A power grid harmonic impedance multipoint equivalent method and system

Abstract

The application discloses a kind of power grid harmonic impedance multi-point equivalent method and system, establish the harmonic impedance model of line branch containing equivalent node but not containing reservation node, to establish the specific harmonic admittance matrix of power grid in the case of not taking into account reservation node, carry out inverse operation to specific harmonic admittance matrix, obtain the impedance matrix under harmonic, extract the first k-dimensional matrix of impedance matrix under harmonic as the impedance matrix after equivalence, carry out inversion to the impedance matrix after equivalence, obtain the system admittance matrix under specific harmonic after equivalence, reconstruct the reconstructed local area power grid.Multiple-point equivalent and harmonic equivalent are fused, so that the harmonic impedance characteristics of power grid system before and after equivalence remain consistent, the original system is equivalent under specific harmonic frequency, the short-circuit impedance and mutual impedance of equivalent node under specific harmonic are consistent with the original system, which provides accurate input for subsequent time-domain analysis or frequency-domain analysis.

Description

Technical Field

[0001] This invention relates to the field of power system analysis technology, and in particular to a method and system for multi-point equivalent assessment of power grid harmonic impedance. Background Technology

[0002] According to the results of a harmonic survey of the domestic power grid, over 10% of 500kV substations and interference source customers have exceeded harmonic limits. In areas with excessive harmonics, some equipment in the main grid layer, such as filters and converter transformers, are operating beyond their design limits. With the construction of new power systems, large-scale offshore wind power and onshore photovoltaic energy storage will be connected to the grid, and the large-scale construction of rectifier power electronic equipment used in industrial production and railway traction substations is expected to generate even more harmonics. Simultaneously, the complex interconnected network structure of the power system will lead to more frequent resonance phenomena at specific frequencies, thereby exacerbating harmonic distortion or amplification. Therefore, harmonic analysis of the power grid is necessary.

[0003] Calculating equivalent harmonic impedance is a means of analyzing the degree of harmonic influence on a region. Existing power grid impedance equivalence schemes include single-point equivalence and multi-point equivalence. While single-point equivalence considers harmonics, it can only consider the Thevenin (or Norton) equivalent circuit at a single access point, greatly limiting the scope of harmonic analysis. It cannot analyze the harmonic distribution near the access point, nor can it verify the effectiveness of harmonic suppression measures. Existing multi-point equivalence schemes are based on the fundamental frequency (50Hz or 60Hz), which cannot ensure consistency with the original system under specific harmonics, introducing errors into subsequent time-domain or frequency-domain analyses. Therefore, researching multi-point equivalence schemes that consider harmonics, achieving equivalence of the original system at specific harmonic orders, and maintaining consistency between the short-circuit impedance and mutual impedance of the equivalent nodes under specific harmonic orders with the original system, thus providing accurate input for subsequent time-domain or frequency-domain analyses, is a technical problem urgently needing to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a multi-point equivalent method and system for power grid harmonic impedance, which is used to perform equivalent measurements on the original system at a specific harmonic order, keeping the short-circuit impedance and mutual impedance of the equivalent nodes consistent with the original system at the specific harmonic order, thus providing accurate input for subsequent time-domain or frequency-domain analysis.

[0005] In view of this, the first aspect of the present invention provides a multi-point equivalent method for power grid harmonic impedance, comprising:

[0006] S1. Establish component models of each power grid component under specific subharmonics;

[0007] S2. Obtain the nodes that need to be equalized and determine the nodes to be retained. Count the number of equalized nodes k and the number of nodes N after excluding the nodes to be retained.

[0008] S3. Establish a harmonic impedance model for line branches that include equivalent nodes but not reserved nodes.

[0009] S4. Based on the harmonic impedance model, establish the specific harmonic admittance matrix of the power grid without considering the reserved nodes. The specific harmonic admittance matrix is ​​an N×N matrix.

[0010] S5. Perform the inverse operation on the admittance matrix of a specific harmonic order to obtain the impedance matrix under the harmonic order, and extract the first k-dimensional matrix of the impedance matrix under the harmonic order as the equivalent impedance matrix.

[0011] S6. Invert the equivalent impedance matrix to obtain the equivalent system admittance matrix under specific harmonics.

[0012] S7. Reconstruct the local power grid based on the equivalent system admittance matrix.

