GPS Synchronous Clock and Its Application in Automation Transformation of Thermal Power Plant
Abstract : This paper introduces the development and application of GPS-based clock synchronization PC card. Based on GPS technology, using W77E58 microcontroller, ISA bus, PC BIOS clock interrupt and program-resident memory technology, successfully solved the technical problem of using GPS time to synchronize different system clocks without affecting the normal operation of the original system. .
0 Introduction Since the introduction of distributed control system (DCS) technology in the middle and late 1980s in China and its application in the unit control of thermal power plants, after decades of development, DCS has been in the control of the unit control system in thermal power plants. Widely used, it greatly improved the automation level of thermal power plants. Turbine Digital Electrohydraulic Control System (DEH) is a real-time control system for turbine generator sets. It is a regulating controller for starting, stopping, normal operation and accident conditions of steam turbines.
At present, many real-time control systems such as DCS and DEH that are being used in thermal power plants are mostly developed many years ago. The clocks of their application systems are mostly based on their respective system clocks. Therefore, the clocks of different systems are not synchronized. This is unacceptable for thermal power plant automation systems that require synchronous data acquisition, accurate measurement using accident recall systems (SOE), and analysis of the cause of the accident. In order to reduce the time error, the method often used is artificially timed. This method is both laborious and does not fundamentally eliminate the time error. The use of Global Positioning System (GPS) technology is the best means to solve the problem of clock synchronization.
1 The method of using GPS to implement accurate clock synchronization There are two main methods to implement clock synchronization using GPS: One is that when developing the application system, the GPS and the circuit design of the application system are organically combined according to the system requirements in advance, for example, GPS-based time synchronization data acquisition systems, etc. [1]; the other is that due to limited conditions in the design, GPS technology is not used, but the internal clocks of the respective operating systems are directly used. Therefore, the clocks of the various parts of the system are not synchronized. .
For the latter case, GPS technology can be used to synchronize the clocks of the various parts of the system. There are two methods: 1 Use software-only methods, that is, use the PC's serial port to synchronize the original system's "patching" program that receives GPS time information. Of course, using the DOS or Windows multitasking process method is not difficult to achieve "i. It should be noted that this method not only takes up a serial port of the PC system, but also does not apply to the real-time control system, because the complete reception of GPS It takes nearly 1 second for navigation information.2 The combination of hardware and software not only does not occupy the serial port resources of the PC system, but also does not affect the normal operation of the original system.This is the design idea of ​​this paper.
2 GPS-based clock synchronization PC card development Based on GPS clock synchronization PC card hardware circuit principle shown in Figure 1. The left side of the dotted line in the figure is the circuit for the CPU (W77E58 microcontroller) receiving GPS time, and the right side is the circuit for rewriting the real clock and system clock of the PC.
In order to avoid the impact of the PC on the operation of the original application system program of the PC when reading/writing the GPS time in the dual-port RAM, and without affecting the real-time updating of the PC card to the system time, the GPS side of the PC receives and The rewrite clock program should be resident in memory [2]. Using the clock interrupt program (1AH) in the ROM-BIOS to rewrite the PC clock in real time is a key technology of the PC card design. The resident clock interrupt routine is fixed in the ROM (27C128) on the card.
The PC card has two external interfaces: one is a decoded GPS time interface, and one frame (18B) of decoded GPS time is sent to the serial port every second, using an RS-485 interface; the other is an undecoded GPS time, Uses RS-232 interface.
3 Application of GPS Synchronous Clock The DEH of a No. 12 300 MW unit in a thermal power plant is the product of Xinhua Power Plant. Its structure is shown in Figure 2. The DCS of the unit is an INFI-90 system developed by Bailey and its structure is shown in Figure 3. The unit SOE time is taken from the loop time of the INFI-90 system.
3.1 Problems that currently exist The above DEH, DCS, and SOE times are taken from their respective operating systems or loops. Therefore, the clocks of each system are not synchronous. The maximum time error has reached several tens of minutes. This gives fault conditions. Analyzing the cause of the accident has brought great difficulties. In order to reduce the time error, the current method is: at regular intervals, the system engineer inputs the standard time into their respective operating systems, and the daily synchronization error is more than a few seconds.
3.2 The basic idea of ​​the transformation and technical solutions The system transformation only involves the INFI-90 system. It does not make any modifications to the original DEH, but at the same time it needs to solve the clock synchronization problem of each system. The key issue is how to use GPS to synchronize its clock without any modification of the DEH.
