An equivalent aggregation method applicable to networks containing new energy sources
By establishing an equivalent aggregation model, the topology of the new energy network is simplified, which solves the problems of long calculation time and non-convergence in traditional methods, improves the speed and accuracy of short-circuit current calculation, and is applicable to distribution networks containing new energy power sources.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-16
- Publication Date
- 2026-04-03
AI Technical Summary
Traditional global iterative methods are time-consuming and prone to non-convergence in distribution networks with a high proportion of renewable energy sources. Furthermore, the calculation results contain a large amount of useless information, making it difficult to effectively simplify the network topology and improve the speed of short-circuit current calculation.
By establishing an equivalent aggregation model for a network containing new energy sources, the network topology is simplified, the number of new energy coupling nodes is reduced, and the influence of new energy sources and network topology parameters on short-circuit current is utilized to establish an equivalent aggregation model, thereby simplifying the network structure and improving computational efficiency.
This approach simplifies network topology in networks containing new energy sources, reduces iterative computation time, improves the speed and accuracy of short-circuit current calculation, avoids the problem of iteration non-convergence, and enhances the reliability and efficiency of computation.
Smart Images
Figure CN115221661B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of new energy power technology, and in particular to an equivalent aggregation method applicable to networks containing new energy sources. Background Technology
[0002] For distribution networks with a high proportion of renewable energy sources, the network topology is often radial. Renewable energy sources exhibit characteristics of small grid-connected capacity but numerous grid-connected points. Using traditional global iterative methods for short-circuit current analysis results in an exceptionally large dimension of the node admittance matrix used in the iterative calculation, leading to long iteration times and a high risk of convergence issues. Furthermore, while traditional methods can obtain fault information for the entire network, fault analysis focuses primarily on the magnitude of the short-circuit current on the faulty main line. Since the current in most branch lines is mainly from renewable energy sources, its value is relatively small and generally does not affect branch line protection; therefore, the value of its short-circuit current is not considered, resulting in excessive and useless information in the calculations.
[0003] With the rapid increase in the proportion of new energy power sources connected to the grid, the global iterative method for calculating the short-circuit current of new energy sources has problems such as long processing time and poor convergence. There is an urgent need to study an equivalent aggregation method for new energy networks that can simplify the network topology and improve the calculation speed of short-circuit current. Summary of the Invention
[0004] The purpose of this invention is to provide an equivalent aggregation method applicable to networks containing new energy sources. This method establishes an equivalent aggregation model of the network containing new energy sources based on the influence of new energy sources and network topology parameters on short-circuit current. This simplifies the network topology and reduces the number of new energy coupling nodes, avoiding the problems of long computation time and non-convergence caused by iterative calculation of the entire new energy network.
[0005] The objective of this invention is achieved through the following technical solution:
[0006] An equivalent aggregation method applicable to networks containing new energy sources, the method comprising:
[0007] Step 1: Preprocess the network topology and parameter information of the new energy network;
[0008] Step 2: When the short-circuit current of the network containing new energy sources is a linear function of the voltage, analyze the influence of the topology parameter information in Step 1 on the short-circuit current and establish an equivalent aggregation model of the network containing new energy sources.
[0009] Step 3: Based on the type of new energy source and combined with the practical expression of the short-circuit current of actual new energy sources, obtain the corresponding equivalent aggregation model.
[0010] As can be seen from the technical solution provided by the present invention, the above method establishes an equivalent aggregation model of a network containing new energy sources based on the influence of new energy sources and network topology parameters on short-circuit current, which simplifies the network topology and reduces the coupling nodes of new energy sources, avoiding the problems of long computation time and non-convergence caused by iterative calculation of the entire new energy network. Attached Figure Description
[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0012] Figure 1 This is a schematic diagram of the equivalent aggregation method applicable to networks containing new energy sources, provided in an embodiment of the present invention.
[0013] Figure 2 This is a schematic diagram of a network containing new energy power sources according to an embodiment of the present invention;
[0014] Figure 3 This is a schematic diagram of the structure of the 69-node network containing new energy sources constructed according to an embodiment of the present invention;
[0015] Figure 4 This is a comparison chart of the equivalent aggregation model curves of the partial power inverter-type new energy lines 8-41-46 in the embodiments of the present invention;
[0016] Figure 5 This is a comparison chart of the equivalent aggregation model curves of the full-power inverter-type new energy line 6-27-34 in the embodiments of the present invention. Detailed Implementation
[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, and do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.
