CN114966324A - Single-phase earth fault positioning method based on improved variational modal decomposition - Google Patents
Single-phase earth fault positioning method based on improved variational modal decomposition Download PDFInfo
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Abstract
The invention discloses a single-phase earth fault positioning method based on improved variational modal decomposition, which comprises the following steps: s1, collecting transient zero sequence current waveform i of fault line d (t) and an initial fault angle phi; s2, for transient zero sequence current waveform i d (t) processing and obtaining zero sequence current waveform f for filtering power frequency component d (t); s3, determining variation modal decomposition parameters K and alpha by using a slime algorithm; s4, filtering out zero sequence current waveform f of power frequency component d (t) carrying out metamorphic modal decomposition, and removing high-frequency and white noise components to obtain a main resonant frequency component u' d，k (g) (ii) a S5, calculating a correlation coefficient between main resonance frequency components of transient zero-sequence currents of adjacent detection points and a set threshold value rho T And comparing to judge the fault section. The method of the invention removes the influence of noise and high-frequency components by utilizing variational modal decomposition, has strong anti-noise interference capability and greatly improves the positioning accuracy.
Description
Technical Field
The invention relates to the field of single-phase earth fault positioning of a power distribution network, in particular to a single-phase earth fault positioning method based on improved variational modal decomposition.
Background
The electric power system in China mostly adopts a mode that a neutral point is not grounded or is grounded through an arc suppression coil, the fault generated in the operation of the grounding mode is mainly a single-phase grounding fault, after the fault occurs, the system can continue to operate for 1-2h, but the voltage continuously increased by a non-fault phase can break down an insulated weak link, so that the interphase short circuit fault is caused, and the serious loss is caused to the electric power system. Therefore, it is necessary to deeply research the single-phase earth fault location of the grounding system so as to quickly and accurately find out the fault location and solve the fault problem.
In view of the positioning of the low-current grounding fault, a large number of scholars at home and abroad have conducted a great deal of research in recent years, but various methods have defects more or less. The active positioning method is high in cost and is easily influenced by detection equipment, while the passive positioning method overcomes some defects of the active positioning method to a certain extent, but the problem of inaccurate positioning also exists under the influence of a noise environment, and in the existing method for judging a fault section by utilizing the waveform similarity of transient zero-sequence currents at the upstream and the downstream of a fault point, the method for extracting the main resonant frequency component of the zero-sequence current is too complicated, and parameters K and alpha in a variational modal decomposition algorithm need to be set artificially, so that the decomposition effect is unstable, and the slime mold algorithm can be well optimized. Therefore, in order to solve the above problems, the present invention provides a single-phase ground fault location method based on improved variational modal decomposition.
The chinese patent literature discloses "a single-phase earth fault positioning method based on power distribution network data processing", whose publication number is CN106990332B, and discloses a single-phase earth fault positioning method based on power distribution network data processing, which includes S01: acquiring mass real-time data of the power distribution network through equipment such as a power distribution terminal, a fault indicator and an intelligent electric meter; s02: establishing a power distribution network real-time flow data analysis platform based on the Storm cluster; s03: designing a streaming data processing topological structure which integrates multiple single-phase earth fault positioning technologies; s04: and outputting and storing results according to the criteria of different single-phase earth fault positioning technologies. However, the chinese patent publication No. CN106990332B is simple in process and does not relate to a specific algorithm.
Disclosure of Invention
The invention solves the problem of inaccurate section positioning of zero-sequence current of a small-current grounding system of a power distribution network when noise, power frequency and high-frequency components exist after a metallic single-phase grounding fault occurs, and provides a single-phase grounding fault positioning method based on improved variational modal decomposition.
In order to achieve the purpose, the invention adopts the following technical scheme: a single-phase earth fault positioning method based on improved variational modal decomposition comprises the following steps:
s1, collecting transient zero sequence current waveform i of fault line d (t) and an initial fault angle phi;
s2, for transient zero sequence current waveform i d (t) processing and obtaining zero sequence current waveform f with power frequency components filtered d (t)；
S3, determining variation modal decomposition parameters K and alpha by using a slime algorithm;
s4, filtering out zero sequence current waveform f of power frequency component d (t) carrying out metamorphic modal decomposition, and removing high-frequency and white noise components to obtain a main resonant frequency component u' d，k (g)；
S5, calculating a correlation coefficient between main resonance frequency components of transient zero-sequence currents of adjacent detection points and a set threshold value rho T And comparing to judge the fault section.
