Grounding resistance measurement method based on zero-point synchronous coding excitation

Abstract

The application discloses a grounding resistance measurement method based on zero-point synchronous coding excitation, which comprises generating a coding excitation signal at a preset measurement frequency, applying a measurement excitation to a measured grounding branch by a pressurizing clamp, collecting a response signal by the pressurizing clamp, performing correlation extraction corresponding to a coding sequence on the response signal, obtaining a measurement response amplitude and calculating a grounding resistance measurement value. The coding excitation adopts a coding switching mode synchronized with the zero point of the measurement pressurizing signal, so that the chip state updating occurs at the zero-crossing position of the measurement pressurizing signal, the switching transient state is reduced, and the pressurizing implementation is improved. One chip corresponds to each half carrier cycle, and a data window with at least one complete coding length is used for correlation extraction. Background noise spectrum can be collected before measurement or a coding sequence can be selected according to a preset scene category, so that the measurement accuracy and stability in a strong interference environment are improved. The application is suitable for ordinary single-branch double-clamp grounding resistance measurement, has the advantages of strong anti-interference ability, convenient digital implementation and high measurement precision.

Description

Technical Field

[0001] This invention relates to the field of grounding parameter measurement technology, and specifically to a grounding resistance measurement method based on zero-point synchronous coding excitation. Background Technology

[0002] The dual-clamp method for measuring grounding resistance typically involves applying a specific frequency AC measurement excitation to the grounded branch under test using a pressure clamp, acquiring the response signal through the measuring clamp, and then calculating the grounding resistance based on the relationship between the excitation and the response. This method has advantages such as requiring no auxiliary grounding electrodes and being convenient for field use, and is therefore widely used in the rapid detection of grounding parameters.

[0003] However, in practical applications, the response signals acquired by the measuring clamp are often superimposed with power frequency interference, harmonic interference, random transient disturbances, and environmental noise. Traditional dual-clamp measurements typically employ a single-frequency sinusoidal excitation with a fixed frequency and amplitude, estimating the response amplitude through single-frequency extraction or synchronous demodulation. Examples include the method for measuring the grounding resistance of transmission towers based on distributed sensing of ground potential field disclosed in CN121703509A, and the method and device for measuring the grounding resistance of multi-grounding lead towers disclosed in CN118259080A. While these methods are simple to implement, in environments with strong interference, non-stationary disturbances near the target measurement frequency can directly affect the extraction results, reducing the stability of the measured values.

[0004] Furthermore, further improving the signal-to-noise ratio by extending the averaging time or increasing the number of repeated measurements would increase the measurement time, which is not conducive to rapid on-site detection. Therefore, a dual-clamp measurement system that can both improve the distinguishability of the target response and be easy to implement with a digital controller is needed to improve the measurement accuracy and stability in complex noisy environments. Summary of the Invention

[0005] 1. The technical problem to be solved:

[0006] To address the aforementioned technical problems, this invention provides a grounding resistance measurement method based on zero-point synchronization coded excitation. By introducing coded modulation on the measurement frequency carrier and performing correlation extraction corresponding to the coded sequence at the response end, the anti-interference capability and detectability of the target response are enhanced. At the same time, zero-point synchronization switching reduces the transient impact of coded excitation on the drive stage and the pressure clamping magnetic circuit, making the system more suitable for implementation by a digital controller.

[0007] 2. Technical Solution:

[0008] A grounding resistance measurement method based on zero-point synchronization coding excitation, characterized in that it includes:

[0009] Step 1: Set up a pressure clamp and a measuring clamp in the grounding branch under test to establish a dual-clamp grounding resistance measurement system;

[0010] Step 2: Inject an coded excitation signal into the branch of resistance under test through a pressure clamp. The coded excitation signal is generated at a preset measurement frequency fm. The measuring clamp simultaneously measures the response signal output by the branch under test.

[0011] Step 3: Based on the preset encoding sequence, perform correlation extraction on the response signal to obtain the measured response amplitude, and calculate the grounding resistance measurement value based on the measured response amplitude and the encoded excitation signal.

