Low-voltage distribution network node voltage prediction based on user shared line impedance

Abstract

The invention provides a low-voltage distribution network node voltage prediction method based on user shared line impedance, which belongs to the technical field of intelligent power grids, and comprises the following steps: S1, carrying out load flow calculation based on a forward and backward substitution method, and calculating the voltage and branch current value of each node through forward and backward substitution processes; s2, a forward-backward substitution method is simplified, and the relation between node voltage and current and user shared line impedance is obtained; s3, based on a Newton-Raphson method, solving user shared line impedance; and S4, based on the obtained user shared line impedance, according to the estimated user load, obtaining the predicted voltage of each node of the low-voltage power distribution network. According to the method, the problem that the network topology structure of the low-voltage distribution network is difficult to obtain is effectively avoided, the difficulty of predicting the node voltage of the low-voltage distribution network is greatly reduced, the prediction process is simpler, more convenient and more practical, and the method is also suitable for the high-voltage distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of smart grids, and in particular relates to low-voltage distribution network node voltage prediction based on user-shared line impedance. Background Art

[0002] As the terminal network of the power system, the low-voltage distribution network has a large number of terminal devices, various types, low intelligence, inconsistent standards, and irregular network wiring. These problems bring huge challenges to the operation and maintenance of the low-voltage distribution network. The power supply reliability and power quality often do not meet user requirements, and voltage over-limit is one of the common problems. Therefore, accurate prediction of the node voltage of the low-voltage distribution network can effectively prevent potential power hazards.

[0003] The typical low-voltage distribution network node voltage prediction method based on mechanism analysis is to achieve node voltage prediction based on topological structure and power flow calculation. This method uses a mathematical model to simulate the flow of power by assuming a series of load values, thereby calculating the voltage of each node in the power grid. Power flow calculation can provide detailed distribution network voltage distribution information to help with power grid planning and operation decisions.

[0004] However, unlike medium and high voltage distribution networks, low voltage distribution networks do not have known topological structures. This situation usually stems from the lack of detailed records of topological information during the operation and maintenance of the power grid. The premise of using traditional power flow calculation methods is to have a complete distribution network line structure and parameters, but this information is missing in low voltage distribution networks for various reasons. Although there are many methods for topological structure identification, most of them are still in the stage of household transformer identification and household phase identification, and cannot obtain the complete distribution network line structure and parameters. Therefore, low voltage distribution network node grid prediction based on topological structure and power flow calculation is very difficult in practice. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, a low-voltage distribution network node voltage prediction based on user shared line impedance is provided.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] This technical solution proposes a low-voltage distribution network node voltage prediction based on user-shared line impedance, including the following steps:

[0008] S1: Calculate the power flow based on the forward and back substitution method, and calculate the voltage and branch current values ​​of each node through the forward and back substitution process;

[0009] S2: By simplifying the forward-backward substitution method, the relationship between the node voltage, current and the user shared line impedance is obtained;

[0010] S3: Based on the Newton-Raphson method, solve the user shared line impedance;

[0011] S4: Based on the obtained user shared line impedance and the estimated user load, the predicted voltage of each node in the low-voltage distribution network is obtained.

[0012] Preferably, in S1, the topological structure of the circuit is determined, leaf nodes are searched as first-layer nodes, parent nodes of leaf nodes are searched as second-layer nodes, and parent nodes of second-layer nodes are searched as third-layer nodes. The search is stopped until all parent nodes of a certain layer are found to be root nodes, nodes in previous layers that are repeated in later layers are deleted, and the node order for flow calculation is determined.

[0013] Preferably, in S1, the power flow calculation includes the following steps:

[0014] S11: Initialization, assigning an initial voltage value to all nodes and an initial current value to all branches;

[0015] S12: Forward push phase, starting from the leaf nodes of the first layer, forward push layer by layer, the leaf nodes use the node voltage and node power to calculate the branch current, as shown in formula (1), and other nodes use Kirchhoff's current law to calculate the branch current, as shown in formula (2), the formula is as follows:

[0016]

[0017] In the formula, is the branch current, is the rate of change of power, is the rate of change of voltage, is the internal current, For external circuit;

[0018] S13: Back-substitution stage, using the known root node voltage and the branch current obtained in the forward stage, the voltage of each node is obtained in sequence from the root node backward, as shown in formula (3), which is as follows:

[0019]

[0020] In the formula, i is the parent node and j is the child node. is the impedance of the branch between i and j, is the updated voltage value, is the initial voltage value;

[0021] S14: Iteration process, calculating whether the voltage amplitude correction amount of each node meets the convergence condition, as shown in formula (4), the formula is as follows:

[0022]

[0023] In the formula, is the voltage change rate of the jth node at time t, is the voltage change rate of the jth node at time t+1, ε is a constant;

[0024] S15: The convergence condition is composed of the number of iterations and the voltage amplitude correction amount. If it is not satisfied, the forward and backward processes are repeated. When the convergence condition is satisfied, the iteration stops and the voltage and branch current values ​​of each node are obtained.

