IRIG-B code optical fiber time transfer method and system based on clock purification

Abstract

This invention relates to the field of high-precision time transfer technology, and provides a method and system for fiber optic time transfer based on clock purification using IRIG-B code. The method includes: acquiring the original GNSS 1PPS second pulse signal and absolute time information via a GNSS satellite receiver; using a negative feedback phase-locked loop to obtain a purified local 10MHz reference frequency signal and a local 1PPS second pulse signal; re-encoding the purified IRIG-B code signal and modulating it to generate a coded electrical signal; transmitting the coded electrical signal to a remote end via a fiber optic link; and regenerating and outputting an IRIG-B code signal synchronized with the source end from the received signal at the remote end, which is then provided to power equipment. This method can improve the time synchronization accuracy of the power system from the nanosecond level to the sub-nanosecond level without any modification to existing IRIG-B code equipment in the power grid.

Description

Technical Field

[0001] This invention relates to the field of high-precision time transfer technology, specifically to an IRIG-B code fiber optic time transfer method and system based on clock purification. Background Technology

[0002] Time synchronization is one of the most critical infrastructures in a power system, ensuring that equipment in all stages from power generation and transmission to distribution works collaboratively under the same precise time reference. With the large-scale integration of new energy sources, such as wind power and photovoltaics, into the grid, inverters for these new energy devices have higher requirements for time synchronization accuracy. They must be able to respond quickly to instantaneous fluctuations in the grid, thereby effectively improving the grid connection stability and absorption capacity of intermittent renewable energy.

[0003] Currently, power systems widely adopt a time synchronization system based on GNSS (General Notification of the Secondary Power Grid) as the source and IRIG-B code (Inter-Range Instrumentation Group-B, US IRIG Standard 200-04) as the carrier. The master station acquires high-precision pulse-per-second (PPS) signals via satellite receivers, encodes them into highly interference-resistant IRIG-B code signals, and distributes them to substations and terminal equipment via fiber optic cables and network cables. This mature solution forms the backbone of the entire network's time reference. Significant progress has been made in fiber optic time transfer technology in recent years. Fiber optics, with its low attenuation coefficient, resistance to external environmental interference, and ability to achieve stable long-distance transmission, demonstrates increasingly prominent technological advantages and practical value by utilizing existing abundant communication fiber optic resources for high-precision time and frequency transfer and comparison. Related technical solutions include: frequency distribution technology based on Synchronous Ethernet (SyncE), time synchronization technology based on the IEEE 1588 Precise Time Protocol (PTP), and the White Rabbit protocol proposed by CERN in 2009. As a cutting-edge high-precision time synchronization solution, fiber optic time transfer technology can achieve synchronization accuracy at the picosecond level or even higher, providing a promising technical route to meet the stringent time synchronization requirements of future new power systems and other scenarios.

[0004] In existing technologies, such as the Chinese invention application CN114584136A, "A High-Stable Crystal Oscillator Discipline and Holding System and Method Based on GNSS," a GNSS receiver board and an OCXO crystal oscillator are included. The second pulse signal outputs of both are connected to a phase difference measurement module, the output of which is connected to a processor. The processor's output is then connected to the OCXO crystal oscillator via a D / A conversion module and a signal conditioning circuit. The OCXO's second pulse is output after frequency division by an FPGA. A temperature sensor is also connected to the OCXO for timekeeping compensation. This solution utilizes the complementary advantages of the long-term stability of GNSS and the short-term stability of the OCXO to achieve automatic frequency holding of the crystal oscillator. However, the purpose of this patent is to provide a high-precision frequency source itself; it does not address how to make this frequency source compatible with existing IRIG-B code terminal equipment in the power grid, nor does it involve technical solutions for using the purified clock for IRIG-B code recoding and subsequent fiber optic transmission. For example, Chinese invention application CN115268570A, entitled "An IRIG-B Code Time Synchronization System," discloses a scheme to achieve high-precision time synchronization at the millisecond / microsecond level based on traditional IRIG-B code (second-level timekeeping). This scheme includes modules such as an IRIG-B code decoder, a date and time generator, an error generator, an adaptive tracker, and a millisecond / microsecond generator, generating fractional-dimensional local time through time increment accumulation. The accuracy improvement is achieved by interpolating and tracking the time information after decoding the IRIG-B code. Essentially, it refines the time information at the decoding end rather than eliminating the inherent jitter of the B-code signal from the signal source (encoded reference clock). Therefore, this scheme cannot solve the core problem of "excessive jitter in the original B-code signal → instability in the fiber optic transmission link."

