Method and system for calculating short circuit current of power grid containing new energy equipment

Abstract

This invention belongs to the field of power system technology and provides a method and system for calculating the short-circuit current of a power grid including renewable energy equipment. The method includes: when a short-circuit fault occurs in the renewable energy equipment, calculating the initial voltage of the renewable energy equipment node and other nodes in the power grid; based on the initial voltage of the renewable energy equipment node and the I / U characteristic table of the renewable energy source, querying the output current of the renewable energy equipment; calculating the correction voltage of the renewable energy equipment node according to its self-impedance to correct the voltage of the renewable energy equipment node; performing iterative correction calculations on the voltage of the renewable energy equipment node until the difference between two consecutive queryed output currents of the renewable energy equipment does not exceed a set threshold, determining the final output current of the renewable energy equipment; performing correction calculations on the voltages of other nodes in the power grid; and calculating the magnitude of the short-circuit current of each branch to determine the protection settings of the corresponding protection devices on each branch.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, and in particular relates to a method and system for calculating the short-circuit current of a power grid that includes new energy equipment. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In power system calculations, the power source is an essential consideration. For an ideal power source, its terminal voltage and output current generally exhibit a linear relationship, such as... Figure 1 As shown. Therefore, according to the requirements of Thevenin's theorem and Norton's theorem, a general power source can be equivalently represented as a voltage source and an impedance connected in series, or a current source and an impedance connected in parallel. A linear relationship between the terminal voltage and output current of the power source is a prerequisite for the validity of Thevenin's theorem and Norton's theorem. When the relationship between the terminal voltage and output current of the power source is non-linear, the above equivalent calculations for the power source are no longer applicable.

[0004] In power flow calculations, when the system operates in a steady state, the grid voltage remains near its rated value, and the voltage and output current of each power source node are essentially linearly related. In grid fault calculations, when the fault point is far from the power source, the voltage drop at the power source's terminals is small, and the relationship between terminal voltage and output current remains linear. However, the inventors discovered that when a fault occurs near the power source, the voltage drop at the terminals is significant, and the relationship between terminal voltage and output current is no longer linear. In this case, the aforementioned equivalent values ​​no longer apply, making it impossible to accurately obtain the grid short-circuit current. This leads to inaccurate protection setting values ​​for protection devices, thereby reducing the overall stability of the power grid operation. Summary of the Invention

[0005] To address the technical problems mentioned above, this invention provides a method and system for calculating the short-circuit current of a power grid including new energy equipment. This method can correct the voltage of each node in the power grid topology based on the I / U characteristic curve of the new energy equipment, accurately calculate the short-circuit current of the power grid based on the corresponding impedance, and then determine the protection settings of the corresponding protection devices on each branch, thereby ensuring the stability of the entire power grid operation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a method for calculating the short-circuit current of a power grid including new energy equipment, comprising:

[0008] When a short-circuit fault occurs in a new energy device, the initial voltage of the new energy device node and other nodes in the power grid is calculated based on the power grid topology and parameters containing the new energy device.

[0009] Based on the initial voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, the output current of the new energy equipment is found. Then, based on the self-impedance at the new energy equipment node, the correction voltage of the new energy equipment node is calculated to correct the voltage of the new energy equipment node.

[0010] Based on the correction voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, the voltage of the new energy equipment node is iteratively corrected and calculated until the difference between the output current of the new energy equipment in two consecutive queries does not exceed the set threshold. The final output current of the new energy equipment is then determined, and the voltage of other nodes in the power grid is corrected and calculated accordingly.

[0011] Based on the corrected voltage of each node in the power grid and the mutual impedance of each branch between each node and the new energy equipment node, the magnitude of the short-circuit current of each branch is calculated, so as to determine the protection setting value of the corresponding protection device on each branch.

[0012] In one implementation, the I / U characteristic table of the new energy equipment is constructed based on the I / U relationship curve of the new energy equipment.

[0013] As one implementation method, based on the I / U relationship curve of new energy equipment, a piecewise linearization method or a point plotting method is used to construct the I / U characteristic table of new energy equipment.

[0014] As one implementation method, the corrected voltage values ​​for other nodes in the power grid are:

[0015] The product of the mutual impedance of the new energy equipment node and other nodes and the final output current of the new energy equipment is then added to the initial voltage of other nodes.

