Power cable reflection coefficient spectrum characteristic analysis method and system

Abstract

The invention relates to the technical field of power cable reflection coefficient analysis, and discloses a power cable reflection coefficient spectrum feature analysis method and system, and the method comprises the steps: obtaining a power cable reflection coefficient spectrum; dividing the reflection coefficient spectrum of the power cable into a plurality of sub-segments, and calculating the third-order cumulant of each sub-segment; calculating the average value of the third-order cumulant sum as the third-order cumulant of the reflection coefficient spectrum of the power cable; and according to the third-order cumulant of the reflection coefficient spectrum of the power cable, constructing a bispectrum, and carrying out feature analysis. The three-order cumulant of the reflection coefficient spectrum of the power cable is calculated by adopting a high-order statistic method, and two-dimensional fast Fourier transform is carried out to obtain the bispectrum characteristic of the reflection coefficient spectrum of the power cable, so that the effectiveness and the reliability of characteristic analysis of the tested cable are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power cable reflection coefficient analysis, and in particular to a power cable reflection coefficient spectrum characteristic analysis method and system. Background Art

[0002] With the continuous growth of electricity demand, the position of power cables in the power system is becoming more and more important. In order to meet the transmission needs in different scenarios, the types and specifications of power cables are constantly enriched. For example, there are low-voltage power cables specifically used for urban underground power grids, and high-voltage and ultra-high-voltage power cables for large hydropower stations and nuclear power plants. As the main carrier of electric energy transmission, power cables have been widely used in urban distribution networks. However, due to factors such as insufficient production technology, irregular laying process, and long-term aging, power cables have defects and the insulation state has deteriorated. Therefore, detecting defects in power cables and diagnosing the insulation state of power cables are necessary means to ensure the safe and stable operation of the distribution system.

[0003] Among the existing power cable detection methods, frequency domain reflectometry (FDR) has been widely used in on-site power cable detection due to its advantage of arbitrarily adjustable scanning frequency band. This method injects a series of sinusoidal signals of different frequencies into the cable under test, and compares the collected output signal (voltage) with the injected signal (voltage) in the frequency domain to obtain the reflection coefficient spectrum (RCS) of the power cable under test. Therefore, RCS is a form of expression of the cable transfer function, which contains all the characteristic information of the cable under test. It is worth noting that RCS is composed of the superposition of many harmonics of different frequencies, which makes it easier to analyze.

[0004] Traditional RCS analysis methods include fast Fourier transform (FFT) based on first-order moments[5], power spectral density (PSD) based on second-order moments, and multiple signal classification (MUSIC) based on spatial spectrum. Since RCS is a non-periodic random signal, a large amount of spectrum leakage exists in the spectrum of FFT, which brings great errors to the detection of defect location, judgment of defect change type and estimation of defect reflection intensity. Although PSD eliminates the interference of pseudo peaks on defect detection through the autocorrelation function of RCS, PSD loses the phase information of the defect and cannot judge the change type of the defect. MUSIC maps RCS into signal subspace and noise subspace to separate signal and noise, which makes the defect location more accurate. However, the MUSIC method ignores the phase information and amplitude information in RCS. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method and system for analyzing the characteristics of a power cable reflection coefficient spectrum, so as to achieve the effectiveness and reliability of the cable characteristic analysis.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0007] A method for analyzing the characteristics of a power cable reflection coefficient spectrum comprises the following steps:

[0008] Get the reflection coefficient spectrum of power cable;

[0009] The reflection coefficient spectrum of the power cable is divided into multiple sub-segments, and the third-order cumulants of each sub-segment are calculated;

[0010] Calculating an average value of the sum of the third-order cumulants as the third-order cumulants of the power cable reflection coefficient spectrum;

[0011] A double spectrum is constructed according to the third-order cumulant of the power cable reflection coefficient spectrum for characteristic analysis.

[0012] Optionally, obtaining the power cable reflection coefficient spectrum includes:

[0013] Modulate sinusoidal signals of different continuous frequencies and inject them into the power cable under test to obtain the reflection coefficient spectrum of the power cable.

