Network equipment capacity assessment method for improving short-circuit ratio indicators of multiple stations

Abstract

The present invention relates to the field of new energy grid connection technology and discloses a method for evaluating the capacity of networking equipment for improving the short-circuit ratio index of multiple stations. The method comprises the following steps: assuming that a networking compensation device is connected to the kth node of the system, the impedance matrix of the i-th row in the new impedance matrix after the networking device is connected is , the impedance matrix of the i-th row in the original impedance matrix before the networking device is connected is , and the impedance matrix of the k-th row in the original impedance matrix before the networking device is connected is ; the short-circuit ratio of the new energy multi-station at assessment point i after the networking device is connected is , the mutual impedance between assessment point i and compensation point k is , the equivalent impedance of the networking device is , and the self-impedance of compensation point k is . By replacing simulation calculations with analytical formulas, a rapid evaluation of the capacity of networking equipment that meets the requirements for improving the short-circuit ratio of new energy stations is achieved.

Description

Technical Field

[0001] The present application relates to the field of power electronic control technology, and in particular to a method for evaluating the capacity of network equipment for improving the short-circuit ratio index of multiple stations. Background Art

[0002] At present, the multiple renewable energy stations shortcircuit ratio (MRSCR) is used as a quantitative assessment indicator for the scale of renewable energy access in China. The MRSCR is defined as the relative ratio of the system nominal voltage to the voltage disturbance caused by renewable energy grid connection.

[0003] In addition, relevant standards stipulate that the new energy access system needs to meet the low MRSCR requirements as a necessary condition for the access system review. This indicator takes into account the amplitude and phase difference of each electrical quantity between different nodes, and takes into account the impact of the reactive power of new energy power generation equipment. It is suitable for the voltage strength assessment calculation of multiple new energy stations accessing the system in various scenarios. The calculation process of this indicator requires the reliance on the node impedance matrix of the entire network. In actual projects, in most cases, the owners of new energy stations can only obtain the system access review report, which can know the short-circuit ratio of multiple stations in the station after the new energy is connected. However, due to the acquisition of full-network data, it is necessary to further entrust the power grid operation department to calculate and analyze the capacity requirements of the network equipment to ensure that the short-circuit ratio of multiple stations after compensation meets the standards. This has certain limitations in guiding the actual decision-making of new energy station investment plans. Summary of the Invention

[0004] This application provides a network equipment capacity assessment method for improving the short-circuit ratio index of multiple stations to solve the problem of how to ensure that the short-circuit ratio of multiple stations after compensation meets the standard.

[0005] In order to solve the above technical problems, this application provides a network equipment capacity assessment method for improving the short-circuit ratio index of multiple stations, including:

[0006] Assume that the current injected into the AC system by each renewable energy grid-connected bus is , then the voltage of each grid-connected bus node is , , the MRSCR at the i-th renewable energy grid-connected bus in the system is ,in, is the nominal voltage of the ith grid-connected busbar node, Inject current into the i-th new energy power generation equipment / station, is the mutual impedance between node i and node k;

[0007] When the kth node of the system is connected to the network compensation device, the i-th row impedance matrix in the new impedance matrix after the network compensation device is connected is: ,in, The impedance matrix of row i in the original impedance matrix before the network equipment is connected, The kth row impedance matrix in the original impedance matrix before the network equipment is connected;

[0008] Will Substitute the MRSCR at the i-th renewable energy grid-connected busbar to obtain the renewable energy multi-station short-circuit ratio at the assessment point i after the grid-connected equipment is connected. : ,in, is the mutual impedance between the test point i and the compensation point k, is the equivalent impedance of the network equipment, is the self-impedance of compensation point k.

[0009] Furthermore, when the network equipment is directly connected to the system, the short-circuit capacity of the compensation point ,in, It is the short-circuit capacity of the new energy station grid connection point before the network equipment is connected. is the transformer short-circuit voltage percentage, is the rated capacity of the transformer. When the network equipment is connected to the system through the step-up transformer, the short-circuit capacity of the compensation point is , after simplifying the per-unit value, the self-impedance of the compensation point is obtained ,in, For the baseline capacity.

[0010] Furthermore, when the networking equipment is directly connected to the system or the networking equipment is connected to the system through a step-up transformer, when 1 standard current is injected at the compensation point k, the new energy station is regarded as a current source, the voltage of the compensation point k and the assessment point i are equal, and the mutual impedance of the assessment point i and the compensation point k.

[0011] Furthermore, when the networking equipment is directly connected to the system or connected to the system via a step-up transformer, if the access report gives the multi-station short-circuit ratio of the compensation point k, the multi-station short-circuit ratio of the compensation point before the networking equipment is connected is directly used.

