Power grid time frequency synchronization system and method based on optical fiber time frequency transmission

Abstract

The invention provides a power grid time-frequency synchronization system and method based on optical fiber time-frequency transmission, and belongs to the field of power system time synchronization, the system comprises a master station and a plurality of slave stations which are annularly connected, the master station comprises a first GNSS receiver, a master station punctuality atomic clock and a first optical fiber time-frequency synchronization device, the slave station comprises a second GNSS receiver, a second optical fiber time-frequency synchronization device, a clock seamless switching device and an electric power timing system device, and the first optical fiber time-frequency synchronization device accesses a time signal and a frequency signal output by the time-keeping atomic clock of the master station; the second optical fiber time-frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time-frequency synchronization device, and the slave station outputs the laser signal to the first optical fiber time-frequency synchronization device for time comparison and then recovers a time signal synchronized with the master station; the space-based GNSS satellite time service system and the ground-based optical fiber time frequency transmission system are standby for each other, the master station and the slave stations are connected in a ring networking mode, and the reliability, safety and accuracy of the time synchronization system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system time synchronization, and in particular to a power grid time-frequency synchronization system and method based on optical fiber time-frequency transmission. Background Art

[0002] High-precision time synchronization is the basis for the normal operation of the power system, the basis for various monitoring systems to conduct data sampling, fault handling, network supervision, information management, accident recall and analysis, and an important part of the safe operation of the system. If any node involved in time synchronization has a time deviation problem, it may affect the stable operation of the power system. As the international security situation becomes increasingly severe, the country is paying more and more attention to the security of public critical infrastructure such as electricity and telecommunications that are related to the national economy and people's livelihood. In the requirements of the "Technical Specifications for Time Synchronization and Monitoring of Power Systems", it is also proposed that the time synchronization device of the power system should have multiple clock source options, with space-based time synchronization as the main and ground-based time synchronization as the auxiliary, to establish a complete and reliable time synchronization system.

[0003] At present, the State Grid system widely uses GNSS space-based clocks such as GPS or Beidou as the main clock source. In some cases, Beidou timing is used as the only clock source, and some substations are still using traditional GPS single clocks for time synchronization and calibration due to old equipment. GPS clocks may fail under the current international situation. The GNSS system uses space clear code transmission signals, and the satellite signals are weak, which is very easy to cause interference attacks and man-in-the-middle attacks to cause the clock system to fail.

[0004] With the increasing maturity of optical fiber time and frequency synchronization technology, synchronization accuracy of picoseconds can now be achieved. For example, the Chinese invention patent application "A high-precision long-distance optical fiber synchronization system" with publication number CN116599619A includes a master station and multiple slave stations that communicate through a long-distance optical fiber bidirectional synchronization link. Before the frequency signal and clock signal generated by the station clock are applied to the optical fiber bidirectional time synchronization, the phase noise of the frequency signal is eliminated in combination with the phase noise processing module, and the jitter elimination module and the first frequency standard obtained after the phase noise elimination are combined to eliminate the jitter of the clock signal. When the ultra-low phase noise first frequency standard and the ultra-low jitter reference clock are applied to the optical fiber bidirectional time synchronization, the measured delay values ​​are as close to the sum of the optical fiber link delay, the hardware delays, and the clock difference, so that the clock difference between the master station and the slave station is as close to the actual clock difference as possible. However, the defects of this fiber optic synchronization system are: (1) Since domestic fiber optic links are often laid along roads, they are easily affected by road construction, etc. When the fiber optic link is interrupted, time synchronization cannot be performed between the master station and the slave station, resulting in signal interruption and reduced system reliability; (2) This fiber optic synchronization system uses wavelength division. Although the nominal wavelength of the bidirectional laser is the same, the wavelength will change due to temperature and aging, making it difficult to maintain the stability of the bidirectional wavelength, thereby reducing the accuracy of time synchronization. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to improve the reliability of a time synchronization system in a power system.

