Grid impedance equivalent calculation method and system considering distributed parameters of components in the area

Abstract

The present invention relates to the technical field of electric power systems, and in particular to a method and system for calculating the equivalent value of grid impedance taking into account the distributed parameters of components within a region. The method comprises: determining the connection between a grid partition and an external grid and obtaining a boundary node; selecting a specific operation mode of the grid according to a load level, a state of a generator set and an operation condition of the equipment; calculating the equivalent parameters of an external grid under the set grid operation mode and constructing an equivalent model including the interconnection relationship between sections; establishing an admittance model of the grid within the region according to the distributed parameter characteristics of components in the grid within the region, and generating an admittance matrix of the grid within the region based on a set frequency range; selecting a target section of the grid within the region, and according to the impedance characteristics of converters at other non-target sections, converting the port characteristics of the relevant converters into the admittance matrix of the grid within the region; solving the equivalent impedance of the port of the target section looking at the grid based on the equivalently corrected admittance matrix of the grid within the region to obtain a final calculation result.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power systems, and in particular to a method and system for calculating the equivalent value of grid impedance taking into account distributed parameters of components within a region. Background Art

[0002] The impedance analysis method looks at the source side and the grid side from the key section, and decomposes the system into a power subsystem and a grid subsystem. The grid side is generally equivalent to a voltage source and impedance series topology, and the converter side is generally equivalent to a current source and impedance parallel topology. The Nyquist stability criterion can be used to analyze the oscillation stability of the converter grid-connected system. Academia and industry have proposed a variety of stability criteria from the perspective of source-side and grid-side impedance matching. The most commonly used one is the phase margin criterion, which compares the amplitude-phase diagram of the source-side impedance and the grid-side impedance, and evaluates the stability of the converter grid-connected by the phase difference corresponding to the frequency of the intersection of the amplitude curve.

[0003] However, there are two main problems with existing technologies when it comes to displaying the equivalent impedance of the grid side: first, the calculation method for the equivalent impedance of the grid is still unclear, and there is a lack of standardized analysis and calculation processes, making it difficult to automate related calculations; second, when there are other power electronic equipment in the grid near the target converter, existing technologies usually ignore their impact, making it difficult to achieve the equivalent impedance calculation of multiple types of converters such as flexible direct current, new energy, SVG (Static Var Generator), and energy storage systems looking at the grid.

[0004] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0005] The present invention provides a method and system for calculating the equivalent value of power grid impedance taking into account the distributed parameters of components within a region, thereby effectively solving the problems in the background technology.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area, comprising the following steps:

[0007] Obtain the type of local grid to which the converter is connected and the grid operating conditions, determine the connection between the grid partition and the external grid, and obtain the external section and boundary nodes;

[0008] Select the specific operation mode of the power grid according to the load level, the status of the generator set and the operation of the equipment;

[0009] Under the set grid operation mode, the equivalent parameters of the grid outside the area are calculated according to the selected boundary nodes, and an equivalent model including the interconnection relationship between each section is constructed;

[0010] According to the distributed parameter characteristics of the components in the regional power grid, the regional power grid admittance model is established, and the regional power grid admittance matrix is ​​generated based on the set frequency range;

[0011] A target section of the intra-regional power grid is selected, and according to the impedance characteristics of the converters at other non-target sections, the port characteristics of the relevant converters are converted into the admittance matrix of the intra-regional power grid;

[0012] On the basis of the admittance matrix of the power grid in the area after equivalent correction, the equivalent impedance of the port of the target section looking toward the power grid is solved to obtain the final calculation result.

[0013] Further, the determining of the connection between the power grid partition and the external power grid and obtaining the external section and boundary node includes:

[0014] According to the analysis accuracy and calculation scale, the multi-level topology connection node of the converter access node is selected to connect the external power transmission channel of the node as the partition external section, and the related nodes are boundary nodes.

[0015] Furthermore, the selection of the converter access node includes the following constraints:

[0016] The voltage level of the section outside the partition shall not be lower than the section where the converter is connected within the partition;

[0017] There is at least one non-transformer node between the partition external section and the converter access node;

[0018] Independent power supply nodes or independent transmission channels should not be used as boundary nodes or boundary sections;

[0019] Independent load nodes or independent power supply channels should not be used as boundary nodes or boundary sections;

[0020] The loads and sources directly connected to the boundary nodes are modeled separately and are not included in the external equivalents.

[0021] Furthermore, the specific operation mode of the power grid includes:

[0022] The load level includes at least three levels: high, medium and low. The new energy output level includes at least three levels: high, medium and low. Multiple transmission lines between nodes in the area are in maintenance / operation status, the busbar is in the combined / denominator operation state, the transformer is in maintenance / operation status, and the reactive compensation equipment is in operation / exit status.