[0014] Alternatively, the power cable reflection coefficient spectrum is expressed as:

[0015]

[0016] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, and ω is the signal frequency.

[0017] Optionally, dividing the power cable reflection coefficient spectrum into a plurality of sub-segments and calculating the third-order cumulants of each sub-segment comprises the following steps:

[0018] Extract the real signal of the power cable reflection coefficient spectrum;

[0019] Dividing the real signal of the power cable reflection coefficient spectrum into a plurality of sub-segments;

[0020] The corresponding third-order cumulants are calculated for each sub-segment of the real signal of the power cable reflection coefficient spectrum.

[0021] Alternatively, the real signal of the power cable reflection coefficient spectrum is expressed as:

[0022]

[0023] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, w i is the sampling noise, and ω is the signal frequency.

[0024] Alternatively, the third-order cumulants are calculated as:

[0025]

[0026] Among them, C k (m1, m2) is the third-order cumulant of the kth subsegment, m1, m2 are time delay parameters, N1 is the sample capacity of the subsegment, L1 = max(0, -m1, -m2), L2 = max(N1-1, N1-1-m1, N1-1-m2), max is the maximum value function, s(j) is the value of the real part of the reflection coefficient of the jth sample point, s(j+m1) is the value of the real part of the reflection coefficient of the j+m1th sample point, and s(j+m2) is the value of the real part of the reflection coefficient of the j+m2th sample point.

[0027] Optionally, the average value of the sum of the third-order cumulants is calculated as the third-order cumulant of the power cable reflection coefficient spectrum, specifically:

[0028]

[0029] Where C(m1,m2) is the third-order cumulant of the real signal of the power cable reflection coefficient spectrum, K is the number of sub-segments of the real signal of the power cable reflection coefficient spectrum, and C k (m1,m2) is the third-order cumulant of the kth subsegment, and m1,m2 are time delay parameters.

[0030] As an option, a dual spectrum is constructed according to the third-order cumulant of the power cable reflection coefficient spectrum, specifically:

[0031]

[0032] Among them, B(ω1,ω2) is the bispectral signal, C(m1,m2) is the third-order cumulant of the real part signal of the power cable reflection coefficient spectrum, W(m1,m2) is the second-order window function, m1,m2 are time delay parameters, and ω1,ω2 are frequency parameters.

[0033] By analyzing the third-order cumulants of the power cable reflection coefficient spectrum and the constructed bispectrum, the distribution characteristics of the power cable reflection coefficient spectrum (for example, whether it has a symmetrical distribution characteristic, whether the third-order cumulants vary with the delay amount, whether it is nonlinear, etc.) and frequency components (for example, the presence of several frequency harmonics, etc.) can be realized.

[0034] As an option, the second-order window function uses a Parzen window, which is expressed as:

[0035]

[0036] Among them, d Parzen (m) is the second-order Parzen window function, m is the time delay parameter, and M is the maximum time delay parameter.

[0037] The present invention also provides a power cable reflection coefficient spectrum characteristic analysis system, comprising:

[0038] An acquisition unit, used for acquiring a reflection coefficient spectrum of a power cable;

[0039] A segmentation unit, used to divide the power cable reflection coefficient spectrum into a plurality of sub-segments, and calculate the third-order cumulant of each sub-segment;

[0040] A calculation unit, used for calculating an average value of the sum of the third-order cumulants as the third-order cumulants of the power cable reflection coefficient spectrum;

[0041] The analysis unit is used to construct a double spectrum according to the third-order cumulant of the power cable reflection coefficient spectrum and perform characteristic analysis.

[0042] The acquisition unit modulates sinusoidal signals of different continuous frequencies and injects them into the power cable under test to acquire the reflection coefficient spectrum of the power cable.

[0043] The power cable reflection coefficient spectrum obtained by the acquisition unit is expressed as:

[0044]

[0045] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, and ω is the signal frequency.