[0013] Optionally, step S7 may be followed by:

[0014] S8. Determine whether each branch of the reconstructed local power grid has negative resistance. If so, readjust the reserved nodes and return to step S2.

[0015] Optionally, step S7 may be followed by:

[0016] If the number of reserved nodes is not zero, then the reserved nodes are added again in the reconstructed local power grid to obtain an equivalent power grid.

[0017] Optionally, step S4 includes:

[0018] S41. Construct an initial N×N matrix where all matrix elements are 0;

[0019] S42. Traverse all branches. If the current branch is not a retained branch, modify the value of the current matrix element according to the harmonic impedance model.

[0020] S43. After completing the traversal and modification of all elements in the initial N×N matrix, the specific harmonic admittance matrix of the power grid is obtained without considering the reserved nodes.

[0021] Optionally, the component models established in step S1 include line harmonic impedance models, transformer harmonic impedance models, load harmonic impedance models, generator harmonic impedance models, and power electronic equipment harmonic impedance models.

[0022] A second aspect of the present invention provides a multi-point equivalent system for power grid harmonic impedance, comprising:

[0023] The component modeling module is used to create component models of various power grid components under specific subharmonics.

[0024] The node statistics module is used to obtain the nodes that need to be equalized and determine the nodes to be retained, and to count the number of equalized nodes k and the number of nodes N after excluding the nodes to be retained;

[0025] The line harmonic impedance model construction module is used to build harmonic impedance models for line branches that include equivalent nodes but not reserved nodes.

[0026] The admittance matrix construction module is used to establish the specific harmonic admittance matrix of the power grid without considering the reserved nodes, based on the harmonic impedance model. The specific harmonic admittance matrix is ​​an N×N matrix.

[0027] The equivalent impedance module is used to invert the admittance matrix of a specific harmonic order to obtain the impedance matrix under the harmonic order, and extract the first k dimensions of the impedance matrix under the harmonic order as the equivalent impedance matrix.

[0028] The equivalent admittance module is used to invert the equivalent impedance matrix to obtain the equivalent system admittance matrix under a specific harmonic.

[0029] The reconstruction module is used to reconstruct the local power grid based on the equivalent system admittance matrix.

[0030] Optionally, it also includes:

[0031] The judgment module is used to determine whether negative resistance occurs in each branch of the reconstructed local power grid. If so, the reserved nodes are readjusted and the process returns to the execution node statistics module.

[0032] Optionally, it also includes:

[0033] The reserved node addition module is used to re-add reserved nodes in the reconstructed local area power grid if the number of reserved nodes is not 0, so as to obtain an equivalent power grid.

[0034] Optionally, the admittance matrix construction module includes:

[0035] The initial matrix construction submodule is used to construct an initial N×N matrix where all matrix elements are 0;

[0036] The traversal submodule is used to traverse all branches. If the current branch is not a reserved branch, the value of the current matrix element is modified according to the harmonic impedance model.

[0037] The output submodule is used to obtain the specific harmonic admittance matrix of the power grid without considering the reserved nodes after traversing and modifying all elements in the initial N×N matrix.

[0038] Optionally, the component models established in the component modeling module include line harmonic impedance models, transformer harmonic impedance models, load harmonic impedance models, generator harmonic impedance models, and power electronic equipment harmonic impedance models.

[0039] As can be seen from the above technical solutions, the multi-point equivalent method for power grid harmonic impedance provided by this invention has the following advantages:

[0040] The multi-point equivalent method for power grid harmonic impedance provided by this invention integrates multi-point equivalent with harmonic equivalent, so that the harmonic impedance characteristics of the power grid system remain consistent before and after the equivalent. It achieves the technical effect of performing equivalent on the original system at a specific harmonic order, keeping the short-circuit impedance and mutual impedance of the equivalent nodes consistent with the original system at that specific harmonic order, and providing accurate input for subsequent time-domain or frequency-domain analysis.

[0041] The multi-point equivalent method for power grid harmonic impedance provided by this invention verifies the negative resistance of each branch of the reconstructed local power grid. When negative resistance occurs, the reserved nodes are readjusted to avoid system oscillation. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a flowchart illustrating a multi-point equivalent method for power grid harmonic impedance provided in this invention.

