Transient large current measurement method and system of ultra-high voltage all-fiber current transformer

Abstract

The application discloses a kind of ultra-high voltage all-optical current transformer's transient large current measurement method and system, method includes: determining credible symbol;According to historical current, calculate current trend quantity;Based on credible symbol, current trend quantity and continuous confirmation length, construct phase interval state machine, determine Faraday phase angle current preset range;Current preset range is divided into candidate subinterval and midpoint is taken as candidate phase;For each candidate phase, counteract harmonic estimate value and construct candidate phase residual;Select the candidate phase of minimum residual and meet threshold as current phase angle, get transient measured current in combination with sensing coefficient;Current is divided into sliding time window and determines tailing entry condition;Using Prony algorithm extracts tailing attenuation component and residual bias;According to bias elimination criterion, execute bias elimination action.Transient large current is realized wide range continuous demodulation, and can accurately distinguish tailing current and residual bias, ensure the reliability of measurement zero after fault.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage current measurement technology in power systems, and particularly relates to a transient high-current measurement method and system for ultra-high voltage all-fiber current transformers. Background Technology

[0002] All-fiber current transformers (FOCTs) utilize the Faraday magneto-optical effect to convert primary current into optical phase. They feature excellent insulation performance, fast dynamic response, strong electromagnetic interference resistance, wide bandwidth, and ease of digital access, and are widely used in UHVDC converter stations, flexible DC transmission projects, and online monitoring of main power grid equipment. During the operation of UHVDC converter stations, FOCTs undertake steady-state current metering and protection measurement tasks, and also need to reliably reflect large current changes under transient conditions such as DC faults, AC side short circuits, converter valve lockout, and fault clearing.

[0003] With the increasing capacity of ultra-high voltage direct current (UHVDC) projects and the increasing complexity of power grid operation, the current measurement range faced by current transformers (FOCTs) is constantly expanding. Under normal operation and light load conditions, the measured current may be within a small amplitude range, requiring the transformer to have high sensitivity and resolution. However, during system faults or transient impacts, the measured current may reach tens of kiloamperes or even higher, requiring the transformer to have a wide range, anti-saturation capabilities, and undistorted phase calculation. Therefore, how to enable sinusoidal modulated FOCTs to balance high sensitivity for small currents with a wide range for large currents is a key problem that needs to be solved in engineering applications.

[0004] Existing fixed demodulation methods for sinusoidal modulation FOCT are usually based on fixed harmonic ratios or fixed arctangent algorithms. They have good sensitivity under small-range phase change conditions, but when transient large currents cause the phase angle to cross multiple intervals or enter the vicinity of the algorithm's critical point, problems such as the multivalued nature of the inverse trigonometric function, misjudgment of phase intervals, and discontinuity of the output waveform are prone to occur.

[0005] Wide-range demodulation methods based on harmonic symbol switching can expand the phase determination range by utilizing the symbol changes of the first to fourth harmonic components. However, if only the positive and negative harmonic symbols are used directly for interval switching, the symbols are prone to jitter when the harmonic amplitude is close to zero, noise increases, or the modulation depth drifts, which may still lead to incorrect interval switching. In addition, the symbol combinations of the second and fourth harmonics are similar in some intervals, and it is difficult to completely eliminate candidate sub-interval confusion based solely on symbol combinations. There is also a lack of consistency verification based on the measured harmonics and the harmonics calculated from the candidate phases.

[0006] On the other hand, after a power system fault is cleared, the fault current typically does not return to zero instantaneously, but rather exhibits a trailing current with DC attenuation characteristics. After being subjected to a large-current transient impact, the FOCT's optical link, electronic conditioning link, digital demodulation stage, or status register may experience transient bias, manifesting as the output current failing to accurately return to zero as the trailing current decays. In existing technologies, wide-range demodulation and post-fault bias processing are often implemented separately, lacking shared state variables between the preceding and following stages. The following stage cannot know whether the preceding stage has experienced large-current cross-region demodulation, whether interval switching instability has occurred, or whether the current demodulation result is reliable, making it difficult to form an integrated transient large-current measurement and recovery process. Furthermore, if only the measurement output is processed during zeroing without simultaneously refreshing the FFT sampling buffer, Prony analysis window, phase interval state machine, and formula switching flag, old transient data may continue to participate in subsequent calculations, affecting post-fault recovery measurements. Summary of the Invention

[0007] This invention provides a transient high current measurement method and system for ultra-high voltage all-fiber current transformers to solve the technical problems in the prior art, such as phase interval mis-switching, sub-interval confusion, discontinuous calculation, difficulty in balancing wide range and low current sensitivity under transient high current conditions, and difficulty in separating tail current and residual bias after faults, as well as incomplete bias elimination.

[0008] In a first aspect, the present invention provides a method for measuring transient high current in an ultra-high voltage all-fiber current transformer, comprising:

[0009] The discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment is obtained, and the discrete sampling sequence is windowed and subjected to fast Fourier transform to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component.

[0010] Calculate the symbol confidence level of each harmonic component, and determine the first confidence symbol of the first harmonic component, the second confidence symbol of the second harmonic component, the third confidence symbol of the third harmonic component, and the fourth confidence symbol of the fourth harmonic component based on the symbol confidence level.

[0011] Calculate the current trend based on historical transient current estimates prior to the current moment;

[0012] A phase interval state machine is constructed based on the first trusted symbol, the third trusted symbol, the current trend quantity, and the preset continuous confirmation length, and the current preset range of the Faraday phase angle is determined according to the phase interval state machine.

[0013] Based on the second trusted symbol and the fourth trusted symbol, the current preset range is divided into multiple candidate sub-intervals, and the midpoint of each candidate sub-interval is taken as the candidate phase.

[0014] For each candidate phase, the estimated values ​​of the first harmonic component, second harmonic component, third harmonic component, and fourth harmonic component are calculated using the Faraday magneto-optical effect theory formula, and the candidate phase residuals are constructed.

[0015] The candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfying the preset residual threshold is selected as the current Faraday phase angle, and the transient measured current is calculated based on the current Faraday phase angle and the preset sensing coefficient.

[0016] The transient measured current is divided into sliding time windows, the current gradient of the current window is calculated, and the preset tailing entry condition is determined based on the current gradient.

[0017] If the preset tail entry condition is met, the Prony algorithm is used to perform complex exponential decomposition on the current sequence in the current time window, extract the tail attenuation component amplitude and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the tail attenuation component amplitude, the dominant attenuation factor and the residual bias.

[0018] If the preset bias elimination criterion is met, the bias elimination action is performed to obtain the final transient measured current.

[0019] Secondly, the present invention provides a transient high-current measurement system for an ultra-high voltage all-fiber current transformer, comprising:

[0020] The acquisition module is configured to acquire the discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment, and to perform windowing and fast Fourier transform on the discrete sampling sequence to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component.

[0021] The first determining module is configured to calculate the symbol confidence of each harmonic component, and determine the first reliable symbol of the first harmonic component, the second reliable symbol of the second harmonic component, the third reliable symbol of the third harmonic component, and the fourth reliable symbol of the fourth harmonic component based on the symbol confidence of each component.

[0022] The calculation module is configured to calculate the current trend based on historical transient current estimates prior to the current moment.