[0005] Therefore, the aforementioned prior art has the following shortcomings: (1) It cannot be directly connected to the B-code interface equipment (relay protection devices, measurement and control units, PMU, etc.) that are widely deployed in the power grid. It is necessary to replace or modify all existing terminal equipment, which has poor engineering feasibility and economy.

[0006] (2) The inherent jitter of the B code was not eliminated from the signal source (encoding reference clock), and the fundamental problem of "excessive jitter of the original B code signal → inability to lock the fiber optic transmission link stably" could not be solved.

[0007] (3) In the existing substation environment, upgrading all the massive IRIG-B code terminal devices to support the WhiteRabbit protocol is extremely costly and has a long implementation period, making it difficult to achieve in engineering in the short term.

[0008] (4) In the traditional IRIG-B code time synchronization scheme, the encoding and decoding process directly uses the 1PPS pulse signal output by the GNSS receiver as the time reference. This signal itself is superimposed with the time jitter introduced by factors such as multipath effect, atmospheric delay fluctuation and internal thermal noise of the receiver during the satellite signal reception process. Summary of the Invention

[0009] The technical problem to be solved by this invention is how to improve the time synchronization accuracy of the power system from the order of nanoseconds to the order of sub-nanoseconds without making any modifications to the existing IRIG-B code equipment in the power grid.

[0010] The present invention solves the above-mentioned technical problems through the following technical means: This invention provides a clock-sanitized IRIG-B code fiber optic time transfer method, comprising the following steps: S1. Obtain the raw GNSS 1PPS second pulse signal and absolute time information through a GNSS satellite receiver; S2. A 10MHz reference frequency signal is generated locally by a temperature-controlled crystal oscillator (OCXO), and a local 1PPS pulse signal that is phase-locked with the OCXO is generated by a digital frequency divider circuit. S3. Construct a negative feedback phase-locked loop based on the time difference between GNSS and local 1PPS second pulse signals to obtain the purified 10MHz reference frequency signal and the purified 1PPS second pulse signal. S4. Using the purified 10MHz reference frequency signal as the master clock of the IRIG-B code encoder, and combining it with absolute time information, the purified IRIG-B code signal is re-encoded. S5. Modulate the purified 1PPS second pulse signal and the purified IRIG-B code signal onto the purified 10MHz reference frequency signal to generate an encoded electrical signal; after electro-optical conversion, the encoded electrical signal is sent to the remote end through an optical fiber link. S6. The remote end regenerates and outputs an IRIG-B code signal synchronized with the source end from the received signal and provides it to the power equipment.

[0011] Further, the negative feedback phase-locked loop mentioned in step S3 includes: A time-to-digital converter (TDC) is used to measure the rising edge time interval between the local 1PPS pulse signal and the GNSS 1PPS pulse signal. The obtained time difference is sent to a digital PI controller. The PI controller outputs a frequency control signal, which is converted into an analog voltage by a DAC. The oscillation frequency and phase of the OCXO are adjusted until the time difference between the local 1PPS pulse signal and the GNSS 1PPS pulse signal converges.

[0012] Furthermore, the accuracy of the time difference convergence is 1×10⁻⁶.- ¹² seconds.

[0013] This invention also provides an IRIG-B code fiber optic time transfer system based on clock purification, comprising a GNSS receiver, a clock purification module, a B code encoder, a fiber optic time transmission module, a fiber optic link, a fiber optic time receiving module, and a B code regeneration module cascaded in sequence; the GNSS receiver outputs a 1PPS second pulse signal to the clock purification module and outputs TOD time code information to the B code encoder; the clock purification module generates a purified 10MHz reference frequency signal and a purified 1PPS second pulse signal, which are output to the B code encoder and the fiber optic time transmission module, respectively.

[0014] Furthermore, the clock purification module is a negative feedback phase-locked loop structure consisting of a time-to-digital converter (TDC), a PI controller, a temperature-controlled crystal oscillator (OCXO), and a digital frequency divider.