[0044] Figure 2 This is another flowchart illustrating a multi-point equivalent method for power grid harmonic impedance provided in this invention;

[0045] Figure 3 This is a schematic diagram of the fundamental π-type circuit of the transmission line provided in this invention;

[0046] Figure 4 This is a schematic diagram of a π-type circuit with lumped parameters for a transmission line provided in this invention;

[0047] Figure 5 This is a schematic diagram of the π-type circuit for distributed parameters of transmission lines provided in this invention;

[0048] Figure 6 This is a schematic diagram of the harmonic amplitude characteristics of a DC system provided in this invention;

[0049] Figure 7This is a schematic diagram of the harmonic angle characteristics of a DC system provided in this invention;

[0050] Figure 8 This is the wiring diagram of the IEEE 9-node system provided in this invention;

[0051] Figure 9 This is the local area power grid contour map obtained by reconstruction in this invention;

[0052] Figure 10 Provided in the invention Figure 9 The equivalent power grid diagram with retained nodes added on top of the existing structure;

[0053] Figure 11 This is a schematic diagram of the structure of a multi-point equivalent system for power grid harmonic impedance provided in this invention. Detailed Implementation

[0054] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] For easier understanding, please refer to Figure 1 This invention provides an embodiment of a multi-point equivalent method for power grid harmonic impedance, comprising:

[0056] Step 101: Establish component models of each power grid component under specific harmonics.

[0057] It should be noted that, based on power grid data, component models are established for each element under specific harmonic orders. The component models can be determined according to the specific application scenario. The component models established in this embodiment include line harmonic impedance models, transformer harmonic impedance models, load harmonic impedance models, generator harmonic impedance models, and power electronic equipment harmonic impedance models. The harmonic order is set to n. f n f As specified by the user, generally n f The values ​​are 3, 5, and 7.

[0058] The line harmonic impedance model is as follows:

[0059]

[0060] Z′ l (n f ) = real(Z l (f0))+j·nf imag(Z) l (f0))

[0061] Among them, Z l (n f Z represents the harmonic impedance of a line in a distributed parameter π-type network. l (n f Y′ is the line harmonic impedance in a lumped-parameter π-type network. l (n f Z represents the ground harmonic admittance in a lumped-parameter π-type network. l (f0) is the line impedance in a traditional π-type circuit, n f Let be the harmonic order, and real(·) and imag(·) be the real and imaginary parts of the complex number, respectively.

[0062] Specifically, the traditional fundamental π-type circuit of the line, such as Figure 2 As shown, according to Figure 2 The model can be used to obtain a lumped parameter π-type circuit model, such as Figure 3 As shown, according to Figure 2 and Figure 3 The following formula can be obtained:

[0063] Z′ l (n f ) = real(Z l (f0))+j·n f imag(Z) l (f0))

[0064]

[0065] Transmission line distributed parameter π-type circuit model as follows Figure 4 As shown, according to Figure 4 We can obtain:

[0066]

[0067]

[0068] Wherein, sinh(·) and tanh(·) are the hyperbolic sine function and the hyperbolic tangent function, respectively.

[0069] The transformer harmonic impedance model is as follows:

[0070] Z t (n f ) = R t (n f )+j·X t (n f )

[0071]

[0072] Among them, Z t (n f ) represents the transformer harmonic impedance, f0 represents the fundamental frequency, and R t (nf) is the resistance of the transformer under the nfth harmonic, R t (f0) is the resistance of the transformer at the fundamental frequency, X t (n f ) is n f The reactance of the transformer under subharmonics, X t (f0) represents the transformer reactance at the fundamental frequency. a, b, c, k1, and k2 are user-defined coefficients. Typically, a = 1.0, b = c = k1 = k2 = 0.0.

[0073] The load harmonic impedance model is as follows:

[0074]

[0075]

[0076] Among them, Z l (n f Let P(nf) be the load harmonic impedance, g(nf) be the load conductance under the nf harmonic, b(nf) be the load susceptance under the nf harmonic, P0 be the active load, Q0 be the reactive load, U be the node voltage, and a1, b1, c1, a2, b2, and c2 be user-defined coefficients. Typically, a1 = a2 = 1.0, b1 = c1 = b2 = c2 = 0.0.

