An online identification method for power system harmonic resonance

Abstract

The application provides an online identification method for harmonic resonance of a power system, comprising the following steps: collecting voltage waveform data and current waveform data at a preset common coupling point in the power system, pre-processing to obtain waveform difference degree, performing multiple transformations on the collected voltage waveform data and current waveform data to obtain current complex matrix and voltage complex matrix of a fundamental wave and each harmonic; determining a fundamental wave and a total harmonic impedance amplitude array of the common coupling point according to an equivalent model of the power system; calculating power factors of the fundamental wave and each harmonic, and obtaining a power factor array after screening; and determining that harmonic resonance occurs in the power system when the waveform difference degree, the harmonic number array and the power factor array simultaneously satisfy a preset resonance condition. The application combines the similarity of the collected waveforms, harmonic impedance and power factors of multiple parameters, and only needs voltage and current waveform data at the PCC point to identify the harmonic resonance in the power system.

Description

Technical Field

[0001] The present invention relates to the technical field of online identification of harmonic resonance in power systems, and in particular to an online identification method for harmonic resonance in power systems. Background Art

[0002] With the continuous development of power systems and the improvement of power supply reliability, power cables have gradually replaced overhead lines as the main transmission force in urban 35kV medium-voltage distribution networks. Distributed generation, electric vehicles, rail transit, and other power electronic equipment / loads, along with traditional electromagnetic equipment, interact with highly cabled urban medium-voltage distribution networks over a wider frequency range and timescale. This can easily induce coupling of power systems within sub- and super-synchronous frequency bands and 2-100th-order wideband frequencies, leading to resonance and causing overvoltage and overcurrent, significantly impacting the safe, reliable, and economical operation of the power grid. Therefore, online identification of harmonic resonance is crucial for the safe and reliable operation of highly cabled urban medium-voltage distribution networks.

[0003] Currently, harmonic resonance identification is based on a single variable, harmonic impedance, using methods such as frequency sweeps, fluctuations, and modal analysis, combined with harmonic content. Local maxima in harmonic impedance indicate harmonic resonance. However, at specific frequencies or frequency bands in power systems, even very small harmonic currents can cause resonant overvoltages. Therefore, harmonic content is not an inherent characteristic of resonance. Furthermore, other abnormalities, such as system overvoltages, can also cause local maxima in harmonic impedance amplitude. Therefore, online identification of power system harmonic resonance based solely on harmonic impedance as a single variable can result in inaccurate resonance identification. Summary of the Invention

[0004] The purpose of the present invention is to propose an online identification method for power system harmonic resonance to solve the technical problems of the existing methods.

[0005] In one aspect, a method for online identification of harmonic resonance in a power system is provided, comprising:

[0006] Collecting voltage waveform data and current waveform data at a preset common coupling point in the power system at a preset sampling frequency, and preprocessing the collected voltage waveform data and current waveform data to obtain a waveform difference;

[0007] Obtaining a complex voltage matrix of a fundamental wave and each harmonic of the power system, and performing multiple transformations on the collected voltage waveform data and current waveform data according to the complex voltage matrix of the fundamental wave and each harmonic to obtain a complex current matrix and a complex voltage matrix of the fundamental wave and each harmonic;

[0008] Determine an array of total impedance amplitudes of the fundamental wave and each harmonic at the common coupling point according to an equivalent model of the power system;

[0009] Determine the harmonic impedance peak value and the harmonic impedance valley value in the total impedance amplitude array, determine the harmonic order array corresponding to the harmonic impedance peak value and the harmonic order array corresponding to the harmonic impedance valley value according to the harmonic impedance peak value and the harmonic impedance valley value, and calculate the power factor of the fundamental wave and each harmonic, and obtain a power factor array after screening;

[0010] It is determined whether the waveform difference, the harmonic order array and power factor array corresponding to the harmonic impedance peak value, and the harmonic order array and power factor array corresponding to the harmonic impedance valley value meet the preset resonance conditions. If so, it is determined that harmonic resonance has occurred in the power system.

[0011] Preferably, the preset sampling frequency is set to a frequency parameter that meets the following conditions:

[0012] F S ≥r×H×50

[0013] Among them, F s is the sampling frequency, H is the maximum harmonic number to be analyzed, and r is the multiple.

