Network construction equipment capacity evaluation method oriented to multi-station short-circuit ratio index improvement

Abstract

The invention relates to the technical field of new energy grid connection, and discloses a multi-station short-circuit ratio index improvement-oriented network construction equipment capacity evaluation method, which comprises the following steps of: assuming that network construction compensation equipment is accessed to the kth node of a system, and after the network construction equipment is accessed, an ith row impedance matrix in a new impedance matrix is # imgabs0 #, the # imgabs1 # is an ith line impedance matrix in the primary impedance matrix before the network construction equipment is accessed, and the # imgabs2 # is a kth line impedance matrix in the primary impedance matrix before the network construction equipment is accessed; new energy multi-station short-circuit ratios # imgabs3 #: # imgabs4 # and # imgabs5 # of the assessment point i after the network construction equipment is accessed are mutual impedance of the assessment point i and the compensation point k, # imgabs6 # is equivalent impedance of the network construction equipment, and # imgabs7 # is self-impedance of the compensation point k. Simulation calculation is replaced by an analytic formula, and rapid evaluation of the capacity of the network construction equipment meeting the requirement for improving the short-circuit ratio of the new energy field station is achieved.

Description

Technical Field

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

[0002] At present in China, the multiple renewable energy stations short-circuit ratio (MRSCR) is used as a quantitative evaluation index for the scale of new energy access. The MRSCR of multiple new energy stations is defined as the relative magnitude of the ratio of the system nominal voltage to the voltage disturbance generated by the grid connection of new energy.

[0003] And relevant standards stipulate the requirement for low MRSCR that new energy access to the system needs to meet as a necessary condition for the review of system access. This index takes into account the amplitudes and phase differences of various electrical quantities between different nodes, and also takes into account the influence of the reactive power of new energy generation equipment, and is applicable to the evaluation and calculation of the voltage strength of multiple new energy stations accessing the system under various different scenarios. The calculation of this index depends on the impedance matrix of all network nodes. In actual engineering, in most cases, the owners of new energy stations can only obtain the system access review report and can know the MRSCR of their own stations after new energy access. However, due to the need to obtain the whole network data, they need to further entrust the power grid operation department to calculate and analyze the capacity requirements of network-forming equipment to ensure that the compensated MRSCR meets the standard, which has certain limitations for guiding the decision-making of actual new energy station investment plans. Summary of the Invention

[0004] This application provides a method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index to solve the problem of how to ensure that the compensated MRSCR meets the standard.

[0005] To solve the above technical problems, this application provides a method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index, including: Let the currents injected by each new energy grid-connected bus into the AC system be , then the node voltages of each grid-connected bus , , and the MRSCR at the i-th new energy grid-connected bus in the system is , where is the nominal voltage of the i-th grid-connected bus node, is the current injected by the i-th new energy generation equipment / station, is the mutual impedance between node i and node k; At the k-th node of the system, a network-forming compensation device is connected. After the network-forming compensation device is connected, the impedance matrix of the i-th row in the new impedance matrix is , where is the impedance matrix of the i-th row in the original impedance matrix before the grid-forming device is connected, is the impedance matrix of the k-th row in the original impedance matrix before the grid-forming device is connected; Substitute into the MRSCR at the i-th new energy grid-connected bus to obtain the short-circuit ratio of the new energy multi-station at the assessment point i after the grid-forming device is connected : , where is the mutual impedance between the assessment point i and the compensation point k, is the equivalent impedance of the grid-forming device, is the self-impedance of the compensation point k.

[0006] Furthermore, when the grid-forming device is directly connected to the system, the short-circuit capacity of the compensation point , where is the short-circuit capacity of the new energy power station connection point before the grid-forming device is connected, is the percentage of the short-circuit voltage of the transformer, is the rated capacity of the transformer. When the grid-forming device is connected to the system through a step-up transformer, the short-circuit capacity of the compensation point is , and after simplification using the per-unit value, the self-impedance of the compensation point is , where is the base capacity.

[0007] Furthermore, when the grid-forming device is directly connected to the system or the grid-forming device is connected to the system through a step-up transformer, when injecting 1 per-unit current at the compensation point k, the new energy power station is regarded as a current source, the voltages of the compensation point k and the assessment point i are equal, and the mutual impedance between the assessment point i and the compensation point k.

[0008] Furthermore, when the grid-forming device is directly connected to the system or the grid-forming device is connected to the system through a step-up transformer, if the short-circuit ratio of the multi-station at the compensation point k is given in the access report, directly use the short-circuit ratio of the multi-station at the compensation point before the grid-forming device is connected.

