Measurement self-correction method and system of clip-on ammeter

Abstract

The invention relates to the technical field of ammeter self-correction, in particular to a measurement self-correction method and system for a clip-on ammeter, and the method comprises the steps: comparing the amplitude of each smooth current signal at a zero frequency in a frequency domain with the mean value of the amplitudes at all frequencies, and determining a first filtering residual value of each smooth current signal; determining the confidence coefficient of each smooth current signal by analyzing the similarity between each smooth current signal and a standard current calibration signal and combining the first filtering residual value; and obtaining an error correction coefficient of each smooth current signal, and carrying out self-correction on the measurement of the clip-on ammeter at the current moment in combination with the confidence coefficient. According to the invention, the interference of harmonic distortion generated by nonlinear load equipment and a circuit and direct current component introduced by load current on the calculation precision of the error correction coefficient of the clip-on ammeter is solved, and the self-correction precision of the clip-on ammeter is improved.

Description

Technical Field

[0001] The present application relates to the technical field of ammeter self-calibration, and in particular to a measurement self-calibration method and system for a clamp ammeter. Background Art

[0002] A clamp-on ammeter is an instrument used to measure the current in a running electrical circuit. Compared to traditional ammeters or transformers, it can measure current without disconnecting the circuit. It is the most widely used basic electricity detection and calibration equipment. However, the clamp-on ammeter will gradually experience measurement inaccuracies during its long-term use, so it needs to be regularly calibrated.

[0003] Among existing clamp-on ammeter calibration methods, real-time calibration methods based on self-calibration technology can calibrate the clamp-on ammeter more quickly and in real time than traditional static calibration methods. This method calculates the error correction coefficient based on the standard current calibration signal generated by the clamp-on ammeter's self-calibration system and the actual mixed current signal collected, thereby achieving calibration. However, this method ignores the harmonic distortion generated by nonlinear load devices and circuits, as well as the DC component introduced into the load current. As a result, when the clamp-on ammeter is self-calibrated in an AC power supply system, the calculated error correction coefficient deviates due to the harmonics and DC component, thereby reducing the self-calibration accuracy of the clamp-on ammeter. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide a measurement self-calibration method and system for a clamp ammeter. The technical solutions adopted are as follows: In a first aspect, an embodiment of the present application provides a measurement self-calibration method for a clamp ammeter, the method comprising the following steps: During the self-calibration process of the clamp ammeter, a standard current calibration signal within a preset time period before the current moment is obtained, and the actual mixed current signal generated by the transformer in the clamp ammeter is obtained multiple times; Each actual mixed current signal after filtering is recorded as a smoothed current signal, and the frequency distribution value of each smoothed current signal is determined by analyzing the amplitude distribution of each smoothed current signal at all frequencies in the frequency domain; the difference between the amplitude of each smoothed current signal at zero frequency in the frequency domain and the frequency distribution value is compared to determine the first filtering residual value of each smoothed current signal; Determining a second filtered residual value of each smoothed current signal by analyzing the similarity between each smoothed current signal and a standard current calibration signal, and determining a comprehensive filtered residual value of each smoothed current signal in combination with the first filtered residual value to determine a confidence level of each smoothed current signal; The error correction coefficient of each smoothed current signal is obtained, and combined with the confidence level, the error correction coefficient of the clamp ammeter at the current moment is determined to perform self-correction on the measurement of the clamp ammeter at the current moment.

[0005] Preferably, the actual mixed current signals after filtering are recorded as smoothed current signals, specifically: Each actual mixed current signal is used as the input of the DC filter and the harmonic filter in turn, and the output signal is recorded as the smoothed current signal.

[0006] Preferably, the frequency distribution value of each smooth current signal is the average value of the amplitude of each smooth current signal at all frequencies in the frequency domain.

[0007] Preferably, the first filtering residual value of each smoothed current signal is a ratio of the amplitude of each smoothed current signal at zero frequency in the frequency domain to the frequency distribution value.

[0008] Preferably, the second filtering residual value of each smoothed current signal is the inverse of the similarity between each smoothed current signal and the standard current calibration signal.

[0009] Preferably, the comprehensive filtering residual value of each smoothed current signal is the average of the normalized value of the first filtering residual value and the normalized value of the second filtering residual value of each smoothed current signal.