[0012] Furthermore, the dual-clamp grounding resistance measurement system includes dual-clamp units deployed on the grounding branch under test; each dual-clamp unit includes a pressure clamp, a measuring clamp, a drive unit, a sampling unit, and a digital control unit; the pressure clamp is used to apply an coded excitation signal to the grounding branch under test; the measuring clamp is used to acquire the response signal of the branch under test; the drive unit is used to generate an coded excitation signal based on a reference signal output by the digital controller; the sampling unit is used to synchronously sample the output of the measuring clamp; the digital control unit is used to generate the coded excitation signal, perform sampling synchronization control, extract the response signal, and calculate the grounding resistance measurement value.

[0013] Furthermore, in step two, the encoded excitation signal is at a preset measurement frequency f. m The AC measurement excitation signal is formed by encoding and modulation on the carrier wave, and the state update of the encoded sequence is synchronized with the zero point of the carrier wave; each half period of the carrier wave corresponds to one chip of the encoded sequence, the encoded sequence b[m] is a bipolar code sequence, and b[m]∈{+1, -1}; the encoded excitation signal u(t) is:

[0014] (1);

[0015] Where U0 is the preset measurement frequency f of the injection. m The amplitude of the carrier voltage signal; T m =1 / f m , is the fundamental period for measurement; b[m] is the encoding sequence of the m-th chip.

[0016] Furthermore, in step two, when the measuring clamp synchronously measures the response signal output by the branch under test, the digital control unit generates a sampling and excitation update sequence based on a unified time base, so that each measurement cycle contains a fixed number of N sampling / update points, and satisfies:

[0017] (2);

[0018] Among them, f sf is the sampling frequency. u The digital control unit for the corresponding branch controls the frequency.

[0019] Further, in step three, when performing correlation extraction on the response signal, correlation extraction is performed based on a data window of at least one complete coding length to obtain the correlation output amplitude of the corresponding coding sequence; let the coding length be L, each chip correspond to a response sample z[m], and the correlation output amplitude A C As shown in the following formula:

[0020] (3)

[0021] According to the relevant output amplitude A c Then, the measured value of the grounding resistance is calculated.

[0022] Furthermore, each half-cycle of the fundamental frequency measurement corresponds to one coded chip. Let the length of the coded sequence be L, and the fundamental frequency measurement be f. m Then, the duration T of a single measurement corresponding to a complete encoded sequence mea satisfy:

[0023] (4);

[0024] And according to the preset measurement duration T set Choose the length L of the encoded sequence such that:

[0025] (5).

[0026] Furthermore, the digital control unit collects background noise data before measurement and selects the sequence with the best autocorrelation from the candidate coding sequences based on the background noise spectrum as the coding sequence for this measurement.

[0027] Furthermore, the digital control unit stores a set of default encoding sequences corresponding to different scene categories, and loads the corresponding encoding sequence as the initial encoding scheme for the measurement stimulus according to the scene category selected by the user.

[0028] 3. Beneficial effects:

[0029] (1) The present invention provides a grounding resistance measurement method based on zero-point synchronous coding excitation. By coding excitation and correlation extraction, the traditional single-frequency measurement is extended to coding matching detection, which is beneficial to suppressing the influence of power frequency, harmonics and random noise on the measurement results.

[0030] (2) The present invention provides a grounding resistance measurement method based on zero-point synchronous coding excitation, which updates the chip state through carrier zero-point synchronous update, so that coding switching occurs at the zero-crossing position of the waveform, reducing drive stage overshoot and magnetic circuit transients, and improving the voltage implementation.

[0031] (3) The grounding resistance measurement method based on zero-point synchronous coding excitation provided by the present invention can be implemented based on a unified time base for sampling, excitation update and correlation extraction, which is convenient for MCU platform engineering implementation; under the condition of one chip per half cycle and preferred code length of 127, the complete correlation extraction time is still within the acceptable range of engineering; the code can be selected by combining background noise spectrum or default code table of scene category to improve the measurement accuracy and stability under different scenarios. Attached Figure Description

[0032] Figure 1 This is a structural block diagram of the dual-clamp grounding resistance measurement system used in this invention to perform the measurement.

