A method and system for equivalence of multi-field off-site power grids with structure preservation

Abstract

The present invention discloses a method and system for equivalence of a multi-station external power grid with structure preservation, which relates to the field of power systems and aims to solve the modeling problems of high-penetration scenarios of new energy sources caused by structural distortion, insufficient precision and unstable parameters of traditional equivalence methods. The present invention comprises the following steps: based on the topology of the multi-station system, the nodes of the new energy station and other nodes are numbered in blocks to construct a block admittance matrix; the Newton-Raphson method is used to perform power flow calculations to obtain the voltage and current vectors of the nodes of the new energy station; the non-new energy node variables are eliminated through Kron order reduction to generate an equivalent admittance matrix and an equivalent balanced node voltage that retain the admittance of the tie line; and the equivalent model of the external power grid with structure preservation is constructed. This technical solution significantly reduces the complexity of the model by constructing a block admittance matrix and using the Kron order reduction method, while retaining the admittance of the tie lines between the new energy stations and the original topological structure, thereby achieving high-precision and high-efficiency equivalent modeling of the multi-station external power grid.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to a method and system for structurally maintaining multi-station off-site power grid equivalence. Background Art

[0002] my country's power system has gradually evolved into a large-scale, multi-regional integrated system with extensive coverage and regional interconnection. Furthermore, with the rapid development of renewable energy, numerous renewable energy stations have been connected to the grid. This complexity presents numerous challenges in analyzing various power system issues. Therefore, the key research area is to rationally simplify the power system network. Effective equivalent simplification can reduce computational complexity and improve analysis efficiency, possessing significant theoretical and engineering application value.

[0003] Numerous methods exist for solving the static equivalence problem in power systems, but each has its own drawbacks. The simple equivalent machine method is widely used in practical engineering, but it can lead to large errors when disturbances occur in the internal network. The Ward equivalent method uses Gaussian elimination to simplify the node admittance matrix and eliminate external network nodes, but it cannot reflect the voltage and reactive power support provided by the external network to the internal network. The REI equivalent method combines the injected power of a set of nodes to be eliminated into a single REI node, but the equivalent admittance obtained by this method changes with the state of the external network. These methods fail to effectively preserve the key structural characteristics of the external network (such as the admittance of the tie lines between stations and the topological connection relationship) during the equivalence process, resulting in the equivalent model being unable to truly reflect the electrical impact of the external network on the internal network. This error is particularly amplified in scenarios with high penetration of new energy stations. Summary of the Invention

[0004] The technical problem to be solved and the technical task to be addressed by the present invention are to improve and enhance existing technical solutions, providing a method and system for structurally maintaining the equivalence of multiple off-site power grids, with the goal of addressing structural distortion, insufficient accuracy, and parameter instability. To this end, the present invention adopts the following technical solutions.

[0005] A method for equivalence of multi-field off-site power grids with structure preservation includes the following steps:

[0006] 1) According to the topological structure of the multi-station power system, the new energy station nodes and other nodes in the network are numbered in blocks to form a block admittance matrix;

[0007] 2) Based on the block admittance matrix, the Newton-Raphson method is used to calculate the system power flow to obtain the voltage vector and current vector of each renewable energy station node;

[0008] 3) Using the Kron order reduction method to perform matrix transformation on the node voltage equation, by eliminating the variables corresponding to the non-new energy station nodes, an equivalent admittance matrix and equivalent balanced node voltage are obtained. The equivalent admittance matrix retains the admittance information of the tie lines between the new energy stations;

[0009] 4) Output the equivalent system node admittance matrix YS and the equivalent equilibrium node voltage E. Based on the equivalent admittance matrix and the equivalent equilibrium node voltage, a structure-preserving external power grid equivalent model is constructed to retain the original topology information between the new energy stations.

[0010] This technical solution uses block admittance matrix construction, Kron reduced-order matrix transformation, and tie-line admittance retention technology to maintain the topological structure and admittance relationship information of the original system while simplifying the model, significantly reducing the complexity of the model and achieving high-precision and high-efficiency equivalent modeling of multi-station external power grids. Specifically, the admittance information is retained through block numbering and matrix transformation to ensure that the equivalent model is consistent with the original system topology; and to avoid the dynamic response error caused by the replacement of equivalent generators in the simple equivalent machine method. By extracting the equivalent balance node voltage, the electrical interaction of the external power grid with the internal network is accurately characterized, and the limitation of the Ward equivalent method that ignores voltage support is overcome. Equivalent parameters are generated based on power flow calculation and fixed admittance matrix to improve the robustness of the model. Compared with the REI equivalent method, the fixed admittance matrix design makes the equivalent parameters unaffected by fluctuations in the external network state.