[0018] like Figure 1 The diagram shown is a schematic flowchart of an equivalent aggregation method applicable to networks containing new energy sources, provided by an embodiment of the present invention. The method includes:
[0019] Step 1: Preprocess the network topology and parameter information of the new energy network;
[0020] In this step, the preprocessing operation includes node numbering and load processing; the information required for the equivalent network includes network topology, line and transformer impedance, transformer turns ratio, load capacity and location, renewable energy capacity and location, and the functional relationship between renewable energy power supply port voltage and current.
[0021] Regarding node numbering, the equivalent radial network consists of a first node and n other nodes, for a total of n+1 nodes. Among these n nodes, the one with the shortest path distance to the first node is node 1, followed by nodes 2, 3, ..., with the nth node being the last node on the path. See the example below for details. Figure 2 ;
[0022] The load processing is in the form of constant impedance, as detailed in equation (1) below;
[0023] Figure 2 The diagram shown is a network diagram containing new energy power sources according to an embodiment of the present invention. It is assumed that node A is the main line node of the network containing new energy sources, i.e., the first node. The line impedance between node 1 and node A is Z1, the line impedance between node 1 and node 2 is Z2, and node 1 and node 2 are respectively connected to new energy power sources.
[0024] When a fault occurs outside the line, the main line node A, branch line nodes 1 and 2 can be equivalent to a new energy node, simplifying the network topology;
[0025] For the new energy power sources connected to nodes 1 and 2, they are equivalent to voltage-controlled current sources, and the functional relationship between their port voltage and current is expressed as follows: Figure 2 In this context, 'f' indicates that the voltage-current functional relationship differs for different types of new energy power sources. The loads connected to nodes 1 and 2 are treated as equivalent to a constant impedance model in short-circuit current calculations, i.e.:
[0026]
[0027] In the formula, U N The node line voltage rating; S L Z represents the load capacity. L The equivalent impedance of the load is given by the subscript i, which represents the i-th node.
[0028] Step 2: When the short-circuit current of the network containing new energy sources is a linear function of the voltage, analyze the influence of the topology parameter information from Step 1 on the short-circuit current and establish an equivalent aggregation model of the network containing new energy sources.
[0029] In this step, according to the example Figure 2 Assuming node A is the backbone node of the renewable energy network, and nodes 1 and 2 are branch lines connected to node A, when the short-circuit current of the renewable energy network is a linear function of its node voltage, i.e., it satisfies:
[0030]
[0031] In the formula, I represents the current flowing into the grid from the new energy source; U represents the port voltage to which the new energy source is connected; subscripts 1 and 2 indicate node positions; k1, k2, b1, and b2 are all constants, whose values are provided by the new energy power station.
[0032] According to circuit theory, the following expression can be obtained:
[0033]
[0034] In the formula, I i ' represents the current injected from node i into bus A, where i = 1, 2;
[0035] Combining (d) to (f) in equation (3), we can obtain:
[0036]
[0037] In the formula, given a fixed network, i.e., k2, Z2, Z... L2 If k2' and b2' are both known, then k2' and b2' are both constants.
[0038] Combining (a) to (c) in equation (3) and substituting (4) into it, we can obtain:
[0039]
[0040] In the formula, U A The voltage at the first node of the equivalent circuit;
[0041] Similarly, k1' and b1' are constants in the formula, and they have a recursive relationship with k2' and b2';
[0042] Following this logic, we can obtain the recursive formula for an n+1 node network containing new energy sources, consisting of the first node A and 1 to n other nodes:
[0043]
[0044] In the formula, I i 'Indicates that node i injects current into bus A;
[0045] As shown in equation (6), k i 'and b i Both can be obtained from the information of the i-th and (i+1)-th nodes, and are constants; the recursive order is from the n-th node to the 1-th node, finally obtaining the equivalent line injected short-circuit current to the first node, i.e., node A; since the (n+1)-th node does not exist, let k' n+1 =b' n+1If the expression is 0, then the recurrence relation is still satisfied; the first node is node A, therefore U0 = U A ;
[0046] Through recursion, the equivalent current injected into the first node (i.e., the external network) by the equivalent circuit is finally obtained as:
[0047]
[0048] Step 3: Based on the type of new energy source and combined with the practical expression of the short-circuit current of actual new energy sources, obtain the corresponding equivalent aggregation model.
