A collector network equivalent method based on improved node equation

Abstract

The invention belongs to the field of wind turbine equivalent parameter calculation, and discloses a collector network equivalent method based on improved node equations. Firstly, a phase-shifting transformer is introduced into a wind turbine group in a wind farm to transform the collector network, so as to ensure that the voltage characteristics of each wind turbine grid-connected point are consistent before and after the equivalent. Then, the improved node voltage equation is directly written for the collector network transformed by introducing the phase-shifting transformer, and the node admittance matrix is ​​solved by a group of simultaneous equations combined with Ward equivalent and multi-port network H parameter transformation. Finally, a transformer π-type equivalent method is used to perform equivalent transformation on the transformer parameter part of the obtained improved node admittance matrix to complete the equivalent processing of the transformer part, and obtain the equivalent parameters. Compared with the method of converting the phase-shifting transformer into a non-phase-shifting transformer and then directly writing the node admittance matrix in the existing scheme, dynamic errors are avoided.

Description

Technical Field

[0001] The invention belongs to the field of wind turbine equivalent parameter calculation, and in particular relates to a collector network equivalent method based on improved node equations. Background Art

[0002] New energy units are characterized by randomness, dispersion, low inertia, and low anti-interference. Whether it is the steady-state operation and transient process of the power grid, or the frequency and voltage characteristics of the power grid, they will change significantly after a high proportion of new energy is connected; therefore, in the context of large-scale access to new energy, it is necessary to carry out research on new energy site modeling.

[0003] In view of the increasing complexity and difficulty caused by the increasing scale of wind farms, it is necessary to perform high-precision equivalence on the wind turbine groups in the wind farm. However, the existing method of introducing a phase-shifting transformer for collector network transformation converts the introduced phase-shifting transformer into a non-phase-shifting transformer, and then directly writes the node admittance matrix and simplifies it, which loses the rigor of mathematical principles and may lead to the existence of dynamic errors, thereby affecting the equivalence accuracy. Therefore, it is necessary to design a collector network equivalence method based on improved node equations to solve the above problems. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a collector network equivalence method based on improved node equations. The method retains the phase-shifting transformer network after introducing a phase-shifting transformer into the wind turbine equivalent. Based on rigorous mathematical principles, an improved node voltage equation is written for the improved collector network. Then, a rigorous node admittance matrix is ​​obtained by jointly solving the improved network equations. The transformer parameter part is then simplified and transformed to obtain equivalent parameters. This solves the problem that the wind turbine equivalent method converts the introduced phase-shifting transformer into a non-phase-shifting transformer network with dynamic errors, resulting in low equivalent accuracy.

[0005] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0006] A collector network equivalent method based on improved node equations includes the following steps:

[0007] S1, introduce a phase-shifting transformer to transform the collection network of the wind turbine group, and retain the network structure of the phase-shifting transformer; so that the dynamic characteristics of the wind turbines in the wind turbine group are not lost;

[0008] S2, construct the node voltage equation after the collector network transformation, combine the Ward equivalent method and the multi-port network H parameter transformation method to solve the improved node admittance matrix;

[0009] S201, constructing an improved node voltage equation for the transformed collector network;

[0010] S202, solving an improved node admittance matrix by solving a set of simultaneous equations in combination with the Ward equivalent method and the multi-port network H parameter transformation method;

[0011] S203, constructing a node admittance matrix including a transformer branch;

[0012] S3, based on the transformer π-type equivalent method, the transformer parameters of the improved node admittance matrix are converted to obtain the equivalent parameters of the wind turbine.

[0013] Preferably, in step S1, a phase-shifting transformer is introduced to transform the wind turbine group's power collection network, and the network structure of the phase-shifting transformer is retained. The specific method is:

[0014] S101, set calculation variables:

[0015] It is assumed that the wind turbines in the wind farm are divided into m groups, the number of wind turbines in the kth group is Nk, the grid connection point voltage of the wind turbines in the group is Ui, and the grid connection point voltage of the equivalent wind turbine in the kth group is Uk; Uk is obtained by taking the average value;

[0016] S102, perform equivalent calculation so that the grid connection point voltage of each wind turbine in the kth group is set to Uk. The calculation method of Uk is:

[0017] ;

[0018] ;

[0019] In the formula, i represents the i-th unit in the k-th group; and are the amplitude and phase angle of the grid connection point voltage Uk of the kth group of equivalent wind turbines respectively; and are the Ui amplitude and phase angle of the grid connection point voltage of the wind turbine in the kth cluster respectively;

[0020] S103, introduce a phase-shifting transformer with a transformation ratio of αi to transform the collector network, retaining the voltage characteristics of each wind turbine grid connection point before and after the equal value:

[0021] ;

[0022] In the formula, It represents the voltage of the wind turbine grid connection point of the collection network after transformation, It represents the voltage phase angle of the wind turbine grid connection point of the collection network after transformation, Indicates the phase angle difference of voltage.

