An Asymmetric Fault Solving Method and Device Applicable to Wind Power Systems

Abstract

The present application provides a method and device for solving asymmetric faults applicable to a wind power system. The method includes obtaining a fault equivalent calculation model of the wind power system, a sequence network admittance matrix, and a sequence component form admittance matrix for different fault types; correlating the sequence network admittance matrix with the sequence component form admittance matrix to obtain a composite sequence network admittance matrix; simplifying the composite sequence network admittance matrix to obtain an equivalent network admittance matrix; iteratively solving the fault current according to the equivalent network admittance matrix; obtaining the sequence voltages of each node according to the solution result, so as to finally obtain the current of the line between the nodes. By establishing the correlation between the wind power fault current and the grid connection point voltage, this method obtains an equivalent calculation model of the wind farm asymmetric fault under different control strategies. By simplifying the composite sequence network admittance matrix, the number of fault network nodes is greatly reduced, and on the basis of ensuring the calculation accuracy, the operation efficiency is improved, which is applicable to the rapid and accurate solution of the asymmetric fault characteristics of a large-scale wind power system.

Description

Technical Field

[0001] The present application relates to the technical field of wind power system fault analysis, and in particular to a method and device for solving asymmetric faults applicable to wind power systems. Background Art

[0002] With the large-scale access of inverter-type renewable energy to the power grid, in order to ensure the safe and stable operation of the power grid, the renewable energy stations connected to the grid are required to have good low voltage ride-through operation capabilities. In particular, a large number of renewable energy systems such as wind power systems are currently connected to the power grid, and the traditional method for solving faults in large-scale grid-connected systems including wind power systems is to use node voltage equations, replace wind power stations with voltage-controlled current sources, and combine iterative correction algorithms for calculation.

[0003] For asymmetric fault types, the sequence network iteration method is usually used, which can better solve the steady-state short circuit under symmetric and asymmetric faults. However, when dealing with asymmetric fault types, the node admittance matrix is ​​not further processed, which makes the equation scale used for iterative solution larger after adding negative-sequence and zero-sequence voltage equations under symmetric component networks. In addition, the control strategy of negative-sequence current is not considered, and the network with negative-sequence current injection cannot be processed.

[0004] For symmetrical fault types, a regional local iteration method is usually used, which can be used for large-scale wind power transmission systems. It proposes to establish an engineering mapping relationship between the voltage and current of the wind power system, and uses a local iteration method to solve the problem of difficult global solutions for large-scale power grids. However, this method will inevitably affect the calculation accuracy due to the use of a local network node set, and only establishes the current mapping relationship under symmetrical faults, and cannot be used for simplified solutions of fault networks under asymmetrical faults.

[0005] Therefore, there is an urgent need for an asymmetric fault solution method that can take into account the large number of nodes in large-scale wind power systems, the high dimension of the node voltage equation caused by the composite sequence network under asymmetric faults, and the complex problem of solving the fault network containing wind power negative sequence current injection, so as to achieve a fast and accurate solution process. Summary of the invention

[0006] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides a method and device for solving asymmetric faults in wind power systems, which specifically adopts the following technical solutions:

[0007] The present application discloses a method for solving asymmetric faults in a wind power system, which comprises the following steps:

[0008] Obtaining a low voltage ride through control strategy and a fault type of the wind power system; the fault type at least includes a single-phase fault, a two-phase short circuit fault, and a two-phase grounding fault;

[0009] Obtain the fault equivalent calculation model of the wind power system under the fault state according to the low voltage ride-through control strategy;

[0010] Obtain the 3n-node fault sequence network admittance matrix according to the positive and negative sequence impedance parameters of the line between n nodes;

[0011] Obtain the sequence component form admittance matrix of the fault node under the corresponding fault type according to the fault type of the wind power system;

[0012] Correlate the 3n-node fault sequence network admittance matrix with the sequence component form admittance matrix of the fault node under the corresponding fault type to obtain the composite sequence network admittance matrix after the fault;

[0013] Use the Gaussian elimination method to simplify the composite sequence network admittance matrix to obtain the simplified equivalent network admittance matrix;

[0014] Iteratively solve the fault current of the wind power system according to the simplified equivalent network admittance matrix;

[0015] Input the result obtained by the iterative solution into the composite sequence network admittance matrix to obtain the sequence voltage of each node; and obtain the current of the line between nodes according to the difference in the sequence voltage of adjacent nodes and the sequence impedance parameters of the line between nodes.

[0016] Optionally: The fault equivalent calculation model includes a positive sequence current source calculation model and a negative sequence current source calculation model:

[0017] The positive sequence current source calculation model is:

[0018] ;

[0019] Where is the reactive power reference value corresponding to the positive sequence current, is the active power reference value corresponding to the positive sequence current, θ pcc is the phase angle of the positive sequence voltage of the wind turbine grid connection, U pcc + is the positive sequence component of the grid connection point voltage; U pcc - is the negative sequence component of the grid connection point voltage; j represents the imaginary unit of complex number operation;

[0020] Among them, the active and reactive power reference values of the positive sequence current are respectively:

[0021] ;

[0022] Where is the reactive power reference value corresponding to the positive sequence current, is the active power reference value corresponding to the positive-sequence current, is the maximum reactive current of the wind power system, I max is the maximum output current of the wind power system, k p is the positive-sequence reactive power ratio coefficient, is the voltage value corresponding to the positive sequence, P 0.pu is the output of the wind power system before the fault;

[0023] The negative-sequence current source calculation model is:

[0024] ;

[0025] where is the reactive power reference value corresponding to the negative-sequence current, is the active power reference value corresponding to the negative-sequence current, θ pcc is the positive-sequence voltage phase angle of the wind power system connected to the grid; U pcc + is the positive-sequence component of the grid-connected point voltage; U pcc - is the negative-sequence component of the grid-connected point voltage, * represents the conjugate operation; j represents the imaginary unit of complex number operation;

[0026] The reference value of the negative-sequence current corresponding to suppressing the negative-sequence current is:

[0027] ;

[0028] The reference value of the negative-sequence current corresponding to suppressing power fluctuations is:

[0029] ;

[0030] where, is the negative-sequence direct-axis voltage component, is the positive-sequence direct-axis voltage component, is the negative-sequence quadrature-axis voltage component; where, ρ= -1 represents suppressing the second harmonic oscillation of the active power of the inverter, ρ= 1 represents the control target of suppressing the reactive power of the inverter;

[0031] The reference value of the negative-sequence current corresponding to absorbing negative-sequence reactive power is:

[0032] ;

[0033] where, k n is the dynamic reactive power ratio coefficient.