[0011] By numbering the nodes of renewable energy stations and other nodes in blocks, a block admittance matrix is ​​formed. This precisely delineates the boundary between renewable energy stations and the external grid, providing a structured data foundation for subsequent matrix order reduction. The block matrix facilitates local operations and reduces overall computational complexity. The block design avoids the topological structure disruption caused by direct node elimination in traditional methods (such as the Ward equivalence method), ensuring the integrity of the admittance of the interconnection lines between renewable energy stations. The Newton-Raphson method is used for power flow calculation, combined with iterative correction of voltage and phase using the Jacobian matrix, to quickly converge to a high-precision solution. Kron order reduction is used to transform the node voltage equations. By eliminating non-renewable energy station node variables, an equivalent admittance matrix and equivalent balanced node voltages are generated. This eliminates redundant non-renewable energy node variables, significantly reducing model dimensionality and improving computational efficiency. It also ensures that the equivalent model is consistent with the original system topology, avoiding the admittance information loss that occurs in traditional methods. The constructed equivalent model preserves the interconnection line admittance and original topological structure between renewable energy stations. It accurately reflects the electrical interaction characteristics of the external grid with the internal network and is suitable for accurate analysis in scenarios with high renewable energy penetration. While reducing model complexity, key admittance and voltage parameters are retained to ensure consistency of simulation results with the full system model.

[0012] As a preferred technical means: in step 1), the nodes of the new energy station are numbered as the first m nodes, and the remaining nodes are numbered as the last nm nodes, where n is the total number of nodes and m is the number of nodes of the new energy station; the method for constructing the block admittance matrix is:

[0013] The block admittance matrix includes the admittance sub-matrix between nodes of the new energy station , mutual admittance matrix between new energy stations and other nodes and , and other inter-node admittance submatrices , which is of the form:

[0014] ;

[0015] in, is an m×m matrix, It is a (nm)×(nm) order matrix.

[0016] By uniformly numbering the nodes of renewable energy stations as the first m nodes and the remaining nodes as the last nm nodes, a clear classification of node types is achieved, clearly distinguishing renewable energy stations from the rest of the power grid. This facilitates quick identification of the relationships between renewable energy station nodes and other nodes, providing an intuitive physical foundation for subsequent block matrix construction. In complex multi-station systems, node classification and numbering can reduce manual intervention errors and improve the automation of model construction.

[0017] Divide the admittance matrix Y into four sub-matrices ( 、 、 、 ), using the mathematical properties of block matrices to optimize operations. (New Energy Inter-station Admittance) and The independent processing of (other node admittance) avoids the complexity of full matrix operation. It significantly reduces the amount of calculation and improves the processing efficiency of large-scale systems. This method fully preserves all admittance information (self-admittance and mutual admittance) between nodes in renewable energy stations, ensuring that the physical connections between them (such as tie line admittance) are fully reflected in the matrix. This avoids the loss of topological information caused by node elimination in traditional methods. This method provides accurate interaction parameters between stations for subsequent equivalent models, supporting precise electrical characteristics analysis.

[0018] Submatrix and Characterize the mutual admittance relationship between the new energy station node and other nodes, distinguish the electrical interaction between the new energy station and the external power grid (such as the power transmission path), and facilitate the analysis of the voltage and reactive power support of the external network to the internal network. and , which can quickly adapt to changes in the access location or number of new energy stations and enhance the scalability of the model.

[0019] The dimensional division of the block admittance matrix naturally adapts to the needs of subsequent order reduction operations. Through the block structure, subsequent steps (such as Kron order reduction) can be directly targeted Eliminate variables to avoid redundant computations of the entire matrix. Block storage reduces direct operations on large sparse matrices and reduces memory requirements.

[0020] As a preferred technical means: the power flow calculation in step 2) specifically includes:

[0021] (a) Input the initial system parameters, including line admittance, active and reactive power of the renewable energy station as the PQ node, and voltage amplitude and phase of the balancing node;

[0022] (b) Iterative calculation of active power error and reactive power error And solve the correction of voltage amplitude and phase angle through Jacobian matrix;

[0023] (c) When the active power error and reactive power error When the voltage amplitude of each node is less than the preset threshold, the output and phase , and substitute into the node voltage equation to calculate the current vector ;

[0024] (d) Calculate the current of non-port nodes , which can be achieved by any of the following methods:

[0025] ⅰ) Substitute the node voltage obtained from the power flow calculation into the block node voltage equation , directly solve ;

[0026] ii) According to the node active power P, reactive power Q and voltage U in the power flow results, the formula Calculate node current ; In the formula, the symbol is the conjugate operator, I is the node current, P is the node active power, Q is the node reactive power, U is the node voltage, and i=m+1,m+2,…,n is the corresponding node number.

[0027] Engineering-grade accuracy of voltage, phase, and current parameters is ensured through parameter input, Newton-Raphson method iteration, error control, and seamless connection of current vectors. The Jacobian matrix and error criterion design optimizes convergence speed and robustness, providing seamless input data for subsequent equivalent steps.