[0010] Preferably, the confidence level of each smoothed current signal is the inverse of a comprehensive filtering residual value of each smoothed current signal.

[0011] Preferably, the expression of the error correction coefficient of the clamp ammeter at the current moment is: Where, Indicates the error correction coefficient of the clamp ammeter at the current moment; Indicates the confidence level of the smoothed current signal; Indicates the error correction coefficient of the smoothed current signal; Indicates the number of all smoothed current signals; Represents the normalization function.

[0012] Preferably, the self-calibration of the clamp ammeter measurement at the current moment includes: The result of multiplying the error correction coefficient of the clamp ammeter at the current moment by the current value measured by the clamp ammeter at the current moment is used as the measurement correction value of the current value at the current moment.

[0013] In a second aspect, an embodiment of the present application also provides a measurement self-correction system for a clamp ammeter, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the system implements the steps of the measurement self-correction method for a clamp ammeter described in any one of the above items.

[0014] This application has at least the following beneficial effects: The present application first performs DC filtering and harmonic filtering on the actual mixed current signal in sequence, thereby effectively reducing the influence of the DC component and harmonic component mixed in the actual mixed current signal on the subsequent calculation of the error correction coefficient of the clamp ammeter; further, the present application constructs the confidence of the smoothed current signal by analyzing the residual degree of DC and harmonics in the filtered signal, quantitatively evaluates the quality of the smoothed current signal, and uses the obtained confidence to perform weighted averaging processing on the error correction coefficients of all smoothed current signals. Compared with the traditional method, it can effectively avoid the large error in the final error correction coefficient caused by the large amount of DC components and harmonic components mixed in the actual mixed current signal collected when the clamp ammeter in the AC power supply system is self-calibrated, effectively eliminating the influence of low-quality data caused by incomplete filtering on the final calibration result, and improving the accuracy of the self-calibration of the clamp ammeter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 A flowchart of a self-calibration method for measuring a clamp ammeter according to an embodiment of the present application; Figure 2 A schematic diagram of the confidence extraction process provided for one embodiment of the present application. DETAILED DESCRIPTION

[0017] To further illustrate the technical means and effectiveness of this application to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementation, structure, features, and effectiveness of a clamp-on ammeter self-calibration method and system proposed in this application. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0018] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0019] The following describes in detail a measurement self-correction method and system for a clamp ammeter provided by the present application with reference to the accompanying drawings.

[0020] See also Figure 1 , which shows a flowchart of a measurement self-calibration method of a clamp ammeter provided by an embodiment of the present application, the method comprising the following steps: Step S1: During the self-calibration process of the clamp ammeter, a standard current calibration signal within a preset time period before the current moment is obtained, and an actual mixed current signal generated by a transformer in the clamp ammeter is obtained multiple times.

[0021] The measurement self-calibration system of the clamp ammeter in this embodiment is used to self-calibrate the clamp ammeter in an AC system. The self-calibration system includes an acquisition module, a signal processing module, and a calibration module.

[0022] During any self-calibration process of the clamp ammeter, the signal acquisition module obtains the standard current calibration signal generated by the clamp ammeter's measurement self-calibration system within a preset time period before the current moment, and obtains the actual mixed current signal generated by the clamp transformer M times in succession. In this embodiment, the number of acquisitions M of the actual mixed current signal is set to 5, and the sampling frequency and sampling time are set to 1 kHz and 200 ms, respectively. The implementer can also set the number of acquisitions, sampling frequency, and sampling time according to specific circumstances. This embodiment does not impose any special restrictions.

[0023] The sampling time is set to be greater than the power frequency of the power system. The power system and its power frequency are well-known technologies, and their specific architecture and concepts are not described in detail here.

[0024] Step S2: Record each actual mixed current signal after filtering as a smoothed current signal, and determine the frequency distribution value of each smoothed current signal by analyzing the amplitude distribution of each smoothed current signal at all frequencies in the frequency domain; compare the difference between the amplitude and the frequency distribution value of each smoothed current signal at zero frequency in the frequency domain to determine the first filtered residual value of each smoothed current signal; determine the second filtered residual value of each smoothed current signal by analyzing the similarity between each smoothed current signal and the standard current calibration signal, and determine the comprehensive filtered residual value of each smoothed current signal in combination with the first filtered residual value to determine the confidence of each smoothed current signal.