Through analysis of the DEH, the system time comes from the DOS clock of the engineering station. Using the clock interrupt program in the ROM-BIOS to rewrite the PC clock in real time is a key technology for the design of the PC card. This program is solidified in the PC card and is always in memory after the system is started.
When the INFI-90 system is being retrofitted, the multifunction processor (MFP) can use the RS-485 interface to receive the GPS time sent by the PC card. The SOE time comes from the loop time of the INFI-90 system. After the INFI-90 system is synchronized with the GPS time, the SOE time naturally synchronizes with the GPS time.
3.3 Software and Hardware Interface The PC card of GPS is inserted in the ISA slot of the IPC of the DEH engineer station, as shown in Figure 2. Since the real-time clock interrupt of the BIOS is 18.2 times per second, the solidified BIOS clock interrupt resident program on the PC card updates the real DEH clock and the system clock every 55 ms. The work on the time is done automatically by the PC Card and has nothing to do with the DEH.
The INFI-90 system shown in Figure 3 uses the RS-485 serial port to read the decoded GPS time information from the RS-485 interface of the GPS PC Card at a rate of 9.6 kbit/s per second (by the synchronization word 18 bytes, including year, year, month, day, hour, minute, second, and check word, etc., and the clock of this system is updated in real time.
The SOE is synchronized by accepting the GPS time sent by the baton's store-and-forward communication protocol on the ring network of the INFI-90 system. The detailed information format can be found in the literature [3].
3.4 Effect of clock synchronization after transformation The modified DEH, DCS and SOE achieve data communication with the GPS, keeping the DEH clock synchronized with the DCS, SOE and other control systems in order to facilitate the historical data over time in the event of an accident. Unification is conducive to accident analysis. Using the PC card of GPS to achieve the purpose of synchronizing the above three system clocks without affecting the normal operation of the original system (DEH), the time error among the systems is within tens of microseconds.
4 Conclusion This article describes the design of GPS-based clock synchronization PC card and its application in the transformation of thermal power plant automation systems. Based on GPS technology, BIOS clock interrupts and program-resident memory technology are used to successfully solve the technical problem of using GPS clocks to synchronize different system time without affecting the normal operation of the original system.
Practice has proved that the GPS PC card circuit design proposed in this paper is correct, and the design ideas and technical solutions of the clock synchronization transformation of the thermal power plant automation system are successful. The GPS PC card has a good application prospect in clock synchronization applications of power systems.
0 Introduction Since the introduction of distributed control system (DCS) technology in the middle and late 1980s in China and its application in the unit control of thermal power plants, after decades of development, DCS has been in the control of the unit control system in thermal power plants. Widely used, it greatly improved the automation level of thermal power plants. Turbine Digital Electrohydraulic Control System (DEH) is a real-time control system for turbine generator sets. It is a regulating controller for starting, stopping, normal operation and accident conditions of steam turbines.
At present, many real-time control systems such as DCS and DEH that are being used in thermal power plants are mostly developed many years ago. The clocks of their application systems are mostly based on their respective system clocks. Therefore, the clocks of different systems are not synchronized. This is unacceptable for thermal power plant automation systems that require synchronous data acquisition, accurate measurement using accident recall systems (SOE), and analysis of the cause of the accident. In order to reduce the time error, the method often used is artificially timed. This method is both laborious and does not fundamentally eliminate the time error. The use of Global Positioning System (GPS) technology is the best means to solve the problem of clock synchronization.
1 The method of using GPS to implement accurate clock synchronization There are two main methods to implement clock synchronization using GPS: One is that when developing the application system, the GPS and the circuit design of the application system are organically combined according to the system requirements in advance, for example, GPS-based time synchronization data acquisition systems, etc. [1]; the other is that due to limited conditions in the design, GPS technology is not used, but the internal clocks of the respective operating systems are directly used. Therefore, the clocks of the various parts of the system are not synchronized. .
For the latter case, GPS technology can be used to synchronize the clocks of the various parts of the system. There are two methods: 1 Use software-only methods, that is, use the PC's serial port to synchronize the original system's "patching" program that receives GPS time information. Of course, using the DOS or Windows multitasking process method is not difficult to achieve "i. It should be noted that this method not only takes up a serial port of the PC system, but also does not apply to the real-time control system, because the complete reception of GPS It takes nearly 1 second for navigation information.2 The combination of hardware and software not only does not occupy the serial port resources of the PC system, but also does not affect the normal operation of the original system.This is the design idea of ​​this paper.