[0016] A second aspect of the present invention provides a system for calculating the short-circuit current of a power grid including new energy equipment, comprising:

[0017] The node initial voltage calculation module is used to calculate the initial voltage of the new energy equipment node and other nodes in the power grid according to the power grid topology and power grid topology parameters when a short circuit fault occurs in the new energy equipment.

[0018] The new energy equipment node voltage correction module is used to look up the output current of the new energy equipment based on the initial voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, and then calculate the correction voltage of the new energy equipment node according to the self-impedance at the new energy equipment node, so as to correct the voltage of the new energy equipment node.

[0019] The final output current determination module is used to perform iterative correction calculations on the voltage of the new energy equipment node based on the correction voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, until the difference between the output current of the new energy equipment found in two consecutive queries does not exceed the set threshold, and then determine the final output current of the new energy equipment, and then perform correction calculations on the voltage of other nodes in the power grid.

[0020] The short-circuit current calculation module is used to calculate the short-circuit current of each branch based on the corrected voltage of each node in the power grid and the mutual impedance of each branch between each node and the new energy equipment node, so as to determine the protection setting value of the corresponding protection device on each branch.

[0021] In one implementation, the I / U characteristic table of the new energy equipment is constructed based on the I / U relationship curve of the new energy equipment.

[0022] As one implementation method, based on the I / U relationship curve of new energy equipment, a piecewise linearization method or a point plotting method is used to construct the I / U characteristic table of new energy equipment.

[0023] In one implementation, in the final output current determination module, the corrected voltage values ​​of other nodes in the power grid are:

[0024] The product of the mutual impedance of the new energy equipment node and other nodes and the final output current of the new energy equipment is then added to the initial voltage of other nodes.

[0025] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the above-described method for calculating the grid short-circuit current including new energy equipment.

[0026] A fourth aspect of the present invention provides a computer device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the above-described method for calculating the short-circuit current of a power grid including new energy equipment.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention is based on the fact that the current of new energy equipment is zero during a short circuit fault and the I / U characteristic curve of the new energy equipment. It determines the final output current of the new energy equipment by determining that the difference between the output current of the new energy equipment obtained from two consecutive queries does not exceed a set threshold. Then, it corrects the voltage of other nodes in the power grid based on the final output current of the new energy equipment. Finally, it accurately calculates the short circuit current of the power grid based on the corresponding impedance, and then determines the protection settings of the corresponding protection devices on each branch, thus ensuring the stability of the entire power grid operation.

[0029] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 It is the curve showing the relationship between the power supply's terminal voltage and output current;

[0032] Figure 2 It is a composite isoorder network;

[0033] Figure 3 This is the IU characteristic curve of the photovoltaic power generation port;

[0034] Figure 4 This is the IU characteristic curve of the doubly fed wind turbine port;

[0035] Figure 5 This is a schematic diagram of the calculation method for grid short-circuit current including new energy equipment according to an embodiment of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] Example 1

[0040] The conventional principle for calculating power grid faults is:

[0041] The power grid is equivalently represented, retaining faulty nodes. The equivalent power grid is then decomposed into positive-sequence, negative-sequence, and zero-sequence networks, where the positive-sequence network is an active network, and the negative-sequence and zero-sequence networks are passive networks. Based on the fault type and fault conditions, the boundary conditions of the fault points are obtained, forming a composite sequence network, such as... Figure 2 As shown; in the composite sequence network, only the positive sequence network provides power. The short-circuit current enters the negative sequence network and the zero sequence network through the associated boundary. First, the positive sequence short-circuit current at the fault point is calculated. Then, the negative sequence current, the zero sequence current, and the positive sequence, negative sequence, and zero sequence voltage at each node are calculated according to the boundary conditions.

[0042] Since the grid power supply output only has positive sequence, only the power supplies in the positive sequence network are considered. As mentioned above, when the fault point is far from the power supply, its terminal voltage is close to the rated value, and the output current has an approximately linear relationship with the terminal voltage. When a fault occurs near the power supply, the terminal voltage drops significantly, and the output current no longer maintains a linear relationship with the terminal voltage; therefore, the output current must be calculated separately.

