DC distribution network fault location method and system based on voltage traveling wave similarity

Abstract

The present invention discloses a method for locating faults in a DC distribution network based on voltage traveling wave similarity, comprising: obtaining the zero-mode voltage of the line, determining the arrival time of the traveling wave head according to the zero-mode voltage mutation amount, and determining the main frequency of the wave head using fast Fourier transform; assuming the location of the fault point according to the dichotomy method, estimating the fault resistance value according to the signal amplitude, and calculating the refraction and reflection coefficients of the fault point and the beginning and end; selecting a square wave with the same frequency as the main frequency of the wave head as the initial traveling wave signal, and calculating the attenuated signal waveform after the initial traveling wave signal has been folded back different times; superimposing the attenuated signal waveform after being folded back different times into a synthetic signal, and calculating the similarity between the synthetic waveform and the measured traveling wave using the Pearson correlation coefficient. The present invention belongs to the field of power grid fault location technology, and specifically provides a DC distribution network fault location system and method whose effectiveness is not affected by line length, transition resistance, and fault location, and the fault location result has high accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid fault location, and in particular relates to a method and system for locating faults in a DC distribution network based on voltage traveling wave similarity. Background Art

[0002] To accommodate the large-scale development of renewable energy, power systems are rapidly evolving toward intelligentization. DC grids, which contain numerous power electronic devices, are a crucial component of intelligent power systems. Short-circuit fault protection is a key technology in power systems. While research on AC grid fault protection is highly mature, that of DC grids is still in its developmental stages. Firstly, DC grids are low-inertia systems, with DC transmission line impedance much lower than that of AC lines. After a short-circuit fault occurs, the energy storage elements in the DC system rapidly discharge, causing the fault current to rise rapidly. Therefore, compared to AC grids, the short-circuit fault current in DC grids increases more rapidly. Secondly, the fault current in DC grids is direct current, and the time it takes for the fault current to reach zero crossing is longer. Therefore, the zero-crossing tripping method used in AC grids cannot be applied to DC grid fault protection. These two factors combine to create significant challenges for DC grid fault protection.

[0003] Doing a good job in fault location in the DC distribution network is of great significance to ensuring the healthy and continuous operation of the DC distribution network, improving the intelligence of the power system, absorbing distributed renewable energy to a greater extent, and solving the current energy crisis and environmental pollution problems. Summary of the Invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a DC distribution network fault location method and system based on voltage traveling wave similarity. The effectiveness is not affected by line length, transition resistance and fault location. Simulation results show that the obtained fault location result has high accuracy.

[0005] The technical solution adopted by the present invention is as follows: A DC distribution network fault location method based on voltage traveling wave similarity of the present invention comprises the following steps:

[0006] S1: Use the zero-mode voltage acquisition device installed at the head and end of the distribution network to obtain the line zero-mode voltage. Determine the arrival time of the traveling wave front based on the zero-mode voltage mutation. Select the waveform of the 5-millisecond time window after the arrival time of the wave front and use the fast Fourier transform to determine the main frequency of the wave front.

[0007] S2: Assume the fault location based on the bisection method, estimate the fault resistance based on the signal amplitude, obtain the signal transfer function upstream and downstream of the fault point based on the fault equivalent circuit, and calculate the refraction and reflection coefficients at the fault point and the beginning and end points;

[0008] S3: Select a square wave with the same frequency as the main frequency of the wave head as the initial traveling wave signal. According to the fault point, the head-end refraction-reflection coefficient and the signal transfer function, calculate the attenuated signal waveform after the initial traveling wave signal is folded back for different times.

[0009] S4: The attenuated signal waveforms after different times of reversal are superimposed into a synthetic signal. The Pearson correlation coefficient is used to calculate the similarity between the synthetic waveform of the 5-millisecond time window and the measured traveling wave. If the waveform similarity at both ends meets the requirements, the hypothetical fault point is considered to be the actual fault point. If it does not meet the requirements, the fault interval is further narrowed by comparing the amplitudes of the synthetic signals at the beginning and end until the waveform similarity requirements are met.

[0010] As a preferred solution, the fault range is further narrowed by comparing the amplitudes of the composite signals at the beginning and end and combining the dichotomy method:

[0011] If the amplitude ratio of the composite signal at the beginning and end is greater than the amplitude ratio of the measured signal, the latter half of the interval is selected;

[0012] If the amplitude ratio of the first and last synthetic signals is less than or equal to the amplitude ratio of the measured signal, the first half of the interval is selected.

