A fast power flow calculation method for active distribution network with looped network

Abstract

The application provides a fast power flow calculation method for a distribution network containing a ring network active power distribution network. Network graph theory knowledge is used to obtain a connected subgraph of the distribution network according to a tree concept; the connected subgraph is used for numbering nodes and tree branches, and the numbering is performed in the order from a root node to a terminal end, and the numbering of the tree branches and the nodes is consistent; a node current-branch current matrix and a branch current-node voltage matrix are obtained by using the relationship among branch currents, node currents and node voltages; it is judged whether the distribution network topology contains a ring network, if the ring network is contained, the matrix is corrected by using KVL and KCL; the node current-branch current matrix and the branch current-node voltage matrix are arranged to obtain a node current-node voltage matrix; the injection currents of the nodes are obtained after equivalent calculation according to the access conditions of the distributed power sources and energy storages of the nodes; and the node voltages are solved according to the currents of the nodes and the node current-node voltage matrix.

Description

Technical Field

[0001] This invention belongs to the field of power flow calculation technology for distribution networks, and in particular relates to a fast power flow calculation method for active distribution networks containing ring networks. Background Technology

[0002] With the continuous development of new energy power generation technologies and the ongoing reforms of the power market in my country, modern power systems are evolving towards cleaner, smarter, and more market-driven models. Traditional centralized power generation methods can no longer meet the development needs of modern power systems, making the widespread integration of distributed generation sources the future direction of power system development. The integration of distributed generation sources into the distribution network can not only reduce the consumption of fossil fuels, primarily coal, and decrease emissions of carbon dioxide and harmful gases, but also improve the voltage level of the distribution network and reduce losses. However, the integration of distributed generation sources transforms the distribution network into a multi-source network, introducing new node types that render traditional power flow calculation methods inapplicable.

[0003] Currently, commonly used power flow calculation methods include the Gauss-Seidel method, Newton's method, tensor method, and PQ decomposition method. The Gauss-Seidel method is relatively simple and requires less computational power, but it has a high number of iterations and poor convergence. When the number of nodes and branches in the distribution network system is large, the number of iterations increases dramatically. Newton's method is the most conventional algorithm, using successive linearization to solve power flow problems. It has good convergence, but the computational cost is enormous, making it unsuitable for online calculations. The tensor method is similar to Newton's method, using second-order Taylor expansion for successive linearization. Compared to Newton's method, it has better convergence and computational speed under heavy load conditions, but the computational cost is still too high for online calculations. The PQ decomposition method is a simplification of Newton's method, ignoring the influence of line resistance, making the Jacobian matrix a constant, greatly accelerating the solution speed. It is suitable for online calculations, but because the line resistance in the distribution network cannot be ignored, this method is not suitable for power flow calculations in distribution networks. With the widespread integration of distributed power sources, the continuous development of distribution network structures, and the increasing demand for online power flow calculation in distribution networks, a fast power flow calculation method for active distribution networks including ring networks is needed. Summary of the Invention

[0004] The purpose of this invention is to solve the problems in the prior art and to propose a fast power flow calculation method for active distribution networks containing ring networks.

[0005] This invention is achieved through the following technical solution: This invention proposes a fast power flow calculation method for active distribution networks containing ring networks, the method comprising:

[0006] Step 1: Using the knowledge of network graph theory, obtain the connected subgraphs of the power distribution network based on the concept of trees;

[0007] Step 2: Number the nodes and branches according to the obtained connected subgraph, in order from the root node to the end, and the numbering of branches and nodes must be consistent.

[0008] Step 3: Based on the distribution network topology and the relationship between branch currents, node currents, and node voltages, obtain the node current-branch current matrix and the branch current-node voltage matrix.

[0009] Step 4: Determine whether the distribution network topology contains a ring network. If it does, then use KVL and KCL to correct the matrix.

[0010] Step 5: Organize the node current-branch current matrix and the branch current-node voltage matrix to obtain the node current-node voltage matrix;

[0011] Step 6: Based on the access status of the distributed power supply at each node, obtain the injection current of each node.

[0012] Step 7: Solve for the node voltage based on the node current and the node current-node voltage matrix.