[0006] The present invention solves the above technical problems through the following technical solutions: a power grid time and frequency synchronization system based on optical fiber time and frequency transmission, including a master station and multiple slave stations connected in a ring, the master station including a first GNSS receiver, a master station timekeeping atomic clock and a first optical fiber time and frequency synchronization device, each slave station including a second GNSS receiver, a second optical fiber time and frequency synchronization device, a clock seamless switching device and a power time synchronization device, the master station timekeeping atomic clock accesses the time signal of the first GNSS receiver and keeps synchronization with the time signal, the first optical fiber time and frequency synchronization device accesses the time signal and frequency signal output by the master station timekeeping atomic clock, and modulates the time signal and frequency signal onto a laser carrier to obtain a laser signal, the second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time and frequency synchronization device, when the second optical fiber time and frequency synchronization device receives the time comparison instruction of the master station, the slave station outputs the laser signal to the first optical fiber time and frequency synchronization device for time comparison, recovers the time signal synchronized with the master station, and transmits it to the clock seamless switching device, the clock seamless switching device is used to send the time signal of the second GMSS receiver or the time signal synchronized with the master station into the power time synchronization device.

[0007] Preferably, the slave station outputs a laser signal to the first optical fiber time-frequency synchronization device for time comparison and then recovers a time signal synchronized with the master station, including: the slave station outputs a laser signal to the master station, firstly performs time comparison at the master station, calculates a first time difference between the time signal of the master station's atomic clock and the slave station's time signal, inputs the time difference together with the master station's time signal to the slave station, compares the time signal of the master station's atomic clock with the slave station's time signal again at the slave station, calculates a second time difference between the time signal output by the master station's atomic clock and the slave station's time signal, calculates a delay compensation amount based on the first time difference value and the second time difference value, and compensates the delay compensation amount to the slave station's time signal, thereby realizing time synchronization between the slave station and the master station.

[0008] Preferably, the master station also includes a first optical splitter, and each slave station includes a second optical splitter, a third optical splitter and a relay device. The laser signal output by the first optical fiber time and frequency synchronization device is divided into two signals through the first optical splitter, one signal enters the second optical splitter through the main link, and the other signal enters the third optical splitter through the backup link. The two signals output by the second optical splitter enter the second optical fiber time and frequency synchronization device and the relay device respectively, and the two signals output by the third optical splitter enter the second optical fiber time and frequency synchronization device and the relay device respectively. The relay device is used to amplify the signal output by the second optical splitter and send it to the third optical splitter, and at the same time amplify the signal output by the third optical splitter and send it to the second optical splitter.

[0009] Preferably, the first optical fiber time and frequency synchronization device includes a first modulation encoder, a first laser, a first circulator, a first time difference measurement module, a first decoding demodulator and a first photodetector. The first modulation encoder is connected to the time signal and frequency signal output by the master station timekeeping atomic clock. The first optical splitter receives the laser signal from the slave station and sends it to the first circulator. The first circulator sends the laser signal of the slave station to the first photodetector to demodulate the coded signal and then sends it to the first decoding demodulator. The first decoding demodulator demodulates the slave station time signal and the slave station site number from the coded signal. The time signal of the master station timekeeping atomic clock and the slave station time signal are input into the first time difference measurement module, and the time difference value t1 between the time signal of the master station timekeeping atomic clock and the slave station time signal is calculated. The time signal and frequency signal, the time difference value and the slave station site number output by the master station timekeeping atomic clock are input into the first modulation encoder for encoding to obtain the coded signal. The coded signal is sequentially passed through the first laser and the first circulator and then sent to the first optical splitter. The first laser is used to modulate the coded signal from the first modulation encoder into the laser carrier signal, and the first circulator is used to couple the laser signal into the optical fiber link and then send it to the first optical splitter.

[0010] Preferably, the second optical fiber time and frequency synchronization device includes a second optical switch, a second circulator, a second photodetector, a second decoding demodulator, a second time difference measurement module, a second time regeneration module, a second modulation encoder, and a second laser. The second optical switch is interconnected with the second optical splitter and the second optical splitter respectively. The laser signal output by the first optical splitter is sequentially input into the second photodetector through the second optical switch and the second circulator. The second photodetector demodulates the coded signal from the laser signal and then sends it to the second decoding demodulator. The second decoding demodulator demodulates the time signal output by the master station timekeeping atomic clock and the first time difference measurement module from the coded signal. The time difference value t1 calculated by the block and the time signal output by the master station timekeeping atomic clock are input into the second time difference measurement module. The second time difference measurement module calculates the time difference value t2 between the time signal output by the master station timekeeping atomic clock and the time signal of the slave station. The time difference value t1 and the time difference value t2 are input into the second time regeneration module together to calculate the delay compensation amount and compensate the time of the slave station. The compensated slave station time signal is respectively sent to the second time difference measurement module, the clock seamless switching device and the second modulation encoder. The second modulation encoder encodes the compensated slave station time and the slave station site number and transmits them to the master station through the second laser and the second circulator in sequence.