[0034] Optionally: Before the admittance matrix of the 3n-node fault sequence network is associated with the sequence component form admittance matrix of the fault node under the corresponding fault type, the admittance matrix of the 3n-node sequence network needs to be preprocessed to obtain the admittance matrix of the pre-fault sequence network Y pre :

[0035] ;

[0036] The sub-matrix on the main diagonal represents the positive, negative, and zero sequence network admittance matrices before the corresponding fault occurs.

[0037] Optionally: The steps of obtaining the composite sequence network admittance matrix according to the admittance matrix of the 3 n node fault sequence network and the sequence component form admittance matrix of the fault node under the corresponding fault type include:

[0038] Obtain the position of the fault node n f and obtain the sequence component form admittance matrix at the fault node under different fault boundary conditions Y f012 ;

[0039] Obtain the fault node association matrix between the fault node and the 3 n node fault sequence network according to the position of the fault node T tr :

[0040] ;

[0041] Based on the fault node association matrix T tr Associate the phase component form admittance matrix at the fault node Y abc to the composite sequence network admittance matrix of the 3 n nodes to obtain the sequence component form admittance matrix at the fault node:

[0042] ;

[0043] wherein, Y abc is the phase component form admittance matrix at the fault node, S is the transformation matrix from sequence components to phase components;

[0044] Parallel the sequence component form admittance matrix at the fault node with the pre-fault sequence network admittance to obtain the post-fault composite sequence network admittance matrix:

[0045] ;

[0046] whereinY f is the fault circuit admittance matrix associated with the composite sequence network admittance matrix; Y f012 is the sequence component form admittance matrix at the fault node; T tr is the fault node incidence matrix; is T tr the transpose matrix of; Y Σ is the composite sequence network admittance matrix considering the fault.

[0047] Optionally: The steps of simplifying the composite sequence network admittance matrix after the fault by using the Gaussian elimination method include:

[0048] Sort the node numbers of the composite sequence network admittance matrix and gather the nodes with non-zero node injection current column vectors:

[0049] ;

[0050] Use the Gaussian elimination method to eliminate the node equations with zero injection current and obtain

[0051] ;

[0052] After taking out the equation where I s is located, obtain:

[0053] ;

[0054] where I s is a current column vector with non-zero elements, U s represents the node voltage corresponding to the node with non-zero injection current, Y 11 、 Y 12 、Y 21 、Y 22 The subscripts of the sub-matrices respectively represent their row and column positions in the admittance matrix, Y Σ.s×s is the simplified composite sequence network admittance matrix, s is the number of reserved nodes.

[0055] Optionally: The steps of iteratively solving the fault current of the wind power system according to the simplified equivalent network admittance matrix include:

[0056] S1. Obtain the iterative function of the fault current in the wind power system according to the simplified equivalent network admittance matrix:

[0057] ;

[0058] where is the sequence voltage component obtained in the k-th iteration; represents the fault equivalent current source model of the wind power system, which includes the positive sequence and negative sequence current calculation models; is the sequence voltage component obtained in the (k + 1)-th iteration; is the sequence current component obtained in the (k + 1)-th iteration; represents the simplified composite sequence network admittance matrix;

[0059] S2. Set all the wind power generation equipment in the wind power system to zero, and use a synchronous machine as the power source excitation to obtain the voltage values of each node in the network;

[0060] S3. Input the node voltage values into the fault equivalent calculation model of the wind power system, obtain the corresponding positive and negative sequence current output values, and update them to the corresponding positions in the node injection current column vector;

[0061] S4. Recalculate the voltage values of each node according to the iterative function, and determine whether the voltage values of the corresponding nodes converge: if the node voltage values do not converge, return to step S3; if the node voltage values converge, record the positive and negative sequence current output values at this time.

[0062] Optionally: The step of obtaining the sequence component form admittance matrix of the fault node under the corresponding fault type according to the fault type of the wind power system includes:

[0063] Obtain the phase component form admittance matrix at the fault node of the corresponding fault type according to the fault type and obtain the phase component relationship between the voltage and current of the corresponding fault type; where the phase component relationship between the voltage and current of the fault type is expressed as:

[0064] ;

[0065] Derive the sequence component form admittance matrix of the corresponding fault type according to the phase component relationship between the current and voltage of the fault circuit and in combination with the corresponding phase component form admittance matrix:

[0066] ;

[0067] where is the sequence component form admittance matrix at the fault node corresponding to the fault type; is the sequence component voltage of the fault node; is the sequence component current of the fault node; S is the transformation matrix from sequence components to phase components; S -1is the invertible matrix of the transformation matrix S.

[0068] Optionally: the phase component form admittance matrix at the fault node corresponding to the fault type includes at least one of a single-phase fault phase component form admittance matrix, a two-phase short-circuit phase component form admittance matrix, and a two-phase grounding phase component form admittance matrix:

[0069] The single-phase fault phase component form admittance matrix is expressed as:

[0070] ;

[0071] The two-phase short-circuit phase component form admittance matrix is expressed as:

[0072] ;

[0073] The two-phase grounding phase component form admittance matrix is expressed as:

[0074] ;

[0075] where is the admittance of the fault transition resistance at the fault node.

[0076] Optionally: the sequence component form admittance matrix at the fault node corresponding to the fault type includes at least one of a single-phase fault sequence component form admittance matrix, a two-phase short-circuit sequence component form admittance matrix, and a two-phase grounding sequence component form admittance matrix:

[0077] The single-phase fault sequence component form admittance matrix is expressed as:

[0078] ;

[0079] The two-phase short-circuit sequence component form admittance matrix is expressed as:

[0080] ;

[0081] The two-phase grounding sequence component form admittance matrix is expressed as:

[0082] ;

[0083] where is the admittance of the fault transition resistance at the fault node.

