A single-ended backup protection method and system based on line model parameter matching

Abstract

The present invention discloses a single - ended quantity backup protection method and system based on line model parameter matching. According to the voltage and current corresponding to a system fault, the voltage and current information collected within the unit data window of the protection device is substituted into the line resistance - inductance equation to form a differential equation set, and a matrix equation of the line resistance - inductance model is obtained; the least - squares method is used to fit and solve the matrix equation, the fitting error calculation within all unit data windows within one cycle is completed, and the fault distance is the first element of the fitting coefficient matrix β r , until the fault distances within all unit data windows within one cycle are obtained; the fault judgment is completed according to the calculation results of the fault distances within all unit data windows within one cycle and the calculation results of the fitting errors. Compared with the prior art, the present invention realizes a backup protection scheme for protecting the entire length of the line.

Description

Technical Field

[0001] The invention belongs to the field of relay protection of electric power systems, and in particular relates to a single-ended quantity backup protection method and system. Background Art

[0002] As new energy sources such as wind power and photovoltaic power account for an increasing proportion in the power system, their impact on relay protection cannot be ignored. For example, wind power access to the grid exhibits weak feedback characteristics, system impedance instability characteristics, frequency deviation characteristics, and high harmonic characteristics. These characteristics seriously affect the accuracy of the impedance measurement of the power frequency impedance distance protection, thereby causing the distance protection to malfunction or refuse to operate. In principle, the time domain distance protection based on the line concentrated parameter model is not affected by changes in the grid frequency and the back-side power supply. Compared with the traditional power frequency distance protection, it is more suitable for the transmission line of the new energy access system. However, there are some technical problems in the traditional time domain distance protection, such as "when there are branch lines in the lower-level lines and the transition resistance is large, it may cause the protection to exceed", which need to be solved urgently. Summary of the invention

[0003] In order to overcome the technical problems existing in the prior art, the present invention proposes a single-ended backup protection method and system based on line model parameter matching. When a power grid line fails and there is a branch line in the lower line where the protection is installed, the fitting error is calculated based on the voltage and current information of this section of the line collected in real time, and a threshold is reasonably set to judge the matching degree between the line resistance and inductance model and the line parameters, so as to determine whether the fault occurs in this section of the line.

[0004] The present invention is achieved by utilizing the following technical solutions:

[0005] A single-ended quantity backup protection method based on line model parameter matching specifically comprises the following steps:

[0006] Step 1: When the line is operating normally, the voltage and current discretely sampled from the protection device in the unit data window are substituted into the differential equation group of the line resistance-inductance model to obtain the matrix equation of the line resistance-inductance model;

[0007] Step 2: In the unit data window, the least square method is used to fit and solve the matrix equation, and the fitting value of the coefficient matrix β to be calculated is obtained as the fitting coefficient matrix β r , the fitting coefficient matrix β r Substituting in, we get the fitting error E r , slide the sampling point to the next unit data window, calculate the fitting error again, until the fitting error calculation in all unit data windows within one cycle is completed, slide the sampling point to the next unit data window, calculate the fault distance again, until the fault distance in all unit data windows within one cycle is obtained;

[0008] If the fault distances in all unit data windows within one cycle are less than the set threshold value and the sum of the squares of the fitting errors is less than the set threshold value, it is determined that an in-zone fault has occurred; otherwise, it is determined that an out-of-zone fault has occurred.

[0009] A single-ended quantity backup protection system based on line model parameter matching includes a sampling module and a fault determination module, wherein:

[0010] The sampling module discretely samples the voltage and current from the protection device in a unit data window to form a differential equation group of the line resistance inductance model and obtain a matrix equation of the line resistance inductance model;

[0011] The fault judgment module fits and solves the matrix equation until the fitting error calculation and fault distance calculation in all unit data windows within one cycle are completed. If the fault distance in all unit data windows within one cycle is less than a set threshold value and the sum of the squares of the fitting errors is less than the set threshold value, it is judged that an in-zone fault has occurred; otherwise, it is judged that an out-of-zone fault has occurred.

