Verification method and system of mutual inductor calibrator based on accurate frequency tracking

Abstract

The invention relates to a verification method and system for a mutual inductor calibrator based on accurate frequency tracking. The method comprises the following steps: sampling output signals of a standard mutual inductor and a mutual inductor to be tested to obtain original signals; sequentially performing high-pass and low-pass digital filtering on the original signal to obtain a filtered signal; performing accurate frequency calculation on the filtering signal by adopting a mode of combining zero crossing point detection and a similar triangle interpolation method, and if an absolute value of a difference value between a current fundamental frequency obtained by calculation and a fundamental frequency measured last time is greater than a set value, updating a hardware sampling interval until the absolute value is smaller than the set value; and discrete Fourier transform calculation is carried out on the filtering signals of the standard mutual inductor and the mutual inductor to be detected respectively, fundamental wave amplitudes and fundamental wave phases of the corresponding signals are obtained, and a ratio difference and an angular difference are calculated to serve as verification results of the mutual inductor calibrator. According to the invention, spectrum leakage and a fence effect in the fundamental wave extraction process can be eliminated, and the verification precision of the angular difference and the ratio error of the mutual inductor calibrator is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of verification of a mutual inductor calibrator, and in particular to a verification method and system of a mutual inductor calibrator based on precise frequency tracking. Background Art

[0002] Transformer calibrators are widely used in power system metering. They verify the technical performance of voltage and current transformers. Based on their operating principles, they are classified into three categories: electrical, electronic, and digital. Currently, the most commonly used types of transformer calibrators in my country are electrical and electronic.

[0003] The electrical calibrator is designed based on the differential measurement circuit of the balanced bridge principle, which has the problems of complex hardware design and the introduction of hardware errors, and its calibration accuracy will be affected by environmental factors such as temperature and humidity. The electronic transformer calibrator abandons the traditional balanced bridge principle and is developed directly based on the principle of obtaining signal amplitude difference and phase difference through software algorithms. Its calibration accuracy is mainly affected by the output accuracy of the standard source and the fundamental wave extraction method.

[0004] Considering that the fundamental frequency of power grid signals often fluctuates or changes suddenly during the field use of transformer calibrators, existing fundamental component extraction algorithms include: full-wave Fourier transform algorithm, HHT algorithm, wavelet transform algorithm, spectrum-based windowed interpolation algorithm, DFT algorithm combined with quasi-synchronous algorithm, and other improved algorithms. These algorithms are all based on asynchronous sampling with a fixed sampling rate and do not use variable sampling rate frequency tracking technology. The extracted fundamental component and the input signal form a nonlinear system signal model, which cannot completely eliminate the impact of low-frequency DC components, disturbance noise, and interharmonics on the fundamental extraction accuracy. Therefore, the existing verification methods of electronic transformer calibrators have principled errors and need further improvement.

[0005] The Chinese invention patent with publication number CN109375142A, "Method and system for calibrating a transformer calibrator based on Kaiser window FFT filtering," provides a fundamental wave extraction algorithm based on Kaiser window FFT filtering for calculating ratio difference and angular difference. Due to asynchronous sampling, although the spectrum leakage of the fundamental wave can be reduced when the frequency fluctuates, it cannot eliminate the errors introduced by harmonics and interharmonics to the fundamental wave.

[0006] The Chinese invention patent publication number CN114280526A, "A Digital Differential Traceability System and Method for Electronic Transformer Calibrators," proposes a traceability method for electronic transformer calibrators based on HHT digital differential signal extraction and RBF neural network signal extension algorithm. The error of the electronic transformer calibrator is represented by the difference between the superimposed standard differential and the indication error of the electronic transformer calibrator, thereby achieving its traceability. However, there are problems such as high computational complexity, modal aliasing, and the need for a large number of training samples. Its practicality needs to be explored.

[0007] The Chinese invention patent publication number CN119511183A, "A Detection System and Method for an Electronic Transformer Calibrator," proposes a measure based on hardware low-pass filtering and synchronous pulse signals to improve the angular error traceability accuracy of electronic transformer calibrators. However, this introduces hardware errors and relies on a synchronous clock, increasing design costs. Summary of the Invention

[0008] The purpose of the present invention is to provide a calibration method and system for a transformer calibrator based on precise frequency tracking, which can eliminate the influence of DC components, low-frequency components, high-frequency interference signals and interharmonics on the frequency measurement accuracy and fundamental wave extraction accuracy, as well as the spectrum leakage and fence effect caused by asynchronous sampling, and improve the calibration accuracy of the transformer calibrator's angular difference and ratio difference, thereby realizing the complete traceability of the transformer calibrator.