In the invention, firstly, the d-th transient zero-sequence current waveform i is collected d (t), initialize d1, filter i d Power frequency component in (t) to obtain f d (t), then determining variation modal decomposition parameters K and alpha by using a slime algorithm, and pairing f by using the number K and alpha d (t) mode of variationDecomposing to obtain K zero-sequence current components u d，k (t) removing u d，k (t) obtaining a primary resonant frequency component waveform u 'from the medium-high frequency component and the noise component' d，k (g) Calculating u' d，k (g) And u' d+1 K (g), and a set threshold value ρ T Comparing and judging a fault section; the method of the invention removes the influence of high-frequency component, power frequency component and noise in the zero sequence current by using the improved variation modal algorithm and the fundamental wave offset method, and compares the correlation coefficients by using the extracted main resonance frequency, thereby improving the accuracy of fault section positioning.
Preferably, the step S1 is specifically: when a power distribution network has a metallic single-phase earth fault, a feeder line terminal device is utilized to collect a transient zero-sequence current waveform i d (t) and initial failure angle φ, i d (t) is the d-th zero-sequence current waveform from the bus end, 0<t<t b ，t b The following relationship is present with respect to the initial fault angle phi:
t b ＝4T b -2|sinφ|
in the formula: t is b Power frequency period, t b Is the acquisition time. In the invention, when a fault occurs, the transient zero sequence current waveform i is processed according to feeder line terminal devices on all detection points of a fault line d (t) and an initial fault angle phi are collected.
Preferably, the step S2 includes the steps of:
s21, firstly, transient zero sequence current waveform i d (t) performing a Hilbert transform, specifically:
s22, constructing a signal
To pair
Obtaining zero sequence current waveform f of filtering power frequency by taking real part d (t). In the present invention, firstly, for i d (t) Hilbert transform, then constructing the signal, and filtering out i d (t) power frequency component to obtain zero sequence current waveform f with power frequency filtered d (t)。
Preferably, the step S3 includes the steps of:
s31, initializing variational modal decomposition f d The number K of the components after (t) and an accuracy factor alpha are used, K and alpha are used as horizontal and vertical coordinates, a coordinate system is established by taking (2, 100) as a coordinate origin, and a node coordinate is X m,n (K, α), initializing M to 1, N to 1, M being the update times, M being the update termination times, N being the coordinate ordinal number, N being the number of coordinate points to be updated;
s32, using X m,n Value pair f of coordinates K and alpha d (t) carrying out variation modal decomposition to obtain K zero-sequence current components u d，k (t), K ═ 1,2, …, K; and carrying out time discretization treatment to obtain u d，k (g) Using fitness function
Updating W m (n), wherein G is a discretization point sequence, G is the total number of discretized points, a d，k (g) Is u d，k (g) The envelope signal of (a) the envelope signal of (b),
E m (n) is the fitness value of the nth node at the mth update, W m (n) is the weight of the nth node at the mth update;
s33, determines whether N > is true, if yes, proceeds to step S34, if no, N is N +1, returns to step S32,
s34, calculating the fitness value E of all the N nodes updated at the m time m And sorting; and denotes E m Middle and smaller half nodes, dis denotes E m Middle and larger half nodes, E b Is E m Middle minimum value, E w Is E m The maximum value is then n is 1;
s35, utilizing
Updating
Wherein rand is a random number uniformly distributed between 0 and1, x min Is (2,10) x max Is (100,20000), rand1 and rand2 are random numbers between 0 and1, X b To a fitness value of E b Node coordinates of (2), X rand1 、X rand2 Two random node coordinates, Z is 0.3, p ═ tanh (E) b -E m (n)), randA is [ -a, a ]]Random number in between, randB is [ -b, b]A is artanh (1-M/M), b is 1-M/M;
s36, determining whether N > is true, if yes, executing step S37, otherwise, returning to step S35;
s37, judging m +1>If M is true or if more than 99% of the nodes are located on the same coordinate, if so, E m If the minimum node coordinate is the optimal solution of the parameters K and α, and if no, m is m +1 and n is 1, the process returns to step S32. The method optimizes the selection of K and alpha values in the variation modal algorithm by using the slime algorithm, and can accurately decompose the transient zero-sequence current without power frequency, thereby accurately positioning the fault.