[0077] The generator harmonic impedance model is as follows:

[0078]

[0079]

[0080] Among them, Z g (n f ) represents the generator harmonic impedance, f0 represents the fundamental frequency, and R a (nf) is the generator resistance under the nfth harmonic, R a (f0) is the generator resistance at the base frequency, X d "(n f ) is n f Generator transient impedance under subharmonics, X d "(f0) is the transient impedance of the generator at the fundamental frequency. a1, b1, c1, d1, e1, a2, b2, c2, d2, and e2 are user-defined coefficients. Typically, a1 = b2 = 1.0, b1 = c1 = d1 = e1 = a2 = c2 = d2 = e2 = 0.0.

[0081] For harmonic impedance models of power electronic equipment, their full-frequency harmonic impedance characteristics can be obtained through theoretical derivation, experimental measurement, or electromagnetic transient simulation. For example, the harmonic impedance characteristics of a DC circuit across the entire frequency band are as follows: Figure 5 and Figure 6 The figures shown are the harmonic amplitude characteristics and harmonic angle characteristics, respectively. In the calculation, only n is needed. f The impedance under the second harmonic is denoted as:

[0082] Z e (n f ) = Mag(n f )∠Pha(n f ).

[0083] The above equation is in polar coordinate form, Z e (n f ) represents the harmonic impedance of power electronic equipment, Mag(n) f Pha(n) represents the harmonic amplitude corresponding to the nf-th harmonic. f ) represents the harmonic angle corresponding to the nfth harmonic.

[0084] Step 102: Obtain the nodes that need to be equalized and determine the nodes to be retained. Count the number of equalized nodes k and the number of nodes N after excluding the nodes to be retained.

[0085] It should be noted that the equivalent nodes are determined by the user based on the equivalence requirements, and the reserved nodes are also determined by the user based on actual needs. Reserved nodes can be nodes and / or the branches where those nodes reside. Let k be the number of equivalent nodes, and N be the number of nodes after excluding reserved nodes.

[0086] Step 103: Establish a harmonic impedance model for line branches that includes equivalent nodes but does not include reserved nodes.

[0087] It should be noted that, based on the component model established in step 101, a harmonic impedance model for the line branch, including equivalent nodes but excluding reserved nodes, is established. Figure 7 The IEEE 9-node system shown is used as an example before equivalence. Assume the retained nodes are Generator 1, Generator 2, Generator 3, Generator 1-Bus 1, Generator 2-Bus 2, and Generator 3-Bus 3, and the nodes requiring equivalence are Bus 1, Bus 2, and Bus 3. Then k = 3, N = 6. Assume the harmonic order n... f If =3, then the harmonic impedance model of the line branch containing equivalent nodes but not reserved nodes is shown in Table 1.

[0088] Table 1

[0089]

[0090]

[0091] Step 104: Based on the harmonic impedance model, establish the specific harmonic admittance matrix of the power grid without considering the reserved nodes. The specific harmonic admittance matrix is ​​an N×N matrix.

[0092] It should be noted that, based on the harmonic impedance model established in step 103, a specific harmonic admittance matrix Y(n) of the power grid is established without considering the reserved nodes. f The number of nodes N after excluding the retained nodes, and the specific harmonic admittance matrix without considering the retained nodes, is an N×N matrix:

[0093]

[0094] Specific subharmonic admittance matrix Y(n) f In the diagram, the diagonal elements represent the node's self-admittance, and the off-diagonal elements represent the mutual admittance between nodes.

[0095] Specifically, the initial construction N All elements in the ×N matrix are 0. Traverse all branches of the power grid. If the current branch is not a reserved branch, modify the value of the current matrix element according to the harmonic impedance model. For example, traverse all line branches. If the traversed line branch is not a reserved branch, assuming the starting node is i and the ending node is j, then:

[0096]

[0097]

[0098]

[0099]

[0100] Traverse all transformer branches. If a traversed transformer branch is not a retained branch, assuming the starting node is i and the ending node is j, then:

[0101]

[0102]

[0103]

[0104]

[0105] Iterate through all loads / generators / power electronic devices. If a node being iterated does not belong to a load / generator / power electronic device, assuming the node being iterated is i, then:

[0106] For load nodes, we have:

[0107] For the generator node, we have:

[0108] For power electronic equipment nodes, we have:

[0109] After traversing and modifying all elements in the initial N×N matrix, the specific harmonic admittance matrix of the power grid without considering the reserved nodes can be obtained.