[0023] Furthermore, the equivalent parameters of the power grid outside the area are calculated according to the selected boundary nodes, and an equivalent model including the interconnection relationship between each section is constructed, including the following steps:

[0024] Use the static equivalent topology method to equalize the complete power grid, so that the equivalent power grid is consistent with the original power grid flow results;

[0025] Obtain the equivalent model of the power grid outside the area under power frequency, including the Thevenin equivalent circuit of the boundary node , and the interconnection impedance between boundary nodes ;

[0026] Frequency expansion is performed on the equivalent value parameters, where f is any frequency point to be analyzed, and f b is the industrial frequency, usually 50 Hz, and i is a complex operator:

[0027] ;

[0028] ;

[0029] In the formula, Represents a boundary node In frequency Thevenin equivalent circuit impedance under For the boundary node In frequency The real part of the equivalent impedance represents the resistance component, For the boundary node In frequency The imaginary part of the equivalent impedance represents the reactance or capacitance component, Represents two boundary nodes and In frequency The interconnect impedance under For the boundary node and In frequency The real part of the lower interconnect impedance represents the resistive component, For the boundary node and In frequency The imaginary part of the lower interconnect impedance, representing the reactance or capacitance component.

[0030] Furthermore, the establishment of the intra-regional power grid admittance model according to the distributed parameter characteristics of the components in the intra-regional power grid includes:

[0031] For transmission lines:

[0032] Angular frequency , assuming that the impedance per unit length of the transmission line with a length of l is , the admittance is ,in is the line resistance per unit length, is the line inductance per unit length, is the line conductance per unit length, C 0 is the capacitance corresponding to the line susceptance per unit length, , are two intermediate parameters related to parameters and frequency;

[0033] The π-type equivalent model of the transmission line taking into account the distributed parameter characteristics is formed:

[0034] , ,in is the hyperbolic sine function, is the hyperbolic cosine function, is the lumped equivalent impedance frequency response corresponding to the line distributed parameter model, is the lumped equivalent susceptance frequency response corresponding to the line distributed parameter model;

[0035] For power transformers:

[0036] Prioritize obtaining the measured impedance-frequency response characteristics of the transformer. If this is not possible, calculate the power frequency characteristics based on the transformer nameplate parameters, and remember that the nameplate parameters are the rated capacity. , Rated line voltage , short circuit loss , short circuit voltage , no-load loss , no-load current , then the short-circuit resistance , transformer reactance , transformer conductance , transformer impedance ;

[0037] Frequency expansion yields: , , , ;

[0038] For power load and reactive power compensation equipment:

[0039] Obtain the impedance-frequency distribution characteristics of the power grid load and reactive compensation equipment in the area, and give priority to using actual test data. If there is no actual test data, form the port voltage-current transfer function according to the topology of the reactive compensation equipment to calculate the impedance-frequency characteristics.

[0040] Furthermore, the generating of the intra-region power grid admittance matrix based on the set frequency range comprises the following steps:

[0041] Sort by non-converter grid-connected nodes within the area, boundary equivalent nodes, and converter grid-connected nodes within the area;

[0042] In the frequency range According to the grid admittance matrix generation method, the admittance matrix is ​​formed according to the network topology in the area and the parameters of the transmission line, power transformer, equivalent load and equivalent model. ;

[0043] According to the impedance-frequency characteristics of the reactive compensation equipment, its influence on the admittance matrix of the power grid in the area is calculated separately. Assume that the impedance-frequency distribution characteristics of the reactive compensation equipment are: When node i is connected, the self-admittance of node i is corrected as , the modified admittance matrix in the region is recorded as ;

[0044] According to the equivalent self-impedance of the external section, the self-admittance of the corresponding node is corrected. Assume that the equivalent self-impedance of the external section corresponding to node i is , then the self-admittance of the modified node i is ; According to the equivalent interconnection impedance between the external sections, the mutual admittance and self-admittance between the corresponding nodes are corrected. Assume that the equivalent interconnection impedance between the corresponding node i and the node j of the external section is , then the self-admittance of node i and node j is corrected to , , the mutual admittance correction is The modified admittance matrix in the region is recorded as .

[0045] Furthermore, the target section of the power grid in the selected area includes:

[0046] The flexible direct current, new energy stations, SVG, and energy storage power electronic converter grid-connected nodes of the regional power grid are taken as target sections. Based on actual analysis requirements, the conventional direct current and synchronous generator grid-connected nodes are considered as target sections.

[0047] When studying any target section, the impedance of other non-target sections is integrated into the admittance matrix. middle.

[0048] Furthermore, the step of converting the port characteristics of the relevant converter into the admittance matrix of the intra-area power grid includes:

[0049] Assume that the impedance-frequency characteristics of the non-target section i connected to the flexible direct current, new energy station, SVG, and energy storage power electronic converter are: , then the self-admittance of the modified node i is, , the modified admittance matrix in the region is recorded as .

[0050] Further, the step of solving the equivalent impedance of the port of the target section looking toward the power grid includes:

[0051] Invert the admittance matrix , To find the inverse function of a matrix, The physical meaning is that after all the electrical components inside and outside the region are equal: any diagonal element Describe the voltage response on node i when a current with unit frequency f is injected into node i when no current is injected into other nodes except node i.

[0052] Any off-diagonal element Describes the voltage at node j when a unit current is injected into node i when no current is injected into other nodes except node i;

[0053] According to the target section corresponding to the target node number x, extract and record , is the equivalent impedance of the target section looking toward the power grid under the current mode.