[0013] Furthermore, in step two, according to the knowledge of network graph theory, a network with n nodes and l branches has n-1 tree branches and m = l-n+1 connecting branches. The distribution network is numbered, and the numbering of branches and nodes must be consistent, that is, the numbering of branches and nodes must follow the same branch order and be numbered from the root node to the end.

[0014] Furthermore, in steps three and four, based on the relationship between node current and branch current, the current B of branch i can be determined. i This is the sum of the currents at each subsequent node. For distribution networks containing loops, the currents of the upstream tree branches are further supplemented based on the location of the connecting branches, resulting in a node current-branch current transfer matrix applicable to radial and ring-containing distribution networks. The obtained node current-branch current transfer matrix is ​​as follows:

[0015]

[0016] Among them, I i (i = 2, 3, 4, ..., n) represents the node current at node i, B mi (i = 2, 3, 4, ..., m) represents the branch current connected to branch i, b i,j Represents B i and I j+1 Does a containment relationship exist between them? If B in the circuit... i Located in I j+1 If there is an inclusion relationship between the upstream and downstream of b, then b i,j If the value is 1, then b is 1 if there is no inclusion relationship.i,j b is 0; 1(i,j) and b 2(i,j) This is a correction for the existence of a loop network. When a loop network exists, the KCL is needed to correct the branch current of the upstream tree branch of the connected branch; when the tree branch current B i Under the branch current B j Upstream of, and with the same current direction, then b j(i,1) =1, b j(i,2) =0; when the tree branch current B i Under the branch current B j When the upstream current is opposite to the upstream current, then b j(i,1) =0, b j(i,2) =1; when the tree branch current B i Not in the branch current B j Upstream of, there is b j(i,1) =0, b j(i,2) =0; Combining the above equation, we get:

[0017]

[0018] Since the voltage difference between node i and node j in a circuit network is the product of the branch currents and impedances of each branch, the voltage difference between nodes in a radial distribution network is easily obtained. When loops exist in the distribution network, the branch current-node voltage matrix needs to include loop information. According to network graph theory, there are m loops in the distribution network. By writing the KVL equations for the loops and adding them to the matrix, we can obtain the following formula:

[0019]

[0020] Among them, △U 1,i Z represents the voltage difference between node 1 and node i. i,j For the corresponding branch current B j The resistance of the circulating branch, Z, is determined if there is a branch between node 1 and node i. i,j This represents the corresponding impedance value; if it is not included, the corresponding position in the matrix is ​​zero; Z k(i,j) Let be the impedance value of a certain section in loop k, corresponding to its branch current, forming the KVL equation of the loop.

[0021] Furthermore, in step five, after substituting equation (2) into equation (3) and performing a reduction in order, we obtain:

[0022] [ΔU]=[VFC][I](4)

[0023] Where [VFC] is the correlation matrix between node voltage and node current;

[0024] Based on the above analysis, the formula for iterative calculation can be obtained as follows:

[0025] [ΔU] k+1 =[VFC][I] k (5)

[0026] [U] k+1 =[U] k +[ΔU] k+1 (6)

[0027] In power distribution systems, node current can be expressed using node power and node voltage, based on the definition of power:

[0028]

[0029] In equation (7), I i Let U be the current at node i. i * Let U be the node voltage at node i. i The conjugate of S Gi * Inject the conjugate of the sum of power into node i, S LDi * It is the conjugate of the load of node i.

[0030] Furthermore, in order to incorporate distributed power sources into the method, it is necessary to process different types of distributed power sources. The equivalent mathematical models of various types of distributed power sources and energy storage in this power flow calculation method include photovoltaic power plant models, synchronous wind turbine models, asynchronous wind turbine models, and energy storage system models.

[0031] Furthermore, the photovoltaic power station model: since the photovoltaic inverter operates in constant current mode, the photovoltaic power generation part is treated as PI; in the first iteration, the photovoltaic power station is regarded as a constant current source, and its current magnitude and angle are calculated; in equation (9), the symbol indicates that the current is flowing out of the node;

[0032]

[0033]

[0034]

[0035] Then, the current angle is updated continuously according to equation (11);

[0036]

[0037]

[0038]

[0039] The current value of node i can be calculated according to equation (13); at this time, the photovoltaic power station can be directly substituted into the method.