[0028] Method 1: The node voltages obtained by Newton-Raphson method power flow calculation are 、 Directly substitute the block node voltage equation to quickly solve it , no additional power data conversion is required, repeated calculations are avoided, and the calculation efficiency is significantly improved. Based on the linear equation solution of the admittance matrix Y, the algorithm is mature and has good convergence. It is especially suitable for large-scale power grids with a large number of non-port nodes, avoiding the divergence problem that may be caused by nonlinear iteration. Directly reuse the voltage parameters in the power flow calculation results to ensure It is strictly consistent with the real-time operating status of the system and is suitable for online dynamic equivalent scenarios.

[0029] Method II: When external grid parameters (such as branch admittance) are incomplete or measurement noise exists, node measurement data can be directly used through the formula: calculate , reducing the dependence on the integrity of the admittance matrix, and is suitable for equivalent scenarios where parameters are missing or measurement-driven. P and Q are updated through real-time measurement This method can capture dynamic characteristics such as wind and solar power fluctuations and time-varying loads, overcoming the limitation of traditional non-topological methods that require a static external grid. It avoids complex block matrix operations and only requires basic complex algebraic operations to complete current calculations, simplifying algorithm implementation and making it suitable for embedded devices or edge computing nodes.

[0030] Method I is suitable for scenarios where parameters are complete and efficient calculations are required; Method II is suitable for scenarios where there is abundant measurement data and dynamic tracking of operating status is required. The combination of the two expands the scope of application of the technical solution. In actual projects where external grid parameters and measurement data are mixed, cross-validation (such as comparing the results of the two methods) can be used to improve the accuracy of the proposed method. Method I continues the classic admittance matrix modeling approach and is compatible with existing simulation platforms. Method II is adapted to measurement systems centered around PMUs (synchronized phasor measurement units) and supports the high-frequency data assimilation needs of power systems.

[0031] As a preferred technical means: the specific method of the matrix transformation in step 3) is:

[0032] First, by the formula Eliminate node voltage at non-new energy stations , after substituting into the original node voltage equation, we get the simplified equation:

[0033]

[0034] Then, the following two branches are used to Perform different combination transformations:

[0035] Branch 1:

[0036]

[0037]

[0038]

[0039] Branch 2:

[0040]

[0041]

[0042]

[0043] in, is the equivalent admittance matrix containing the tie line admittance information;

[0044] Next, take the equivalent equilibrium node voltage E and the corresponding admittance parameter , and finally get the equivalent model equation: .

[0045] By formula Eliminate node voltage at non-new energy stations , reducing the original high-dimensional node voltage equation to a simplified equation containing only the new energy station nodes. Eliminating (nm) non-new energy node variables significantly reduces the equation dimension and reduces the subsequent computational effort.

[0046] Equivalued admittance matrix Completely preserve the admittance of the interconnection lines between new energy stations and the equivalent interaction admittance of the external power grid ( This avoids the loss of tie-line admittance caused by directly eliminating nodes in traditional methods (such as the Ward equivalence method), ensuring that the equivalent model is consistent with the original system topology. By retaining key admittance parameters, the equivalent model accurately represents the power interaction between renewable energy stations and the electrical impact of the external grid.

[0047] By extracting the equivalent equilibrium node voltage E and admittance parameters , overcome the defect of the Ward equivalent method that ignores the voltage support of the external power grid, and improve the accuracy of the equivalent model in reactive power-voltage analysis. Based on the fixed admittance matrix generation, the limitation of the REI equivalent method that the parameters fluctuate with the external network state is avoided.

[0048] Through two branching methods Perform combined transformation and finally extract the equivalent equilibrium node voltage E and admittance parameters ,Branch 1 separates the equivalent current term X of the external grid, intuitively reflects the current contribution of the external grid, and facilitates the analysis of the equivalent current contribution of the external grid. Branch 2: Directly generate through admittance matrix operation , simplify the parameter extraction process, reduce intermediate variables, and improve calculation efficiency. Both branches are simplified , ensuring interface standardization.

[0049] As a preferred technical means: the equivalent equilibrium node voltage E is obtained by the formula Calculate, where , is the equivalent admittance matrix The element in row k and column p of ; is the kth element of the equivalent current term X of the external power grid obtained by power flow calculation; through the above calculation, The error between the amplitude of the voltage and the voltage amplitude of the node of the new energy station does not exceed the preset threshold; then the average values ​​of the module values ​​of each element in the equivalent balanced node voltage E obtained by the two branches are compared, and a group of branch results close to 1 are selected as the output results.