[0023] Preferably, in step S2, the node voltage equation after the collector network transformation is constructed, and the specific method of solving the improved node admittance matrix by combining the Ward equivalent method and the multi-port network H parameter transformation method includes:

[0024] S201, construct an improved node voltage equation for the collector network after the phase-shifting transformer is introduced and transformed:

[0025] For the transformed collector network, let the voltage and injection current of the PCC common connection point be and , the voltage and injection current of the wind turbine grid connection point are U ’ and I ’ , U ’ = [ U 1 ’ , U 2 ’ ,…, Un' ]T,I ’ = [ I 1 ’ , I 2 ’ ,…, In' ]T; n is the number of wind turbines in the wind farm; Un' Indicates the grid connection point voltage of the nth group of wind turbines, In' It represents the current injected into the grid connection point of the nth group of wind turbines; the collector network equation is written as follows:

[0026] ;

[0027] Where, YZZ represents the node admittance matrix without considering wind turbines; YZP represents the mutual admittance vector between the wind turbine grid connection point and the PCC public connection point without considering wind turbines; YPZ represents the mutual admittance vector between the PCC public connection point and the wind turbine grid connection point without considering wind turbines; Ypp represents the self-admittance of the PCC public connection point; Represents the injected current provided by the wind turbine to the grid connection point, and the equations are established as follows:

[0028] ;

[0029] Where, I is the current injected into the high-voltage side of the wind turbine transformer; Indicates the ratio of the phase-shifting transformer conjugation of; represents the conjugate of the phase-shifting transformer ratio of the 1st, 2nd, ..., nth group of fans; represents the high-voltage side injection current of the transformer at the end of the 1st, 2nd, ..., nth wind turbine group; T represents the transpose of the vector; represents the conjugate of the phase-shifting transformer ratio of the nth group of fans; represents the current injected into the high-voltage side of the transformer at the end of the nth group of wind turbines; diag is the diag function, which means constructing a diagonal matrix;

[0030] Based on the high-voltage side voltage U of the wind turbine transformer, the following equations are established:

[0031] ;

[0032] Where I is the high voltage side voltage of the wind turbine transformer. Indicates the transformation ratio of the phase-shifting transformer; Indicates the transformation ratio of the phase-shifting transformer of the nth group of fans; Indicates the high-voltage side voltage of the transformer at the end of the nth group of wind turbines; Indicates the phase-shifting transformer ratio of the 1st, 2nd, ..., nth group of fans, Indicates the high-voltage side voltage of the transformer at the machine end of the 1st, 2nd, …, nth group of wind turbines.

[0033] Preferably, in step S2, the node voltage equation after the collector network transformation is constructed, and the specific method of solving the improved node admittance matrix by combining the Ward equivalent method and the multi-port network H parameter transformation method includes:

[0034] S202, solve the improved node admittance matrix by combining the simultaneous equations with the Ward equivalent method and the multi-port network H parameter transformation method:

[0035] The network equation and the system of equations in step S201 are combined:

[0036] ;

[0037] Eliminate the same group node on the high voltage side of the wind turbine generator transformer, and the formula is transformed into:

[0038] ;

[0039] ;

[0040] ;

[0041] ;

[0042] ;

[0043] In the formula, The phase-shifting transformer of the kth group of equivalent wind turbines and the i Equivalent transformation ratio of each wind turbine grid connection point; Represents the current vector injected into the high-voltage side of the transformer at the end of the equivalent wind turbine, It represents the high-voltage side injection current of the transformer of the k-th wind turbine group; Represents the grid connection point voltage vector of equivalent wind turbines; represents the grid connection point voltage of the kth wind turbine group; It represents the transformation ratio matrix of the equivalent phase-shifting transformer of the equivalent wind turbine, and its elements are ; express conjugation of; express The transpose of ; m represents the total number of wind turbine group groups in the wind farm;

[0044] When I'= 0, the formula is transformed into:

[0045] ;

[0046] Further simplified to the multi-port network H parameter form, and H 12 ≠H 21 T :

[0047] ;

[0048] ;

[0049] Convert the H parameter form of the multi-port network into the Y parameter form to obtain the node admittance matrix Y of the equivalent network net as follows:

[0050] ;

[0051] ;

[0052] In the formula, is the node admittance matrix of the equivalent network.