[0110] for Figure 7 The embodiments shown in Figure 1 and Table 1 yield the specific subharmonic admittance matrix Y(n) of the power grid without considering reserved nodes. f )for:

[0111]

[0112] Step 105: Perform the inverse operation on the admittance matrix of a specific harmonic order to obtain the impedance matrix under the harmonic order, and extract the first k dimensions of the impedance matrix under the harmonic order as the equivalent impedance matrix.

[0113] It should be noted that, after step 104, the specific subharmonic admittance matrix Y(n) of the power grid is obtained without considering the reserved nodes. f After that, for a specific harmonic admittance matrix Y(n) f Performing the inverse operation yields the inverse matrix, which is the impedance matrix Z(n) under the harmonic order. f ):

[0114]

[0115] Impedance matrix Z(n) at harmonic order f The first k-dimensional matrix in ) is used as the equivalent impedance matrix Z′(n) f ):

[0116]

[0117] for Figure 7 The impedance matrix Z(n) under harmonic orders in the embodiments shown in Figure 1 and Table 1 f )for:

[0118]

[0119] Here, * indicates values ​​that do not need to be considered, because the number of equivalent nodes k = 3, so the first 3 dimensions of the matrix are extracted.

[0120] Equivalent impedance matrix Z′(n) f )for:

[0121]

[0122] Step 106: Invert the equivalent impedance matrix to obtain the equivalent system admittance matrix under a specific harmonic.

[0123] It should be noted that for the equivalent impedance matrix Z′(n) f Inverse the equation to obtain the equivalent system admittance matrix Y′(n) under a specific harmonic. f ):

[0124]

[0125] for Figure 7 The system admittance matrix Y′(n) under specific harmonics after being equivalent to the embodiments shown in Figure 1 and Table 1 is... f )for:

[0126]

[0127] Step 107: Reconstruct the local power grid based on the equivalent system admittance matrix.

[0128] It should be noted that the local power grid can be directly reconstructed based on the equivalent system admittance matrix. For the branch formed by nodes i and j, its harmonic impedance is:

[0129]

[0130] Among them, the harmonic impedance of the branch formed by nodes i and j, Y′ ij The equivalent system admittance matrix Y′(n) under a specific harmonic is... f The element in the i-th row and j-th column of ).

[0131] The fundamental impedance of the branch formed by nodes i and j is:

[0132] Z′ ij (f0) = real(Z′) ij (n f ))+j·imag(Z′ ij (n f )) / n f

[0133] Among them, Z′ ij (f0) is the fundamental impedance of the branch formed by nodes i and j.

[0134] As for the impedance to ground of node i, its harmonic impedance is:

[0135]

[0136] Among them, Z′ ii (n f Let be the harmonic impedance to ground of node i.

[0137] The fundamental impedance of node i is:

[0138] Z′ ii (f0) = real(Z) ii (n f ))+j·imag(Z ii (n f )) / n f

[0139] Among them, Z ii (f0) is the fundamental impedance of node i.

[0140] for Figure 7 The embodiments shown in the figure and Table 1 can be calculated as follows:

[0141] The harmonic impedance of the busbar 1-busbar 2 branch is: Z′ 12 (f0) = 0.035 + j·0.22489

[0142] The harmonic impedance of the branch from busbar 1 to busbar 3 is: Z′ 13 (f0) = 0.04506 + j·0.23601

[0143] The harmonic impedance of the branch from busbar 2 to busbar 3 is: Z′ 23 (f0) = 0.01855 + j·0.1649

[0144] The ground harmonic impedance of the ground branch of busbar 1 is: Z′ 11 (f0) = 0.01513 + j·0.14254

[0145] The ground harmonic impedance of the ground branch of busbar 2 is: Z′ 22 (f0) = 0.02718 + j·0.24831

[0146] The ground harmonic impedance of the ground branch of busbar 3 is: Z′ 33 (f0) = 0.03748 + j·0.29834

[0147] The reconstructed local power grid isomorphic map is as follows: Figure 8 As shown.

[0148] In one embodiment, in the local power grid obtained in step 107, there may be cases where the reconstructed branches exhibit negative resistance, i.e., real(Z′) ii (n f ))<0 or real(Z′ ij (nf If the resistance of a branch is less than 0, to avoid system oscillation problems caused by negative resistance in the branch, such as... Figure 9 As shown, step 108 can also be performed.