[0012] Compared with the prior art, the present invention can form a backup protection scheme that protects the entire length of the line. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is an overall flow chart of a single-ended quantity backup protection method based on line model parameter matching of the present invention;

[0014] Figure 2 It is a schematic diagram of an example of a new energy grid connection with branch lines;

[0015] Figure 3 Schematic diagram of the sliding data window selection method for fitting calculation;

[0016] Figure 4 A module diagram of a single-ended backup protection system based on line model parameter matching of the present invention;

[0017] Reference numerals:

[0018] 100, sampling module, 200, fault determination module. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0020] like Figure 1The figure shows an overall flow chart of a single-ended backup protection method based on line model parameter matching of the present invention. The present invention calculates the fault point location according to a time-domain differential equation based on the resistance-inductance model by making the line equivalent to a resistance-inductance model with fixed resistance and inductance per unit length. "Parameter matching" is to substitute the calculated fault distance back into the resistance-inductance equation, and judge whether the measured voltage, measured current and calculated fault distance conform to the equation based on the line resistance-inductance model according to the size of the defined fitting error. If it matches, it means that there are only resistance and inductance representing this section of the line between the protection and the fault point, which is an internal fault. If it does not match, it means that there are not only resistance and inductance representing this section of the line between the protection and the fault point, which is an external fault. The method specifically includes the following steps:

[0021] Step 1: According to the voltage and current during the normal operation of the system, the voltage and current information obtained by discrete sampling from the protection device within the unit data window (sampling interval, 1ms) is substituted into the line resistance inductance equation to form a differential equation group, which is expressed as follows:

[0022]

[0023] Among them, u mA (·),i mA (·) are the instantaneous values ​​of voltage and current of fault phase A on the m side where the protection device is installed, i m0 (·) is the zero-sequence current, x is the distance between the fault point and the installation location of the protection device, r1 and l1 are the positive-sequence resistance and inductance per unit length of the line, respectively. r is the resistance zero-sequence compensation coefficient, k l is the inductor zero-sequence compensation coefficient, and k r =(r0-r1) / 3r1, k l =(l0-l1) / 3l1, r0, l0 are the zero-sequence resistance and inductance per unit length of the line, and R′ F is the equivalent transition resistance at the fault point, R′ F =R F / C F , R F is the actual fault transition resistance, C F is the zero-sequence shunt coefficient at the protection installation, Δt is the sampling interval, 1, 2, ..., j, ..., n is the number of the current sampling point, k is the number of sampling points in the unit data window, and since differential operation is required, the number of differential equations formed by the data in the unit data window is k-2, and in the formed differential equation group, j = n-k+2, n-k+3, ..., n-1;

[0024] Using the voltage and current information continuously collected by the protection device, a series of line resistance and inductance equations are obtained and organized into a matrix form. The expression is as follows:

[0025] U=Iβ (2)

[0026] Matrices U, β, and I are the voltage information matrix, the coefficient matrix to be determined, and the current information matrix respectively:

[0027] U=[u mA (n-k+2),u mA (n-k+3),...,u mA (n-1)] T (3)

[0028]

[0029] β=[x R' F ] T (5)

[0030] Among them, p(j) is the sequence used for calculation:

[0031] p(j)=(i mA (j)+3k r i m0 (j))r1+(i mA (j+1)+3k r i m0 (j+1)-i mA (j-1)-3k l i m0 (j-1))l1 / (2Δt) (6);

[0032] Step 2: In the unit data window, the least square method is used to fit and solve the matrix equation, and the fitting value of the coefficient matrix β to be calculated is obtained as the fitting coefficient matrix β r , the fitting coefficient matrix β r Substituting in, we get the fitting error E r , and slide the sampling point to the next unit data window, and calculate the fitting error again until the fitting error calculation in all unit data windows within one cycle is completed; the specific process is:

[0033] Based on certain redundant sampling point information, the redundancy is due to the fact that the matrix (difference equation group) in formula (2) contains only two unknowns, so two difference equations consisting of four sampling point data (differential requires data of one sampling point before and after each) can solve the matrix. Therefore, the difference equation group based on multiple sampling point data is redundant for solving two unknowns, and certain corresponds to a few milliseconds to one cycle (20ms);

[0034] The least squares method is used to fit and solve the matrix equation, and the fitting value of the coefficient matrix β to be determined is obtained as the fitting coefficient matrix β r, the obtained fitting value of the coefficient matrix β satisfies the minimum distance between the calculated value Iβ of the voltage matrix in the data window and the actual value U of the voltage matrix in the Euclidean space. The Euclidean distance E between the two is expressed as follows:

[0035] E 2 =||U-Iβ||2 2 (7)