[0053] Furthermore, for the equivalent network, an actual complex wind farm is simplified into a network model formed by one or more equivalent wind turbines, which is called an equivalent network; this equivalent model can reflect the main impacts of the wind farm on the power grid, such as power output, voltage stability, etc., while reducing the amount of calculation and complexity; through the equivalent model, the performance and potential impact of the wind farm after connecting to the power grid can be more conveniently evaluated.

[0054] Preferably, in step S2, the node voltage equation after the collector network transformation is constructed, and the specific method of solving the improved node admittance matrix by combining the Ward equivalent method and the multi-port network H parameter transformation method includes:

[0055] S203, construct the node admittance matrix containing the transformer branch:

[0056] By step S202 12 ≠H 21 T It can be seen that the node admittance matrix solved in step S202 is is asymmetric and has no corresponding equivalent network; therefore, the present invention constructs a network as close as possible to The equivalent node admittance matrix Y net ':

[0057] according to Construct node admittance matrix Y net ':

[0058] ;

[0059] In the formula y pk represents the branch admittance of the phase-shifting transformer between the grid connection point of the k-th group-equivalent wind turbine and the PCC common connection point; represents the set of wind farm clustering sequences, ,m is equal to the number of groups; symbol represents a difference set; for example Indicates removing element 1 from the original set; is a subscript, indicating the PCC common connection point; , , , , , , , , , , , are all node admittance matrices Elements in

[0060] The nonlinear equations are constructed as follows:

[0061] ;

[0062] Where Y net,ij and Y net,ij ′ represents the matrix Y net and Y net The element in the i-th row and j-th column of ′; this formula can be quickly solved using the Newton-Raphson method.

[0063] Preferably, in step S3, based on the transformer π-type equivalent method, the transformer parameters of the improved node admittance matrix are converted to obtain the equivalent parameters of the wind turbine. The specific method is:

[0064] For an impedance of y k , the transformation ratio is 1: t k The transformer branch, the admittance matrix is ​​as follows:

[0065] ;

[0066] Admittance to ground in the equivalent circuit diagram of the equivalent three-machine diagram without transformer branch Y i0 The branch impedance is calculated as follows:

[0067] ;

[0068] ;

[0069] In the formula, i ∈Ω n = { p ,1,2,…, m}; i + Represents Ω n Medium Element i The following set of elements, such as p + ={1,2,…,m}; i - Represents Ω n Medium Element i The previous set of elements, such as p - = Ø; represents the mutual admittance between the grid connection point of the i-th equivalent wind turbine and the grid connection point of the j-th equivalent wind turbine; represents the admittance between the grid connection point of the kth equivalent wind turbine and the PCC common connection point node; k pk represents the transformation ratio of the phase-shifting transformer between the grid connection point of the k-th wind turbine group and the PCC common connection point, y pk represents the branch admittance of the corresponding phase-shifting transformer; y ij ,like y 12 , y 23 , indicating the i The high voltage side of the transformer at the end of the wind turbine is equal to the j Admittance between the high voltage sides of the transformers at the end of wind turbines of equal value;k ij ,like k 12 , k 23 , represents the transformation ratio of the corresponding phase-shifting transformer; represents the mutual admittance between the grid connection point of the k-th equivalent wind turbine and the grid connection point of the i-th equivalent wind turbine, Indicates the transformation ratio of the corresponding phase-shifting transformer.

[0070] The beneficial effects of the present invention are as follows:

[0071] 1. The present application introduces a phase-shifting transformer to transform the collector network of a wind turbine group. Compared with the conventional method of converting a phase-shifting transformer into a non-phase-shifting transformer and then directly writing a node admittance matrix, the present application directly writes an improved node voltage equation for the collector network after the phase-shifting transformer is introduced, and solves the node admittance matrix by a group of simultaneous equations combined with Ward equivalent and multi-port network H parameter transformation, thereby avoiding dynamic errors; and then uses the transformer π-type equivalent to transform the transformer parameter part of the solved improved node admittance matrix to obtain the wind turbine equivalent parameters.

[0072] 2. This application simplifies the entire wind farm into multiple equivalent wind turbines and ensures that the equivalent model can accurately reflect the dynamic and static behaviors of the wind farm in the power system; the simplified equivalent model can significantly reduce the calculation time and the required computing resources, making the power system stability analysis, fault simulation, planning research and other processes more efficient; the equivalent wind farm model is easier to analyze the stability and dynamic performance of the power system, and is also more convenient for the control strategy design and optimization of the power system; the equivalent model helps power companies make grid planning and operation decisions, including power flow calculation, voltage stability analysis, fault recovery strategy formulation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 It is a schematic diagram of the process of the present invention;

[0074] Figure 2 It is a schematic diagram of a six-machine power collection network of the prior art in the first embodiment of the present invention;

[0075] Figure 3 It is a schematic diagram of a six-machine power collection network after adding a phase-shifting transformer in Embodiment 1 of the present invention;