Preferably, the step S4 includes the steps of:
s41, for f d (t) carrying out variational modal decomposition to obtain K zero-sequence current components u d，k (t)，k＝1,2,…,K，u d，k (t) represents f d (t) the k-th zero-sequence current component obtained by decomposition, for u d，k (t) performing time discretization to obtain u d，k (g) Calculating the kth discretized current component u d，k (g) Energy of
S42, taking maximum value max (Q) of K current components 1 ，Q 2 ，…，Q k ) U of a component of energy max d，k (g) Is a main resonance frequencyAmount, recorded as u' d，k (g) And removing high frequency and white noise components. In the present invention, K and a are used to f d (t) carrying out variational modal decomposition to obtain K zero-sequence current components u d，k (t) use of u d，k (t) energy is used for distinguishing each component, and high-frequency components and noise components are removed to obtain a main resonance frequency component waveform u' d，k (g)。
Preferably, the step S5 includes the steps of:
s51, calculating u' d，k (g) And u' d+1，k (g) Coefficient of correlation between
In the formula: u' d ， k (g) And u' d+1，k (g) The transient zero-sequence current main resonance frequency components of the d-th detection point and the d + 1-th detection point respectively represent a section between the d-th detection point and the d + 1-th detection point on the line;
s52, if the correlation coefficient rho d Less than a set threshold value rho T If yes, the d-th section is determined to be a fault section, otherwise, step S53 is executed; s53, d +1, and d is judged>If the result is positive, the system judges the section after D +1 is a fault section and quits; if not, the process returns to step S2. In the invention, starting from a fault line bus section, calculating a main resonance frequency component u 'of transient zero-sequence current waveforms of two adjacent detection points' d，k (g) And u' d+1，k (g) Coefficient of correlation between p d Finally according to the correlation coefficient rho d And judging a fault section.
The invention has the beneficial effects that: the method of the invention selects the optimal waveform duration by utilizing the initial fault angle, thus shortening the time required for subsequent similarity judgment; power frequency is removed by power frequency filtering, so that the influence of the power frequency on similarity judgment is eliminated; the selection of K and alpha values in the variation modal algorithm is optimized by utilizing the slime algorithm, and the transient zero-sequence current without power frequency can be accurately decomposed, so that the fault location is accurately carried out; and the influence of noise and high-frequency components is removed by utilizing the variation modal decomposition, the anti-noise interference capability is strong, and the positioning accuracy is greatly improved.
Drawings
FIG. 1 is a flow chart of a single-phase earth fault location method based on improved variational modal decomposition according to the present invention;
FIG. 2 is a schematic diagram of a power distribution network based on an improved variational modal decomposition single-phase earth fault location method of the present invention;
FIG. 3 is a schematic diagram of an original zero-sequence current waveform and a waveform after power frequency filtering in a single-phase earth fault positioning method based on improved variational modal decomposition according to the present invention;
fig. 4 is a schematic diagram of waveforms of components of a zero-sequence current after decomposition and filtering by using a variational modal algorithm when K and alpha values are determined in the single-phase earth fault location method based on the improved variational modal decomposition of the present invention.
Detailed Description
Example 1:
the embodiment provides a single-phase earth fault positioning method based on improved variational modal decomposition, and referring to fig. 1, the method mainly includes the following steps.
Step S1, collecting transient zero sequence current waveform i of fault line d (t) and an initial fault angle phi; specifically, in this step, when a metallic single-phase earth fault occurs in the power distribution network, a feeder line terminal device at all detection points of the fault line is used to collect a transient zero-sequence current waveform i d (t) and initial failure angle φ, i d (t) is the D-th zero-sequence current waveform from the bus end, the initialized D is 1, D is the number of the fault line detection to be diagnosed, and 0<t<t b ，t b The following relationship is associated with the initial fault angle phi: t is t b ＝4T b -2|sinφ|
Wherein: t is b Representing the power frequency period, t b Indicating the acquisition time period.