[0040] Furthermore, the synchronous wind turbine model: The synchronous generator adjusts the reactive power by controlling the excitation, so it is necessary to calculate the reactive power injected into the power bus first and then calculate the injection current; according to the power factor of the synchronous generator, the reactive power it generates can be obtained as shown in equation (14):

[0041]

[0042] Then, substitute equation (14) into equation (7), and the result is similar to that of equation (8); then iterate continuously to update the node injection current value. Except for equation (14), the other calculation formulas are similar to equations (11)-(13); after the above processing, the synchronous wind turbine generator is transformed into the current expression form, which is suitable for the proposed fast power flow calculation method.

[0043] Furthermore, the asynchronous wind turbine model: The active power output of an asynchronous wind turbine is related to the wind speed, therefore, it is necessary to determine the reactive power of the wind turbine for a given active power. Based on the relationship between the active power, reactive power, and terminal voltage of the asynchronous generator, the expression for reactive power can be obtained as follows:

[0044]

[0045] Where, x c and x m The inductance of the terminal capacitor and the leakage reactance of the stator and rotor are respectively; then, by substituting equation (15) into equation (7), we can obtain a result similar to that of equation (8); except for equation (15), the remaining calculation formulas of the conversion equivalent model are similar to those of equations (11)-(13); after these processing, we can obtain an asynchronous generator model suitable for the proposed fast power flow calculation method.

[0046] Furthermore, the energy storage system model: the energy storage system is in the process of charging and discharging, so it can inject power into the distribution network and absorb power from the distribution network; therefore, the formula for the energy storage system injecting power into the distribution network is (16), and the formula for the energy storage system absorbing power from the distribution network is (17).

[0047]

[0048]

[0049] Substituting (16) and (17) into (7), the result is similar to that of (8); then iteratively updating the node injection current value, except for (16) and (17), the remaining calculation formulas are similar to those of (11)-(13); after these processing, an energy storage system model suitable for the proposed fast power flow calculation method can be obtained.

[0050] The beneficial effects of this invention are as follows:

[0051] The power flow calculation method proposed in this invention can quickly calculate the power flow distribution of distribution networks containing ring networks and distributed generation sources, and can accurately calculate parameters such as voltage and power. It provides a fast and convergent calculation method for online power flow calculation application scenarios, and facilitates the study of the impact of distributed generation sources on distribution networks containing ring networks. Attached Figure Description

[0052] Figure 1 This is a flowchart of a fast power flow calculation method for a distribution network according to an embodiment of the present invention;

[0053] Figure 2 This is an equivalent circuit diagram of a power distribution network according to an embodiment of the present invention;

[0054] Figure 3 This is a power distribution network connectivity diagram according to an embodiment of the present invention. Detailed Implementation

[0055] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Combination Figure 1-3 This invention proposes a fast power flow calculation method for active distribution networks containing ring networks, the method comprising:

[0057] Step 1: Using the knowledge of network graph theory, obtain the connected subgraphs of the power distribution network based on the concept of trees;

[0058] Step 2: Number the nodes and branches according to the obtained connected subgraph, in order from the root node to the end, and the numbering of branches and nodes must be consistent.

[0059] Step 3: Based on the distribution network topology and the relationship between branch currents, node currents, and node voltages, obtain the node current-branch current matrix and the branch current-node voltage matrix.

[0060] Step 4: Determine whether the distribution network topology contains a ring network. If it does, then use KVL and KCL to correct the matrix.

[0061] Step 5: Organize the node current-branch current matrix and the branch current-node voltage matrix to obtain the node current-node voltage matrix;

[0062] Step 6: Based on the access status of the distributed power supply at each node, obtain the injection current of each node.

[0063] Step 7: Solve for the node voltage based on the node current and the node current-node voltage matrix.

[0064] In step two, based on network graph theory, a network with n nodes and l branches has n-1 tree branches and m = l-n+1 connecting branches. The distribution network is numbered, and the branch and node numbering must be consistent, meaning they should follow the same branch sequence from the root node to the end. This ensures that the resulting node current-branch current matrix is ​​an upper triangular matrix, and the branch current-node voltage matrix is ​​a lower triangular matrix, which improves the solution speed.