[0046] The segmentation unit divides the power cable reflection coefficient spectrum into a plurality of sub-segments, and calculates the third-order cumulants of each sub-segment, including:

[0047] An extraction module, used for extracting the real signal of the reflection coefficient spectrum of the power cable;

[0048] A division module, used for dividing the real signal of the power cable reflection coefficient spectrum into a plurality of sub-segments;

[0049] The sub-segment calculation module is used to calculate the corresponding third-order cumulant for each sub-segment of the real signal of the power cable reflection coefficient spectrum.

[0050] The real signal of the power cable reflection coefficient spectrum extracted by the extraction module is expressed as:

[0051]

[0052] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, w i is the sampling noise, and ω is the signal frequency.

[0053] The sub-segment calculation module calculates the third-order cumulant in the following way:

[0054]

[0055] Among them, C k (m1, m2) is the third-order cumulant of the kth subsegment, m1, m2 are time delay parameters, N1 is the sample capacity of the subsegment, L1 = max(0, -m1, -m2), L2 = max(N1-1, N1-1-m1, N1-1-m2), max is the maximum value function, s(j) is the value of the real part of the reflection coefficient of the jth sample point, s(j+m1) is the value of the real part of the reflection coefficient of the j+m1th sample point, and s(j+m2) is the value of the real part of the reflection coefficient of the j+m2th sample point.

[0056] The calculation unit calculates the average value of the sum of the third-order cumulants as the third-order cumulants of the power cable reflection coefficient spectrum, specifically:

[0057]

[0058] Where C(m1,m2) is the third-order cumulant of the real signal of the power cable reflection coefficient spectrum, K is the number of sub-segments of the real signal of the power cable reflection coefficient spectrum, and C k (m1,m2) is the third-order cumulant of the kth subsegment, and m1,m2 are time delay parameters.

[0059] The analysis unit constructs a dual spectrum according to the third-order cumulant of the power cable reflection coefficient spectrum, specifically:

[0060]

[0061] Among them, B(ω1,ω2) is the bispectral signal, C(m1,m2) is the third-order cumulant of the real part signal of the power cable reflection coefficient spectrum, W(m1,m2) is the second-order window function, m1,m2 are time delay parameters, and ω1,ω2 are frequency parameters.

[0062] The second-order window function used by the analysis unit is a Parzen window, which is expressed as:

[0063]

[0064] Among them, d Parzen (m) is the second-order Parzen window function, m is the time delay parameter, and M is the maximum time delay parameter.

[0065] The power cable reflection coefficient spectrum characteristic analysis method and system provided by the present invention have the following beneficial effects:

[0066] The present invention adopts a high-order statistics method to calculate the third-order cumulant of the power cable reflection coefficient spectrum, and performs a two-dimensional fast Fourier transform to obtain the dual-spectrum characteristics of the power cable reflection coefficient spectrum, which can simultaneously retain the phase information and amplitude information of the cable reflection wave, thereby improving the effectiveness and reliability of the characteristic analysis of the tested cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 A schematic flow chart of a method for analyzing the characteristics of a power cable reflection coefficient spectrum provided in Example 1;

[0068] Figure 2 Schematic diagram of the traveling wave process of a defective power cable model;

[0069] FIG3( a ) is a schematic diagram of the third-order cumulants of a defect-free cable model within 0.15 MHz-100 MHz;

[0070] FIG3( b ) is a schematic diagram of the double spectrum of the defect-free cable model within 0.15 MHz-100 MHz;

[0071] Figure 4(a) is a schematic diagram of the third-order cumulants of the defective cable model within 0.15MHz-100MHz;

[0072] FIG4( b ) is a schematic diagram of the double spectrum of the defective cable model within 0.15 MHz-100 MHz;

[0073] Figure 5 This is a schematic diagram of the structure of the power cable reflection coefficient spectrum characteristic analysis system provided in Example 2. DETAILED DESCRIPTION

[0074] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0075] Example 1

[0076] like Figure 1 As shown, this embodiment provides a method for analyzing the characteristics of a power cable reflection coefficient spectrum, comprising the following steps S1 to S4:

[0077] S1. Obtain the reflection coefficient spectrum of the power cable.

[0078] In an optional embodiment of the present invention, obtaining the power cable reflection coefficient spectrum includes:

[0079] Modulate sinusoidal signals of different continuous frequencies and inject them into the power cable under test to obtain the reflection coefficient spectrum of the power cable.