[0036] Take the partial derivative of the coefficient matrix β in the above expression and set the partial derivative equal to 0, and then get the fitting coefficient matrix β r The expression is:

[0037] β r =(I T I) -1 I T U (8)

[0038] When performing a single least squares fitting calculation on the matrix equation formed by the line resistance inductance model, it is necessary to select an appropriate number of sampling points, that is, to select an appropriate data window length. There are existing studies that include calculation schemes for sliding data windows. Figure 3 The figure shows a schematic diagram of the sliding data window selection method in the fitting calculation. Among them, 1, 2, ..., n are sampling point numbers, and there are k sampling points in the unit data window, as shown in the box in the figure. Each time the sampling point in the box is selected for fitting calculation, when the next sampling point enters, the previous sampling point is discarded and the new sampling point is read in to keep the sampling point in the fitting calculation data window constant;

[0039] The fitting coefficient matrix β obtained by performing a least squares fitting calculation in the unit data window r Substituting into, we get the fitting error E of a single fitting calculation r , the expression is as follows:

[0040]

[0041] Among them, single refers to the result obtained by sliding a unit data window of the data window;

[0042] Continuously calculate the fitting error of the sliding data window: slide the sampling point to the next unit data window, and calculate the fitting error again until the fitting error calculation in all unit data windows within one cycle is completed.

[0043] And the fault distance is the fitting coefficient matrix β r The first element of , slides the sampling point to the next unit data window, and calculates the fault distance again until the fault distances in all unit data windows within one cycle are obtained;

[0044] If the fault distance is less than the set threshold value, and the sum of the squares of the fitting errors in all unit data windows within one cycle is less than the set threshold value, that is, it satisfies formula (5), then it is determined to be an internal fault, that is, it satisfies the following judgment formula:

[0045]

[0046] Among them, t q is the starting time for backup protection judgment, T is the power frequency cycle (set to 20ms), Δt is the sampling interval of the protection device, n is the current sampling point, E r-set is the power setting value of the fitting error, x set is the fault distance setting value of the protection zone, x(n), E r (n) are the fault distance and fitting error obtained by fitting calculation at the current moment;

[0047] Otherwise, it is determined that an out-of-zone fault has occurred.

[0048] The threshold value of the fault distance is 85% of the line length, and the threshold value of the fitting error is set to 10 -3 .

[0049] like Figure 4 , which is a module diagram of a single-ended quantity backup protection system based on line model parameter matching of the present invention. The system includes a sampling module 100 and a fault determination module 200 .

[0050] The sampling module 100 discretely samples the voltage and current from the protection device in a unit data window to form a differential equation group of the line resistance inductance model. The matrix equation expression of the series of line resistance inductance models is as follows:

[0051] U=Iβ (11)

[0052] The matrices U, , and β are the voltage matrix, the coefficient matrix to be determined, and the current matrix respectively:

[0053] U=[u mA (n-k+2),u mA (n-k+3),...,u mA (n-1)] T (12)

[0054]

[0055] β=[x R' F ] T (14)

[0056] Where n is the sampling point number at the current moment, k is the number of sampling points in the unit data window, and p(.) is the function of the sampling current, expressed as follows:

[0057] p(j)=(i mA (j)+3k r i m0 (j))r1+(i mA (j+1)+3k r i m0 (j+1)-i mA (j-1)-3k l i m0 (j-1))l1 / (2Δt) (15), The sampling point number j in the differential equation group, j = n-k+2, n-k+3, ..., n-1;

[0058] The fault determination module 300 performs fitting and solving of the matrix equation until the fitting error calculation in all unit data windows within one cycle is completed. If the fault distance is less than a set threshold value and the sum of the squares of the fitting errors in all unit data windows within one cycle is less than the set threshold value, it is determined that an in-zone fault has occurred; that is, the following formula is satisfied:

[0059]

[0060] Among them, t q is the starting time for backup protection judgment, T is the power frequency cycle, Δt is the sampling interval, n is the current sampling point, E r-set is the power setting value of the fitting error, x set is the fault distance setting value of the protection zone, x(n), E r (n) are the fault distance and fitting error obtained by fitting calculation at the current moment;

[0061] Otherwise, it is determined that an out-of-zone fault has occurred.

[0062] The threshold value of the fault distance is 85% of the line length, and the threshold value of the fitting error is set to 10 -3 .