[0012] Furthermore, when the access report only provides new energy machine side and short-circuit ratio of multiple stations at the grid connection point When the short circuit ratio of multiple stations at the compensation point before the network equipment is connected is : Where, The per unit impedance value of the boost transformer main transformer in the new energy station is It is the per unit value of the variable impedance of the new energy station unit.

[0013] Furthermore, when the networking equipment is directly connected to the system, the equivalent impedance of the networking equipment is , is the overcurrent multiple, is the base capacity, is the rated capacity of the equipment.

[0014] Furthermore, when the networking equipment is connected to the system via a step-up transformer, the step-up transformer and the networking equipment are considered as one, and their equivalent impedance is ,in, is the overcurrent multiple, transformer impedance ,in, is the transformer short-circuit voltage percentage, is the rated capacity of the transformer, As the benchmark capacity, the equivalent impedance of the networking equipment is changed by adjusting the capacity of the networking equipment to meet the short-circuit ratio standard of the new energy multi-station at the assessment point i after the networking equipment is connected.

[0015] The present invention provides a method for evaluating the capacity of networking equipment for improving the short-circuit ratio index of multiple stations. Under the condition that the short-circuit ratio of multiple stations of new energy stations before configuring the networking equipment is known, a quantitative calculation formula for the improvement value of the short-circuit ratio of multiple stations of different capacities and structures of networking equipment is derived. This method can be used to quickly evaluate the capacity of networking equipment that needs to be configured to meet the short-circuit ratio standard in the absence of full network data, simplifying the data input requirements for the calculation of the short-circuit ratio of multiple stations, not relying on the impedance matrix of the full network node, and being able to quickly calculate the short-circuit ratio of multiple stations based on the short-circuit ratio of multiple stations at the assessment point before the compensation equipment is connected in the new energy station access report, the short-circuit capacity of the grid connection point, and the parameters of the transformer and line in the station. By replacing the simulation calculation with an analytical formula, a rapid evaluation of the capacity of networking equipment that meets the improvement value of the short-circuit ratio of new energy stations is achieved. The method for evaluating the capacity of networking equipment for improving the short-circuit ratio index of multiple stations provided by the present invention is used in power grid planning under scenarios with high penetration of new energy, especially providing rapid decision support for the early planning stage, reducing the trial and error cost and the data collection threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 This is a structural diagram of a system in which the kth node is connected to a network compensation device according to an embodiment of the present invention;

[0018] Figure 2A schematic diagram of the structure of a direct access system for networking equipment provided in an embodiment of the present invention;

[0019] Figure 3 A schematic diagram of the system structure in which the networking equipment provided in an embodiment of the present invention is connected via a step-up transformer. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in this application in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0021] In the description of this application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal connections between two components; they can refer to wireless connections or wired connections. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0023] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0024] This application provides a method for evaluating the capacity of network equipment for improving the short-circuit ratio index of multiple sites, including:

[0025] Assume that the current injected into the AC system by each renewable energy grid-connected bus is , then the voltage of each grid-connected bus node is , , the MRSCR at the i-th renewable energy grid-connected bus in the system is ,in, is the nominal voltage of the ith grid-connected busbar node, Inject current into the i-th new energy power generation equipment / station, is the mutual impedance between node i and node k;

[0026] When the kth node of the system is connected to the network compensation device, the i-th row impedance matrix in the new impedance matrix after the network compensation device is connected is: ,in, The impedance matrix of row i in the original impedance matrix before the network equipment is connected, The kth row impedance matrix in the original impedance matrix before the network equipment is connected;

[0027] Will Substitute the MRSCR at the i-th renewable energy grid-connected busbar to obtain the renewable energy multi-station short-circuit ratio at the assessment point i after the grid-connected equipment is connected. : ,in, is the mutual impedance between the test point i and the compensation point k, is the equivalent impedance of the network equipment, is the self-impedance of compensation point k.

[0028] Figure 1 This is a schematic diagram of the structure of the kth node of the system connected to the network compensation device according to an embodiment of the present invention. Figure 1 , a network compensation device is connected to the kth node of the system to improve the multi-station short-circuit ratio (MRSCR) of node i. Connecting a network device to node k is equivalent to adding a radial branch to a new node q at node k and grounding node q, which is equivalent to closing a loop to the reference node. The network impedance matrix without the network device is: When the network equipment is connected to the compensation point k, since the q node is connected to the reference point (i.e., the grounding point), Vq=0. Cronus reduction can be performed to form a new network impedance matrix: From the above in, The impedance matrix of row i in the original impedance matrix before the network equipment is connected (i.e., assessment point i). The kth row impedance matrix (compensation point k) in the original impedance matrix before the network equipment is connected. is the mutual impedance between the test point i and the compensation point k, is the equivalent impedance of the network equipment, is the self-impedance of compensation point k.