[0033] Figure 2 This is a schematic diagram of the zero-point synchronization encoding and pressurization waveform in this invention;

[0034] Figure 3 This is a typical raw response waveform diagram of a measuring clamp;

[0035] Figure 4 This is the output after extracting the relevant information from the full code length window;

[0036] Figure 5 This is a flowchart of the coding excitation grounding resistance measurement method of the present invention. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings.

[0038] As attached Figure 1 To be continued Figure 5 As shown, the grounding resistance measurement method based on zero-point synchronization coding excitation is characterized by comprising:

[0039] Step 1: Set up a pressure clamp and a measuring clamp in the grounding branch under test to establish a dual-clamp grounding resistance measurement system;

[0040] Step 2: Inject an coded excitation signal into the branch of resistance under test through a pressure clamp. The coded excitation signal is generated at a preset measurement frequency fm. The measuring clamp simultaneously measures the response signal output by the branch under test.

[0041] Step 3: Based on the preset encoding sequence, perform correlation extraction on the response signal to obtain the measured response amplitude, and calculate the grounding resistance measurement value based on the measured response amplitude and the encoded excitation signal.

[0042] Furthermore, the dual-clamp grounding resistance measurement system includes dual-clamp units deployed on the grounding branch under test; each dual-clamp unit includes a pressure clamp, a measuring clamp, a drive unit, a sampling unit, and a digital control unit; the pressure clamp is used to apply an coded excitation signal to the grounding branch under test; the measuring clamp is used to acquire the response signal of the branch under test; the drive unit is used to generate an coded excitation signal based on a reference signal output by the digital controller; the sampling unit is used to synchronously sample the output of the measuring clamp; the digital control unit is used to generate the coded excitation signal, perform sampling synchronization control, extract the response signal, and calculate the grounding resistance measurement value.

[0043] Furthermore, in step two, the encoded excitation signal is at a preset measurement frequency f. m The AC measurement excitation signal is formed by encoding and modulation on the carrier wave, and the state update of the encoded sequence is synchronized with the zero point of the carrier wave; each half period of the carrier wave corresponds to one chip of the encoded sequence, the encoded sequence b[m] is a bipolar code sequence, and b[m]∈{+1, -1}; the encoded excitation signal u(t) is:

[0044] (1);

[0045] Where U0 is the preset measurement frequency f of the injection. m The amplitude of the carrier voltage signal; T m =1 / f m , is the fundamental period for measurement; b[m] is the encoding sequence of the m-th chip.

[0046] Furthermore, in step two, when the measuring clamp synchronously measures the response signal output by the branch under test, the digital control unit generates a sampling and excitation update sequence based on a unified time base, so that each measurement cycle contains a fixed number of N sampling / update points, and satisfies:

[0047] (2);

[0048] Among them, f s f is the sampling frequency. u The digital control unit for the corresponding branch controls the frequency.

[0049] Further, in step three, when performing correlation extraction on the response signal, correlation extraction is performed based on a data window of at least one complete coding length to obtain the correlation output amplitude of the corresponding coding sequence; let the coding length be L, each chip correspond to a response sample z[m], and the correlation output amplitude A C As shown in the following formula:

[0050] (3)

[0051] According to the relevant output amplitude A c Then, the measured value of the grounding resistance is calculated.

[0052] Furthermore, each half-cycle of the fundamental frequency measurement corresponds to one coded chip. Let the length of the coded sequence be L, and the fundamental frequency measurement be f. m Then, the duration T of a single measurement corresponding to a complete encoded sequence mea satisfy:

[0053] (4);

[0054] The length L of the encoded sequence is based on a preset measurement duration T. set Choose such that:

[0055] (5).

[0056] Furthermore, the digital control unit collects background noise data before measurement and selects the sequence with the best autocorrelation from the candidate coding sequences based on the background noise spectrum as the coding sequence for this measurement.

[0057] Furthermore, the digital control unit stores a set of default encoding sequences corresponding to different scene categories, and loads the corresponding encoding sequence as the initial encoding scheme for the measurement stimulus according to the scene category selected by the user.