[0013] As a further elaboration of the scheme, the present invention also discloses a DC distribution network fault location system based on voltage traveling wave similarity, comprising a zero-mode voltage acquisition device, a communication network, an information collection device, a storage medium, and a processor;

[0014] The zero-mode voltage acquisition device is installed at the beginning and end of each section line, and is used to collect the zero-mode voltage at the beginning and end of each cable section;

[0015] The communication network connects the zero-mode voltage acquisition device, the information collection device and the fault location processor in communication;

[0016] The information collection device collects and processes the data recorded by the zero-mode voltage collection device within its coverage area;

[0017] The storage medium is used to store instructions and data;

[0018] The processor is configured to operate according to the instructions to execute any one of the steps of the fault location method.

[0019] This solution provides a DC distribution network fault location method and system based on voltage traveling wave similarity. The beneficial effects achieved by the present invention using the above solution are as follows: Early-stage faults in DC distribution networks are usually short-lived, making it difficult to obtain steady-state signals, and existing fault location methods based on steady-state signals are ineffective. The fault characteristics of the traveling wave head are obvious, making it suitable for early-stage fault location. Taking into account the refractive-reflective characteristics of the traveling wave head, the similarity between the measured traveling wave head at the beginning and end of the cable and the synthesized traveling wave head is used to achieve accurate fault location. This method is applicable to both early-stage faults and stability faults in DC distribution networks, and its effectiveness is not affected by line length, transition resistance, or fault location. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments and in conjunction with the accompanying drawings, wherein:

[0021] Figure 1 Flowchart of the DC distribution network fault location method based on voltage traveling wave similarity provided by this solution;

[0022] Figure 2 This is the DC distribution network simulation model built in this embodiment;

[0023] Figure 3 Schematic diagram of traveling wave refraction and reflection.

[0024] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] like Figure 1-3 As shown, the present invention provides a DC distribution network fault location method based on voltage traveling wave similarity, comprising the following steps:

[0028] (1) Use the zero-mode voltage acquisition device installed at the head and end of the distribution network to obtain the line zero-mode voltage, determine the arrival time of the traveling wave head according to the zero-mode voltage mutation, select the waveform of the 5-millisecond time window after the arrival time of the wave head, and use the fast Fourier transform to determine the main frequency of the wave head;

[0029] Perform differential operation on the zero-mode voltage signal, and determine the time when the absolute value of the differential is greater than the set threshold as the arrival time of the traveling wave head;

[0030] The calculation formula of zero-mode voltage difference ΔU0(k) is shown in formula (1):

[0031] ΔU0(k)=U0(k+1)-U0(k) (k=0,1,…,n) Formula (1)

[0032] In formula (1), U0(k) is the measured zero-mode voltage signal, and k is the number of sampling points;

[0033] The criterion for fault occurrence is shown in formula (2):

[0034] |ΔU0(k)|>U 0N Formula (2)

[0035] In formula (2), |ΔU0(k)| is the calculated absolute value of the zero-mode voltage difference, U 0N is the set threshold.

[0036] Among them, the threshold U 0N The method for obtaining U is as follows: based on the simulation system, the simulation system disturbance situation, obtain the maximum differential absolute value of the zero-mode voltage under different disturbances, and take the maximum value of the maximum differential absolute value as U 0N .

[0037] (2) Assume the fault point location based on the bisection method, estimate the fault resistance value based on the signal amplitude, obtain the signal transfer function upstream and downstream of the fault point based on the fault equivalent circuit, calculate the voltage wave refraction and reflection coefficient based on the network topology, line parameters, transformer parameters and fault resistance estimation, and calculate the refraction and reflection coefficient at the fault point and the beginning and end points;

[0038] The initial traveling wave signal U0 propagates on the line, and its amplitude will attenuate; refraction and reflection occur at the fault point and the head and end, causing the waveform to be distorted and the amplitude to attenuate;

[0039] Taking the initial traveling wave propagating from the fault point to the head and end for the first time as an example, the waveform of the initial traveling wave propagating to the head and end becomes:

[0040] U U1 =U0×H U Formula (3)

[0041] U D1 =U0×H D Formula (4)

[0042] In formula (3), H U is the upstream transfer function of the fault point, in formula (4), H D is the downstream transfer function of the fault point.