[0149] Step 108: Determine whether each branch of the reconstructed local power grid has negative resistance. If so, readjust the reserved nodes and return to step 102.

[0150] In one embodiment, the number of retained nodes in step 102 can be 0 or not. When the number of retained nodes is not 0, such as... Figure 9 As shown, step 109 can also be performed.

[0151] Step 109: If the number of retained nodes is not 0, then the retained nodes are added again in the reconstructed local area power grid to obtain the equivalent power grid.

[0152] It should be noted that when the number of reserved nodes is not zero, after obtaining the reconstructed local area power grid in step 107, reserved nodes are added back to the local area power grid to obtain the final equivalent power grid, such as... Figure 10 As shown.

[0153] The multi-point equivalent method for power grid harmonic impedance provided by this invention integrates multi-point equivalent with harmonic equivalent, so that the harmonic impedance characteristics of the power grid system remain consistent before and after the equivalent. It achieves the technical effect of performing equivalent on the original system at a specific harmonic order, keeping the short-circuit impedance and mutual impedance of the equivalent nodes consistent with the original system at that specific harmonic order, and providing accurate input for subsequent time-domain or frequency-domain analysis.

[0154] The multi-point equivalent method for power grid harmonic impedance provided by this invention verifies the negative resistance of each branch of the reconstructed local power grid. When negative resistance occurs, the reserved nodes are readjusted to avoid system oscillation.

[0155] For easier understanding, please refer to Figure 11 This invention provides an embodiment of a multi-point equivalent system for power grid harmonic impedance, comprising:

[0156] The component modeling module is used to create component models of various power grid components under specific subharmonics.

[0157] The node statistics module is used to obtain the nodes that need to be equalized and determine the nodes to be retained, and to count the number of equalized nodes k and the number of nodes N after excluding the nodes to be retained;

[0158] The line harmonic impedance model construction module is used to build harmonic impedance models for line branches that include equivalent nodes but not reserved nodes.

[0159] The admittance matrix construction module is used to establish the specific harmonic admittance matrix of the power grid without considering the reserved nodes, based on the harmonic impedance model. The specific harmonic admittance matrix is ​​an N×N matrix.

[0160] The equivalent impedance module is used to invert the admittance matrix of a specific harmonic order to obtain the impedance matrix under the harmonic order, and extract the first k dimensions of the impedance matrix under the harmonic order as the equivalent impedance matrix.

[0161] The equivalent admittance module is used to invert the equivalent impedance matrix to obtain the equivalent system admittance matrix under a specific harmonic.

[0162] The reconstruction module is used to reconstruct the local power grid based on the equivalent system admittance matrix.

[0163] Also includes:

[0164] The judgment module is used to determine whether negative resistance occurs in each branch of the reconstructed local power grid. If so, the reserved nodes are readjusted and the process returns to the execution node statistics module.

[0165] Also includes:

[0166] The reserved node addition module is used to re-add reserved nodes in the reconstructed local area power grid if the number of reserved nodes is not 0, so as to obtain an equivalent power grid.

[0167] The admittance matrix construction module includes:

[0168] The initial matrix construction submodule is used to construct an initial N×N matrix where all matrix elements are 0;

[0169] The traversal submodule is used to traverse all branches. If the current branch is not a reserved branch, the value of the current matrix element is modified according to the harmonic impedance model.

[0170] The output submodule is used to obtain the specific harmonic admittance matrix of the power grid without considering the reserved nodes after traversing and modifying all elements in the initial N×N matrix.

[0171] The component models established in the component modeling module include line harmonic impedance models, transformer harmonic impedance models, load harmonic impedance models, generator harmonic impedance models, and power electronic equipment harmonic impedance models.

[0172] The multi-point equivalent system for power grid harmonic impedance provided in this embodiment of the invention is used to execute the multi-point equivalent method for power grid harmonic impedance provided in this invention. Its principle and the technical effects achieved are the same as those of the multi-point equivalent method for power grid harmonic impedance provided in this invention, and will not be repeated here.