[0049] In this step, the practical expression of the actual new energy short-circuit current is divided into multiple stages according to the different degrees of voltage drop at the grid connection point. The expressions for different stages are different, so it is necessary to explore the boundaries of different stages in the equivalent aggregation model.
[0050] In practice, the functional relationship between the current and voltage at the new energy port, i.e., the voltage-current mapping relationship of the new energy source, is a piecewise linear function. When there are two stages, its expression is:
[0051]
[0052] In the formula, U (1,2) These are the segmented critical voltage values, which are provided by the new energy power plants.
[0053] Step 2 solves the functional relationship between the equivalent current injected by the equivalent line and the voltage of the first node of the equivalent line, i.e., the equivalent aggregation model expression. However, Step 2 assumes that the functional relationship between the port voltage and current of the new energy power source is not piecewise, as shown in Equation (2). When the voltage-current mapping relationship of the new energy is a piecewise linear function as shown in Equation (8), the expression of the equivalent current and the voltage of the first node is also a piecewise function. Therefore, the piecewise critical voltage value in the equivalent aggregation model is obtained below.
[0054] The renewable energy capacity varies at different nodes. When considering capacity, the voltage-current mapping relationship of renewable energy at node m, m∈[1,n] can be obtained as follows:
[0055]
[0056] In the formula, S m The capacity of the new energy source connected to node m;
[0057] If there is l new energy sources on a line containing a new energy network, according to equation (8), the network containing new energy sources has l+1 states, as shown in Table 1:
[0058] Table 1 Summary of Network Status for Each New Energy Source
[0059]
[0060] Note: S in the table i (i = 1, 2, ..., l) represent l new energy sources, P1 represents the new energy node in stage I of the voltage-current mapping curve, and P2 represents the new energy node in stage II of the voltage-current mapping curve.
[0061] Considering that the voltage difference between the first and last nodes on the same line is not large, as the voltage increases, when a new energy source on the line transitions from the first stage to the second stage, the new energy sources at the remaining nodes (excluding the first and last nodes) will also transition to the second stage. To avoid overly complex models and facilitate engineering application, the intermediate processes are omitted, and only the scenario where all new energy nodes are in both the first and second stages is considered. The steps for determining the segmented critical voltage values in the equivalent aggregation model are as follows:
[0062] When all new energy nodes are in the first stage, the expression for the controlled current source in the equivalent aggregation model is:
[0063]
[0064] In the formula, I1 ’(1) U is the equivalent current injected into the first node (i.e., the external network) by the equivalent circuit when all new energy nodes are in the first stage, and U A k1 is the voltage at the first node of the equivalent line; ’(1) b1 ’(1) It can be obtained through step 2, equation (6);
[0065] When all new energy nodes are in the second stage, the expression for the controlled current source in the equivalent aggregation model is:
[0066]
[0067] In the formula, I1 ’(2) k1 represents the equivalent current injected into the first node (i.e., the external network) by the equivalent circuit when all new energy nodes are in the second stage; ’(2) b1 ’(2) It can be obtained through step 2, equation (6);
[0068] At this point, the segmented critical voltage value U of the first and second stages. A ’(1,2 for:
[0069]
[0070] Therefore, the equivalent aggregation model expression for a new energy network with a two-stage mapping relationship is as follows:
[0071]
[0072] In the formula, I A The equivalent current injected by the equivalent circuit into the first node, i.e., the external network;
[0073] Furthermore, when the expression for the new energy mapping relationship is multi-stage, the segmented critical voltage values of adjacent stages can be obtained using the above method.
[0074] The following example illustrates the implementation process and effects of the above method. This example demonstrates the construction of a 69-node system in PSCAD / EMTDC. Figure 3 The diagram shows the structure of a 69-node renewable energy network constructed according to an embodiment of the present invention. The system contains multiple renewable energy sources, each with a capacity of 0.5MW. Some system parameters are shown in Table 2.
[0075] Table 2 contains parameters of new energy power network systems.
[0076]
[0077] Note: The active and reactive power values in the table represent the load power connected to the end node of the line.