[0015] Furthermore, the PI controller uses the time difference value measured by the time-to-digital converter (TDC). The frequency control word is output after digital PI algorithm calculation, converted into an analog voltage by digital-to-analog converter (DAC), and applied to the voltage-controlled input of the temperature-controlled crystal oscillator (OCXO) to adjust its oscillation frequency; the proportional term is based on the current time difference. Provides transient phase correction Used for rapid response to instantaneous phase deviation; the integral term accumulates historical time difference. Provide frequency correction amount It is used to eliminate steady-state frequency deviation and make the long-term average frequency of the OCXO accurately locked to the GNSS time reference; the loop update cycle of the PI controller is synchronized with the arrival cycle of the GNSS 1PPS signal, and the loop bandwidth is designed to be on the order of 0.01Hz.

[0016] Preferably, the digital converter TDC uses a TDC-AS6500 multi-channel time measurement chip with a single measurement resolution better than 10 picoseconds, and performs precise time difference measurement on the rising edge time interval between the local 1PPS second pulse signal and the GNSS 1PPS second pulse signal.

[0017] Furthermore, the B-code encoder encodes the purified 10MHz reference frequency signal, the purified 1PPS second pulse signal, and absolute time information to generate a standard format IRIG-B code signal; wherein, the purified 10MHz reference frequency signal serves as the master clock, and after frequency division, it generates the 1kHz sine wave carrier signal required for B-code modulation, while also providing the symbol timing clock.

[0018] Furthermore, the fiber optic time transmission module modulates the purified 1PPS second pulse signal and the IRIG-B code signal onto the purified 10MHz reference frequency signal to form an coded electrical signal; this coded electrical signal is then converted from electro-optical signal and transmitted to the remote end via a fiber optic link; the fiber optic link carries complete time and frequency information, including the purified high-precision 10MHz reference frequency signal, the purified 1PPS second pulse signal, and the B code time information.

[0019] Furthermore, the fiber optic time receiving module recovers the purified 10MHz reference frequency signal, the purified 1PPS second pulse signal, and the B code time information from the received signal; the B code regeneration module uses the recovered 10MHz quasi-frequency signal as the reference clock, the recovered 1PPS second pulse signal as the frame synchronization reference, and the recovered B code time code information as the data source to regenerate the IRIG-B code signal synchronized with the source end reference signal.

[0020] The advantages of this invention are: (1) By inserting the intermediate step of “B code purification”, this invention improves the available time synchronization accuracy from the nanosecond level of the traditional scheme to the sub-nanosecond (hundred picosecond) level without modifying the existing IRIG-B code terminal equipment (relay protection device, measurement and control unit, PMU, etc.) of the power grid. The accuracy is improved by about two orders of magnitude, which solves the contradiction between “existing compatibility” and “accuracy improvement” in the high-precision time synchronization upgrade of the power grid. It has strong engineering applicability and economy.

[0021] (2) This invention reduces the residual jitter of the reference signal to the picosecond level through OCXO phase-locked loop purification, thus fully realizing the picosecond-level accuracy potential of the optical fiber transmission system. The OCXO, TDC chip, ARM processor, FPGA, and optical fiber transceiver module used are all mature commercial devices, requiring no customized development. The system has high integration, controllable cost, and is easy to deploy and implement in existing substation environments.

[0022] (4) When GPS / BeiDou signals fail for a short time (tens of minutes to several hours) due to interference or obstruction, the OCXO can maintain the system output accuracy within an acceptable range by virtue of its excellent short-term frequency stability and low aging rate, thus achieving high-precision time retention function, providing different levels of time reference protection for key power grid equipment, and improving the resilience of the time synchronization system.

