Abstract: This paper introduces the current status of auxiliary workshop control systems in large and medium-sized thermal power plants in China. Based on the analysis and comparison of the similarities and differences between standard Ethernet and industrial Ethernet, an overall design scheme for the centralized control system of the auxiliary workshop of Jiaxing Power Plant is proposed, and the key technologies for realizing centralized monitoring of the auxiliary workshop are summarized. Keywords: HMI; switch; industrial Ethernet; auxiliary workshop; centralized control. Currently, in large and medium-sized thermal power plants in China, the main control unit has generally adopted DCS control system, and the peripheral auxiliary systems are also controlled by PLC + host computer, which greatly improves the efficiency of unit operation. The use of network communication technology to strengthen the operation and management of power plants is also being promoted and applied. Recently, some power plant control experts at home and abroad have been considering the application of the latest network technology to realize the integration of various control and management systems of power plants, and corresponding software and hardware manufacturers have gradually launched control product software that can adapt to large-scale network systems. That is to say, in the control and management system of large and medium-sized power plants, the basic conditions for realizing centralized monitoring of the entire power plant using today's advanced computer and network communication technologies are mature. Realizing a centralized monitoring system for auxiliary workshops is the premise and foundation for realizing centralized monitoring of the entire plant. 1 Current Status of Auxiliary Workshop Control Systems For the auxiliary workshop control systems of large and medium-sized thermal power plants that have been put into operation, the following problems are common: (1) The number of I/O points of the auxiliary workshop control system is huge. Taking Jiaxing Power Plant in Zhejiang Province as an example, the total number of I/O points of the auxiliary system is about 5635, of which there are 980 analog points and 4655 digital points (excluding coal conveying program control). If the coal conveying system and wastewater treatment system are added, the number of I/O points of the auxiliary system exceeds 7000. (2) The physical location of the auxiliary workshop is dispersed. The auxiliary systems are distributed in various places in the power plant, and the distance between them is far and the dispersion is large. For example, the circulating pump room of Jiaxing Power Plant is about 1.2 km away from the main plant. Therefore, it is necessary to solve the problems of long-distance communication and signal attenuation. (3) The auxiliary control systems are of different types and have a large number of interfaces. Because each auxiliary control system uses different control equipment, such as the Modicon 984-685 and Siemens S7-300 control systems in the chemical workshop of Jiaxing Power Plant, the S5-115H system in the ash control workshop, the 984-380 system in soot blowing, the OMRON system in the fire pump, the dedicated control system with the 80C196 microcontroller as the core of the electrostatic precipitator, and the 232 interface in the survey instrument. The communication interfaces of each control system use different communication protocols, and even different physical interfaces. To achieve centralized monitoring, it is necessary to solve the problem of network communication protocol conversion and ensure reliable and accurate data transmission and exchange between different interfaces and protocols. At the same time, it is necessary to provide open real-time data interfaces to provide real-time information to the power plant's SIS system. (4) The human-machine interfaces of the operator stations are different. Because the control systems of each auxiliary workshop are supplied by different manufacturers, the human-machine interfaces of their operator stations are likely to be inconsistent. For example, some use the FIX interface, some use the INTOUCH interface, some use the KingSCADA interface, and some use their own dedicated interface. Therefore, to achieve centralized control of the auxiliary workshop, a unified human-machine interface must be designed, and a unified style and operation method must be adopted. 2 Differences and similarities between industrial Ethernet and standard Ethernet To improve the reliability of the auxiliary workshop centralized control system and strengthen the openness and standardization of the control network, the auxiliary workshop centralized control system adopts industrial Ethernet. The following compares the differences and similarities between industrial Ethernet and standard Ethernet. Industrial Ethernet and standard Ethernet use the same communication principle, both conform to the IEEE 802.3S standard, and have the same network topology; industrial Ethernet and standard Ethernet are compatible, and any application that can run in the industrial Ethernet environment can run in the standard Ethernet environment. However, industrial Ethernet needs to work stably under extreme conditions, therefore: (1) Industrial Ethernet is designed with hardening, for example, using industrial-grade chips, industrial-grade connectors and plugs, and generally does not use cooling fans. (2) Industrial Ethernet HUB and SWITCHHUB generally have built-in redundant network managers and support redundant or parallel power supplies. (3) Industrial Ethernet has a millisecond-level fast spanning tree algorithm, while the fast spanning tree algorithm of standard Ethernet generally takes tens of seconds, so the redundant network switching of industrial Ethernet can be done without disturbance. (4) Industrial Ethernet equipment has a wide operating temperature range, such as 0～60℃. (5) It has plug-and-play quick installation technology, etc. In short, the differences between industrial Ethernet and standard Ethernet can be compared with the differences between industrial control computers and commercial computers. Industrial Ethernet is a standard Ethernet specifically designed for industrial environments and applications. 