[0078] The practical short-circuit current expression for a partially power inverter power supply is:
[0079]
[0080] The practical short-circuit current expression for a full-power inverter power supply is:
[0081]
[0082] like Figure 3 As shown, we take the branch line 8-41-46, which is connected to a partial power inverter energy source, for analysis. Based on its line parameters and new energy and load data, according to equation (13), the equivalent aggregation model of this branch line can be obtained as follows:
[0083]
[0084] like Figure 4 The figure shown is a comparison of the equivalent aggregation model curves of the partial power inverter-type new energy lines 8-41-46 in the embodiments of the present invention, showing the current I under different voltage drop conditions. 8_NE Comparison between simulated values and calculated values from equivalent models Figure 4 In the simulation, the equivalent aggregation model value and the simulation value are basically consistent. The only difference between the two is at the boundary where the new energy sources are in different stages. As the grid connection voltage U8 increases, the simulated current changes from the point where all new energy sources are in the first stage (U8) to the point where the simulated current is in the first stage. slim ) to the point where all new energy sources are in the second stage (U8>U blim When calculating the equivalent line, there are still three transition stages, which are related to the number of new energy sources on the line. The number of transition stages is one less than the number of new energy sources. Since the proportion of intermediate transition stages is relatively small, and the number of transition stages is large when there are many new energy sources on the equivalent line, it is not conducive to practical application to consider all of them. Therefore, in the aggregated equivalent model, only all new energy sources are considered to be in the same stage. The critical voltage is calculated in this way. While ensuring the calculation accuracy, the number of segments in the equivalent aggregated model is reduced, so that it is consistent with the number of segments in the mapping curve of single-machine new energy sources, thus improving the engineering applicability.
[0085] In addition, Figure 4 In the simulation, if the load is not considered and the equivalent value of a single unit is ignored, all new energy sources on the line are connected to grid connection point 8. The result is the result of the new energy mapping curve multiplied by the new energy capacity, which is far from the simulation value. If the load is considered and the equivalent value of a single unit is considered and all new energy sources and loads on the line are connected to grid connection point 8, the influence of line parameters is ignored, which also has a large error.
[0086] For branch line 6-27-34 connected to a full-power inverter-type renewable energy source, its equivalent aggregation model is:
[0087]
[0088] like Figure 5 The figure shown is a comparison of the equivalent aggregation model curves of the full-power inverter-type new energy line 6-27-34 in the embodiment of the present invention, showing the current I under different voltage drop conditions. 6_NE The comparison between simulated values and calculated values from the equivalent model is as follows: Figure 5 It can be seen that the equivalent aggregation model value and the simulation value basically coincide.
[0089] As can be seen from the above analysis, the equivalent aggregation model obtained by the method in the embodiments of the present invention has high computational accuracy.
[0090] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.
[0091] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.
Claims
1. An equivalent aggregation method applicable to networks containing new energy sources, characterized in that, The method includes: Step 1: Preprocess the network topology and parameter information of the new energy network; Step 2: When the short-circuit current of the network containing new energy sources is a linear function of the voltage, analyze the influence of the topology parameter information in Step 1 on the short-circuit current and establish an equivalent aggregation model of the network containing new energy sources. Step 3: Based on the type of new energy source and combined with the practical expression of the short-circuit current of actual new energy sources, obtain the corresponding equivalent aggregation model; In step 3, the practical expression of the actual new energy short-circuit current is divided into multiple stages according to the different voltage drop at the grid connection point. The expressions for different stages are different, so it is necessary to explore the boundaries of different stages in the equivalent aggregation model. In practice, the functional relationship between the current and voltage at the new energy port is a piecewise linear function. When there are two stages, its expression is: （8） In the formula, U (1,2) These are the segmented critical voltage values, which are provided by the new energy power plants. When the voltage-current mapping relationship of new energy is a piecewise linear function as shown in equation (8), the expression of the equivalent current and the first node voltage is also a piecewise function. Therefore, the piecewise critical voltage value in the equivalent aggregation model is obtained below. The renewable energy capacity varies at different nodes. When considering capacity, the node... The voltage-current mapping relationship of new energy sources is as follows: （9） In the formula, S m For nodes m The capacity of the new energy source connected; If there are lines containing new energy networks l A new energy source, according to formula (8), contains a new energy network. l +1 state; Considering that the voltage difference between the first and last nodes on the same line is not large, as the voltage increases, when a new energy source on the line transitions from the first stage to the second stage, the new energy sources at the remaining nodes (excluding the first and last nodes) will also transition to the second stage. To avoid overcomplication, we only consider all new energy nodes to be in both the first and second stages. Therefore, the steps for determining the segmented critical voltage values in the equivalent aggregation model are as follows: When all new energy nodes are in the first stage, the expression for the controlled current source in the equivalent aggregation model is: （10） In the formula, I 1 ’(1) This refers to the equivalent current injected into the first node (i.e., the external network) by the equivalent circuit when all new energy nodes are in the first stage. U A The voltage at the first node of the equivalent circuit; k 1 ’(1) , b 1 ’(1) The result is obtained using equation (6); When all new energy nodes are in the second stage, the expression for the controlled current source in the equivalent aggregation model is: （11） In the formula, I 1 ’(2) This refers to the equivalent current injected into the first node, i.e., the external network, by the equivalent circuit when all new energy nodes are in the second stage. k 1 ’(2) , b 1 ’(2) The result is obtained using equation (6); At this point, the segmented critical voltage values for the first and second stages are... U A ’(1,2) for: （12） Therefore, the equivalent aggregation model expression for a new energy network with a two-stage mapping relationship is as follows: （13） In the formula, I A The equivalent current injected by the equivalent circuit into the first node, i.e., the external network; When the expression for the new energy mapping relationship is multi-stage, the segmented critical voltage values of adjacent stages can be obtained using the above method.
