A method and system for improving transient performance of an optical fiber current transformer

Abstract

The present application relates to the technical field of power system, especially to a kind of optical fiber current transformer transient performance promotion method and system, method includes: the phase response model of the structure of reflection type optical fiber current transformer is built and parameter is initialized;Homologous clock is built and linear frequency modulation chirp reference sequence is generated, and linear frequency modulation chirp reference sequence is loaded into phase modulator simultaneously, while homologous clock is sent into ADC sampling link;The pre-processing sequence is obtained by pre-processing to the sampled photoelectric signal, and the pre-processing sequence is parallel into steady channel and transient channel to execute steady-state processing and transient processing;Photoelectric signal state is discriminated based on the steady state and transient state after output, and according to state discrimination result, double-channel fusion and delay compensation output are executed. It can improve the transient response performance of optical fiber current transformer from the level of signal processing without changing the basic structure of optical fiber sensor head, and meet the needs of steady-state measurement accuracy and transient high-speed measurement.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method and system for improving the transient performance of fiber optic current transformers. Background Technology

[0002] Reflective Sagnac fiber optic current transformers operate based on the Faraday magneto-optical effect. Existing reflective Sagnac fiber optic current transformers typically employ a fixed-frequency phase modulation and low-pass integrator demodulation scheme. The phase modulator applies a phase bias to the optical path at a fixed frequency. The interference signal, after photoelectric detection, amplification, and filtering, is demodulated by a low-pass filter and integrator to extract the DC or power frequency component proportional to the measured current. This scheme exhibits high measurement accuracy and stability in power frequency steady-state metering scenarios.

[0003] However, in scenarios such as flexible DC transmission faults, traveling wave protection, lightning strikes, transient switching operations, and fault recording, the fault current exhibits characteristics of steep edges, wide spectral components, and short duration. Existing single demodulation links suffer from the following technical problems: First, due to the long time constants of the low-pass filter and integrator, integrating and averaging the signal during the transient edge smooths the edge information, resulting in the loss of details in the original abrupt waveform. Second, the amplitude-frequency characteristics of the low-pass filter cause different frequency components to have different delays, resulting in a large group delay. For high-frequency transient components, the actual output has a significant delay relative to the input, affecting the speed of protection action. Simultaneously, due to the large overall time delay of the demodulation link, there is a time lag in the detection and output of the fault signal, which may lead to delayed protection action, affecting the speed requirements of power system protection. Furthermore, fixed-frequency modulation only has high sensitivity near the modulation frequency, with limited response capability to high-frequency transient components, and broadband spectral information cannot be effectively observed and preserved.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for improving the transient performance of fiber optic current transformers, which can improve the transient response performance of fiber optic current transformers from the signal processing level without changing the basic structure of the fiber optic sensing head, while taking into account both steady-state measurement accuracy and transient high-speed measurement requirements.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for improving the transient performance of an optical fiber current transformer, comprising the following steps: Construct a Faraday phase response model of a reflective Sagnac fiber optic current transformer structure and initialize its parameters; A co-source clock is constructed using an FPGA or high-speed DDS to generate a linear frequency modulation (LFM) chirped reference sequence, and the LFM chirped reference sequence is synchronously loaded into the phase modulator. At the same time, the co-source clock is sent into the ADC sampling link. The sampled photoelectric signal is preprocessed to obtain a preprocessed sequence, and the preprocessed sequence is entered in parallel into the steady-state channel and the transient channel to perform steady-state processing and transient processing. The state of the photoelectric signal is determined based on the steady-state and transient states after output, and dual-channel fusion and delay compensation are performed according to the state determination results.

[0007] Furthermore, the Faraday phase response model represents the change in polarization state or phase difference caused by the measured current in the fiber optic current transformer through the Faraday magneto-optical effect. For a reflective optical path, the equivalent phase change can be expressed as: ; in, The Faraday phase caused by the measured current. It is the Verdet constant. This represents the equivalent number of turns of the sensing fiber. The measured current, It is the equivalent current-phase scaling factor.

[0008] Furthermore, the step of constructing a co-source clock using an FPGA or high-speed DDS and generating a linear frequency modulated chirped reference sequence, synchronously loading the linear frequency modulated chirped reference sequence onto the phase modulator, and simultaneously sending the co-source clock into the ADC sampling link includes the following steps: The DDS, DAC, and ADC are simultaneously driven by the FPGA's internal PLL or an external low-jitter clock, so that the modulation reference sequence and the sampling sequence have a definite phase relationship and establish a common clock source. In the Each sampling point generates a DDS frequency control word. The modulation phase is obtained through a phase accumulator. ; Will Alternatively, the pre-distorted modulated waveform is output by the DAC and drives the phase modulator, resulting in an output bandwidth chirped modulated waveform. The FPGA generates a marker at the beginning of each chirp cycle and simultaneously stores an in-phase reference. and orthogonal reference ; The linear frequency modulated chirped reference sequence is output by continuously measuring periodically chirped frames and setting short protection zones between adjacent frames or by using phase continuous splicing.