Step S2, for transient zero sequence current waveform i d (t) processing and obtaining zero sequence current waveform f for filtering power frequency component d (t); specifically, the present step includes two substeps, step S21 and step S22.
Step S21, for transient zero sequence current waveform i d (t) performing a Hilbert transform,specifically, the following formula is shown:
step S22, constructing a signal
To pair
Obtaining zero sequence current waveform f of filtering power frequency by taking real part d (t) of (d). Specifically, in this embodiment, in the present invention, first, i is treated d (t) Hilbert transform, then constructing the signal, and filtering out i d (t) power frequency component to obtain zero sequence current waveform f with power frequency filtered d (t)。
Step S3, determining variation modal decomposition parameters K and alpha by using a slime mold algorithm; specifically, the method comprises the following substeps.
Step S31, initializing variational modal decomposition f d The number K of the components after (t) and an accuracy factor alpha are used, K and alpha are used as horizontal and vertical coordinates, a coordinate system is established by taking (2, 100) as a coordinate origin, and a node coordinate is X m,n (K, α), initializing M ═ 1, N ═ 1, M denotes the number of updates, M denotes the number of update terminations, N denotes the coordinate ordinal number, N denotes the number of coordinate points to be updated; specifically, K is a random natural number between 2 and 10; alpha is a natural number between 100 and 20000.
Step S32, by X m,n Value pair f of coordinates K and alpha d (t) carrying out variation modal decomposition to obtain K zero-sequence current components u d，k (t), K ═ 1,2, …, K; and carrying out time discretization treatment to obtain u d，k (g) Using fitness function
Updating W m (n) in the above formula, G represents a discretization point sequence, G represents the total number of discretized points, a d，k (g) Represents u d，k (g) Envelope signal of (1), wherein
E m (n) denotes the fitness value of the nth node at the mth update, W m (n) represents the weight of the nth node at the mth update.
In step S33, it is determined whether N > is true, if yes, step S34 is executed, and if no, N is N +1, and the process returns to step S32.
Step S34, calculating the fitness value E of all the N nodes updated at the m-th time m And sorting; and is E m Middle and smaller half nodes, dis is E m Middle and larger half nodes, E b Represents E m Middle minimum value, E w Represents E m And n is 1 again.
Step S35, use
Updating
Wherein rand denotes a random number uniformly distributed between 0 and1, x min Denotes (2,10), x max Denotes (100,20000), rand1, rand2 denote random numbers between 0 and1, X b Representing a fitness value of E b Node coordinates of (2), X rand1 、X rand2 Represents two random node coordinates, in this embodiment, Z is specifically 0.3, and p ═ tanh (| E) b -E m (n) |), randA [ -a, a ]]Random number in between, randB denotes [ -b, b [ - ]]A is artanh (1-M/M), b is 1-M/M;
in step S36, it is determined whether N > is true, if so, step S37 is executed, and if not, N is N +1, and the process returns to step S35.
Step S37, judge m +1>If M is true or if more than 99% of the nodes are located on the same coordinate, if so, E m If the minimum node coordinate is the optimal solution of the parameters K and α, and if no, m is m +1 and n is 1, the process returns to step S32. The method optimizes the selection of K and alpha values in the variational modal algorithm by utilizing the slime algorithm, and can be accurate and zeroAnd the transient zero-sequence current with the power frequency removed is decomposed by mistake, so that the fault location is accurately carried out.
Step S4, filtering the zero sequence current waveform f of the power frequency component d (t) performing metamorphic modal decomposition, and removing high-frequency and white noise components to obtain a main resonant frequency component u' d，k (g) In that respect Specifically, the method comprises the following substeps.
