A method for online monitoring and fault location for complex cable systems

Abstract

The application discloses a kind of online monitoring and fault location methods for complex cable system, including S1.Signal source generates the ZC sequence signal of length N, as cable test test signal, is transmitted to test unit and time synchronization unit respectively;S2.test unit receives the test signal from signal source, and utilizes the test signal to test the cable to be measured, obtains the required reflected signal;S3.based on the reflected signal obtained, line fixed reflection calibration is carried out, and the signal obtained by reflection calibration is transmitted to time synchronization unit;S4.based on the signal after reflection calibration and the test signal generated by signal source, the time delay value of test process is determined, and is transmitted to test result unit;S5.cable test result unit receives the time delay estimation value from time delay estimation unit, and calculates the distance of fault location.The application reduces the interference of non-effective signal in environment, and improves signal-to-noise ratio.

Description

Technical Field

[0001] This invention relates to circuit monitoring and fault location, and in particular to an online monitoring and fault location method for complex cable systems. Background Technology

[0002] Traditional cable testing methods for online detection of intermittent cable faults mainly include the following three approaches: 1. Noise reflection method: This method utilizes the time-domain autocorrelation properties of the effective transmission signal or a wide-bandgap noise signal in the cable during normal operation to determine the online location of the cable fault; 2. Carrier wave method: The basic principle is to inject a modulated carrier signal into the cable under test, and at the receiving end, collect and demodulate the carrier wave returned from the fault point to recover the original baseband signal. Fault location is achieved by detecting the bit error rate generated during baseband signal transmission and reflection; 3. Spread spectrum time-domain reflection method: The main idea is to generate a PN sequence to modulate a cosine wave with a carrier wave, forming an incident signal which is then injected into the cable under test. The delayed reference signal and the collected reflected signal are sent to a time-domain correlator to obtain the signal delay time, thereby determining the fault location of the cable. The type of cable fault is then determined based on the polarity of the peak point of the correlation function.

[0003] In the noise reflection method, the time-domain autocorrelation property of the effective transmission signal or a wide-bandgap noise signal in the cable is used to complete the online fault location of the cable. The advantage of this method is that it does not require injecting an additional test signal into the cable under test. However, this makes the incident signal uncontrollable, which is not practical. The carrier wave testing method injects a modulated carrier signal into the cable under test, but this method still has many difficulties and the results are not satisfactory. The spread spectrum time-domain reflection method distorts the reflected signal collected at the measuring end due to losses caused by the medium and resistance, mainly manifested as reduced amplitude and increased pulse width. After time-domain correlation with the original test signal, the peak point is weak, making it difficult to accurately identify the location and type of cable fault. In addition, large attenuation of the reflected signal at the fault point or a low signal-to-noise ratio will lead to insufficient fault location accuracy. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an online monitoring and fault location method for complex cable systems. It utilizes time-domain self-interference channel estimation to perform fixed reflection calibration of the line, thereby reducing interference from ineffective signals in the environment and improving the signal-to-noise ratio.

[0005] The objective of this invention is achieved through the following technical solution: A method for online monitoring and fault location of complex cable systems includes:

[0006] S1. The signal source generates a ZC sequence signal of length N, which is used as the test signal for cable testing and transmitted to the test unit and the time synchronization unit respectively;

[0007] S2. The test unit receives the test signal from the signal source and uses the test signal to test the cable under test to obtain the required reflected signal;

[0008] S3. Based on the obtained reflection signal, perform line fixed reflection calibration and transmit the signal obtained from the reflection calibration to the time synchronization unit;

[0009] S4. Based on the signal after reflection calibration and the test signal generated by the signal source, determine the time delay value of the test process and transmit it to the test result unit;

[0010] S5. The cable test result unit receives the time delay estimate from the time delay estimation unit and calculates the distance to the fault location.