[0076] Figure 4 This is a schematic diagram of a three-machine equivalent diagram with a transformer branch in the first embodiment of the present invention;

[0077] Figure 5 This is a schematic diagram of a three-machine equivalent diagram after the transformer is equivalent in the first embodiment of the present invention;

[0078] Figure 6 This is a schematic diagram of a PSASP simulation detailed model of a wind farm in the second embodiment of the present invention;

[0079] Figure 7 This is a schematic diagram of an active power curve of a PCC common connection point of a wind farm in Embodiment 2 of the present invention;

[0080] Figure 8 This is a schematic diagram of a reactive power curve of a PCC common connection point of a wind farm in Embodiment 2 of the present invention;

[0081] Fig. 9 This is a schematic diagram of a voltage curve of a PCC common connection point in a wind farm in the second embodiment of the present invention;

[0082] Fig.10 This is a schematic diagram of a current curve of a PCC common connection point in a wind farm in the second embodiment of the present invention. DETAILED DESCRIPTION

[0083] Embodiment 1:

[0084] like Figure 1 As shown, a collector network equivalent method based on improved node equations includes the following steps:

[0085] S1, introduce a phase-shifting transformer to transform the collection network of the wind turbine group, and retain the network structure of the phase-shifting transformer; so that the dynamic characteristics of the wind turbines in the wind turbine group are not lost;

[0086] S2, construct the node voltage equation after the collector network transformation, combine the Ward equivalent method and the multi-port network H parameter transformation method to solve the improved node admittance matrix;

[0087] S201, constructing an improved node voltage equation for the collector network after the phase-shifting transformer is introduced and transformed;

[0088] S202, solving an improved node admittance matrix by solving a set of simultaneous equations in combination with the Ward equivalent method and the multi-port network H parameter transformation method;

[0089] S203, constructing a node admittance matrix including a transformer branch;

[0090] S3, based on the transformer π-type equivalent method, the transformer parameters of the improved node admittance matrix are converted to obtain the equivalent parameters of the wind turbine.

[0091] Preferably, in step S1, a phase-shifting transformer is introduced to transform the wind turbine group's power collection network, and the network structure of the phase-shifting transformer is retained. The specific method is:

[0092] S101, set calculation variables:

[0093] It is assumed that the wind turbines in the wind farm are divided into m groups, the number of wind turbines in the kth group is Nk, the grid connection point voltage of the wind turbines in the group is Ui, and the grid connection point voltage of the equivalent wind turbine in the kth group is Uk; Uk is obtained by taking the average value;

[0094] S102, perform equivalent calculation so that the grid connection point voltage of each wind turbine in the kth group is set to Uk. The calculation method of Uk is:

[0095] ;

[0096] ;

[0097] In the formula, i represents the i-th unit in the k-th group; and are the amplitude and phase angle of the grid connection point voltage Uk of the kth group of equivalent wind turbines respectively; and are the Ui amplitude and phase angle of the grid connection point voltage of the wind turbine in the kth cluster respectively;

[0098] S103, the equivalent value calculation in step S102 objectively sets the grid connection point voltage of each wind turbine in the kth group to Uk , but this changes the voltage characteristics of each wind turbine grid connection point before and after the equal value. In order to ensure the voltage characteristics of each wind turbine grid connection point before and after the equal value, such as Figure 2 and Figure 3 As shown in the figure, taking six wind turbines as an example, a phase-shifting transformer with a transformation ratio of αi is introduced to transform the collector network, retaining the voltage characteristics of each wind turbine grid connection point before and after the equal value:

[0099] ;

[0100] In the formula, It represents the voltage of the wind turbine grid connection point of the collection network after transformation, It represents the voltage phase angle of the wind turbine grid connection point of the collection network after transformation, Indicates the phase angle difference of voltage.

[0101] Preferably, in step S2, the node voltage equation after the collector network transformation is constructed, and the specific method of solving the improved node admittance matrix by combining the Ward equivalent method and the multi-port network H parameter transformation method includes:

[0102] S201, construct an improved node voltage equation for the collector network after the phase-shifting transformer is introduced and transformed:

[0103] For the transformed collector network, let the voltage and injection current of the PCC common connection point be and , the voltage and injection current of the wind turbine grid connection point are U ’ and I ’ , U ’ = [ U 1 ’ , U 2 ’ ,…, Un' ]T,I ’ = [ I 1 ’ , I 2 ’ ,…, In' ]T; n is the number of wind turbines in the wind farm; Un' Indicates the grid connection point voltage of the nth group of wind turbines, In' It represents the current injected into the grid connection point of the nth group of wind turbines; the collector network equation is written as follows:

[0104] ;

[0105] Where, YZZ represents the node admittance matrix without considering wind turbines; YZP represents the mutual admittance vector between the wind turbine grid connection point and the PCC public connection point without considering wind turbines; YPZ represents the mutual admittance vector between the PCC public connection point and the wind turbine grid connection point without considering wind turbines; Ypp represents the self-admittance of the PCC public connection point; Represents the injected current provided by the wind turbine to the grid connection point, and the equations are established as follows:

[0106] ;

[0107] Where, I is the current injected into the high-voltage side of the wind turbine transformer; Indicates the ratio of the phase-shifting transformer conjugation of; represents the conjugate of the phase-shifting transformer ratio of the 1st, 2nd, ..., nth group of fans; represents the high-voltage side injection current of the transformer at the end of the 1st, 2nd, ..., nth wind turbine group; T represents the transpose of the vector; represents the conjugate of the phase-shifting transformer ratio of the nth group of fans; represents the current injected into the high-voltage side of the transformer at the end of the nth group of wind turbines; diag is the diag function, which means constructing a diagonal matrix;

[0108] Based on the high-voltage side voltage U of the wind turbine transformer, the following equations are established:

[0109] ;

[0110] Where I is the high voltage side voltage of the wind turbine transformer. Indicates the transformation ratio of the phase-shifting transformer; Indicates the transformation ratio of the phase-shifting transformer of the nth group of fans; Indicates the high-voltage side voltage of the transformer at the end of the nth group of wind turbines; Indicates the phase-shifting transformer ratio of the 1st, 2nd, ..., nth group of fans, Indicates the high-voltage side voltage of the transformer at the machine end of the 1st, 2nd, …, nth group of wind turbines.

[0111] Preferably, in step S2, the node voltage equation after the collector network transformation is constructed, and the specific method of solving the improved node admittance matrix by combining the Ward equivalent method and the multi-port network H parameter transformation method includes:

[0112] S202, solve the improved node admittance matrix by combining the simultaneous equations with the Ward equivalent method and the multi-port network H parameter transformation method:

[0113] The network equation and the system of equations in step S201 are combined:

[0114] ;

[0115] Eliminate the same group node on the high voltage side of the wind turbine generator transformer, and the formula is transformed into:

[0116] ;

[0117] ;

[0118] ;

[0119] ;

[0120] ;

[0121] In the formula, The phase-shifting transformer of the kth group of equivalent wind turbines and the i Equivalent transformation ratio of each wind turbine grid connection point; Represents the current vector injected into the high-voltage side of the transformer at the end of the equivalent wind turbine, It represents the high-voltage side injection current of the transformer of the k-th wind turbine group; Represents the grid connection point voltage vector of equivalent wind turbines; represents the grid connection point voltage of the kth wind turbine group; It represents the transformation ratio matrix of the equivalent phase-shifting transformer of the equivalent wind turbine, and its elements are ; express conjugation of; express The transpose of ; m represents the total number of wind turbine group groups in the wind farm;

[0122] When I'= 0, the formula is transformed into:

[0123] ;

[0124] Further simplified to the multi-port network H parameter form, and H 12 ≠H 21 T :

[0125] ;

[0126] ;

[0127] Convert the H parameter form of the multi-port network into the Y parameter form to obtain the node admittance matrix Y of the equivalent network net as follows:

[0128] ;

[0129] ;

[0130] In the formula, is the node admittance matrix of the equivalent network.

[0131] Furthermore, for the equivalent network, an actual complex wind farm is simplified into a network model formed by one or more equivalent wind turbines, which is called an equivalent network; this equivalent model can reflect the main impacts of the wind farm on the power grid, such as power output, voltage stability, etc., while reducing the amount of calculation and complexity; through the equivalent model, the performance and potential impact of the wind farm after connecting to the power grid can be more conveniently evaluated.

[0132] Preferably, in step S2, the node voltage equation after the collector network transformation is constructed, and the specific method of solving the improved node admittance matrix by combining the Ward equivalent method and the multi-port network H parameter transformation method includes:

[0133] S203, construct the node admittance matrix containing the transformer branch:

[0134] By step S202 12 ≠H 21 T It can be seen that the node admittance matrix solved in step S202 is is asymmetric, and obviously there is no corresponding equivalent network; therefore, the present invention constructs a network as close as possible to The equivalent node admittance matrix Y net ',like Figure 4As shown, a three-machine equivalent diagram with a transformer branch is disclosed. The transformer branch is introduced because of the complex number. The constructed node admittance matrix contains the transformer branch part, which is as follows:

[0135] according to Construct node admittance matrix Y net ':

[0136] ;

[0137] In the formula, y pk represents the branch admittance of the phase-shifting transformer between the grid connection point of the k-th group-equivalent wind turbine and the PCC common connection point; represents the set of wind farm clustering sequences, ,m is equal to the number of groups; symbol represents a difference set; for example Indicates removing element 1 from the original set; is a subscript, indicating the PCC common connection point; , , , , , , , , , , , are all node admittance matrices Elements in

[0138] The nonlinear equations are constructed as follows:

[0139] ;

[0140] Where Y net,ij and Y net,ij ′ represents the matrix Y net and Y net The element in the i-th row and j-th column of ′; this formula can be quickly solved using the Newton-Raphson method.