[0080] In this embodiment, firstly, based on circuit theory and electromagnetic field theory, the electrical characteristics of the power cable in the process of transmitting electric energy are modeled to construct a transmission line model of the power cable. In the transmission line model, the power cable is usually regarded as a group of distributed circuit elements composed of parameters such as resistance, inductance, capacitance and conductance. These parameters reflect the voltage drop, current distribution, electromagnetic field distribution and other phenomena generated by the cable when transmitting electric energy. Through the precise calculation and simulation of these parameters, the performance of the cable under different working conditions can be predicted, such as voltage fluctuation, power loss, signal transmission quality, etc. The wave process of a defective power cable model is as follows: Figure 2 As shown, U0 is the voltage of the frequency sweep signal, R0 is the input impedance of the test terminal (terminal A), Z0 is the characteristic impedance of the cable model, and Z d is the characteristic impedance of the defect, l1 is the location of the defect, d is the length of the defect, l is the length of the cable model, and Z L is the load impedance of the load terminal (Terminal B).

[0081] According to the traveling wave theory, the reflected voltage wave at l1 is:

[0082]

[0083] Among them, ρ0 and ρ1 are the reflection coefficients at terminal A and defect, respectively. γ is the propagation coefficient of the cable model.

[0084] The reflected voltage wave at l1+d is:

[0085]

[0086] The reflected voltage wave at l is:

[0087]

[0088] Therefore, all the voltage waves collected at terminal A are:

[0089] U(ω)=U1(ω)+U2(ω)+U3(ω)

[0090] Therefore, the RCS of the cable model can be obtained as:

[0091]

[0092] Among them, the propagation coefficient γ can be expressed as:

[0093] γ=α+jβ

[0094] Among them, α is the attenuation factor and β is the phase information.

[0095] Therefore, according to Euler's formula, the RCS of the cable model is a complex number, and RCS is expressed as:

[0096]

[0097] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, and ω is the signal frequency.

[0098] According to the above formula, RCS is composed of a series of harmonics of different frequencies.

[0099] S2. Divide the power cable reflection coefficient spectrum into multiple sub-segments and calculate the third-order cumulant of each sub-segment.

[0100] In an optional embodiment of the present invention, the reflection coefficient spectrum of the power cable is divided into a plurality of sub-segments, and the third-order cumulants of each sub-segment are calculated, comprising the following steps:

[0101] Extract the real signal of the power cable reflection coefficient spectrum;

[0102] Dividing the real signal of the power cable reflection coefficient spectrum into a plurality of sub-segments;

[0103] The corresponding third-order cumulants are calculated for each sub-segment of the real signal of the power cable reflection coefficient spectrum.

[0104] In this embodiment, the bispectrum, as a key concept in high-order spectrum analysis, has a series of significant characteristics, which make it have important application value in the fields of signal processing, communication, biomedical engineering, etc. First, the bispectrum focuses on the interaction between multiple frequency components of the signal. By calculating the two-dimensional discrete Fourier transform of the third-order cumulant, the bispectrum can reveal the phase coupling and amplitude dependence between different frequency components in the signal, thereby more comprehensively reflecting the intrinsic characteristics of the signal. Secondly, the bispectrum has a complex number characteristic, that is, it contains amplitude and phase information. This enables the bispectrum to not only describe the intensity distribution of the signal, but also reveal the phase relationship between the frequency components in the signal. This phase information is crucial for understanding the structure and dynamic characteristics of the signal. In addition, the bispectrum has symmetry and periodicity. The symmetry is caused by the symmetry of the cumulant, while the periodicity is reflected when the bispectrum is a function of frequency. These properties help to simplify the calculation and analysis process of the bispectrum. Finally, the bispectrum has unique advantages in the processing of non-Gaussian signals. The bispectrum of a Gaussian signal is zero, so the bispectrum is particularly suitable for analyzing and detecting nonlinear characteristics and structures in non-Gaussian signals. In signal processing, this property enables bispectrum to effectively identify nonlinear components and phase relationships in signals.

