0 Introduction Object Linking and Embedding (OLE) for Process Control (OPC) is an advanced process control technology with powerful process control capabilities. It can realize a variety of advanced control algorithms such as integrated self-tuning and optimized substation control, and has flexible product configuration. Using OPC technology, the entire substation automatic control system can be based entirely on fieldbus technology, fully supporting ProfibusDP, compatible with Foundation Fieldbus (FF) and CAN (Control Area Network) buses, and can flexibly connect to various instruments, sensors and actuators in the substation field, and can provide predictive maintenance information for substation equipment [1]. The OPC system is based on Internet technology, which allows users to browse the entire substation field through the Internet, and conduct remote equipment maintenance and expert consultation [2]. Since the OPC system is based on the open Microsoft and Intel hardware and software platform, it has high reliability and can fully meet the needs of substation automation at different voltage levels in the power industry. The substation automatic control system developed using OPC technology can provide multiple open standard connections, allowing users to easily integrate substation control information into various application systems and applications within power enterprises. It easily connects to Enterprise Resource Planning (ERP) and Management Information System (MIS), facilitating the integration of power enterprise management and control with Device Management System (DMS). This enables the complete integration of various information systems within the power enterprise in the power market environment, meeting more decision-making needs and avoiding automation silos. High integration of information systems allows power enterprises to make rapid decisions in an increasingly competitive power market environment, adapt to market demands, and quickly adjust the supply and demand relationship of electricity products, thereby bringing greater benefits to the enterprise. 1. Fieldbus In recent years, fieldbus technology, which has emerged with the development of computer technology, communication technology, information technology, integrated circuit technology, and intelligent sensing technology, has brought a profound revolution to the field of power industry control. Fieldbus represents a groundbreaking control concept, changing the original control architecture and truly achieving distributed hazard, distributed control, centralized monitoring, and full digitalization. Fieldbus technology has the following characteristics: (1) Intelligent instruments using fieldbus can provide more information, enabling power supply companies to perform predictive maintenance and replacement of equipment. Due to the use of fully digital serial communication, functions can be completely distributed, thus greatly reducing the complexity and cost of substation automation systems. (2) Various instruments in the substation can be connected to the centralized control station via fieldbus, greatly reducing the number of controllers and I/O subsystems. Some field instruments can also perform control and calculations, thereby reducing the number of cables and the associated construction and wiring burden, lowering the overall cost of the substation construction project, and also reducing the information processing burden of the dispatching master station system. (3) Substations generally have strong interference sources. Due to the use of fully digital fieldbus technology, it has good anti-interference capabilities, making signal attenuation negligible, thus making the entire substation automation system more robust. Fully digital communication uses multiple error correction mechanisms to ensure reliable transmission between the substation automation system and the power grid dispatching system. (4) Open international standards allow users to flexibly choose intelligent instruments and control equipment from different manufacturers, thereby expanding the scope and field of monitorable objects and increasing the interoperability and interchangeability of the system [3]. (5) Wide support for the currently popular fieldbus standards effectively protects users' past investments and long-term interests. (6) Instrument and equipment management systems can be integrated into the system, which can help power companies reduce power outage time. Fieldbus-based instruments and equipment can also provide a variety of predictive maintenance information. 2 FCS Control System In the field of automatic control, the 1970s to 1990s are generally referred to as the era of distributed control systems (DCS). By 2000, automatic control technology began to enter a new stage of development, namely the era of fieldbus control systems (FCS). The development process of automatic control systems In the past, control systems were not designed specifically for fieldbus intelligent transmitters, so they did not realize the various information that substation instruments themselves could provide. 3 Open Standard OPC OPC technology adopts Microsoft's object linking and embedding method for industrial process control, ensuring that the substation automatic control system can easily integrate various field devices without any driver problems. OPC function ensures maximum integration of substation field data, thereby providing more data and information for power supply enterprise ERP to support enterprise decision-making and management. This high degree of data sharing avoids the automation island phenomenon that was easy to occur in the past automatic control system. The fast and efficient server can exchange more than a thousand data per second, and the system maintains high performance while having data sharing flexibility. The OPC server can provide an environment for various information systems inside the power enterprise to access various real-time and historical data in the substation automatic control system, and can even reference field data in office software Word or Excel, which makes the data in reports or statements more realistically reflect the actual power production; OPC clients can integrate various devices that provide OPC drivers into the system, and any device and software that supports OPC will become a part of the system. The adoption of OPC technology also provides customers with more hardware options, making system integration more convenient [4]. 