Step S41, for f d (t) carrying out variational modal decomposition to obtain K zero-sequence current components u d，k (t), wherein K is 1,2, …, K, u d，k (t) represents f d (t) the k-th zero-sequence current component obtained by decomposition, for u d，k (t) performing time discretization to obtain u d，k (g) Calculating the kth discretized current component u d，k (g) Energy of
In step S42, the K current components are maximized to max (Q) 1 ，Q 2 ，…，Q k ) U of a component of energy max d，k (g) Is a primary resonant frequency component, denoted as u' d，k (g) And removing high frequency and white noise components. In this example, K and α are used to pair f d (t) carrying out variational modal decomposition to obtain K zero-sequence current components u d，k (t) use of u d，k (t) distinguishing each component by energy, and removing high-frequency component and noise component to obtain main resonance frequency component waveform u d，k (g)。
Step S5, calculating the correlation coefficient between the main resonance frequency components of the transient zero-sequence current at the adjacent detection points and the set threshold value rho T And comparing to judge the fault section. Specifically, the correlation coefficient is first obtained, and then a comparison judgment is performed, and in step S51, u' d，k (g) And u' d+1，k (g) Coefficient of correlation between
Wherein: u' d，k (g) And u' d+1，k (g) Respectively representing the transient zero-sequence current main resonance of the d-th detection point and the d + 1-th detection pointAnd a frequency component d is a section between the d-th detection point and the d + 1-th detection point on the line.
Step S52, if the correlation coefficient ρ is not equal to the predetermined value d Less than a set threshold value rho T Then the d-th section is determined to be a faulty section, otherwise step S53 is performed.
In step S53, d +1 is determined>If the result is positive, the system judges the section after D +1 is a fault section and quits; if not, the process returns to step S2. In this embodiment, starting from the fault line bus segment, the main resonant frequency component u 'of the transient zero-sequence current waveforms of two adjacent detection points is calculated' d，k (g) And u' d+1，k (g) Coefficient of correlation between p d Finally according to the correlation coefficient rho d And judging a fault section.
In the invention, firstly, the waveform i of the d-th transient zero-sequence current is collected d (t), initialize d1, filter i d Power frequency component in (t) to obtain f d (t), then determining variation modal decomposition parameters K and alpha by using a slime algorithm, and pairing f by using the number K and alpha d (t) carrying out variational modal decomposition to obtain K zero-sequence current components u d，k (t) removing u d，k (t) obtaining a primary resonant frequency component waveform u 'from the medium-high frequency component and the noise component' d，k (g) Calculating u' d，k (g) And u' d+1，k (g) Coefficient of correlation between, and a set threshold value ρ T Comparing and judging a fault section; the method of the invention removes the influence of high-frequency component, power frequency component and noise in the zero sequence current by using the improved variation modal algorithm and the fundamental wave offset method, and compares the correlation coefficients by using the extracted main resonance frequency, thereby improving the accuracy of fault section positioning.
Referring to fig. 1, the working principle of the present invention is specifically as follows: when a small current grounding system has a metallic single-phase grounding fault, transient zero-sequence current is collected by using a feeder line terminal device of a power distribution network circuit, and the optimal duration of a waveform to be collected is calculated through an initial fault angle; then, carrying out power frequency filtering on the acquired transient zero-sequence current waveform by using a fundamental wave offset method; determining K and alpha values of variable mode decomposition by using a slime algorithm, decomposing the filtered zero sequence current waveform by using the variable mode algorithm, removing noise and high-frequency components, and extracting a main resonance frequency component; and finally, judging the fault section by using the obtained correlation coefficient of the main resonant frequency components at the two ends of each section.
Example 2:
on the basis of example 1, a simulation experiment is used to describe in more detail, and referring to fig. 2, the system of fig. 2 is a cable-overhead line hybrid line, and the system capacitance current is 73A; the arc suppression coil adopts overcompensation with 8% of compensation degree, the equivalent inductance is 0.244H, and the series resistance is 1.53 omega; specific line parameters are shown in table 1; and setting a detection point M, N, P, Q on the fault line, wherein M is a bus end detection point, and the fault point is O. This allows the division into 4 sectors MN (4km), NP (7km), PQ (2km) and the end-stream sector (the distance is represented by H). Other parameters are shown in fig. 2 and table 1.