[0009] In order to achieve the above object, the present invention provides a method for calibrating a transformer calibrator based on precise frequency tracking, comprising the following steps:

[0010] S1. Using a transformer calibrator, sample the output signals of a standard transformer and a transformer to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain original signals;

[0011] S2, performing high-pass digital filtering and low-pass digital filtering on the original signal in sequence to obtain a filtered signal;

[0012] S3, using a combination of zero-crossing detection and similar triangle interpolation to perform precise frequency calculation on the filtered signal, if the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is greater than a set value, then updating the hardware sampling interval based on the current fundamental frequency, until the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is less than the set value, completing precise frequency tracking;

[0013] S4. Perform discrete Fourier transform calculation on the filtered signals of the standard transformer and the transformer to be tested respectively to obtain the fundamental amplitude and fundamental phase of the corresponding signals and calculate the ratio difference and angle difference as the verification results of the transformer calibrator.

[0014] Optionally, the sampling frequency of the verification signal is 128 times the current fundamental frequency.

[0015] Optionally, a first-order high-pass IIR filter is used to perform the high-pass digital filtering.

[0016] Optionally, a sixth-order elliptic low-pass IIR filter is used to perform the low-pass digital filtering.

[0017] Optionally, the sixth-order elliptic low-pass IIR filter is implemented by cascading three second-order subsystems.

[0018] Optionally, performing accurate frequency calculation on the filtered signal by combining zero-crossing detection with similar triangle interpolation includes:

[0019] Continuously buffer the filtered signal for more than 11 cycles and search for 11 zero crossings that meet the following criteria:

[0020] s2[k]>0,s2[k+1]≥0,s2[k+2]<0,s2[k+3]<0

[0021] Among them, s2[k], s2[k+1], s2[k+2], and s2[k+3] are four consecutive sampling values, and k is the sampling value sequence number;

[0022] The times corresponding to the first and eleventh zero-crossing points are calculated using the similar triangle interpolation method. The calculation formula is as follows:

[0023]

[0024] Among them, t is the time corresponding to the zero crossing point, t s2[k] is the time corresponding to the sampling value of s2[k];

[0025] Calculate the exact frequency f of the current filtered signal according to the following formula s ′:

[0026] f s ′=10 / ΔT

[0027] Wherein, ΔT is the difference between the first and 11th zero-crossing points.

[0028] Optional, ratio difference e a The calculation formula is as follows:

[0029]

[0030] Wherein, A1 and A2 are amplitudes obtained by performing discrete Fourier transform calculation on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, respectively;

[0031] Angular difference The calculation formula is as follows:

[0032]

[0033] in, The phases are obtained by performing discrete Fourier transform calculation on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, respectively.

[0034] Optionally, the verification method further includes:

[0035] A homologous signal is applied to the standard mutual inductor and the mutual inductor to be tested, and the angular difference calculated according to S1-S4 is used as the angular difference bias value. Then, in the next measurement, the angular difference calculated by S4 is corrected using the angular difference bias value, and the corrected angular difference is used as the final calibration result of the mutual inductor calibrator.

[0036] Optionally, the output signal is a phase voltage or current signal of a voltage / current transformer in the power system.

[0037] Based on the same inventive concept, the present invention also provides a calibration system for a transformer calibrator based on precise frequency tracking, comprising a transformer calibrator, a standard transformer, and a transformer to be tested; wherein the transformer calibrator comprises:

[0038] An acquisition module, configured to sample the output signals of the standard mutual inductor and the mutual inductor to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain original signals;

[0039] A filtering module, configured to sequentially perform high-pass digital filtering and low-pass digital filtering on the original signal to obtain a filtered signal;

[0040] A precise frequency tracking module is configured to perform precise frequency calculation on the filtered signal by combining zero-crossing detection with a similar triangle interpolation method. If the absolute value of the difference between the calculated current fundamental frequency and the last measured fundamental frequency is greater than a set value, the hardware sampling interval is updated based on the current fundamental frequency until the absolute value of the difference between the calculated current fundamental frequency and the last measured fundamental frequency is less than the set value, completing precise frequency tracking.