[0043] For a conventional generator, its output characteristics are represented by a calculated current curve. This curve shows that the generator's output current is related to its equivalent load impedance. When the equivalent impedance of the power supply node is determined, the output current I at different time points can be obtained by referring to a table. d .

[0044] It can be seen that, under the condition of the equivalent impedance of the power supply, the generator's output current I d Since the value is not fixed, it can be considered as a current source superimposed on the power grid. Assuming the voltage node is d, the voltage ΔU generated by this current source at any node i can be calculated using the following formula. i :

[0045] ΔU i =I d ·Z id (1)

[0046] Among them, Z id Let be the mutual impedance between the generator node and any node i.

[0047] Based on the superposition principle, by adding this voltage to the node voltages obtained from fault calculations, the voltages of each node in the power grid considering the generators can be obtained. The implementation steps are as follows:

[0048] Initiate routine fault calculation to calculate the voltage at each voltage node after a fault.

[0049] Select a generator near the short-circuit point, extract the self-impedance of the generator node, and then look up the generator calculation curve table based on the self-impedance to determine the corresponding short-circuit current, which is the generator output current.

[0050] The correction voltage generated by the generator output current at each node is calculated according to equation (1), and the voltage at each node is superimposed and corrected.

[0051] For new energy equipment (such as photovoltaic power generation equipment, doubly fed wind turbines, etc.), when its terminal voltage decreases, the characteristics of the output current are related to the node voltage. Unlike conventional generators, the output current cannot be directly calculated and the node voltage cannot be corrected.

[0052] Figure 3 and Figure 4 The output current characteristics of photovoltaic power generation equipment and doubly-fed wind turbines are given respectively. It can be seen that the magnitude of their output current is related to the terminal voltage. When the terminal voltage is high, the output current remains constant. When the terminal voltage is lower than a certain threshold (0.2 times the rated value for photovoltaic power generation equipment and 0.4 times the rated value for doubly-fed wind turbines), the output current decreases sharply.

[0053] Since the output current of the aforementioned new energy equipment is related to the terminal voltage, and the magnitude of the output current in turn affects the magnitude of the terminal voltage, this embodiment introduces an iterative method in fault calculation to calculate the magnitude of the output current of the new energy equipment after a grid fault.

[0054] Reference Figure 5 The method for calculating the grid short-circuit current of new energy equipment in this embodiment specifically includes the following steps:

[0055] Step 1: When a short-circuit fault occurs in the new energy equipment, calculate the initial voltage of the new energy equipment node and other nodes in the power grid according to the power grid topology structure and parameters containing the new energy equipment.

[0056] In practical implementation, in power grid systems that include new energy equipment, the new energy equipment is equivalent to a variable current source, a power grid topology is constructed, and then the self-impedance Z at the node of the new energy equipment is obtained based on the power grid topology parameters. d and the mutual impedance Z between this node and other nodes i di .

[0057] Step 2: Based on the initial voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, look up the output current of the new energy equipment, and then calculate the correction voltage of the new energy equipment node according to the self-impedance at the new energy equipment node, so as to correct the voltage of the new energy equipment node.

[0058] The I / U characteristic table of the new energy equipment is constructed based on the I / U relationship curve of the new energy equipment. For example, the I / U characteristic table of the new energy equipment can be constructed using a piecewise linearization method or a point plotting method based on the I / U relationship curve of the new energy equipment.

[0059] Step 3: Based on the correction voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, perform iterative correction calculation on the voltage of the new energy equipment node until the difference between the output current of the new energy equipment in two consecutive queries does not exceed the set threshold, determine the final output current of the new energy equipment, and then perform correction calculation on the voltage of other nodes in the power grid.

[0060] Let the initial voltage of the new energy node be U, and let U d =U. According to U d Consult the corresponding I / U characteristic table to obtain the output current ΔI of the device, substitute it into formula (2), and calculate the node correction voltage ΔU. d .

[0061] ΔU d =Z d ·Δl (2)

[0062] Then substitute it into the following equation (3):

[0063] U d =U+ΔU d (3)

[0064] According to U d Continue to consult the I / U characteristic table and perform iterative calculations. The difference between the output current of the new energy equipment obtained from two consecutive queries does not exceed the set threshold ε (generally, ε is 10). -7 )until.