[0173] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-point equivalent method for power grid harmonic impedance, characterized in that, include: S1. Establish component models of each power grid component under specific subharmonics; S2. Obtain the nodes that need to be equalized and determine the nodes to be retained. Count the number of equalized nodes k and the number of nodes N after excluding the nodes to be retained. S3. Establish a harmonic impedance model for line branches that include equivalent nodes but not reserved nodes. S4. Based on the harmonic impedance model, establish the specific harmonic admittance matrix of the power grid without considering the reserved nodes. The specific harmonic admittance matrix is ​​an N×N matrix. S5. Perform the inverse operation on the admittance matrix of a specific harmonic order to obtain the impedance matrix under the harmonic order, and extract the first k-dimensional matrix of the impedance matrix under the harmonic order as the equivalent impedance matrix. S6. Invert the equivalent impedance matrix to obtain the equivalent system admittance matrix under specific harmonics. S7. Reconstruct the local power grid based on the equivalent system admittance matrix.

2. The method for multi-point equivalent assessment of power grid harmonic impedance according to claim 1, characterized in that, Step S7 is followed by: S8. Determine whether each branch of the reconstructed local power grid has negative resistance. If so, readjust the reserved nodes and return to step S2.

3. The method for multi-point equivalent assessment of power grid harmonic impedance according to claim 1 or 2, characterized in that, Step S7 is followed by: If the number of reserved nodes is not zero, then the reserved nodes are added again in the reconstructed local power grid to obtain an equivalent power grid.

4. The method for multi-point equivalent assessment of power grid harmonic impedance according to claim 1, characterized in that, Step S4 includes: S41. Construct an initial N×N matrix where all matrix elements are 0; S42. Traverse all branches. If the current branch is not a retained branch, modify the value of the current matrix element according to the harmonic impedance model. S43. After completing the traversal and modification of all elements in the initial N×N matrix, the specific harmonic admittance matrix of the power grid is obtained without considering the reserved nodes.

5. The method for multi-point equivalent assessment of power grid harmonic impedance according to claim 1, characterized in that, The component models established in step S1 include line harmonic impedance models, transformer harmonic impedance models, load harmonic impedance models, generator harmonic impedance models, and power electronic equipment harmonic impedance models.

6. A multi-point equivalent system for power grid harmonic impedance, characterized in that, include: The component modeling module is used to create component models of various power grid components under specific subharmonics. The node statistics module is used to obtain the nodes that need to be equalized and determine the nodes to be retained, and to count the number of equalized nodes k and the number of nodes N after excluding the nodes to be retained; The line harmonic impedance model construction module is used to build harmonic impedance models for line branches that include equivalent nodes but not reserved nodes. The admittance matrix construction module is used to establish the specific harmonic admittance matrix of the power grid without considering the reserved nodes, based on the harmonic impedance model. The specific harmonic admittance matrix is ​​an N×N matrix. The equivalent impedance module is used to invert the admittance matrix of a specific harmonic order to obtain the impedance matrix under the harmonic order, and extract the first k dimensions of the impedance matrix under the harmonic order as the equivalent impedance matrix. The equivalent admittance module is used to invert the equivalent impedance matrix to obtain the equivalent system admittance matrix under a specific harmonic. The reconstruction module is used to reconstruct the local power grid based on the equivalent system admittance matrix.

7. The multi-point equivalent system for power grid harmonic impedance according to claim 6, characterized in that, Also includes: The judgment module is used to determine whether negative resistance occurs in each branch of the reconstructed local power grid. If so, the reserved nodes are readjusted and the process returns to the execution node statistics module.

8. The multi-point equivalent system for power grid harmonic impedance according to claim 6 or 7, characterized in that, Also includes: The reserved node addition module is used to re-add reserved nodes in the reconstructed local area power grid if the number of reserved nodes is not 0, so as to obtain an equivalent power grid.

9. The multi-point equivalent system for power grid harmonic impedance according to claim 6, characterized in that, The admittance matrix construction module includes: The initial matrix construction submodule is used to construct an initial N×N matrix where all matrix elements are 0; The traversal submodule is used to traverse all branches. If the current branch is not a reserved branch, the value of the current matrix element is modified according to the harmonic impedance model. The output submodule is used to obtain the specific harmonic admittance matrix of the power grid without considering the reserved nodes after traversing and modifying all elements in the initial N×N matrix.

10. The multi-point equivalent system for power grid harmonic impedance according to claim 6, characterized in that, The component models established in the component modeling module include line harmonic impedance models, transformer harmonic impedance models, load harmonic impedance models, generator harmonic impedance models, and power electronic equipment harmonic impedance models.

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