TABLE 1 line model parameters
| Line parameters | Overhead line | Cable with a protective layer |
| Positive sequence resistance/(omega. km) -1 ) | 0.17 | 0.27 |
| Zero sequence resistance/(omega km) -1 ) | 0.32 | 2.7 |
| Positive sequence inductance/(mH.km) -1 ) | 1.017 | 0.255 |
| Zero sequence inductance/(mH km) -1 ) | 3.56 | 1.109 |
| Positive sequence capacitance/(μ F · km) -1 | 0.115 | 0.376 |
| Zero sequence capacitance/(mu F km) -1 | 0.0062 | 0.276 |
When the O point generates single-phase earth fault, the system is A-phase earth fault and the fault line is L 5 Fault distance MO 9km, H2 km, fault initial phase angle phi 90 DEG and grounding resistance R g 0.5. omega. and NP is a failure segment.
Referring to fig. 3 and 4, transient zero-sequence current waveforms of the detection points M, N, P, Q are collected, the waveform length is selected to be 2 power frequency cycles (the power frequency cycle is 0.02s, and waveforms between 0.025s and 0.065s in fig. 3 and 4) by using an initial fault angle, gaussian white noises with signal-to-noise ratios of 10dB, 5dB, 15dB and 10dB are respectively injected into the collected M, N, P, Q-point signals, and then zero-sequence current waveforms required for decomposition are obtained; performing power frequency filtering on the waveform by using a fundamental wave offset method to obtain a waveform as shown in fig. 3; k and alpha values of variation modal decomposition are determined by using a slime algorithm, K and alpha values at M, N points are determined to be 3 and 2058, K and alpha values at P, Q points are determined to be 3 and 1721, transient zero-sequence current waveforms at four detection points are all NMF1 component energy highest and are main resonance frequency, and specific waveform components are shown in FIG. 4. And finally, carrying out similarity comparison (the threshold value is set to be 0.8 in the simulation experiment) by utilizing the correlation coefficient between the main resonant frequency component waveforms of the zero sequence current waveforms of each point and the set threshold value, thereby carrying out fault section positioning and obtaining simulation data as shown in table 2.
TABLE 2 positioning results
As can be seen from Table 2, when the similarity of zero sequence current containing noise, power frequency and high frequency components is judged, the system makes a misjudgment, and after the power frequency component and the noise are filtered by the method, the fault section can be accurately judged; when noise with lower signal-to-noise ratio is further injected into the transient zero-sequence current (3 dB, 5dB and 5dB noise are respectively injected into each point M, N, P, Q), the method can still accurately judge the fault section.
In summary, in a noise environment, the transient zero-sequence current waveform similarity comparison is affected by noise, power frequency and high-frequency components, so that the fault location is misjudged; the method selects the optimal waveform duration by utilizing the initial fault angle, so that the time required for subsequent similarity judgment is shortened; and after filtering power frequency components and removing noise components and high frequency components by a variation modal decomposition algorithm after optimizing parameters by a fundamental wave offset method and a slime bacteria algorithm, similarity judgment is carried out by using the extracted main resonance frequency components, and accuracy of section positioning is greatly improved.
The above embodiments are further illustrated and described in order to facilitate understanding of the invention, and no unnecessary limitations are to be understood therefrom, and any modifications, equivalents, and improvements made within the spirit and principle of the invention should be included therein.
Claims (6)
1. A single-phase earth fault positioning method based on improved variational modal decomposition is characterized by comprising the following steps:
s1, collecting transient zero sequence current waveform i of fault line d (t) and an initial fault angle phi;
s2, for transient zero sequence current waveform i d (t) treating and filtering offZero sequence current waveform f of power frequency component d (t)；
S3, determining variation modal decomposition parameters K and alpha by using a slime algorithm;
s4, filtering out zero sequence current waveform f of power frequency component d (t) carrying out metamorphic modal decomposition, and removing high-frequency and white noise components to obtain a main resonant frequency component u' d，k (g)；
S5, calculating a correlation coefficient between main resonance frequency components of transient zero-sequence currents of adjacent detection points and a set threshold value rho T And comparing to judge the fault section.
2. The single-phase earth fault location method based on improved variational modal decomposition according to claim 1, wherein the step S1 specifically comprises: when a power distribution network has a metallic single-phase earth fault, a feeder line terminal device is utilized to collect a transient zero-sequence current waveform i d (t) and initial failure angle φ, i d (t) is the d-th zero-sequence current waveform from the bus end, 0<t<t b ，t b The following relationship is present with respect to the initial fault angle phi:
t b ＝4T b -2|sinφ|
in the formula: t is b Power frequency period, t b Is the acquisition time.