[0009] Furthermore, the phase modulator generates a time-varying instantaneous modulation frequency at each sampling moment as follows: ; ; The phase modulation signal is replaced by the instantaneous frequency integral, and the modulation signal sweeps through one period. to The output bandwidth chirped modulation waveform for the specified frequency band is as follows: ; in, To modulate the phase amplitude, For the initial phase, The starting frequency of the chirp. For the termination frequency, For one chirping cycle, This represents the frequency modulation slope.

[0010] Furthermore, the preprocessing of the sampled photoelectric signal includes DC removal, amplitude normalization, outlier limiting, temperature drift compensation, chirped synchronous demodulation, and phase reconstruction.

[0011] Furthermore, the chirped synchronization demodulation and phase reconstruction processing includes the following steps: Short-window orthogonal correlation processing is performed on the normalized sequence and the chirped reference to obtain the instantaneous phase estimate; Subtract the known modulation phase and bias phase to obtain the phase estimate corresponding to the measured current; The phase estimate is converted into the raw current. .

[0012] Furthermore, the process of entering the preprocessed sequence into the steady-state channel for steady-state processing includes: The original current After low-pass filtering and integral averaging, the steady-state current output is obtained. : ; in, These are the coefficients of a low-pass filter or an integral-average filter. The steady-state channel window length, The larger the value, the lower the steady-state noise, but the greater the group delay. This indicates that the original current sampling signal is in The value at that location.

[0013] Furthermore, the process of the preprocessed sequence entering the transient channel for transient processing includes: The original current High-frequency components are obtained after short-window high-pass filtering. And calculate the first intermediate component of the high-frequency component respectively. and second-order difference components ; Calculate the short-time high-frequency energy based on the high-frequency components and the transient short window length. ; The phase change rate is calculated by differentiating the phase sequence using a transient channel. ; Based on the phase change rate Short-term high-frequency energy , a difference component or second-order difference components The comparison result with the entry threshold determines whether the photoelectric signal has high-frequency characteristics; If so, enter the transient candidate state.

[0014] Furthermore, the determination of the photoelectric signal state based on the steady-state and transient states after output includes the following steps: The comprehensive transient criterion and transient determination conditions are defined as follows: ; ; in, , , These are the differential threshold, the high-frequency energy threshold, and the phase change rate threshold, respectively. , , These are the weighting coefficients. This represents the number of sampling points that continuously meet the threshold condition. Minimum number of duration points; Based on the photoelectric signal processing characteristics of entering the transient candidate state, it is determined in real time whether it is in a transient state; like Below the exit threshold and continuing If a certain number of sampling points are reached, the transient state is considered to have ended, and the output returns to steady state.

[0015] Furthermore, the step of performing dual-channel fusion and delay compensation output based on the state discrimination result includes the following steps: Adjust the steady-state weights based on the state discrimination results. and transient weights Perform adaptive fusion to obtain the fused output. ; The steady-state and transient channels are time-delayed and aligned. For the two-way propagation delay of reflective Sagnac optical path fiber Perform timestamp compensation and output current waveform, transient flag, fault edge time and high-frequency energy index.

[0016] Furthermore, the steady-state weights and transient weights The following conditions must be met: ; The fusion output The expression is: ; in, For transient channel output, and These are the equivalent delays for the steady-state and transient channels, respectively. , This indicates the steady-state channel output current. This indicates the transient channel output current. It represents a discrete time series.

[0017] The present invention also provides a system for improving the transient performance of an optical fiber current transformer, comprising: Optical front end, including broadband light source, coupler, polarizer, broadband phase modulator, fiber delay line, sensing fiber ring, mirror and photodetector; The electronic signal processing module includes a transimpedance amplifier, an anti-aliasing filter, a high-speed ADC, a DDS chirped modulation generator, a steady-state demodulation channel, a transient detection channel, a state discrimination module, a fusion output module, and an FPGA processing unit. Specifically, a common clock is constructed and a linear frequency modulation (LFM) chirped reference sequence is generated through the impedance amplifier, anti-aliasing filter, high-speed ADC, and DDS chirped modulation generator. The LFM chirped reference sequence is synchronously loaded into the phase modulator, and the common clock is sent into the ADC sampling link. The sampled photoelectric signal is preprocessed through the steady-state demodulation channel and the transient detection channel to obtain a preprocessing sequence, and steady-state processing and transient processing are performed in parallel. The state discrimination module determines the state of the photoelectric signal based on the steady-state and transient states after output. The fusion output module and the FPGA processing unit perform dual-channel fusion and delay compensation output according to the state discrimination results.