[0105] In this embodiment, the real part of RCS is analyzed and expressed as:

[0106]

[0107] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, w i is the sampling noise, ω is the signal frequency. Obviously, s(ω) is a stationary random signal with zero mean.

[0108] Assume that the sample size of s(ω) is N, and divide s(ω) into K sub-segments, and the sample size of each sub-segment is N1. Then the third-order cumulant in the kth (k=1,2,...,K) sub-segment is estimated as:

[0109]

[0110] Among them, C k(m1, m2) is the third - order cumulant of the k - th sub - segment. m1 ∈ [-M, M] and m2 ∈ [-M, M] are time - delay parameters. M < N1 - 1, where N1 is the sample size of the sub - segment. L1 = max(0, -m1, -m2), L2 = max(N1 - 1, N1 - 1 - m1, N1 - 1 - m2), max is the maximum - value function. s(j) is the real - part value of the reflection coefficient at the j - th sample point, s(j + m1) is the real - part value of the reflection coefficient at the j + m1 - th sample point, and s(j + m2) is the real - part value of the reflection coefficient at the j + m2 - th sample point.

[0111] S3. Calculate the average value of the sum of the third - order cumulants as the third - order cumulant of the power - cable reflection - coefficient spectrum.

[0112] In an alternative embodiment of the present invention, the average value of the third - order cumulants of all sub - segments is taken as the third - order cumulant of the entire s(ω), expressed as:

[0113]

[0114] where C(m1, m2) is the third - order cumulant of the real - part signal of the power - cable reflection - coefficient spectrum, K is the number of sub - segments of the real - part signal of the power - cable reflection - coefficient spectrum, C k (m1, m2) is the third - order cumulant of the k - th sub - segment, and m1, m2 are time - delay parameters.

[0115] S4. Construct a bispectrum based on the third - order cumulant of the power - cable reflection - coefficient spectrum for feature analysis.

[0116] In an alternative embodiment of the present invention, in this embodiment, the bispectrum of the power - cable reflection - coefficient spectrum is estimated according to the third - order cumulant of the power - cable reflection - coefficient spectrum, specifically:

[0117]

[0118] where B(ω1, ω2) is the bispectrum signal, C(m1, m2) is the third - order cumulant of the real - part signal of the power - cable reflection - coefficient spectrum, W(m1, m2) is the second - order window function, m1, m2 are time - delay parameters, and ω1, ω2 are frequency parameters.

[0119] where the second - order window function adopts the Parzen window, expressed as:

[0120]

[0121] where d Parzen (m) is the second - order Parzen window function, m is the time - delay parameter, and M is the maximum time - delay parameter.

[0122] The following is a dual-spectrum simulation analysis of the power cable reflection coefficient spectrum with specific examples.

[0123] according to Figure 2 The cable model shown in the figure simulates a 500m long, defect-free power cable model. In this process, the various physical properties of the cable and the various situations it may encounter during power transmission are fully considered. First, we need to carefully study Figure 1 The cable model in the simulation is used to understand its structure, materials and electrical parameters. These parameters include but are not limited to the conductor material of the cable, the properties of the insulation layer, the structure of the sheath and the cross-sectional area of ​​the cable. These parameters are crucial for subsequent simulation work because they will directly affect the electrical performance and transmission efficiency of the cable. Next, the professional power simulation software MATLAB 2017b will be used to model the cable according to the actual parameters of the cable. During the modeling process, special attention will be paid to the length of the cable, which is 500 meters. This length will affect the electrical characteristics of the cable, such as resistance, inductance, capacitance, etc., so it needs to be accurately reflected in the model. After the model is established, a simulation test will be performed, and the capacitance value of the test line is set to 0.8 times that of the cable. By injecting a 0.15MHz-100MHz sine signal (scanning interval is △f=0.01MHz), the response of the cable model is observed. These simulation tests will help understand the performance of the cable in actual operation. According to the power cable reflection coefficient spectrum characteristic analysis method based on bispectral analysis given in the previous embodiment, the power cable reflection coefficient spectrum characteristic analysis is performed on the simulated cable; during the analysis process, the power cable reflection coefficient spectrum is divided into K sub-segments, K = 10. The third-order cumulant obtained by simulation is shown in Figure 3(a), and the bispectral result of the simulation model is shown in Figure 3(b).