[0014] Preferably, the preprocessing of the collected voltage waveform data and current waveform data includes:

[0015] The voltage waveform data and the current waveform data are normalized and standardized according to the following formulas:

[0016]

[0017] Among them, U Pi is the normalized voltage waveform data of the ith voltage, I Pi is the normalized i-th current waveform data, U′ Pi is the i-th voltage waveform data after normalization, I′ Pi is the i-th current waveform data after normalization;

[0018] Calculate the mean square error of voltage and current and the waveform difference according to the following formula:

[0019]

[0020] DF=|U Prms -I Prms |

[0021] Among them, U Prms is the mean square error of voltage, I Prmsis the mean square error of the current, and N is the length of the collected voltage and current waveform data.

[0022] Preferably, the current complex matrix of obtaining the fundamental wave and each harmonic includes:

[0023] The collected voltage waveform data and current waveform data are grouped into a preset number of cycles and subjected to fast Fourier transform respectively. After the preset number of transformations, the voltage complex matrix of the fundamental wave and each harmonic, and the current complex matrix of the fundamental wave and each harmonic are obtained; wherein the number of cycles and the number of transformations are both positive integers.

[0024] Preferably, the determining of the array of total impedance amplitudes of the fundamental wave and each harmonic at the common coupling point comprises:

[0025] Determining a matrix A according to an equivalent model of the power system and determining an estimated value of the matrix A;

[0026] Harmonic impedances are filtered according to the following formula to obtain the impedance amplitude arrays on the system side and the impedance amplitude arrays on the load side:

[0027]

[0028] Among them, Re(k i ) is a complex number k i The real part of i is 1, 2; Z S is the Thevenin equivalent impedance of the power system; Z C is the Norton equivalent load impedance on the load side of the power system; is the estimated value of matrix A;

[0029] Substituting the system-side impedance amplitude array and the load-side impedance amplitude array into the following formula, we can obtain the fundamental wave and total harmonic impedance amplitude array of the power system at the common coupling point:

[0030]

[0031] Among them, Z all It is an array of the total impedance amplitudes of the fundamental wave and each harmonic of the power system at the common coupling point.

[0032] Preferably, the harmonic order array corresponding to the harmonic impedance peak value and the harmonic order array corresponding to the harmonic impedance valley value include:

[0033] The serial numbers of the columns corresponding to the harmonic impedance peak value and the harmonic impedance valley value in the total impedance amplitude array are respectively input into the harmonic order array corresponding to the harmonic impedance peak value and the harmonic order array corresponding to the harmonic impedance valley value.

[0034] Preferably, the power factors of the fundamental wave and each harmonic wave are calculated, and after screening, a power factor array is obtained, which includes:

[0035] The power factors of the fundamental wave and each harmonic wave are calculated according to the following formula to obtain a power factor matrix:

[0036] PF f(i,j) = cos (θ uf(i,j) - θ If(i,j) )

[0037] Wherein, PF f(i,j) is the power factor corresponding to the i-th row and the j-th column, θ uf(i,j) is the harmonic voltage phase angle at the frequency f after the fast Fourier transform, and θ If(i,j) is the current phase angle at the frequency f after the fast Fourier transform.

[0038] Preferably, it further includes:

[0039] Based on the order number of the column corresponding to the harmonic number, the number of times that the value of each column in the power factor matrix is greater than the preset power factor threshold is counted to obtain a statistical array; wherein, the corresponding column of the statistical array is the number of times that the value of each column in the power factor matrix is greater than the preset power factor threshold.

[0040] Preferably, it further includes:

[0041] The corresponding column number in the statistical array whose value is greater than the preset power factor number threshold is determined, and the result is put into the power factor array.

[0042] Preferably, the preset resonance condition includes:

[0043] The similarity of the waveform meets:

[0044] 1-DF≥ΔS

[0045] Wherein, DF is the waveform difference, and ΔS is the waveform similarity threshold of the voltage waveform data and the current waveform data;

[0046] The intersection of the harmonic number array corresponding to the harmonic impedance peak value and the power factor array is not an empty set;

[0047] The intersection of the harmonic number array corresponding to the harmonic impedance valley value and the power factor array is not an empty set.