4 Support Internet Function Connecting Internet technology with the substation automatic control system allows automation engineers to understand the situation happening at the power production site every minute and every second in real time. OPC is based entirely on the TCP/IP protocol and can access the Internet/Intranet/Extranet. Users can remotely operate and browse the production status at the central station, and can also manage all substations of the power supply company from anywhere. It can achieve the following: (1) Understanding on-site information anytime and anywhere. The real-time data and historical trends provided by OPC will help the power supply company solve business management problems and make various reasonable business decisions. (2) Reducing the required resources through cooperation and information sharing, so that various relevant management personnel of the power company can obtain more information. Instrument maintenance engineers can reduce the number of instruments that need to be disassembled and installed during the power company's major overhaul by providing predictive maintenance information, thereby reducing power outage time and increasing the company's economic benefits. (3) All management personnel related to the power supply company can learn about the information they need through the office network, instead of having all personnel go to the site in person as before. (4) If important production equipment in remote substations malfunctions, the equipment supplier can provide timely and professional guidance through remote diagnosis to help users eliminate the fault problem as soon as possible, restore production, and reduce unnecessary losses. (5) All personnel only need to use browser software, without the need for special software and training. [b]5 Integrated Management and Control[/b] Now, information is increasingly becoming the key to improving product quality and maximizing production efficiency. The new generation of substation automation system can be connected to the ERP system of the power supply company. Various departments of the company can grasp more production information, thereby providing better services to end users. The finance department can quickly and directly understand the company's electricity sales and the status of bank electricity payment. In the power market environment, it is particularly important for power supply companies to realize integrated management and control, which can help companies gain the initiative and seize the opportunity in the competition. 6 OPC Architecture The OPC architecture is shown in Figure 4. It has the following characteristics: (1) Real-time. The controller CPU adopts Pentium-level chip and is based on the ONX embedded real-time operating system to ensure accurate, real-time and efficient control. (2) Reliability. The system adopts multiple redundant structures (network, controller, power module, I/O module) to ensure safety, stability and reliability. (3) Advanced. The flexible client/server architecture is suitable for I/O, alarms, reports, and trend analysis of large-scale systems. The Time server can be distributed to ensure data consistency and load sharing. OPC also has a feature-rich HMI human-machine interface, flexible and powerful control software, and supports offline simulation and online download. (4) Economy. The fieldbus system design effectively saves overall project investment and reduces operation and maintenance costs. TCP/IP technology makes the network structure simple and can be remotely browsed and accessed via the Internet. (5) Ease of use. Intelligent device management, fault diagnosis, accuracy correction, hot-plugging, rich human-machine interface and humanized design of the whole system. (6) Continuity. The operator station adopts a general software/hardware platform and can be upgraded synchronously with the continuous improvement of information technology. 6.1 Network Operating System The new generation of substation automation system should adopt Windows NT as its own network operating system. It adopts a platform that users are familiar with, which is easy for users to use and integrate with other software, thereby reducing users' learning and training time and increasing the openness and flexibility of the system. It should conform to the standard Client/Server architecture, which represents the development trend of DCS. 6.2 Distributed Database In a large-scale system, users can distribute the processing of large amounts of data to reduce the load on a single machine. The functions of the OPC server can be divided into five tasks: ① I/O server; ② Monitoring and alarm server; ③ Report server; ④ Historical trend server; ⑤ Time server. 6.3 Comprehensive Redundancy The server software adopts dynamic fault-tolerant technology. The two servers run application software independently, maintaining synchronization and data redundancy between the two machines through reliable means. This mainly includes: ① Network redundancy; ② Controller redundancy; ③ I/O redundancy; ④ I/O Server redundancy; ⑤ Operator station redundancy. 6.4 Control Station System The real-time multi-tasking embedded operating system can run on various hardware platforms such as Intelx86, Pentium, and PowerPC. It is designed according to the POSIX1003 standard and is a multi-tasking, multi-user, distributed, real-time embedded operating system. It truly supports multi-processor parallel computing, supports multiple processors, and has a customizable system kernel. The kernel is small and refined (as small as tens of KB) and manages a large memory space. Supports TCP/IP protocol and remote Internet access and debugging. The I/O field control station main control unit uses a Pentium-level CPU, a ring Profibus DP fieldbus topology, and a maximum communication speed of 12Mbps, ensuring real-time communication. The I/O field control station operating system uses the ONX operating system, which supports multi-CPU parallel processing technology and multi-tasking. Each field I/O control station is a dual-redundant main control unit. 6.5 Field I/O Modules All field I/O modules are intelligent modules with microprocessors. Analog input/output paths are isolated. All I/O modules are manufactured using the world's most advanced SMT surface mount technology, featuring dual-redundant analog input/output and digital input/output modules. 