[0124] As can be seen from Figure 3(a), the third-order cumulative amount of RCS has corresponding peaks in the six sector areas, which indicates that RCS has a symmetrical distribution characteristic within 0.15MHz-100MHz. However, as the delay changes, the value of the third-order cumulative amount of RCS also fluctuates. This shows that the RCS within 0.15MHz-100MHz may be non-stationary. Since the bispectrum is defined as 12 sector areas, in Figure 3(b), only the bispectrum in the first quadrant needs to be analyzed. Figure 3(b) shows that RCS is nonlinear and is composed of the superposition of two harmonics of different frequencies.

[0125] Then the present invention simulates a defective cable model, aiming to simulate various defects that may exist in actual cables, so as to further study the impact of these defects on cable performance, and thus propose effective solutions and optimization measures. When constructing the defective cable model, the most common defect type of underground cables, namely moisture intrusion, is considered. In order to ensure the accuracy and authenticity of the model, the location and degree of the defect in the cable are also considered to simulate the changes in cable performance under different conditions. The parameters of the defective cable model are set as follows: l1=200m, d=0.5m, l=500m, the capacitance value of the test line is set to 0.8 times that of the cable, and the capacitance value of the defect is increased to 1.2 times that of the cable. By injecting a 0.15MHz-100MHz sinusoidal signal (scanning interval is △f=0.01MHz), the response of the cable model is observed. In the simulation experiment, the reflection coefficient spectrum of the defective cable model is observed and recorded, and its third-order cumulant and bispectrum are obtained, as shown in Figure 4(a) and Figure 4(b), respectively.

[0126] Comparing Figure 4(a) with Figure 3(a), it can be seen that when there are defects in the cable model, some coupling peaks are obviously increased in the third-order cumulative amount, which indicates that many non-Gaussian signals are added to the reflection coefficient spectrum, and there is a mutual coupling relationship between them. Comparing Figure 4(b) with Figure 3(b), it can be seen that when there are defects in the cable model, a spectrum peak obviously appears in the first fan-shaped area without other interference spectrum peaks, which indicates that the dual spectrum can effectively suppress the interference of other coupling signals. At the same time, the existence of spectrum peaks indicates that the cable reflection coefficient spectrum is nonlinear, and the reflection coefficient spectrum of the simulation model is composed of the superposition of three harmonics of different frequencies.

[0127] The above-mentioned power cable reflection coefficient spectrum characteristic analysis method provided by the present invention analyzes its distribution characteristics and frequency components by estimating the third-order cumulant and bispectrum of the cable reflection coefficient spectrum, and can simultaneously retain the phase information and amplitude information of the cable reflection wave. Theoretically, the third-order cumulant and bispectrum of the noise are zero, so the method can give an effective and reliable analysis result, providing a theoretical basis for subsequent processing. The feasibility of the proposed method is verified by simulating a defect-free cable model and a defective cable model.

[0128] Example 2

[0129] like Figure 5 As shown, this embodiment provides a power cable reflection coefficient spectrum characteristic analysis system including:

[0130] An acquisition unit, used for acquiring a reflection coefficient spectrum of a power cable;

[0131] A segmentation unit, used to divide the power cable reflection coefficient spectrum into a plurality of sub-segments, and calculate the third-order cumulant of each sub-segment;

[0132] A calculation unit, used for calculating an average value of the sum of the third-order cumulants as the third-order cumulants of the power cable reflection coefficient spectrum;

[0133] The analysis unit is used to construct a double spectrum for the power cable reflection coefficient spectrum according to the third-order cumulant and perform characteristic analysis.

[0134] The acquisition unit modulates sinusoidal signals of different continuous frequencies and injects them into the power cable under test to acquire the reflection coefficient spectrum of the power cable.

[0135] The power cable reflection coefficient spectrum obtained by the above acquisition unit is expressed as:

[0136]

[0137] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, and ω is the signal frequency.