[0048] In summary, the embodiment of the present application has the following beneficial effects:

[0049] The online identification method for power system harmonic resonance provided by the present invention combines multiple parameters such as the similarity of collected waveforms, harmonic impedance, and power factor to achieve accurate and faster identification. It can simultaneously identify series harmonic resonance and parallel harmonic resonance in the power system. It does not require detailed modeling, only the voltage and current waveform data at the PCC point, and is not constrained by the usage scenario, so it can be widely used at the PCC point of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0051] Figure 1 1 is a schematic diagram of the main process of an online identification method for harmonic resonance of a power system according to an embodiment of the present invention.

[0052] Figure 2 It is an equivalent model of a power system in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0054] like Figure 1 FIG. 1 is a schematic diagram of an embodiment of an online identification method for harmonic resonance of a power system provided by the present invention. In this embodiment, the method includes the following steps:

[0055] Step S1, collecting voltage waveform data and current waveform data at a preset common coupling point in the power system at a preset sampling frequency, and preprocessing the collected voltage waveform data and current waveform data to obtain waveform difference; that is, using the power quality online synchronous monitoring device to record the voltage waveform and current waveform at the PCC point in the power system, and calculate the similarity of the voltage and current waveforms.

[0056] In a specific embodiment, the sampling frequency F s Collect voltage waveform data U at the PCC point (Point of Common Coupling) in the power system P and current waveform data I P The preset sampling frequency F s Set the frequency parameters to meet the following conditions:

[0057] Fs ≥r×H×50

[0058] Among them, F s is the sampling frequency, H is the maximum harmonic number to be analyzed, and r is the multiple.

[0059] Specifically, the collected voltage and current waveform data are normalized and standardized to obtain a waveform difference DF. The preprocessing of the collected voltage waveform data and current waveform data includes: normalizing and standardizing the voltage waveform data and the current waveform data according to the following formula:

[0060]

[0061] Among them, U Pi is the normalized voltage waveform data of the ith voltage, I Pi is the normalized i-th current waveform data, U′ Pi is the i-th voltage waveform data after normalization, I′ Pi is the i-th current waveform data after normalization;

[0062] Calculate the mean square error of voltage and current and the waveform difference according to the following formula:

[0063]

[0064] DF=|U Prms -I Prms |

[0065] Among them, U Prms is the mean square error of voltage, I Prms is the mean square error of the current, and N is the length of the collected voltage and current waveform data.

[0066] Step S2, obtaining the voltage complex matrix of the fundamental wave and each harmonic of the power system, and performing multiple transformations on the collected voltage waveform data and the current waveform data according to the voltage complex matrix of the fundamental wave and each harmonic, to obtain the current complex matrix and voltage complex matrix of the fundamental wave and each harmonic; that is, performing fast Fourier transform, and obtaining the voltage complex matrix of the fundamental wave and each harmonic after L transformations. Complex matrix of current of fundamental wave and each harmonic

[0067] In a specific embodiment, the current complex matrix and voltage complex matrix of the fundamental wave and each harmonic are obtained by performing fast Fourier transform on the collected voltage waveform data and current waveform data, with a preset number of cycles as a group, and obtaining the voltage complex matrix of the fundamental wave and each harmonic, and the current complex matrix of the fundamental wave and each harmonic after a preset number of transformations; wherein the number of cycles and the number of transformations are both positive integers. It is understandable that the collected voltage waveform data U P and current waveform data I P , take m integer cycles as a group, perform fast Fourier transform respectively, after L times transformation, the voltage complex matrix of fundamental wave and each harmonic is obtained Complex matrix of current of fundamental wave and each harmonic Among them, the total time of data collection meets Both m and L are positive integers.

[0068] Step S3, determining the fundamental wave and the total harmonic impedance amplitude array of the common coupling point according to the equivalent model of the power system; that is, using the complex independent component method, the fundamental wave and the total harmonic impedance amplitude array (Z all ) 1×H .

[0069] In a specific embodiment, determining the array of total impedance amplitudes of the fundamental wave and each harmonic at the common coupling point includes:

[0070] Determining a matrix A according to an equivalent model of the power system and determining an estimated value of the matrix A;

[0071] Harmonic impedances are filtered according to the following formula to obtain the impedance amplitude arrays on the system side and the impedance amplitude arrays on the load side:

[0072]

[0073] Among them, Re(k i ) is a complex number k i The real part of i is 1, 2; Z S is the Thevenin equivalent impedance of the power system; Z C is the Norton equivalent harmonic source and load impedance on the load side of the power system; is the estimated value of matrix A;

[0074] Substituting the system-side impedance amplitude array and the load-side impedance amplitude array into the following formula, we can obtain the fundamental wave and total harmonic impedance amplitude array of the power system at the common coupling point:

[0075]

[0076] Among them, Z allIt is an array of the total impedance amplitudes of the fundamental wave and each harmonic of the power system at the common coupling point.