[0023] The second determining module is configured to construct a phase interval state machine based on the first trusted symbol, the third trusted symbol, the current trend quantity, and a preset continuous confirmation length, and determine the current preset range of the Faraday phase angle according to the phase interval state machine.

[0024] The partitioning module is configured to divide the current preset range into multiple candidate sub-intervals based on the second trusted symbol and the fourth trusted symbol, and take the midpoint of each candidate sub-interval as a candidate phase;

[0025] The construction module is configured to back-calculate the estimated values ​​of the first harmonic component, the second harmonic component, the third harmonic component, and the fourth harmonic component for each candidate phase using the Faraday magneto-optical effect theory formula, and construct the candidate phase residual.

[0026] The first output module is configured to select the candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfy a preset residual threshold as the current Faraday phase angle, and calculate the transient measured current based on the current Faraday phase angle and the preset sensing coefficient.

[0027] The judgment module is configured to divide the transient measured current into sliding time windows, calculate the current gradient of the current window, and determine whether the preset tailing entry condition is met based on the current gradient.

[0028] The extraction module is configured to use the Prony algorithm to perform complex exponential decomposition on the current sequence within the current time window if the preset tail entry condition is met, extract the amplitude of the tail attenuation component and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the amplitude of the tail attenuation component, the dominant attenuation factor and the residual bias.

[0029] The second output module is configured to perform a bias elimination action if the preset bias elimination criterion is met, so as to obtain the final transient measured current.

[0030] Thirdly, an electronic device is provided, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the steps of the transient high current measurement method of an ultra-high voltage all-fiber current transformer according to any embodiment of the present invention.

[0031] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the steps of the transient high current measurement method of the ultra-high voltage all-fiber current transformer according to any embodiment of the present invention.

[0032] The transient high current measurement method and system for ultra-high voltage all-fiber current transformers disclosed in this application have the following beneficial effects:

[0033] Introducing harmonic symbol reliability avoids incorrect phase interval switching caused by symbol jitter when the harmonic amplitude is close to zero or when the noise is large, thus improving the reliability of phase interval switching.

[0034] By back-calculating the first to fourth harmonics of the candidate phase and constructing the candidate phase residuals, the phase solution that best matches the measured harmonics can be selected under the same or similar harmonic symbol combinations, thereby improving the accuracy of transient large current cross-regional solution.

[0035] By extracting the tail attenuation component using the Prony algorithm and further estimating the residual bias component, it is possible to distinguish between the actual tail current and the zero-point bias after the FOCT transient impact, thereby reducing the risks of false zeroing, missed zeroing, and residual bias.

[0036] During bias elimination, output clearing, sampling buffer refresh, phase interval state machine reset, and tail identification state reset are performed simultaneously to prevent fault transient old data from continuing to affect subsequent steady-state measurements.

[0037] This invention mainly adds credibility calculation, state machine, residual verification and bias estimation to the existing FOCT digital demodulation, state judgment and control execution links. It does not rely on complex artificial intelligence models or large-scale hardware modification, and is easy to embed into station-end monitoring devices, protection and control devices or host computer programs. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart illustrating a transient high current measurement method for an ultra-high voltage all-fiber current transformer according to an embodiment of the present invention;

[0040] Figure 2 This is a structural block diagram of a transient high current measurement system for an ultra-high voltage all-fiber current transformer provided in an embodiment of the present invention;

[0041] Figure 3This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0042] 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 with reference to the accompanying drawings. 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.

[0043] Please see Figure 1 The flowchart illustrates a transient high current measurement method for an ultra-high voltage all-fiber current transformer according to this application.

[0044] like Figure 1 As shown, the transient high current measurement of an ultra-high voltage all-fiber optic current transformer specifically includes the following steps:

[0045] Step S101: Obtain the discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment, and perform windowing and fast Fourier transform on the discrete sampling sequence to extract the first harmonic component, second harmonic component, third harmonic component and fourth harmonic component.

[0046] In this step, the analog voltage signal output from the photodetector of the sinusoidal modulated all-fiber current transformer (FOCT) is first synchronously sampled. A high-precision analog-to-digital converter is used for sampling, with the sampling rate set to 1 MHz to ensure effective capture of the modulation frequency and its harmonics. The resulting discrete numerical sequence is continuously stored in a first-in, first-out buffer.

[0047] To perform transient high current measurements, the system uses a fixed time window (e.g., 20 milliseconds) as the unit of analysis. Whenever the current time reaches the window boundary, all sampling points within the current window are retrieved from the buffer. First, a Hanning window is applied to these sampling points; that is, each sampling point is multiplied by a window function coefficient composed of cosine functions to reduce spectral leakage.

[0048] Subsequently, a Fast Fourier Transform (FFT) is performed on the windowed sequence to convert the time-domain signal to the frequency domain. The number of points in the Fourier Transform is taken as an integer power of 2 (e.g., 16384 points) to ensure sufficient frequency resolution. The transformed signal yields complex spectral lines in the frequency domain.

[0049] Based on the known modulation frequency (e.g., 50 kHz) of the all-fiber current transformer, the spectral line positions corresponding to the first, second, third, and fourth harmonics of this frequency are calculated. Considering that the actual frequency may have slight drift, the spectral line with the largest amplitude is searched near each target frequency, and energy centroid correction is performed using several adjacent spectral lines to accurately extract the frequency domain value of that harmonic.

[0050] For the extracted first, second, third, and fourth harmonics, their amplitudes are recorded. Simultaneously, the sign (positive or negative) of each harmonic is determined by analyzing the real and imaginary parts of the frequency domain data. Furthermore, to assess the reliability of the harmonics, the noise level in the frequency bands near each harmonic needs to be estimated: several continuous spectral lines adjacent to the harmonic spectral lines but not containing harmonic energy are selected, and the average amplitude of these spectral lines is calculated as the noise estimate for that harmonic.

[0051] After the above processing, each analysis window yields the amplitude, sign, and estimated nearby noise values ​​for the first, second, third, and fourth harmonics. These data will be used for subsequent symbol confidence calculations and phase interval determination. The entire analysis process is completed in real time in a digital signal processor or field-programmable gate array, with a window update rate typically of 50 Hz, which meets the real-time requirements of transient high-current measurements.

[0052] Step S102: Calculate the symbol confidence level of each harmonic component, and determine the first confidence symbol of the first harmonic component, the second confidence symbol of the second harmonic component, the third confidence symbol of the third harmonic component, and the fourth confidence symbol of the fourth harmonic component based on the confidence level of each symbol.

[0053] In this step, the expression for calculating the symbol confidence of each harmonic component is:

[0054] ,

[0055] In the formula, Let r be the r-th harmonic component at time t. Let be the amplitude of the r-th harmonic component at time t. Let be the noise estimate for the frequency band near the r-th harmonic at time t. To prevent tiny positive numbers with a denominator of zero;

[0056] It should be noted that the confidence level of a certain symbol of a certain harmonic component at the current moment is obtained, and it is determined whether the confidence level of a certain symbol at the current moment is less than a preset symbol confidence level threshold. The certain harmonic component is any one of the first harmonic component, the second harmonic component, the third harmonic component, and the fourth harmonic component.