[0050] It is the sum of the admittance of the new energy station nodes, reflecting the admittance contribution between stations. E is obtained by normalizing the equivalent current term of the external grid. , directly represents the voltage support effect of the external power grid on the new energy station. For current terms Normalization is performed to ensure that the magnitude of E is close to the actual voltage magnitude at the nodes of renewable energy stations. This magnitude of E is close to the actual voltage magnitude at renewable energy stations, avoiding model distortion caused by neglecting voltage support in traditional methods (such as the Ward equivalence method). Based on fixed admittance matrix The columns and calculations are based on the dynamic external grid state parameters. It is a static parameter and does not change with the external grid operation state, ensuring that the generation process of E is not affected by external grid fluctuations. Compared with the REI equivalent method, it avoids the problem of equivalent admittance fluctuating with external grid power, improving the long-term applicability of the model. The formula only requires the admittance matrix The column sum calculation is performed without complex iteration or matrix decomposition. Compared with the method that requires dynamic update of admittance parameters (such as REI equivalent method), the calculation amount of this formula is significantly reduced, which is suitable for real-time or large-scale system analysis. The model accurately reflects the electrical interaction characteristics between renewable energy stations and is suitable for multi-station grid-connected scenarios, ensuring the accuracy of the equivalent model at high penetration rates. Multi-path verification reduces computational errors and numerical instability that may exist with a single method. The rationality of the model output is ensured by using a voltage modulus close to 1 as a benchmark (the ideal voltage amplitude in a per-unit system).

[0051] Another technical solution of the present invention is: a structure-maintained multi-station off-site power grid equivalent system, the system comprising:

[0052] The block module is used to block and number the new energy station nodes and other nodes in the network according to the topological structure of the multi-station power system to generate a block admittance matrix;

[0053] A power flow calculation module, based on the block admittance matrix, uses the Newton-Raphson method to perform system power flow calculation to obtain the voltage vector and current vector of each new energy station node;

[0054] The matrix transformation module uses the Kron order reduction method to perform matrix transformation on the node voltage equation. By eliminating the variables corresponding to the non-new energy station nodes, the equivalent admittance matrix and the equivalent balanced node voltage are obtained. The equivalent admittance matrix retains the tie line admittance information between the new energy stations.

[0055] The equivalent model construction module constructs a structure-preserving external power grid equivalent model based on the equivalent admittance matrix and the equivalent balanced node voltage, and retains the original topological structure information between the new energy stations.

[0056] The block module generates a structured admittance matrix, and the matrix transformation module eliminates redundant variables based on Kron reduction. The two work together to reduce the computational dimension. The matrix transformation module preserves the tie line admittance ( ) and the equivalent equilibrium node voltage (E), the equivalent model construction module maintains the original topology structure, avoids the structural distortion problem of the traditional equivalent method, and accurately characterizes the electrical interaction between new energy sites and the support role of the external power grid.

[0057] As a preferred technical means: in the block module, the nodes of the new energy station are numbered as the first m nodes, and the remaining nodes are numbered as the last nm nodes, where n is the total number of nodes and m is the number of nodes of the new energy station; the block module includes:

[0058] New energy station node admittance sub-matrix generation unit, generating m×m order matrix ;

[0059] Mutual admittance matrix generation unit, generating the mutual admittance matrix between the new energy station and other nodes and ;

[0060] Other inter-node admittance sub-matrix generation units generate (nm)×(nm) order matrices ; The form of the block admittance matrix is:

[0061] .

[0062] As a preferred technical means: the power flow calculation module includes: (a) a parameter input interface for receiving the initial system parameters, including line admittance, active and reactive power of the new energy station as a PQ node, and voltage amplitude and phase of the balancing node; (b) an iterative calculation unit for iteratively calculating the active power error based on the input parameters and reactive power error , and solve the voltage amplitude and phase angle correction through the Jacobian matrix; (c) Error judgment unit, when max(| ∣,∣Δ ∣)< When the voltage amplitude of each node is output and phase , is the preset error threshold;

[0063] (d) Current calculation unit, including a first current calculation submodule and a second current calculation submodule. The first current calculation submodule substitutes the voltage amplitude and phase into the node voltage equation to calculate the current vector The second current calculation submodule is used to calculate the node active power P, reactive power Q and voltage U according to the flow results, through the formula Calculate node current ; In the formula, the symbol is the conjugate operator, I is the node current, P is the node active power, Q is the node reactive power, U is the node voltage, and i=m+1,m+2,…,n is the corresponding node number.

[0064] As a preferred technical means: the matrix transformation module includes:

[0065] The voltage elimination unit is calculated by the formula Eliminate node voltage at non-new energy stations ;

[0066] The equation simplification unit substitutes the eliminated result into the original node voltage equation to generate a simplified equation:

[0067] Branch 1:

[0068]

[0069] Branch 2:

[0070]

[0071] Equivalent parameter extraction unit, extracting equivalent equilibrium node voltage E and admittance parameters from simplified equations , generating the equivalent model equation: ;in, is the equivalent admittance matrix that preserves the tie line admittance.