[0029] From the formula It can be seen that the solution to the capacity of the network equipment required to meet the short-circuit ratio of multiple stations can be transformed into the solution of a single-variable algebraic equation, and only the following variables need to be obtained: the short-circuit ratio of multiple stations at the assessment point before the network equipment is connected , the short-circuit ratio of multiple stations at the compensation point before the network equipment is connected , the self-impedance of compensation point k , the mutual impedance between the test point i and the compensation point k , the equivalent impedance z of the network equipment.

[0030] Figure 2 This is a schematic diagram of the structure of the network equipment direct access system provided by the embodiment of the present invention. Figure 2 , when the network equipment is directly connected to the compensation point k, solve:

[0031] (1) Self-impedance at compensation point k The new energy station access report will provide the short-circuit capacity of the new energy station grid connection point before the network equipment is connected, and the short-circuit capacity of the equipment compensation point. , short-circuit capacity of equipment compensation point ,in, It is the short-circuit capacity of the new energy station grid connection point before the network equipment is connected. is the transformer short-circuit voltage percentage, is the rated capacity of the transformer. According to the definition of self-impedance, the self-impedance of a node is equal to the equivalent impedance of the node. The self-impedance of the compensation point is obtained by simplifying the per-unit value. ,in, For the baseline capacity.

[0032] (2) Mutual impedance between compensation point k and test point i; New energy passes Figure 2 When the typical unit wiring form shown is connected to the grid, combined with the definition of node mutual impedance, when a 1-unit current is injected into the compensation point k, the new energy station is regarded as a current source (i.e., open circuit), the voltage of the compensation point k is equal to that of the assessment point i, and the mutual impedance of the assessment point i and the compensation point k is equal. .

[0033] (3) Short-circuit ratio of multiple stations at the compensation point before network equipment is connected If the access report provides the short-circuit ratio of multiple stations at compensation point k, the short-circuit ratio of multiple stations at the compensation point before the network equipment is connected is directly used; if the access report only provides the short-circuit ratio of the new energy machine end and short-circuit ratio of multiple stations at the grid connection point When the short circuit ratio of multiple stations at the compensation point before the network equipment is connected is : Where, The per unit impedance value of the boost transformer main transformer in the new energy station is It is the per unit value of the variable impedance of the new energy station unit.

[0034] (4) Equivalent impedance of network equipment ;Equivalent impedance of network equipment , is the overcurrent multiple, is the base capacity, is the rated capacity of the equipment.

[0035] Figure 3 This is a schematic diagram of the structure of the network equipment connected to the system through a step-up transformer according to the embodiment of the present invention. Figure 3 When the network equipment is connected to the compensation point k through the step-up transformer, the self-impedance of the compensation point k is , the mutual impedance between compensation point k and assessment point i and the short-circuit ratio of multiple stations at the compensation point before the network equipment is connected The solution to the compensation point k is the same as that for directly connecting the network equipment, so it will not be repeated here.

[0036] When the networking equipment is connected to the system through a step-up transformer, the step-up transformer and the networking equipment can be considered as one, so their equivalent impedance ,in, is the overcurrent multiple, transformer impedance ,in, is the transformer short-circuit voltage percentage, is the rated capacity of the transformer, As the benchmark capacity, the equivalent impedance of the networking equipment is changed by adjusting the capacity of the networking equipment to meet the short-circuit ratio of the new energy multi-station at the assessment point i after the networking equipment is connected. , if the short circuit ratio of the new energy multi-station at the assessment point i after the network equipment is connected is As a fixed value, calculate the capacity of network equipment.

[0037] In the embodiment of the present invention, all impedances refer to per-unit values ​​under the system reference capacity, and the networking equipment may also refer to a phase shifter.

[0038] In the Power System Analysis and Synthesis Program (PSASP), the reliability of the proposed calculation method is verified by taking a regional power grid as an example. The boundary conditions are as follows: before the network equipment is connected, the assessment point =1.68, network equipment capacity 100MVA; overcurrent multiple 3pu.

[0039] The calculated and simulated values ​​of the assessment point i for the direct access system calculation of the network equipment are shown in Table 1.

[0040] Table 1

[0041] Calculated value of assessment point i after network equipment is connected Simulation value of assessment point i after network equipment is connected MRSCR 3.37 3.39

[0042] The calculated and simulated values ​​of the assessment point i calculated by the network equipment through the step-up transformer access system are shown in Table 2.

[0043] Table 2

[0044] Calculated value of assessment point i after network equipment is connected Simulation value of assessment point i after network equipment is connected MRSCR 2.15 2.377

[0045] According to Table 1 and Table 2, the calculated value of assessment point i is close to the simulated value of assessment point i, and the error is within the allowable range.