[0054] The present invention also includes a system for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area, using the above method, the system comprising:

[0055] The boundary node acquisition module is used to obtain the type of the local power grid to which the converter is connected and the power grid operating conditions, determine the connection between the power grid partition and the external power grid, and obtain the external section and boundary nodes;

[0056] The operation mode selection module is used to select the specific operation mode of the power grid according to the load level, the status of the generator set and the operation status of the equipment;

[0057] The module for constructing an equivalent model of an out-of-region power grid is used to calculate the equivalent parameters of the out-of-region power grid according to the selected boundary nodes under the set power grid operation mode, and to construct an equivalent model including the interconnection relationship between each section;

[0058] An intra-regional power grid admittance matrix generation module is used to establish an intra-regional power grid admittance model according to the distributed parameter characteristics of the components in the intra-regional power grid, and to generate an intra-regional power grid admittance matrix based on a set frequency range;

[0059] An admittance matrix correction module is used to select a target section of the intra-regional power grid and, based on the impedance characteristics of the converters at other non-target sections, equate the relevant converter port characteristics to the intra-regional power grid admittance matrix;

[0060] The calculation result acquisition module is used to solve the equivalent impedance of the port looking at the power grid from the target section based on the equivalently corrected admittance matrix of the power grid in the area to obtain the final calculation result.

[0061] The present invention also includes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method described above is implemented.

[0062] The present invention also includes a storage medium on which a computer program is stored. When the computer program is executed by a processor, the method described above is implemented.

[0063] The beneficial effects of the present invention are as follows: the present invention takes into account the distributed parameter characteristics of the grid components in the area; fully considers the influence of reactive compensation equipment and other power electronic equipment on the impedance characteristics of the nearby grid; and proposes a universal grid impedance expression, which is convenient for programming and automation. It realizes a more accurate and convenient calculation of the grid-side impedance, and provides an efficient solution tool for the oscillation stability analysis of the power electronic power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0065] Figure 1 is a flow chart of the method in Example 1;

[0066] Figure 2 It is a structural schematic diagram of the system in Example 1;

[0067] Figure 3 is a flow chart of the method in Example 2;

[0068] Figure 4 It is a schematic diagram of the sections and nodes inside and outside the power grid area in Example 2;

[0069] Figure 5 It is a schematic diagram of the external section and nodes of the power grid partition in Example 2;

[0070] Figure 6 is the overhead line distributed parameter equivalent circuit in Example 2;

[0071] Figure 7 is the transformer equivalent circuit in Example 2;

[0072] Figure 8 The HP8 AC filter and its impedance characteristics in Example 2;

[0073] Fig. 9 This is a schematic diagram of calculating the equivalent impedance in the power grid area in Example 2;

[0074] Fig.10 It is a schematic diagram of the structure of a computer device; DETAILED DESCRIPTION

[0075] The technical solutions in the embodiments of the present invention will be described clearly and completely 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.

[0076] Embodiment 1:

[0077] like Figure 1 As shown: A method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area, comprising the following steps:

[0078] Obtain the type of local grid to which the converter is connected and the grid operating conditions, determine the connection between the grid partition and the external grid, and obtain the external section and boundary nodes;

[0079] Select the specific operation mode of the power grid according to the load level, the status of the generator set and the operation of the equipment;

[0080] Under the set grid operation mode, the equivalent parameters of the grid outside the area are calculated according to the selected boundary nodes, and an equivalent model including the interconnection relationship between each section is constructed;

[0081] According to the distributed parameter characteristics of the components in the regional power grid, the regional power grid admittance model is established, and the regional power grid admittance matrix is ​​generated based on the set frequency range;

[0082] The target section of the power grid in the area is selected, and according to the impedance characteristics of the converters at other non-target sections, the port characteristics of the relevant converters are converted into the admittance matrix of the power grid in the area;

[0083] Based on the equivalently corrected admittance matrix of the power grid in the area, the equivalent impedance of the port looking toward the power grid at the target section is solved to obtain the final calculation result.

[0084] By taking into account the distributed parameter characteristics of the grid components in the area; it is suitable for the equivalent calculation of the impedance of the local grid connected to multiple types of converters such as flexible direct current, new energy, SVG, and energy storage, and fully considers the impedance-frequency characteristics of the local grid electrical components and other power electronic equipment in the vicinity of the converter grid connection, and realizes the equivalent of the static characteristics in the grid area through the frequency-divided and layered admittance matrix correction, and proposes a universal solution algorithm for the calculation of the grid-side impedance, fully considering the influence of reactive compensation equipment and other power electronic equipment on the impedance characteristics of the nearby grid; a universal grid impedance expression is proposed, which is easy to program and automate. It realizes a more accurate and convenient calculation of the grid-side impedance, and provides an efficient solution tool for the oscillation stability analysis of the power electronic power system.

[0085] In this embodiment, determining the connection between the power grid partition and the external power grid and obtaining the external section and boundary node includes:

[0086] According to the analysis accuracy and calculation scale, the multi-level topology connection node of the converter access node is selected to connect the external power transmission channel as the partition external section, and the related nodes are boundary nodes.