[0023] (5) This invention reduces the jitter of the symbol edge from several nanoseconds to tens of nanoseconds to hundreds of picoseconds through B code purification. It is not a simple indicator optimization, but rather a breakthrough in the technical barrier between the existing industrial standard B code interface and the picosecond-level optical fiber transmission capability. The purified B code signal not only fully retains the interface compatibility with existing equipment, but also has the signal quality to drive high-precision optical fiber transmission links. It is a key enabling technology for the smooth upgrade of the power system time synchronization backbone network. Attached Figure Description

[0024] Figure 1 This is a block diagram of an IRIG-B code fiber optic time transfer system based on clock cleanup, according to an embodiment of the present invention. Figure 2 This is a schematic diagram showing the difference in code element edge jitter before and after code B purification in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 The IRIG-B code time synchronization scheme widely deployed in current power grid systems is limited by its encoding method and transmission link, resulting in synchronization accuracy typically on the order of nanoseconds. This makes it difficult to meet the synchronization requirements of future new energy power equipment, which demand nanosecond-level or even higher precision. Fiber optic time transfer systems can achieve picosecond-level time synchronization. However, if the existing IRIG-B code signal is directly used as the reference clock source for the fiber optic time transfer system, its inherent time jitter will prevent the fiber optic transmission system from achieving stable locking, thus failing to realize the picosecond-level ultra-high precision potential of fiber optic technology itself. This contradiction constitutes the core bottleneck for upgrading power system time synchronization technology. The root of this bottleneck lies in a technical obstacle that has not been fully recognized by those skilled in the art: the inherent time jitter of the IRIG-B code signal (on the order of several nanoseconds to tens of nanoseconds) causes the digital phase-locked loop (PLL) of the fiber optic transmission link to fail to achieve stable locking due to excessive phase noise in the reference signal, specifically manifested as frequent loss of lock or periodic slippage. Those skilled in the art typically focus on "how to improve the anti-interference capability of B-code transmission links" or "how to replace B-code with higher-precision protocols (such as PTP)," failing to recognize that the jitter of the GNSS 1PPS signal itself constitutes the "first-level bottleneck" limiting the entire time synchronization link between the GNSS time source and the B-code encoder. This bottleneck is propagated and amplified downstream in the fiber optic transmission link. Furthermore, there is a default technical bias in the power system time synchronization field: that IRIG-B code, as a mature industry standard, has nanosecond-level synchronization accuracy that is "inherent" and "unimprovable"; to achieve picosecond-level accuracy, B-code must be abandoned in favor of new protocols such as PTP / White Rabbit. However, this would mean replacing a massive amount of existing equipment. In other words, those skilled in the art generally believe that "B-code format compatibility" and "picosecond-level accuracy" are irreconcilable contradictions, and only one can be chosen.

[0027] This embodiment provides a clock-cleaned IRIG-B code fiber optic time transfer method, constructing a clock-cleaning intermediate conversion stage between an existing IRIG-B code time source and a high-precision fiber optic time transfer system. This stage uses a high-stability local crystal oscillator and phase-locked loop (PLL) technology to reconstruct and suppress noise in the input time base signal. While accurately preserving its long-term time reference information, it filters out noise and jitter from the signal, ultimately outputting a high-purity clock signal with extremely low phase noise and time jitter on the order of ten picoseconds. The IRIG-B code signal regenerated from this cleaned clock completely retains the IRIG-B code format, thus being directly compatible with existing terminal equipment, while its accuracy meets the requirements for driving the fiber optic time transfer system. The specific implementation process of the method includes the following steps: S1. Obtain the raw GNSS 1PPS second pulse signal and absolute time information through a GNSS satellite receiver; that is, TOD time code information, including year, month, day, hour, minute, second, etc.

[0028] S2. A 10MHz reference frequency signal is generated locally by a temperature-controlled crystal oscillator (OCXO), and a local 1PPS pulse signal that is phase-locked with the OCXO is generated by a digital frequency divider circuit. S3. Construct a negative feedback phase-locked loop based on the time difference between GNSS and local 1PPS second pulse signals to obtain a purified 10MHz reference frequency signal and a purified 1PPS second pulse signal; the negative feedback phase-locked loop includes: A time-to-digital converter (TDC) is used to measure the rising edge time interval between the local 1PPS second pulse signal and the GNSS 1PPS second pulse signal. The obtained time difference is sent to a digital PI controller. The PI controller outputs a frequency control signal, which is converted into an analog voltage by a DAC to adjust the oscillation frequency and phase of the OCXO until the time difference between the local and GNSS 1PPS second pulse signals converges. The convergence accuracy of the time difference is 1×10⁻⁶. - ¹² seconds.

