution.
Second, the scale of the decentralized control system chooses the scale of the decentralized control system, that is, the configuration of the number and function of the main controller.
1. Determined by the size of the control task - generally determined by two factors.
That is, depending on the specific power plant control functions and the number of control objects. The control function mainly refers to the function range of the distributed control system. The general power station distributed control system has the following functions:
DAS - data acquisition function (including electrical quantity);
SCS - sequence control (including main and auxiliary interlocks, protection and electrical controls, etc.):
CCS - coordinated control;
ETS - Accidental Trip System (thermal protection system):
FSSS - furnace safety monitoring system;
DEH - Turbine Control System:
SOE - event sequence records.
Due to the different configuration of different power plant control systems, their functions may be different, such as FSSS.DEH may be supplied separately with the main equipment. However, the current decentralized control system increasingly controls the power plant as a whole, and the scope of thermal control is more and more the coordinated control of the whole plant equipment as a unified whole. The division and concept of mechanics, electrics, and thermal control professionals are also qualitatively different from the traditional concept of division of labor. Therefore, different control objects and different control function requirements determine the scale of the distributed control system and the number of main controllers.
2. The main controller's function determines the stronger the main controller's load capacity. The main indicators such as memory, CPU level, main frequency, communication speed, and I/O point capability directly determine the scale of the decentralized control system and needs to be configured. The number of master controllers. Therefore, the number of main controllers in the control system of large-scale thermal power units above 300MW is also an important indicator reflecting the strength of the distributed control system used. For the same project, such as the use of different manufacturers of the main controller, the number is not the same, the number of cabinets will be different, the project cost, commissioning, installation, wiring and other engineering quantities are not the same. In the 2nd 600MW unit project of Zouxian Phase 3, the decentralized control systems of two manufacturers were compared. A manufacturer needs 40 pairs of master controllers to implement one unit control, which requires about 40 cabinets; while another manufacturer only needs 20 pairs of master controllers to realize one unit control and only 20 cabinets. Therefore, the function of the main controller has a direct impact on the scale of the control system, affecting the installation, commissioning and reliability of the project. This is an important evaluation factor for determining the configuration and quantity of the main controller.
Third, the general sequence of the main controller configuration of the decentralized control system (1) determine the specific decentralized control system manufacturers and their products (technical and economic evaluation)
(2) Determine the main control functions and control range of the power station;
(3) Determine the total I/O points of the power station control system:
(4) Determine the number of master controllers based on the capabilities of the master controller with I/O points;
(5) Optimize the main controller function assignment.
Take the Zouxian Power Plant Phase III project as an example, the Zou County Power Plant selects the Westinghouse WDPF system, and the FSSS and DEH are supplied by the main equipment manufacturer. Therefore, the distributed control system functions mainly include DAS, SCS, CCS, and SOE, and the total I/O points. as follows:
T/C RTD 4~20mA AO DI DO PI SOE Total Design 742 268 792 118 3065 1155 50 285 6475
Actual use 684 269 782 116 2627 1107 39 240 5864
Actual configuration 774 296 981 135 2820 1216 50 285 6557
Westinghouse WDPF main controller performance indicators are INTEL80486, 32B-25, ROM/128KB, RAM/128KB.
Westinghouse 1 main controller DPU with up to 4 racks, 12 card pieces, a total of 48 card pieces, such as with expansion slots can be expanded to 96 cards (Zou County Power Plant Phase III project without expansion). One DPU has 64x4 and two 256 addresses. After removing 13 internal addresses, there are only 243 valid addresses, and different cards occupy different effective addresses. According to the aforementioned requirements for the performance indicators of the decentralized control system and the number of I/O addresses, after complex calculations, it was finally decided to use 20 pairs of DPU master controllers to implement the control functions of the entire plant.
IV. Principles and Techniques for Distributing Control System Master Controller Function Distribution
1. Main controller function distribution method Distributed control system Main controller function allocation There are generally two methods.
(1) According to the functional area, it is the dedicated main controller function allocation. Such as
DAS control main controller FSSS control main controller
SCS control main controller DEH control main controller
CCS control main controllers divided by functions are mainly to make the main controller functions simple, easy to configure, consistent with the traditional division of labor of the control system, but not conducive to give full play to the main controller's resource advantages, the main controller function distribution load is uniform Poor performance, large amount of data traffic, poor master controller autonomy, and multiple signal crossings, prone to communication errors and congestion. Unless limited by a decentralized control system, it is generally not recommended.
(2) Divided by control object. The full-function master controller is used for function allocation. The master controller can be used for data acquisition as well as for sequential control and coordinated control. The master controller performs full-function control of the entire process for the same object. The function division of the main controller is completely carried out according to different control target systems, and the same main controller implements all the control functions according to the requirements of the control object, that is, the aforementioned full-function main controller. ·
2. Principles and Techniques for Function Allocation of Full-Featured Master Controllers (1) Classification shall be made according to the classification and relationship of the controlled objects to minimize crossover and communication between systems to ensure control autonomy and integrity within the control range of the same host controller. Sex. Specifically speaking, for the thermal power system, the boiler system, the turbine system, and the electrical system are arranged in three stages to overcome signal crossover and interference of different professions and ensure smooth cable arrangement and convenient operation and maintenance in the future.