[0011] The beneficial effects of this invention are: this invention uses time-domain self-interference channel estimation to perform fixed reflection calibration of the line, which reduces interference from ineffective signals in the environment and improves the signal-to-noise ratio. Attached Figure Description

[0012] Figure 1 This is a schematic diagram illustrating the fault location principle of the present invention. Detailed Implementation

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0014] To improve the ranging accuracy of cable testing, this invention proposes a novel online monitoring and fault location method for complex cable systems based on the traditional Spread Spectrum Time Domain Reflectometry (SSTDR) method. This testing method uses the SSTDR method to obtain phase data of the reflected signal to achieve more accurate ranging estimation. Simultaneously, addressing the complex interference problems in communication systems, a self-interference signal suppression model is proposed. Time-domain self-interference channel estimation is used for fixed reflection calibration of the line, reducing interference from ineffective signals in the environment and improving the signal-to-noise ratio. The cable testing method proposed in this invention is a simple, efficient, and highly accurate solution, specifically:

[0015] like Figure 1 As shown, an online monitoring and fault location method for complex cable systems is characterized by the following steps:

[0016] S1. Signal source 1 generates a ZC sequence signal of length N (N=64) as the test signal for cable testing, and transmits it to test unit 2 and time synchronization unit 5 respectively;

[0017] S2. Test unit 2 receives the test signal from signal source 1 and uses the test signal to test the cable under test to obtain the required reflected signal;

[0018] S201. Test unit 2 receives the test signal from signal source 1, passes the test signal through an attenuator and a routing switch, then passes it through the circulator input port, and outputs the signal from the circulator isolation port to the cable under test;

[0019] S202. A reflected signal will be generated at the fault point of the cable under test. The reflected signal is input from the isolation port of the circulator, output from the output port of the circulator, and returns to the test unit 2 after passing through the attenuator. This signal is the required reflected signal.

[0020] S3. Based on the obtained reflection signal, perform line fixed reflection calibration and transmit the signal obtained from the reflection calibration to the time synchronization unit 5;

[0021] S301. The test signal generated by the signal source 1 passes through the test unit 2, and the reflected signal connected to the load matching through the circulator port of the test unit 2 is sent to the self-interference reconstruction unit 3 for line fixed reflection calibration.

[0022] S302. Since the line fixed reflection calibration requires reconstruction of the self-interference signal, and subsequent modeling of the self-interference signal is required, the self-interference reconstruction unit 3 needs to use the load-matched connection of the circulator port of test unit 2 as the data source. At this time, the signal is approximately a self-interference signal, and time-domain self-interference channel estimation is performed. The estimation process includes:

[0023] S3021. Construct its Toeplitz matrix by cyclically shifting the test signal x(k) generated by signal source 1:

[0024]

[0025] S3022. Model the self-interference signal y(n) as a matrix form of y = Ah + w;

[0026] The maximum likelihood estimation of the channel parameter h(n) is achieved by finding the pseudo-inverse of the Toeplitz matrix, using the formula h = ∑y i a i Find the channel parameters h(n), where a i Each column of the pseudo-inverse matrix is ​​represented by rows of 64 bytes each, with the received connection load matching signal divided into rows. The i-th row represents y. i The channel parameter h(n) is obtained by multiplying and summing the parameters according to the formula, where w is the receiver noise floor.

[0027] S3023. Using the estimated channel parameter h(n) as the FIR filter coefficient, the test signal generated by the signal source 1 is passed through the filter, and the filtered result is the reconstructed self-interference signal, which is sent to the reflection calibration unit 4.

[0028] S303. The reflection calibration unit 4 receives the test signal from the test unit 2 and the self-interference reconstruction signal from the self-interference reconstruction unit 3, subtracts the self-interference reconstruction signal from the test signal to achieve the purpose of calibrating the reflection signal, and sends the signal after passing through the reflection calibration unit 4 to the time synchronization unit 5.

[0029] S4. Based on the signal after reflection calibration and the test signal generated by signal source 1, determine the time delay value of the test process and transmit it to the test result unit 9;

[0030] S401. Time synchronization unit 5 receives the signal after passing through reflection calibration unit 4 and the test signal generated by signal source 1, and performs the following two steps:

[0031] S4011. The 64-length ZC sequence generated by signal source 1 is used as the FIR filter coefficient of the receiver. The signal after reflection calibration unit 4 and the test signal generated by signal source 1 are coarsely synchronized in time by FIR filter filtering and sliding correlation. The position of the correlation peak in coarse synchronization is the absolute time delay of the signal, which is an integer multiple of the time delay value of the signal. The time delay value is sent to the time delay estimation unit 8.