[0025] Due to the increasing number of nonlinear loads on the power grid, such as semiconductor rectifiers, high-frequency lighting equipment, and air conditioning frequency conversion circuits, the AC power supply system where the clamp-on transformer is located has caused power quality pollution problems such as DC ingress and harmonic distortion. This in turn causes harmonics and DC components to appear in the collected actual mixed current signal. Therefore, to prevent the harmonics and DC components mixed in the collected actual mixed current signal from affecting the final error correction coefficient calculation results, each actual mixed current signal is filtered as follows: Each actual mixed current signal is used as the input of the DC filter and the harmonic filter in turn, and the output signal is recorded as a smoothed current signal. Among them, the DC filter and the harmonic filter are both well-known technologies, and the specific process of filtering the actual mixed current signal will not be repeated here.

[0026] However, existing DC filters and harmonic filters cannot completely filter out all DC components and harmonic components in the collected current signal. Therefore, this embodiment determines the frequency distribution value of each smoothed current signal by analyzing the amplitude distribution of each smoothed current signal at all frequencies in the frequency domain; compares the difference between the amplitude of each smoothed current signal at zero frequency in the frequency domain and the frequency distribution value, and determines the first filtering residual value of each smoothed current signal to evaluate the degree of filtering of the DC component in the smoothed current signal. The specific process is as follows: As an implementation manner, in this embodiment, the average value of the amplitude of each smoothed current signal at all frequencies in the frequency domain is used as the frequency distribution value of each smoothed current signal.

[0027] Furthermore, in this embodiment, the ratio of the amplitude of each smoothed current signal at zero frequency in the frequency domain to the frequency distribution value is used as the first filtering residual value of each smoothed current signal.

[0028] According to the first filtering residual value of each smooth current signal, it can be understood that the first filtering residual value is used to measure the ratio of the residual DC component in the smooth current signal to the average amplitude of the smooth current signal. The amplitude at the frequency of 0 directly represents the size of the DC component, and the average of the amplitudes at all frequencies represents the average fluctuation amplitude of the smooth current signal. If the first filtering residual value of the current smooth current signal is larger, it means that after the DC filter processing, the DC offset still existing in the current smooth current signal is more obvious relative to the AC fluctuation part of the smooth current signal. On the contrary, if the first filtering residual value of the current smooth current signal is smaller, it means that after the DC filtering processing, the DC offset in the smooth current signal is already very small, and can be ignored relative to the AC fluctuation part of the current signal, and the filtering effect is better.

[0029] Furthermore, since the DC component in the AC signal generally only causes the entire waveform of the AC signal to move upward or downward, while the harmonic component in the AC signal generally causes the waveform of the AC signal to change, this embodiment determines the second filtered residual value of each smoothed current signal by analyzing the similarity between each smoothed current signal and the standard current calibration signal, specifically: In this embodiment, the inverse of the similarity between each smoothed current signal and the standard current calibration signal is used as the second filtering residual value of each smoothed current signal.

[0030] It should be noted that there are many commonly used methods for measuring the similarity between signals. In this embodiment, the cosine similarity between each smoothed current signal and the standard current calibration signal is used as the similarity between each smoothed current signal and the standard current calibration signal. In actual application, as other implementation methods, the implementer may also adopt the reciprocal of the Euclidean distance or other methods for measuring the similarity between signals based on specific circumstances. This embodiment does not impose any special restrictions on the selection of the method for measuring the similarity between signals.

[0031] The calculation method of cosine similarity is a well-known technology, and its specific calculation process will not be described in detail.

[0032] According to the second filtering residual value of each smoothed current signal, it can be understood that the second filtering residual value is used to measure the residual degree of harmonics in the smoothed current signal. The higher the similarity, the closer the waveform of the smoothed current signal is to that of the standard current calibration signal, which means that the residual harmonic components after filtering are less, and therefore, the corresponding second filtering residual value is smaller; conversely, if the similarity between the smoothed current signal and the standard current calibration signal is smaller, it means that the difference between the waveforms after the smoothed current signal and the standard current absorption is greater, which means that the residual harmonic components after filtering are more, and therefore, the corresponding second filtering residual value is larger.