3. The single-phase earth fault location method based on improved variational modal decomposition according to claim 1 or 2, wherein said step S2 comprises the steps of:
s21, firstly, transient zero sequence current waveform i d (t) performing a Hilbert transform, specifically:
s22, constructing a signal
To pair
Obtaining zero sequence current waveform f of filtering power frequency by taking real part d (t)。
4. The single-phase earth fault location method based on improved variational modal decomposition according to claim 1 or 2, wherein said step S3 comprises the steps of:
s31, initializing variational modal decomposition f d The number K of the components after (t) and an accuracy factor alpha are used, K and alpha are used as horizontal and vertical coordinates, a coordinate system is established by taking (2, 100) as a coordinate origin, and a node coordinate is X m,n (K, α), initializing M to 1, N to 1, M being the update times, M being the update termination times, N being the coordinate ordinal number, N being the number of coordinate points to be updated;
s32, using X m,n Value pair f of coordinates K and alpha d (t) carrying out variation modal decomposition to obtain K zero-sequence current components u d，k (t), K ═ 1,2, …, K; and carrying out time discretization treatment to obtain u d，k (g) Using fitness function
Updating W m (n), wherein G is a discretization point sequence, G is the total number of points after discretization, a d，k (g) Is u d，k (g) The envelope signal of (a) is determined,
E m (n) is the fitness value of the nth node at the mth update, W m (n) is the weight of the nth node at the mth update;
s33, determines whether N > is true, if yes, proceeds to step S34, if no, N is N +1, returns to step S32,
s34, calculating the fitness value E of all the N nodes updated at the m time m And sorting; and denotes E m Middle and smaller half nodes, dis denotes E m Middle and larger half nodes, E b Is E m Middle minimum value, E w Is E m The maximum value is then n is 1;
s35, utilizing
Updating
Wherein rand is a random number uniformly distributed between 0 and1, x min Is (2,10) x max Is (100,20000), rand1 and rand2 are random numbers between 0 and1, X b To a fitness value of E b Node coordinates of (a), X rand1 、X rand2 Two random node coordinates, Z is 0.3, p ═ tanh (| E) b -E m (n) |), randA is [ -a, a ]]Random number in between, randB is [ -b, b]A is artanh (1-M/M), b is 1-M/M;
s36, determining whether N > is true, if yes, executing step S37, if no, N is N +1, returning to step S35;
s37, judging m +1>If M is true or if more than 99% of the nodes are located on the same coordinate, if so, E m If the minimum node coordinate is the optimal solution of the parameters K and α, and if no, m is m +1 and n is 1, the process returns to step S32.
5. The single-phase earth fault location method based on improved variational modal decomposition according to claim 4, wherein said step S4 comprises the steps of:
s41, for f d (t) carrying out variational modal decomposition to obtain K zero-sequence current components u d，k (t)，k＝1,2,…,K，u d，k (t) represents f d (t) the k-th zero-sequence current component obtained by decomposition, for u d，k (t) performing time discretization to obtain u d，k (g) Calculating the kth discretized current component u d，k (g) Energy of
S42, taking maximum value max (Q) of K current components 1 ，Q 2 ，…，Q k ) U of a component of energy max d，k (g) Is a primary resonant frequency component, denoted as u' d，k (g) And removing high frequency and white noise components.
6. The single-phase earth fault location method based on improved variational modal decomposition according to claim 5, wherein said step S5 comprises the steps of:
s51, calculating u' d，k (g) And u' d+1，k (g) Coefficient of correlation therebetween
In the formula: u' d，k (g) And u' d+1，k (g) The transient zero-sequence current main resonance frequency components of the d-th detection point and the d + 1-th detection point respectively represent a section between the d-th detection point and the d + 1-th detection point on the line;
s52, if the correlation coefficient rho d Less than a set threshold value rho T If yes, the d-th section is determined to be a fault section, otherwise, step S53 is executed;
s53, determining whether D > is D +1, if so, the system determines that the section after D +1 is a fault section, and exits; if not, the process returns to step S2.
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