[0011] Preferably, when the GNSS satellite signal of the slave station is normal, the clock seamless switching device sends the GNSS time signal to the power time system device; when the GNSS satellite signal of the slave station is abnormal, the clock seamless switching device sends the optical fiber time signal synchronized with the master station to the power time system device.

[0012] Preferably, when the main link is available, the second optical switch selects to connect to the second optical splitter, and the laser signal emitted by the master station is transmitted to the slave station through the main link, and the laser signal emitted by the slave station is transmitted to the master station through the main link; when the main link is unavailable, the second optical switch selects to connect to the third optical splitter, and the laser signal emitted by the master station is transmitted to the slave station through the backup link, and the laser signal emitted by the slave station is transmitted to the master station through the backup link.

[0013] Preferably, the formula for calculating the delay compensation amount by the second time regeneration module is:

[0014] T D =(t2-t1) / 2

[0015] Among them, T D is the delay compensation amount, t1 is the time difference value calculated by the first time difference measurement module, and t2 is the time difference value calculated by the second time difference measurement module.

[0016] The present invention also provides a power grid time and frequency synchronization method based on optical fiber time and frequency transmission, using the power grid time and frequency synchronization system, including: a master station and multiple slave stations are ring-networked, the master station's timekeeping atomic clock is connected to the time signal of the first GNSS receiver and keeps synchronization with the time signal, the first optical fiber time and frequency synchronization device is connected to the time signal and frequency signal output by the master station's timekeeping atomic clock, and the time signal and frequency signal are modulated onto a laser carrier to obtain a laser signal, the second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time and frequency synchronization device, when the second optical fiber time and frequency synchronization device receives the time comparison instruction of the master station, the slave station outputs the laser signal to the first optical fiber time and frequency synchronization device for time comparison, and then recovers the time signal synchronized with the master station, and transmits it to the clock seamless switching device, the clock seamless switching device is used to send the time signal of the second GMSS receiver or the time signal synchronized with the master station into the power time system device.

[0017] Preferably, the specific process of recovering the time signal synchronized with the master station after outputting the laser signal from the slave station to the first optical fiber time-frequency synchronization device for time comparison is as follows: the slave station outputs the laser signal to the master station, firstly performs time comparison in the first time difference measurement module in the master station, calculates the time difference t1 between the time signal of the master station's atomic clock and the time signal of the slave station, and inputs the time difference value together with the master station's time signal into the slave station, and the second time difference measurement module in the slave station compares the time signal of the master station's atomic clock with the slave station's time signal again, calculates the time difference t2 between the time signal output by the master station's atomic clock and the slave station's time signal, and the time difference t1 and the time difference t2 are input together into the second time regeneration module, and the delay compensation amount is calculated by averaging, and the delay compensation amount is compensated to the slave station's time signal, thereby realizing time synchronization between the slave station and the master station.

[0018] The advantages provided by the present invention are:

[0019] 1. In the power grid time and frequency synchronization system of the present invention, the space-based GNSS satellite timing system and the ground-based optical fiber time and frequency transmission system serve as backup for each other. In the ground-based optical fiber time and frequency transmission system, the master station and multiple slave stations are connected in a ring networking manner. The second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal from the master station. When receiving the time comparison instruction of the master station, the slave station sends a laser signal to the master station to the first optical fiber time and frequency synchronization device for time comparison and then restores the time signal synchronized with the master station. In the slave station, when the time signal of the second GNSS receiver is normal, the clock seamless switching device sends the time signal of the second GMSS receiver to the power time synchronization device. When the time signal of the second GNSS receiver is abnormal, the clock seamless switching device sends the time signal synchronized with the master station output by the second optical fiber time and frequency synchronization device to the power time synchronization device. When the optical fiber link connecting a slave station to the master station is interrupted, the slave station can achieve time synchronization with the master station through the backup optical fiber link, thereby achieving time synchronization of each slave station on the ring link, thereby improving the reliability, safety and accuracy of the time synchronization system in the power system.