[0041] The calculation module is used to perform discrete Fourier transform calculation on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, obtain the fundamental amplitude and fundamental phase of the corresponding signals, and calculate the ratio difference and angle difference as the verification results of the mutual inductor calibrator.

[0042] In the verification method and system for a transformer calibrator based on precise frequency tracking provided by the present invention, dual digital filtering technology, a high-precision frequency measurement algorithm, and an angular difference compensation measure are used to achieve precise frequency tracking, fundamental signal extraction, and angular difference ratio calculation, thereby greatly improving the verification accuracy of the transformer calibrator and achieving accurate and complete traceability. The method and system have at least one of the following beneficial effects:

[0043] 1) The dual digital filtering algorithm eliminates the effects of DC components, low-frequency components, high-frequency interference signals, and interharmonics on frequency measurement accuracy and fundamental wave extraction accuracy. In particular, it eliminates the picket fence effect error introduced by interharmonics on the fundamental wave when intercepting non-integer frequency signals.

[0044] 2) Based on precise frequency measurement, hardware frequency tracking technology is used to ensure that the sampling duration can accurately match the period of the fundamental signal, completely eliminating the spectrum leakage of the fundamental signal and perfectly avoiding the defects of the asynchronous sampling window interpolation algorithm;

[0045] 3) The present invention has an angular difference synchronization correction function, so no synchronous pulse signal is required for sampling synchronization, and no hardware difference measurement circuit is required. It has high cost performance and good adaptability. It can be used for traditional electromagnetic mutual inductors, as well as electronic mutual inductors and digital mutual inductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Those skilled in the art will appreciate that the accompanying drawings are provided for a better understanding of the present invention and do not constitute any limitation on the scope of the present invention.

[0047] Figure 1 A flow chart of a method for verifying a transformer calibrator based on precise frequency tracking provided by one embodiment of the present invention;

[0048] Figure 2 A schematic diagram of the amplitude-frequency characteristics of a first-order high-pass filter provided by an embodiment of the present invention;

[0049] Figure 3 A schematic diagram of the amplitude-frequency characteristics of a sixth-order elliptical low-pass filter provided in one embodiment of the present invention;

[0050] Figure 4 This is an example diagram of the effect of double filtering of a typical signal provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, advantages and features of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Any modification of the structure, change in the proportional relationship or adjustment of the size, under the condition that the effect produced by the present invention and the purpose that can be achieved are the same or similar, should still fall within the scope of the technical content disclosed by the present invention.

[0052] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. As used herein, the term "or" is generally used in a sense including "and / or" unless the context clearly dictates otherwise.

[0053] Please refer to Figure 1 This embodiment provides a method for calibrating a transformer calibrator based on precise frequency tracking, comprising the following steps:

[0054] S1. Using a transformer calibrator, sample the output signals of a standard transformer and a transformer to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain original signals;

[0055] S2, performing high-pass digital filtering and low-pass digital filtering on the original signal in sequence to obtain a filtered signal;

[0056] S3, using a combination of zero-crossing detection and similar triangle interpolation to perform precise frequency calculation on the filtered signal, if the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is greater than a set value, then updating the hardware sampling interval based on the current fundamental frequency, until the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is less than the set value, completing precise frequency tracking;

[0057] S4. Perform discrete Fourier transform calculation on the filtered signals of the standard transformer and the transformer to be tested respectively, obtain the fundamental amplitude and fundamental phase of the corresponding signals, and calculate the ratio difference and angle difference as the verification results of the transformer calibrator.

[0058] In view of the fundamental errors existing in the asynchronous sampling and windowed interpolation fundamental wave extraction algorithm used by existing electronic transformer calibrators when the calibration site signals have frequency fluctuations, high-frequency noise, DC bias and interharmonics, the present invention first designs high-precision digital filtering technology to eliminate the influence of high-frequency noise, DC components and interharmonics, and then realizes accurate frequency calculation and dynamic fundamental wave frequency tracking, completely eliminating the spectrum leakage and fence effect in the fundamental wave extraction process, improving the calibration accuracy of the transformer calibrator's angular difference ratio, and thus realizing the complete traceability of the transformer calibrator.