[0141] Preferably, in step S3, based on the transformer π-type equivalent method, the transformer parameters of the improved node admittance matrix are converted to obtain the equivalent parameters of the wind turbine. The specific method is:

[0142] For an impedance of y k , the transformation ratio is 1: t k The transformer branch, the admittance matrix is ​​as follows:

[0143] ;

[0144] like Figure 5 As shown in the equivalent circuit diagram of the equivalent three-machine diagram without the transformer branch, the ground admittance Y i0 The branch impedance is calculated as follows:

[0145] ;

[0146] ;

[0147] In the formula, i ∈Ω n = { p ,1,2,…, m}; i + Represents Ω n Medium Element i The following set of elements, such as p + ={1,2,…,m}; i - Represents Ω n Medium Element i The previous set of elements, such as p - = Ø; represents the mutual admittance between the grid connection point of the i-th equivalent wind turbine and the grid connection point of the j-th equivalent wind turbine; It represents the admittance between the grid connection point of the kth equivalent wind turbine and the PCC common connection point node. k pk represents the transformation ratio of the phase-shifting transformer between the grid connection point of the k-th wind turbine group and the PCC common connection point, y pk represents the branch admittance of the corresponding phase-shifting transformer; y ij ,like y 12 , y 23 , indicating the i The high voltage side of the transformer at the end of the wind turbine is equal to the j Admittance between the high voltage sides of the transformers at the end of wind turbines of equal value; k ij ,like k 12 , k 23 , represents the transformation ratio of the corresponding phase-shifting transformer; represents the mutual admittance between the grid connection point of the k-th equivalent wind turbine and the grid connection point of the i-th equivalent wind turbine, Indicates the transformation ratio of the corresponding phase-shifting transformer.

[0148] Embodiment 2:

[0149] The method of the present invention is verified in an actual case involving 25 doubly-fed induction generators DFIGs; under the premise of applying only the collector network equivalence and three-machine equivalence, the effectiveness of the proposed collector network equivalence method is verified by comparing it with several other commonly used collector network equivalence methods.

[0150] like Figure 6 This is the detailed PSASP simulation model for the wind farm.

[0151] The system transient parameters are shown in Table 1.

[0152]

[0153] Table 1: System transient parameters;

[0154] The generator parameters and transmission chain parameters, control system parameters and collection system data parameters of the wind turbine units in the wind farm are shown in Table 2, Table 3 and Table 4 respectively.

[0155]

[0156] Table 2: Wind turbine generator parameters and transmission chain parameters;

[0157]

[0158] Table 3: Wind turbine control system parameters;

[0159]

[0160] Table 4: Current collection system parameters;

[0161] According to the type of parameters, this embodiment first obtains the parameters of equivalent wind turbines through the capacity weighted average method and the typical value method. For the convenience of demonstration, the present invention names the constant power loss method as Method1, the parallel conversion method as Method2, and the constant voltage drop method as Method3.

[0162] Figure 7 and Figure 8 This is the power comparison curve of the collector network equivalent method of the proposed improved node equation. It can be seen that the active power curve and reactive power curve of the wind turbine grid-connected point obtained under the proposed method are closest to the detailed model of the wind turbine, and the deviation is very small, and the obtained power curves are almost identical. From the perspective of active power and reactive power at the wind turbine grid-connected point, the effectiveness and accuracy of the proposed equivalent method for wind turbine parameter equivalence are verified, and the example test results can meet the actual simulation needs.

[0163] Fig. 9 and Fig.10 The voltage and current comparison curves of the proposed improved node equation collector network equivalent method show that the voltage and current curves of the wind turbine grid connection point obtained by the proposed method are closest to the detailed model of the wind turbine, and the deviation is very small, and the obtained voltage and current curves are almost the same. From the perspective of the voltage and current of the wind turbine grid connection point, the effectiveness and accuracy of the proposed equivalent method for wind turbine parameter equivalents are verified, and the example test results can meet the actual simulation needs.