[0029] S4. The purified 10MHz reference frequency signal is used as the master clock of the IRIG-B code encoder (the 1kHz carrier signal and symbol timing clock required for B code modulation are generated by frequency division). Combined with absolute time information, the purified IRIG-B code signal with symbol edge jitter reduced to the level of hundreds of picoseconds is re-encoded. S5. Modulate the purified 1PPS second pulse signal and the purified IRIG-B code signal onto the purified 10MHz reference frequency signal to generate an encoded electrical signal; after electro-optical conversion, the encoded electrical signal is sent to the remote end through an optical fiber link. S6. The remote end regenerates and outputs an IRIG-B code signal synchronized with the source end from the received signal, with a 1PPS signal deviation better than ±50ps (peak-to-peak value), and provides it to the power equipment.

[0030] Through simulation experiments, such as Figure 2 As shown, before purification, the edge jitter of the B code symbol is about 5~15ns (1σ). When the B code signal with this jitter level directly drives the optical fiber transmission link, the link cannot work normally because it cannot be stably locked. After purification, the edge jitter of the B code symbol is reduced to ≤100ps (peak-to-peak value), and the optical fiber transmission link can be stably locked and transmit normally, achieving a two-order-of-magnitude leap in accuracy.

[0031] Example 2 It should be further explained that, based on the same inventive concept, this embodiment provides an IRIG-B code fiber optic time transfer system based on clock cleanup. The system executes the method described in Embodiment 1 during operation, such as... Figure 1 As shown, the system includes a GNSS receiver, a clock purification module, a B-code encoder, an optical fiber time transmission module, an optical fiber link, an optical fiber time receiving module, and a B-code regeneration module, all cascaded in sequence. The GNSS receiver outputs a 1PPS pulse signal to the clock purification module and outputs TOD time code information to the B-code encoder. The clock purification module generates a purified 10MHz reference frequency signal and a purified 1PPS pulse signal, which are output to the B-code encoder and the optical fiber time transmission module, respectively.

[0032] The clock purification module is a negative feedback phase-locked loop structure consisting of a time-to-digital converter (TDC), a PI controller, a temperature-controlled crystal oscillator (OCXO), and a digital frequency divider.

[0033] The PI controller uses the time difference value measured by the time-to-digital converter (TDC). The frequency control word is output after digital PI algorithm calculation, converted into an analog voltage by digital-to-analog converter (DAC), and applied to the voltage-controlled input of the temperature-controlled crystal oscillator (OCXO) to adjust its oscillation frequency; the proportional term is based on the current time difference. Provides transient phase correction Used for rapid response to instantaneous phase deviation; the integral term accumulates historical time difference. Provide frequency correction amount This is used to eliminate steady-state frequency offset, ensuring the long-term average frequency of the OCXO is precisely locked to the GNSS time reference. The loop update cycle of the PI controller is synchronized with the arrival cycle of the GNSS 1PPS signal (typically once per second), and the loop bandwidth is designed to be on the order of 0.01Hz. This achieves an optimal balance between GNSS noise suppression and OCXO frequency drift tracking, ensuring that its output 10MHz clock maintains a time difference with the GPS time reference better than ±50ps (peak-to-peak) and a long-term frequency accuracy better than 1×10⁻⁶. - ¹² phase synchronization.

[0034] The digital converter TDC uses the TDC-AS6500 multi-channel time measurement chip, with a single measurement resolution better than 10 picoseconds, to perform precise time difference measurement on the rising edge time interval between the local 1PPS second pulse signal and the GNSS 1PPS second pulse signal.

[0035] The B-code encoder encodes a standard-format IRIG-B code signal based on a purified 10MHz reference frequency signal, a purified 1PPS second pulse signal, and absolute time information. The purified 10MHz reference frequency signal serves as the master clock, which, after frequency division, generates a 1kHz sinusoidal carrier signal required for B-code modulation (10MHz ÷ 200 = 50kHz, then divided by 50 to obtain 1kHz), simultaneously providing a symbol timing clock. Since this 10MHz clock has undergone the aforementioned phase-locked loop purification process and has extremely low phase noise, the symbol edge jitter of the generated B-code signal is significantly reduced, thus outputting a "purified" IRIG-B code signal. This is the key signal link for achieving B-code purification in this embodiment: generating purified B-code using a purified clock.