[0025] Preferably, in S2, the forward-backward method calculates the current on each line segment in the forward process, calculates the voltage drop on each line segment and the voltage of each node in the back-substitution process, calculates the voltage at the user end by iteration, and solves the voltage of user 3 by equations (5) to (7): The formula is as follows:

[0026]

[0027] In the formula, are the currents of user 1, user 2 and user 3 respectively, t represents the number of iterations.

[0028] Preferably, formula (5) and formula (6) are substituted into formula (7) to obtain formula (8), which is as follows:

[0029]

[0030] Arrange formula (8) to obtain formula (9), which is as follows:

[0031]

[0032] The line voltage drop in formula (8) is obtained by adding up the voltage drops of each line segment. Each iteration needs to calculate the sum of the currents passing through each line segment using topology information.

[0033] Formula (9) describes the voltage drop as the superposition of the voltage drop of each user's current and the same line through which the current user's current passes. By calculating the total impedance of the shared transmission line between each user and other users, the impedance matrix is ​​obtained.

[0034] Preferably, the impedance matrix is ​​obtained by the following method:

[0035] In the formula, The total impedance of the transmission line shared by user j and user i is called the user shared line impedance, and the user shared line impedance matrix is ​​obtained, as shown in formula (10). The formula is as follows:

[0036]

[0037] according to From the definition of User shared line impedance matrix is a symmetric matrix;

[0038] The iterative process is shown in formula (11), and the formula is as follows:

[0039]

[0040] In the formula, is the current value of the tth iteration, is the voltage value of the tth iteration.

[0041] Preferably, the iterative term in formula (11) is replaced by a steady-state term, which is the state when the circuit is running, to obtain formula (12), which is as follows:

[0042]

[0043] In the formula, is the user voltage, is the user current, i=1…N user , is the transformer voltage, and the user shared line impedance matrix is ​​obtained by calculating through formula (12):

[0044] Preferably, in S3, for N user The voltage of user m is shown in formula (13), which is as follows:

[0045]

[0046] In the formula, is the transformer output voltage, is the shared line impedance of user m and user n, with the transformer output voltage Taking the phase of as the reference, decompose equation (13) into real part and imaginary part to get equation (14) and equation (15), the formula is as follows:

[0047]

[0048] In the formula, is the voltage phase angle of user n, is the power factor angle of user n.

[0049] Preferably, the power factor angle Through formula (16), the formula is as follows:

[0050]

[0051] In the formula, φ s is the power factor angle, P is the active power, U is the voltage, and I is the current;

[0052] For any user-side voltage, equations (14) and (15) can be constructed, where the unknown quantity is the voltage phase angle of each user: And all user resistance and reactance R mn , X mn , the modified equations of the Newton-Raphson method are written as shown in equation (17):

[0053]

[0054] After calculating the data at each moment and performing multiple iterations, the line impedances R and X are obtained. Preferably, in S4, based on the obtained line impedances R and X, the user shared line impedance Substituting into equation (12), the predicted voltage of each node in the low-voltage distribution network is obtained according to the estimated user load.

[0055] Compared with the prior art, the present invention has the following advantages:

[0056] The low-voltage distribution network node voltage prediction method proposed in this application does not require a known topology structure, and can effectively predict the node voltage based on only a few node voltage, current measurement values, and load estimation values. It effectively avoids the difficulty of knowing the low-voltage distribution network topology structure, greatly reduces the difficulty of predicting the low-voltage distribution network node voltage based on mechanism analysis, makes the prediction process simpler, more convenient, and more practical, and can also be applied to high-voltage distribution networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0058] Figure 1 It is the overall flow chart of the present invention;

[0059] Figure 2 It is a schematic diagram of the low-voltage distribution network model of the present invention. DETAILED DESCRIPTION