[0072] As a preferred technical means: in the equivalent parameter extraction unit, the calculation module of the equivalent equilibrium node voltage E is calculated by the formula: Calculate, where , is the equivalent admittance matrix The element in row k and column p of ; is the kth element of the equivalent current term X of the external power grid obtained by power flow calculation; through the above calculation, The error between the amplitude and the voltage amplitude of the new energy station node does not exceed the preset threshold; finally, the average values ​​of the module values ​​of each element in the equivalent balanced node voltage E obtained by the two branches are compared, and a group of branch results close to 1 are selected as the output results.

[0073] Beneficial effects:

[0074] This technical solution maintains the topology and admittance relationship of the original system while simplifying the model through block admittance matrix construction, Kron matrix reduction transformation and tie line admittance preservation technology.

[0075] This technical solution retains the admittance through block numbering and matrix transformation, ensuring that the equivalent model is consistent with the original system topology; and avoids the dynamic response error caused by the replacement of equivalent generators in the simple equivalent machine method.

[0076] This technical solution accurately characterizes the electrical interaction between the external power grid and the internal network by extracting the equivalent balance node voltage; by extracting the equivalent balance node voltage, it overcomes the limitation of the Ward equivalent method that ignores voltage support.

[0077] This technical solution generates equivalent parameters based on power flow calculation and a fixed admittance matrix to improve the robustness of the model. Compared with the REI equivalent method, the fixed admittance matrix design makes the equivalent parameters unaffected by fluctuations in the external network state. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 This is a schematic diagram of a multi-machine grid-connected system.

[0079] Figure 2 It is a flow chart of the present invention.

[0080] Figure 3 This is a topology diagram of a 3-machine 9-node system used in an embodiment of the present invention. DETAILED DESCRIPTION

[0081] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings.

[0082] Example 1:

[0083] like Figure 2As shown, the present invention includes the following steps:

[0084] S1: According to the topological structure of the multi-station power system, the new energy station nodes and other nodes in the network are numbered in blocks to form a block admittance matrix;

[0085] like Figure 1 The figure shows a schematic diagram of a new energy multi-station grid-connected system, which includes a local AC network and nodes for integrating new energy power generation stations. The AC network contains loads, interconnection nodes, and other possible synchronous generators. First, the system nodes are numbered according to the research object. Assuming that there are n nodes in the system and m new energy stations, the nodes of the new energy stations are numbered as , number the remaining nodes as The system admittance matrix is ​​formed as follows:

[0086] (1)

[0087] Where, is the admittance value between corresponding nodes, When , it represents the mutual admittance between nodes; When , it indicates the self-admittance of the node.

[0088] At the same time, the corresponding conductance and susceptance values ​​between nodes are obtained according to the model parameters, and the following equations are given:

[0089]

[0090] (2)

[0091] Where, represents the corresponding conductance value, represents the corresponding susceptance value, means taking the real part of the corresponding number, It means taking the imaginary part of the corresponding number.

[0092] The node voltage equation of the multi-station system is further constructed as shown in equation (2).

[0093] (3)

[0094] In the formula, for the current matrix I and voltage matrix U, the subscript S represents the new energy station node, and the subscript L represents other nodes in the network, such as load nodes, contact nodes, etc. Etc. is the block matrix composed of the elements at the corresponding positions of the system's total admittance matrix Y. The order of each matrix is ​​determined by the number of nodes of each type.

[0095] S2: Based on the block admittance matrix, the Newton-Raphson method is used to calculate the system power flow to obtain the voltage vector and current vector of each new energy station node;

[0096] According to the corresponding system structure, system parameters such as admittance value and power value of each node are input into the power flow calculation program, and the Newton-Raphson method is used to solve the system power flow. The power flow calculation method is as follows.

[0097] (1) Input the initial system data, such as the admittance values ​​of each line, the active and reactive powers given by each load point and the new energy station as the PQ node, and the voltage amplitude and phase given by the balancing node. Set the number of iterations l = 0.

[0098] (2) Using the given system parameter values ​​and other initial values, calculate the active power error using formula (4): and reactive power Error. Determine whether the maximum error is less than the allowable value. If it is satisfied, go to step (6) to output the voltage of each node. If not, go to step (3).

[0099]

[0100] (4)

[0101] Where i and j represent node numbers, is the active power of each node, is the reactive power of each node, is the voltage phase of each node, is the phase angle difference between nodes i and j, and n is the total number of nodes in the system.

[0102] (3) Substitute the values ​​of each parameter and calculate the values ​​of each element of the Jacobian matrix J using equations (6) and (7) to form the Jacobian matrix.

[0103] (5)

[0104] Where H, N, M, and L are the sub-matrix blocks that constitute the Jacobian matrix.