[0087] When selecting the converter access node, the following constraints are included:

[0088] The voltage level of the section outside the partition shall not be lower than the section where the converter is connected within the partition;

[0089] There is at least one non-transformer node between the partition external section and the converter access node;

[0090] Independent power supply nodes or independent transmission channels should not be used as boundary nodes or boundary sections;

[0091] Independent load nodes or independent power supply channels should not be used as boundary nodes or boundary sections;

[0092] The loads and sources directly connected to the boundary nodes are modeled separately and are not included in the external equivalents.

[0093] As a preferred embodiment of the above, the specific operation mode of the power grid includes:

[0094] The load level includes at least three levels: high, medium and low. The new energy output level includes at least three levels: high, medium and low. Multiple transmission lines between nodes in the area are in maintenance / operation status, the busbar is in the combined / denominator operation state, the transformer is in maintenance / operation status, and the reactive compensation equipment is in operation / exit status.

[0095] The equivalent parameters of the power grid outside the area are calculated according to the selected boundary nodes, and an equivalent model including the interconnection relationship between each section is constructed, including the following steps:

[0096] Use the static equivalent topology method to equalize the complete power grid, so that the equivalent power grid is consistent with the original power grid flow results;

[0097] Obtain the equivalent model of the power grid outside the area under power frequency, including the Thevenin equivalent circuit of the boundary node , and the interconnection impedance between boundary nodes ;

[0098] Frequency expansion is performed on the equivalent value parameters, where f is any frequency point to be analyzed, and f b is the power frequency. For the Chinese power grid, the power frequency is usually 50 Hz. i is a complex operator:

[0099] ;

[0100] ;

[0101] In the formula, Represents a boundary node In frequency Thevenin equivalent circuit impedance under For the boundary node In frequency The real part of the equivalent impedance represents the resistance component, For the boundary node In frequency The imaginary part of the equivalent impedance represents the reactance or capacitance component, Represents two boundary nodes and In frequency The interconnect impedance under For the boundary node and In frequency The real part of the lower interconnect impedance represents the resistive component, For the boundary node and In frequency The imaginary part of the lower interconnect impedance, representing the reactance or capacitance component.

[0102] In this embodiment, according to the distributed parameter characteristics of the components in the intra-regional power grid, an intra-regional power grid admittance model is established, including:

[0103] For transmission lines:

[0104] Angular frequency , assuming that the impedance per unit length of the transmission line with a length of l is , the admittance is ,in is the line resistance per unit length, is the line inductance per unit length, is the line conductance per unit length, C 0 is the capacitance corresponding to the line susceptance per unit length, , are two intermediate parameters related to parameters and frequency;

[0105] The π-type equivalent model of the transmission line taking into account the distributed parameter characteristics is formed:

[0106] , ,in is the hyperbolic sine function, is the hyperbolic cosine function, is the lumped equivalent impedance frequency response corresponding to the line distributed parameter model, is the lumped equivalent susceptance frequency response corresponding to the line distributed parameter model;

[0107] For power transformers:

[0108] Prioritize obtaining the measured impedance-frequency response characteristics of the transformer. If this is not possible, calculate the power frequency characteristics based on the transformer nameplate parameters, and remember that the nameplate parameters are the rated capacity. , Rated line voltage , short circuit loss , short circuit voltage , no-load loss , no-load current , then the short-circuit resistance , transformer reactance , transformer conductance , transformer impedance ;

[0109] Frequency expansion yields: , , , ;

[0110] For power load and reactive power compensation equipment:

[0111] Obtain the impedance-frequency distribution characteristics of the power grid load and reactive compensation equipment in the area, and give priority to using actual test data. If there is no actual test data, form the port voltage-current transfer function according to the topology of the reactive compensation equipment to calculate the impedance-frequency characteristics.

[0112] Generating the admittance matrix of the power grid in the area based on the set frequency range includes the following steps:

[0113] Sort by non-converter grid-connected nodes within the area, boundary equivalent nodes, and converter grid-connected nodes within the area;

[0114] In the frequency range According to the grid admittance matrix generation method, the admittance matrix is ​​formed according to the network topology in the area and the parameters of the transmission line, power transformer, equivalent load and equivalent model. ;

[0115] According to the impedance-frequency characteristics of the reactive compensation equipment, its influence on the admittance matrix of the power grid in the area is calculated separately. Assume that the impedance-frequency distribution characteristics of the reactive compensation equipment are: When node i is connected, the self-admittance of node i is corrected as , the modified admittance matrix in the region is recorded as ;

[0116] According to the equivalent self-impedance of the external section, the self-admittance of the corresponding node is corrected. Assume that the equivalent self-impedance of the external section corresponding to node i is , then the self-admittance of the modified node i is ; According to the equivalent interconnection impedance between the external sections, the mutual admittance and self-admittance between the corresponding nodes are corrected. Assume that the equivalent interconnection impedance between the corresponding node i and the node j of the external section is , then the self-admittance of node i and node j is corrected to , , the mutual admittance correction is The modified admittance matrix in the region is recorded as .