[0084] The present invention also discloses an asymmetric fault solving device applicable to a wind power system, and the device includes:

[0085] A first acquisition module, configured to acquire a low voltage ride-through control strategy and a fault type of the wind power system; the fault type includes at least a single-phase fault, a two-phase short-circuit fault, and a two-phase grounding fault;

[0086] The second acquisition module is used to obtain the fault equivalent calculation model of the wind power system under fault conditions according to the low-voltage ride-through control strategy;

[0087] The third acquisition module is used to obtain the 3n-node fault sequence network admittance matrix according to the positive and negative sequence impedance parameters of the lines between n-node networks;

[0088] The fourth acquisition module is used to obtain the sequence component form admittance matrix of the fault nodes under the corresponding fault types according to the fault types of the wind power system;

[0089] The fault circuit association module is used to associate the 3n-node fault sequence network admittance matrix with the sequence component form admittance matrix at the fault nodes under the corresponding fault types to obtain the post-fault composite sequence network admittance matrix;

[0090] The composite sequence network simplification module is used to simplify the composite sequence network admittance matrix by using the Gaussian elimination method to obtain the simplified equivalent network admittance matrix;

[0091] The iterative solution module is used to iteratively solve the fault current of the wind power system according to the simplified equivalent network admittance matrix;

[0092] The parameter output module is used to input the result obtained by the iterative solution into the composite sequence network admittance matrix to obtain the sequence voltage of each node; and obtain the current value of the line between nodes according to the sequence voltage difference between adjacent nodes and the sequence impedance parameters of the lines between nodes.

[0093] Beneficial effects

[0094] The technical solution of this application has obtained the following beneficial effects:

[0095] (1) For the problem of complex fault characteristics caused by the nonlinear and strongly control-related characteristics of fault electrical quantities under different current control strategies in a wind farm under asymmetric faults, the asymmetric fault solution method of this application establishes an asymmetric fault equivalent calculation model, and by simplifying the composite sequence network admittance matrix, the total number of nodes in the composite network is greatly reduced. On the basis of ensuring the accuracy of iterative calculation, the operation efficiency is improved, and the fault characteristics of large-scale wind power systems under asymmetric faults are quickly and accurately solved.

[0096] (2) The asymmetric fault solution method of this application unifies and standardizes the composite sequence network admittance matrices under different fault positions and different fault types, so that the sequence component form admittance matrices at different fault positions and different fault types are associated with the admittance matrix of the entire network, forming a unified association rule, which reduces the difficulty of computer programming, and at the same time reduces the dimension of the equation used for iterative solution and reduces the calculation amount.

[0097] (3) The asymmetric fault solution method of this application addresses the complex fault characteristics of different current control strategies in a wind farm under asymmetric faults. It proposes an equivalent calculation model for asymmetric faults, which can accurately depict fault characteristics and quickly and accurately calculate the fault current distribution. The error between its calculation results and the simulation results is only 1%, solving the problem of solving the new energy fault network under different negative sequence current control strategies. Description of the Drawings

[0098] Figure 1 It is a schematic diagram of the main circuit and its control structure of a new energy voltage source converter.

[0099] Figure 2 It is a schematic diagram of the flow of the traditional sequence network iteration method.

[0100] Figure 3 It is a schematic diagram of the flow of the traditional regional local iteration method.

[0101] Figure 4 It is a schematic diagram of the flow of the asymmetric fault solution method in the embodiment of this application.

[0102] Figure 5 It is a schematic diagram of the flow of iteratively solving the fault current of a wind power system using the equivalent network admittance matrix in the embodiment of this application.

[0103] Figure 6 It is a schematic diagram of the equivalent current source model of the wind power system in the embodiment of this application.

[0104] Figure 7 It is a schematic diagram of the model of the additional node of the traditional composite sequence network in the embodiment of this application.

[0105] Figure 8 It is an equivalent schematic diagram of the connection of the sequence network under asymmetric faults in the embodiment of this application. Among them Figure 8 (a) is the equivalent schematic diagram of the composite sequence network for single-phase faults; Figure 8 (b) is the equivalent schematic diagram of the composite sequence network for two-phase short circuits; Figure 8 (c) is the equivalent schematic diagram of the composite sequence network for two-phase grounding; Figure 8 (d) is the equivalent schematic diagram of the phase component circuit for single-phase faults; Figure 8 (e) is the equivalent schematic diagram of the phase component circuit for two-phase short circuits; Figure 8 (f) is the equivalent schematic diagram of the phase component circuit for two-phase grounding.

[0106] Figure 9 It is a schematic diagram of the structure of a large-scale wind power new energy transmission system in the embodiment of this application.

[0107] Figure 10 It is a schematic diagram of the negative sequence voltage amplitude under single-phase faults in the embodiment of this application.

[0108] Figure 11 This is a schematic structural diagram of the asymmetric fault current calculation device for the wind power system in the embodiment of the present application.

[0109] Figure 12 This is a schematic structural diagram of an electronic device in the embodiment of the present application. Detailed implementation manners

[0110] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Therefore, those of ordinary skill in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, the description below omits the description of well-known functions and structures. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0111] With the large-scale access of inverter-based new energy to the power grid, in order to ensure the safe and stable operation of the power grid, it is required that the new energy power stations connected to the grid (such as wind power systems, photovoltaic systems, etc.) should have good low voltage ride-through operation capabilities. As Figure 1 shown, this is the main circuit and its control structure of a voltage source converter (VSC). The inverter adopts power decoupling control, and the inner control loop is a positive and negative sequence current closed-loop control. Through the negative sequence current component, collaborative control objectives such as controlling the three-phase current balance, suppressing the active power fluctuation, and suppressing the reactive power fluctuation are achieved. Usually, the new energy operates in a grid-connected state with a unity power factor under normal operating conditions. During a fault, when the voltage at the new energy grid connection point deviates from the rated value and enters the low voltage ride-through period, according to the requirements of new energy low voltage ride-through, it is necessary for the new energy to inject positive sequence reactive current into the power grid to support the recovery of the positive sequence voltage. The low voltage ride-through control strategy for a wind farm is as follows:

[0112] The active and reactive reference values of the positive sequence current are respectively:

[0113] ;

[0114] where is the reactive reference value corresponding to the positive sequence current, is the active reference value corresponding to the positive sequence current, is the maximum reactive current of the wind power system, I max is the maximum output current of the wind power system, k p is the positive sequence reactive proportional coefficient, is the voltage value corresponding to the positive sequence, P 0.pu is the output of the wind power system before the fault.