[0059] First, execute S1 and use the transformer calibrator to sample the output signals of the standard transformer and the transformer to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain the original signal s. The sampling frequency for sampling the calibration signal is the current fundamental frequency f s An integer multiple of .

[0060] In this embodiment, the sampling frequency of the test signal is the current fundamental frequency f s 128 times, that is, the output signals of the standard transformer and the transformer to be tested are 128×f s The sampling rate is used to sample the original signal, f s The fundamental frequency of the transformer calibrator is 50 Hz, and sampling is performed at a sampling rate of 128 points per cycle to obtain the original signal s. The output signal is the voltage or current signal of a particular phase of the voltage / current transformer in the power system. It is understood that any phase voltage or current signal of the voltage / current transformer in the power system can be calibrated using the calibration method provided by the present invention. This embodiment describes the steps using only a voltage or current signal of a particular phase.

[0061] Then, S2 is executed to sequentially perform high-pass digital filtering and low-pass digital filtering on the original signal to obtain a filtered signal. In this embodiment, a first-order high-pass IIR filter is used to filter out the DC and low-frequency components in the original signal s, while a sixth-order elliptic low-pass IIR filter is used to filter out the high-frequency noise and interharmonic components in the signal, given that the power grid signal at the transformer tester calibration site contains frequency fluctuations, high-frequency noise, DC offset, and interharmonics.

[0062] The first-order high-pass IIR filter is based on the first-order high-pass filter transfer function of the s-plane The transfer function of the z plane is obtained by bilinear transformation:

[0063]

[0064] And converted into the following time domain difference equation for high-pass filtering operation:

[0065]

[0066] Where x(n) and y(n) are the signals before and after filtering respectively.

[0067] The first-order high-pass IIR filter has Figure 2 From the amplitude-frequency characteristics shown in the figure, it can be seen that the filter can filter out the DC component and the low-frequency component with a frequency less than 2 Hz. The original signal s is filtered by a first-order high-pass IIR filter to obtain the signal s1.

[0068] The low-pass digital filter uses a sixth-order elliptic low-pass IIR filter to filter out high-frequency components and interharmonics in signal s1. Its passband cutoff frequency is 60Hz, the stopband cutoff frequency is 90Hz, the passband maximum attenuation is 0.02dB, and the stopband minimum attenuation is 40dB. In practice, Matlab is used to obtain a cascade of three second-order subsystems to implement this sixth-order elliptic low-pass filter to reduce the impact of quantization error on system performance. The filter coefficients of the three cascaded subsystems are written in matrix form as follows:

[0069] sos[3][6]=

[0070] {{1.00000000,-1.77456257,1.00000000,1.00000000,-1.83651757,0.84564590},

[0071] {1.00000000,-1.96163114,1.00000000,1.00000000,-1.91272569,0.92629397},

[0072] {1.00000000,-1.97547865,1.00000000,1.00000000,-1.96512962,0.98123697}}

[0073] The six elements in each row of the above matrix represent the filter coefficients of a second-order subsystem, denoted as: {a1, a2, a3, b1, b2, b3}, where a1, a3, and b1 are fixed to 1. The corresponding z-plane transfer function is as follows:

[0074]

[0075] Converted to the following time domain difference equation for low-pass filtering operation:

[0076] y(n)=x(n)+b2x(n-1)+b3x(n-2)-a2y(n-1)-y(n-2)

[0077] The sixth-order elliptic low-pass IIR filter has Figure 3 The amplitude-frequency characteristics shown in the figure show that the filter has a passband cutoff frequency of 60.15625 Hz and a stopband cutoff frequency of 88.08594 Hz. The interval (60.15625 Hz, 88.08594 Hz) is the transition band, which is consistent with the design parameters proposed in this invention. It can filter out all frequency components above 88 Hz, including higher harmonics and interharmonics. Signal s1 is filtered by a sixth-order elliptic low-pass IIR filter to obtain signal s2.