[0020] 2. In the present invention, the first optical fiber time and frequency synchronization device in the master station and the second optical fiber time and frequency synchronization device in the slave station have their own unique device address numbers. The first optical fiber time and frequency synchronization device uses time division multiple access to poll the second optical fiber time and frequency synchronization device of each slave station to perform two-way time comparison. The master station uses time division to synchronize with each station to avoid backscattering and interference from reflected signals, thereby improving the signal-to-noise ratio.

[0021] 3. The power grid time and frequency synchronization system of the present invention adopts multi-fiber routing for time synchronization. In the case of a main link interruption, the backup link can be used to complete the time synchronization. When the main link is interrupted, the signal can be transmitted from other links, thereby improving the availability of the system. An optical switch is used to select the signal, so that the second photodetector in the slave station can only receive optical signals in one direction at a time, thereby preventing the slave station from receiving bidirectional optical signals at the same time and causing mutual interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a power grid time-frequency synchronization system based on optical fiber time-frequency transmission provided by an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of a power grid time and frequency synchronization system based on optical fiber time and frequency transmission provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the technical solution of the present invention is clearly and completely described below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] like Figure 1 As shown, the present invention provides a power grid time and frequency synchronization system based on optical fiber time and frequency transmission, including a master station and multiple slave stations connected in a ring, the master station including a first GNSS receiver, a master station timekeeping atomic clock and a first optical fiber time and frequency synchronization device, each slave station respectively includes a second GNSS receiver, a second optical fiber time and frequency synchronization device, a clock seamless switching device and a power time synchronization device, the master station timekeeping atomic clock accesses the time signal of the first GNSS receiver and keeps synchronization with the time signal, the first optical fiber time and frequency synchronization device accesses the time signal and frequency signal output by the master station timekeeping atomic clock, and modulates the time signal and frequency signal onto a laser carrier to obtain a laser signal, the second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time and frequency synchronization device, when the second optical fiber time and frequency synchronization device receives the time comparison instruction of the master station, the slave station outputs the laser signal to the first optical fiber time and frequency synchronization device for time comparison, recovers the time signal synchronized with the master station, and transmits it to the clock seamless switching device, the clock seamless switching device is used to send the time signal of the second GMSS receiver or the time signal synchronized with the master station into the power time synchronization device.

[0026] In the power grid time and frequency synchronization system of the present invention, the space-based GNSS satellite timing system and the ground-based optical fiber time and frequency transmission system serve as backup for each other. In the ground-based optical fiber time and frequency transmission system, the master station and multiple slave stations are connected in a ring networking manner. The second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal from the master station. When receiving the time comparison instruction of the master station, the slave station sends a laser signal to the master station to the first optical fiber time and frequency synchronization device for time comparison and then restores the time signal synchronized with the master station. In the slave station, when the time signal of the second GNSS receiver is normal, the clock seamless switching device sends the time signal of the second GMSS receiver to the power time synchronization device. When the time signal of the second GNSS receiver is abnormal, the clock seamless switching device sends the time signal synchronized with the master station output by the second optical fiber time and frequency synchronization device to the power time synchronization device. When the optical fiber link connecting a slave station to the master station is interrupted, the slave station can achieve time synchronization with the master station through the backup optical fiber link, thereby achieving time synchronization of each slave station on the ring link, thereby improving the reliability, safety and accuracy of the time synchronization system in the power system.

[0027] It should be noted that the space-based GNSS satellite timing system refers to the system time maintained by the Beidou satellite navigation system or the GPS satellite navigation system, the Galileo satellite navigation system, etc. The master station timekeeping atomic clock maintains both the time signal and the frequency signal, and is synchronized with the standard time through satellite timing, satellite synchronization, etc. The master station timekeeping atomic clock can also be connected to the time and frequency signal of the external optical fiber timing system to achieve higher precision time synchronization.