[0117] Among them, the target section of the power grid in the selected area includes:

[0118] The flexible direct current, new energy stations, SVG, and energy storage power electronic converter grid-connected nodes of the regional power grid are taken as target sections. Based on actual analysis requirements, the conventional direct current and synchronous generator grid-connected nodes are considered as target sections.

[0119] When studying any target section, the impedance of other non-target sections is integrated into the admittance matrix. middle.

[0120] As a preferred embodiment of the above, the relevant converter port characteristics are converted into an intra-area power grid admittance matrix, including:

[0121] Assume that the impedance-frequency characteristics of the non-target section i connected to the flexible direct current, new energy station, SVG, and energy storage power electronic converter are: , then the self-admittance of the modified node i is, , the modified admittance matrix in the region is recorded as .

[0122] In this embodiment, solving the equivalent impedance of the port of the target section looking toward the power grid includes:

[0123] Invert the admittance matrix , To find the inverse function of a matrix, The physical meaning is that after all the electrical components inside and outside the region are equal: any diagonal element Describe the voltage response on node i when a current with unit frequency f is injected into node i when no current is injected into other nodes except node i.

[0124] Any off-diagonal element Describes the voltage at node j when a unit current is injected into node i when no current is injected into other nodes except node i;

[0125] According to the target section corresponding to the target node number x, extract and record , is the equivalent impedance of the target section looking toward the power grid under the current mode.

[0126] like Figure 2 As shown, this embodiment also includes a grid impedance equivalent calculation system taking into account the distributed parameters of components in the area, using the above method, the system includes:

[0127] The boundary node acquisition module is used to obtain the type of the local power grid to which the converter is connected and the power grid operating conditions, determine the connection between the power grid partition and the external power grid, and obtain the external section and boundary nodes;

[0128] The operation mode selection module is used to select the specific operation mode of the power grid according to the load level, the status of the generator set and the operation status of the equipment;

[0129] The module for constructing an equivalent model of an out-of-region power grid is used to calculate the equivalent parameters of the out-of-region power grid according to the selected boundary nodes under the set power grid operation mode, and to construct an equivalent model including the interconnection relationship between each section;

[0130] An intra-regional power grid admittance matrix generation module is used to establish an intra-regional power grid admittance model according to the distributed parameter characteristics of the components in the intra-regional power grid, and to generate an intra-regional power grid admittance matrix based on a set frequency range;

[0131] The admittance matrix correction module is used to select the target section of the power grid in the area, and according to the impedance characteristics of the converters at other non-target sections, convert the relevant converter port characteristics into the admittance matrix of the power grid in the area;

[0132] The calculation result acquisition module is used to solve the equivalent impedance of the port looking at the power grid from the target section based on the equivalent corrected admittance matrix of the power grid in the area to obtain the final calculation result.

[0133] Embodiment 2:

[0134] like Figure 3 As shown, this embodiment provides a method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area, comprising the following steps:

[0135] For local power grids connected to multiple types of converters such as flexible direct current, new energy, SVG, and energy storage, the connection between the power grid partitions and the external power grid is determined based on analysis requirements, and the boundary nodes are clarified; further information on the selected power grid operation mode is determined, such as load level, traditional power supply startup method, new energy unit startup method, and operation / maintenance method of electrical equipment in the area.

[0136] The operation mode of the power grid to be analyzed is selected. First, the equivalent parameters of the power grid outside the area are calculated. Each section is connected through an equivalent interconnection impedance, and each is connected to an ideal voltage source through an equivalent self-impedance. A distributed parameter model of the power grid within the area is established, and the distributed parameter characteristics of transformers and lines are considered to form an admittance matrix of the power grid within a frequency range.

[0137] The target section of the power grid in the area is selected, which is usually the section where the converters such as flexible direct current, new energy, SVG and energy storage are connected. According to the converter impedance characteristics at other non-target sections, the relevant converter port characteristics are added to the admittance matrix of the power grid in the area, and the equivalent impedance of the port of the target section looking at the power grid is further solved.

[0138] like Figure 4 As shown, the method for determining the external section of the power grid partition includes:

[0139] The multi-level topological connection nodes of the converter access nodes are usually selected according to the analysis accuracy and calculation scale. The external transmission channel of the nodes is the external section of the partition, and the related nodes are the boundary nodes. The selection generally conforms to the following principles:

[0140] (1) The voltage level of the section outside the partition shall not be lower than the section where the converter is connected within the partition;

[0141] (2) There is at least one non-transformer node between the partition external section and the converter access node;

[0142] (3) Independent power supply nodes or independent transmission channels should not be used as boundary nodes or boundary sections;

[0143] (4) Independent load nodes or independent power supply channels should not be used as boundary nodes or boundary sections;

[0144] (5) Loads and power sources directly connected to boundary nodes should be modeled separately and should not be included in external equivalent values.

[0145] The selection of power grid operation mode includes:

[0146] The calculation results of grid impedance equivalence are used to check the impedance matching characteristics of converter access. The grid operation mode should include the main operation modes of the regional grid. The load levels include high, medium and low modes. The output levels of new energy include high, medium and low modes. Multiple transmission lines between nodes in the area are in maintenance / operation status, the busbar is in a combined / denominator operation state, the transformer is in maintenance / operation status, and the reactive compensation equipment is in operation / exit status.