[0077] It is understandable that the impedance amplitude array (Z) on the system side and the load side is obtained by using the complex independent component method. S ) 1×H 、(Z C ) 1×H , the calculation process is as follows:

[0078] According to the equivalent model of the power system in the attached figure, the following formula can be listed:

[0079]

[0080] Among them: U S , Z S are the Thevenin equivalent power source and impedance of the power system side respectively; I C , Z C Norton equivalent harmonic sources and load impedances on the load side of the power system respectively.

[0081] The above formula can be expressed as the following formula using the complex independent component method, and multiplication is performed on both sides of the equal sign. The transposed matrix of and After that, further decomposition can get the estimated value of matrix A

[0082] X=AS

[0083]

[0084] In order to eliminate the influence of amplitude scaling in the calculation results of the complex independent component method, it is assumed that the scaling matrix is:

[0085]

[0086] Combining the above three formulas, we get:

[0087]

[0088] Combining the above formula with matrix A, we can get:

[0089]

[0090] Then we have:

[0091]

[0092] From the above formula we can get:

[0093]

[0094] In order to eliminate the influence of the uncertain results of the complex independent component algorithm, the following definitions are given:

[0095]

[0096] Since the real part of the impedance of the power system is non-negative, the harmonic impedance can be screened through the above formula:

[0097]

[0098] Where: Re(k i ) is the real part of the complex number k i , and i takes 1 and 2.

[0099] The voltage complex matrix of the fundamental and each harmonic and the current complex matrix of the fundamental and each harmonic are brought into the above series of formulas, and the impedance amplitude array (Z S ) 1×H of the system side and the impedance amplitude array (Z C ) 1×H of the load side are obtained.

[0100] Step 4.2, the impedance amplitude array (Z S ) 1×H of the system side and the impedance amplitude array (Z C ) 1×H of the load side are brought into the following formula, and the impedance amplitude array (Z all ) 1×H of the total impedance of the fundamental and each harmonic at the PCC point is obtained:

[0101]

[0102] Step S4, determine the harmonic impedance peak value and the harmonic impedance valley value in the total impedance amplitude array, determine the harmonic number array corresponding to the harmonic impedance peak value and the harmonic number array corresponding to the harmonic impedance valley value according to the harmonic impedance peak value and the harmonic impedance valley value, and calculate the power factor of the fundamental and each harmonic, and obtain the power factor array after screening; that is, find the local peak value and the local valley value in the total impedance amplitude array (Z all ) 1×H by using the peak finding function (for example, the findpeaks function in MATLAB 2019a version), and place the serial numbers of the corresponding columns (the serial numbers of the columns correspond to the harmonic numbers) of the peak value and the valley value in the array (Z all ) 1×H in the harmonic number array T1 1 corresponding to the harmonic impedance peak value and the harmonic number array T1 2Calculate the power factors of the fundamental wave and each harmonic, and obtain the power factor array T2 after screening.

[0103] In a specific embodiment, determining the harmonic order array corresponding to the harmonic impedance peak and the harmonic order array corresponding to the harmonic impedance valley includes: inputting the serial numbers of the corresponding columns of the harmonic impedance peak and the harmonic impedance valley in the total impedance amplitude array into the harmonic order array corresponding to the harmonic impedance peak and the harmonic order array corresponding to the harmonic impedance valley, respectively.

[0104] In this embodiment, the power factor of the fundamental wave and each harmonic is calculated, and the power factor array is obtained after screening, including: the power factor of the fundamental wave and each harmonic is calculated according to the following formula to obtain a power factor matrix (PF): L×H :

[0105] PF f(i,j) =cos(θ uf(i,j) -θ If(i,j) )

[0106] Among them, PF f(i,j) is the power factor corresponding to the i-th row and j-th column, θ uf(i,j) is the phase angle of harmonic voltage at frequency f after fast Fourier transform, θ If(i,j) is the current phase angle at frequency f after fast Fourier transform.