[0057] If the credibility of a certain symbol at the current moment is not less than the preset symbol credibility threshold, then the actual symbol of the first harmonic component at the current moment is determined as a credible symbol.

[0058] If the credibility of a symbol at the current moment is less than the preset symbol credibility threshold, then the historical credible symbol of the first harmonic component at the previous moment is determined as a credible symbol.

[0059] In one specific embodiment, taking the first harmonic as an example, the symbol confidence level of the first harmonic is first calculated. The symbol confidence level is defined as the amplitude of the first harmonic divided by the sum of the noise estimate in its vicinity and a very small positive number. The noise estimate, obtained in step S101, represents the average intensity of the background noise near the harmonic; the very small positive number is used to prevent the denominator from being zero, for example, taking one-thousandth of the rated amplitude. This ratio reflects the relative strength of the first harmonic's signal strength compared to the noise: the larger the ratio, the more prominent the harmonic, and the more reliable its symbol; the smaller the ratio, the more likely the harmonic is submerged by noise, and the lower the symbol confidence level.

[0060] The symbol confidence levels of the second, third, and fourth harmonics were calculated in the same manner.

[0061] Next, the reliable symbols for each harmonic are determined. For any harmonic, the symbol reliability of that harmonic at the current moment is first obtained and compared with a pre-set symbol reliability threshold. This threshold is typically tuned based on experimental or historical data, for example, to three or four. The symbol reliability threshold is used to determine whether the harmonic signal is strong enough to be trusted to have its actual symbol.

[0062] If the symbol confidence level at the current moment is greater than or equal to the preset threshold, then the actual symbol of the harmonic is considered reliable, and the actual positive and negative symbols of the harmonic at the current moment are taken as the reliable symbols at the current moment.

[0063] If the symbol reliability at the current moment is less than a preset threshold, the actual symbol of that harmonic is considered potentially unreliable due to noise interference. In this case, the actual symbol cannot be used directly; instead, the historical reliable symbol of that harmonic from the previous moment is used as the reliable symbol for the current moment. This avoids erroneous symbol jumps caused by instantaneous noise and maintains symbol stability.

[0064] For the initial time (e.g., the first analysis window), since there is no historical reliable symbol from the previous time, it is necessary to pre-set the default reliable symbol for each harmonic. The default value is usually positive because when there is no current or a small current initially, the phase angle is near zero, the first harmonic is positive, the third harmonic is negative, and the first harmonic symbol is usually positive.

[0065] According to the above rules, the first, second, third, and fourth harmonics are processed independently, and four reliable symbols are finally obtained at the current time: the first reliable symbol of the first harmonic, the second reliable symbol of the second harmonic, the third reliable symbol of the third harmonic, and the fourth reliable symbol of the fourth harmonic.

[0066] This mechanism, based on a reliability threshold and historical preservation, effectively filters out symbol glitches caused by noise, ensuring high reliability of the symbols used in subsequent phase interval determination and sub-interval division. This step can be completed in real-time in a digital signal processor through simple comparison and register saving operations, with minimal computational load and no significant impact on overall processing time.

[0067] Step S103: Calculate the current trend based on the historical transient current estimates prior to the current moment.

[0068] In this step, the transient current estimates at time t-1 and time t-2 are obtained;

[0069] The current trend at time t is calculated based on the estimated transient current at time t-1 and the estimated transient current at time t-2, expressed as follows:

[0070] ,

[0071] In the formula, Let be the current trend at time t. This is the estimated value of the transient current at time t-1. This is the estimated value of the transient current at time t-2.

[0072] Step S104: Construct a phase interval state machine based on the first trusted symbol, the third trusted symbol, the current trend quantity, and the preset continuous confirmation length, and determine the current preset range of the Faraday phase angle according to the phase interval state machine.

[0073] In this step, a preset range number is defined for time t. initial value And define a continuous confirmation counter at time t. initial value ;

[0074] When the first reliable symbol at time t is positive, the third reliable symbol at time t is negative, and the current trend at time t is not less than the preset change threshold, the switching direction is set to increase.

[0075] When the first reliable symbol at time t is negative, the third reliable symbol at time t is positive, and the current trend at time t is less than the preset change threshold, the switching direction is set to decrease.

[0076] If the continuous confirmation status at the previous time step meets the preset conditions, then the continuous confirmation counter at time t will be updated. Increment by 1, otherwise continuously confirm the counter at time t. Reset to 0;

[0077] The continuous confirmation counter at time t Reaching the preset continuous confirmation length At that time, the preset range number is updated according to the switching direction, specifically as follows:

[0078] If the switching direction is to increase, then If the switching direction is to decrease, then and reset the continuous confirmation counter. ,in, Pre-determine the range number for time t-1;

[0079] Determine the Faraday phase angle at time t. The current preset range is .

[0080] In one specific embodiment, based on the first reliable symbol of the first harmonic and the third reliable symbol of the third harmonic obtained in step S102, and the current trend calculated in step S103, the current preset range of the Faraday phase angle is determined by a phase interval state machine. The preset range number indicates that the Faraday phase angle is in an interval divided by integer multiples of pi. For example, number 0 corresponds to zero to pi, number 1 corresponds to pi to twice pi, and so on.

[0081] I. Initialization

[0082] Before starting the measurement, the internal variables of the state machine are first initialized. The preset range number for the current moment is set to zero, indicating that the initial default Faraday phase angle is between zero and pi. Simultaneously, the continuous acknowledgment counter is set to zero. The continuous acknowledgment counter records the number of continuous analysis windows that meet the switching conditions, preventing momentary erroneous switching due to noise disturbances.

[0083] II. Determining the Switching Direction

[0084] At each analysis window (current moment), the system determines whether a phase interval switch is needed based on the current first and third trusted symbols and the current trend, and determines the switching direction.

[0085] First, check if the first reliable symbol is positive and the third reliable symbol is negative. Simultaneously, check if the current trend is greater than or equal to a pre-set threshold for change (this threshold is adjusted based on the normal transient current change rate, for example, a change of several amperes per millisecond). If all three conditions are met, it indicates that the current is rising rapidly and the Faraday phase angle is increasing positively. At this point, the system will set the switching direction to "increase," meaning the preset range number should move in the direction of increasing value.

[0086] Otherwise, check if the first confidence symbol is negative and the third confidence symbol is positive, and simultaneously check if the current trend is less than the negative of the change threshold (i.e., the negative value of the current trend is greater than the change threshold). If all three conditions are met, it indicates that the current is rapidly decreasing and the Faraday phase angle is decreasing in the opposite direction. At this time, the system will set the switching direction to "decreasing", indicating that the preset range number should move in the direction of decreasing value.

[0087] If neither of the above two conditions is met, the switching direction is set to "unchanged", indicating that the conditions for interval switching are not met at present, and the preset range number remains unchanged.

[0088] III. Continuous Confirmation Mechanism

[0089] To enhance the system's anti-jitter capability and avoid erroneous switching due to single noise or accidental fulfillment of conditions, a continuous confirmation mechanism has been introduced.

[0090] When the switching direction is "increase" or "decrease", the system checks whether the continuous acknowledgment status of the previous moment meets the preset start condition. Typically, the start condition is defined as the switching direction of the previous moment being the same as the current moment, or simply that counting is allowed to begin at the initial moment. If the condition is met, the continuous acknowledgment counter is incremented by one; otherwise, the continuous acknowledgment counter is reset to zero.