6.6 System Specifications The time from input change to display change is less than the sampling period + 1s; the time from operation output to actual output change is less than 1s; the screen switching time is less than 1s; the fastest loop control cycle is 20ms; the fastest logic control cycle is 5ms; and the SOE resolution is less than 1ms. Standard control station measured performance (single control station): Total system points: 500; Analog inputs: 300; Analog outputs: 100; Digital inputs/outputs: 100; Control loop has 70 single-loop PID controllers and 30 cascaded PID controllers; Control algorithm: PID and cascade control; Loop control cycle: 50ms; Fast loop control cycle: 10ms; Logic control cycle: 5ms. 6.7 Easy Maintenance The application of OPC technology disperses the risks in the substation automatic control system. Each I/O module uses 8 analog inputs/outputs per module and 16 digital inputs/outputs per module, making the physical points of the system more dispersed. A failure in one module will not affect other equipment. The use of fieldbus minimizes the functionality of individual devices, improving system reliability and providing abundant hardware redundancy, such as bus redundancy, operator station redundancy, and power supply redundancy. Seamless power switching ensures power supply to field instruments; users can also choose UPS power supply for the system. Fieldbus ensures data validity and high-level integrity, functions that were impossible in systems designed for 4-20mA. Each I/O module has a built-in microprocessor that automatically performs system self-tests, output readbacks, and communication checks, automatically issuing alarms in case of faults, allowing users to quickly detect and repair problems. All I/O modules are hot-swappable, enabling rapid resolution of individual module failures and minimizing their impact on the system. Replacing a single faulty module requires no changes to the existing system wiring, reducing the workload of I/O module replacement. [b]7 Software System[/b] The software includes: controller software, responsible for generating and maintaining the system control station control program; field controller operation software, responsible for running the system control station control program; human-machine interface software, responsible for online monitoring, operation, control, debugging, and maintenance of the system; WebView software, responsible for Internet browsing; OPCPacket, the OPC toolkit software; and DMS software, responsible for equipment management. 7.1 Controller Software The controller software features offline simulation, online download, and supports offline simulation debugging of algorithms, effectively improving engineering efficiency, reducing error rates, and lowering risks. Advantages include: ① independence from controller configuration and simulation debugging; ② ability to set breakpoints and monitor variables; ③ single-step execution and single-loop execution; ④ jump-in execution and call-out execution; ⑤ viewing the call stack and displaying flow control; ⑥ forced output. It supports online incremental non-disruptive data download, and database download supports both incremental and full download methods. It supports data readback functionality, allowing the reading of all data from the controller for the current project, including all parameters. ConMaker provides a resource manager for resource switching, project structure design, a program editor, library manager, cross-reference table, call tree, and information window design. ConMaker has a rich control algorithm library, including arithmetic operation functions, type conversion functions, emergency event functions, continuous control functions, file operation functions, and timer/counter/trigger functions. 7.2 Powerful Development Language The system employs a programming language conforming to the IEC 1131-3 standard. Excel can import and export data from the Facview database, accelerating project configuration and preventing errors. Five control programming languages ​​can be cross-referenced for configuring control algorithms (and internal calculations), namely equipment configuration, database configuration, control scheme configuration, graphical configuration, and report configuration. The system should have flexible Visual C++ and Visual Basic application interfaces, infinitely scaled vector animation capabilities, and the ability to flexibly and conveniently call custom function blocks from any application. 7.3 ActiveX Control Support The system can easily use third-party controls. Users can obtain numerous practical engineering controls through various channels. By using custom controls, related objects, static data, and dynamic data can be merged into a single object for use. User-defined pop-up controller interfaces can be created using controls. Centralized parameter configuration, batch interface configuration, and batch device operation and control are supported. Controls can be saved as dedicated library files for repeated use. 7.4 Reports and Statistics Supports multiple report formats including Excel, RTF, TXT (plain ASCII text), and DBF (database file). The system provides statistical functions based on various industrial field practices, such as maximum, minimum, and average values. [b]8 Conclusion[/b] Fieldbus technology, which emerged with the development of computer technology, communication technology, information technology, and intelligent sensing technology, has brought about a profound revolution in the power industry control field. Adopting OPC technology allows the entire substation automatic control system to be based entirely on fieldbus technology and can provide predictive maintenance information for substation equipment. Based on Internet technology, the OPC system enables remote equipment maintenance and expert consultation. The OPC system also has excellent openness, easily realizing integrated management and control of power enterprises and integrated equipment management systems, enabling the complete integration of various information systems of the entire power enterprise in the power market environment to meet more decision-making needs and avoid the phenomenon of automation silos. [b]9 References[/b] 1 Du Xueqiang. Enterprise Management Control Integration and OPC. Microcomputer Information, 2001 2 OPC Found. OPC Technical Overview. 2000 3 Li Zilian. Application of Fieldbus Technology in Power Plants. Beijing: China Electric Power Press, 2002 4 Yang Xianhui. Fieldbus Technology and Its Application. Beijing: Tsinghua University Press, 1999