[0018] The beneficial effects of this invention are as follows: This invention improves the observability of phase disturbances for high-frequency components by constructing a modulation reference and a broadband demodulation basis function covering multiple frequency points through broadband chirped modulation; by distributing the same optoelectronic signal in parallel to the steady-state high-precision channel and the transient high-speed channel through dual-channel detection, and by adaptively fusing and delay compensating according to the signal state in the FPGA, the system can improve the transient response performance of the fiber optic current transformer from the signal processing level, taking into account steady-state measurement accuracy, transient response speed and fault time-stamp accuracy. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the method for improving the transient performance of an optical fiber current transformer in an embodiment of the present invention. Figure 2 This is a schematic diagram of the overall signal link for broadband chirped modulation and dual-channel detection in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the digital generation and synchronous sampling process of the broadband chirped modulated signal in an embodiment of the present invention; Figure 4 This is a schematic diagram of the steady-state / transient separation and fusion process based on signal processing in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] like Figures 1 to 4 The method for improving the transient performance of fiber optic current transformers, as shown, includes: Construct a Faraday phase response model of a reflective Sagnac fiber optic current transformer structure and initialize its parameters; A co-source clock is constructed using an FPGA or high-speed DDS to generate a linear frequency modulation (LFM) chirped reference sequence, which is then synchronously loaded onto the phase modulator. Simultaneously, the co-source clock is fed into the ADC sampling link. The sampled photoelectric signal is preprocessed to obtain a preprocessed sequence, and the preprocessed sequence is then fed into the steady-state channel and the transient channel in parallel to perform steady-state processing and transient processing. The state of the photoelectric signal is determined based on the steady-state and transient states after output, and dual-channel fusion and delay compensation are performed based on the state determination results.

[0025] This invention improves the observability of phase disturbances for high-frequency components by constructing a modulation reference and a broadband demodulation basis function covering multiple frequency points through broadband chirped modulation. By using dual-channel detection to distribute the same photoelectric signal in parallel to the steady-state high-precision channel and the transient high-speed channel, and by adaptively fusing and delay compensating for the signal state in the FPGA, the system can improve the transient response performance of the fiber optic current transformer from the signal processing level, taking into account steady-state measurement accuracy, transient response speed, and fault time-stamp accuracy.

[0026] Specifically, the system adopts a reflective Sagnac fiber optic current transformer structure. The optical front end includes a broadband light source, coupler, polarizer, broadband phase modulator, fiber delay line, sensing fiber ring, mirror, and photodetector. The electronic and signal processing part includes a transimpedance amplifier, anti-aliasing filter, high-speed ADC, DDS chirped modulator generator, steady-state demodulation channel, transient detection channel, state discrimination module, fusion output module, and FPGA processing unit.

[0027] like Figure 2As shown, unlike single-frequency fixed modulation, this scheme generates a linear frequency-modulated chirped reference sequence using an FPGA or high-speed DDS, and synchronously loads this sequence into the phase modulator, while simultaneously sending a co-source clock to the ADC sampling link. The sampled photoelectric signal first undergoes DC removal, normalization, chirped synchronous demodulation, and phase reconstruction, and then enters the steady-state and transient channels in parallel. The steady-state channel focuses on low noise, long-time window integration, and accurate amplitude recovery; the transient channel focuses on short-time windows, high-pass differential, phase change rate, and high-frequency energy detection.

[0028] The initialization process includes: setting the chirp start and stop frequencies, determining the frequency modulation slope; setting the chirp period; and setting the sampling rate, which is set to ensure sufficient bandwidth for the transient detection channel. The maximum analysis frequency should be met at least. More than twice that of the standard, and anti-aliasing margin is reserved in the engineering; a steady-state window is set, the length of which affects the steady-state channel noise level and group delay; a transient window is set, the length of which affects the transient channel response speed and edge fidelity; differential threshold, high-frequency energy threshold, and phase change rate threshold are set for transient discrimination; weighting coefficients are set for comprehensive criterion calculation.

[0029] As a preferred embodiment, the chirp start frequency ranges from 3MHz to 10MHz, the stop frequency ranges from 30MHz to 50MHz, and the chirp period ranges from 10μs to 100μs; the selection of this frequency band takes into account the bandwidth matching with the phase modulator and the coverage of high-frequency transient components.