[0091] When the switching direction is "unchanged", the system will continuously reset the confirmation counter to zero, indicating that there is no longer a switching trend.

[0092] IV. Update the preset range number

[0093] The system has a preset consecutive confirmation length, such as three or five. When the value of the consecutive confirmation counter reaches this consecutive confirmation length, it indicates that the switching condition has been stably met within multiple consecutive analysis windows, at which point the actual preset range number update is performed.

[0094] Specifically, if the switching direction is "increase", the current preset range number is set to the previous preset range number plus one. If the switching direction is "decrease", the current preset range number is set to the previous preset range number minus one. After the update is complete, the continuous confirmation counter is immediately reset to zero for use in the next switching judgment.

[0095] If the continuous confirmation counter has not reached the continuous confirmation length, the preset range number will remain unchanged from the previous value.

[0096] V. Determine the current preset range

[0097] After the state machine processing described above, the preset range number for the current moment is obtained. Therefore, the current preset range of the Faraday phase angle is the interval with the lower limit being the number multiplied by pi and the upper limit being the next integer multiplied by pi. For example, when the number is two, the Faraday phase angle is within the open interval from two times pi to three times pi.

[0098] This phase interval state machine, by utilizing reliable harmonic symbols, current trend quantities, and continuous acknowledgment lengths, can accurately follow phase cross-region changes caused by transient large currents, while effectively suppressing erroneous switching caused by noise and random disturbances. This provides a reliable phase range basis for subsequent sub-interval selection and residual verification. The entire state machine logic can be efficiently implemented in a digital signal processor through conditional judgments and counter read / write operations.

[0099] Step S105: Based on the second trusted symbol and the fourth trusted symbol, the current preset range is divided into multiple candidate sub-intervals, and the midpoint of each candidate sub-interval is taken as the candidate phase.

[0100] In this step, the current preset range is divided into 8 sub-intervals according to the range of Faraday phase angle values. Each sub-interval corresponds to a sub-interval number, where the first sub-interval is... The phase range of each sub-interval is , ;

[0101] Based on the positive and negative combinations of the second and fourth trusted symbols, candidate sub-intervals are selected according to the following rules:

[0102] When the second trusted symbol is positive and the fourth trusted symbol is positive, sub-interval numbers 1 and 2 are selected as candidate sub-intervals; when the second trusted symbol is negative and the fourth trusted symbol is positive, sub-interval numbers 3 and 4 are selected as candidate sub-intervals; when the second trusted symbol is negative and the fourth trusted symbol is negative, sub-interval numbers 5 and 6 are selected as candidate sub-intervals; when the second trusted symbol is positive and the fourth trusted symbol is negative, sub-interval numbers 7 and 8 are selected as candidate sub-intervals.

[0103] The midpoint of each candidate sub-interval, i.e., the phase value This serves as a candidate phase for the corresponding candidate sub-interval.

[0104] In one specific embodiment, firstly, the current preset range obtained in step S104 (e.g., the open interval from a certain integer multiple of pi to the next integer multiple of pi) is uniformly subdivided in terms of phase angle values. Specifically, the entire width of pi (i.e., the length between two adjacent integer multiples of pi) is divided into eight completely equal sub-intervals. Each sub-interval corresponds to a sub-interval number, numbered sequentially from smallest to largest phase angle as 1, 2, 3, 4, 5, 6, 7, 8. The larger the sub-interval number, the closer the phase angle is to the upper limit of the preset range.

[0105] Since the lower limit of the current preset range is an integer multiple of pi, and the upper limit is the next integer multiple of pi, the width of each sub-interval is exactly one-eighth of pi. This division method ensures uniform resolution of the phase angle within the preset range, providing a foundation for subsequent accurate determination of the phase angle.

[0106] In step S102, the system has obtained the second reliable symbol of the second harmonic and the fourth reliable symbol of the fourth harmonic, each reliable symbol taking the value "positive" or "negative". Based on the positive and negative combinations of these two symbols, it can be preliminarily determined which sub-intervals the Faraday phase angle is more likely to appear within a preset range. This principle is based on the law of variation of the second and fourth harmonic symbols with the phase angle in the Faraday magneto-optical effect theory.

[0107] The specific filtering rules are as follows:

[0108] When the second and fourth confidence symbols are both positive, it indicates that the phase angle is in the earlier part of the preset range. At this time, sub-interval numbers 1 and 2 are selected as candidate sub-intervals.

[0109] When the second trusted symbol is negative and the fourth trusted symbol is positive, the phase angle is located in the middle-front position within the preset range, and sub-interval numbers 3 and 4 are selected as candidate sub-intervals.

[0110] When the second and fourth trusted symbols are negative, the phase angle is located in the middle to rear position within the preset range, and sub-interval numbers 5 and 6 are selected as candidate sub-intervals.

[0111] When the second trusted symbol is positive and the fourth trusted symbol is negative, the phase angle is located in the latter part of the preset range, and sub-interval numbers 7 and 8 are selected as candidate sub-intervals.

[0112] This mapping rule allows each symbol combination to select at most two candidate sub-intervals, thus greatly reducing the possible range of phase angles.

[0113] For each selected candidate sub-interval, the system takes its geometric midpoint (i.e., the center phase value of the sub-interval) as a candidate phase corresponding to that sub-interval. Since the width of each candidate sub-interval is one-eighth of pi, the midpoint phase value is equal to the lower limit of the sub-interval plus one-sixteenth of pi.

[0114] Therefore, the midpoint of subinterval number 1 is the lower limit plus one-sixteenth of pi, the midpoint of subinterval number 2 is the lower limit plus three-sixteenths of pi, and so on. These midpoint phase values ​​are recorded as candidate phases according to the subinterval numbering order.

[0115] If the rule selects two candidate sub-intervals (such as 1 and 2), then two candidate phases are obtained; if only one sub-interval is selected due to special symbol combinations or initial boundary conditions (a very rare case), then only one candidate phase is obtained. Generally, two candidate phases are obtained at each time step.

[0116] After the above processing, the system obtains a list of candidate phases, where each candidate phase corresponds to a potentially correct Faraday phase angle approximation. These candidate phases are passed to the next step (step S106) to inversely calculate the harmonic estimate and construct the residual, and then the final Faraday phase angle is determined by comparing the residuals.

[0117] This implementation method subdivides a wide preset range into fine sub-intervals of one-eighth of a circle, and then quickly filters out the most likely sub-intervals based on the reliable symbol combinations of the second and fourth harmonics. This significantly reduces the number of candidate phases while maintaining positioning accuracy, thereby reducing the computational load of subsequent residual calculations. The entire division and filtering process involves only simple interval arithmetic and logical comparisons, making it suitable for efficient execution in embedded processors.

[0118] Step S106: For each candidate phase, the estimated values ​​of the first harmonic component, second harmonic component, third harmonic component, and fourth harmonic component are calculated using the Faraday magneto-optical effect theory formula, and the candidate phase residuals are constructed.