[0032] S4012. Since the 64-length ZC sequence generated by signal source 1 is a complex signal, the data is transmitted in two paths, I and Q. Therefore, the sliding correlation process will also generate two results, I and Q. The fault type is determined by the polarity of the I and Q signal results in the sliding correlation. When an open-circuit fault occurs in the transmission line, the polarity of the reflected signal is the same as that of the test signal sent by signal source 1. When a short-circuit fault occurs in the transmission line, the polarity of the reflected signal is opposite to that of the test signal sent by signal source 1. At the same time, the two synchronized signals are sent to the cross power spectrum calculation unit 6.

[0033] S402. The cross-power spectrum calculation unit 6 receives two coarsely synchronized signals from the time synchronization unit 5 and performs the following two steps on the two signals:

[0034] S4021. According to the formula The two signals are frequency domain transformed and their respective power spectrum functions are obtained by power normalization.

[0035] S4022. According to the formula The power spectrum functions of each signal are conjugate and cross-multiplied to obtain the cross power spectrum function of the two signals, and then the function is sent to the phase extraction unit 7.

[0036] S403. Phase extraction unit 7 receives the cross power spectrum function from cross power spectrum calculation unit 6, and performs the following two parts of processing on it:

[0037] S4031. Obtain the phase function curve by extracting the phase angle;

[0038] S4032. Divide the phase curve data into a periodic curve of length 64, perform differential processing on it to obtain a uniformly changing curve and two periodic edge changes of convexity, discard the convex part, select the uniformly changing smooth part, and send the selected signal into the time delay estimation unit 8.

[0039] S404. The delay estimation unit 8 receives the integer delay value from the time synchronization unit 5 and the smoothed portion of the signal from the phase extraction unit 7, and performs the following three parts of processing:

[0040] S4041. Calculate the mean of the smoothed portion of the signal to obtain a stable slope value;

[0041] S4042. According to the formula After applying coefficient compensation to the mean result, the final result is the precise decimal multiple of the time delay value.

[0042] S4043. Add the integer multiple delay value and the fractional multiple delay value together to obtain the delay value of the entire test process, and output the delay value to the test result unit 9.

[0043] S5. Cable test result unit 9 receives the time delay estimate from time delay estimation unit 8 and calculates the distance to the fault location.

[0044] Specifically: according to the distance measurement formula The distance to the fault location is calculated using the known propagation speed v of the traveling wave in the cable and the estimated time delay t.

[0045] The foregoing description illustrates and describes a preferred embodiment of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for online monitoring and fault location of complex cable systems, characterized in that: Includes the following steps: S1. The signal source (1) generates a ZC sequence signal of length N, which is used as the test signal for cable testing and transmitted to the test unit (2) and the time synchronization unit (5) respectively. S2. The test unit (2) receives the test signal from the signal source (1) and uses the test signal to test the cable under test to obtain the required reflected signal; S3. Based on the obtained reflection signal, perform line fixed reflection calibration and transmit the signal obtained from the reflection calibration to the time synchronization unit (5). S301. The test signal generated by the signal source (1) passes through the test unit (2), and the reflected signal connected to the load matching through the circulator port of the test unit (2) is sent to the self-interference reconstruction unit (3) for line fixed reflection calibration. S302. Since the line fixed reflection calibration requires reconstruction of the self-interference signal, and subsequent modeling of the self-interference signal is required, the self-interference reconstruction unit (3) needs to use the load matching situation of the circulator port of the test unit (2) as the data source. At this time, the signal is approximately a self-interference signal, and time-domain self-interference channel estimation is performed. The estimation process includes: S3021. Test signal generated by signal source (1) Its Toeplitz matrix is ​​constructed by cyclic shifting: ； S3022. Remove self-interference signal Modeling as Matrix form; Channel parameters are obtained by finding the pseudo-inverse of the Toeplitz matrix. The maximum likelihood estimate is obtained through the formula. Determine the channel parameters ,in The i-th column of the pseudo-inverse matrix is ​​represented by rows of length N, with the received connection load matched signal divided into rows. Actions represent The channel parameters can be obtained by multiplying and summing them according to the formula. , For receiver noise floor; S3023. Using the estimated channel parameters As FIR filter coefficients, the test signal generated by the signal source (1) is passed through the filter, and the result after filtering is the reconstructed self-interference signal, which is sent to the reflection calibration unit (4). S303. The reflection calibration unit (4) receives the test signal from the test unit (2) and the self-interference reconstruction signal from the self-interference reconstruction unit (3), subtracts the self-interference reconstruction signal from the test signal to achieve the purpose of calibrating the reflection signal, and sends the signal after passing through the reflection calibration unit (4) into the time synchronization unit (5). S4. Based on the signal after reflection calibration and the test signal generated by the signal source (1), determine the time delay value of the test process and transmit it to the test result unit (9). S5. The cable test result unit (9) receives the time delay estimate from the time delay estimation unit (8) and calculates the distance to the fault location.