[0078] To further illustrate the filtering effect of the dual filter used in the present invention, the following test signal s is constructed:

[0079] s=5+sin(2*pi*t)+10*sin(2*pi*50*t)

[0080] +2*sin(2*pi*150*t)+2*sin(2*pi*217*t)

[0081] In the above formula, t is the time array, and 12800 points are continuously taken at a sampling interval of 1 / (128*50)=0.00015625 seconds, corresponding to 2 seconds.

[0082] In addition to the fundamental signal 10*sin(2*pi*50*t) with a peak value of 10 and a frequency of 50Hz, this signal also contains a DC component with an amplitude of 5, a low-frequency component sin(2*pi*t) with a peak value of 1 and a frequency of 1Hz, a third harmonic component 2*sin(2*pi*150*t) with a peak value of 2 and a frequency of 150Hz, and an interharmonic component 2*sin(2*pi*217*t) with a peak value of 2 and a frequency of 217Hz. The signal s is filtered by a first-order high-pass filter to obtain signal s1, and then filtered by a sixth-order elliptical low-pass filter to obtain signal s2. The effect of the double filtering is shown in the figure below. Figure 4 As shown in the figure, it can be seen that the original signal contains DC component, low-frequency component, high-frequency component and interharmonics. The S1 signal filters out the DC component and low-frequency component, and the S2 signal further filters out the high-frequency component and simple harmonics, retaining only the fundamental component, which verifies the effectiveness of the filtering algorithm proposed in this invention.

[0083] It should be noted that although the fundamental frequency in this example is 50 Hz, since the passband cutoff frequency of the designed sixth-order elliptical low-pass filter is 60 Hz, the expected effect can still be achieved after the double filtering proposed in the present invention for all mixed signals with a fundamental frequency below 60 Hz.

[0084] Then execute S3, and use a combination of zero-crossing point detection and similar triangle interpolation to perform precise frequency calculation on the filtered signal. If the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is greater than the set value, the hardware sampling interval is updated based on the current fundamental frequency until the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is less than the set value, thereby completing precise frequency tracking.

[0085] Specifically, the method of combining zero-crossing detection with similar triangle interpolation to accurately calculate the frequency of the filtered signal includes:

[0086] Continuously buffer the filtered signal for more than 11 cycles and search for 11 zero crossings that meet the following criteria:

[0087] s2[k]>0,s2[k+1]≥0,s2[k+2]<0,s2[k+3]<0

[0088] Among them, s2[k], s2[k+1], s2[k+2], and s2[k+3] are four consecutive sampling values, and k is the sampling value sequence number;

[0089] The times corresponding to the first and 11th zero-crossing points are calculated using the similar triangle interpolation method. The calculation formula is as follows:

[0090]

[0091] Among them, t is the time corresponding to the zero crossing point, t s2[k] is the time corresponding to the sampling value of s2[k];

[0092] Calculate the exact frequency f of the current filtered signal according to the following formula s ′:

[0093] f s ′=10 / Δt

[0094] Wherein, ΔT is the difference between the first and 11th zero-crossing points.

[0095] In this embodiment, if |f s ′-f s |≥0.01Hz, then according to the current fundamental frequency f s 'Update the hardware sampling interval and calculate the current fundamental frequency f s ' is used as the new fundamental frequency, where the sampling interval is T s ' is divided into 128 points per week, that is, Then return to step 1 and resample the output signals of the standard transformer and the transformer to be tested at an integer multiple of the fundamental frequency, i.e. 128×f s′ is sampled until |f s ′-f s |<0.01Hz, that is, until accurate frequency tracking is completed, and then go to S4. In this embodiment, 0.01Hz can be adjusted according to actual conditions, and the present invention does not limit this.

[0096] Then, S4 is executed to perform discrete Fourier transform (DFT) calculation on the filtered signals of the standard transformer and the transformer to be tested, respectively, to obtain the fundamental amplitude and fundamental phase of the corresponding signals and to calculate the ratio difference and angle difference as the verification results of the transformer calibrator.

[0097] It should be noted that the filtered signal used for discrete Fourier transform calculation is the one that satisfies |f in S3 s ′-f s The filtered signal after the original signal with a frequency of |<0.01Hz is double-filtered by s2.