[0119] In this step, the expression for the candidate phase residual is:

[0120] ,

[0121] In the formula, The candidate phase residual at time t corresponds to the k-th candidate phase and is used to measure the degree of agreement between the candidate phase and the measured harmonics and current continuity. Here are the preset weighting coefficients for the r-th harmonic in the residual calculation. Let be the measured amplitude of the r-th harmonic component at time t. To be based on candidate phase The estimated value of the r-th harmonic component obtained by inverse calculation using the Faraday magneto-optical effect theory formula, For absolute value operations, To prevent tiny positive numbers with a denominator of zero, Preset weighting coefficients for current continuity. The value of the current at time t is calculated based on the candidate phase k. This is the estimated value of the transient current at time t-1. This is the reference value for the rated current.

[0122] Step S107: Select the candidate phase with the smallest candidate phase residual among all candidate phase residuals that meets the preset residual threshold as the current Faraday phase angle, and calculate the transient measured current based on the current Faraday phase angle and the preset sensing coefficient.

[0123] In step S106, the system has calculated a residual value for each candidate phase (usually two). This residual value comprehensively reflects the degree of matching between the candidate phase and the measured harmonics, as well as the consistency with the current variation trend: the smaller the residual value, the closer the candidate phase is to the true Faraday phase angle.

[0124] The system first iterates through the residual values ​​corresponding to all candidate phases at the current time and finds the smallest residual value. It also records the candidate phase corresponding to this smallest residual value. If multiple candidate phases have the same smallest residual value, any one of them can be selected (e.g., the one with the smaller sub-interval number), or secondary judgment conditions can be added according to actual engineering needs, such as prioritizing the candidate phase with a phase angle closer to the previous time step to ensure output continuity.

[0125] To prevent unreliable phase angle outputs under abnormal conditions (such as when all candidate phases have poor matching with measured data), the system pre-sets a residual threshold value. This threshold value is obtained through experiments or statistical analysis of historical data and represents the upper limit of acceptable phase matching error.

[0126] After finding the minimum residual value, the system compares it with a preset residual threshold. Only when the minimum residual value is less than or equal to the threshold is the corresponding candidate phase considered reliable enough to be accepted as the current Faraday phase angle.

[0127] If the minimum residual value exceeds a preset threshold, it indicates that the consistency between all current candidate phases and the measured data is not ideal, possibly due to excessive noise, modulation depth drift, or other interference. In this case, the system should not risk outputting an unreliable phase angle. One approach is to keep the Faraday phase angle from the previous moment unchanged and output a flag indicating low reliability, or to enter a waiting state until the residual value recovers to within the threshold at the next moment. Another approach is to use a backup solution method (such as the traditional arctangent solution) as the current phase angle and record the abnormal event. In practical engineering, an appropriate strategy can be selected based on the requirements for real-time performance and reliability.

[0128] When the minimum residual value meets a preset threshold, the system determines the candidate phase corresponding to the minimum residual value as the Faraday phase angle at the current moment. This phase angle has already taken into account the preset range determined by the phase interval state machine, and the residual verification has compensated for the possible sub-interval confusion caused by the same symbol combination, thus having high accuracy.

[0129] All-fiber current transformers are calibrated with a sensing coefficient during manufacturing or calibration. This coefficient reflects the linear proportional relationship between the Faraday phase angle and the measured current. The sensing coefficient is typically expressed in radians per kiloampere.

[0130] The system divides the current Faraday phase angle determined in the previous step by the sensing coefficient to obtain the transient measured current value at the current moment. For example, if the sensing coefficient is a certain value and the Faraday phase angle is a certain radian, the quotient is the current value in kiloamperes. If the output needs to be in amperes, the result can be multiplied by one thousand.

[0131] Finally, the system outputs the calculated transient measured current value to subsequent measurement data links, such as to protection and control devices, station monitoring systems, or fault recorders. Simultaneously, this current value is also stored in a historical cache for calculating the current trend at the next moment (step S103). The output format can be a signed floating-point number or an integer, with the positive or negative sign indicating the current direction.

[0132] If the phase angle cannot be updated in the previous residual judgment because the minimum residual value exceeds the threshold, the system can choose to output the current value of the previous moment and set an alarm bit of "invalid data" or "phase unreliable" for the upper layer application to judge.

[0133] Through the above implementation method, step S107 completes the entire process of selecting the optimal solution from multiple candidate phases and finally outputting the transient measured current. This process combines the principle of residual minimization and reliability threshold verification, ensuring accurate and stable current values ​​output under normal operating conditions, while avoiding the output of seriously erroneous data under abnormal conditions, demonstrating the robustness and engineering practicality of the method.

[0134] Step S108: Divide the transient measured current into sliding time windows, calculate the current gradient of the current window, and determine whether the preset tailing entry condition is met based on the current gradient.

[0135] In this step, the transient measured current is... The time window is divided into consecutive sliding windows according to a preset time window length, and each time window corresponds to a window number.

[0136] Calculate the first RMS value of current sequence within a time window The expression is:

[0137] ,

[0138] In the formula, The number of sampling points within a single time window. For the first Within the first time window Current values ​​at each sampling point;

[0139] According to the The first time window and the first Calculate the current gradient for the current window based on the RMS current value of each time window. The expression is:

[0140] ,

[0141] In the formula, For the first The effective value of the current sequence within a time window;

[0142] Determine the current gradient in the current time window. Whether it is less than a preset gradient threshold, where if it is less than the preset gradient threshold, it means that the preset tailing entry condition is met.

[0143] In a more preferred embodiment, the preset tailing entry conditions further include: the high current cross-region flag is 1; the fault blocking or protection blocking has been released; and the overall harmonic reliability has recovered to the preset allowable range. That is, the tailing current candidate window is only entered when the following conditions are met simultaneously:

[0144] High current cross-regional marking This indicates that the preceding stage has experienced a high-current transient.

[0145] The fault lockout or protection lockout has been released;

[0146] Overall Harmonic Reliability To restore the data to the preset allowable range, ensuring the reliability of the current measurement data and the overall harmonic reliability. The expression is:

[0147] ,

[0148] In the formula, These are the weighting coefficients for each harmonic order. These are the weighting coefficients for each harmonic order. The symbol confidence threshold is the value of the r-th harmonic.

[0149] Current gradient If the current is less than the preset gradient threshold, it indicates that the current change has become gradual.

[0150] Step S109: If the preset tail entry condition is met, the Prony algorithm is used to perform complex exponential decomposition on the current sequence in the current time window, extract the tail attenuation component amplitude and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the tail attenuation component amplitude, the dominant attenuation factor and the residual bias.

[0151] In this step, the expression for the residual bias is:

[0152] ,

[0153] ,

[0154] ,

[0155] In the formula, For the first Residual bias estimates for each time window, This represents the number of sampling points within the current time window. This represents the measured current value at the nth sampling point within the current time window. The tailing component corresponding to the nth sampling point. This represents the actual trailing attenuation component corresponding to the nth sampling point. For the true residual bias component, For the noise term corresponding to the nth sampling point, The amplitude of the DC attenuation component. As the dominant decay factor, For the first The attenuation factor of each AC component. The sampling period is For the first The frequency of each AC component, For the first The initial phase angle of each AC component, The sampling point number within the current time window. For the first The amplitude of each AC component, This represents the total number of exchange components.

[0156] In step S110, if the preset bias elimination criterion is met, the bias elimination action is performed to obtain the final transient measured current.