[0028] like Figure 2 As shown, the master station also includes a first optical splitter, and each slave station includes a second optical splitter, a third optical splitter and a relay device. The laser signal output by the first optical fiber time-frequency synchronization device is divided into two signals through the first optical splitter, one signal enters the second optical splitter through the main link, and the other signal enters the third optical splitter through the backup link. The two signals output by the second optical splitter enter the second optical fiber time-frequency synchronization device and the relay device respectively, and the two signals output by the third optical splitter enter the second optical fiber time-frequency synchronization device and the relay device respectively. The relay device is used to amplify the signal output by the second optical splitter and send it to the third optical splitter, and at the same time, amplify the signal output by the third optical splitter and send it to the second optical splitter. The laser signal will attenuate when propagating in the optical fiber link, and the relay device can amplify the power of the laser signal.

[0029] It should be noted that the main link and the backup link are only used to distinguish the different optical fiber links between a slave station and the master station. Figure 1 Taking slave station B as an example, the optical fiber link between the master station and slave station B is defined as the main link. The laser signal emitted by the master station passes through the optical fiber link between the master station and slave station C, the optical fiber link between slave station C and slave station N, the optical fiber link between slave station N and slave station D, and the optical fiber link between slave station D and slave station B. These are defined as backup links. When time synchronization is required between the master station and slave station B, the transmission of the laser signal between the master station and slave station B can be transmitted through the main link or through the backup link. The main link and the backup link are backups for each other, and can deal with the problem of affecting the time synchronization of the slave station when the optical fiber link is damaged.

[0030] like Figure 2As shown, the first optical fiber time and frequency synchronization device includes a first modulation encoder, a first laser, a first circulator, a first time difference measurement module, a first decoding demodulator and a first photoelectric detector. The first modulation encoder is connected to the time signal and frequency signal output by the master station timekeeping atomic clock. The first optical splitter receives the laser signal from the slave station and sends it to the first circulator. The first circulator sends the laser signal of the slave station to the first photoelectric detector to demodulate the coded signal and then send it to the first decoding demodulator. The first decoding demodulator demodulates the slave station time signal and the slave station site number from the coded signal. The time signal of the master station timekeeping atomic clock and the slave station time signal are input to the first time difference measurement module, and the time difference value t1 between the time signal of the master station timekeeping atomic clock and the slave station time signal is calculated. The time signal and frequency signal, the time difference value and the slave station site number output by the master station timekeeping atomic clock are input to the first modulation encoder for encoding to obtain the coded signal. The coded signal passes through the first laser and the first circulator in sequence and is sent to the first optical splitter. The first laser is used to modulate the coded signal from the first modulation encoder into the laser carrier signal, and the first circulator is used to couple the laser signal into the optical fiber link and then send it to the first optical splitter.

[0031] The second optical fiber time and frequency synchronization device includes a second optical switch, a second circulator, a second photoelectric detector, a second decoding demodulator, a second time difference measurement module, a second time regeneration module, a second modulation encoder, and a second laser. The second optical switch is interconnected with the second optical splitter and the second optical splitter respectively. The laser signal output by the first optical splitter is sequentially input into the second photoelectric detector through the second optical switch and the second circulator. The second photoelectric detector demodulates the coded signal from the laser signal and sends it to the second decoding demodulator. The second decoding demodulator demodulates the time signal output by the master station timekeeping atomic clock and the time difference value calculated by the first time difference measurement module from the coded signal. The time signal output by the master station's atomic clock is input into the second time difference measurement module. The second time difference measurement module calculates the time difference t2 between the time signal output by the master station's atomic clock and the slave station's time signal. The time difference t1 and t2 calculated by the first time difference measurement module are input into the second time regeneration module to calculate the delay compensation amount and compensate the slave station's time. The compensated slave station time signal is respectively sent to the second time difference measurement module, the clock seamless switching device and the second modulation encoder. The second modulation encoder encodes the compensated slave station time and the slave station site number and transmits them to the master station through the second laser and the second circulator in sequence.

[0032] The first optical fiber time and frequency synchronization device in the master station and the second optical fiber time and frequency synchronization device in the slave station have their own unique device address numbers. The first optical fiber time and frequency synchronization device uses time division multiple access to poll the second optical fiber time and frequency synchronization device of each slave station for two-way time comparison. The master station uses time division to synchronize with each station to avoid backscattering and interference from reflected signals, thereby improving the signal-to-noise ratio.