[0065] In steps three and four, based on the relationship between node current and branch current, the current B in branch i can be determined. i This is the sum of the currents at each subsequent node. For distribution networks containing loops (i.e., networks with connecting branches), the currents of the upstream branches are further supplemented based on the location of the connecting branches to obtain the node current-branch current transfer matrix applicable to radial and ring-containing distribution networks. The obtained node current-branch current transfer matrix is ​​as follows:

[0066]

[0067] Among them, I i (i = 2, 3, 4, ..., n) represents the node current at node i, B mi (i = 2, 3, 4, ..., m) represents the branch current connected to branch i, b i,j Represents B i and I j+1 Does a containment relationship exist between them? If B in the circuit... i Located in I j+1 If there is an inclusion relationship between the upstream and downstream of b, then b i,j If the value is 1, then b is 1 if there is no inclusion relationship. i,j b is 0; 1(i,j) and b 2(i,j) This is a correction for the existence of a loop network. When a loop network exists, the KCL is needed to correct the branch current of the upstream tree branch of the connected branch; when the tree branch current B i Under the branch current Bj Upstream of, and with the same current direction, then b j(i,1) =1, b j(i,2) =0; when the tree branch current B i Under the branch current B j When the upstream current is opposite to the upstream current, then b j(i,1) =0, b j(i,2) =1; when the tree branch current B i Not in the branch current B j Upstream of, there is b j(i,1) =0, b j(i,2) =0; Combining the above equation, we get:

[0068]

[0069] Since the voltage difference between node i and node j in a circuit network is the product of the branch currents and impedances of each branch, the voltage difference between nodes in a radial distribution network is easily obtained. When loops exist in the distribution network, the branch current-node voltage matrix needs to include loop information. According to network graph theory, there are m loops in the distribution network. By writing the KVL equations for the loops and adding them to the matrix, we can obtain the following formula:

[0070]

[0071] Among them, △U 1,i Z represents the voltage difference between node 1 and node i. i,j For the corresponding branch current B j The resistance of the circulating branch, Z, is determined if there is a branch between node 1 and node i. i,j This represents the corresponding impedance value; if it is not included, the corresponding position in the matrix is ​​zero; Z k(i,j) Let be the impedance value of a certain section in loop k, corresponding to its branch current, forming the KVL equation of the loop.

[0072] In step five, substituting equation (2) into equation (3) and performing order reduction, we obtain:

[0073] [ΔU]=[VFC][I](4)

[0074] Where [VFC] is the correlation matrix between node voltage and node current;

[0075] Based on the above analysis, the formula for iterative calculation can be obtained as follows:

[0076] [ΔU] k+1 =[VFC][I] k (5)

[0077] [U] k+1 =[U]k +[ΔU] k+1 (6)

[0078] In power distribution systems, node current can be expressed using node power and node voltage, based on the definition of power:

[0079]

[0080] In equation (7), I i Let U be the current at node i. i * Let U be the node voltage at node i. i The conjugate of S Gi * Inject the conjugate of the sum of power into node i, S LDi * It is the conjugate of the load of node i.

[0081] In step six, to incorporate distributed power sources into the method, different types of distributed power sources need to be processed to meet the usage conditions of this method. The equivalent mathematical models for various types of distributed power sources and energy storage in this power flow calculation method include photovoltaic power plant models, synchronous wind turbine models, asynchronous wind turbine models, and energy storage system models.

[0082] Photovoltaic power plant model: Since the photovoltaic inverter operates in constant current mode, the photovoltaic power generation part is treated as PI; in order to use the photovoltaic power plant model in the method described in this invention, it needs to be modified. In the first iteration, the photovoltaic power plant is regarded as a constant current source, and its current magnitude and angle are calculated; in equation (9), the symbol indicates that the current is flowing out of the node;

[0083]

[0084]

[0085]

[0086] Then, the current angle is updated continuously according to equation (11);

[0087]

[0088]

[0089]

[0090] The current value of node i can be calculated according to equation (13); at this time, the photovoltaic power station can be directly substituted into the method.

[0091] Synchronous wind turbine model: Synchronous generators adjust reactive power by controlling excitation, so it is necessary to calculate the reactive power injected into the power bus first and then calculate the injection current; the reactive power generated by the synchronous generator can be obtained from the power factor of the synchronous generator as shown in equation (14):

[0092]

[0093] Then, substitute equation (14) into equation (7), and the result is similar to that of equation (8); then iterate continuously to update the node injection current value. Except for equation (14), the other calculation formulas are similar to equations (11)-(13); after the above processing, the synchronous wind turbine generator is transformed into the current expression form, which is suitable for the proposed fast power flow calculation method.