[0105] 1) When When , the calculation method of each element is as follows:

[0106]

[0107]

[0108]

[0109] (6)

[0110] 2) When , the calculation method of each element is as follows:

[0111]

[0112]

[0113]

[0114] (7)

[0115] (4) Apply equation (8) to solve the correction equation and obtain the correction values ​​of voltage amplitude and phase angle.

[0116] (8)

[0117] (5) Calculate the corresponding corrected parameter value as shown in formula (9), that is, the new initial value, and set the number of iterations to be 1, and return to step (2) to continue execution.

[0118]

[0119] (9)

[0120] (6) Output calculation results .

[0121] The Newton-Raphson method is used to solve the system power flow and obtain the voltage amplitude of each node And the voltage phase of each node , thus forming the voltage of each node .

[0122] Calculate the current based on the system power flow results , for application in the following equivalent simplification steps of the present invention. The present invention provides the required current obtained by flow calculation There are two methods.

[0123] Method 1:

[0124] According to the voltage amplitude of each node And the voltage phase of each node , thus forming the voltage of each node .

[0125] Substituting the obtained voltage values ​​of each node into formula (3), the current can be obtained , for application in the following equivalent simplified steps of the present invention.

[0126] Method 2:

[0127] The Newton-Raphson method is used to solve the system power flow, which is the same as the method 1, and the voltage of each node is obtained And the active power P and reactive power Q of each node. Then the current is calculated as follows:

[0128] (10)

[0129] In the formula, the symbol is the conjugate operator, I is the node current, P is the node active power, Q is the node reactive power, U is the node voltage, and i=m+1,m+2,…,n is the corresponding node number.

[0130] S3: Using the Kron order reduction method to perform matrix transformation on the node voltage equation, by eliminating the variables corresponding to the non-new energy station nodes, an equivalent admittance matrix and an equivalent balanced node voltage are obtained, wherein the equivalent admittance matrix retains the tie line admittance between the new energy stations;

[0131] From the perspective of each new energy station, the external power grid is equivalent. According to the Kron order reduction method, the original system node voltage equation is processed. First, Make the following changes:

[0132] (11)

[0133] Substitute equation (10) into equation (3) and eliminate ,have to:

[0134] (12)

[0135] Then, the following two branches are used to Perform different combination transformations:

[0136] Branch 1:

[0137]

[0138] (13)

[0139] make:

[0140]

[0141] (14)

[0142] Branch 2:

[0143]

[0144] (15)

[0145] make:

[0146]

[0147] (16)

[0148] Through this method, The original information of the admittance part of the tie line between stations is retained, which has certain structural preservation characteristics. In addition, each matrix is ​​further processed and X is equivalently transformed into The equivalent balance nodes of the system are extracted in the form of , and E is the voltage matrix composed of the balance nodes. The calculation method of each element is described as follows.

[0149] Assumption Matrix for According to the characteristics of self-admittance and mutual-admittance in the total admittance matrix of the system, The elements are:

[0150] (17)

[0151] In the formula, k and p both indicate the position of the element in the matrix.

[0152] The voltage of each equilibrium node is:

[0153] (18)

[0154] Finally, the node voltage equation of the equivalent simplified system model is obtained as follows:

[0155] (19)

[0156] Thus, the system admittance matrix after equivalent simplification can be output 、 As well as the extracted equivalent equilibrium node voltage E, the equivalence of multi-station off-grid power grid considering structural preservation is realized.

[0157] S4: Based on the equivalent admittance matrix and the equivalent balanced node voltage, an equivalent model of the external power grid with structure preservation is constructed, and the original topology structure between the new energy stations is retained.

[0158] This method realizes the equivalence of the external power grid viewed from multiple renewable energy stations, providing a new and reliable method for the equivalence of the external power grid of the power system.

[0159] Specific implementation examples

[0160] The specific example of the present invention uses a 3-machine 9-node system for corresponding explanation. The system nodes are numbered, and the 3 motor nodes are used as new energy stations and are numbered as nodes 1, 2, and 3. The remaining nodes are numbered in sequence. After the numbering is completed, the system topology diagram is as follows Figure 3 As shown in Figure 3 The initial parameters of each power station are shown in Table 1.

[0161] Table 1 Initial parameters of each power station

[0162]

[0163] The total admittance matrix Y of the system can be obtained from the parameters of the 3-machine 9-node system. It is divided into blocks according to the number of nodes of each type to obtain each block matrix. The system power flow is solved using the Newton-Raphson method according to the system parameters to obtain the voltage vector of each node, which is further solved by the method described in step 2. The results are shown in Table 2.

[0164] Table 2 Current value of each node in

[0165]

[0166] Then perform system equivalent simplification. By changing the matrix and comparing the two branch results, the output As shown in formula (20). (20)

[0167] From formula (17), we get the matrix for:

[0168] (twenty one)

[0169] The corresponding output voltage value is further calculated from equation (18) as equation (22). The amplitudes of the elements in E are: 1.1764, 1.1796, and 1.1545.