[0030] Based on the above embodiments, the Faraday phase response model represents the change in polarization state or phase difference caused by the measured current in the fiber optic current transformer through the Faraday magneto-optical effect. For a reflective optical path, the equivalent phase change can be expressed as: ; in, The Faraday phase caused by the measured current. It is the Verdet constant. This represents the equivalent number of turns of the sensing fiber. The measured current, It is the equivalent current-phase scaling factor.

[0031] In the broadband chirped modulation sequence generation and synchronization step, the FPGA or DDS generates a linear frequency-modulated chirped reference sequence. The instantaneous modulation frequency changes linearly with time, sweeping from the start frequency to the end frequency. The modulation phase is obtained by integrating the instantaneous frequency, ensuring phase continuity. Synchronous generation of in-phase and quadrature reference sequences, along with a chirped period start flag, is also performed. The chirped period covers a wide bandwidth from the set start frequency to the end frequency, allowing the modulation reference to carry information from multiple frequency points.

[0032] Based on the above embodiments, such as Figure 3 As shown, a co-source clock is constructed using an FPGA or high-speed DDS to generate a linear frequency modulated chirped reference sequence, and the linear frequency modulated chirped reference sequence is synchronously loaded onto the phase modulator. Simultaneously, the co-source clock is fed into the ADC sampling link. This includes the following steps: The DDS, DAC, and ADC are simultaneously driven by the FPGA's internal PLL or an external low-jitter clock, so that the modulation reference sequence and the sampling sequence have a definite phase relationship and establish a common clock source. In the Each sampling point generates a DDS frequency control word. The modulation phase is obtained through a phase accumulator. ; Will Alternatively, the pre-distorted modulated waveform is output by the DAC and drives the phase modulator, resulting in an output bandwidth chirped modulated waveform. The FPGA generates a marker at the beginning of each chirp cycle and simultaneously stores an in-phase reference. and orthogonal reference ; The linear frequency modulated chirped reference sequence is output by continuously measuring periodically chirped frames and setting short protection zones between adjacent frames or by using phase continuous splicing.

[0033] Based on the above embodiments, the phase modulator generates a time-varying instantaneous modulation frequency at each sampling moment as follows: ; ; The phase modulation signal is replaced by the instantaneous frequency integral, and the modulation signal sweeps through one period. to The output bandwidth chirped modulation waveform for the specified frequency band is as follows: ; in, To modulate the phase amplitude, For the initial phase, The starting frequency of the chirp. For the termination frequency, For one chirping cycle, This represents the frequency modulation slope.

[0034] Specifically, the FPGA simultaneously generates in-phase and quadrature reference sequences for subsequent digital quadrature demodulation. The FPGA generates a `chirp_start` flag at the start of each chirped cycle for chirped cycle synchronization and frame alignment. Periodically chirped frames are used for continuous measurements. Short protection zones or phase-continuous splicing can be used between adjacent frames to avoid false edges caused by frequency bounce. Predistortion processing compensates for the uneven amplitude-frequency response of the modulator, ensuring consistent effective modulation depth within the target frequency band. This allows the same optoelectronic output to carry phase response information at multiple modulation frequencies, facilitating the acquisition of transient high-frequency components through matched demodulation and short-time spectrum analysis.

[0035] Based on the above embodiments, the preprocessing of the sampled photoelectric signal includes DC removal, amplitude normalization, outlier limiting, temperature drift compensation, chirped synchronous demodulation, and phase reconstruction.

[0036] Specifically, the photodetector output is amplified by transimpedance and filtered by anti-aliasing before being sampled by a high-speed ADC. The ADC then samples the data to obtain a discrete sequence. ; in, Indicates the first The output signal value corresponding to each sampling point express time The sampled values ​​of each sampling point Indicates the sampling interval. This indicates the sampling rate.

[0037] The output of the photodetector after interference can be expressed as: ; in, It is the DC light intensity term. The correlation coefficient is the interferometric visibility coefficient. For the bias phase, To modulate link delay, To sense the optical path delay, This includes relative intensity noise from the light source, detector noise, and electronic noise. For phase modulation amount, This represents the change in Faraday phase difference.

[0038] Adaptive normalization is performed using the moving mean and moving standard deviation:

[0039] in, It is the moving average. For the sliding standard deviation, To prevent division by zero by small constants, normalization ensures a consistent amplitude range for signals under different light intensities. Abnormal limiting suppresses sampling anomalies and sudden noise interference. Temperature drift compensation corrects gain drift by tracking slow changes in the signal's statistical characteristics.