3 Overall Design Scheme of Auxiliary Workshop Centralized Control System Since the communication interfaces of various control systems use different communication protocols, and even different physical interfaces, in order to achieve centralized monitoring, it is necessary to solve the problem of network communication protocol conversion and ensure reliable and accurate data transmission and exchange between different interfaces and protocols. The centralized control system of Jiaxing Power Plant auxiliary workshop adopts multimode optical cable and industrial-grade switch to establish an industrial Ethernet ring network. It adopts a unified network platform and software platform to interconnect various different auxiliary control systems and realize centralized control of peripheral auxiliary systems. The following is a brief introduction to the network architecture of the entire auxiliary workshop centralized control system. The specific system configuration diagram of the auxiliary workshop centralized control system architecture is shown in Figure 1. (1) The dosing and sampling control system is connected to the workshop switchboard by inserting an industrial Ethernet module CP343-ITCP into the rack of the S7-300. The switchboard is connected to a fiber optic switch. The backup monitoring computer in the dosing workshop collects data through the workshop switchboard, or through the MPI interface. (2) The chemical makeup water control system, condensate polishing control system, reverse osmosis control system, and fire pump control are all located in the water treatment workshop. Therefore, they share one switchboard. The Modbus protocol is converted to the Ethernet protocol using an MB+ bridge. To increase system reliability and ease of maintenance, three MB+ bridges are used. The water treatment control system is connected to the workshop switchboard through an MB+ bridge. The switchboard is connected to a fiber optic switch. The backup monitoring computer in the water treatment workshop collects data through the workshop switchboard for local monitoring. (3) The ash removal control system, slag removal control system, and electrostatic precipitator control are all located in the ash control workshop, so they share one SWITCHHUB. The Modbus protocol is converted to the ETHERNET protocol using an MB+ bridge. The S5 protocol is converted to the ETHERNET protocol by inserting an industrial Ethernet module CP1430TCP into the S5-115H rack. Since the electrostatic precipitator control system is a dedicated system, only a computer can be used as the gateway. The ash control workshop is connected to the fiber optic switch through the workshop SWITCHHUB, and the workshop's backup monitoring computer collects data through the workshop SWITCH-HUB for local monitoring. (4) The circulating pump room, fuel pump room, and integrated pump room share a CPU module and are connected together through a remote I/O network to achieve distributed control. The CPU module, remote I/O module, and Ethernet module are redundantly configured. The circulating pump room workshop is connected to the fiber optic switch through the workshop SWITCHHUB, and the workshop's backup monitoring computer collects data through the workshop SWITCH-HUB for local monitoring. (5) The soot blowing control system uses an MB+ bridge to convert the Modbus protocol to the Ethernet protocol. There are two MB+ bridges for Units 1 and 2. The generator temperature monitoring instruments of Units 1 and 2 use two 232 serial port converters to convert the 232 serial port to the Ethernet protocol. Then they are connected to the fiber optic switch through the workshop SWITCHHUB. (6) The operator station of the auxiliary workshop centralized control system is placed in the central control room and connected to each control system through industrial Ethernet. The three operator stations operate redundantly. If any one station fails, it will not affect the operator's monitoring of the entire system, and the entire network will continue to work normally. 4 Key technologies for realizing centralized monitoring of auxiliary workshops Due to the large number of I/O points of the auxiliary workshop control system, the dispersed physical location of the auxiliary workshop, the different types of auxiliary control systems, the large number of interfaces, and the presence of strong electromagnetic fields, the following key technologies and engineering selection issues must be emphasized in the implementation of the auxiliary workshop monitoring system. 4.1 Selection of industrial control network The control network of the auxiliary workshop centralized monitoring system must meet the characteristics of safety, reliability, high speed and real-time, and good openness. This monitoring system uses switched full-duplex industrial Ethernet, mainly based on the following considerations: (1) Conventional shared Ethernet only works in half-duplex mode, and the network cannot send and receive data at the same time. Full-duplex Ethernet can receive and send at the same time. At the same time, full-duplex, data; facilitates unlimited network distance expansion; isolates faults, and the fault will not spread to the entire network; facilitates system expansion and other advantages. (2) Industrial switched Ethernet is a completely industrial-grade network product with a robust heavy-duty design, and its performance indicators far exceed those of ordinary OA network products. The switch adopts dual power supply redundancy input, and the fiber optic ring network has line redundancy function. The backbone network of this centralized control system is a 100M full-duplex switched fiber optic ring network. Since all switches are used, the entire network is divided into multiple different network segments, and each computer and PLC connected to the network belongs to a different type of domain, thereby ensuring the real-time data transmission. The entire network has single-point fault tolerance function. When any point of the ring optical cable is broken or a node fails, the entire network can still communicate normally. In addition, Ethernet conforms to the current technology development trend, is easy to obtain technical support, and spare parts issues are easy to solve. 4.2 Network Anti-interference Technology The auxiliary system network adopts LUCENT metal armored outdoor multimode direct-buried optical cable to form the backbone communication network of the monitoring system, which can solve the problems of the physical location of the auxiliary system being dispersed, the distance being long, and the signal being susceptible to interference. Shielded twisted pair cables should be used as much as possible as communication cables for operator stations, fiber optic switches, bridges and SWITCHHUBs. Other communication cables should use dedicated cables to ensure the reliability of communication signals and reduce the bit error rate. 5 Conclusion Using PLC + industrial Ethernet + HMI configuration software to realize centralized monitoring of the auxiliary system is relatively flexible, convenient and low cost. Whether the auxiliary workshop centralized control system can achieve its design goals depends to a large extent on the automatic commissioning of the auxiliary system itself, in addition to its own technology. Therefore, the quality of the actuator, the flexible and reliable operation of the limit switch, and the accuracy of the transmitter should be ensured. In addition, since the control center is far away from the field, the primary equipment involved in the automatic control process should be controllable and there should be no manual valves or similar equipment. This is to ensure that the automatic commissioning is well implemented and that the auxiliary system is effectively monitored from the control center. References [1] Qiu Gongwei. Programmable Controller Network Communication and Application [M]. Beijing: Tsinghua University Press, 2000