[0170] (twenty two)

[0171] This achieves a structure-preserving multi-station external power grid equivalence, retains the original interconnection admittance between stations, and outputs the admittance between the balancing nodes. As well as the balanced node voltage E, the amplitude of each element in E is close to 1, which verifies the effectiveness of the method of the present invention.

[0172] Example 2:

[0173] A structure-maintained multi-station off-site power grid equivalent system, the system comprising:

[0174] The block module is used to block and number the new energy station nodes and other nodes in the network according to the topological structure of the multi-station power system to generate a block admittance matrix;

[0175] A power flow calculation module, based on the block admittance matrix, uses the Newton-Raphson method to perform system power flow calculation to obtain the voltage vector and current vector of each new energy station node;

[0176] The matrix transformation module uses the Kron order reduction method to perform matrix transformation on the node voltage equation. By eliminating the variables corresponding to the non-new energy station nodes, the equivalent admittance matrix and the equivalent balanced node voltage are obtained. The equivalent admittance matrix retains the tie line admittance information between the new energy stations.

[0177] The equivalent model construction module constructs a structure-preserving external power grid equivalent model based on the equivalent admittance matrix and the equivalent balanced node voltage, and retains the original topology structure between the new energy stations.

[0178] The block module generates a structured admittance matrix, and the matrix transformation module eliminates redundant variables based on Kron reduction. The two work together to reduce the computational dimension. The matrix transformation module preserves the tie line admittance ( ) information and the equivalent equilibrium node voltage (E), the equivalent model construction module maintains the original topology structure, avoids the structural distortion problem of the traditional equivalent method, and accurately characterizes the electrical interaction between new energy sites and the support role of the external power grid.

[0179] The specific functions of each module correspond to the aforementioned method and will not be repeated here.

[0180] The above-mentioned method and system for maintaining the equivalence of multiple off-site power grids with a structure is a specific embodiment of the present invention, which has embodied the substantial characteristics and progress of the present invention. According to actual use needs and under the guidance of the present invention, equivalent modifications in shape, structure, etc. can be made to the system, which are all within the scope of protection of this scheme.

Claims

1. A method for equivalence of multi-station off-site power grids with structure preservation, characterized in that: The following steps are involved: 1) According to the topological structure of the multi-station power system, the new energy station nodes and other nodes in the network are numbered in blocks to form a block admittance matrix; 2) Based on the block admittance matrix, the Newton-Raphson method is used to calculate the system power flow to obtain the voltage vector and current vector of each renewable energy station node; 3) Using the Kron order reduction method to perform matrix transformation on the node voltage equation, by eliminating the variables corresponding to the non-new energy station nodes, an equivalent admittance matrix and equivalent balanced node voltage are obtained. The equivalent admittance matrix retains the admittance information of the tie lines between the new energy stations; 4) Output the equivalent system node admittance matrix YS and equivalent equilibrium node voltage E. Based on the equivalent admittance matrix and equivalent equilibrium node voltage, construct a structure-preserving external power grid equivalent model, retaining the original topology information between the new energy stations; The specific method of the matrix transformation in step 3) is: First, by the formula Eliminate node voltage at non-new energy stations , after substituting into the original node voltage equation, we get the simplified equation: in: is the admittance matrix between nodes of new energy stations, and is the mutual admittance matrix between the new energy station and other nodes, is the admittance matrix between other nodes ; New energy station node voltage; New energy station node current; Node current of non-new energy stations; Then, the following two branches are used to Perform different combination transformations: Branch 1: in: ; ; Branch 2: in: ; ; and is the equivalent admittance matrix containing the tie line admittance information; Next, extract the equivalent equilibrium node voltage E and the corresponding admittance parameter , and finally get the equivalent model equation: or .

2. The method for equivalence of multiple off-site power grids with structure preservation according to claim 1 is characterized in that: In step 1), the nodes of the new energy station are numbered as the first m nodes, and the remaining nodes are numbered as the last nm nodes, where n is the total number of nodes and m is the number of nodes of the new energy station; the method for constructing the block admittance matrix is: The block admittance matrix includes the admittance sub-matrix between nodes of the new energy station , mutual admittance matrix between new energy stations and other nodes and , and other inter-node admittance submatrices , which has the form: in, is an m×m matrix, It is a (nm)×(nm)-order matrix; the subscript S represents the new energy station node, and the subscript L represents other nodes in the network.

