Line Fault Location Method for DC Distribution System Based on Current Integration

Abstract

The present invention provides a method for locating line faults in a DC power distribution system based on current integration. First, the collected DC bus current is subjected to a fast Fourier transform, and the energy entropy of the transformed result is calculated to determine whether the fault occurs. Then, the currents before and after the fault at both ends of the DC distribution line are integrated, and the cosine similarity calculation is performed on the current integral. A criterion is constructed based on the similarity comparison result to realize fault location. It is verified by simulation data that the present invention still has good accuracy and speed even in strong noise conditions, and can be applied to DC distribution networks of various topological structures, providing a strong guarantee for the safe, reliable and economical operation of the DC distribution network.

Description

Technical Field

[0001] The invention relates to the technical field of direct current distribution system line fault location, and specifically discloses a direct current distribution system line fault location method based on current integration. Background Art

[0002] With the emergence of environmental problems and energy crises, green and environmentally friendly distributed power sources have received widespread attention from all over the world. Common distributed power sources include wind power generation, photovoltaic power generation, gas turbines, etc. These power sources have the advantages of low loss and strong power supply reliability. However, whether these power sources generate DC or AC power, a large number of converters are required to access the AC power grid, which will not only increase economic costs, but also increase power loss and reduce the power factor of the power grid. If a DC power grid is used, the use of converters can be greatly reduced, thereby reducing power loss and construction costs. However, since the protection technology of DC distribution networks is not mature enough, its development is restricted. Compared with AC distribution networks, the fault process of DC distribution networks develops rapidly, the fault current peak is high and the change rate is large, which will cause great harm to the DC system. Therefore, the protection action time should be in milliseconds to achieve rapid fault removal. Among them, fast and reliable fault location technology is an indispensable part of the protection solution.

[0003] The current DC distribution network fault location technology can be simply divided into two categories according to different principles: the location method based on traveling waves and the fault analysis method using line parameters. Among them, the location method based on traveling waves requires accurate identification of the traveling wave head. Due to the fast speed of traveling waves, high requirements are placed on the sampling equipment. Therefore, in practical applications, the problem of difficult identification of the traveling wave head will be encountered. The fault analysis method using line parameters analyzes and calculates the voltage and current information collected at the measurement point, and locates according to the difference in electrical quantities between the fault area and the normal area, which has higher reliability. However, in order to ensure the accurate start of fault location, a fast and reliable fault detection algorithm is also essential. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a method for locating line faults in a DC power distribution system based on current integration. First, the collected DC bus current is subjected to a fast Fourier transform, and the energy entropy of the transformed result is calculated to determine whether a fault has occurred. Then, the currents before and after the fault at both ends of the DC distribution line are integrated, and the cosine similarity of the current integral is calculated. According to the comparison result of the similarity, a criterion is constructed to realize fault location. It is verified by simulation data that the present invention still has good accuracy and speed even in strong noise conditions, and can be applied to DC distribution networks of various topological structures, providing a strong guarantee for the safe, reliable and economical operation of the DC distribution network.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] A method for locating line faults in a DC power distribution system based on current integration, characterized in that: firstly, a fast Fourier transform is performed on the collected DC bus current, and the energy entropy is calculated for the transformed result to judge whether a fault occurs, then the currents before and after the fault at both ends of the DC distribution line are integrated, and then the cosine similarity calculation is performed on the current integral, and a criterion is constructed according to the similarity comparison result to realize fault location.

[0007] Furthermore, a protection device is installed on the DC line, and the current waveform of the DC line is collected by using the protection device.

[0008] Furthermore, performing a fast Fourier transform on the collected DC bus current and calculating the energy entropy of the transformed result to determine whether a fault occurs specifically includes the following steps:

[0009] Step S21: Perform fast Fourier decomposition on the collected discrete bus current signal according to formula (1):

[0010]

[0011] in, N represents the number of sampling points, x(2n) and x(2n+1) represent the even and odd sequences of the current signal respectively, and X(k) represents the transformed complex sequence;

[0012] Step S22: Calculate the energy entropy of the result of fast Fourier decomposition:

[0013] Step 1: Decompose the current signal of a data window into N frequency components using equation (1), each frequency component is represented by a k +jb k , k = 1, 2, ..., N, calculate the energy of each frequency component according to formula (2):

[0014] E k =a k 2 +b k 2 (2)

[0015] Step 2: Calculate the relative energy of each frequency component according to formula (3):

[0016]

[0017] Step 3: Calculate the energy entropy according to formula (4):

[0018]

[0019] Step S23: Set a threshold δ. When FEE>δ, it is determined that a fault has occurred.