[0040] Based on the above embodiments, the chirped synchronization demodulation and phase reconstruction processing includes the following steps: The normalized sequence is subjected to short-window orthogonal correlation with the chirped reference to obtain instantaneous phase estimation. The correlation operation is performed within a finite-length window, which allows for matched integration between the preprocessed sequence and the chirped reference to extract the signal energy correlated with the co-frequency component of the chirped reference. Specifically, the window length L is much smaller than the chirped period Tc. The orthogonal correlation calculation formula is as follows: ; ; Where L is the demodulation window length; This is a window function used to suppress discontinuities at window edges. For in-phase correlation integral output, For sequence shifting, As the in-phase chirped reference sequence, The output is an orthogonal correlation integral. This is an orthogonal chirping reference sequence; Subtract the known modulation phase and bias phase to obtain the phase estimate corresponding to the measured current; Specifically, the instantaneous phase estimate is calculated from the orthogonal correlation components, and the expression is: ; in, The total phase estimate is continuously recovered. For phase untangling, The function generates a four-quadrant phase estimate, and the phase expansion is eliminated. The jump transitions to continuous phase; After subtracting the known modulation phase and bias phase, the Faraday phase estimate corresponding to the measured current is obtained: ; in, This is the Faraday phase estimate. To modulate the phase, For the first The sequence number of each sample. For the bias phase, This represents the number of sampling points corresponding to the modulation link delay. The relationship between the Faraday phase and the measured current is as follows: ,in It is the Verdet constant. This represents the equivalent number of turns of the sensing fiber. Convert the phase estimate into the raw current. The expression is: .

[0041] The phase reconstruction results are simultaneously fed into both the steady-state and transient detection channels. The steady-state channel uses a longer window length to reduce noise, while the transient channel uses a shorter window length to reduce group delay. Both channels share the same phase estimation sequence reconstruction basis but employ different filtering and discrimination strategies.

[0042] like Figure 4 As shown, based on the above embodiments, the steady-state detection channel is used to output high-precision measurement values ​​of power frequency, DC, and low-frequency slowly varying currents. This channel does not directly undertake the task of triggering the fastest fault; it is used for metering and steady-state display. Its processing flow can be summarized as follows: phase reconstruction, narrowband / low-pass filtering, integral averaging, temperature compensation, proportional coefficient calibration, and steady-state current output.

[0043] Specifically, the process of entering the preprocessed sequence into the steady-state channel for steady-state processing includes: The original current After low-pass filtering and integral averaging, the steady-state current output is obtained. : ; in, These are the coefficients of a low-pass filter or an integral-average filter. The steady-state channel window length, The larger the value, the lower the steady-state noise, but the greater the group delay. This indicates that the original current sampling signal is in The value is determined at this location. Therefore, this channel is used for metering and steady-state display, and does not directly undertake the task of triggering the fastest fault.

[0044] For AC power frequency signals, the fundamental amplitude and phase can be further extracted using synchronous detection or phase-locked loop algorithms. ; ; ; in, It is the power frequency angular frequency. This is the length of the synchronous detection window. For in-phase components, For orthogonal components, The fundamental amplitude, For synchronous demodulation reference signal, The fundamental frequency amplitude is obtained by synthesizing the in-phase component and the quadrature component as the reference signal for quadrature demodulation.

[0045] Building upon the above embodiments, the transient detection channel is used to quickly identify current surges, traveling wave edges, and inrush currents. Instead of long-time integration, this channel employs short-window high-pass, differential, and energy detection to achieve a low-latency response.

[0046] Specifically, the process of the preprocessed sequence entering the transient channel for transient processing includes: The original current High-frequency components are obtained after short-window high-pass filtering. The expression is: ; in, For a short-window low-pass filter, the high-frequency component is obtained by subtracting the low-frequency component from the original current. This is a high-pass filter. The time constant of a short-window low-pass filter is much smaller than that of a steady-state low-pass filter.

[0047] Calculate the first difference component of the high-frequency components separately. and second-order difference components ; ; ; in, Represents high-frequency components. This is a first-order difference used to represent the rate of change of current; This is a second-order difference, used to highlight edge inflection points. Difference operations have extremely low group delay, with a response speed close to the sampling interval. This is the original current signal at the current sampling time. This is the original current signal from the previous sampling time. This represents the original current signal at the first two sampling times.