[0063] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, 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 codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0064] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0065] 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 including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0066] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0067] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0068] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A single-ended backup protection method based on line model parameter matching, characterized in that: The method comprises the following steps: Step 1: When the line is operating normally, the voltage and current discretely sampled from the protection device in the unit data window are substituted into the differential equation group of the line resistance-inductance model to obtain the matrix equation of the line resistance-inductance model; Step 2: In the unit data window, the least square method is used to fit and solve the matrix equation, and the fitting value of the coefficient matrix β to be calculated is obtained as the fitting coefficient matrix β r , the fitting coefficient matrix β r Substituting in, we get the fitting error E r , slide the sampling point to the next unit data window, and calculate the fitting error again until the fitting error calculation in all unit data windows within one cycle is completed, and the fault distance is the fitting coefficient matrix β r The first element of , slides the sampling point to the next unit data window, and calculates the fault distance again until the fault distances in all unit data windows within one cycle are obtained; Step 3: If the fault distances in all unit data windows within one cycle are less than the set threshold value and the sum of the squares of the fitting errors is less than the set threshold value, it is determined that an in-zone fault has occurred; otherwise, it is determined that an out-of-zone fault has occurred.

2. A single-ended quantity backup protection method based on line model parameter matching as claimed in claim 1, characterized in that: In the step 1, The difference equations are expressed as follows: Among them, u mA (·),i mA (·) are the instantaneous values ​​of voltage and current of fault phase A on the m side where the protection device is installed, i m0 (·) is the zero-sequence current, x is the distance between the fault point and the installation location of the protection device, r1 and l1 are the positive-sequence resistance and inductance per unit length of the line, respectively, k r is the resistance zero-sequence compensation coefficient, k l is the inductance zero-sequence compensation coefficient, R′ F is the equivalent transition resistance at the fault point, 1, 2, …, j, …, n is the number of the current sampling point, Δt is the sampling interval, and k is the number of sampling points in the unit data window; Equivalent transition resistance R′ at the fault point F The expression is as follows: Among them, R F is the actual fault transition resistance, C F To protect the zero-sequence shunt coefficient at the installation location; Resistance zero sequence compensation coefficient k r , inductance zero sequence compensation coefficient k l The expressions are as follows: to r =(r0-r1) / 3r1,k l =(l0-l1) / 3l1 Among them, r0 and l0 are the zero-sequence resistance and inductance per unit length of the line respectively; The matrix equation of the line resistance inductance model is expressed as follows: U=Iβ Among them, U, I, and β are the voltage matrix, the fitting coefficient matrix to be calculated, and the current matrix respectively: U=[u mA (n-k+2),u mA (n-k+3),...,u mA (n-1)] T β=[x R' F ] T Where n is the sampling point number at the current moment, k is the number of sampling points in the unit data window, and p(.) is the function of the sampling current, expressed as follows: p(j)=(i mA (j)+3k r i m0 (j))r1+(i mA (j+1)+3k r i m0 (j+1)-i mA (j-1)-3k l i m0 (j-1))l1 / (2Δt), j is the sampling point number in the differential equation group, j=n-k+2,n-k+3,…,n-1.

3. A single-ended quantity backup protection method based on line model parameter matching as claimed in claim 1, characterized in that: When performing a single least squares fitting calculation on the differential equation group formed by the line resistance inductance model, the number of sampling points is selected by selecting the data window length, and the fitting calculation is performed using the sampling points selected each time. When the next sampling point enters, the previous sampling point is discarded and the new sampling point is read in, so that the sampling points in the fitting calculation data window remain constant.

4. A single-ended quantity backup protection method based on line model parameter matching as claimed in claim 1, characterized in that: The fitting coefficient matrix β in step 2 r The expression is as follows: β r =(I T I) -1 I T U The above fitting coefficient matrix β r Substituting, we first get the fitting error E of a single fitting calculation r , the expression is as follows: Among them, β r is the fitting coefficient matrix, n is the sampling point number at the current moment, k is the number of sampling points in the unit data window, U, I, β are the voltage matrix, the fitting coefficient matrix to be calculated and the current matrix respectively, and j is the sampling point number in the differential equation group.

5. A single-ended quantity backup protection method based on line model parameter matching as claimed in claim 1, characterized in that: The fitting value of the coefficient matrix β to be determined satisfies the requirement that the distance between the calculated value Iβ of the voltage matrix in the data window and the actual value U of the voltage matrix in the Euclidean space is minimized.