[0060] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0061] like Figure 1-Figure 2As shown, this embodiment proposes a low-voltage distribution network node voltage prediction based on user shared line impedance, including the following steps:

[0062] S1: Calculate the power flow based on the forward and back substitution method, and calculate the voltage and branch current values ​​of each node through the forward and back substitution process;

[0063] S2: By simplifying the forward-backward substitution method, the relationship between the node voltage, current and the user shared line impedance is obtained;

[0064] S3: Based on the Newton-Raphson method, solve the user shared line impedance;

[0065] S4: Based on the obtained user shared line impedance and the estimated user load, the predicted voltage of each node in the low-voltage distribution network is obtained.

[0066] The forward and back substitution method is a method for power flow calculation, which is suitable for radial networks. It calculates voltage and power through the forward and back substitution process, which is simple and efficient.

[0067] In low-voltage distribution networks, due to its radial network structure, that is, the power flow radiates outward from the transformer to each user, the forward-backward substitution method becomes a very applicable and efficient power flow calculation method. In this network, each user node has only one upstream node (except the root node) and multiple downstream nodes (except the leaf nodes), which greatly simplifies the power flow calculation process.

[0068] When the load conditions at the user end are known, the forward-backward method can effectively calculate the voltage level of each user node. This method starts from the leaf node, forward-forwards the input current and input power phase of each node along the network, and then back-forwards from the root node to correct the node voltage. This process is iterated continuously until the convergence condition is met, that is, the change in node voltage is less than a preset threshold.

[0069] The advantage of the forward-backward method is that its calculation process is simple and converges quickly, which is particularly suitable for radial networks. In low-voltage distribution networks, due to the relatively simple network structure, the forward-backward method can quickly and accurately calculate the voltage of each user node.

[0070] In S1, when using the forward-backward method for power flow calculation, it is first necessary to determine the topological structure of the circuit, search for leaf nodes as the first-level nodes, search for the parent nodes of leaf nodes as the second-level nodes, and continue to search for the parent nodes of the second-level nodes as the third-level nodes. Repeat the search until all the parent nodes of a certain level are root nodes, stop the search, delete the nodes in the previous level that are repeated in the later levels, form a true hierarchical relationship, and determine the node order for power flow calculation.

[0071] In S1, the power flow calculation includes the following steps:

[0072] S11: Initialization, assigning an initial voltage value to all nodes, usually assuming that the voltage of the root node is known (usually the nominal voltage), and assigning an initial current value to all branches, usually assumed to be 0;

[0073] S12: Forward push phase, starting from the leaf nodes of the first layer, forward push layer by layer, the leaf nodes use the node voltage and node power to calculate the branch current, as shown in formula (1), and other nodes use Kirchhoff's current law to calculate the branch current, as shown in formula (2), the formula is as follows:

[0074]

[0075] In the formula, is the branch current, is the rate of change of power, is the rate of change of voltage, is the internal current, For external circuit;

[0076] S13: Back-substitution stage, using the known root node voltage and the branch current obtained in the forward stage, the voltage of each node is obtained in sequence from the root node backward, as shown in formula (3), which is as follows:

[0077]

[0078] In the formula, i is the parent node and j is the child node. is the impedance of the branch between i and j, is the updated voltage value, is the initial voltage value;

[0079] S14: Iteration process, calculating whether the voltage amplitude correction amount of each node meets the convergence condition, as shown in formula (4), the formula is as follows:

[0080]

[0081] In the formula, is the voltage change rate of the jth node at time t, is the voltage change rate of the jth node at time t+1, ε is a constant;

[0082] S15: The convergence condition is composed of the number of iterations and the voltage amplitude correction amount. If it is not satisfied, the forward and backward processes are repeated. When the convergence condition is satisfied, the iteration stops and the voltage and branch current values ​​of each node are obtained.

[0083] The forward back-substitution method is simple and easy to implement, especially in radial networks, and it usually converges quickly with only a few iterations.

[0084] In S2, the forward-backward method calculates the current on each line segment during the forward process, and calculates the voltage drop on each line segment and the voltage of each node during the back-substitution process. Figure 2 For example, Figure 2 It is a schematic diagram of the low-voltage distribution network model of the present invention. The voltage at the user end is calculated by iteration, and the voltage of user 3 is solved by equations (5) to (7). The formula is as follows:

[0085]

[0086] In the formula, are the currents of user 1, user 2 and user 3 respectively, t represents the number of iterations.