[0048] Calculate the short-time high-frequency energy based on the high-frequency components and the transient short window length. ; The phase change rate is calculated by differentiating the phase sequence using a transient channel. ; Based on the phase change rate Short-term high-frequency energy , a difference component or second-order difference components The comparison result with the entry threshold determines whether the photoelectric signal has high-frequency characteristics, that is, the short-time high-frequency energy is calculated for transient feature detection: ; in, The transient short window length is typically much smaller than the steady-state channel window. , For the first in the sequence One; the short-time energy integration window is short, which can track the rapid changes of high-frequency components; Calculate the phase change rate as one of the transient criteria: ; in, For Faraday phase change rate, For the first The Faraday phase estimated at each sampling time point The sampling interval; If so, it indicates that the current signal has high-frequency abrupt change characteristics and enters a transient candidate state.

[0049] Based on the above embodiments, in order to avoid the situation where the distinction between steady state and transient state depends on manually set thresholds or fixed pattern discrimination, which is prone to misjudgment in noisy environments or under gradually changing signal conditions, this embodiment determines the current signal state in real time based on signal processing characteristics.

[0050] Specifically, determining the state of a photoelectric signal based on its steady-state and transient states after output includes the following steps: The comprehensive transient criterion and transient determination conditions are defined as follows: ; ; in, , , These are the differential threshold, the high-frequency energy threshold, and the phase change rate threshold, respectively. , , These are the weighting coefficients. This represents the number of sampling points that continuously meet the threshold condition. The minimum number of sustained points is used to eliminate interference from single-point glitches and avoid misjudgments triggered by noise spikes. Based on the photoelectric signal processing characteristics of entering the transient candidate state, it is determined in real time whether it is in a transient state; like Below the exit threshold and continuing If a certain number of sampling points are reached, the transient state is considered to have ended, and the output returns to steady state.

[0051] In addition, to avoid triggering jitter, a threshold is reached. and exit threshold Hysteresis design is adopted: ; The hysteresis interval width is adaptively adjusted based on the noise floor level. If If the value falls below the release threshold and continues for Nrel sampling points, the transient state is considered to have ended, and the system returns to steady state, which dominates the output.

[0052] Based on the above embodiments, and according to the state discrimination result, the dual-channel fusion and delay compensation output includes the following steps: Adjust the steady-state weights based on the state discrimination results. and transient weights Perform adaptive fusion to obtain the fused output. ; Perform time-delay alignment on the steady-state and transient channels; For the two-way propagation delay of reflective Sagnac optical path fiber Perform timestamp compensation and output current waveform, transient flag, fault edge time and high-frequency energy index.

[0053] Based on the above embodiments, a dual-channel fusion and delay compensation output method is provided, which automatically outputs the data by adaptively adjusting the ratio of steady-state weights and transient weights according to the state discrimination result. The steady-state weights... and transient weights The following conditions must be met: ; Fusion output The expression is: ; in, For transient channel output, and These are the equivalent delays for the steady-state and transient channels, respectively. .

[0054] Furthermore, since the two channels have different equivalent delays, delay alignment is required before fusion. The delay difference is... By adding a small-depth FIFO to the transient channel or by timestamping the output of the steady-state channel, the two channels can be aligned at the same physical moment.

[0055] For reflective Sagnac optical paths, the two-way propagation delay of the optical fiber should also be compensated:

[0056] in, The total propagation time delay corresponding to the two counter-propagating beams of the Sagnac interferometer completing one round of two-way transmission. The refractive index of the optical fiber. This is the equivalent fiber length. The speed of light in a vacuum. The FPGA output will push back the time of the fault edge occurrence. This improves the accuracy of the time stamp in the protection criteria.

[0057] The system output includes current waveform, transient flags, fault edge times, and high-frequency energy indicators. Timestamp correction uses linear prediction or direct backward calculation to compensate for the optical path propagation delay from the sensing point to the ADC sampling point.

[0058] The present invention also provides a system for improving the transient performance of an optical fiber current transformer, comprising: Optical front end, including broadband light source, coupler, polarizer, broadband phase modulator, fiber delay line, sensing fiber ring, mirror and photodetector; The electronic signal processing module includes a transimpedance amplifier, an anti-aliasing filter, a high-speed ADC, a DDS chirped modulation generator, a steady-state demodulation channel, a transient detection channel, a state discrimination module, a fusion output module, and an FPGA processing unit. Among them, a common clock is constructed by using a blocking amplifier, an anti-aliasing filter, a high-speed ADC, and a DDS chirped modulation generator to generate a linear frequency modulation chirped reference sequence. The linear frequency modulation chirped reference sequence is then synchronously loaded into the phase modulator, and the common clock is sent into the ADC sampling link. The sampled photoelectric signal is preprocessed through a steady-state demodulation channel and a transient detection channel to obtain a preprocessing sequence, and steady-state processing and transient processing are performed in parallel. The state discrimination module determines the state of the photoelectric signal based on the steady-state and transient states after output. The fusion output module and FPGA processing unit perform dual-channel fusion and delay compensation output based on the state discrimination results.