[0107] Based on the harmonic order corresponding to the column number, the number of times the value of each column in the power factor matrix is ​​greater than the preset power factor threshold is counted to obtain a statistical array; wherein the corresponding column of the statistical array is the number of times the value of each column in the statistical power factor matrix is ​​greater than the preset power factor threshold; it can be understood that the power factor matrix (PF) is counted in units of columns (the column number corresponds to the harmonic order). L×H The number of times the value of each column is greater than ΔPF, and the statistical results are placed in the array (T PF1 ) 1×H in the corresponding column.

[0108] Determine the corresponding column number whose value in the statistical array is greater than the preset threshold value of times that the power factor is satisfied, and put the result into the power factor array. PF1 ) 1×H The median value is greater than ΔT PF1 In (T PF1 ) 1×H The corresponding column number of the power factor array T2 is placed in the power factor array T2; where: ΔPF is the power factor threshold, ΔPF ≥ 0.85; ΔT PF1 To meet the power factor times threshold ΔT PF1 Take a positive integer, and ΔT PF1 ≥L×0.9.

[0109] Step S5, judge whether the waveform difference degree, the harmonic number array and the power factor array corresponding to the harmonic impedance peak value and the harmonic number array and the power factor array corresponding to the harmonic impedance valley value meet the preset resonance condition, if meet, determine that the harmonic resonance occurs in the power system. That is, if the following conditions are met at the same time, it indicates that the harmonic resonance occurs in the system, and the parallel harmonic resonance number is placed in the set , and the series harmonic resonance number is placed in the set .

[0110] In specific embodiments, the preset resonance condition includes:

[0111] The similarity of the collected waveforms meets:

[0112] 1-DF≥ΔS

[0113] Wherein, DF is the waveform difference degree, and ΔS is the waveform similarity threshold of the voltage waveform data and the current waveform data. It can be understood that the similarity of the collected waveforms meets: 1-DF≥ΔS; wherein ΔS is the waveform similarity threshold of U P and I P .

[0114] The intersection of the harmonic number array and the power factor array corresponding to the harmonic impedance peak value is not an empty set;

[0115] The intersection set of the harmonic number array and the power factor array corresponding to the harmonic impedance valley value is not an empty set. It can be understood that the intersection of the harmonic number array and the power factor array T2 corresponding to the harmonic impedance peak value is The intersection set of the harmonic number array and the power factor array T2 corresponding to the harmonic impedance valley value is and is not an empty set.

[0116] In summary, the embodiment of the present application has the following beneficial effects:

[0117] The online identification method of the power system harmonic resonance provided by the present application combines the similarity of the collected waveforms, the harmonic impedance and the power factor multiple parameters, and is accurate and faster in identification. It can identify the series harmonic resonance and the parallel harmonic resonance in the power system at the same time, and only needs the voltage and current waveform data at the PCC point, without the need for fine modeling, without the constraint of the use scene, and can be used at the PCC point of the power system.

[0118] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. An online identification method for harmonic resonance of a power system, characterized in that: include: Collecting voltage waveform data and current waveform data at a preset common coupling point in the power system at a preset sampling frequency, and preprocessing the collected voltage waveform data and current waveform data to obtain a waveform difference; Obtaining a complex voltage matrix of a fundamental wave and each harmonic of the power system, and performing multiple transformations on the collected voltage waveform data and current waveform data according to the complex voltage matrix of the fundamental wave and each harmonic to obtain a complex current matrix and a complex voltage matrix of the fundamental wave and each harmonic; Determine an array of total impedance amplitudes of the fundamental wave and each harmonic at the common coupling point according to an equivalent model of the power system; Determine the harmonic impedance peak value and the harmonic impedance valley value in the total impedance amplitude array, determine the harmonic order array corresponding to the harmonic impedance peak value and the harmonic order array corresponding to the harmonic impedance valley value according to the harmonic impedance peak value and the harmonic impedance valley value, and calculate the power factor of the fundamental wave and each harmonic, and obtain a power factor array after screening; It is determined whether the waveform difference, the harmonic order array and power factor array corresponding to the harmonic impedance peak value, and the harmonic order array and power factor array corresponding to the harmonic impedance valley value meet the preset resonance conditions. If so, it is determined that harmonic resonance has occurred in the power system.