[0033] The slave station continuously receives the laser signal sent by the master station. When the slave station receives the time comparison instruction from the master station, the slave station outputs the laser signal to the master station. First, the first time difference measurement module in the master station performs time comparison to calculate the time difference t1 between the time signal of the master station's punctual atomic clock and the slave station's time signal. This time difference value is input into the slave station together with the master station's time signal. The second time difference measurement module in the slave station compares the master station's time signal (the time signal of the master station's punctual atomic clock) with the slave station's time signal again to calculate the time difference t2 between the time signal output by the master station's punctual atomic clock and the slave station's time signal. The time difference value t1 and the time difference value t2 are input together into the second time regeneration module to calculate the delay compensation amount, that is, the time difference between the slave station and the master station. By compensating the time of the slave station, a time signal synchronized with the master station time can be obtained, and the time signal is sent to the clock seamless switching device. When the GNSS satellite signal of the slave station is normal, the clock seamless switching device sends the GNSS time signal to the power time system device. When the GNSS satellite signal of the slave station is abnormal, the clock seamless switching device sends the optical fiber time signal synchronized with the master station to the power time system device to ensure the continuity of the signal and improve the reliability of the power time synchronization system.

[0034] Any slave station can receive the laser signal from the master station through the main link and the backup link at the same time. However, in order to prevent the slave station from receiving the bidirectional optical signal at the same time and causing mutual interference, an optical switch is used to select the signal so that the second photodetector in the slave station can only receive the optical signal in one direction at a time. The second optical switch is used to select the main link or backup link for the signal transmission between the slave station and the master station. When the main link is available, the second optical switch selects to connect the second optical splitter. The laser signal emitted by the master station is transmitted to the slave station through the main link, and the laser signal emitted by the slave station is transmitted to the master station through the main link. When the main link is unavailable, the second optical switch selects to connect the third optical splitter. The laser signal emitted by the master station is transmitted to the slave station through the backup link, and the laser signal emitted by the slave station is transmitted to the master station through the backup link. The optical fiber time synchronization system uses multi-fiber routing for time synchronization. In the case of a main link interruption, the backup link can be used to complete time synchronization. When the main link is interrupted, the signal can be transmitted from other links, which improves the availability of the system.

[0035] The formula for calculating the delay compensation amount by the second time regeneration module is:

[0036] T D =(t2-t1) / 2

[0037] Among them, T D is the delay compensation amount, t1 is the time difference value calculated by the first time difference measurement module, and t2 is the time difference value calculated by the second time difference measurement module.

[0038] The present invention also provides a power grid time and frequency synchronization method based on optical fiber time and frequency transmission, including: a master station and multiple slave stations are ring-networked, the master station's timekeeping atomic clock is connected to the time signal of the first GNSS receiver and keeps synchronization with the time signal, the first optical fiber time and frequency synchronization device is connected to the time signal and frequency signal output by the master station's timekeeping atomic clock, and the time signal and frequency signal are modulated onto a laser carrier to obtain a laser signal, the second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time and frequency synchronization device, when the second optical fiber time and frequency synchronization device receives the time comparison instruction of the master station, the slave station outputs the laser signal to the first optical fiber time and frequency synchronization device for time comparison, and then recovers the time signal synchronized with the master station, and transmits it to the clock seamless switching device, the clock seamless switching device is used to send the time signal of the second GMSS receiver or the time signal synchronized with the master station into the power time synchronization device.

[0039] The specific process of recovering the time signal synchronized with the master station after the slave station outputs the laser signal to the first optical fiber time-frequency synchronization device for time comparison is as follows: the slave station outputs the laser signal to the master station, firstly the first time difference measurement module in the master station performs time comparison, calculates the time difference t1 between the time signal of the master station's atomic clock and the time signal of the slave station, and the time difference value is input to the slave station together with the master station's time signal, and the second time difference measurement module in the slave station compares the master station's time signal (the time signal of the master station's atomic clock) with the slave station's time signal again, calculates the time difference t2 between the time signal output by the master station's atomic clock and the time signal of the slave station, and the time difference t1 and the time difference t2 are input to the second time regeneration module together, and the delay compensation amount, i.e. the time difference between the slave station and the master station, is calculated by taking the average, and the time signal synchronized with the master station can be obtained by compensating the slave station's time.