[0059] The complete signal processing flow of the above system is as follows: After system initialization, the FPGA starts the DDS to generate a wideband chirped modulation sequence. The DAC and ADC are driven synchronously by the same source clock. The interference signal output by the photodetector is amplified by transimpedance, filtered by anti-aliasing, and sampled by the ADC to obtain a discrete photoelectric sequence. After the sampled sequence is preprocessed by DC removal, normalization, abnormal limiting and temperature drift compensation, it is demodulated by short-window orthogonal correlation with the chirped reference sequence. The demodulated phase is subtracted from the modulation phase and the bias phase to obtain the Faraday phase estimate, which is converted into the original current.

[0060] The raw current enters the steady-state detection channel and the transient detection channel in parallel. The steady-state channel obtains a high-precision steady-state output through low-pass filtering, integral averaging and synchronous detection. The transient channel obtains transient characteristics through high-pass filtering, differential and short-time energy calculation. The comprehensive transient criterion is calculated based on differential, high-frequency energy and phase change rate, and combined with the duration point condition and hysteresis mechanism to determine the current signal state.

[0061] Based on the state discrimination results, the steady-state weight and transient weight are adjusted for adaptive fusion, the two channels are time-aligned, the additional delay introduced by the long filtering window of the steady-state channel is compensated, and the time stamp compensation is performed on the two-way propagation delay of the reflective optical path. Finally, the current waveform, transient flag, fault edge time and high-frequency energy index are output.

[0062] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the transient performance of an optical fiber current transformer, characterized in that, Includes the following steps: Construct a Faraday phase response model of a reflective Sagnac fiber optic current transformer structure and initialize its parameters; A co-source clock is constructed using an FPGA or high-speed DDS to generate a linear frequency modulation (LFM) chirped reference sequence, and the LFM chirped reference sequence is synchronously loaded into the phase modulator. At the same time, the co-source clock is sent into the ADC sampling link. The sampled photoelectric signal is preprocessed to obtain a preprocessed sequence, and the preprocessed sequence is entered in parallel into the steady-state channel and the transient channel to perform steady-state processing and transient processing. The state of the photoelectric signal is determined based on the steady-state and transient states after output, and dual-channel fusion and delay compensation are performed according to the state determination results.

2. The method for improving the transient performance of an optical fiber current transformer according to claim 1, characterized in that, The Faraday phase response model represents the change in polarization state or phase difference caused by the measured current in the fiber optic current transformer through the Faraday magneto-optical effect. For a reflective optical path, the equivalent phase change can be expressed as: ； in, The Faraday phase caused by the measured current. It is the Verdet constant. This represents the equivalent number of turns of the sensing fiber. The measured current, It is the equivalent current-phase scaling factor.

3. The method for improving the transient performance of an optical fiber current transformer according to claim 1, characterized in that, The process of constructing a co-source clock using an FPGA or high-speed DDS and generating a linear frequency modulated chirped reference sequence, synchronously loading the linear frequency modulated chirped reference sequence onto the phase modulator, and simultaneously sending the co-source clock into the ADC sampling link includes the following steps: The DDS, DAC, and ADC are simultaneously driven by the FPGA's internal PLL or an external low-jitter clock, so that the modulation reference sequence and the sampling sequence have a definite phase relationship and establish a common clock source. In the Each sampling point generates a DDS frequency control word. The modulation phase is obtained through a phase accumulator. ; Will Alternatively, the pre-distorted modulated waveform is output by the DAC and drives the phase modulator, resulting in an output bandwidth chirped modulated waveform. The FPGA generates a marker at the beginning of each chirp cycle and simultaneously stores an in-phase reference. and orthogonal reference ; The linear frequency modulated chirped reference sequence is output by continuously measuring periodically chirped frames and setting short protection zones between adjacent frames or by using phase continuous splicing.

4. The method for improving the transient performance of an optical fiber current transformer according to claim 3, characterized in that, The phase modulator generates a time-varying instantaneous modulation frequency at each sampling moment as follows: ； ； The phase modulation signal is replaced by the instantaneous frequency integral, and the modulation signal sweeps through one period. to The output bandwidth chirped modulation waveform for the specified frequency band is as follows: ； in, To modulate the phase amplitude, For the initial phase, The starting frequency of the chirp. For the termination frequency, For one chirping cycle, This represents the frequency modulation slope.