[0164] The collector network equivalent method based on the improved node equation includes the following specific steps:

[0165] Step 1: Introduce a phase-shifting transformer to transform the collection network of the wind turbine group;

[0166] Step 2, improving the node voltage equation and obtaining an improved node admittance matrix;

[0167] Step 3: Based on the transformer π-type equivalent, the transformer parameter part of the obtained node admittance matrix is ​​converted to obtain the wind turbine equivalent parameters.

[0168] In summary, the present invention proposes a collector network equivalence method based on improved node equations, and its technical characteristics are: introducing a phase-shifting transformer to transform the collector network of a wind turbine group to ensure that the electrical characteristics of each wind turbine grid-connected point remain consistent before and after the equivalence, and then writing an improved node voltage equation based on the transformed network and obtaining a solved node admittance matrix, and using the transformer π-type equivalence method to process the transformer part in the node admittance matrix to obtain the wind turbine equivalent parameters; specifically including the following steps: introducing a phase-shifting transformer to transform the collector network of a wind turbine group; improving the node voltage equation and obtaining an improved node admittance matrix; based on the transformer π-type equivalence, converting the transformer parameter part of the obtained node admittance matrix to obtain the wind turbine equivalent parameters; the present invention considers that the electrical characteristics of the wind turbine grid-connected point before and after the equivalence remain unchanged, and improves the collector network equivalence method of the node equation combined with the transformer π-type equivalence method to obtain the wind turbine equivalent parameters to support accurate modeling and precise simulation of wind farms.