[0043] (3) Select a square wave with the same frequency as the main frequency of the wave head as the initial traveling wave signal. According to the fault point, the head-end refraction-reflection coefficient and the signal transfer function, calculate the attenuated signal waveform after the initial traveling wave signal is folded back for different times;

[0044] The attenuated signal waveforms after folding back different times are superimposed into a synthetic signal. The calculation formula is shown as follows:

[0045] U U =U U1 +U U2 +U U3 +…+U Un Formula (5)

[0046] U D =U D1 +U D2 +U D3 +…+U Dn Formula (6)

[0047] In formula (5), U U is the composite waveform after the traveling waves at the head end are superimposed. In formula (6), U D is the synthetic waveform after the terminal traveling waves are superimposed, U Un 、U Dn These are the waveforms arriving at the head and the end for the nth time, and the number of signal refraction and reflection is selected according to the line length.

[0048] (4) The attenuated signal waveforms after different times of reversal are superimposed into a synthetic signal. The similarity between the synthetic waveform of the 5 millisecond time window and the measured traveling wave is calculated using the Pearson correlation coefficient. The U U 、U D If the similarity between the waveform at both ends of the line and the measured voltage traveling wave meets the requirements, the assumed fault point is considered to be the actual fault point. If it does not meet the requirements, the fault interval is further narrowed until the waveform similarity requirements are met.

[0049] The similarity between the synthetic traveling waves at the beginning and end and the measured traveling waves is compared. If the similarity at both ends is greater than 0.7, the assumed fault point location is considered to be the actual fault point location. Otherwise, the fault interval is further narrowed using the bisection method until the similarity of the traveling wave heads at both ends is greater than 0.7.

[0050] (5) Compare the amplitudes of the composite signals at the beginning and end and combine them with the dichotomy method to further narrow the fault range:

[0051] If the amplitude ratio of the composite signal at the beginning and end is greater than the amplitude ratio of the measured signal, the latter half of the interval is selected;

[0052] If the amplitude ratio of the first and last synthetic signals is less than or equal to the amplitude ratio of the measured signal, the first half of the interval is selected.

[0053] Example 2

[0054] Based on the same inventive concept as Example 1, an embodiment of the present invention provides a DC distribution network fault location system based on voltage traveling wave similarity, including a zero-mode voltage acquisition device, a communication network, an information collection device, a storage medium, and a processor;

[0055] The zero-mode voltage acquisition device is installed at the beginning and end of each section line, and is used to collect the zero-mode voltage at the beginning and end of each cable section;

[0056] The communication network connects the zero-mode voltage acquisition device, the information collection device and the fault location processor in communication;

[0057] The information collection device collects and processes the data recorded by the zero-mode voltage collection device within its coverage area;

[0058] The storage medium is used to store instructions and data;

[0059] The processor is configured to operate according to the instruction to execute the steps of any one of the fault location methods.

[0060] Example 3

[0061] like Figure 2 As shown, in order to verify the reliability and effectiveness of the present invention, the following Figure 2 In the DC distribution network simulation model shown, the traveling wave sampling frequency is 100 kHz. The line lengths are set to 5 km, 10 km, and 20 km. The fault resistances are 1 Ω and 100 Ω, respectively. The positioning results under different fault conditions are shown in Table 1.

[0062] Table 1 Fault location results under different fault conditions

[0063]

[0064] It can be seen from Table 1 that under different line lengths, different transition resistances and different fault locations, the DC distribution network fault location method based on voltage traveling wave similarity provided by the present invention has high location accuracy.

