Distributed Control System The distributed control system is a new-generation instrument control system based on microprocessors, with control functions dispersed, display operation centralized, balanced and autonomous and comprehensive coordination design principles. The distributed control system, referred to as DCS, can also be literally translated as "distributed control system" or "distributed computer control system."
It adopts the basic design idea of ​​controlling the decentralization, operation and management concentration, and adopts the structure of multi-level hierarchical and cooperative autonomy. Its main feature is its centralized management and decentralized control. At present, DCS has been widely used in various industries such as power, metallurgy and petrochemical.
Reliability is the life of DCS development. There are three main measures to ensure the high reliability of DCS: one is the extensive application of high-reliability hardware equipment and production technology; the second is the extensive use of redundancy technology; the third is widely implemented in software design. System fault tolerance technology, fault self-diagnosis and automatic processing technology. Most of today's distributed control systems have MTBFs of tens of thousands or even hundreds of thousands of hours.
Development trend of distributed control system
In recent years, there have been many new developments in the field of DCS related, mainly in the following aspects.
(1) System function The structure of the traditional DCS developed in an open direction is closed, and it is difficult to be compatible between DCSs of different manufacturers. The open DCS will give users greater autonomy in system integration. Users can select devices from different vendors and software resources to connect to the control system according to actual needs to achieve optimal system integration. This includes not only the integration of DCS and DCS, but also the general integration of DCS with PLC, FCS and various control equipment and software resources.
(2) The development of instrument technology into the intelligent, networked development of industrial control equipment in the direction of digitization, intelligence and network can promote the function of process control to be further dispersed and achieve "all-digital" and "fully dispersed" in the true sense. "control. In addition, because these smart meters have high precision, good repeatability, high reliability, and two-way communication and self-diagnosis functions, the installation, use and maintenance of the system is more convenient.
(3) Industrial control software is developing in the direction of advanced control. Widely applying various advanced control and optimization technologies is the most effective, direct and most valuable development direction for mining and improving the comprehensive performance of DCS, including advanced control, process optimization, and information. Development and industrialization of software such as integration and system integration. In the future, industrial control software will continue to move toward standardization, networking, intelligence and openness.
(4) System architecture is developing in the direction of FCS. From the perspective of technology, there are three ways to integrate fieldbus into DCS at this stage:
1 Fieldbus integration on the DCS system I/O bus - hangs on the DCS I/O bus through a fieldbus interface card, so that the information from the fieldbus seen by the DCS controller is like a traditional The same as the DCS device card. For example, the DeltaV system introduced by Fisher-Rosemount uses this integration solution.
2 The integration of the fieldbus in the network layer of the DCS system is to integrate the fieldbus system on the higher layer of the DCS network. This integration method does not require changes to the DCS control station, and has less impact on the original system. For example, Smar's 302 series fieldbus products can integrate their fieldbus functions at the DCS system network layer.
3 Fieldbus is integrated in parallel with the DCS system via the gateway – the fieldbus and DCS can also be parallel integrated via gateway bridge. For example, SUPCON's fieldbus system uses the HART protocol bridge to connect the system operator station and field instruments to achieve communication between the fieldbus device management system operator station and the HART protocol field instrument.
The focus of DCS has always been on control, which uses "scatter" as a key. However, modern development is more focused on the comprehensive management of system-wide information. In the future, “integration†will become its key point, and it will develop towards the comprehensive automation of control system, operation system, planning system and management system, and implement real-time control from the lowest level. The optimization control has risen to the production scheduling, operation management, and even the highest level of strategic decision-making, forming a flexible and highly automated integrated management and control system.
In fact, all products on the DCS system are defective. Often, when the manufacturer bids, the technical specification is rarely deviated. Once the technical agreement is signed, it is not said that this cannot meet the requirements, that is to say, it cannot meet the requirements. It’s a headache. Now we analyze and compare the following products (Xinhua, Lishi, Keyuan, Zhejiang University Central Control).
First, and Lee:
The fatal injury to the macs system is that of the server. Now that the location has been changed - the alarm, communication, processing, and reporting are shared at different operator stations, but the actual situation is still there, and the server crashes (although the probability is small), the system will have problems.
1. The biggest problem with MACSII is that it can't be downloaded offline. Although the manufacturer says it is ok, the manufacturer does not dare to download it online during the configuration, only when the unit is completely stopped. It is understood that an online download test was conducted at a power plant in Taicang, which really led to a system reset. I wonder if the smartproMACS (MACSV) that is being released now solves the problem that it cannot be downloaded online.