[0138] The segmentation unit divides the power cable reflection coefficient spectrum into multiple sub-segments and calculates the third-order cumulants of each sub-segment, including:

[0139] An extraction module, used for extracting the real signal of the reflection coefficient spectrum of the power cable;

[0140] A division module, used for dividing the real signal of the power cable reflection coefficient spectrum into a plurality of sub-segments;

[0141] The sub-segment calculation module is used to calculate the corresponding third-order cumulant for each sub-segment of the real signal of the power cable reflection coefficient spectrum.

[0142] The real signal of the power cable reflection coefficient spectrum extracted by the above extraction module is expressed as:

[0143]

[0144] Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, β i (ω) is the phase information of the i-th reflected wave, x i is the reflection position of the i-th reflected wave, w i is the sampling noise, and ω is the signal frequency.

[0145] The calculation method of the above sub-segment calculation module for the third-order cumulant is:

[0146]

[0147] Among them, C k (m1,m2) is the third-order cumulant of the k-th subsegment, m1,m2 are time delay parameters, N1 is the sample capacity of the subsegment, L1=max(0,-m1,-m2), L2=max(N1-1,N1-1-m1,N1-1-m2), max is the maximum value function, s(j) is the real part of the reflection coefficient of the j-th sample point, s(j+m1) is the real part of the reflection coefficient of the j+m-th sample point. 1 The real part of the reflection coefficient of the sample point, s(j+m2) is the real part of the reflection coefficient of the j+mth sample point. 2 The value of the real part of the reflection coefficient at each sample point.

[0148] The above calculation unit calculates the average value of the sum of the third-order cumulants of all sub-segments as the third-order cumulant of the power cable reflection coefficient spectrum, specifically:

[0149]

[0150] Where C(m1,m2) is the third-order cumulant of the real signal of the power cable reflection coefficient spectrum, K is the number of sub-segments of the real signal of the power cable reflection coefficient spectrum, and C k (m1,m2) is the third-order cumulant of the kth subsegment, and m1,m2 are time delay parameters.

[0151] The above analysis unit constructs a dual spectrum according to the third-order cumulant of the power cable reflection coefficient spectrum, specifically:

[0152]

[0153] Among them, B(ω1,ω2) is the bispectral signal, C(m1,m2) is the third-order cumulant of the real part signal of the power cable reflection coefficient spectrum, W(m1,m2) is the second-order window function, m1,m2 are time delay parameters, and ω1,ω2 are frequency parameters.

[0154] The second-order window function used in the above analysis unit is the Parzen window, which is expressed as:

[0155]

[0156] Among them, d Parzen (m) is the second-order Parzen window function, m is the time delay parameter, and M is the maximum time delay parameter.

[0157] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0158] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0159] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0160] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0161] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A method for analyzing the characteristics of power cable reflection coefficient spectrum. It is characterized in that include: Get the reflection coefficient spectrum of power cable; Dividing the power cable reflection coefficient spectrum into a plurality of sub-segments, and calculating the third-order cumulants of each sub-segment; Calculating an average value of the sum of the third-order cumulants as the third-order cumulants of the power cable reflection coefficient spectrum; A double spectrum is constructed based on the third-order cumulant of the power cable reflection coefficient spectrum for characteristic analysis.

2. A method for analyzing the reflection coefficient spectrum characteristics of a power cable according to claim 1, It is characterized in that Obtaining the power cable reflection coefficient spectrum includes: Modulate sinusoidal signals of different continuous frequencies and inject them into the power cable under test to obtain the reflection coefficient spectrum of the power cable.

3. A method for analyzing the reflection coefficient spectrum characteristics of a power cable according to claim 2, It is characterized in that The reflection coefficient spectrum of power cable is expressed as: Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, βi(ω) is the phase information of the i-th reflected wave, and x i is the reflection position of the i-th reflected wave, and ω is the signal frequency.

4. A method for analyzing the characteristics of a power cable reflection coefficient spectrum according to claim 1, It is characterized in that The power cable reflection coefficient spectrum is divided into multiple sub-segments, and the third-order cumulants of each sub-segment are calculated, including: Extract the real signal of the power cable reflection coefficient spectrum; Dividing the real signal of the power cable reflection coefficient spectrum into a plurality of sub-segments; The corresponding third-order cumulant is calculated for each sub-segment of the real signal of the power cable reflection coefficient spectrum.