[0115] According to different negative sequence control objectives, the reference values of negative sequence current are different:

[0116] The reference value of negative sequence current corresponding to suppressing negative sequence current is:

[0117] ;

[0118] The reference value of negative sequence current corresponding to suppressing power fluctuation is:

[0119] ;

[0120] Among them, is the reactive power reference value corresponding to the negative sequence, is the active power reference value corresponding to the negative sequence, is the negative sequence direct-axis voltage component, is the positive sequence direct-axis voltage component, is the negative sequence quadrature-axis voltage component; among them, ρ= -1 represents suppressing the second harmonic oscillation of the active power of the inverter, ρ= 1 represents the control objective of suppressing the reactive power of the inverter.

[0121] The reference value of negative sequence current corresponding to absorbing negative sequence reactive power is:

[0122] ;

[0123] Among them, k n is the dynamic reactive power proportionality coefficient.

[0124] Since traditional inverter-based new energy adopts low voltage ride-through control strategy and current closed-loop control, the inertia time constant of inverter-based new energy is very small during the fault stage, the transient process is short, and the output current quickly reaches the current reference value. Compared with traditional synchronous machine power sources, new energy has non-linear characteristics such as phase mutation and amplitude limitation of positive and negative sequence output currents during faults, and the output current reference value is related to the grid connection point voltage. However, there is usually coupling between the positive and negative sequences of the grid connection point voltage and mutual influence between multiple stations in the fault current of a large-scale transmission system of multiple new energy stations, and the accuracy of the calculated fault current results is not high.

[0125] Currently, for solving the fault current of a large-scale grid-connected system containing inverter-based new energy, the nodal voltage equation is mostly used, the new energy station is replaced by a voltage-controlled current source, and an iterative correction algorithm is combined to solve the fault current. For example Figure 2The sequence network iteration method shown can better solve the steady-state short-circuit current under symmetrical and asymmetrical faults. However, when dealing with asymmetrical fault types, since the nodal admittance matrix is not further processed, the scale of the equations used for iterative solution after adding the additional negative-sequence and zero-sequence voltage equations in the symmetrical component network is large. And because the control strategy of negative-sequence current is not considered, the network with negative-sequence current injection cannot be processed.

[0126] However, as Figure 3 shown, the regional local iteration method can solve the problem of a large number of network nodes for large-scale new energy transmission systems. However, the iterative method using the local network node set will inevitably affect the calculation accuracy, and this method only establishes the current mapping relationship under symmetrical faults and cannot be used for the simplified solution of the fault network under asymmetrical faults.

[0127] In the embodiment of the present application, taking the wind power system as an example, in order to solve the problems of a large number of nodes in the current large-scale wind power system, a high dimension of the complex sequence network nodal voltage equation under asymmetrical faults, and the complex solution of the fault network containing the negative-sequence current injection of the wind power system, it simplifies the fault network through the equivalent network iterative solution and the full-network non-iterative calculation method. At the same time, this method can accurately solve the fault distribution characteristics of multiple wind farm stations with negative-sequence current injection.

[0128] As Figure 4 shown, the embodiment of the present application specifically discloses an asymmetrical fault solution method applicable to the wind power system, which includes the following steps:

[0129] Step 1: Obtain the low-voltage ride-through control strategy and fault type of the wind power system; the fault type at least includes single-phase fault, two-phase short-circuit fault, and two-phase grounding fault.

[0130] Step 2: Obtain the fault equivalent calculation model of the wind power system according to the low-voltage ride-through control strategy.

[0131] Combined with Figure 6 shown, in the embodiment of the present application, the equivalent current source model includes a positive-sequence current source calculation model and a negative-sequence current source calculation model:

[0132] The positive-sequence current source calculation model is:

[0133] ;

[0134] The negative-sequence current source calculation model is:

[0135] ;

[0136] Where is the reactive power reference value corresponding to the positive-sequence current, is the active power reference value corresponding to the positive-sequence current, is the reactive power reference value corresponding to the negative-sequence, is the active power reference value corresponding to the negative-sequence, θ pcc is the positive-sequence voltage phase angle of the wind power system connected to the grid, U pcc + is the positive-sequence component of the grid connection point voltage; U pcc - is the negative-sequence component of the grid connection point voltage, where * represents the conjugate operation; j represents the imaginary unit of complex number operation.

[0137] The negative-sequence current source calculation model at the new energy position in the negative-sequence network established in the embodiment of the present application can be adapted to solve the fault current in a wind power system with different negative-sequence current control parameters, so as to solve the problem of complex solution of a fault network with negative-sequence current injection from a wind power system.

[0138] Step 3: According to the positive and negative sequence impedance parameters of the lines between n nodes, without considering the fault circuit, the 3n-node fault sequence network admittance matrix before the fault can be obtained.

[0139] It should be noted that after obtaining the 3n-node fault sequence network admittance matrix in the embodiment of the present application, preprocessing is required to obtain the pre-fault sequence network admittance matrix Y pre :

[0140] ;

[0141] Among them, the sub-matrix on the main diagonal represents the positive, negative, and zero sequence network admittance matrices before the corresponding fault occurs. It should be understood that there is no coupling between the sequence networks in this sequence network admittance matrix.

[0142] Step 4: Obtain the sequence component form admittance matrix of the fault node under the corresponding fault type according to the fault type of the wind power system.

[0143] Generally, the traditional asymmetric fault calculation method based on the composite sequence network needs to connect the formed sequence networks in series or parallel at the fault node. For example, one way to process the connection of the sequence networks is: add two endpoints in the sequence network, denoted as additional fault nodes n f and the ground node n g , and the mutual admittance is taken as infinity to indicate that the two nodes are connected, as shown in Figure 7 .

[0144] In the embodiment of the present application, a faulty circuit also needs to be connected in parallel or in series to the faulty node. The sequence network parameters do not change under different types of faults. However, due to the different admittance matrices in the phase component form of the faulty circuit, the connection condition of the sequence network ports is changed, as Figure 8 shown. Therefore, the sequence component form admittance matrix of the faulty circuit can be adopted in this solution to obtain a unified and standardized sequence network composite admittance matrix.

[0145] Specifically, the specific process of obtaining the sequence component form admittance matrix of the faulty node under the corresponding fault type in this step is as follows:

[0146] First, obtain the admittance matrix in the phase component form at the faulty node corresponding to the fault type and obtain the phase component relationship between the voltage and current corresponding to the fault type; the phase component relationship between the voltage and current corresponding to the fault type is expressed as:

[0147] ;

[0148] It should be noted that in the above formula, a, b, and c respectively represent single-phase electricity in three-phase electricity.