Claims

1. A collector network equivalent method based on improved node equations, characterized in that: The following steps are involved: S1, introduce a phase-shifting transformer to transform the wind turbine group's collection network, and retain the phase-shifting transformer network structure. The specific method is: S101, set calculation variables: Assume that the wind turbines in the wind farm are divided into m groups, the number of wind turbines in the kth group is Nk, the grid connection point voltage of the wind turbines in the group is Ui, and the grid connection point voltage of the equivalent wind turbine in the kth group is Uk; S102, perform equivalent calculation so that the grid connection point voltage of each wind turbine in the kth group is set to Uk. The calculation method of Uk is: ； ； In the formula, i represents the i-th unit in the k-th group; and are the amplitude and phase angle of the grid connection point voltage Uk of the kth group of equivalent wind turbines respectively; and are the Ui amplitude and phase angle of the grid connection point voltage of the wind turbine in the kth cluster respectively; S103, introduce a phase-shifting transformer with a transformation ratio of αi to transform the collector network, retaining the voltage characteristics of each wind turbine grid connection point before and after the equal value: ； In the formula, It represents the voltage of the wind turbine grid connection point of the collection network after transformation, Indicates the voltage phase angle of the wind turbine grid connection point of the collection network after transformation; Indicates the phase angle difference of voltage; S2, construct the node voltage equation after the collector network transformation, combine the Ward equivalent method and the multi-port network H parameter transformation method to solve the improved node admittance matrix; S201, constructing an improved node voltage equation for the collector network after the phase-shifting transformer is introduced and transformed; Specifically: For the transformed collector network, let the voltage and injection current of the PCC common connection point be and , the voltage and injection current of the wind turbine grid connection point are U ’ and I ’ , U ’ = [ U 1 ’ , U 2 ’ ,…, Un' ]T,I ’ = [ I 1 ’ , I 2 ’ ,…, In' ]T; n is the number of wind turbines in the wind farm; Un' Indicates the grid connection point voltage of the nth group of wind turbines, In' It represents the current injected into the grid connection point of the nth group of wind turbines; the collector network equation is written as follows: ； Where, YZZ represents the node admittance matrix without considering wind turbines; YZP represents the mutual admittance vector between the wind turbine grid connection point and the PCC public connection point without considering wind turbines; YPZ represents the mutual admittance vector between the PCC public connection point and the wind turbine grid connection point without considering wind turbines; Ypp represents the self-admittance of the PCC public connection point; Represents the injected current provided by the wind turbine to the grid connection point, and the equations are established as follows: ； Where, I is the current injected into the high-voltage side of the wind turbine transformer; Indicates the ratio of the phase-shifting transformer conjugation of; represents the conjugate of the phase-shifting transformer ratio of the 1st, 2nd, ..., nth group of fans; represents the high-voltage side injection current of the transformer at the end of the 1st, 2nd, ..., nth wind turbine group; T represents the transpose of the vector; represents the conjugate of the phase-shifting transformer ratio of the nth group of fans; represents the current injected into the high-voltage side of the transformer at the end of the nth group of wind turbines; diag is the diag function, which means constructing a diagonal matrix; Based on the high-voltage side voltage U of the wind turbine transformer, the following equations are established: ； Where I is the high voltage side voltage of the wind turbine transformer. Indicates the transformation ratio of the phase-shifting transformer; Indicates the transformation ratio of the phase-shifting transformer of the nth group of fans; Indicates the high-voltage side voltage of the transformer at the end of the nth group of wind turbines; Indicates the phase-shifting transformer ratio of the 1st, 2nd, ..., nth group of fans, Indicates the high-voltage side voltage of the transformer at the end of the 1st, 2nd, ..., nth group of wind turbines; S202, by solving the simultaneous equations and combining the Ward equivalent method and the multi-port network H parameter transformation method, the improved node admittance matrix is ​​solved, specifically: The network equation and the system of equations in step S201 are combined: ； Eliminate the same group node on the high voltage side of the wind turbine generator transformer, and the formula is transformed into: ； ； ； ； ； In the formula, The phase-shifting transformer of the kth group of equivalent wind turbines and the i Equivalent transformation ratio of each wind turbine grid connection point; Represents the current vector injected into the high-voltage side of the transformer at the end of the equivalent wind turbine, It represents the high-voltage side injection current of the transformer of the k-th wind turbine group; Represents the grid connection point voltage vector of equivalent wind turbines; represents the grid connection point voltage of the kth wind turbine group; It represents the transformation ratio matrix of the equivalent phase-shifting transformer of the equivalent wind turbine, and its elements are ; express conjugation of; express The transpose of ; m represents the total number of wind turbine group groups in the wind farm; When I'= 0, the formula is transformed into: ； Further simplified to the multi-port network H parameter form: ； ； Convert the H parameter form of the multi-port network into the Y parameter form to obtain the node admittance matrix Y of the equivalent network net as follows: ； ； In the formula, is the node admittance matrix of the equivalent network; S203, constructing a node admittance matrix containing a transformer branch, specifically: according to Construct the node admittance matrix Y containing the transformer branch net ': ； In the formula, represents the set of wind farm clustering sequences, ,m is equal to the number of groups; symbol represents the difference set; is a subscript, indicating the PCC common connection point; y pk represents the branch admittance of the phase-shifting transformer between the grid connection point of the kth wind turbine group and the PCC common connection point, where k= ; k pk It represents the transformation ratio of the phase-shifting transformer between the grid connection point of the k-th wind turbine group and the PCC common connection point, where k= ;y ij represents the admittance between the high-voltage side of the transformer at the end of the i-th equivalent wind turbine and the high-voltage side of the transformer at the end of the j-th equivalent wind turbine, k ij represents the transformation ratio of the corresponding phase-shifting transformer, i=1,2,…,m, j=1,2,…,m; y p1 / k p1 is the equivalent admittance from the grid connection point of wind turbine 1 to the PCC point. Similarly, y pm / k pm is the equivalent admittance from the grid connection point of equivalent wind turbine m to the PCC point; 12 / k 12 is the mutual admittance between the grid connection point of equivalent wind turbine 1 and the grid connection point of equivalent wind turbine 2. Similarly, y m-1，m / k m-1，m is the mutual admittance between the equivalent wind turbine m-1 and the equivalent wind turbine m; The nonlinear equations are constructed as follows: ； In the formula, and Respectively represent matrices and The element of the i-th row and j-th column, when i≠j, represents the mutual admittance of node i and node j in the equivalent network, and when i=j, represents the self-admittance of node i and node j in the equivalent network; S3, based on the transformer π-type equivalent method, the transformer of the equivalent network with transformer branches is converted to equivalent value to obtain the equivalent parameters of the fan. The specific method is: For the impedance , the transformation ratio is 1: t k The transformer branch, the admittance matrix is ​​as follows: ； Admittance to ground in equivalent circuit diagram without transformer branch and branch admittance , The calculation formula is as follows: ； ； Where, i∈Ωn = {p,1,2,…,m}, j∈Ωn = {p,1,2,…,m}; i+ represents the set of elements after element i in Ωn; i- represents the set of elements before element i in Ωn; represents the mutual admittance between the grid connection point of the i-th equivalent wind turbine and the grid connection point of the j-th equivalent wind turbine; represents the admittance between the grid connection point of the kth equivalent wind turbine and the PCC common connection point node; represents the transformation ratio of the phase-shifting transformer between the grid connection point of the k-th wind turbine group and the PCC common connection point, represents the branch admittance of the corresponding phase-shifting transformer; represents the admittance between the high-voltage side of the transformer at the end of the i-th equivalent wind turbine and the high-voltage side of the transformer at the end of the j-th equivalent wind turbine; Indicates the transformation ratio of the corresponding phase-shifting transformer; represents the mutual admittance between the grid connection point of the k-th equivalent wind turbine and the grid connection point of the i-th equivalent wind turbine, Indicates the transformation ratio of the corresponding phase-shifting transformer.

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