A method for extracting time difference of FMCW signal under attenuation and distortion condition

Abstract

The present application belongs to the technical field of power distribution and measurement and testing, and specifically relates to a FMCW signal time difference extraction method under attenuation and distortion conditions. The present application belongs to a FMCW signal time difference extraction method used in live positioning of local defects of power distribution cables. First, the FMCW signal output by a signal source is used as a matched filter template signal. Then, the signal output by a mixer to an oscilloscope is convolved with the template signal to obtain a signal-to-noise ratio curve. Since the signal in the mixer includes both the incident signal output by the signal source and the reflected signal of the cable, the signal-to-noise ratio curve obtained by convolution will have two peaks, representing the incident signal and the reflected signal, respectively. Finally, the time difference of the signal can be obtained according to the time at which the two peaks of the signal ratio curve are located, thereby realizing positioning of the defect. The FMCW signal time difference can be extracted under attenuation and distortion conditions. The time difference extraction is calculated based on the peak value, and the result is more accurate.

Description

Technical Field

[0001] This invention belongs to the field of power distribution and measurement testing technology, specifically a method for extracting the time difference of FMCW signals under attenuation and distortion conditions. It is a method for extracting the time difference of FMCW signals used in live-line location of local defects in power distribution cables. Background Technology

[0002] Currently, distribution cables are numerous and have become a core component of modern power distribution networks. Localized aging, moisture absorption, and insulation defects such as damaged outer sheaths have become major causes of power system failures, seriously affecting the safe operation of the power grid. Current detection methods for these defects are mainly divided into Time Domain Reflectometry (TDR) and Frequency Domain Reflectometry (FDR). FDR technology, represented by broadband impedance spectroscopy, has made significant progress due to its high sensitivity. A cable local defect location method based on Frequency Modulated Continuous Wave (FMCW) has been proposed within this branch. Due to its higher defect detection sensitivity and detection distance compared to BIS, it has broad application prospects in the cable field. Using capacitive coupling, FMCW-based cable local defect location can be performed on live distribution cables, greatly improving the method's applicability. However, due to the severe attenuation and distortion of the reflected signal caused by injecting the FMCW signal through capacitive coupling, it is submerged in background noise, making it impossible to accurately extract the time difference between the injected and reflected signals, severely affecting the accuracy of cable local defect location. Therefore, a method for extracting the time difference of FMCW signals under attenuation and distortion conditions is proposed. Summary of the Invention

[0003] The purpose of this invention is to provide a method for extracting the time difference of FMCW signals under attenuation and distortion conditions to address the above-mentioned shortcomings, thereby solving the problem of energized localization of local defects in FMCW cables. The method uses a template of the incident signal as a matched filter, and maximizes the signal-to-noise ratio by convolving the received signal with a known signal template, thereby extracting the reflected signal and obtaining the signal time difference to achieve energized localization of the defect.

[0004] The technical solution of this invention is: a method for extracting the time difference of an FMCW signal under attenuation and distortion conditions, characterized in that, firstly, the FMCW signal output from the signal source is used as the template signal of the matched filter; then, the signal output from the mixer to the oscilloscope is convolved with the template signal to obtain a signal-to-noise ratio (SNR) curve. Since the signal in the mixer includes both the incident signal output from the signal source and the reflected signal from the cable, the SNR curve obtained by convolution will have two peaks, representing the incident signal and the reflected signal, respectively; finally, the time difference of the signal can be obtained based on the time of the two peaks of the SNR curve, thereby realizing the location of the defect.

[0005] The FMCW signal has an amplitude of 1V and a frequency of 1μHz-1MHz.

[0006] This invention offers the following advantages: 1. It enables the extraction of time difference in FMCW signals under conditions of attenuation and distortion. When injecting FMCW signals using capacitive coupling, the attenuation and distortion of the reflected signal are severe, becoming submerged in background noise. This makes it impossible to accurately extract the time difference between the injected and reflected signals, hindering localization. However, the method proposed in this invention extracts the time difference by using a signal-to-noise ratio (SNR) curve obtained through convolution, effectively avoiding the impact of attenuation and distortion of the reflected signal. 2. Time difference extraction is calculated based on peak values, resulting in more accurate results. FMCW signals are slowly varying signals, and direct extraction of the time difference is easily affected by background noise. The SNR curve obtained in this invention converts the incident and reflection times of the FMCW signal into peak values. Calculating the time difference using these peak values ​​is unaffected by background noise, resulting in higher accuracy.

[0007] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0008] Figure 1 A schematic diagram of the live detection method for local defects in FMCW cables according to the present invention is shown.

[0009] Figure 2 The diagram shows the injected signal, reflected signal, and mixed signal according to the present invention.

[0010] Figure 3 The SNR curve calculated according to one embodiment of the method is shown.