[0149] As Figure 8 shown, the admittance matrix in the phase component form at the faulty node corresponding to the fault type in the embodiment of the present application includes at least one of the single-phase fault phase component form admittance matrix, the two-phase short-circuit phase component form admittance matrix, and the two-phase grounding phase component form admittance matrix:

[0150] The single-phase fault phase component form admittance matrix is expressed as:

[0151] ;

[0152] The two-phase short-circuit phase component form admittance matrix is expressed as:

[0153] ;

[0154] The two-phase grounding phase component form admittance matrix is expressed as:

[0155] ;

[0156] Where is the admittance of the fault transition resistance of the faulty node.

[0157] Secondly, deduce the sequence component form admittance matrix corresponding to the fault type according to the phase component relationship between the current and voltage of the faulty circuit and in combination with the corresponding admittance matrix in the phase component form:

[0158] ;

[0159] Where is the admittance matrix of the positive, negative, and zero sequence components of the fault node corresponding to the fault type; are the positive, negative, and zero sequence component voltages of the fault node; are the positive, negative, and zero sequence component currents of the fault node; S is the transformation matrix from sequence components to phase components; S -1 is the inverse matrix of the transformation matrix S.

[0160] According to the above derivation model, it can be known that the admittance matrix of the sequence components at the fault node corresponding to the fault type described in the embodiment of the present application at least includes one of the admittance matrix of the single-phase fault sequence components, the admittance matrix of the two-phase short-circuit sequence components, and the admittance matrix of the two-phase grounding sequence components:

[0161] Table 1 Admittance Matrix of the Sequence Components of the Fault Circuit

[0162]

[0163] As shown in Table 1, the admittance matrix of the single-phase fault sequence components is expressed as:

[0164] ;

[0165] The admittance matrix of the two-phase short-circuit sequence components is expressed as:

[0166] ;

[0167] The admittance matrix of the two-phase grounding sequence components is expressed as:

[0168] ;

[0169] where is the admittance of the fault transition resistance of the fault node.

[0170] Step Five: Correlate the 3n-node sequence network admittance matrix with the admittance matrix of the sequence components at the fault node under the corresponding fault type to obtain the composite sequence network admittance matrix.

[0171] Specifically, the process of obtaining the composite sequence network admittance matrix in this step is as follows:

[0172] First, obtain the position of the fault node n f and obtain the admittance matrix of the sequence components at the fault node under different fault boundary conditions Y f012 ;

[0173] Then, obtain the fault node correlation matrix between the fault node and the 3 n node fault sequence network admittance matrix according to the position of the fault node T tr :

[0174] ;

[0175] Subsequently, based on the fault node incidence matrix T tr the admittance matrix in phase component form at the fault node Y abc is associated with the admittance matrix of the composite sequence network at node 3 n to obtain the admittance matrix in sequence component form at the fault node:

[0176] ;

[0177] Finally, the admittance matrix of the composite sequence network is obtained by paralleling the admittance matrix in sequence component form at the fault node with the pre-fault sequence network admittance. It should be noted that at this time, the admittance matrix of the composite sequence network can be regarded as having a fault circuit paralleled at the fault node of the corresponding sequence network. The admittance matrix of the composite sequence network formed at any fault location can be uniformly expressed as:

[0178] ;

[0179] where Y f is the admittance matrix of the fault circuit associated with the admittance matrix of the composite sequence network; Y abc is the admittance matrix in phase component form at the fault node corresponding to different fault boundary conditions; Y f012 is the admittance matrix in sequence component form at the fault node; T tr is the fault node incidence matrix; is T tr the transpose matrix of; Y Σ is the admittance matrix of the composite sequence network considering the fault.

[0180] It should be understood that in the embodiments of the present application, this step can unify and standardize the admittance matrices of the composite sequence network under different fault locations and different fault types, so that the admittance matrices in sequence component form under different fault locations and different fault types can be associated with the admittance matrix of the entire network through a unified admittance matrix of the composite sequence network. It forms a unified association rule and is more conducive to computer programming to achieve automatic program solving.

[0181] Step Six: Simplify the admittance matrix of the composite sequence network using the Gaussian elimination method to obtain the simplified equivalent network admittance matrix;

[0182] Specifically, the steps of simplifying the admittance matrix of the composite sequence network using the Gaussian elimination method in this step are:

[0183] First, number and sort the nodes of the composite sequence network admittance matrix, and gather the nodes with non-zero column vectors of the injected node currents for subsequent processing:

[0184] ;

[0185] Subsequently, use the Gaussian elimination method to eliminate the node equations with zero injected currents to obtain:

[0186] ;

[0187] Finally, after extracting the equation where I s is located, we obtain:

[0188] ;

[0189] where I s is a column vector of currents with non-zero elements, U s represents the node voltages corresponding to the nodes with non-zero injected currents, U n1 、 U n2 are respectively the column vectors of voltages corresponding to the nodes with non-zero injected currents; Y 11 、Y 12 、Y 21 、Y 22 The subscripts of the sub-matrices respectively represent their row and column positions in the admittance matrix, Y Σ.s×s is the simplified composite sequence network admittance matrix, s is the number of reserved nodes.

[0190] It should be understood that in the embodiments of the present application, the dimension of the equivalent network admittance matrix Y Σ.s×s depends on the number of excitations in the network, and the nodes with no injected currents do not appear in the equivalent network admittance matrix. This step can significantly reduce the total number of nodes in the composite network, reduce the dimension of the equations for subsequent iterative solution, reduce the computational amount, and speed up the solution speed.

[0191] Step Seven: Iteratively solve the fault current of the wind power system according to the simplified equivalent network admittance matrix.