[0098] In this embodiment, DFT calculation is performed on the filtered signals s2 of each phase of the standard mutual inductor and the mutual inductor to be tested, and the fundamental amplitude A1 and fundamental phase of a phase of the standard mutual inductor are obtained respectively. The fundamental wave amplitude A2 and fundamental wave phase of the corresponding phase of the transformer to be tested are Then calculate the ratio difference and angle difference respectively according to the following formulas:

[0099] Ratio difference e a The calculation formula is as follows:

[0100]

[0101] Among them, A1 and A2 are the fundamental wave amplitudes obtained by discrete Fourier transform calculation of the filtered signals of the standard transformer and the transformer to be tested respectively;

[0102] Angular difference The calculation formula is as follows:

[0103]

[0104] in, The fundamental wave phases are obtained by performing discrete Fourier transform calculation on the filtered signals of the standard transformer and the transformer to be tested, respectively.

[0105] Output ratio difference e a and angular difference The verification result of the transformer calibrator is output to the operation interface to complete the traceability of the angle difference and ratio difference.

[0106] Preferably, the verification method further comprises:

[0107] Apply a homologous signal to the standard transformer and the transformer to be measured, use the angle difference calculated according to S1-S4 as the angle difference offset value, and then use the angle difference offset value to calculate the angle difference obtained by S4 in the next measurement.

[0108] In this embodiment, in order to further eliminate the inherent angular difference between the standard transformer and the transformer under test and the combined angular difference bias caused by asynchronous sampling, a voltage / current signal of the same source is applied to the standard transformer and the transformer under test, wherein the voltage signal is connected in parallel and the current signal is connected in series. Then, the current angular difference is calculated as the angular difference bias value according to steps S1-S4. Then, in the next measurement, calculate the final angular difference according to the following correction formula:

[0109]

[0110] The final output ratio difference e a and the corrected angular difference The final verification result of the transformer calibrator is output to the operation interface to complete the traceability of the angle difference and ratio difference.

[0111] In this embodiment, the angular difference offset value may be recalibrated each time a new transformer to be tested is connected to the transformer calibrator to ensure the accuracy of the angular difference.

[0112] The verification method proposed in the present invention has the function of synchronous correction of angular difference, so no synchronous pulse signal is required for sampling synchronization, and no hardware difference measurement circuit is required. It has high cost performance and good adaptability, and can be used for traditional electromagnetic mutual inductors as well as electronic mutual inductors and digital mutual inductors.

[0113] Based on this, an embodiment of the present invention further provides a calibration system for a transformer calibrator based on precise frequency tracking, including a transformer calibrator, a standard transformer, and a transformer to be tested; wherein the transformer calibrator includes:

[0114] An acquisition module, configured to sample the standard mutual inductor and the mutual inductor to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain original signals;

[0115] A filtering module, configured to sequentially perform high-pass digital filtering and low-pass digital filtering on the original signal to obtain a filtered signal;

[0116] A precise frequency tracking module is configured to perform precise frequency calculation on the filtered signal by combining zero-crossing detection with a similar triangle interpolation method. If the absolute value of the difference between the calculated current fundamental frequency and the last measured fundamental frequency is greater than a set value, the hardware sampling interval is updated based on the current fundamental frequency until the absolute value of the difference between the calculated current fundamental frequency and the last measured fundamental frequency is less than the set value, completing precise frequency tracking.

[0117] The calculation module is used to perform discrete Fourier transform calculation on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, obtain the fundamental amplitude and fundamental phase of the corresponding signals, and calculate the ratio difference and angle difference as the verification results of the mutual inductor calibrator.

[0118] In summary, the embodiments of the present invention provide a method and system for calibrating a transformer calibrator based on precise frequency tracking. This method, in principle, eliminates the effects of DC components, low-frequency components, high-frequency interference signals, and interharmonics on frequency measurement accuracy and fundamental wave extraction accuracy. Hardware frequency tracking technology is used to avoid spectrum leakage and fence effect problems, greatly improving the calibration accuracy of the transformer calibrator and enabling accurate and complete traceability. It also features an angular error synchronization correction function, eliminating the need for a synchronous pulse signal and hardware differential measurement circuit, resulting in high cost-effectiveness and good adaptability.