[0058] Example:

[0059] As attached Figure 1 As shown, the dual-clamp grounding resistance measurement system of the present invention includes: a pressure clamp for applying coded measurement excitation to the grounding branch under test; a measurement clamp for acquiring the response signal of the branch under test; a drive unit for generating the actual injection waveform according to the reference signal output by the digital controller; a sampling unit for synchronously sampling the output of the measurement clamp; and a digital control unit for generating coded excitation, executing sampling synchronization control, performing correlation extraction, and calculating the grounding resistance measurement value.

[0060] In this invention, the digital control unit uses a unified time base to generate sampling and injection update sequences, such that:

[0061] Each measurement cycle contains a fixed number of N sampling / update points, and satisfies:

[0062] (2)

[0063] Among them, f s f is the sampling frequency. u The local digital control unit controls the frequency, f m To measure the frequency, f must satisfym =1 / T m N can be taken from 32 to 128 to balance the complexity of digital implementation and waveform resolution.

[0064] In this invention, each half-cycle of the fundamental frequency corresponds to one chip, the encoded sequence b[m] is a bipolar code sequence, b[m]∈{+1, -1}, and the encoded excitation signal u(t) satisfies:

[0065] (1)

[0066] In this embodiment, multiple zero-point synchronization encoding and pressurization waveforms are pre-set. Then, based on the background noise spectrum collected during the embodiment, the sequence with the best autocorrelation is selected from the candidate encoding sequences for this measurement, thus obtaining the encoding sequence as shown in the attached figure. Figure 2 The zero-point synchronization encoded voltage waveform shown shows that, since the chip state is updated at each carrier zero-crossing point and the instantaneous value of the carrier at that position is zero, the switching of adjacent chips does not cause significant amplitude abrupt changes. This is beneficial for reducing the switching transients of the drive unit, reducing additional high-frequency components, and improving the feasibility of voltage application. Because the zero-point synchronization encoded voltage waveform needs to be distinguishable from other signals (background noise) in the natural environment (without applied excitation), that is, only the response obtained from the injected voltage signal exhibits this sequence pattern, while the response waveform to background noise does not exhibit this pattern, thus achieving the effect of shielding background noise, it is necessary to select the sequence with the optimal autocorrelation from the candidate encoding sequences as the encoding sequence for this measurement.

[0067] Based on the noise immunity requirements and measurement duration, it is recommended that the encoding sequence length be 100-200 when the MCU is running at 10kHz.

[0068] The length L of the encoded sequence is based on the preset measurement duration T. set Choose such that:

[0069] (5);

[0070] Such as the preset measurement duration T set Select 0.1s, for example, when setting the measurement frequency f. m When the frequency is 800Hz, substituting into the above formula, we can obtain that L should satisfy ≤160. In this embodiment, the encoding length is selected as L=127.

[0071] At the measurement frequency f m Nearby, the signal gain of the entire "pressure clamp—tested branch—measuring clamp—conditioning sampling link" is equivalent to a linear steady channel, which is in f m The amplitude attenuation coefficient K can be used to determine the value. r Phase lag Characterization; then the measured clamp response y(t) can be approximately expressed as:

[0072] (6)

[0073] Where n(t) represents power frequency interference, harmonic components, random noise, and other background disturbances; this formula shows that, under ideal linear conditions, the measurement clamp response maintains the symbol modulation characteristics consistent with the coded sequence, only superimposed with amplitude attenuation, phase lag, and noise interference. The original response waveform of the measurement clamp in this embodiment is shown in the attached figure. Figure 3 As shown.

[0074] Let the duration of each chip be T. c =T m / 2, N is collected within each chip. c There are 1 sampling point. For the m-th chip, perform synchronous extraction on its response signal to obtain the single chip response sample z[m]:

[0075] (7)

[0076] Among them, y m (t) represents the discrete response sample corresponding to the m-th chip; substituting the aforementioned approximate response model formula (6) into it, we can obtain:

[0077] (8)

[0078] Here, h[m] represents the equivalent noise term after synchronous extraction. Therefore, it can be seen that the single-chip response sample z[m] still maintains a consistent relationship with the encoded sequence b[m].