[0033] Furthermore, this embodiment uses the average of the normalized value of the first filtered residual value and the normalized value of the second filtered residual value of each smoothed current signal as the comprehensive filtered residual value of each smoothed current signal, and uses the inverse of the comprehensive filtered residual value of each smoothed current signal as the confidence of each smoothed current signal.

[0034] Preferably, the confidence extraction process diagram provided in this embodiment is as follows Figure 2 shown.

[0035] Among them, the normalized value is calculated using the maximum and minimum normalization method. In actual application, as other implementation methods, the implementer may also select other normalization methods such as the z-score normalization method based on specific circumstances. Regarding the selection of the normalization method, this embodiment does not impose any special restrictions. Among them, the maximum and minimum normalization method is a well-known technology, and the specific process of normalizing the data using the maximum and minimum normalization method will not be repeated.

[0036] According to the confidence level of each smoothed current signal, it can be understood that the confidence level is an evaluation indicator of the accuracy of the error correction coefficient calculated for the smoothed current signal after DC filtering and harmonic filtering. The larger the first filtering residual value, the larger the ratio of the DC component to the average amplitude of the smoothed current signal, that is, the more obvious the DC component residue is, the larger the corresponding comprehensive filtering characteristic value is, and the smaller the confidence level is, indicating that the accuracy of the error correction coefficient calculated based on this smoothed current signal is low. At the same time, if the second filtering residual value is larger, it means that the waveform difference between the smoothed current signal and the standard current calibration signal is greater, that is, the more obvious the harmonic component residue is, the larger the corresponding comprehensive filtering characteristic value is, and the smaller the confidence level is, indicating that the accuracy of the error correction coefficient calculated based on this smoothed current signal is low. Conversely, a smaller first filter residual value means a smaller ratio of the DC component to the average amplitude of the smoothed current signal, meaning the DC component residue is less pronounced. This results in a smaller corresponding integrated filter eigenvalue and a greater confidence level, indicating that the error correction coefficient calculated based on this smoothed current signal is more accurate because the DC filter is more effective. Meanwhile, a smaller second filter residual value means a smaller waveform difference between the smoothed current signal and the standard current calibration signal, meaning the harmonic component residue is less pronounced. This also results in a smaller corresponding integrated filter eigenvalue and a greater confidence level, indicating that the error correction coefficient calculated based on this smoothed current signal is more accurate because the harmonic filter is more effective.

[0037] At this point, this embodiment analyzes the residual DC and harmonic levels in the filtered signal, quantitatively evaluates the quality of each measurement signal, and assigns weights to the calculated error correction coefficients accordingly, effectively eliminating the impact of low-quality data caused by incomplete filtering on the final calibration result, and improving the accuracy of the clamp ammeter's self-calibration.

[0038] Step S3: Obtain the error correction coefficient of each smoothed current signal, and determine the error correction coefficient of the clamp ammeter at the current moment in combination with the confidence level, so as to perform self-correction on the measurement of the clamp ammeter at the current moment.

[0039] After step S2, the confidence level of each smoothed current signal is evaluated. Therefore, further, this embodiment obtains the error correction coefficient of each smoothed current signal and determines the error correction coefficient of the clamp ammeter at the current moment in combination with the confidence level, so as to perform self-calibration on the measurement of the clamp ammeter at the current moment. Specifically, the error correction coefficient is: In the correction module, the smoothed current signals after filtering and the standard current calibration signal are used as the input of the self-calibration system of the clamp ammeter, and the error correction coefficients of the smoothed current signals are output respectively. Among them, the calculation and acquisition method of the error correction coefficients are well-known technologies, and the specific acquisition principles and processes are not repeated here.

[0040] Furthermore, as an implementation manner, in this embodiment, the expression of the error correction coefficient of the clamp ammeter at the current moment is: Where, Indicates the error correction coefficient of the clamp ammeter at the current moment; Indicates the confidence level of the smoothed current signal; Indicates the error correction coefficient of the smoothed current signal; Indicates the number of all smoothed current signals; Represents the normalization function.