2. The method according to claim 1, wherein The preset sampling frequency is set to a frequency parameter that meets the following conditions: F S ≥r×H×50 Among them, F s is the sampling frequency, H is the maximum harmonic number to be analyzed, and r is the multiple.

3. The method according to claim 2, wherein The preprocessing of the collected voltage waveform data and current waveform data includes: The voltage waveform data and the current waveform data are normalized and standardized according to the following formulas: Among them, U Pi is the normalized voltage waveform data of the ith voltage, I Pi is the normalized i-th current waveform data, U′ Pi is the i-th voltage waveform data after normalization, I′ Pi is the i-th current waveform data after normalization; The waveform difference of the mean square error of voltage and current is calculated according to the following formula: DF=|U Prms -I Prms | Among them, U Prms is the mean square error of voltage, I Prms is the mean square error of the current, and N is the length of the collected voltage and current waveform data.

4. The method according to claim 3, wherein The current complex matrix and voltage complex matrix obtained by obtaining the fundamental wave and each harmonic include: The collected voltage waveform data and current waveform data are grouped into a preset number of cycles and subjected to fast Fourier transform respectively. After the preset number of transformations, the voltage complex matrix of the fundamental wave and each harmonic, and the current complex matrix of the fundamental wave and each harmonic are obtained; wherein the number of cycles and the number of transformations are both positive integers.

5. The method according to claim 4, wherein The determining of the total impedance amplitude array of the fundamental wave and each harmonic at the common coupling point includes: Determining a matrix A according to an equivalent model of the power system and determining an estimated value of the matrix A; Harmonic impedances are filtered according to the following formula to obtain the impedance amplitude arrays on the system side and the impedance amplitude arrays on the load side: Among them, Re(k i ) is a complex number k i The real part of i is 1, 2; Z S is the Thevenin equivalent impedance of the power system; Z C is the Norton equivalent load impedance on the load side of the power system; is the estimated value of matrix A; Substituting the system-side impedance amplitude array and the load-side impedance amplitude array into the following formula, we can obtain the fundamental wave and total harmonic impedance amplitude array of the power system at the common coupling point: Among them, Z all It is an array of the total impedance amplitudes of the fundamental wave and each harmonic of the power system at the common coupling point.

6. The method according to claim 5, wherein The harmonic order array corresponding to the harmonic impedance peak value and the harmonic order array corresponding to the harmonic impedance valley value include: The serial numbers of the columns corresponding to the harmonic impedance peak value and the harmonic impedance valley value in the total impedance amplitude array are respectively input into the harmonic order array corresponding to the harmonic impedance peak value and the harmonic order array corresponding to the harmonic impedance valley value.

7. The method according to claim 6, wherein The power factor array obtained by calculating the power factor of the fundamental wave and each harmonic after screening includes: The power factor matrix is ​​obtained by calculating the power factor of the fundamental wave and each harmonic according to the following formula: PF f(i,j) =cos(θ uf(i,j) -θ If(i,j) ) Among them, PF f(i,j) is the power factor corresponding to the i-th row and j-th column, θ uf(i,j) is the phase angle of harmonic voltage at frequency f after fast Fourier transform, θ If(i,j) is the current phase angle at frequency f after fast Fourier transform.

8. The method according to claim 7, wherein Also includes: Based on the harmonic order corresponding to the column number, the number of times the value of each column in the power factor matrix is ​​greater than the preset power factor threshold is counted to obtain a statistical array; wherein the corresponding column of the statistical array is the number of times the value of each column in the statistical power factor matrix is ​​greater than the preset power factor threshold.

9. The method according to claim 8, wherein Also includes: Determine whether the value in the statistical array is greater than the corresponding column number of the preset power factor meeting the threshold value, and put the result into the power factor array.

10. The method according to claim 9, wherein The preset resonance conditions include: The similarity of the collected waveforms satisfies: 1-DF≥ΔS Wherein, DF is the waveform difference, ΔS is the waveform similarity threshold of the voltage waveform data and the current waveform data; The intersection of the harmonic order array and the power factor array corresponding to the harmonic impedance peak is not an empty set; The intersection set of the harmonic order array and the power factor array corresponding to the harmonic impedance valley value is not an empty set.

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