[0079] To improve anti-interference capability, correlation extraction is preferably performed based on a data window of at least one full coding length. Let the coding length be L, then the correlation output amplitude within a full coding window is:

[0080] (3)

[0081] In this embodiment, the relevant operation result R[k] is performed within a full code length window of length L, using the encoded sequence b[m] as a reference:

[0082] (9)

[0083] Where k is the current chip index during sliding correlation calculation, representing the sliding position of the correlation window along the chip sequence. By calculating the correlation output using a sliding window approach, we can obtain... Figure 4 The relevant output curves are shown below.

[0084] Depend on Figure 4As can be seen, when the correlation window is perfectly aligned with the coded sequence (i.e., k is an integer multiple of L), a significant peak appears in the correlation output amplitude. However, at other misaligned positions, the positive and negative code chips in the coded sequence cancel each other out during the correlation operation, resulting in only low-amplitude random fluctuations in the correlation output. This characteristic indicates that the measurement signal under coded excitation can be effectively extracted from noise and power frequency interference through correlation processing, resulting in a significant peak in the correlation output, thereby improving the signal-to-noise ratio and identifiability of the measurement signal. By detecting the amplitude of the correlation output peak, an effective estimate of the measurement response can be obtained and further used to calculate parameters such as grounding resistance. In practical applications, the current measurement result is considered valid only when the correlation output continuously meets the preset stability criterion.

[0085] Substituting the approximation of the single-chip response sample into the equation, we get:

[0086] (10);

[0087] This formula shows that the effective signal term accumulates linearly with the coding length L, while the noise term that is not related to the coding sequence is suppressed during the correlation process. Therefore, the full code length correlation extraction has a higher signal-to-noise ratio and stronger anti-interference ability.

[0088] It should be understood that, in addition to the full code length window, sliding windows or overlapping windows can also be used to update the relevant results; however, the final measurement is preferably given based on at least one full code length window.

[0089] Related output amplitude A c It can be combined with the applied pressure reference amplitude, measurement frequency, and system calibration parameters to calculate the measured value of grounding resistance. It can be summarized as follows: :

[0090] (11);

[0091] Where F() is the mapping function established based on the system calibration relationship. F() can be a linear calibration relationship, or it can be a lookup table, a piecewise linear approximation, or other conversion relationship obtained through calibration. (Appendix) Figure 5 This is a schematic diagram of the single-chip response extraction and full code length correlation processing flow of the present invention.

[0092] like Figure 5As shown, the coding-excited grounding resistance measurement method of the present invention includes the following steps: S1: Initialize the measurement parameters, set the measurement signal frequency, sampling frequency, and coding sequence length; S2: Determine the coding sequence. A suitable coding sequence for the current environment can be selected by collecting background noise and performing spectrum analysis before measurement, or a default coding sequence can be loaded according to a preset application scenario; S3: Generate a zero-point synchronization coding excitation signal based on the selected coding sequence and apply it to the grounding conductor under test using a pressure clamp; S4: Collect the response signal in the grounding conductor using a measurement clamp; S5: Construct a synchronization reference signal based on the measurement signal frequency, and perform chip-by-chip integration on the response signal to obtain the chip response sequence z[m]; S6: Perform correlation calculations within the complete code length window to obtain the correlation output amplitude A. c S7: Detect relevant output peak values ​​and extract effective response amplitude; S8: Calculate the grounding resistance measurement value based on the injected excitation signal and response amplitude and output the measurement result.

[0093] In a specific embodiment of the present invention, the local digital control unit collects background noise data and obtains the background noise spectrum before the formal measurement, and selects a coding scheme suitable for the current noise environment from the candidate coding sequence set. Furthermore, the system pre-sets default coding sequence sets corresponding to different scenario categories, such as towers of different voltage levels and different types of grounding grids. Users can select the corresponding coding sequence as the initial coding scheme for the measurement excitation according to the application scenario. Before the measurement operation, a default code table can be loaded according to the scenario category, and then a secondary optimization selection can be performed based on the background noise snapshot.