2. The system is unstable and the accumulation will be automatically cleared. There are many small problems, and the structural design of the controller and module does not conform to the current mainstream development trend.
3. The connection speed between the communication and the DCS is too slow, and sometimes the delay is long when starting up. Sometimes there is a crash, the data sometimes does not move or is 0. The data of the communication cannot be recorded. 4. The software timer cannot be reset. Once the timer is started, it cannot be reset. Some functions may not be performed according to normal logic. 5, module quality In the process of debugging, there will be burning parts, and the output terminal board resistance loop matching may have problems. Advantages The MACS system is generally simple, easy to use, and comprehensive in function. C/S communication is a feature of him.
Product FM series card and MACS software
2. GE Xinhua (referred to as Xinhua):
Xinhua's system is relatively stable. However, since the acquisition by GE, the follow-up development strength is obviously insufficient, the price is high, and the after-sales service of engineering and technical personnel is poor (the rest day is not easy to find someone). Focusing on large thermal power stations, there are many achievements in domestic thermal power stations. The original Xinhua company has a strict management style, stable and reliable equipment quality, and stable technical staff. However, after being acquired by GE, it is going downhill. The good national brands have not been able to develop well. The most concentrated problem of their users is the high after-sales service and the high cost of spare parts. Let's compare the Hollysys MACS II/III with Xinhua XPDS from the network structure:
There is a redundant server between the monitoring layer and the field control layer. The server plays important functions such as uploading and downloading data, calculating alarm functions, and storing historical data. Such a structure makes the function of the server too concentrated and the data traffic is large. Although the server uses redundancy technology to reduce the risk that the entire system cannot be monitored due to the failure of the server itself or power failure, the DCS is essentially back.
To the stage of centralized control. I think this structure has drawbacks and poor reliability.
The network structure of Xinhua Company can be said to be a true DCS. The commands for uploading, downloading and controlling data are all carried out through the data line. It is a direct point-to-point operation that is significantly better than the Hollysys system.
I/O card hardware problem, I think the current DCS system is the biggest difference between the DCS system and the foreign DCS system. Domestic product hardware and foreign countries are very different. Whether it is Hollysys, Xinhua or other domestic company products, there are bad card parts during installation and commissioning, and the bad reason is that the product quality is not good, such as anti-jamming of card parts. Ability, self-protection of the card and stability of the card. Although there are common features on the hardware, there are still differences between the products of Hollysys and the products of Xinhua, which have their own advantages and disadvantages.
The product card of Hollysys has the advantages of small size, full package, convenient installation, good stability and direct connection of the base. However, the disadvantage is that the card has a high failure rate and poor self-protection capability (the outer circuit is short-circuited, the grounding, the over-voltage may burn the card), and the over-range function is not available.
Xinhua's products have the advantages of low failure rate and certain self-protection capabilities. The card is a bare board, which has poor dustproof effect, requires terminal board, is inconvenient to install, has poor stability, and has poor anti-interference ability.
Third, Zhejiang University Central Control:
The system has a certain performance in the chemical industry. It started late in the power industry, and its performance is not much. The number of points per card is too small, and the analog input is group-separated (not good, it is best to do a little bit of isolation) The DPU has low processing power. Not suitable for larger systems. Emphasis on the advanced nature of control software, some are not necessarily practical. Zhejiang JX300X is its mainstream, but the system scale is too small; the ECS100 system launched is still not perfect, I heard that the system integration (ECS200 system) of Japan Fuji has just started.
Fourth, Branch Yuan:
Using British Continental technology, I heard that the system is relatively stable, the maintenance is small, spare parts are not easy to buy, and some performances in the southern small power plants are doing well. There may be differences between the other terminals on the terminals. If you don’t know enough about Keyuan, just say this.
The above is only a more specific analysis of Hollysys and Xinhua. After all, Lishi was half of the small thermal power in the early days, and the Xinhua system was a domestically produced leader.
In fact, which manufacturer will not do it online, even if it is guaranteed. Hardware problems are common problems in domestic systems. The hardware problem is fatal injury to domestic DCS manufacturers and PLC manufacturers. The reliable operation of the system is not only related to hardware and software, but also related to engineering design and on-site commissioning personnel. For a small power plant, which of the above can be used, the key is to look at the quality of the project manager and field engineers and on-site experience, Bi Jingren is the most important software.
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