[0041] Furthermore, this embodiment uses the result of multiplying the error correction coefficient of the clamp ammeter at the current moment by the current value currently measured by the clamp ammeter as the measurement correction value of the current value at the current moment, thereby completing the measurement self-calibration of the clamp ammeter.

[0042] Thus, this embodiment processes the actual current signal by filtering and analyzing the residual DC and harmonic components to evaluate the signal quality. Based on this quality evaluation, the error correction coefficient is assigned different weights for weighted averaging, effectively filtering out the influence of low-quality data, thereby improving the accuracy of the clamp ammeter self-calibration.

[0043] Based on the same inventive concept as the above-mentioned method, an embodiment of the present application also provides a measurement self-correction system for a clamp ammeter, comprising a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned measurement self-correction methods for a clamp ammeter are implemented.

[0044] It should be noted that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0045] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0046] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A self-calibration method for measuring a clamp ammeter, characterized in that: The method comprises the following steps: During the self-calibration process of the clamp ammeter, a standard current calibration signal within a preset time period before the current moment is obtained, and the actual mixed current signal generated by the transformer in the clamp ammeter is obtained multiple times; Each actual mixed current signal after filtering is recorded as a smoothed current signal, and the frequency distribution value of each smoothed current signal is determined by analyzing the amplitude distribution of each smoothed current signal at all frequencies in the frequency domain; the difference between the amplitude of each smoothed current signal at zero frequency in the frequency domain and the frequency distribution value is compared to determine the first filtering residual value of each smoothed current signal; Determining a second filtered residual value of each smoothed current signal by analyzing the similarity between each smoothed current signal and a standard current calibration signal, and determining a comprehensive filtered residual value of each smoothed current signal in combination with the first filtered residual value to determine a confidence level of each smoothed current signal; The error correction coefficient of each smoothed current signal is obtained, and combined with the confidence level, the error correction coefficient of the clamp ammeter at the current moment is determined to perform self-correction on the measurement of the clamp ammeter at the current moment.

2. The self-calibration method for a clamp ammeter according to claim 1, wherein: The actual mixed current signals after filtering are recorded as smoothed current signals, specifically: Each actual mixed current signal is used as the input of the DC filter and the harmonic filter in turn, and the output signal is recorded as the smoothed current signal.

3. The self-calibration method for a clamp ammeter according to claim 1, wherein: The frequency distribution value of each smooth current signal is the average value of the amplitude of each smooth current signal at all frequencies in the frequency domain.

4. The self-calibration method for a clamp ammeter according to claim 1, wherein: The first filtering residual value of each smoothed current signal is a ratio of the amplitude of each smoothed current signal at zero frequency in the frequency domain to the frequency distribution value.

5. The self-calibration method for a clamp ammeter according to claim 1, wherein: The second filtering residual value of each smoothed current signal is the inverse of the similarity between each smoothed current signal and the standard current calibration signal.

6. The self-calibration method for a clamp ammeter according to claim 1, wherein: The comprehensive filtering residual value of each smoothed current signal is the average of the normalized value of the first filtering residual value and the normalized value of the second filtering residual value of each smoothed current signal.

7. The self-calibration method for a clamp ammeter according to claim 1, wherein: The confidence level of each smoothed current signal is the inverse of a comprehensive filtering residual value of each smoothed current signal.

8. The self-calibration method for a clamp ammeter according to claim 1, wherein: The expression of the error correction coefficient of the clamp ammeter at the current moment is: Where, Indicates the error correction coefficient of the clamp ammeter at the current moment; Indicates the confidence level of the smoothed current signal; Indicates the error correction coefficient of the smoothed current signal; Indicates the number of all smoothed current signals; Represents the normalization function.

9. The self-calibration method for a clamp ammeter according to claim 1, wherein: The self-calibration of the clamp ammeter measurement at the current moment includes: The result of multiplying the error correction coefficient of the clamp ammeter at the current moment by the current value measured by the clamp ammeter at the current moment is used as the measurement correction value of the current value at the current moment.

10. A self-calibration system for a clamp ammeter, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein: When the processor executes the computer program, the processor implements the steps of the self-calibration method for measuring a clamp ammeter as described in any one of claims 1 to 9.

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