[0157] In this step, to ensure the reliability of the criterion, a multi-window continuous confirmation mechanism is adopted: when And continuously meet the preset quantity Only after a certain time window is the bias elimination condition confirmed to be met, in order to reduce the risk of false triggering caused by noise disturbance.

[0158] The expression for the bias elimination criterion is:

[0159] ,

[0160] In the formula, For the first The offset elimination criterion flag for each time window For the first The amplitude of the trailing decay component within each time window This is the threshold for the final stage of tail decay. For the first Residual bias estimates for each time window, This is the minimum bias threshold that needs to be corrected. For the first Fault protection within a time window, This is an indicator function; it takes the value 1 when the condition is true, and 0 otherwise.

[0161] When the bias elimination condition is met, the system performs one or more of the following bias elimination actions:

[0162] 1. Offset subtraction: And record the correction amount, where, This is the corrected current value at time t obtained after subtracting the residual bias from the original measurement value;

[0163] 2. Forced Zeroing of Output: Send a forced zeroing command to the FOCT output register or digital measurement output interface to set the current measurement output to zero;

[0164] 3. Sampling buffer refresh: refresh the circular sampling buffer used for FFT, harmonic symbol determination, candidate phase residual verification and Prony analysis to prevent fault transient old data from continuing to participate in subsequent calculations;

[0165] 4. Event Log: Store the zeroing time, residual current before and after zeroing, tailing identification parameters, bias estimate, and execution result in the event log.

[0166] In summary, the method of this application extracts the first to fourth harmonics from the output signal of the photodetector using a windowed Fourier transform; calculates the confidence level of each harmonic symbol and determines the reliable symbol; calculates the current trend based on historical current; constructs a phase interval state machine based on the reliable symbol, current trend, and continuous confirmation length to determine the current preset range of the Faraday phase angle; divides the current preset range into candidate sub-intervals and takes the midpoint as the candidate phase; back-calculates the harmonic estimate for each candidate phase and constructs the candidate phase residual; selects the candidate phase with the smallest residual that meets the threshold as the current phase angle, and obtains the transient measured current by combining the sensing coefficient; divides the current into sliding time windows and determines the tailing entry condition; uses the Prony algorithm to extract the tailing attenuation component and residual bias; executes the bias elimination action according to the bias elimination criterion; achieves wide-range continuous demodulation of transient large currents, and can accurately distinguish between tailing current and residual bias, ensuring the reliability of measurement zeroing after a fault.

[0167] Please see Figure 2 The diagram shows a structural block diagram of a transient high current measurement system for an ultra-high voltage all-fiber current transformer according to this application.

[0168] like Figure 2 As shown, the transient high current measurement system 200 includes an acquisition module 210, a first determination module 220, a calculation module 230, a second determination module 240, a division module 250, a construction module 260, a first output module 270, a judgment module 280, an extraction module 290, and a second output module 2100.

[0169] The acquisition module 210 is configured to acquire the discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment, and to perform windowing and fast Fourier transform on the discrete sampling sequence to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component.

[0170] The first determining module 220 is configured to calculate the symbol confidence of each harmonic component, and determine the first reliable symbol of the first harmonic component, the second reliable symbol of the second harmonic component, the third reliable symbol of the third harmonic component, and the fourth reliable symbol of the fourth harmonic component based on the symbol confidence of each component.

[0171] Calculation module 230 is configured to calculate the current trend based on historical transient current estimates prior to the current moment;

[0172] The second determining module 240 is configured to construct a phase interval state machine based on the first trusted symbol, the third trusted symbol, the current trend quantity, and a preset continuous confirmation length, and determine the current preset range of the Faraday phase angle according to the phase interval state machine.

[0173] The partitioning module 250 is configured to divide the current preset range into multiple candidate sub-intervals based on the second trusted symbol and the fourth trusted symbol, and take the midpoint of each candidate sub-interval as a candidate phase.

[0174] The construction module 260 is configured to back-calculate the estimated values ​​of the first harmonic component, the second harmonic component, the third harmonic component, and the fourth harmonic component for each candidate phase using the Faraday magneto-optical effect theory formula, and construct the candidate phase residual.

[0175] The first output module 270 is configured to select the candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfy a preset residual threshold as the current Faraday phase angle, and calculate the transient measured current based on the current Faraday phase angle and the preset sensing coefficient.

[0176] The judgment module 280 is configured to divide the transient measured current into sliding time windows, calculate the current gradient of the current window, and determine whether the preset tailing entry condition is met based on the current gradient.

[0177] The extraction module 290 is configured to use the Prony algorithm to perform complex exponential decomposition on the current sequence in the current time window if the preset tail entry condition is met, extract the amplitude of the tail attenuation component and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the amplitude of the tail attenuation component, the dominant attenuation factor and the residual bias.

[0178] The second output module 2100 is configured to perform a bias elimination action if the preset bias elimination criterion is met, so as to obtain the final transient measured current.

[0179] It should be understood that Figure 2 The modules and references described in the document Figure 1 The steps described in the text correspond to those in the method described above. Therefore, the operations, features, and corresponding technical effects described above also apply to the method described in the text. Figure 3 The various modules in the document will not be described in detail here.

[0180] In other embodiments, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the transient high current measurement method for ultra-high voltage all-fiber current transformers in any of the above method embodiments.

[0181] In one embodiment, the computer-readable storage medium of the present invention stores computer-executable instructions, which are configured as follows:

[0182] The discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment is obtained, and the discrete sampling sequence is windowed and subjected to fast Fourier transform to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component.

[0183] Calculate the symbol confidence level of each harmonic component, and determine the first confidence symbol of the first harmonic component, the second confidence symbol of the second harmonic component, the third confidence symbol of the third harmonic component, and the fourth confidence symbol of the fourth harmonic component based on the symbol confidence level.

[0184] Calculate the current trend based on historical transient current estimates prior to the current moment;

[0185] A phase interval state machine is constructed based on the first trusted symbol, the third trusted symbol, the current trend quantity, and the preset continuous confirmation length, and the current preset range of the Faraday phase angle is determined according to the phase interval state machine.

[0186] Based on the second trusted symbol and the fourth trusted symbol, the current preset range is divided into multiple candidate sub-intervals, and the midpoint of each candidate sub-interval is taken as the candidate phase.

[0187] For each candidate phase, the estimated values ​​of the first harmonic component, second harmonic component, third harmonic component, and fourth harmonic component are calculated using the Faraday magneto-optical effect theory formula, and the candidate phase residuals are constructed.

[0188] The candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfying the preset residual threshold is selected as the current Faraday phase angle, and the transient measured current is calculated based on the current Faraday phase angle and the preset sensing coefficient.

[0189] The transient measured current is divided into sliding time windows, the current gradient of the current window is calculated, and the preset tailing entry condition is determined based on the current gradient.

[0190] If the preset tail entry condition is met, the Prony algorithm is used to perform complex exponential decomposition on the current sequence in the current time window, extract the tail attenuation component amplitude and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the tail attenuation component amplitude, the dominant attenuation factor and the residual bias.

[0191] If the preset bias elimination criterion is met, the bias elimination action is performed to obtain the final transient measured current.