[0087] Since only the user voltage is concerned Therefore, when calculating, equation (5) and equation (6) can be substituted into equation (7) to obtain equation (8), which is as follows:

[0088]

[0089] Arrange formula (8) to obtain formula (9), which is as follows:

[0090]

[0091] The line voltage drop in formula (8) is obtained by adding up the voltage drops of each line segment. Each iteration needs to calculate the sum of the currents passing through each line segment using topology information.

[0092] Formula (9) describes the voltage drop as the superposition of the voltage drop of each user's current and the same line through which the current user's current passes. By calculating the total impedance of the shared transmission line between each user and other users, the impedance matrix is ​​obtained, and there is no need to recalculate it in each subsequent iteration.

[0093] The impedance matrix is ​​obtained as follows:

[0094] In the formula, The total impedance of the transmission line shared by user j and user i is called the user shared line impedance, and the user shared line impedance matrix is ​​obtained, as shown in formula (10). The formula is as follows:

[0095]

[0096] according to From the definition of User shared line impedance matrix is a symmetric matrix;

[0097] The iterative process is shown in formula (11), and the formula is as follows:

[0098]

[0099] In the formula, is the current value of the tth iteration, is the voltage value of the tth iteration.

[0100] Formula (11) is the forward-backward iterative formula that only calculates the user voltage. It is known that the power flow calculation can be solved. The iterative term in equation (11) is replaced by the steady-state term, which is the state of the circuit when it is running, and equation (12) is obtained. The formula is as follows:

[0101]

[0102] In the formula, is the user voltage, is the user current, i=1…N user , is the transformer voltage. These data are all metering data. Therefore, the user shared line impedance matrix is ​​obtained by calculation through formula (12):

[0103] In S3, for N user The voltage of user m is shown in formula (13), which is as follows:

[0104]

[0105] In the formula, is the transformer output voltage, is the shared line impedance of user m and user n, with the transformer output voltage Taking the phase of as the reference, decompose equation (13) into real part and imaginary part to get equation (14) and equation (15), the formula is as follows:

[0106]

[0107] In the formula, is the voltage phase angle of user n, is the power factor angle of user n.

[0108] Since the low-voltage distribution network can only collect the amplitude of voltage, current and power, the voltage phase angle Unknown, power factor angle Through formula (16), the formula is as follows:

[0109]

[0110] In the formula, φ s is the power factor angle, P is the active power, U is the voltage, and I is the current;

[0111] For any user-side voltage, equations (14) and (15) can be constructed, where the unknown quantity is the voltage phase angle of each user: And all user resistance and reactance R mn , X mn , the modified equations of the Newton-Raphson method are written as shown in equation (17):

[0112]

[0113] In the formula,

[0114]

[0115] After calculating the data at each moment and multiple iterations, the line impedances R and X are obtained.

[0116] In S4, based on the obtained line impedance R and X, users share the line impedance Substituting into equation (12), the predicted voltage of each node in the low-voltage distribution network is obtained according to the estimated user load.

[0117] The low-voltage distribution network node voltage prediction method proposed by the present invention does not require a known topology structure, and can effectively predict the node voltage based on only a few node voltage, current measurement values ​​and load estimation values. It effectively avoids the difficulty of knowing the low-voltage distribution network topology structure, greatly reduces the difficulty of predicting the low-voltage distribution network node voltage based on mechanism analysis, makes the prediction process simpler, more convenient and practical, and can also be applied to high-voltage distribution networks.

[0118] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. Low-voltage distribution network node voltage prediction based on user-shared line impedance, characterized in that: The following steps are involved: S1: Calculate the power flow based on the forward and back substitution method, and calculate the voltage and branch current values ​​of each node through the forward and back substitution process; S2: By simplifying the forward-backward substitution method, the relationship between the node voltage, current and the user shared line impedance is obtained; S3: Based on the Newton-Raphson method, solve the user shared line impedance; S4: Based on the obtained user shared line impedance and the estimated user load, the predicted voltage of each node in the low-voltage distribution network is obtained.

2. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 1 is characterized in that: In S1, the topological structure of the circuit is determined, leaf nodes are searched as first-layer nodes, parent nodes of leaf nodes are searched as second-layer nodes, and parent nodes of second-layer nodes are searched as third-layer nodes. The search is stopped until all parent nodes of a certain layer of nodes are root nodes, and nodes in the previous layers that are repeated in the later layers are deleted to determine the node order for the power flow calculation.

3. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 1 is characterized in that: In S1, the power flow calculation includes the following steps: S11: Initialization, assigning an initial voltage value to all nodes and an initial current value to all branches; S12: Forward push phase, starting from the leaf nodes of the first layer, forward push layer by layer, the leaf nodes use the node voltage and node power to calculate the branch current, as shown in formula (1), and other nodes use Kirchhoff's current law to calculate the branch current, as shown in formula (2), the formula is as follows: In the formula, is the branch current, is the rate of change of power, is the rate of change of voltage, is the internal current, For external circuit; S13: Back-substitution stage, using the known root node voltage and the branch current obtained in the forward stage, the voltage of each node is obtained in sequence from the root node backward, as shown in formula (3), which is as follows: In the formula, i is the parent node and j is the child node. is the impedance of the branch between i and j, is the updated voltage value, is the initial voltage value; S14: Iteration process, calculating whether the voltage amplitude correction amount of each node meets the convergence condition, as shown in formula (4), the formula is as follows: In the formula, is the voltage change rate of the jth node at time t, is the voltage change rate of the jth node at time t+1, ε is a constant; S15: The convergence condition is composed of the number of iterations and the voltage amplitude correction amount. If it is not satisfied, the forward and backward processes are repeated. When the convergence condition is satisfied, the iteration stops and the voltage and branch current values ​​of each node are obtained.

4. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 1 is characterized in that: The forward-backward method calculates the current on each line segment in the forward process, and calculates the voltage drop on each line segment and the voltage of each node in the back-substitution process. The voltage at the user end is calculated by iteration, and the voltage of user 3 is solved by equations (5) to (7): The formula is as follows: In the formula, are the currents of user 1, user 2 and user 3 respectively, t represents the number of iterations.

5. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 4 is characterized in that: Substituting equation (5) and equation (6) into equation (7) yields equation (8), which is as follows: Arrange formula (8) to obtain formula (9), which is as follows: The line voltage drop in formula (8) is obtained by adding up the voltage drops of each line segment. Each iteration needs to calculate the sum of the currents passing through each line segment using topology information. Formula (9) describes the voltage drop as the superposition of the voltage drop of each user's current and the same line through which the current user's current passes. By calculating the total impedance of the shared transmission line between each user and other users, the impedance matrix is ​​obtained.

6. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 5 is characterized in that: The impedance matrix is ​​obtained as follows: In the formula, The total impedance of the transmission line shared by user j and user i is called the user shared line impedance, and the user shared line impedance matrix is ​​obtained, as shown in formula (10). The formula is as follows: according to From the definition of User shared line impedance matrix is a symmetric matrix; The iterative process is shown in formula (11), and the formula is as follows: In the formula, is the current value of the tth iteration, is the voltage value of the tth iteration.

7. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 6 is characterized in that: Replace the iterative term in equation (11) with the steady-state term, which is the state of the circuit when it is running, and get equation (12), which is as follows: In the formula, is the user voltage, is the user current, i=1…N user , is the transformer voltage, and the user shared line impedance matrix is ​​obtained by calculating through formula (12):

8. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 1 is characterized in that: In S3, for N user The voltage of user m is shown in formula (13), which is as follows: In the formula, is the transformer output voltage, is the shared line impedance of user m and user n, with the transformer output voltage Taking the phase of as the reference, decompose equation (13) into real part and imaginary part to get equation (14) and equation (15), the formula is as follows: In the formula, is the voltage phase angle of user n, is the power factor angle of user n.

9. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 8, characterized in that: Power factor angle Through formula (16), the formula is as follows: In the formula, is the power factor angle, P is the active power, U is the voltage, and I is the current; For any user-side voltage, equations (14) and (15) can be constructed, where the unknown quantity is the voltage phase angle of each user: And all user resistance and reactance R mn , X mn , the modified equations of the Newton-Raphson method are written as shown in equation (17): After calculating the data at each moment and multiple iterations, the line impedances R and X are obtained.

10. The low-voltage distribution network node voltage prediction based on user shared line impedance according to claim 9, characterized in that: In S4, based on the obtained line impedance R and X, the user shares the line impedance Substituting into equation (12), the predicted voltage of each node in the low-voltage distribution network is obtained according to the estimated user load.

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