[0065] Step 4: Based on the corrected voltage of each node in the power grid and the mutual impedance of each branch between each node and the new energy equipment node, calculate the magnitude of the short-circuit current of each branch, so as to determine the protection setting value of the corresponding protection device on each branch.

[0066] The corrected voltage values ​​of other nodes in the power grid are: the product of the mutual impedance of the new energy equipment node and other nodes and the final output current of the new energy equipment, plus the sum of the initial voltages of other nodes.

[0067] Specifically, based on the final output current ΔI of the new energy equipment, the voltage correction of other nodes in the power grid can be calculated and substituted into the following formula:

[0068] U i =U i +Z di ·Δl (4)

[0069] The corrected node voltages obtained from the above calculation process are positive sequence quantities. Figure 2 The composite sequence network shown can be further used to calculate the values ​​of the negative and zero sequence components.

[0070] It should be noted that the relationship between the magnitude of the short-circuit current and the protection setting of the corresponding branch protection device is existing technology. Those skilled in the art can match and set the protection device according to its specific type and model, which will not be elaborated here.

[0071] The above algorithm based on the superposition principle is applicable to power generation equipment with various characteristics in the power grid. When the output current of the equipment is dependent on the terminal voltage, the iterative algorithm can effectively handle the influence of the output current on the calculation results of power grid faults and realize the correction calculation of node voltage.

[0072] This embodiment is based on the fact that the current of the new energy equipment is zero during a short circuit fault and the I / U characteristic curve of the new energy equipment. It determines the final output current of the new energy equipment based on the fact that the difference between the output current of the new energy equipment obtained from two consecutive queries does not exceed a set threshold. Then, it corrects the voltage of other nodes in the power grid based on the final output current of the new energy equipment. Finally, it accurately calculates the short circuit current of the power grid based on the corresponding impedance, and then determines the protection setting value of the corresponding protection device on each branch, thus ensuring the stability of the entire power grid operation.

[0073] Example 2

[0074] This embodiment provides a system for calculating the short-circuit current of a power grid that includes new energy equipment, comprising:

[0075] (1) Node initial voltage calculation module, which is used to calculate the initial voltage of new energy equipment nodes and other nodes in the power grid according to the power grid topology structure and power grid topology parameters when a short circuit fault occurs in the new energy equipment.

[0076] (2) New energy equipment node voltage correction module, which is used to look up the output current of the new energy equipment based on the initial voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, and then calculate the correction voltage of the new energy equipment node based on the self-impedance at the new energy equipment node, so as to correct the voltage of the new energy equipment node.

[0077] In the specific implementation process, the I / U characteristic table of the new energy equipment is constructed based on the I / U relationship curve of the new energy equipment.

[0078] Specifically, based on the I / U relationship curve of new energy equipment, a piecewise linearization method or a point plotting method is used to construct the I / U characteristic table of new energy equipment.

[0079] (3) The final output current determination module is used to perform iterative correction calculation on the voltage of the new energy equipment node based on the correction voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, until the difference between the output current of the new energy equipment in two consecutive queries does not exceed the set threshold, and then determine the final output current of the new energy equipment, and then perform correction calculation on the voltage of other nodes in the power grid.

[0080] (4) Short-circuit current calculation module, which is used to calculate the short-circuit current of each branch based on the corrected voltage of each node in the power grid and the mutual impedance of each branch between each node and the new energy equipment node, so as to determine the protection setting value of the corresponding protection device on each branch.

[0081] In the specific implementation process, in the final output current determination module, the corrected voltage values ​​of other nodes in the power grid are:

[0082] The product of the mutual impedance of the new energy equipment node and other nodes and the final output current of the new energy equipment is then added to the initial voltage of other nodes.

[0083] It should be noted that each module in this embodiment corresponds one-to-one with each step in Embodiment 1, and their specific implementation processes are the same, so they will not be repeated here.