6. A single-ended quantity backup protection method based on line model parameter matching as claimed in claim 1, characterized in that: The fault determination in step 3 satisfies the following formula: Among them, t q is the starting time for backup protection judgment, T is the power frequency cycle, Δt is the sampling interval, n is the current sampling point, E r-set is the power setting value of the fitting error, x set is the fault distance setting value of the protection zone, x(n), E r (n) are the fault distance and fitting error obtained by fitting calculation at the current moment.

7. A single-ended quantity backup protection system based on line model parameter matching, which implements the single-ended quantity backup protection method based on line model parameter matching as claimed in any one of claims 1 to 6, characterized in that: The system includes a sampling module and a fault determination module, wherein: The sampling module discretely samples the voltage and current from the protection device in a unit data window to form a line resistance and inductance model differential equation group, thereby obtaining a matrix equation of the line resistance and inductance model; The fault judgment module fits and solves the matrix equation until the fitting error calculation and fault distance calculation in all unit data windows within one cycle are completed. If the fault distance in all unit data windows within one cycle is less than a set threshold value and the sum of the squares of the fitting errors is less than the set threshold value, it is judged that an in-zone fault has occurred; otherwise, it is judged that an out-of-zone fault has occurred.

8. A single-ended backup protection system based on line model parameter matching as claimed in claim 7, characterized in that: In the sampling module, The difference equations are expressed as follows: Among them, u mA (·),i mA (·) are the instantaneous values ​​of voltage and current of fault phase A on the m side where the protection device is installed, i m0 (·) is the zero-sequence current, x is the distance between the fault point and the installation location of the protection device, r1 and l1 are the positive-sequence resistance and inductance per unit length of the line, respectively, k r is the resistance zero-sequence compensation coefficient, k l is the inductance zero-sequence compensation coefficient, R′ F is the equivalent transition resistance at the fault point, 1, 2, …, j, …, n is the number of the current sampling point, Δt is the sampling interval, and k is the number of sampling points in the unit data window; Equivalent transition resistance R′ at the fault point F The expression is as follows: R′ F =R F / C F Among them, R F is the actual fault transition resistance, C F To protect the zero-sequence shunt coefficient at the installation location; Resistance zero sequence compensation coefficient k r , inductance zero sequence compensation coefficient k l The expressions are as follows: to r =(r0-r1) / 3r1,k l =(l0-l1) / 3l1 Among them, r0 and l0 are the zero-sequence resistance and inductance per unit length of the line respectively; The matrix equation expression of the line resistance inductance model is as follows: U=Iβ The matrices U, , and β are the voltage matrix, the coefficient matrix to be determined, and the current matrix respectively: U=[u mA (n-k+2),u mA (n-k+3),...,u mA (n-1)] T β=[x R' F ] T Where n is the sampling point number at the current moment, k is the number of sampling points in the unit data window, and p(.) is the function of the sampling current, expressed as follows: p(j)=(i mA (j)+3k r i m0 (j))r1+(i mA (j+1)+3k r i m0 (j+1)-i mA (j-1)-3k l i m0 (j-1))l1 / (2Δt), the sampling point number j in the differential equation group, j=n-k+2,n-k+3,…,n-1.

9. A single-ended quantity backup protection system based on line model parameter matching as claimed in claim 7, characterized in that: In the fault judgment module, the fitting coefficient matrix β r The expression is as follows: β r =(I T I) -1 I T U The above fitting coefficient matrix β r Substituting, we first get the fitting error E of a single fitting calculation r , the expression is as follows: Among them, β r is the fitting coefficient matrix, n is the sampling point number at the current moment, k is the number of sampling points in the unit data window, U, I, β are the voltage matrix, the fitting coefficient matrix to be calculated and the current matrix respectively, and j is the sampling point number in the differential equation group.

10. A single-ended backup protection system based on line model parameter matching as claimed in claim 7, characterized in that: In the fault determination module, the fault determination process satisfies the following formula: Among them, t q is the starting time for backup protection judgment, T is the power frequency cycle, Δt is the sampling interval, n is the current sampling point, E r-set is the power setting value of the fitting error, x set is the fault distance setting value of the protection zone, x(n), E r (n) are the fault distance and fitting error obtained by fitting calculation at the current moment.

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