[0192] Computer-readable storage media may include a program storage area and a data storage area. The program storage area may store an operating system and an application program required for at least one function. The data storage area may store data created based on the use of the transient high-current measurement system of the UHV all-fiber current transformer. Furthermore, the computer-readable storage medium may include high-speed random access memory, and may also include memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the computer-readable storage medium may optionally include memory remotely configured relative to a processor, which can be connected to the transient high-current measurement system of the UHV all-fiber current transformer via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0193] Figure 3 This is a schematic diagram of the structure of the electronic device provided in the embodiment of the present invention, such as... Figure 3 As shown, the device includes a processor 310 and a memory 320. The electronic device may also include an input device 330 and an output device 340. The processor 310, memory 320, input device 330, and output device 340 can be connected via a bus or other means. Figure 3 Taking a bus connection as an example, the memory 320 is the computer-readable storage medium described above. The processor 310 executes various server functions and data processing by running non-volatile software programs, instructions, and modules stored in the memory 320, thereby realizing the transient high-current measurement method for the ultra-high voltage all-fiber optic current transformer described in the above embodiment. The input device 330 can receive input digital or character information and generate key signal inputs related to user settings and function control of the transient high-current measurement system for the ultra-high voltage all-fiber optic current transformer. The output device 340 may include a display screen or other display device.

[0194] The aforementioned electronic device can execute the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0195] In one implementation, the aforementioned electronic device is applied to a transient high-current measurement system for an ultra-high voltage all-fiber current transformer, serving as a client, and includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to:

[0196] The discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment is obtained, and the discrete sampling sequence is windowed and subjected to fast Fourier transform to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component.

[0197] Calculate the symbol confidence level of each harmonic component, and determine the first confidence symbol of the first harmonic component, the second confidence symbol of the second harmonic component, the third confidence symbol of the third harmonic component, and the fourth confidence symbol of the fourth harmonic component based on the symbol confidence level.

[0198] Calculate the current trend based on historical transient current estimates prior to the current moment;

[0199] A phase interval state machine is constructed based on the first trusted symbol, the third trusted symbol, the current trend quantity, and the preset continuous confirmation length, and the current preset range of the Faraday phase angle is determined according to the phase interval state machine.

[0200] Based on the second trusted symbol and the fourth trusted symbol, the current preset range is divided into multiple candidate sub-intervals, and the midpoint of each candidate sub-interval is taken as the candidate phase.

[0201] For each candidate phase, the estimated values ​​of the first harmonic component, second harmonic component, third harmonic component, and fourth harmonic component are calculated using the Faraday magneto-optical effect theory formula, and the candidate phase residuals are constructed.

[0202] The candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfying the preset residual threshold is selected as the current Faraday phase angle, and the transient measured current is calculated based on the current Faraday phase angle and the preset sensing coefficient.

[0203] The transient measured current is divided into sliding time windows, the current gradient of the current window is calculated, and the preset tailing entry condition is determined based on the current gradient.

[0204] If the preset tail entry condition is met, the Prony algorithm is used to perform complex exponential decomposition on the current sequence in the current time window, extract the tail attenuation component amplitude and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the tail attenuation component amplitude, the dominant attenuation factor and the residual bias.

[0205] If the preset bias elimination criterion is met, the bias elimination action is performed to obtain the final transient measured current.

[0206] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0207] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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 measuring transient high current in an ultra-high voltage all-fiber optic current transformer, characterized in that, include: The discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment is obtained, and the discrete sampling sequence is windowed and subjected to fast Fourier transform to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component. Calculate the symbol confidence level of each harmonic component, and determine the first confidence symbol of the first harmonic component, the second confidence symbol of the second harmonic component, the third confidence symbol of the third harmonic component, and the fourth confidence symbol of the fourth harmonic component based on the symbol confidence level. Calculate the current trend based on historical transient current estimates prior to the current moment; A phase interval state machine is constructed based on the first trusted symbol, the third trusted symbol, the current trend quantity, and the preset continuous confirmation length, and the current preset range of the Faraday phase angle is determined according to the phase interval state machine. Based on the second trusted symbol and the fourth trusted symbol, the current preset range is divided into multiple candidate sub-intervals, and the midpoint of each candidate sub-interval is taken as the candidate phase. For each candidate phase, the estimated values ​​of the first harmonic component, second harmonic component, third harmonic component, and fourth harmonic component are calculated using the Faraday magneto-optical effect theory formula, and the candidate phase residuals are constructed. The candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfying the preset residual threshold is selected as the current Faraday phase angle, and the transient measured current is calculated based on the current Faraday phase angle and the preset sensing coefficient. The transient measured current is divided into sliding time windows, the current gradient of the current window is calculated, and the preset tailing entry condition is determined based on the current gradient. If the preset tail entry condition is met, the Prony algorithm is used to perform complex exponential decomposition on the current sequence in the current time window, extract the tail attenuation component amplitude and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the tail attenuation component amplitude, the dominant attenuation factor and the residual bias. If the preset bias elimination criterion is met, the bias elimination action is performed to obtain the final transient measured current.

2. The method according to claim 1, wherein, The expression for calculating the sign confidence level of each harmonic component is as follows: ， wherein is the rth harmonic component at the tth time, is the amplitude of the rth harmonic component at the tth time, is the noise estimate of the rth harmonic band at the tth time, is a small positive number to prevent the denominator from being zero; The determination of the first reliable symbol of the first harmonic component, the second reliable symbol of the second harmonic component, the third reliable symbol of the third harmonic component, and the fourth reliable symbol of the fourth harmonic component based on the reliability of each symbol includes: The confidence level of a certain symbol of a certain harmonic component at the current time is obtained, and it is determined whether the confidence level of a certain symbol at the current time is less than a preset symbol confidence level threshold. The certain harmonic component is any one of the first harmonic component, the second harmonic component, the third harmonic component, and the fourth harmonic component. If the credibility of a certain symbol at the current moment is not less than the preset symbol credibility threshold, then the actual symbol of the first harmonic component at the current moment is determined as a credible symbol. If the credibility of a symbol at the current moment is less than the preset symbol credibility threshold, then the historical credible symbol of the first harmonic component at the previous moment is determined as a credible symbol.

3. The transient high current measurement method for an ultra-high voltage all-fiber optic current transformer according to claim 1, characterized in that, The calculation of the current trend based on historical transient current estimates prior to the current moment includes: Obtain the transient current estimates at time t-1 and time t-2; The current trend at time t is calculated based on the estimated transient current at time t-1 and the estimated transient current at time t-2, expressed as follows: ， In the formula, Let be the current trend at time t. This is the estimated value of the transient current at time t-1. This is the estimated value of the transient current at time t-2.