[0084] This embodiment is based on the fact that the current of the new energy equipment is zero during a short circuit fault and the I / U characteristic curve of the new energy equipment. It determines the final output current of the new energy equipment based on the fact that the difference between the output current of the new energy equipment obtained from two consecutive queries does not exceed a set threshold. Then, it corrects the voltage of other nodes in the power grid based on the final output current of the new energy equipment. Finally, it accurately calculates the short circuit current of the power grid based on the corresponding impedance, and then determines the protection setting value of the corresponding protection device on each branch, thus ensuring the stability of the entire power grid operation.

[0085] Example 3

[0086] This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps in the above-described method for calculating the grid short-circuit current of new energy equipment.

[0087] Example 4

[0088] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the above-described method for calculating the short-circuit current of a power grid containing new energy equipment.

[0089] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of calculating short circuit current of a power grid comprising a new energy device, characterized by, include: When a short-circuit fault occurs in a new energy device, the initial voltage of the new energy device node and other nodes in the power grid is calculated based on the power grid topology and parameters containing the new energy device. Based on the initial voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, the output current of the new energy equipment is found. Then, based on the self-impedance at the new energy equipment node, the correction voltage of the new energy equipment node is calculated to correct the voltage of the new energy equipment node. Based on the correction voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, the voltage of the new energy equipment node is iteratively corrected and calculated until the difference between the output current of the new energy equipment in two consecutive queries does not exceed the set threshold. The final output current of the new energy equipment is then determined, and the voltage of other nodes in the power grid is corrected and calculated accordingly. The corrected voltage values ​​for other nodes in the power grid are: The product of the mutual impedance of the new energy equipment node and other nodes and the final output current of the new energy equipment is then added to the initial voltage of other nodes. Based on the corrected voltage of each node in the power grid and the mutual impedance of each branch between each node and the new energy equipment node, the magnitude of the short-circuit current of each branch is calculated, so as to determine the protection setting value of the corresponding protection device on each branch.

2. The method for calculating the short-circuit current of the power grid including new energy equipment as described in claim 1, characterized in that, The I / U characteristic table of the new energy equipment is constructed based on the I / U relationship curve of the new energy equipment.

3. The method for calculating the short-circuit current of the power grid including new energy equipment as described in claim 2, characterized in that, Based on the I / U relationship curves of new energy equipment, a table of I / U characteristics of new energy equipment is constructed using a piecewise linearization method or a point plotting method.

4. A system for calculating the short-circuit current of a power grid including new energy equipment, characterized in that, include: The node initial voltage calculation module is used to calculate the initial voltage of the new energy equipment node and other nodes in the power grid according to the power grid topology and power grid topology parameters when a short circuit fault occurs in the new energy equipment. The new energy equipment node voltage correction module is used to look up the output current of the new energy equipment based on the initial voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, and then calculate the correction voltage of the new energy equipment node according to the self-impedance at the new energy equipment node, so as to correct the voltage of the new energy equipment node. The final output current determination module is used to perform iterative correction calculations on the voltage of the new energy equipment node based on the correction voltage of the new energy equipment node and the corresponding I / U characteristic table of the new energy, until the difference between the output current of the new energy equipment found in two consecutive queries does not exceed the set threshold, and then determine the final output current of the new energy equipment, and then perform correction calculations on the voltage of other nodes in the power grid. In the final output current determination module, the corrected voltage values ​​of other nodes in the power grid are: The product of the mutual impedance of the new energy equipment node and other nodes and the final output current of the new energy equipment is then added to the initial voltage of other nodes. The short-circuit current calculation module is used to calculate the short-circuit current of each branch based on the corrected voltage of each node in the power grid and the mutual impedance of each branch between each node and the new energy equipment node, so as to determine the protection setting value of the corresponding protection device on each branch.

5. The power grid short-circuit current calculation system including new energy equipment as described in claim 4, characterized in that, The I / U characteristic table of the new energy equipment is constructed based on the I / U relationship curve of the new energy equipment.

6. The power grid short-circuit current calculation system including new energy equipment as described in claim 5, characterized in that, Based on the I / U relationship curves of new energy equipment, a table of I / U characteristics of new energy equipment is constructed using a piecewise linearization method or a point plotting method.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the method for calculating the short-circuit current of the power grid including new energy equipment as described in any one of claims 1-3.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for calculating the grid short-circuit current including new energy equipment as described in any one of claims 1-3.

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