[0147] like Figure 5 As shown in the figure, the method for calculating the equivalent value of the out-of-region power grid includes:

[0148] Including but not limited to using Ward equivalent method and REI (Redial Equivalent Independent) equivalent method to equalize the complete power grid to ensure that the equivalent power grid is consistent with the original power grid flow results;

[0149] The above method is used to obtain the equivalent model of the power grid outside the area under power frequency, including the Thevenin equivalent circuit of the boundary node ( , ) and the interconnection impedance between boundary nodes ( ).

[0150] Frequency-expand the parameters:

[0151] ;

[0152] ;

[0153] This embodiment provides a method and system for calculating the equivalent value of grid impedance taking into account the distributed parameters of components within a region. The establishment of a distributed parameter model of the grid within a region includes:

[0154] (1) Transmission lines

[0155] like Figure 6 As shown, , assuming that the impedance and admittance per unit length of the transmission line with a length of l are , ,but , .

[0156] Form a π-type equivalent model of the transmission line taking into account the distributed parameter characteristics, , .

[0157] (2) Power transformer

[0158] like Figure 7 As shown, the measured impedance-frequency response characteristics of the transformer are obtained first. If it is not available, the power frequency characteristics can be calculated according to the transformer nameplate parameters. The nameplate parameters are recorded as the rated capacity. , Rated line voltage , short circuit loss , short circuit voltage , no-load loss , no-load current ,but , , , .

[0159] Further frequency expansion yields: , , , .

[0160] (3) Power load and reactive power compensation equipment

[0161] Obtain the impedance-frequency distribution characteristics of the power grid load and reactive compensation equipment in the area, and give priority to using actual test data. If there is no actual test data, form the port voltage-current transfer function according to the topology of the reactive compensation equipment to calculate the impedance-frequency characteristics.

[0162] Taking the typical HP8 AC filter as an example, let s be the Laplace operator, and calculate its impedance transfer function based on its device parameters:

[0163] ;

[0164] Draw its amplitude-phase characteristic curve as Figure 8 shown.

[0165] The formation of the intra-regional power grid admittance matrix includes:

[0166] Step 1: Sort the nodes in the area according to non-converter grid-connected nodes, boundary equivalent nodes, and converter grid-connected nodes in the area.

[0167] Step 2 in the frequency range According to the conventional grid admittance matrix generation method, the admittance matrix is ​​formed at each frequency point according to the network topology in the area and the parameters of the transmission line, power transformer, equivalent load and equivalent model. .

[0168] Step 3: Since the input / output of reactive compensation equipment will greatly affect the impedance characteristics of the power grid in the area, its impact on the admittance matrix of the power grid in the area should be calculated separately according to its impedance-frequency characteristics. Assume that the impedance-frequency distribution characteristics of the reactive compensation equipment are When node i is connected, the self-admittance of node i is corrected as , the modified admittance matrix in the region is recorded as .

[0169] Step 4: Correct the self-admittance of the corresponding node according to the equivalent self-impedance of the external section. Suppose the equivalent self-impedance of the corresponding node i of the external section is , then the self-admittance of the modified node i is ; According to the equivalent interconnection impedance between the external sections, the mutual admittance and self-admittance between the corresponding nodes are corrected. Assume that the equivalent interconnection impedance between the corresponding node i and the node j of the external section is , then the self-admittance of node i and node j is corrected to , , the mutual admittance correction is The modified admittance matrix in the region is recorded as .

[0170] Target section selection includes:

[0171] Usually, the grid-connected nodes of power electronic converters such as flexible direct current, new energy stations, SVG, and energy storage in the regional power grid are taken as target sections. According to actual analysis requirements, conventional direct current and synchronous generator grid-connected nodes can also be considered as target sections. When studying any target section, the impedance of converters in other non-target sections should be integrated into the admittance matrix. middle.

[0172] The non-fused target section current transformer impedance methods include:

[0173] Assume that the impedance-frequency characteristics of non-target section i connected to flexible direct current, new energy station, SVG, energy storage and other power electronic converters are: , then the self-admittance of the modified node i is, , the modified admittance matrix in the region is recorded as .

[0174] like Fig. 9 As shown in the figure, the calculation of equivalent impedance of the target section looking toward the power grid includes:

[0175] Invert the admittance matrix , Find the inverse function for a matrix. The physical meaning is that after all the electrical components inside and outside the region are equal: any diagonal element Describes the voltage response at node i when a unit frequency f current is injected into node i when no current is injected into other nodes except node i. Any non-diagonal element Describes the voltage at node j when a unit current is injected into node i when no current is injected into other nodes except node i.

[0176] According to the target section corresponding to the target node number x, extract and record , is the equivalent impedance of the target section looking toward the power grid under the current mode.

[0177] See also Fig.10 A computer device 400 provided in an embodiment of the present application includes: a processor 410 and a memory 420, wherein the memory 420 stores a computer program executable by the processor 410, and when the computer program is executed by the processor 410, the above method is executed.