[0046] The present invention provides a method for evaluating the capacity of networking equipment for improving the short-circuit ratio index of multiple stations. Under the condition that the short-circuit ratio of multiple stations of new energy stations before configuring the networking equipment is known, a quantitative calculation formula for the improvement value of the short-circuit ratio of multiple stations of different capacities and structures of networking equipment is derived. This method can be used to quickly evaluate the capacity of networking equipment that needs to be configured to meet the short-circuit ratio standard in the absence of full network data, simplifying the data input requirements for the calculation of the short-circuit ratio of multiple stations, not relying on the impedance matrix of the entire network node, and being able to quickly calculate the short-circuit ratio of multiple stations based on the short-circuit ratio of multiple stations at the assessment point before the compensation equipment is connected in the new energy station access report, the short-circuit capacity of the grid connection point, and the parameters of the transformer and line in the station. By replacing the simulation calculation with an analytical formula, a rapid evaluation of the capacity of networking equipment that meets the improvement value of the short-circuit ratio of the new energy station is achieved. The method for evaluating the capacity of networking equipment for improving the short-circuit ratio index of multiple stations provided by the present invention is used in power grid planning under scenarios with high penetration of new energy, especially providing rapid decision support for the early planning stage, reducing the trial and error cost and the data collection threshold.

[0047] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A network equipment capacity assessment method for improving the short-circuit ratio index of multiple stations, characterized by: include: Assume that the current injected into the AC system by each renewable energy grid-connected bus is , then the voltage of each grid-connected bus node is , , the MRSCR at the i-th renewable energy grid-connected bus in the system is ,in, is the nominal voltage of the ith grid-connected busbar node, Inject current into the i-th new energy power generation equipment / station, is the mutual impedance between node i and node k; When the kth node of the system is connected to the network compensation device, the i-th row impedance matrix in the new impedance matrix after the network compensation device is connected is: , ,in, The impedance matrix of row i in the original impedance matrix before the network equipment is connected, The kth row impedance matrix in the original impedance matrix before the network equipment is connected; Will Substitute the MRSCR at the i-th renewable energy grid-connected busbar to obtain the renewable energy multi-station short-circuit ratio at the assessment point i after the grid-connected equipment is connected. : ,in, is the mutual impedance between the test point i and the compensation point k, is the equivalent impedance of the network equipment, is the self-impedance of compensation point k.

2. The method for evaluating network equipment capacity for improving short-circuit ratio indicators of multiple stations according to claim 1 is characterized in that: When the network equipment is directly connected to the system, the short-circuit capacity of the compensation point ,in, It is the short-circuit capacity of the new energy station grid connection point before the network equipment is connected. is the transformer short-circuit voltage percentage, is the rated capacity of the transformer. When the network equipment is connected to the system through the step-up transformer, the short-circuit capacity of the compensation point is , after simplifying the per-unit value, the self-impedance of the compensation point is obtained ,in, The base capacity.

3. The method for evaluating network equipment capacity for improving short-circuit ratio indicators of multiple stations according to claim 2 is characterized in that: When the networking equipment is directly connected to the system or connected to the system through a step-up transformer, when a 1-unit current is injected at the compensation point k, the new energy station is regarded as a current source, the voltage of the compensation point k is equal to that of the assessment point i, and the mutual impedance of the assessment point i and the compensation point k is equal. .

4. The method for evaluating network equipment capacity for improving short-circuit ratio indicators of multiple stations according to claim 1 is characterized in that: When the networking equipment is directly connected to the system or connected to the system via a step-up transformer, if the access report gives the multi-station short-circuit ratio of the compensation point k, the multi-station short-circuit ratio of the compensation point before the networking equipment is connected shall be directly used.

5. The method for evaluating network equipment capacity for improving short-circuit ratio indicators of multiple stations according to claim 4 is characterized in that: When the access report only provides new energy machine side and short-circuit ratio of multiple stations at the grid connection point When the short circuit ratio of multiple stations at the compensation point before the network equipment is connected is : Where, The per unit impedance value of the boost transformer main transformer in the new energy station is It is the per unit value of the variable impedance of the new energy station unit.

6. The method for evaluating network equipment capacity for improving short-circuit ratio indicators of multiple stations according to claim 1 is characterized in that: When the networking equipment is directly connected to the system, the equivalent impedance of the networking equipment is , is the overcurrent multiple, is the base capacity, is the rated capacity of the equipment.

7. The method for evaluating network equipment capacity for improving short-circuit ratio indicators of multiple stations according to claim 1 is characterized in that: When the networking equipment is connected to the system via a step-up transformer, the step-up transformer and the networking equipment are considered as one, and their equivalent impedance is ,in, is the overcurrent multiple, transformer impedance ,in, is the transformer short-circuit voltage percentage, is the rated capacity of the transformer, As the benchmark capacity, the equivalent impedance of the networking equipment is changed by adjusting the capacity of the networking equipment to meet the short-circuit ratio standard of the new energy multi-station at the assessment point i after the networking equipment is connected.

Images