(2) For thermal objects, the same type of systems that are backed up or supported by each other are dispersed in different main controllers to spread the risks and ensure the minimum failure rate. Such as A, B side to send the wind system, A, B side of the primary fan system, A, B small turbine control, etc., both sides of the system dispersed in different groups of the main controller to control.
(3) Each group of master controllers should ensure sufficient redundancy. Each chassis of the main controller requires hardware redundancy. Each I/O point has more than 10% redundant configuration to ensure the need for modification and optimization during operation. For the performance redundancy of the main controller, it is necessary to ensure the real-time response reliability of the main controller. For example, if the main controller memory occupancy rate is no more than 50%, the main controller load rate is no more than 40%. For the configuration I/O points to be controlled and optimized to ensure that the main controller has sufficient physical and performance redundancy, the factory must conduct rigorous test verification, otherwise it should be adjusted or re-performed the main controller function assignment.
(4) The function division of the main controller should be uniform, the load rate should not be too high, it should be basically the same, and it should not be too low or too high to cause waste or bottlenecks. The over-concentration of the functions of a certain group of master controllers will affect the overall reliability of the system. Once a fault occurs, the risk of the accident expansion will be high.
(5) The main controller's important control signals shall be directly adopted by the main controller of this group, such as signals for interlock protection and signals for the coordinated control system, and shall have three or two or three redundant configurations.
(6) For signals that are particularly important in a decentralized control system, different main controllers can use alternate cross-acquisition, such as the main steam temperature signal water supply system and the desuperheating water system, which can be used independently, or can be independently adopted in combination with principle (5), or Another point is set to enter another group of main controllers to prevent the failure of a certain group of main controllers from causing loss of important signal monitoring and control.
(7) Especially important protection and control systems should be dispersed with the objects of the controlled system. The control functions are divided into different main controllers to prevent the concentration of dangers. If the number of main controllers is insufficient, the number of main controllers should be appropriately increased according to the optimization. This should be carefully studied in detail in the specific configuration to determine the optimal master controller function assignment.
(8) In the same group of main controllers, attention should be paid to the balanced configuration of the switching and analog signals to ensure maximum utilization of the main controller's processing capability. If the equipment is started or stopped frequently during start-up and shut-down of the unit, the switching signal processing will be more. In the normal operation, the parameter adjustment will change more and the adjustment amount will be more, while the DAS signal runs through the operation of the unit. Relatively stable. The ratio of switch quantity and analog quantity should be appropriate in the same group of main controllers.
The DPU function allocation plans of 20 main controllers of 2 600MW units in Zouxian Power Plant are as follows:
DPUl/51-11/61 is the main controller for boiler side control, a total of 11
DPUl2/62-19/29 are main controllers for steam turbine side control, total 8
DPU20/80 is the main controller for electric quantity and other DAS, and 1 is the fifth, the advantages and disadvantages of the function allocation using full-function master controller
1. Advantages of using the full-featured main controller function allocation (1) The main controller has a clear task and basically implements all control of the system with a certain system or a main and auxiliary machine as a unit, with strong correspondence and strong autonomy. Strong, easy to divide maintenance.
(2) Give full play to the characteristics of a decentralized control system, make full use of computer resources, decentralize functions, control decentralization, and risk dispersion. Problems in one system only affect local systems, and do not substantially affect the overall operation of the unit.
(3) Because each master controller has strong autonomy, the interdependence between the master controllers and the dependence on the network are reduced, the signal crossover is reduced, the communication load is reduced, and communication blocking is prevented.
(4) There is little crossover between programs, but information exchange can be optimized, reasonable, and convenient.
(5) The main controller load and the number of operations are reasonably uniform, reducing the calculation peak and even load distribution, so that the main controller is relatively uniform in space and working time throughout the unit operation. At the time of factory inspection, the WDPF system load rate of the third phase project of Zouxian Power Plant was low, with an average of 8.18% and a maximum of 13.8%.
(6) The cable is easy to install and clear, and the cables are arranged in a straight line with reasonable crossover.
2. Disadvantages of using full-featured main controller function allocation (1) The same group of main controllers realizes the functions of control, monitoring, interlocking, protection, and alarming of related equipment or systems, and requires high quality of maintenance personnel and requires comprehensive knowledge. .
(2) There is a high requirement for optimizing the redundancy of I/O. Since signals such as control and monitoring enter the same group of master controllers, certain I/O redundancy or other master controllers should be considered for some important signals. Configuration method.
(3) High requirements for designers, requirements must be carefully analyzed according to different systems, optimize the function of the main controller, and reasonably allocate the functions of the main controller.

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