[0192] Specifically, the specific process of iterative solution in this step is as follows:

[0193] S1. Obtain the iterative function of the fault current in the wind power system according to the simplified equivalent network admittance matrix, and its iterative format can be expressed as:

[0194] ;

[0195] where is the sequence voltage component obtained in the k-th iteration; represents the fault equivalent current source model of the wind power system, which includes the positive-sequence and negative-sequence current calculation models; is the sequence voltage component obtained in the (k + 1)-th iteration; is the sequence current component obtained in the (k + 1)-th iteration; represents the simplified combined sequence network admittance matrix;

[0196] S2. Set all the wind power generation equipment in the wind power system to zero, and use a synchronous machine as the power source excitation to obtain the voltage values of each node in the network;

[0197] S3. Input the initial voltage value or the node voltage value obtained in the previous iteration into the fault equivalent calculation model of the wind power system, obtain the corresponding positive and negative sequence current output values, and update them to the corresponding positions in the node injection current column vector;

[0198] S4. Recalculate the voltage values of each node according to the iterative function, and determine whether the voltage values of the corresponding nodes converge: for example, set the convergence threshold , if the difference between the node voltage values in this iteration and the previous iteration is greater than or equal to , it indicates that the node voltage values do not converge, and return to step S3; if the difference between the node voltage values in this iteration and the previous iteration is less than , it indicates that the node voltage values converge, and record the positive and negative sequence current output values at this time.

[0199] Step Eight: Input the results obtained by iterative solution into the combined sequence network admittance matrix to obtain the node sequence voltages of each node; and obtain the currents of the lines between nodes according to the sequence voltage differences between adjacent nodes and the sequence impedance parameters of the lines between nodes, thereby realizing the non-iterative solution of the fault distribution characteristics of the entire network.

[0200] It should be noted that the method of this embodiment can be applied not only to the wind power system, but also to other new energy power generation systems such as photovoltaic power generation systems, hydropower systems, and thermal power systems for asymmetric fault analysis and solution.

[0201] To further verify the accuracy of the asymmetric fault solution method in this application embodiment, the calculation results of the MATLAB program and the simulation data of PSCAD / EMTDC are used for comparative verification.

[0202] Such as Figure 9As shown, it is the structure of the large-scale wind power system adopted in this embodiment. The stations in the system are scattered. There are 6 wind farm stations or photovoltaic stations in the network, each with a capacity of 150 MW. They are sent out through the station collection lines and connected to the power grid through a 330 kV channel.

[0203] (1) Under single-phase faults, the number of sequence network nodes is 48. After simplifying the equivalent network, the number of nodes is reduced to 13, and the dimension of the iterative equation decreases. In this embodiment, the low-voltage ride-through strategy of the wind farm station or photovoltaic station is set to suppress the active power fluctuation. Node 10 is set as the fault node with a transition resistance of 0.5 ohm. The calculation and simulation results of the positive and negative sequence components of the fault current of the wind farm station or photovoltaic station are shown in Table 2. It can be seen that the calculation and simulation errors of the fault output current of the wind farm station or photovoltaic station are both below 1%.

[0204] Table 2 New energy current results after the fault of Node 10

[0205]

[0206] (2) Subsequently, change the fault location to Node 8 and set the transition resistance to 0.1 ohm. The results are shown in Table 3, which indicates that the calculation results still have high accuracy, demonstrating that the calculation method of this application has good applicability to different fault locations.

[0207] Table 3 New energy current results after the fault of Node 8

[0208]

[0209] (3) Further set a single-phase fault occurs in the wind farm station or photovoltaic station, and analyze the calculation and simulation results of the negative sequence voltage at Node 9 under the negative sequence current control strategies of ρ = 0, 1, -1 respectively adopted by Station 2, as Figure 10 shown, which can demonstrate that the method of this application has good applicability in solving the fault quantities of wind power systems or photovoltaic systems considering different negative sequence current controls.

[0210] In addition, as Figure 11 shown, this embodiment of the application also discloses an asymmetric fault solving device applicable to wind power systems. The device includes:

[0211] A first acquisition module for acquiring the low-voltage ride-through control strategy and fault type of the wind power system; the fault type includes at least single-phase faults, two-phase short-circuit faults, and two-phase grounding faults;

[0212] A second acquisition module for obtaining the fault equivalent calculation model of the wind power system under fault conditions according to the low-voltage ride-through control strategy;

[0213] A third acquisition module, configured to obtain a pre-fault 3n-node fault sequence network admittance matrix according to the positive and negative sequence impedance parameters of the lines between n-node networks;

[0214] A fourth acquisition module, configured to obtain an admittance matrix in the form of sequence components of a fault node under a corresponding fault type according to the fault type of the wind power system;

[0215] A fault circuit association module, configured to associate the 3n-node fault sequence network admittance matrix with the admittance matrix in the form of sequence components at the fault node under the corresponding fault type to obtain a post-fault composite sequence network admittance matrix;

[0216] A composite sequence network simplification module, configured to simplify the composite sequence network admittance matrix by using the Gaussian elimination method to obtain a simplified equivalent network admittance matrix;

[0217] An iterative solution module, configured to iteratively solve the fault current of the wind power system according to the simplified equivalent network admittance matrix;

[0218] A parameter output module, configured to input the result obtained by the iterative solution into the full-node admittance matrix of the fault network to obtain the node sequence voltage of each node; and obtain the current value of the line between nodes according to the sequence voltage difference between adjacent nodes and the sequence impedance parameters of the lines between nodes.

[0219] The device provided by the embodiment of the present application can implement Figure 4 each process implemented by the method embodiment. To avoid repetition, it will not be elaborated here.

[0220] As Figure 12 shown, the embodiment of the present application further provides an electronic device, including a processor and a memory, a program or instruction stored on the memory and executable on the processor. When the program or instruction is executed by the processor, it implements each process of the method embodiment as shown in Figure 4 and can achieve the same technical effect. To avoid repetition, it will not be elaborated here.

[0221] The embodiment of the present application further provides a readable storage medium, on which a program or instruction is stored. When the program or instruction is executed by the processor, it implements each process of the above-mentioned Figure 4 method embodiment and can achieve the same technical effect. To avoid repetition, it will not be elaborated here.

[0222] The embodiment of the present application further provides a computer program product, including a computer instruction. When the computer instruction is executed by the processor, it implements each process of the above-mentioned Figure 4 method embodiment and can achieve the same technical effect. To avoid repetition, it will not be elaborated here.

[0223] It should be understood that the "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, the "in one embodiment" or "in an embodiment" that appears throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present application, the magnitude of the serial numbers of the above processes does not mean the sequence of execution, and the execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application. The serial numbers of the embodiments of the present application above are only for description and do not represent the advantages or disadvantages of the embodiments.