5. A method for analyzing the reflection coefficient spectrum characteristics of a power cable according to claim 4, It is characterized in that The real signal of the power cable reflection coefficient spectrum is expressed as: Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, βi(ω) is the phase information of the i-th reflected wave, and x i is the reflection position of the i-th reflected wave, w i is the sampling noise, and ω is the signal frequency.

6. A method for analyzing the characteristics of a power cable reflection coefficient spectrum according to claim 4, It is characterized in that The third-order cumulant is calculated as: Among them, Ck(m 1 ,m 2 ) is the third-order cumulant of the kth sub-segment, m 1 ,m 2 is the time delay parameter, N 1 is the sample size of the sub-segment, L 1 =max(0,-m 1 ,-m 2 ), L 2 =max(N 1 -1,N 1 -1-m 1 ,N 1 -1-m 2 ), max is the maximum value function, s(j) is the real part of the reflection coefficient of the jth sample point, s(j+m 1 ) is the j+mth 1 The real part of the reflection coefficient of the sample point, s(j+m 2 ) is the j+mth 2 The value of the real part of the reflection coefficient at each sample point.

7. A method for analyzing the characteristics of a power cable reflection coefficient spectrum according to claim 1, It is characterized in that The average value of the sum of the third-order cumulants is calculated as the third-order cumulant of the power cable reflection coefficient spectrum, specifically: Among them, C(m 1 ,m 2 ) is the third-order cumulative amount of the real signal of the power cable reflection coefficient spectrum, K is the number of sub-segments of the real signal of the power cable reflection coefficient spectrum, Ck(m 1 ,m 2 ) is the third-order cumulant of the kth sub-segment, m 1 ,m 2 is the time delay parameter.

8. A method for analyzing the characteristics of a power cable reflection coefficient spectrum according to claim 1, It is characterized in that The double spectrum is constructed according to the third-order cumulant of the power cable reflection coefficient spectrum, specifically: Among them, B(ω 1 ,ω 2 ) is the bispectral signal, C(m 1 ,m 2 ) is the third-order cumulant of the real part of the power cable reflection coefficient spectrum, W(m 1 ,m 2 ) is the second-order window function, m 1 ,m 2 is the time delay parameter, ω 1 ,ω 2 is the frequency parameter.

9. A method for analyzing the characteristics of a power cable reflection coefficient spectrum according to claim 8, It is characterized in that The second-order window function uses the Parzen window, which is expressed as: Among them, d Parzen (m) is the second-order Parzen window function, m is the time delay parameter, and M is the maximum time delay parameter.

10. A power cable reflection coefficient spectrum characteristic analysis system, It is characterized in that include: An acquisition unit, used for acquiring a reflection coefficient spectrum of a power cable; A segmentation unit, used to divide the power cable reflection coefficient spectrum into a plurality of sub-segments, and calculate the third-order cumulant of each sub-segment; A calculation unit, used for calculating an average value of the sum of the third-order cumulants as the third-order cumulants of the power cable reflection coefficient spectrum; The analysis unit is used to construct a dual spectrum according to the third-order cumulant of the power cable reflection coefficient spectrum and perform characteristic analysis.

11. A power cable reflection coefficient spectrum characteristic analysis system according to claim 10, It is characterized in that The acquisition unit modulates sinusoidal signals of different continuous frequencies and injects the signals into the power cable under test to acquire the reflection coefficient spectrum of the power cable.

12. A power cable reflection coefficient spectrum characteristic analysis system according to claim 11, It is characterized in that The power cable reflection coefficient spectrum obtained by the acquisition unit is expressed as: Among them, q is the number of reflected waves, a i (ω) is the amplitude of the i-th reflected wave, α i (ω) is the attenuation factor of the i-th reflected wave, βi(ω) is the phase information of the i-th reflected wave, and x i is the reflection position of the i-th reflected wave, and ω is the signal frequency.

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