[0020] Furthermore, integrating the currents before and after the fault at both ends of the DC distribution line and then performing cosine similarity calculation on the current integrals specifically includes the following steps:

[0021] Step S31: Calculate the integral series of the currents before and after the fault period according to formula (5):

[0022]

[0023] Where m = 1, 2, ..., L-1; where L represents the size of the sampling window;

[0024] Step S32: Calculate the cosine similarity of the current integrals before and after the fault at both ends of the section according to formula (6):

[0025]

[0026] In the formula, a i Indicates the current integral value before the fault period, b i Indicates the current integral value after the fault period.

[0027] Furthermore, constructing a criterion based on the similarity comparison result to realize fault location specifically includes the following steps:

[0028] Step S41: Set a threshold σ. When the calculation result satisfies formula (7), it is determined to be a fault section:

[0029] (S1-σ)(S2-σ)<0 (7)

[0030] Where S1 and S2 represent the cosine similarity of the current integrals at both ends of the segment;

[0031] Step S42: Determine the faulty pole according to equations (8) to (10):

[0032] Positive ground fault:

[0033]

[0034] Negative ground fault:

[0035]

[0036] Inter-pole short circuit fault:

[0037]

[0038] In the formula, S P1 , SP2 and S N1 and S N2 are the cosine similarities of the current integral series at both ends of the positive and negative lines, respectively.

[0039] Compared with the prior art, the present invention and its preferred solution use fast Fourier to decompose the bus current signal, and calculate the energy entropy of the decomposition result to realize fault detection of the DC distribution network, and further integrate the current of each section and calculate the cosine similarity, and judge the fault section and fault pole according to the calculation results. The whole process takes a short time and has a certain anti-interference ability. At the same time, it has strong applicability and can be applied to various DC distribution network structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of a DC distribution network fault location method according to an embodiment of the present invention;

[0041] Figure 2 The figure is a schematic diagram of locating a fault line in a DC distribution network according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail as follows:

[0043] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0045] like Figure 1 , Figure 2 As shown, this embodiment provides a DC distribution network fault location method based on current integration characteristics, comprising the following steps:

[0046] Step S1: installing a protection device on a DC line, and using the protection device to collect a current waveform of the DC line.

[0047] Step S2: performing fault detection on the collected current;

[0048] Step S3: calculating the integral series of the current waveforms before and after the fault period at both ends of each section, and calculating the cosine similarity of the integral results;

[0049] Step S4: determining the fault section and the fault pole according to the calculation result of the fault section;

[0050] In this embodiment, step S2 specifically includes the following steps:

[0051] Step S21: Perform fast Fourier decomposition on the collected discrete bus current signal according to formula (1):

[0052]

[0053] in, N represents the number of sampling points, x(2n) and x(2n+1) represent the even and odd sequences of the current signal respectively, and X(k) represents the transformed complex sequence;

[0054] Step S22: Calculate the energy entropy of the result of fast Fourier decomposition:

[0055] Step 1: Decompose the current signal of a data window into N frequency components using equation (1), each frequency component is represented by a k +jb k , k = 1, 2, ..., N, calculate the energy of each frequency component according to formula (2):

[0056] E k =a k 2 +b k 2 (2)

[0057] Step 2: Calculate the relative energy of each frequency component according to formula (3):

[0058]

[0059] Step 3: Calculate the energy entropy according to formula (4):

[0060]

[0061] Step S23: Set a threshold δ. When FEE>δ, it is determined that a fault has occurred.