2 GPS-based clock synchronization PC card development Based on GPS clock synchronization PC card hardware circuit principle shown in Figure 1. The left side of the dotted line in the figure is the circuit for the CPU (W77E58 microcontroller) receiving GPS time, and the right side is the circuit for rewriting the real clock and system clock of the PC.
In order to avoid the impact of the PC on the operation of the original application system program of the PC when reading/writing the GPS time in the dual-port RAM, and without affecting the real-time updating of the PC card to the system time, the GPS side of the PC receives and The rewrite clock program should be resident in memory [2]. Using the clock interrupt program (1AH) in the ROM-BIOS to rewrite the PC clock in real time is a key technology of the PC card design. The resident clock interrupt routine is fixed in the ROM (27C128) on the card.
The PC card has two external interfaces: one is a decoded GPS time interface, and one frame (18B) of decoded GPS time is sent to the serial port every second, using an RS-485 interface; the other is an undecoded GPS time, Uses RS-232 interface.
3 Application of GPS Synchronous Clock The DEH of a No. 12 300 MW unit in a thermal power plant is the product of Xinhua Power Plant. Its structure is shown in Figure 2. The DCS of the unit is an INFI-90 system developed by Bailey and its structure is shown in Figure 3. The unit SOE time is taken from the loop time of the INFI-90 system.
3.1 Problems that currently exist The above DEH, DCS, and SOE times are taken from their respective operating systems or loops. Therefore, the clocks of each system are not synchronous. The maximum time error has reached several tens of minutes. This gives fault conditions. Analyzing the cause of the accident has brought great difficulties. In order to reduce the time error, the current method is: at regular intervals, the system engineer inputs the standard time into their respective operating systems, and the daily synchronization error is more than a few seconds.
3.2 The basic idea of ​​the transformation and technical solutions The system transformation only involves the INFI-90 system. It does not make any modifications to the original DEH, but at the same time it needs to solve the clock synchronization problem of each system. The key issue is how to use GPS to synchronize its clock without any modification of the DEH.
Through analysis of the DEH, the system time comes from the DOS clock of the engineering station. Using the clock interrupt program in the ROM-BIOS to rewrite the PC clock in real time is a key technology for the design of the PC card. This program is solidified in the PC card and is always in memory after the system is started.
When the INFI-90 system is being retrofitted, the multifunction processor (MFP) can use the RS-485 interface to receive the GPS time sent by the PC card. The SOE time comes from the loop time of the INFI-90 system. After the INFI-90 system is synchronized with the GPS time, the SOE time naturally synchronizes with the GPS time.
3.3 Software and Hardware Interface The PC card of GPS is inserted in the ISA slot of the IPC of the DEH engineer station, as shown in Figure 2. Since the real-time clock interrupt of the BIOS is 18.2 times per second, the solidified BIOS clock interrupt resident program on the PC card updates the real DEH clock and the system clock every 55 ms. The work on the time is done automatically by the PC Card and has nothing to do with the DEH.
The INFI-90 system shown in Figure 3 uses the RS-485 serial port to read the decoded GPS time information from the RS-485 interface of the GPS PC Card at a rate of 9.6 kbit/s per second (by the synchronization word 18 bytes, including year, year, month, day, hour, minute, second, and check word, etc., and the clock of this system is updated in real time.
The SOE is synchronized by accepting the GPS time sent by the baton's store-and-forward communication protocol on the ring network of the INFI-90 system. The detailed information format can be found in the literature [3].
3.4 Effect of clock synchronization after transformation The modified DEH, DCS and SOE achieve data communication with the GPS, keeping the DEH clock synchronized with the DCS, SOE and other control systems in order to facilitate the historical data over time in the event of an accident. Unification is conducive to accident analysis. Using the PC card of GPS to achieve the purpose of synchronizing the above three system clocks without affecting the normal operation of the original system (DEH), the time error among the systems is within tens of microseconds.
4 Conclusion This article describes the design of GPS-based clock synchronization PC card and its application in the transformation of thermal power plant automation systems. Based on GPS technology, BIOS clock interrupts and program-resident memory technology are used to successfully solve the technical problem of using GPS clocks to synchronize different system time without affecting the normal operation of the original system.
Practice has proved that the GPS PC card circuit design proposed in this paper is correct, and the design ideas and technical solutions of the clock synchronization transformation of the thermal power plant automation system are successful. The GPS PC card has a good application prospect in clock synchronization applications of power systems.
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