[0036] The fiber optic time transmission module modulates the purified 1PPS second pulse signal and the IRIG-B code signal onto the purified 10MHz reference frequency signal to form an coded electrical signal. This coded electrical signal is then converted from electro-optical signal and transmitted to the remote end via a fiber optic link. The fiber optic link carries complete time and frequency information, including the purified high-precision 10MHz reference frequency signal, the purified 1PPS second pulse signal, and the B code time information.

[0037] The fiber optic time receiving module recovers the purified 10MHz reference frequency signal, the purified 1PPS second pulse signal, and B-code time information from the received signal. The B-code regeneration module uses the recovered 10MHz quasi-frequency signal as the reference clock, the recovered 1PPS second pulse signal as the frame synchronization reference, and the recovered B-code time code information as the data source to regenerate an IRIG-B-code signal synchronized with the source reference signal. This regenerated signal can be directly connected to power equipment (such as protection devices and measurement and control units) that require an IRIG-B-code interface. Because it has eliminated transmission jitter, the time synchronization accuracy obtained by the equipment is much higher than that of B-code transmitted in the traditional way. At the same time, the system can also provide a low-jitter 10MHz frequency signal and PPS second pulse for synchronizing other precision instruments. The entire process can achieve a significant improvement in network-wide time synchronization accuracy from nanosecond to picosecond levels without modifying or replacing the existing power equipment's B-code interface. This system innovatively inserts a "B-code regeneration and purification" step based on a local high-stability frequency source between the standard time source and the high-precision fiber optic transmission medium, successfully solving the compatibility problem between the high-precision fiber optic transmission system and the low-precision industrial standard interface, and providing a practical and feasible technical path for building a new generation of ultra-high precision synchronization network for power systems.

[0038] In summary, the system provided in this embodiment aims to improve the usable accuracy of the time reference by several orders of magnitude without requiring any modifications to existing IRIG-B code equipment in the power grid, thereby enabling stable and reliable driving of fiber optic time transfer systems. This system successfully integrates the existing reliable time architecture of the power system with the ultra-high precision capabilities of fiber optic transmission, laying a key technological foundation for constructing a nanosecond to picosecond-level globally unified time synchronization network for new power systems. It should be noted that this system introduces a high-stability oven-controlled crystal oscillator (OCXO) as a local frequency reference source in the signal link. The short-term frequency stability (Allan variance) of this OCXO is better than 1×10⁻⁶. - ¹² @1s, compared to the 1PPS signal directly output by a GPS receiver, its short-term stability is 2-3 orders of magnitude higher. The extremely low phase noise characteristic provided by the OCXO forms the physical basis of the "cleaning" function. The technical principle of this system is as follows: GPS provides long-term time accuracy (anchored to the UTC time reference), while the OCXO provides excellent short-term frequency stability (low phase noise). The two complement each other through a digital phase-locked loop—the 1PPS signal output by the GPS receiver performs long-term frequency calibration on the OCXO, while the OCXO, with its low-pass filtering characteristics, filters out short-term jitter in the GPS signal, ultimately outputting a high-purity clock signal that combines long-term accuracy and short-term stability.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for IRIG-B code optical fiber time transfer based on clock purification, characterized in that, Includes the following steps: S1. Obtain the raw GNSS 1PPS second pulse signal and absolute time information through a GNSS satellite receiver; S2. A 10MHz reference frequency signal is generated locally by a temperature-controlled crystal oscillator (OCXO), and a local 1PPS pulse signal that is phase-locked with the OCXO is generated by a digital frequency divider circuit. S3. Construct a negative feedback phase-locked loop based on the time difference between GNSS and local 1PPS second pulse signals to obtain the purified 10MHz reference frequency signal and the purified 1PPS second pulse signal. S4. Using the purified 10MHz reference frequency signal as the master clock of the IRIG-B code encoder, and combining it with absolute time information, the purified IRIG-B code signal is re-encoded. S5. Modulate the purified 1PPS second pulse signal and the purified IRIG-B code signal onto the purified 10MHz reference frequency signal to generate an encoded electrical signal; after electro-optical conversion, the encoded electrical signal is sent to the remote end through an optical fiber link. S6. The remote end regenerates and outputs an IRIG-B code signal synchronized with the source end from the received signal and provides it to the power equipment.