[0224] It should be noted that in this text, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0225] In several embodiments provided by the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined, or can be integrated into another device, or some features can be ignored, or not executed. In addition, the coupling, direct coupling or communication connection between the components shown or discussed with each other can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0226] The units described above as separate components may or may not be physically separated, and the components shown as units may or may not be physical units; they can be located in one place or distributed to multiple network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0227] In addition, each functional unit in the embodiments of the present application can be all integrated in a processing unit, or each unit can be separately used as a unit, or two or more units can be integrated in one unit; the above integrated units can be implemented in the form of hardware, or in the form of a combination of hardware and software functional units.

[0228] Those of ordinary skill in the art can understand that all or part of the steps of implementing the above method embodiments can be completed by hardware related to program instructions. The foregoing program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps including those of the above method embodiments; and the foregoing storage medium includes: mobile storage devices, read-only memory (ROM), magnetic disks, or optical discs and other various media that can store program codes.

[0229] Alternatively, if the above integrated units of the present application are implemented in the form of software function modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the embodiments of the present application, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a device (which can be a terminal or a platform, etc.) to execute all or part of the methods described in the various embodiments of the present application. And the foregoing storage medium includes: mobile storage devices, ROM, magnetic disks, or optical discs and other various media that can store program codes.

[0230] The foregoing are only the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present application, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A method for solving asymmetric faults in wind power systems, characterized in that: The steps include: Obtaining a low voltage ride through control strategy and a fault type of the wind power system; the fault type at least includes a single-phase fault, a two-phase short circuit fault, and a two-phase grounding fault; According to the low voltage ride-through control strategy, the fault equivalent calculation model of the wind power system under fault condition is obtained; The 3n-node fault sequence network admittance matrix is ​​obtained based on the positive and negative sequence impedance parameters of the line between n nodes; and the 3n-node fault sequence network admittance matrix is ​​preprocessed to obtain the pre-fault sequence network admittance matrix Y pre : ； The sub-matrices on the main diagonal represent the positive and negative zero-sequence network admittance matrices before the corresponding fault occurs; According to the fault type of the wind power system, the sequence component form admittance matrix of the fault node under the corresponding fault type is obtained; According to the association between the 3n-node fault sequence network admittance matrix and the sequence component form admittance matrix of the faulty node under the corresponding fault type, the composite sequence network admittance matrix after the fault is obtained: Get the location of the failed node n f And obtain the sequence component form admittance matrix at the fault node under different fault boundary conditions Y f012 ; According to the location of the faulty node, obtain the faulty node and 3 n Fault node association matrix of node fault sequence network T tr : ； Based on the fault node association matrix T tr The phase component at the fault node is converted into an admittance matrix Y abc Link to 3 n The composite sequence network admittance matrix of the node is used to obtain the sequence component form admittance matrix at the faulty node: ； in, Y abc is the phase component form admittance matrix at the fault node, S is the transformation matrix from sequence component to phase component; The composite sequence network admittance matrix after the fault is obtained by connecting the sequence component form admittance matrix at the fault node in parallel with the sequence network admittance before the fault: ； in Y f is the fault circuit admittance matrix associated to the composite sequence network admittance matrix; Y f012 is the sequence component form admittance matrix at the fault node; T tr is the fault node association matrix; for T tr The transposed matrix of Y Σ is the composite sequence network admittance matrix taking into account faults; The Gaussian elimination method is used to simplify the composite sequence network admittance matrix to obtain the simplified equivalent network admittance matrix: Sort the node numbers of the composite sequence network admittance matrix and collect the nodes with non-zero node injection current column phasors: ； The Gaussian elimination method is used to eliminate the node equations where the injected current is zero, and the following is obtained: ； Will I s After the equation is proposed, we obtain: ； in I s is a current column vector with non-zero elements, U s represents the node voltage corresponding to the node with non-zero injection current, Y 11 、Y 12 、 Y 21 、Y 22 The subscripts of the submatrices represent their row and column positions in the admittance matrix. Y Σ.s×s is the simplified composite sequence network admittance matrix, s is the number of nodes to be retained; The fault current of the wind power system is iteratively solved according to the simplified equivalent network admittance matrix; The results obtained by iterative solution are input into the composite sequence network admittance matrix to obtain the node sequence voltage of each node; and the current of the line between the nodes is obtained according to the node sequence voltage difference of adjacent nodes and the sequence impedance parameters of the line between the nodes.

2. The asymmetric fault solving method according to claim 1, characterized in that: The fault equivalent calculation model includes a positive sequence current source calculation model and a negative sequence current source calculation model: The positive sequence current source calculation model is: ； in is the reactive power reference value corresponding to the positive sequence current, is the active reference value corresponding to the positive sequence current, θ pcc is the positive sequence voltage phase angle of the wind power system connected to the grid, U pcc + is the positive sequence component of the grid connection point voltage; U pcc - is the negative sequence component of the grid connection point voltage; j An imaginary unit representing complex number operations; Among them, the active and reactive reference values ​​of the positive sequence current are: ； in is the reactive power reference value corresponding to the positive sequence current, is the active reference value corresponding to the positive sequence current, is the maximum reactive current of the wind power system, I max is the maximum output current of the wind power system, k p is the positive sequence reactive power proportional coefficient, is the voltage value corresponding to the positive sequence, P 0.pu Provide power for the wind power system before the fault; The negative sequence current source calculation model is: ； in is the reactive power reference value corresponding to the negative sequence current, is the active reference value corresponding to the negative sequence current, θ pcc is the positive sequence voltage phase angle of the wind power system connected to the grid; U pcc + is the positive sequence component of the grid connection point voltage; U pcc - is the negative sequence component of the grid connection point voltage, * indicates the conjugate operation; j An imaginary unit representing complex number operations; The corresponding negative sequence current reference value when suppressing negative sequence current is: ； The corresponding negative sequence current reference value when suppressing power fluctuations is: ； in, is the negative sequence direct axis voltage component, is the positive sequence direct axis voltage component, is the negative sequence quadrature axis voltage component; where, ρ = -1 means to suppress the double frequency oscillation of the active power of the inverter. ρ = 1 represents the control target of suppressing the reactive power of the inverter; The reference value of negative sequence current corresponding to the absorption of negative sequence reactive power is: ； in, k n is the dynamic reactive power proportional coefficient.