[0119] Furthermore, it should be recognized that although the present invention has been disclosed above with reference to preferred embodiments, the above embodiments are not intended to limit the present invention. Any person skilled in the art can utilize the above disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or modify it into equivalent embodiments with equivalent variations, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for calibrating a transformer calibrator based on precise frequency tracking, characterized in that: The following steps are involved: S1. Using a transformer calibrator, sample the output signals of a standard transformer and a transformer to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain original signals; S2, performing high-pass digital filtering and low-pass digital filtering on the original signal in sequence to obtain a filtered signal; S3, using a combination of zero-crossing detection and similar triangle interpolation to perform precise frequency calculation on the filtered signal, if the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is greater than a set value, then updating the hardware sampling interval based on the current fundamental frequency, until the absolute value of the difference between the calculated current fundamental frequency and the fundamental frequency measured last time is less than the set value, completing precise frequency tracking; S4. Perform discrete Fourier transform calculation on the filtered signals of the standard transformer and the transformer to be tested respectively to obtain the fundamental amplitude and fundamental phase of the corresponding signals and calculate the ratio difference and angle difference as the verification results of the transformer calibrator.

2. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: The sampling frequency of sampling the detection signal is 128 times the current fundamental frequency.

3. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: A first-order high-pass IIR filter is used to perform the high-pass digital filtering.

4. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: A sixth-order elliptic low-pass IIR filter is used to perform the low-pass digital filtering.

5. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 4, characterized in that: The sixth-order elliptic low-pass IIR filter is implemented by cascading three second-order subsystems.

6. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: The method of combining zero-crossing detection with similar triangle interpolation to accurately calculate the frequency of the filtered signal includes: Continuously buffer the filtered signal for more than 11 cycles and search for 11 zero crossings that meet the following criteria: s2[k]>0,s2[k+1]≥0,s2[k+2]<0,s2[k+3]<0 Among them, s2[k], s2[k+1], s2[k+2], and s2[k+3] are four consecutive sampling values, and k is the sampling value sequence number; The times corresponding to the first and eleventh zero-crossing points are calculated using the similar triangle interpolation method. The calculation formula is as follows: Among them, t is the time corresponding to the zero crossing point, t s2[k] is the time corresponding to the sampling value of s2[k]; Calculate the exact frequency f of the current filtered signal according to the following formula s ′: f s ′=10 / ΔT Wherein, ΔT is the difference between the first and 11th zero-crossing points.

7. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: Ratio difference e a The calculation formula is as follows: Wherein, A1 and A2 are fundamental wave amplitudes obtained by performing discrete Fourier transform calculation on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, respectively; Angular difference The calculation formula is as follows: in, The fundamental wave phases are obtained by performing discrete Fourier transform calculations on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, respectively.

8. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: The verification method further comprises: A homologous signal is applied to the standard mutual inductor and the mutual inductor to be tested, and the angular difference calculated according to S1-S4 is used as the angular difference bias value. Then, in the next measurement, the angular difference calculated by S4 is corrected using the angular difference bias value, and the corrected angular difference is used as the final calibration result of the mutual inductor calibrator.

9. The method for calibrating a transformer calibrator based on precise frequency tracking according to claim 1, characterized in that: The output signal is a phase voltage or current signal of a voltage / current transformer in the power system.

10. A calibration system for a transformer calibrator based on precise frequency tracking, characterized in that: The instrument transformer calibrator comprises a standard instrument transformer and an instrument transformer to be tested; wherein the instrument transformer calibrator comprises: An acquisition module, configured to sample the output signals of the standard mutual inductor and the mutual inductor to be tested at a sampling rate that is an integer multiple of the fundamental frequency to obtain original signals; A filtering module, configured to sequentially perform high-pass digital filtering and low-pass digital filtering on the original signal to obtain a filtered signal; A precise frequency tracking module is configured to perform precise frequency calculation on the filtered signal by combining zero-crossing detection with a similar triangle interpolation method. If the absolute value of the difference between the calculated current fundamental frequency and the last measured fundamental frequency is greater than a set value, the hardware sampling interval is updated based on the current fundamental frequency until the absolute value of the difference between the calculated current fundamental frequency and the last measured fundamental frequency is less than the set value, completing precise frequency tracking. The calculation module is used to perform discrete Fourier transform calculation on the filtered signals of the standard mutual inductor and the mutual inductor to be tested, obtain the fundamental amplitude and fundamental phase of the corresponding signals, and calculate the ratio difference and angle difference as the verification results of the mutual inductor calibrator.

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