[0094] Asynchronous wind turbine model: Since asynchronous wind turbines lack an excitation system, they inherently lack reactive power regulation capabilities. Simultaneously, asynchronous generators absorb reactive power from the distribution network. The magnitude of this absorbed reactive power is related to the generator's terminal voltage. Therefore, the asynchronous generator model needs to be modified to adapt to the proposed fast power flow calculation method. The active power output of the asynchronous wind turbine is related to wind speed; therefore, it is necessary to determine the reactive power of the wind turbine for a given active power. Based on the relationship between the asynchronous generator's active power, reactive power, and terminal voltage, the expression for reactive power can be obtained as follows:

[0095]

[0096] Where, x c and x m The inductance of the terminal capacitor and the leakage reactance of the stator and rotor are respectively; then, by substituting equation (15) into equation (7), we can obtain a result similar to that of equation (8); except for equation (15), the remaining calculation formulas of the conversion equivalent model are similar to those of equations (11)-(13); after these processing, we can obtain an asynchronous generator model suitable for the proposed fast power flow calculation method.

[0097] Energy storage system model: For energy storage systems, the output of the energy storage battery is DC voltage, and the energy storage device is generally connected to the distribution network through an inverter. For the output of the inverter, the power is generally controlled by controlling its delay angle. Similarly, it is still necessary to calculate the reactive power and current injected into the energy storage system. The energy storage system has charging and discharging situations, so it can inject power into the distribution network and absorb power from the distribution network; therefore, the formula for the energy storage system injecting power into the distribution network is (16), and the formula for the energy storage system absorbing power from the distribution network is (17).

[0098]

[0099]

[0100] Substituting (16) and (17) into (7), the result is similar to that of (8); then iteratively updating the node injection current value, except for (16) and (17), the remaining calculation formulas are similar to those of (11)-(13); after these processing, an energy storage system model suitable for the proposed fast power flow calculation method can be obtained.

[0101] The present invention will be further described below with reference to the accompanying drawings and examples to facilitate understanding;

[0102] Example 1

[0103] like Figure 1 As shown, Figure 1 The flowchart of the method described in this invention is as follows: This invention proposes a fast power flow calculation method for an active distribution network containing a ring network, the specific steps of which include:

[0104] Step 1: Read the distribution network data to obtain the connectivity subgraph of the distribution network;

[0105] Step 2: Number the branch currents and nodes according to the obtained connected subgraph;

[0106] Step 3: Based on the topology of the distribution network and the relationship between branch currents, node currents and node voltages in the topology, the node current-branch current matrix and the branch current-node voltage matrix can be obtained.

[0107] Step 4: Determine whether the distribution network topology contains a ring network. If it does, use KVL and KCL to correct the matrix.

[0108] Step 5: Organize the node current-branch current matrix and the branch current-node voltage matrix to obtain the node current-node voltage matrix.

[0109] Step 6: Obtain the injection current of each node based on the access status of the distributed power supply at each node.

[0110] Step 7: Solve for the node voltage based on the node current and the node current-node voltage matrix.

[0111] The following example uses a 33-node distribution network to further illustrate the invention. To include ring networks in the distribution network and verify the method proposed in this invention, the 33-node distribution network was modified to include two ring networks, as shown in the following diagram. Figure 2 As shown, distributed generation sources of different types and capacities are connected at nodes 16, 25, and 31. The power reference value for the distribution network system is selected as 10 MVA, the voltage reference value as 12.66 kV, and the convergence accuracy as 10...-5 .

[0112] The specific configuration scheme is shown in Table 1:

[0113] Table 1 Distributed Power Supply Access Scheme

[0114] Access Node Distributed power type Access capacity 1 Access capacity 2 Access capacity 3 16 Photovoltaic power station 200kW 100kW 50kW 25 Synchronous wind turbine 500kW 300kW 100kW 31 asynchronous wind turbine 300kW 200kW 100kW

[0115] The asynchronous wind turbine has a single unit capacity of 100kW, a rated terminal voltage of 2.4kV, a stator reactance of 3.658Ω, a rotor reactance of 4.242Ω, a magnetizing reactance of 140.6Ω, and a rotor resistance of 0.1356Ω.