[0094] This invention extends traditional single-frequency measurement to coded correlation detection measurement by combining fixed-frequency dual-clamp measurement with a zero-point synchronization coding system. Compared with methods that only use single-frequency sinusoidal injection and single-point amplitude extraction, this invention can significantly improve the detectability of the target response under strong power frequency, harmonic, and non-stationary interference conditions. Through zero-point synchronization switching, the coding state update occurs at the carrier zero-crossing position, making digital drive smoother and more stable. Through complete code length correlation extraction, the signal-to-noise ratio of response extraction is further improved. Combined with pre-measurement code selection and scenario code selection strategies, the measurement adaptability and stability under different field conditions can be enhanced.

[0095] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A grounding resistance measurement method based on zero-point synchronous coding excitation, characterized in that: include: Step 1: Set up a pressure clamp and a measuring clamp in the grounding branch under test to establish a dual-clamp grounding resistance measurement system; Step 2: Inject an coded excitation signal into the branch of the resistor under test through a pressure clamp. The coded excitation signal is at a preset measurement frequency f. m The measurement clamp simultaneously measures the response signal output by the branch under test. Step 3: Based on the preset encoding sequence, perform correlation extraction on the response signal to obtain the measured response amplitude, and calculate the grounding resistance measurement value based on the measured response amplitude and the encoded excitation signal.

2. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 1, characterized in that: The dual-clamp grounding resistance measurement system includes dual-clamp units deployed on the grounding branch under test; each dual-clamp unit includes a pressure clamp, a measuring clamp, a drive unit, a sampling unit, and a digital control unit; the pressure clamp is used to apply an coded excitation signal to the grounding branch under test; the measuring clamp is used to acquire the response signal of the branch under test; the drive unit is used to generate an coded excitation signal based on a reference signal output by the digital controller; the sampling unit is used to synchronously sample the output of the measuring clamp. The digital control unit is used to generate coded excitation signals, perform sampling synchronization control, extract response signals, and calculate grounding resistance measurements.

3. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 1, characterized in that: In step two, the encoded excitation signal is at a preset measurement frequency f. m The AC measurement excitation signal is formed by encoding and modulation on the carrier wave, and the state update of the encoded sequence is synchronized with the zero point of the carrier wave; each half period of the carrier wave corresponds to one chip of the encoded sequence, the encoded sequence b[m] is a bipolar code sequence, and b[m]∈{+1, -1}; the encoded excitation signal u(t) is: （1）； Where U0 is the preset measurement frequency f of the injection. m The amplitude of the carrier voltage signal; T m =1 / f m , is the fundamental period for measurement; b[m] is the encoding sequence of the m-th chip.

4. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 3, characterized in that: In step two, when the measuring clamp synchronously measures the response signal output by the branch under test, the digital control unit generates a sampling and excitation update sequence based on a unified time base, so that each measurement cycle contains a fixed number of N sampling / update points, and satisfies: （2）； Among them, f s f is the sampling frequency. u The digital control unit for the corresponding branch controls the frequency.

5. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 4, characterized in that: In step three, when performing correlation extraction on the response signal, correlation extraction is performed based on a data window of at least one complete code length to obtain the correlation output amplitude of the corresponding coded sequence; let the code length be L, each chip correspond to a response sample z[m], and the correlation output amplitude A C As shown in the following formula: （3）； According to the relevant output amplitude A c Then, the measured value of the grounding resistance is calculated.

6. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 4, characterized in that: Each half-cycle of the fundamental frequency measurement corresponds to one coded chip. Let the length of the coded sequence be L, and the fundamental frequency measurement be f. m Then, the duration T of a single measurement corresponding to a complete encoded sequence mea satisfy: （4）； The length L of the encoded sequence is based on a preset measurement duration T. set Choose such that: （5）。 7. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 1, characterized in that: Before measurement, the digital control unit collects background noise data and selects the sequence with the best autocorrelation from the candidate coding sequences based on the background noise spectrum as the coding sequence for this measurement.

8. The grounding resistance measurement method based on zero-point synchronization coding excitation according to claim 1, characterized in that: The digital control unit stores a set of default encoding sequences corresponding to different scene categories, and loads the corresponding encoding sequence as the initial encoding scheme for the measurement stimulus according to the scene category selected by the user.

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