4. The transient high current measurement method for an ultra-high voltage all-fiber optic current transformer according to claim 1, characterized in that, The step of constructing a phase interval state machine based on the first trusted symbol, the third trusted symbol, the current trend quantity, and a preset continuous confirmation length, and determining the current preset range of the Faraday phase angle based on the phase interval state machine, includes: Define the preset range number at time t initial value And define a continuous confirmation counter at time t. initial value ; When the first reliable symbol at time t is positive, the third reliable symbol at time t is negative, and the current trend at time t is not less than the preset change threshold, the switching direction is set to increase. When the first reliable symbol at time t is negative, the third reliable symbol at time t is positive, and the current trend at time t is less than the preset change threshold, the switching direction is set to decrease. If the continuous confirmation status at the previous time step meets the preset conditions, then the continuous confirmation counter at time t will be updated. Increment by 1, otherwise continuously confirm the counter at time t. Reset to 0; The continuous confirmation counter at time t Reaching the preset continuous confirmation length At that time, the preset range number is updated according to the switching direction, specifically as follows: If the switching direction is to increase, then If the switching direction is to decrease, then and reset the continuous confirmation counter. ,in, Pre-determine the range number for time t-1; Determine the Faraday phase angle at time t. The current preset range is .

5. The transient high current measurement method for an ultra-high voltage all-fiber current transformer according to claim 1, characterized in that, The step of dividing the current preset range into multiple candidate sub-intervals based on the second and fourth trusted symbols, and taking the midpoint of each candidate sub-interval as a candidate phase, includes: The current preset range is divided into 8 sub-intervals according to the range of Faraday phase angle values. Each sub-interval corresponds to a sub-interval number, where the first sub-interval is... The phase range of each sub-interval is , ; Based on the positive and negative combinations of the second and fourth trusted symbols, candidate sub-intervals are selected according to the following rules: When the second trusted symbol is positive and the fourth trusted symbol is positive, sub-interval numbers 1 and 2 are selected as candidate sub-intervals; when the second trusted symbol is negative and the fourth trusted symbol is positive, sub-interval numbers 3 and 4 are selected as candidate sub-intervals; when the second trusted symbol is negative and the fourth trusted symbol is negative, sub-interval numbers 5 and 6 are selected as candidate sub-intervals; when the second trusted symbol is positive and the fourth trusted symbol is negative, sub-interval numbers 7 and 8 are selected as candidate sub-intervals. The midpoint of each candidate sub-interval, i.e., the phase value This serves as a candidate phase for the corresponding candidate sub-interval.

6. The transient high current measurement method for an ultra-high voltage all-fiber optic current transformer according to claim 1, characterized in that, The expression for the candidate phase residual is: ， In the formula, The candidate phase residual at time t corresponds to the k-th candidate phase and is used to measure the degree of agreement between the candidate phase and the measured harmonics and current continuity. Here are the preset weighting coefficients for the r-th harmonic in the residual calculation. Let be the measured amplitude of the r-th harmonic component at time t. To be based on candidate phase The estimated value of the r-th harmonic component obtained by inverse calculation using the Faraday magneto-optical effect theory formula, For absolute value operations, To prevent tiny positive numbers with a denominator of zero, Preset weighting coefficients for current continuity. The value of the current at time t is calculated based on the candidate phase k. This is the estimated value of the transient current at time t-1. This is the reference value for the rated current.

7. The transient high current measurement method for an ultra-high voltage all-fiber optic current transformer according to claim 1, characterized in that, The step of dividing the transient measured current into a sliding time window, calculating the current gradient of the current window, and determining whether the preset tailing entry condition is met based on the current gradient includes: Transient measured current The time window is divided into consecutive sliding windows according to a preset time window length, and each time window corresponds to a window number. Calculate the first RMS value of current sequence within a time window The expression is: ， In the formula, The number of sampling points within a single time window. For the first Within the first time window Current values ​​at each sampling point; According to the The first time window and the first Calculate the current gradient for the current window based on the RMS current value of each time window. The expression is: ， In the formula, For the first The effective value of the current sequence within a time window; Determine the current gradient in the current time window. Whether it is less than a preset gradient threshold, where if it is less than the preset gradient threshold, it means that the preset tailing entry condition is met.

8. The transient high current measurement method for an ultra-high voltage all-fiber optic current transformer according to claim 1, characterized in that, The expression for the residual bias is: ， ， ， In the formula, For the first Residual bias estimates for each time window, This represents the number of sampling points within the current time window. This represents the measured current value at the nth sampling point within the current time window. The tailing component corresponding to the nth sampling point. This represents the actual trailing attenuation component corresponding to the nth sampling point. For the true residual bias component, For the noise term corresponding to the nth sampling point, The amplitude of the DC attenuation component. As the dominant decay factor, For the first The attenuation factor of each AC component. The sampling period is For the first The frequency of each AC component, For the first The initial phase angle of each AC component, The sampling point number within the current time window. For the first The amplitude of each AC component, This represents the total number of exchange components.

9. The transient high current measurement method for an ultra-high voltage all-fiber optic current transformer according to claim 1, characterized in that, The expression for the bias elimination criterion is: ， In the formula, For the first The offset elimination criterion flag for each time window For the first The amplitude of the trailing decay component within each time window This is the threshold for the final stage of tail decay. For the first Residual bias estimates for each time window, This is the minimum bias threshold that needs to be corrected. For the first Fault protection within a time window, This is an indicator function; it takes the value 1 when the condition is true, and 0 otherwise.

10. A transient high-current measurement system for an ultra-high voltage all-fiber optic current transformer, characterized in that, include: The acquisition module is configured to acquire the discrete sampling sequence output by the photodetector of the sinusoidal-modulated all-fiber current transformer at the current moment, and to perform windowing and fast Fourier transform on the discrete sampling sequence to extract the first harmonic component, the second harmonic component, the third harmonic component and the fourth harmonic component. The first determining module is configured to calculate the symbol confidence of each harmonic component, and determine the first reliable symbol of the first harmonic component, the second reliable symbol of the second harmonic component, the third reliable symbol of the third harmonic component, and the fourth reliable symbol of the fourth harmonic component based on the symbol confidence of each component. The calculation module is configured to calculate the current trend based on historical transient current estimates prior to the current moment. The second determining module is configured to construct a phase interval state machine based on the first trusted symbol, the third trusted symbol, the current trend quantity, and a preset continuous confirmation length, and determine the current preset range of the Faraday phase angle according to the phase interval state machine. The partitioning module is configured to divide the current preset range into multiple candidate sub-intervals based on the second trusted symbol and the fourth trusted symbol, and take the midpoint of each candidate sub-interval as a candidate phase; The construction module is configured to back-calculate the estimated values ​​of the first harmonic component, the second harmonic component, the third harmonic component, and the fourth harmonic component for each candidate phase using the Faraday magneto-optical effect theory formula, and construct the candidate phase residual. The first output module is configured to select the candidate phase with the smallest candidate phase residual among all candidate phase residuals and satisfy a preset residual threshold as the current Faraday phase angle, and calculate the transient measured current based on the current Faraday phase angle and the preset sensing coefficient. The judgment module is configured to divide the transient measured current into sliding time windows, calculate the current gradient of the current window, and determine whether the preset tailing entry condition is met based on the current gradient. The extraction module is configured to use the Prony algorithm to perform complex exponential decomposition on the current sequence within the current time window if the preset tail entry condition is met, extract the amplitude of the tail attenuation component and the dominant attenuation factor, estimate the residual bias based on the mean residual between the measured current and the tail fitting component, and determine whether the preset bias elimination criterion is met based on the amplitude of the tail attenuation component, the dominant attenuation factor and the residual bias. The second output module is configured to perform a bias elimination action if the preset bias elimination criterion is met, so as to obtain the final transient measured current.

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