[0062] In this embodiment, step S3 specifically includes the following steps:

[0063] Step S31: Calculate the integral series of the currents before and after the fault period according to formula (5):

[0064]

[0065] Where m = 1, 2, ..., L-1; where L represents the size of the sampling window;

[0066] Step S32: Calculate the cosine similarity of the current integrals before and after the fault at both ends of the section according to formula (6):

[0067]

[0068] In the formula, a i Indicates the current integral value before the fault period, b i Indicates the current integral value after the fault period.

[0069] In this embodiment, step S4 specifically includes the following steps:

[0070] Step S41: Set a threshold σ. When the calculation result satisfies formula (7), it is determined to be a fault section:

[0071] (S1-σ)(S2-σ)<0 (7)

[0072] Where S1 and S2 represent the cosine similarity of the current integrals at both ends of the segment;

[0073] Step S42: Determine the faulty pole according to equations (8) to (10):

[0074] Positive ground fault:

[0075]

[0076] Negative ground fault:

[0077]

[0078] Inter-pole short circuit fault:

[0079]

[0080] In the formula, S P1 , S P2 and S N1 and S N2 are the cosine similarities of the current integral series at both ends of the positive and negative lines, respectively.

[0081] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, devices, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0082] The present invention is described with reference to flowcharts of methods, devices (apparatus), and computer program products according to embodiments of the present invention. It should be understood that each process in the flowchart, as well as the combination of processes in the flowchart, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the process in the flowchart. Figure 1 A device that specifies functions in a process or multiple processes.

[0083] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple functions specified in a flowchart.

[0084] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 The steps of a specified function in a process or multiple processes.

[0085] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

[0086] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of DC distribution system line fault location methods based on current integration under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A method for locating line faults in a DC power distribution system based on current integration, characterized in that: First, the collected DC bus current is subjected to fast Fourier transform, and the energy entropy is calculated for the transformed result to determine whether a fault has occurred. Then, the currents before and after the fault at both ends of the DC distribution line are integrated, and the cosine similarity of the current integral is calculated. Based on the similarity comparison results, a criterion is constructed to realize fault location. Performing fast Fourier transform on the collected DC bus current and calculating the energy entropy of the transformed result to judge whether a fault occurs specifically includes the following steps: Step S21: Perform fast Fourier decomposition on the collected discrete bus current signal according to formula (1): in, N represents the number of sampling points, x(2n) and x(2n+1) represent the even and odd sequences of the current signal respectively, and X(k) represents the transformed complex sequence; Step S22: Calculate the energy entropy of the result of fast Fourier decomposition: Step 1: Decompose the current signal of a data window into N frequency components using equation (1), each frequency component is represented by a k +jb k , k = 1, 2, ..., N, calculate the energy of each frequency component according to formula (2): E k =a k 2 +b k 2 (2) Step 2: Calculate the relative energy of each frequency component according to formula (3): Step 3: Calculate the energy entropy according to formula (4): Step S23: setting a threshold δ, when FEE>δ, it is determined that a fault occurs; Integrating the currents before and after the fault at both ends of the DC distribution line and then performing cosine similarity calculation on the current integrals specifically includes the following steps: Step S31: Calculate the integral series of the currents before and after the fault period according to formula (5): Where m = 1, 2, ..., L-1; where L represents the size of the sampling window; Step S32: Calculate the cosine similarity of the current integrals before and after the fault at both ends of the section according to formula (6): In the formula, a i Indicates the current integral value before the fault period, b i Indicates the current integral value after the fault period; The construction of the criterion based on the similarity comparison result to realize fault location specifically includes the following steps: Step S41: Set a threshold σ. When the calculation result satisfies formula (7), it is determined to be a fault section: (S1-σ)(S2-σ)<0 (7) where S1 and S2 represent the cosine similarity of the current integrals at both ends of the segment; Step S42: Determine the faulty pole according to equations (8) to (10): Positive ground fault: Negative ground fault: Inter-pole short circuit fault: In the formula, S P1 , S P2 and S N1 and S N2 are the cosine similarities of the current integral series at both ends of the positive and negative lines, respectively.

2. The method for locating a DC power distribution system line fault based on current integration according to claim 1, characterized in that: The protection device is installed on the DC line, and the current waveform of the DC line is collected by using the protection device.

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