2. The online monitoring and fault location method for complex cable systems according to claim 1, characterized in that: Step S2 includes the following sub-steps: S201. Test unit (2) receives the test signal from signal source (1), passes the test signal through attenuator and routing switch and then through circulator input port, and outputs the signal from circulator isolation port to the cable under test; S202. A reflected signal will be generated at the fault point of the cable under test. The reflected signal is input from the isolation port of the circulator, output from the output port of the circulator, and returns to the test unit (2) after passing through the attenuator. This signal is the required reflected signal.

3. The online monitoring and fault location method for complex cable systems according to claim 1, characterized in that: Step S5 includes the following sub-steps: S401. The time synchronization unit (5) receives the signal after passing through the reflection calibration unit (4) and the test signal generated by the signal source (1), and performs the following two steps: S4011. The N-length ZC sequence generated by the signal source (1) is used as the FIR filter coefficient of the receiver. The signal after passing through the reflection calibration unit (4) and the test signal generated by the signal source (1) are coarsely synchronized in time by the FIR filter filtering and sliding correlation. The position of the correlation peak in the coarse synchronization is the absolute time delay of the signal, which is also an integer multiple of the time delay value of the signal. The time delay value is sent to the time delay estimation unit (8). S4012. Since the N-length ZC sequence generated by the signal source (1) is a complex signal, the data is sent in two paths, I and Q. Therefore, the sliding correlation process will also generate two paths, I and Q. The fault type is determined by the polarity of the I and Q signal results in the sliding correlation. When the transmission line has an open circuit fault, the polarity of the reflected signal is the same as that of the test signal sent by the signal source (1). When the transmission line has a short circuit fault, the polarity of the reflected signal is opposite to that of the test signal sent by the signal source (1). At the same time, the two synchronized signals are sent to the cross power spectrum calculation unit (6). S402. The cross power spectrum calculation unit (6) receives two coarsely synchronized signals from the time synchronization unit (5) and performs the following two steps on the two signals: S4021. According to the formula , The two signals are frequency domain transformed and their respective power spectrum functions are obtained by power normalization. S4022. According to the formula Find the conjugate of their respective power spectrum functions and cross-multiply them to obtain the cross power spectrum function of the two signals, and send the function into the phase extraction unit (7). S403. The phase extraction unit (7) receives the cross power spectrum function from the cross power spectrum calculation unit (6), and the phase extraction unit (7) processes it in the following two parts: S4031. Obtain the phase function curve by extracting the phase angle; S4032. Divide the phase curve data into periodic curves of length N, perform differential processing on them to obtain a uniformly changing curve and two periodic edge changes of convexity. Discard the convex part and select the uniformly changing smooth part. The selected signal is sent to the time delay estimation unit (8). S404. The delay estimation unit (8) receives the integer delay value from the time synchronization unit (5) and the smoothed portion signal from the phase extraction unit (7), and performs the following three parts of processing: S4041. Calculate the mean of the smoothed portion of the signal to obtain a stable slope value; S4042. According to the formula The mean result is compensated by a coefficient, and the final result is the accurate decimal multiple of the time delay value. S4043. Add the integer multiple delay value and the fractional multiple delay value together to obtain the delay value of the entire test process, and output the delay value to the test result unit (9).

4. The online monitoring and fault location method for complex cable systems according to claim 1, characterized in that: In step S5, according to the distance measurement formula Based on the known propagation speed of traveling waves in a cable and delay estimates Calculate the distance from the fault location to the receiver.

Images