[0040] The time signal is sent to the clock seamless switching device. When the GNSS satellite signal of the slave station is normal, the clock seamless switching device sends the GNSS time signal to the power time synchronization device. When the GNSS satellite signal of the slave station is abnormal, the clock seamless switching device sends the optical fiber time signal synchronized with the master station to the power time synchronization device to ensure the continuity of the signal and improve the reliability of the power time synchronization system.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A power grid time-frequency synchronization system based on optical fiber time-frequency transmission, characterized in that: The invention comprises a master station and a plurality of slave stations connected in a ring, wherein the master station comprises a first GNSS receiver, a master station timekeeping atomic clock and a first optical fiber time and frequency synchronization device, and each slave station comprises a second GNSS receiver, a second optical fiber time and frequency synchronization device, a clock seamless switching device and an electric power time synchronization device, the master station timekeeping atomic clock accesses the time signal of the first GNSS receiver and keeps synchronization with the time signal, the first optical fiber time and frequency synchronization device accesses the time signal and the frequency signal output by the master station timekeeping atomic clock, and modulates the time signal and the frequency signal onto a laser carrier to obtain a laser signal, the second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time and frequency synchronization device, when the second optical fiber time and frequency synchronization device receives the time comparison instruction of the master station, the slave station outputs the laser signal to the first optical fiber time and frequency synchronization device for time comparison, recovers the time signal synchronized with the master station, and transmits it to the clock seamless switching device, the clock seamless switching device is used to send the time signal of the second GMSS receiver or the time signal synchronized with the master station into the electric power time synchronization device.

2. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 1, characterized in that: The slave station outputs a laser signal to the first optical fiber time-frequency synchronization device for time comparison and then recovers a time signal synchronized with the master station, including: the slave station outputs a laser signal to the master station, firstly performs time comparison at the master station, calculates a first time difference between the time signal of the master station's atomic clock and the slave station's time signal, inputs the time difference together with the master station's time signal into the slave station, compares the time signal of the master station's atomic clock with the slave station's time signal again at the slave station, calculates a second time difference between the time signal output by the master station's atomic clock and the slave station's time signal, calculates a delay compensation amount based on the first time difference value and the second time difference value, and compensates the delay compensation amount to the slave station's time signal, thereby realizing time synchronization between the slave station and the master station.

3. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 1, characterized in that: The master station also includes a first optical splitter, and each slave station includes a second optical splitter, a third optical splitter and a relay device. The laser signal output by the first optical fiber time and frequency synchronization device is divided into two signals through the first optical splitter, one signal enters the second optical splitter through the main link, and the other signal enters the third optical splitter through the backup link. The two signals output by the second optical splitter enter the second optical fiber time and frequency synchronization device and the relay device respectively, and the two signals output by the third optical splitter enter the second optical fiber time and frequency synchronization device and the relay device respectively. The relay device is used to amplify the signal output by the second optical splitter and send it to the third optical splitter, and at the same time amplify the signal output by the third optical splitter and send it to the second optical splitter.

4. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 3 is characterized in that: The first optical fiber time and frequency synchronization device includes a first modulation encoder, a first laser, a first circulator, a first time difference measurement module, a first decoding demodulator and a first photoelectric detector. The first modulation encoder is connected to the time signal and frequency signal output by the master station timekeeping atomic clock. The first optical splitter receives the laser signal from the slave station and sends it to the first circulator. The first circulator sends the laser signal of the slave station to the first photoelectric detector to demodulate the coded signal and then send it to the first decoding demodulator. The first decoding demodulator demodulates the slave station time signal and the slave station site number from the coded signal. The time signal of the master station timekeeping atomic clock and the slave station time signal are input to the first time difference measurement module, and the time difference value t1 between the time signal of the master station timekeeping atomic clock and the slave station time signal is calculated. The time signal and frequency signal, the time difference value and the slave station site number output by the master station timekeeping atomic clock are input to the first modulation encoder for encoding to obtain the coded signal. The coded signal is sequentially passed through the first laser and the first circulator and then sent to the first optical splitter. The first laser is used to modulate the coded signal from the first modulation encoder into the laser carrier signal, and the first circulator is used to couple the laser signal into the optical fiber link and then send it to the first optical splitter.

5. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 3, characterized in that: The second optical fiber time and frequency synchronization device comprises a second optical switch, a second circulator, a second photodetector, a second decoding demodulator, a second time difference measurement module, a second time regeneration module, a second modulation encoder, and a second laser. The second optical switch is interconnected with the second optical splitter and the second optical splitter respectively. The laser signal output by the first optical splitter is sequentially input into the second photodetector through the second optical switch and the second circulator. The second photodetector demodulates the coded signal from the laser signal and sends it to the second decoding demodulator. The second decoding demodulator demodulates the time signal output by the master station timekeeping atomic clock and the time signal of the first time difference measurement module from the coded signal. The calculated time difference value t1 and the time signal output by the master station's atomic clock are input into the second time difference measurement module. The second time difference measurement module calculates the time difference value t2 between the time signal output by the master station's atomic clock and the slave station's time signal. The time difference value t1 and the time difference value t2 are input into the second time regeneration module together to calculate the delay compensation amount and compensate the slave station's time. The compensated slave station time signal is respectively sent to the second time difference measurement module, the clock seamless switching device and the second modulation encoder. The second modulation encoder encodes the compensated slave station time and the slave station site number and transmits them to the master station through the second laser and the second circulator in sequence.

6. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 1, characterized in that: When the GNSS satellite signal of the slave station is normal, the clock seamless switching device sends the GNSS time signal to the power time system device. When the GNSS satellite signal of the slave station is abnormal, the clock seamless switching device sends the optical fiber time signal synchronized with the master station to the power time system device.

7. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 5, characterized in that: When the main link is available, the second optical switch selects to connect the second optical splitter, and the laser signal emitted by the master station is transmitted to the slave station through the main link, and the laser signal emitted by the slave station is transmitted to the master station through the main link. When the main link is unavailable, the second optical switch selects to connect the third optical splitter, and the laser signal emitted by the master station is transmitted to the slave station through the backup link, and the laser signal emitted by the slave station is transmitted to the master station through the backup link.

8. The power grid time-frequency synchronization system based on optical fiber time-frequency transmission according to claim 5, characterized in that: The formula for calculating the delay compensation amount by the second time regeneration module is: T D =(t2-t1) / 2 Among them, T D is the delay compensation amount, t1 is the time difference value calculated by the first time difference measurement module, and t2 is the time difference value calculated by the second time difference measurement module.

9. A method for power grid time-frequency synchronization based on optical fiber time-frequency transmission, using the power grid time-frequency synchronization system according to any one of claims 1 to 8, characterized in that: include: The master station and multiple slave stations are ring-networked. The master station's atomic clock accesses the time signal of the first GNSS receiver and keeps synchronization with the time signal. The first optical fiber time and frequency synchronization device accesses the time signal and frequency signal output by the master station's atomic clock, and modulates the time signal and frequency signal onto the laser carrier to obtain a laser signal. The second optical fiber time and frequency synchronization device of each slave station continuously receives the laser signal output by the first optical fiber time and frequency synchronization device. When the second optical fiber time and frequency synchronization device receives the time comparison instruction of the master station, the slave station outputs the laser signal to the first optical fiber time and frequency synchronization device for time comparison, and then recovers the time signal synchronized with the master station and transmits it to the clock seamless switching device. The clock seamless switching device is used to send the time signal of the second GMSS receiver or the time signal synchronized with the master station to the power time system device.

10. The method for power grid time-frequency synchronization based on optical fiber time-frequency transmission according to claim 9, characterized in that: The specific process of the slave station outputting the laser signal to the first optical fiber time-frequency synchronization device for time comparison and then recovering the time signal synchronized with the master station is as follows: the slave station outputs the laser signal to the master station, firstly the first time difference measurement module in the master station performs time comparison, calculates the time difference t1 between the time signal of the master station's atomic clock and the time signal of the slave station, and the time difference value is input to the slave station together with the master station's time signal, and the second time difference measurement module in the slave station compares the time signal of the master station's atomic clock with the slave station's time signal again, calculates the time difference t2 between the time signal output by the master station's atomic clock and the slave station's time signal, and the time difference t1 and the time difference t2 are input to the second time regeneration module together, and the delay compensation amount is calculated by averaging, and the delay compensation amount is compensated to the slave station's time signal, thereby realizing the time synchronization between the slave station and the master station.

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