3. The method for equivalence of multiple off-site power grids with structure preservation according to claim 2 is characterized in that: The power flow calculation in step 2) specifically includes: (a) Input the initial system parameters, including line admittance, active and reactive power of the renewable energy station as the PQ node, and voltage amplitude and phase of the balancing node; (b) Iterative calculation of active power error and reactive power error And solve the correction of voltage amplitude and phase angle through Jacobian matrix; (c) When the active power error and reactive power error When the voltage amplitude of each node is less than the preset threshold, the output and phase ; (d) Calculate the current of non-port nodes , achieved by any of the following methods: ⅰ) Substitute the node voltage obtained from the power flow calculation into the block node voltage equation , directly solve ; ii) According to the node active power P, reactive power Q and voltage U in the power flow results, the formula Calculate node current ; In the formula, the symbol is the conjugate operator, I is the node current, P is the node active power, Q is the node reactive power, U is the node voltage, and i=m+1,m+2,…,n is the corresponding node number.

4. The method for equivalence of multiple off-site power grids with structure preservation according to claim 3 is characterized in that: The equivalent equilibrium node voltage E is expressed by the formula Calculate, where , is the equivalent admittance matrix The element in row k and column p of ; is the kth element of the equivalent current term X of the external power grid obtained by power flow calculation; through the above calculation, The error between the amplitude of the voltage and the voltage amplitude of the node of the new energy station does not exceed the preset threshold; Then, the average values ​​of the module values ​​of each element in the equivalent equilibrium node voltage E obtained from the two branches are compared, and a group of branch results close to 1 are selected as the output results.

5. A structure-maintained multi-station off-site power grid equivalent system using the structure-maintained multi-station off-site power grid equivalent method according to claim 1, characterized in that: include: The block module is used to block and number the new energy station nodes and other nodes in the network according to the topological structure of the multi-station power system to generate a block admittance matrix; A power flow calculation module, based on the block admittance matrix, uses the Newton-Raphson method to perform system power flow calculation to obtain the voltage vector and current vector of each new energy station node; The matrix transformation module uses the Kron order reduction method to perform matrix transformation on the node voltage equation. By eliminating the variables corresponding to the non-new energy station nodes, the equivalent admittance matrix and the equivalent balanced node voltage are obtained. The equivalent admittance matrix retains the tie line admittance between the new energy stations. The equivalent model construction module constructs a structure-preserving external power grid equivalent model based on the equivalent admittance matrix and the equivalent balanced node voltage, and retains the original topology structure between the new energy stations.

6. The structure-maintained multi-station off-site power grid equivalent system according to claim 5, characterized in that: In the block module, the nodes of the new energy station are numbered as the first m nodes, and the remaining nodes are numbered as the last nm nodes, where n is the total number of nodes and m is the number of nodes of the new energy station; the block module includes: New energy station node admittance sub-matrix generation unit, generating m×m order matrix ; Mutual admittance matrix generation unit, generating the mutual admittance matrix between the new energy station and other nodes and ; Other inter-node admittance sub-matrix generation units generate (nm)×(nm) order matrices ; The form of the block admittance matrix is: 。 7. The structure-maintained multi-station off-site power grid equivalent system according to claim 6, characterized in that: The power flow calculation module includes: Parameter input interface, used to receive initial system parameters, including line admittance, active and reactive power of new energy stations as PQ nodes, and voltage amplitude and phase of balancing nodes; Iterative calculation unit, iteratively calculates the active power error based on the input parameters and reactive power error And solve the correction of voltage amplitude and phase angle through Jacobian matrix; Error judgment unit, when max(| ∣,∣ ∣)< When the voltage amplitude of each node is output and phase , is the preset error threshold; The current calculation unit includes a first current calculation submodule and a second current calculation submodule. The first current calculation submodule substitutes the voltage amplitude and phase into the node voltage equation to calculate the current vector The second current calculation submodule is used to calculate the node active power P, reactive power Q and voltage U according to the flow results through the formula Calculate node current ; In the formula, the symbol is the conjugate operator, I is the node current, P is the node active power, Q is the node reactive power, U is the node voltage, and i=m+1,m+2,…,n is the corresponding node number.

8. The structure-maintained multi-station off-site power grid equivalent system according to claim 7, characterized in that: The matrix transformation module includes: The voltage elimination unit is calculated by the formula Eliminate node voltage at non-new energy stations ; The equation simplification unit substitutes the eliminated result into the original node voltage equation to generate a simplified equation: Branch 1: Branch 2: Equivalent parameter extraction unit, extracting equivalent equilibrium node voltage E and admittance parameters from simplified equations , generating the equivalent model equation: in, is the equivalent admittance matrix that preserves the tie line admittance.

9. The structure-maintained multi-station off-site power grid equivalent system according to claim 8, characterized in that: In the equivalent parameter extraction unit, the calculation module of the equivalent equilibrium node voltage E is calculated by the formula: Calculate, where , is the equivalent admittance matrix The element in row k and column p of ; is the kth element of the equivalent current term X of the external power grid obtained by power flow calculation; through the above calculation, The error between the amplitude and the voltage amplitude of the new energy station node does not exceed the preset threshold; finally, the average values ​​of the module values ​​of each element in the equivalent balanced node voltage E obtained by the two branches are compared, and a group of branch results close to 1 are selected as the output results.

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