[0011] In the diagram, signal source 1, power divider 2, circulator 3, ring coupling capacitor 4, mixer 5, oscilloscope 6, computer 7, cable 8, reference signal 9, incident signal S1, reflected signal S2, and mixed signal S3. Detailed Implementation

[0012] See Figure 1 , 2 3. A method for extracting the time difference of FMCW signals under attenuation and distortion conditions. The working principle is as follows: the template of the input FMCW signal is used as a matched filter. By convolving the received reflected signal with the known signal template, the signal-to-noise ratio is maximized, thereby extracting the reflected signal S2. Based on this, the signal time difference is obtained to realize the charged location of the defect.

[0013] Specifically, it is a method for extracting the time difference of FMCW signals under attenuation and distortion conditions. First, the time difference of FMCW signals is extracted. Figure 1 The FMCW signal output from signal source 1 is used as the template signal for the matched filter. Then, for... Figure 1The signal output from mixer 5 to oscilloscope 6 is convolved with the template signal to obtain the signal-to-noise ratio (SNR) curve. Since the signal in mixer 5 includes both the incident signal S1 from signal source 1 and the reflected signal S2 from the cable, the convolved SNR curve will have two peaks, representing the incident signal S1 and the reflected signal S2, respectively. Finally, the time difference of the signal can be obtained based on the timing of the two peaks in the SNR curve, thus enabling defect location.

[0014] Figure 1 This diagram illustrates a method for detecting localized defects in FMCW cables while they are still charged. The method includes: a signal source 1, a power divider 2, a circulator 3, a ring coupling capacitor 4, a mixer 5, an oscilloscope 6, and a computer 7. The sequence is as follows: Signal source 1 → Power divider 2 → Circulator 3 → Mixer 5 → Oscilloscope 6 → Computer 7. Alternatively, the sequence could be: Signal source 1 → Power divider 2 → Circulator 3 → Ring coupling capacitor 4 → Cable 8 → Circulator 3 → Mixer 5 → Oscilloscope 6 → Computer 7. Finally, the sequence could be: Power divider 2 → Mixer 5, where: Signal source 1 is used to generate an FMCW signal, preferably with an amplitude of 1V and a frequency of 1μHz-1MHz.

[0015] The power divider 2 is used to divide the FMCW signal generated by the signal source 1 into two parts: the incident signal S1 and the reference signal 9. Preferably, the power distribution ratio between the incident signal S1 and the reference signal 9 is 7:3.

[0016] Circulator 3 is used to transmit the incident signal S1 to the ring coupling capacitor 4 and receive the reflected signal S2 reflected back from the ring coupling capacitor 4.

[0017] The ring coupling capacitor 4 is used to inject FMCW into the cable 8 and receive the reflected signal S2.

[0018] Mixer 5 is used to mix the reference signal 9 and the reflected signal S2.

[0019] The mixed signal S3 output from oscilloscope 6 and mixer 5 is convolved with the template signal to obtain the signal-to-noise ratio curve.

[0020] Figure 1 , 2 Figure 3 shows an example of an incident signal S1, a reflected signal S2, and a mixed signal S3 output by mixer 5. It can be seen that due to signal attenuation and distortion, the incident and emitted FMCW signals are completely unrecognizable, and the time difference between the signals cannot be extracted.

[0021] Calculate the matched filter output according to equation (1): 1) Where N is the length of the signal sampling point, and preferably the number of sampling points corresponding to 1ms time is selected.

[0022] Calculate the signal-to-noise ratio (SNR) according to formula (2): 2) Figure 3 The SNR curve calculated using the above method is shown, clearly displaying two peaks, corresponding to the times of the incident signal S1 and the reflected signal S2, respectively. The time difference between them is the time difference of the FMCW signal.

[0023] The above description is merely a specific embodiment of the present invention, and the various examples do not constitute a limitation on the substantive content of the present invention.

Claims

1. A method for extracting the time difference of an FMCW signal under attenuation and distortion conditions, characterized in that, First, the FMCW signal output from signal source 1 is used as the template signal for the matched filter. Then, the signal output from mixer 5 to oscilloscope 6 is convolved with the template signal to obtain the signal-to-noise ratio (SNR) curve. Since the signal in mixer 5 includes the incident signal S1 output from signal source 1 and the reflected signal S2 from cable 8, the SNR curve obtained by convolution will have two peaks, representing the incident signal S1 and the reflected signal S2, respectively. Finally, the time difference of the signal can be obtained based on the time of the two peaks of the signal ratio curve, thereby realizing the location of the defect.

2. The method for extracting the time difference of an FMCW signal under attenuation and distortion conditions according to claim 1, characterized in that... The FMCW signal has an amplitude of 1V and a frequency of 1μHz-1MHz.

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