5. The method for improving the transient performance of an optical fiber current transformer according to claim 1, characterized in that, The preprocessing of the sampled photoelectric signal includes DC removal, amplitude normalization, outlier limiting, temperature drift compensation, chirped synchronous demodulation, and phase reconstruction.

6. The method for improving the transient performance of an optical fiber current transformer according to claim 5, characterized in that, The chirped synchronization demodulation and phase reconstruction process includes the following steps: Short-window orthogonal correlation processing is performed on the normalized sequence and the chirped reference to obtain the instantaneous phase estimate; Subtract the known modulation phase and bias phase to obtain the phase estimate corresponding to the measured current; The phase estimate is converted into the raw current. .

7. The method for improving the transient performance of an optical fiber current transformer according to claim 1, characterized in that, The process of entering the preprocessed sequence into the steady-state channel for steady-state processing includes: The original current After low-pass filtering and integral averaging, the steady-state current output is obtained. : ； in, These are the coefficients of a low-pass filter or an integral-average filter. The steady-state channel window length, The larger the value, the lower the steady-state noise, but the greater the group delay. This indicates that the original current sampling signal is in The value at that location.

8. The method for improving the transient performance of an optical fiber current transformer according to claim 1, characterized in that, The process of the preprocessed sequence entering the transient channel for transient processing includes: The original current High-frequency components are obtained after short-window high-pass filtering. And calculate the first-order difference component of the high-frequency component respectively. and second-order difference components ; Calculate the short-time high-frequency energy based on the high-frequency components and the transient short window length. ; The phase change rate is calculated by differentiating the phase sequence using a transient channel. ; Based on the phase change rate Short-term high-frequency energy , a difference component or second-order difference components The comparison result with the entry threshold determines whether the photoelectric signal has high-frequency characteristics; If so, enter the transient candidate state.

9. The method for improving the transient performance of an optical fiber current transformer according to claim 8, characterized in that, The determination of the photoelectric signal state based on the steady-state and transient states after output includes the following steps: The comprehensive transient criterion and transient determination conditions are defined as follows: ； ； in, , , These are the differential threshold, the high-frequency energy threshold, and the phase change rate threshold, respectively. , , These are the weighting coefficients. This represents the number of sampling points that continuously meet the threshold condition. Minimum number of duration points; Based on the photoelectric signal processing characteristics of entering the transient candidate state, it is determined in real time whether it is in a transient state; like Below the exit threshold and continuing If a certain number of sampling points are reached, the transient state is considered to have ended, and the output returns to steady state.

10. The method for improving the transient performance of an optical fiber current transformer according to claim 1, characterized in that, The process of performing dual-channel fusion and delay compensation output based on the state discrimination result includes the following steps: Adjust the steady-state weights based on the state discrimination results. and transient weights Perform adaptive fusion to obtain the fused output. ; The steady-state and transient channels are time-delayed and aligned. For the two-way propagation delay of reflective Sagnac optical path fiber Perform timestamp compensation and output current waveform, transient flag, fault edge time and high-frequency energy index.

11. The method for improving the transient performance of an optical fiber current transformer according to claim 10, characterized in that, The steady-state weight and transient weights The following conditions must be met: ； The fusion output The expression is: ； in, For transient channel output, and These are the equivalent delays for the steady-state and transient channels, respectively. , This indicates the steady-state channel output current. This indicates the transient channel output current. It represents a discrete time series.

12. A system for improving the transient performance of an optical fiber current transformer, characterized in that, include: Optical front end, including broadband light source, coupler, polarizer, broadband phase modulator, fiber delay line, sensing fiber ring, mirror and photodetector; The electronic signal processing module includes a transimpedance amplifier, an anti-aliasing filter, a high-speed ADC, a DDS chirped modulation generator, a steady-state demodulation channel, a transient detection channel, a state discrimination module, a fusion output module, and an FPGA processing unit. Specifically, a common clock is constructed and a linear frequency modulation (LFM) chirped reference sequence is generated through the impedance amplifier, anti-aliasing filter, high-speed ADC, and DDS chirped modulation generator. The LFM chirped reference sequence is synchronously loaded into the phase modulator, and the common clock is sent into the ADC sampling link. The sampled photoelectric signal is preprocessed through the steady-state demodulation channel and the transient detection channel to obtain a preprocessing sequence, and steady-state processing and transient processing are performed in parallel. The state discrimination module determines the state of the photoelectric signal based on the steady-state and transient states after output. The fusion output module and the FPGA processing unit perform dual-channel fusion and delay compensation output according to the state discrimination results.

Images