2. The equivalent aggregation method applicable to networks containing new energy sources according to claim 1, characterized in that, In step 1, the preprocessing operation includes node numbering and load processing; Regarding node numbering, the equivalent radial network consists of the first node and others. n Composed of nodes, totaling n +1 node, for this n Of the nodes, node 1 is the closest to the first node in terms of line distance, followed by nodes 2, 3, and so on, with the last node being the [missing node]. n One node; The load processing is in constant impedance form; Assume node A is the main node, i.e., the first node, of the backbone network containing new energy sources, and the line impedance between node 1 and node A is... Z 1. The line impedance between node 1 and node 2 is Z 2. Node 1 and Node 2 are respectively connected to new energy power sources; When a fault occurs outside the line, the main line node A, branch line nodes 1 and 2 can be equivalent to a new energy node, simplifying the network topology; For the new energy power sources connected to nodes 1 and 2, they are equivalent to voltage-controlled current sources, and the functional relationship between their port voltage and current is expressed as follows: f This indicates that the voltage and current functional relationships differ for different types of new energy power sources. The loads connected to nodes 1 and 2 are treated as equivalent to a constant impedance model in short-circuit current calculations, i.e.: （1） In the formula, U N This refers to the rated value of the node line voltage; S L Indicates load capacity, Z L The equivalent impedance of the load is indicated by the subscript. i Representing the i Each node.
3. The equivalent aggregation method applicable to networks containing new energy sources according to claim 1, characterized in that, In step 2, assuming node A is the main line node of the renewable energy network, and nodes 1 and 2 are branch lines connected to node A, when the short-circuit current of the renewable energy network is a linear function of its node voltage, i.e., the following condition is met: （2） In the formula, I This represents the current flowing into the power grid from new energy sources. U This indicates the port voltage to which the new energy power source is connected; subscripts 1 and 2 indicate the node position. k 1, k 2, b 1, b Both 2 are constants, and their values are provided by the new energy power plants; According to circuit theory, the following expression can be obtained: （3） In the formula, I i ’ Represents a node i The current injected into bus A, i =1,2; Combining (d) to (f) in equation (3), we can obtain: （4） In the formula, given a fixed network... , , , If all are known, then k 2 ' and b 2 ' All are constants; Combining (a) to (c) in equation (3) and substituting (4) into the equation, we get: （5） In the formula, U A The voltage at the first node of the equivalent circuit; Similarly, in the formula k 1 ' and b 1 ' Both are constants, and their relationship with... k 2 ' and b 2 ' There is a recursive relationship; And so on, we obtain the result consisting of the first node A and the other nodes 1 to 1. n A group of nodes containing new energy n The recursive formula for a +1 node network is as follows: （6） In the formula, I i ’ Represents a node i Inject current into bus A; As shown in equation (6), k i ' and b i ' All by the first i The and the ( i The information from +1) nodes is obtained, and all are constants; The recursive order is from the first n From node () to node 1, the equivalent short-circuit current injected into the first node (node A) is finally obtained; due to the () n If +1) nodes do not exist, let... k ’ n+1 = b ’ n+1 If the expression is 0, then the recurrence relation is still satisfied; the first node is node A, therefore... U 0 =U A ; Through recursion, the equivalent current injected into the first node (i.e., the external network) by the equivalent circuit is finally obtained as: （7）。