[0178] The embodiment of the present application further provides a storage medium 430 on which a computer program is stored. When the computer program is run by the processor 410, the above method is executed.

[0179] Among them, the storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable red-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, disk or optical disk.

[0180] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0181] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0182] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0183] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0184] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection with one or more wires (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0185] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0186] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0187] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in a region, characterized in that: The steps include: Obtain the type of local grid to which the converter is connected and the grid operating conditions, determine the connection between the grid partition and the external grid, and obtain the external section and boundary nodes; Select the specific operation mode of the power grid according to the load level, the status of the generator set and the operation of the equipment; Under the set grid operation mode, the equivalent parameters of the grid outside the area are calculated according to the selected boundary nodes, and an equivalent model including the interconnection relationship between each section is constructed; According to the distributed parameter characteristics of the components in the regional power grid, the regional power grid admittance model is established, and the regional power grid admittance matrix is ​​generated based on the set frequency range; A target section of the intra-regional power grid is selected, and according to the impedance characteristics of the converters at other non-target sections, the port characteristics of the relevant converters are converted into the admittance matrix of the intra-regional power grid; On the basis of the admittance matrix of the power grid in the area after equivalent correction, the equivalent impedance of the port of the target section looking toward the power grid is solved to obtain the final calculation result; The equivalent parameters of the out-of-region power grid are calculated based on the selected boundary nodes, and an equivalent model including the interconnection relationship between each section is constructed, including the following steps: (1) the complete power grid is equivalently calculated using the static equivalent topology method, so that the equivalent power grid is consistent with the original power grid flow result; the equivalent model of the out-of-region power grid under the power frequency is obtained, including the boundary node Thevenin equivalent circuit e Si (f b ), and the interconnection impedance z between boundary nodes Sij (f b )=α Sij (f b )+iβ Sij (f b );(2) Frequency expansion of equivalent parameters, f is any frequency point to be analyzed, f b is the industrial frequency, and i is a complex operator: In the formula, z Si (f b ), α Si (f b ), β Si (f b ) represent the boundary nodes Si at frequency f b Thevenin equivalent circuit impedance, the real part of the equivalent impedance and the imaginary part of the equivalent impedance under z Sij (f b ), α Sij (f b ), β Sij (f b ) represent the two boundary nodes Si and Sj at frequency f b The interconnect impedance, the real part of the interconnect impedance, and the imaginary part of the interconnect impedance under ; The method of establishing an intra-regional power grid admittance model according to the distributed parameter characteristics of the components in the intra-regional power grid comprises: for a transmission line: setting the angular frequency ω=2πf, setting the unit length impedance of the transmission line with a length of l to z0=r0+iωL0, and the admittance to y0=g0+iωC0, wherein r0 is the unit length line resistance, L0 is the unit length line inductance, g0 is the unit length line conductance, C0 is the capacitance corresponding to the unit length line admittance, and are two intermediate parameters related to parameters and frequency; Forming a π-type equivalent model of the transmission line taking into account the distributed parameter characteristics: L (f) = z0sh(γ(f)l), y L (f) = 2(ch(γ(f)l)-1) / (z0sh(γ(f)l)), where sh() is the hyperbolic sine function, ch() is the hyperbolic cosine function, and z L (f) is the lumped equivalent impedance frequency response corresponding to the line distributed parameter model, y L (f) is the lumped equivalent susceptance frequency response corresponding to the line distributed parameter model; for power transformers: first obtain the measured impedance-frequency response characteristics of the transformer. If it is not available, calculate the power frequency characteristics according to the transformer nameplate parameters. The nameplate parameters are recorded as the rated capacity S N , Rated line voltage V N , short circuit loss ΔP s , short circuit voltage P S %, no-load loss Δp0, no-load current I0%, then the short-circuit resistance Transformer Reactance Transformer Conductance Transformer Susceptance Frequency expansion gives: r T (f) = r T , x T (f) = x T ×f / f b , g T (f) = g T , b T (f) = b T ×f b / f; For power loads and reactive compensation equipment: obtain the impedance-frequency distribution characteristics of the power grid load and reactive compensation equipment in the area, and give priority to using actual test data. If there is no actual test data, form the port voltage-current transfer function according to the topology of the reactive compensation equipment to calculate the impedance-frequency characteristics.

2. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 1, characterized in that: Determining the connection between the power grid partition and the external power grid, and obtaining the external section and boundary node, includes: According to the analysis accuracy and calculation scale, the multi-level topology connection node of the converter access node is selected to connect the external power transmission channel as the partition external section, and the related nodes are boundary nodes.

3. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 2, characterized in that: The selection of the converter access node includes the following constraints: The voltage level of the section outside the partition shall not be lower than the section where the converter is connected within the partition; There is at least one non-transformer node between the partition external section and the converter access node; Independent power supply nodes or independent transmission channels should not be used as boundary nodes or boundary sections; Independent load nodes or independent power supply channels should not be used as boundary nodes or boundary sections; The loads and sources directly connected to the boundary nodes are modeled separately and are not included in the external equivalent values.

4. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 1, characterized in that: The specific operation mode of the power grid includes: The load level includes at least three levels: high, medium and low. The new energy output level includes at least three levels: high, medium and low. Multiple transmission lines between nodes in the area are in maintenance / operation status, the busbar is in the combined / denominator operation state, the transformer is in maintenance / operation status, and the reactive compensation equipment is in operation / exit status.

5. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 1, characterized in that: The method of generating an intra-regional power grid admittance matrix based on a set frequency range comprises the following steps: Sort by non-converter grid-connected nodes within the area, boundary equivalent nodes, and converter grid-connected nodes within the area; In the frequency range f l ~f h According to the grid admittance matrix generation method, the admittance matrix Y is formed at each frequency point according to the network topology in the area and the parameters of the transmission line, power transformer, equivalent load and equivalent model. G0 (f); According to the impedance-frequency characteristics of the reactive compensation equipment, its influence on the admittance matrix of the power grid in the area is calculated separately. Assume that the impedance-frequency distribution characteristics of the reactive compensation equipment are Z Qi (f) When node i is connected, the self-admittance of node i is modified to be y G1，ii (f) = y G0，ii (f)+1 / z Qi (f), the modified admittance matrix in the region is denoted as Y G1 (f); According to the equivalent self-impedance of the external section, the self-admittance of the corresponding node is corrected. Assume that the equivalent self-impedance of the external section corresponding to node i is z Si (f), then the corrected self-admittance of node i is y G2，ii (f) = y G1，ii (f)+1 / z Qi (f); According to the equivalent interconnection impedance between the external sections, the mutual admittance and self-admittance between the corresponding nodes are corrected. Assume that the equivalent interconnection impedance between the corresponding node i of the external section is equal to that of the node, and z Sij (f), then the self-admittance of node i and node j is corrected to y G2，ii (f) = y G1，ii (f)+1 / z Sij (f), y G2ij (f) = y G1，jj (f)+1 / z Sij (f), the mutual admittance is corrected to y G2，ij (f) = y G1，ij (f)-1z Sij (f), the modified admittance matrix in the region is denoted as Y G2 (f).

6. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 5, characterized in that: The target section of the power grid in the selected area includes: The flexible direct current, new energy stations, SVG, and energy storage power electronic converter grid-connected nodes of the regional power grid are taken as target sections. Based on actual analysis requirements, the conventional direct current and synchronous generator grid-connected nodes are considered as target sections. When studying any target section, the impedance of other non-target sections is integrated into the admittance matrix Y G2 (f) 7. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 5, characterized in that: The step of converting the port characteristics of the relevant converter into the admittance matrix of the intra-area power grid comprises: Assume that the impedance-frequency characteristic of the non-target section i connected to the flexible direct current, new energy station, SVG, and energy storage power electronic converter is z C，i (f), then the self-admittance of the modified node i is, y G3，ii (f) = y G2，ii (f)+1 / z C，i (f), the modified admittance matrix in the region is denoted as Y G3 (f).

8. The method for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area according to claim 5, characterized in that: The method of solving the equivalent impedance of the port of the target section looking toward the power grid includes: Inverse the admittance matrix Z G3 (f) = inv[Y G3 (f)], inv[] is the matrix inversion function, the matrix Z G3 The physical meaning of (f) is that after all the electrical components inside and outside the region are equal, any diagonal element z G3，ii (f) describes the voltage response on node i when no current is injected into other nodes except node i and a current with unit frequency f is injected into node i; Any off-diagonal element z G3，ij (f) describes the voltage of node i when no current is injected into other nodes except node i and a unit current is injected into node i; According to the target section corresponding to the target node number x, extract and record z G3，xx (f) is the equivalent impedance of the target section looking toward the power grid under the current method.

9. A system for calculating the equivalent value of grid impedance taking into account the distributed parameters of components in the area, characterized in that: Using the method according to any one of claims 1 to 8, the system comprises: The boundary node acquisition module is used to obtain the type of the local power grid to which the converter is connected and the power grid operating conditions, determine the connection between the power grid partition and the external power grid, and obtain the external section and boundary nodes; The operation mode selection module is used to select the specific operation mode of the power grid according to the load level, the status of the generator set and the operation status of the equipment; The module for constructing an equivalent model of an out-of-region power grid is used to calculate the equivalent parameters of the out-of-region power grid according to the selected boundary nodes under the set power grid operation mode, and to construct an equivalent model including the interconnection relationship between each section; An intra-regional power grid admittance matrix generation module is used to establish an intra-regional power grid admittance model according to the distributed parameter characteristics of the components in the intra-regional power grid, and to generate an intra-regional power grid admittance matrix based on a set frequency range; An admittance matrix correction module is used to select a target section of the intra-regional power grid and, based on the impedance characteristics of the converters at other non-target sections, equate the relevant converter port characteristics to the intra-regional power grid admittance matrix; The calculation result acquisition module is used to solve the equivalent impedance of the port looking at the power grid from the target section based on the equivalently corrected admittance matrix of the power grid in the area to obtain the final calculation result.

10. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 8 is implemented.

11. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

Images