3. The asymmetric fault solving method according to claim 1, characterized in that: The step of iteratively solving the fault current of the wind power system according to the simplified equivalent network admittance matrix comprises: S1. Obtain the iterative function of the fault current of the wind power system based on the simplified equivalent network admittance matrix: ； in is the sequence voltage component obtained in the kth iteration; represents the equivalent current source model of the wind power system fault, which includes the positive sequence and negative sequence current calculation models; is the sequence voltage component obtained in the k+1th iteration; is the sequence current component obtained in the k+1th iteration; represents the simplified composite sequence network admittance matrix; S2. Set all wind power generation equipment in the wind power system to zero, and use the synchronous machine as the power source to excite and obtain the voltage value of each node in the network; S3. Input the node voltage value into the fault equivalent calculation model of the wind power system, obtain the corresponding positive and negative sequence current output values, and update them to the corresponding position of the node injection current column vector; S4. Recalculate the voltage value of each node according to the iterative function, and determine whether the voltage value of the corresponding node converges: if the node voltage value does not converge, return to step S3; if the node voltage value converges, record the positive and negative sequence current output values ​​at this time.

4. The asymmetric fault solving method according to claim 1, characterized in that: The step of obtaining the sequence component form admittance matrix of the fault node corresponding to the fault type according to the fault type of the wind power system comprises: According to the fault type, a phase component form admittance matrix at a fault node corresponding to the fault type is obtained, and a phase component relationship of a voltage and current corresponding to the fault type is obtained; wherein the phase component relationship of the voltage and current of the fault type is expressed as: ； According to the phase component relationship of the fault circuit current and voltage and combined with the corresponding phase component form admittance matrix, the sequence component form admittance matrix of the corresponding fault type is derived: ; in is the sequence component form admittance matrix at the fault node corresponding to the fault type; is the sequence component voltage of the fault node; is the sequence component current of the fault node; S is the transformation matrix from sequence component to phase component; S -1 is the invertible matrix of the transformation matrix S.

5. The asymmetric fault solving method according to claim 4, characterized in that: The phase component form admittance matrix at the fault node corresponding to the fault type includes at least one of a single-phase fault phase component form admittance matrix, a two-phase short-circuit phase component form admittance matrix, and a two-phase grounding phase component form admittance matrix: The single-phase fault phase component form admittance matrix is ​​expressed as: ； The two-phase short-circuit phase component form admittance matrix is ​​expressed as: ； The two-phase grounding phase component form admittance matrix is ​​expressed as: ； in is the admittance of the fault transition resistance of the fault node.

6. The asymmetric fault solving method according to claim 4, characterized in that: The sequence component form admittance matrix at the fault node corresponding to the fault type includes at least one of a single-phase fault sequence component form admittance matrix, a two-phase short-circuit sequence component form admittance matrix, and a two-phase grounding sequence component form admittance matrix: The single-phase fault sequence component form admittance matrix is ​​expressed as: ； The two-phase short-circuit sequence component form admittance matrix is ​​expressed as: ； The two-phase ground sequence component form admittance matrix is ​​expressed as: ； in is the admittance of the fault transition resistance of the fault node.

7. An asymmetric fault solving device applicable to a wind power system, characterized in that: The device comprises: A first acquisition module is used to acquire a low voltage ride through control strategy and a fault type of a wind power system; the fault type includes at least a single-phase fault, a two-phase short circuit fault and a two-phase grounding fault; The second acquisition module is used to obtain a fault equivalent calculation model of the wind power system under a fault state according to a low voltage ride-through control strategy; The third acquisition module is used to obtain the 3n-node fault sequence network admittance matrix according to the positive and negative sequence impedance parameters of the lines between the n-node networks; and pre-process the 3n-node fault sequence network admittance matrix to obtain the fault pre-sequence network admittance matrix Y pre : ； The sub-matrices on the main diagonal represent the positive and negative zero-sequence network admittance matrices before the corresponding fault occurs; A fourth acquisition module is used to acquire, according to the fault type of the wind power system, a sequence component form admittance matrix of the fault node corresponding to the fault type; The fault circuit association module is used to associate the 3n-node fault sequence network admittance matrix with the sequence component form admittance matrix at the fault node under the corresponding fault type to obtain the composite sequence network admittance matrix after the fault: Get the location of the failed node n f And obtain the sequence component form admittance matrix at the fault node under different fault boundary conditions Y f012 ; According to the location of the faulty node, obtain the faulty node and 3 n Fault node association matrix of node fault sequence network T tr : ； Based on the fault node association matrix T tr The phase component at the fault node is converted into an admittance matrix Y abc Link to 3 n The composite sequence network admittance matrix of the node is used to obtain the sequence component form admittance matrix at the faulty node: ； in, Y abc is the phase component form admittance matrix at the fault node, S is the transformation matrix from sequence component to phase component; The composite sequence network admittance matrix after the fault is obtained by connecting the sequence component form admittance matrix at the fault node in parallel with the sequence network admittance before the fault: ； in Y f is the fault circuit admittance matrix associated to the composite sequence network admittance matrix; Y f012 is the sequence component form admittance matrix at the fault node; T tr is the fault node association matrix; for T tr The transposed matrix of Y Σ is the composite sequence network admittance matrix taking into account faults; The composite sequence network simplification module is used to simplify the composite sequence network admittance matrix using Gaussian elimination method to obtain the simplified equivalent network admittance matrix: Sort the node numbers of the composite sequence network admittance matrix and collect the nodes with non-zero node injection current column phasors: ； The Gaussian elimination method is used to eliminate the node equations where the injected current is zero, and the following is obtained: ； Will I s After the equation is proposed, we obtain: ； in I s is a current column vector with non-zero elements, U s represents the node voltage corresponding to the node with non-zero injection current, Y 11 、Y 12 、 Y 21 、Y 22 The subscripts of the submatrices represent their row and column positions in the admittance matrix. Y Σ.s×s is the simplified composite sequence network admittance matrix, s is the number of nodes to be retained; An iterative solution module, used for iteratively solving the fault current of the wind power system according to the simplified equivalent network admittance matrix; The parameter output module is used to input the results obtained by iterative solution into the composite sequence network admittance matrix to obtain the node sequence voltage of each node; and obtain the current value of the line between the nodes according to the sequence voltage difference between adjacent nodes and the sequence impedance parameters of the line between the nodes.

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