2. The IRIG-B code optical time transfer method based on clock purification according to claim 1, characterized in that, The negative feedback phase-locked loop mentioned in step S3 includes: A time-to-digital converter (TDC) is used to measure the rising edge time interval between the local 1PPS pulse signal and the GNSS 1PPS pulse signal. The obtained time difference is sent to a digital PI controller. The PI controller outputs a frequency control signal, which is converted into an analog voltage by a DAC. The oscillation frequency and phase of the OCXO are adjusted until the time difference between the local 1PPS pulse signal and the GNSS 1PPS pulse signal converges.

3. The IRIG-B code optical time transfer method based on clock purification according to claim 2, characterized in that, The precision of the time difference convergence is 1 x 10 - 12 seconds.

4. An IRIG-B code fiber optic time transfer system based on the method of any of claims 1-3, wherein, The system includes a GNSS receiver, a clock purification module, a B-code encoder, an optical fiber time transmission module, an optical fiber link, an optical fiber time receiving module, and a B-code regeneration module, all cascaded in sequence. The GNSS receiver outputs a 1PPS pulse signal to the clock purification module and outputs TOD time code information to the B-code encoder. The clock purification module generates a purified 10MHz reference frequency signal and a purified 1PPS pulse signal, which are output to the B-code encoder and the optical fiber time transmission module, respectively.

5. The IRIG-B code optical fiber time transfer system of claim 4, wherein, The clock purification module is a negative feedback phase-locked loop structure consisting of a time-to-digital converter (TDC), a PI controller, a temperature-controlled crystal oscillator (OCXO), and a digital frequency divider.

6. The IRIG-B code fiber optic time transfer system according to claim 5, characterized in that, The PI controller uses the time difference value measured by the time-to-digital converter (TDC). The frequency control word is output after digital PI algorithm calculation, converted into an analog voltage by digital-to-analog converter (DAC), and applied to the voltage-controlled input of the temperature-controlled crystal oscillator (OCXO) to adjust its oscillation frequency; the proportional term is based on the current time difference. Provides transient phase correction Used for rapid response to instantaneous phase deviation; the integral term accumulates historical time difference. Provide frequency correction amount It is used to eliminate steady-state frequency deviation and make the long-term average frequency of the OCXO accurately locked to the GNSS time reference; the loop update cycle of the PI controller is synchronized with the arrival cycle of the GNSS 1PPS signal, and the loop bandwidth is designed to be on the order of 0.01Hz.

7. The IRIG-B code fiber optic time transfer system according to claim 5, characterized in that, The digital converter TDC uses the TDC-AS6500 multi-channel time measurement chip, with a single measurement resolution better than 10 picoseconds, to perform precise time difference measurement on the rising edge time interval between the local 1PPS second pulse signal and the GNSS 1PPS second pulse signal.

8. The IRIG-B code fiber optic time transfer system according to claim 4, characterized in that, The B-code encoder encodes a standard IRIG-B code signal based on a purified 10MHz reference frequency signal, a purified 1PPS second pulse signal, and absolute time information. The purified 10MHz reference frequency signal serves as the master clock, which is divided to generate a 1kHz sine wave carrier signal required for B-code modulation, and also provides a symbol timing clock.

9. The IRIG-B code fiber optic time transfer system according to claim 4, characterized in that, The fiber optic time transmission module modulates the purified 1PPS second pulse signal and the IRIG-B code signal onto the purified 10MHz reference frequency signal to form an coded electrical signal. This coded electrical signal is then converted from electro-optical signal and transmitted to the remote end via a fiber optic link. The fiber optic link carries complete time and frequency information, including the purified high-precision 10MHz reference frequency signal, the purified 1PPS second pulse signal, and the B code time information.

10. The IRIG-B code fiber optic time transfer system according to claim 4, characterized in that, The fiber optic time receiving module recovers the purified 10MHz reference frequency signal, the purified 1PPS second pulse signal, and the B code time information from the received signal; the B code regeneration module uses the recovered 10MHz quasi-frequency signal as the reference clock, the recovered 1PPS second pulse signal as the frame synchronization reference, and the recovered B code time code information as the data source to regenerate the IRIG-B code signal synchronized with the source end reference signal.

Images