[0116] The connected subgraph obtained from the distribution network topology is shown in the attached figure. Figure 3 As shown.

[0117] according to Figure 3 The node current-branch current matrix and the branch current-node voltage matrix can be obtained. Then, considering that the distribution network topology includes two ring networks, the matrices are corrected. The node current-branch current matrix and the branch current-node voltage matrix are rearranged to obtain the node current-node voltage matrix. Based on the distributed generation access situation in Table 1, the node currents are corrected, and then the power flow is solved. The results are shown in Tables 2 and 3.

[0118] Table 2 shows the power flow calculation results for distributed distribution networks with ring networks.

[0119]

[0120]

[0121] Table 3 Comparison of the method of the present invention with the Niu La method

[0122]

[0123] As shown in Table 2, the power flow calculation results of the distribution network after the integration of distributed generation effectively improved the voltage level of the distribution network. Table 3 shows that, compared with the Newton-Raphson method, the method proposed in this invention can quickly calculate the power flow of the distribution network. While it requires more iterations than the Newton-Raphson method, the matrix obtained by the proposed method is a fixed matrix, eliminating the need to update the matrix in each iteration. This contrasts with the Newton-Raphson method, which requires updating the Jacobian matrix and inverting the matrix in each iteration, thus saving computation time more effectively.

[0124] The power flow calculation method proposed in this invention can quickly calculate the power flow distribution of distribution networks containing ring networks and distributed generation sources, and can accurately calculate parameters such as voltage and power. It provides a fast and convergent calculation method for online power flow calculation application scenarios, and facilitates the study of the impact of distributed generation sources on distribution networks containing ring networks.

[0125] The fast power flow calculation method for an active distribution network with ring network proposed in this invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of this invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A fast power flow calculation method for an active distribution network containing ring networks, characterized in that: The method includes: Step 1: Using the knowledge of network graph theory, obtain the connected subgraphs of the power distribution network based on the concept of trees; Step 2: Number the nodes and branches according to the obtained connected subgraph, in order from the root node to the end, and the numbering of branches and nodes must be consistent. Step 3: Based on the distribution network topology and the relationship between branch currents, node currents, and node voltages, obtain the node current-branch current matrix and the branch current-node voltage matrix. Step 4: Determine whether the distribution network topology contains a ring network. If it does, then use KVL and KCL to correct the matrix. Step 5: Organize the node current-branch current matrix and the branch current-node voltage matrix to obtain the node current-node voltage matrix; Step 6: Based on the access status of the distributed power supply at each node, obtain the injection current of each node. Step 7: Solve for the node voltage based on the node current and the node current-node voltage matrix; In step two, based on knowledge of network graph theory, it is known that possessing n Each node l A network of branch roads, with n -1 tree branch, m = l - n +1 branch, number the distribution network, and the numbering of branches and nodes must be consistent, that is, the numbering of branches and nodes should follow the same branch sequence from the root node to the end. In steps three and four, based on the relationship between node current and branch current, it can be known that the branch... i current B i This is the sum of the currents at each subsequent node. For distribution networks containing loops, the currents of the upstream tree branches are further supplemented based on the location of the connecting branches, resulting in a node current-branch current transfer matrix applicable to radial and ring-containing distribution networks. The obtained node current-branch current transfer matrix is ​​as follows: (1) in, I i ( i =2,3,4,…, n ) is a node i node current, B mi ( i =2,3,4,…, m ) is a branch i The branch current, b i,j It represents B i and I j+1 Does a containment relationship exist between them? If in the circuit B i lie in I j+1 If there is an inclusion relationship between the upstream and downstream, then b i,j The value is 1 if there is no containment relationship. b i,j =0; b 1(i,j) and b 2(i,j) This is a correction for the existence of a loop network. When a loop network exists, the KCL (Knowledge, Current, and Chaining) is needed to correct the branch current of the upstream tree branch of the connected branch; when the tree branch current... B i In the branch current B j Upstream of, and with the same current direction, then we have b j (i,1) =1、 b j(i,2) =0; when the tree branch current B i In the branch current B j When the upstream current is opposite to the upstream current, then we have b j (i,1) =0、 b j(i,2) =1; when the tree branch current B i Not in the branch current B j Upstream, there is b j (i,1) =0、 b j(i,2) =0; Combining the above equation, we get: (2)。 2. The method according to claim 1, characterized in that, Based on the nodes in the circuit network i and nodes j The voltage difference between nodes is the product of the branch currents and the impedances of each branch. Therefore, the voltage difference between nodes in a radial distribution network is easily obtained. When loops exist in the distribution network, the branch current-node voltage matrix needs to include loop information. According to network graph theory, there are loops in the distribution network. m For each loop, by writing out the KVL equations for the loops and adding them to the matrix, we can obtain the following formula: (3) Among them, △ U 1,i From node 1 to node i voltage difference, Z i,j For the corresponding branch current B j The resistance of the current branch, if node 1 and node i If there are branches between them Z i,j This represents the corresponding impedance value; if it is not included, the corresponding position in the matrix is ​​zero. Z k(i,j) For loop k The impedance value of a certain section, corresponding to the current in its branch, forms the KVL equation for the loop.