[0065] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0066] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0067] The present invention and its embodiments are described above. This description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs structures and embodiments similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A DC distribution network fault location method based on voltage traveling wave similarity, characterized in that: The following steps are involved: S1: Use the zero-mode voltage acquisition device installed at the head and end of the distribution network to obtain the line zero-mode voltage. Determine the arrival time of the traveling wave front based on the zero-mode voltage mutation. Select the waveform of the 5-millisecond time window after the arrival time of the wave front and use the fast Fourier transform to determine the main frequency of the wave front. S2: Assume the fault location based on the bisection method, estimate the fault resistance based on the signal amplitude, obtain the signal transfer function upstream and downstream of the fault point based on the fault equivalent circuit, and calculate the refraction and reflection coefficients at the fault point and the beginning and end points; S3: Select a square wave with the same frequency as the main frequency of the wave head as the initial traveling wave signal. According to the fault point, the head-end refraction-reflection coefficient and the signal transfer function, calculate the attenuated signal waveform after the initial traveling wave signal is folded back for different times. Initial traveling wave signal When propagating on the line, the amplitude will be attenuated; refraction and reflection occur at the fault point and the head and end, causing the waveform to be distorted and the amplitude to be attenuated; Taking the initial traveling wave propagating from the fault point to the head and end for the first time as an example, the waveform of the initial traveling wave propagating to the head and end becomes: Formula (1) Formula (2) In formula (1), is the upstream transfer function of the fault point, in formula (2), is the downstream transfer function of the fault point; S4: The attenuated signal waveforms after different times of folding are superimposed into a composite signal. The Pearson correlation coefficient is used to calculate the similarity between the composite waveform of the 5-millisecond time window and the measured traveling wave. If the waveform similarity at both the beginning and the end meets the requirements, the hypothetical fault point is considered to be the actual fault point. If not, the fault interval is further narrowed by comparing the amplitudes of the composite signals at the beginning and the end until the waveform similarity requirements are met. The attenuated signal waveforms after folding back different times are superimposed into a synthetic signal. The calculation formula is shown as follows: Formula (3) Formula (4) In formula (3), is the synthetic waveform after the head-end traveling wave is superimposed, in formula (4), is the synthetic waveform after the terminal traveling waves are superimposed, 、 These are the waveforms arriving at the head and the end for the nth time, and the number of signal refraction and reflection is selected according to the line length.

2. The DC distribution network fault location method based on voltage traveling wave similarity according to claim 1 is characterized in that: Perform differential operation on the zero-mode voltage signal. If the absolute value of the differential is greater than the set threshold, it is determined to be the arrival time of the traveling wave head. Zero-mode voltage differential The calculation formula is shown in formula (5): Formula (5) In formula (1), is the measured zero-mode voltage signal, k is the number of sampling points; The criterion for fault occurrence is shown in formula (6): Formula (6) In formula (2), is the calculated absolute value of the zero-mode voltage difference, is the set threshold.

3. The DC distribution network fault location method based on voltage traveling wave similarity according to claim 2 is characterized in that: The fault location is assumed using the bisection method, the fault resistance is estimated based on the signal amplitude, and the signal transfer functions upstream and downstream of the fault point are constructed based on the line parameters. The voltage wave refraction and reflection coefficient is calculated based on the network topology, line parameters, transformer parameters and the estimated fault resistance.

4. The DC distribution network fault location method based on voltage traveling wave similarity according to claim 3 is characterized in that: Pearson correlation coefficient was used to calculate 、 The similarity between the synthetic traveling wave at the beginning and end of the line and the measured voltage traveling wave is compared. If the similarity at both ends is greater than 0.7, the assumed fault point is considered to be the actual fault point. Otherwise, the fault interval is further narrowed using the binary method until the similarity of the traveling wave heads at both ends is greater than 0.

7.

5. The DC distribution network fault location method based on voltage traveling wave similarity according to claim 4 is characterized in that 5. In step S4, the process of further narrowing the fault range by comparing the amplitudes of the composite signals at the head and the end and combining the dichotomy method includes the following steps: If the amplitude ratio of the composite signal at the beginning and end is greater than the amplitude ratio of the measured signal, the latter half of the interval is selected; If the amplitude ratio of the first and last synthetic signals is less than or equal to the amplitude ratio of the measured signal, the first half of the interval is selected.

6. The DC distribution network fault location method based on voltage traveling wave similarity according to claim 5, characterized in that: The fault location method is suitable for accurate location of faults after single-pole grounding.

7. The DC distribution network fault location method based on voltage traveling wave similarity according to claim 6, characterized in that: The threshold The acquisition method is as follows: based on the simulation system, the simulation system disturbance situation, obtain the maximum differential absolute value of the zero-mode voltage under different disturbances, and take the maximum value of the maximum differential absolute value as .

8. A DC distribution network fault location system based on voltage traveling wave similarity, characterized by: It includes a zero-mode voltage acquisition device, a communication network, an information collection device, a storage medium and a processor; The zero-mode voltage acquisition device is installed at the beginning and end of each section line, and is used to collect the zero-mode voltage at the beginning and end of each cable section; The communication network connects the zero-mode voltage acquisition device, the information collection device and the fault location processor in communication; The information collection device collects and processes the data recorded by the zero-mode voltage collection device within its coverage area; The storage medium is used to store instructions and data; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 7.

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