3. The method according to claim 2, characterized in that, In step five, substituting equation (2) into equation (3) and performing order reduction, we obtain: (4) in,[ VFC [ ] represents the correlation matrix between node voltages and node currents; Based on the above analysis, the formula for iterative calculation can be obtained as follows: (5) (6) In power distribution systems, node current can be expressed using node power and node voltage, based on the definition of power: (7) In equation (7), I i For nodes i The current, U i * For nodes i Node voltage U i conjugate, S Gi * For nodes i The conjugate of the sum of injected power, S LDi * For nodes i The conjugate of the load.

4. The method according to claim 3, characterized in that, In order to incorporate distributed power sources into the method, different types of distributed power sources need to be processed. The equivalent mathematical models of various types of distributed power sources and energy storage in this power flow calculation method include photovoltaic power plant models, synchronous wind turbine models, asynchronous wind turbine models, and energy storage system models.

5. The method according to claim 4, characterized in that, Photovoltaic power station model: Since the photovoltaic inverter operates in constant current mode, the photovoltaic power generation part is treated as PI; in the first iteration, the photovoltaic power station is regarded as a constant current source, and its current magnitude and angle are calculated; in equation (9), the symbol indicates that the current is flowing out of the node; (8) (9) (10) Then, the current angle is updated continuously according to equation (11); (11) (12) (13) The nodes can be calculated according to equation (13). i The current value; at this point, the photovoltaic power station can be directly substituted into the method described above.

6. The method according to claim 5, characterized in that, Synchronous wind turbine model: Synchronous generators adjust reactive power by controlling excitation, so it is necessary to calculate the reactive power injected into the power bus first and then calculate the injection current; the reactive power generated by the synchronous generator can be obtained from the power factor of the synchronous generator as shown in equation (14): (14) Then, substitute equation (14) into equation (7), and the result is similar to that of equation (8); then iterate continuously to update the node injection current value. Except for equation (14), the other calculation formulas are similar to equations (11)-(13); after the above processing, the synchronous wind turbine generator is transformed into the current expression form, which is suitable for the proposed fast power flow calculation method.

7. The method according to claim 5, characterized in that, Asynchronous wind turbine model: The active power output of an asynchronous wind turbine is related to the wind speed, therefore, it is necessary to determine the reactive power of the wind turbine for a given active power. Based on the relationship between the active power, reactive power, and terminal voltage of the asynchronous generator, the expression for reactive power can be obtained as follows: (15) in, x c and x m The inductance of the terminal capacitor and the leakage reactance of the stator and rotor are respectively; then, by substituting equation (15) into equation (7), we can obtain a result similar to that of equation (8); except for equation (15), the remaining calculation formulas of the conversion equivalent model are similar to those of equations (11)-(13); after these processing, we can obtain an asynchronous generator model suitable for the proposed fast power flow calculation method.

8. The method according to claim 5, characterized in that, Energy storage system model: The energy storage system is in the process of charging and discharging, so it can inject power into the distribution network and absorb power from the distribution network; therefore, the formula for the energy storage system injecting power into the distribution network is (16), and the formula for the energy storage system absorbing power from the distribution network is (17); (16) (17) Substituting (16) and (17) into (7), the result is similar to that of (8); then iteratively updating the node injection current value, except for (16) and (17), the remaining calculation formulas are similar to those of (11)-(13); after these processing, an energy storage system model suitable for the proposed fast power flow calculation method can be obtained.

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