[0009] Furthermore, when the access report only provides the new energy machine terminal and the short-circuit ratio of the multi-station at the connection point , the short-circuit ratio of the multi-station at the compensation point before the grid-forming device is connected : In the formula, is the per-unit value of the main transformer impedance of the new energy power station step-up transformer, is the per-unit value of the unit transformer impedance of the new energy power station.

[0010] Furthermore, when the grid-forming device is directly connected to the system, the equivalent impedance of the grid-forming device is , is the overcurrent multiple, is the base capacity, is the rated capacity of the device.

[0011] Further, when the network-forming device is connected to the system through a step-up transformer, the step-up transformer of the network-forming device and the network-forming device are regarded as a whole, and its equivalent impedance is , where is the overcurrent multiple, and the transformer impedance , where is the percentage of the short-circuit voltage of the transformer, is the rated capacity of the transformer, is the base capacity. By adjusting the capacity of the network-forming device, the equivalent impedance of the network-forming device is changed to meet the requirement that the short-circuit ratio of the multi-station of new energy at the assessment point i reaches the standard after the network-forming device is connected.

[0012] The method for evaluating the capacity of the network-forming device for improving the multi-station short-circuit ratio provided by the present invention derives a quantitative calculation formula for the improvement value of the multi-station short-circuit ratio of network-forming devices with different capacities and structures under the condition of knowing the multi-station short-circuit ratio of new energy stations before configuring the network-forming device. It can be used to quickly evaluate the capacity of the network-forming device that needs to be configured to meet the short-circuit ratio standard under the condition of lacking the whole network data, simplifies the data input requirements for calculating the multi-station short-circuit ratio, does not rely on the whole network node impedance matrix, and can realize the rapid calculation of the multi-station short-circuit ratio based on the multi-station short-circuit ratio, the short-circuit capacity at the grid connection point, and the parameters of transformers, lines, etc. at the assessment point before the compensation device is connected in the new energy station access report. By replacing the simulation calculation with an analytical formula, the rapid evaluation of the capacity of the network-forming device to meet the improvement of the short-circuit ratio of the new energy station is realized; the method for evaluating the capacity of the network-forming device for improving the multi-station short-circuit ratio provided by the present invention is applicable to the power grid planning in the new energy high-penetration scenario, especially provides rapid decision-making support for the early planning stage, and reduces the trial-and-error cost and the data acquisition threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0014] Figure 1 is a schematic structural diagram of the k-th node of the system in the embodiment of the present invention accessing the network-forming compensation device; Figure 2 is a schematic structural diagram of the network-forming device directly connected to the system provided by the embodiment of the present invention; Figure 3 is a schematic structural diagram of the network-forming device connected to the system through a step-up transformer provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The technical solutions in the present application will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0016] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0017] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can also be the communication inside two elements. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0018] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0019] The present application provides a method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index of multiple substations, including: Let the currents injected by each new energy grid-connected bus into the AC system be , then the node voltages of each grid-connected bus , , and the MRSCR at the i-th new energy grid-connected bus in the system is , where is the nominal voltage of the i-th grid-connected bus node, is the current injected by the i-th new energy power generation device / substation, is the mutual impedance between node i and node k; Connect a network-forming compensation device to the k-th node of the system. After the network-forming compensation device is connected, the impedance matrix of the i-th row in the new impedance matrix is , where is the impedance matrix of the i-th row in the original impedance matrix before the network-forming device is connected, is the impedance matrix of the k-th row in the original impedance matrix before the grid-forming device is connected; Substitute into the MRSCR at the i-th new energy grid-connected bus to obtain the short-circuit ratio of multiple new energy power stations at the assessment point i after the grid-forming device is connected : , where is the mutual impedance between the assessment point i and the compensation point k, is the equivalent impedance of the grid-forming device, is the self-impedance of the compensation point k.

[0020] Figure 1 is the structural schematic diagram of the k-th node of the system in the embodiment of the present invention when the grid-forming compensation device is connected. Refer to Figure 1 , when the grid-forming compensation device is connected to the k-th node of the system to improve the short-circuit ratio MRSCR of multiple power stations at the node i, connecting the grid-forming device to the node k is equivalent to adding a radial branch to a new node q at the node k and grounding the node q, that is, equivalent to closing a loop to the reference node. The network impedance matrix before the grid-forming device is connected is , when the grid-forming device is connected to the compensation point k, since the q node is connected to the reference point (i.e., the grounding point), so Vq = 0, and Kron reduction can be performed to form a new network impedance matrix: From the above, we get where is the impedance matrix of the i-th row in the original impedance matrix before the grid-forming device is connected (i.e., the assessment point i), is the impedance matrix of the k-th row in the original impedance matrix before the grid-forming device is connected (i.e., the compensation point k), is the mutual impedance between the assessment point i and the compensation point k, is the equivalent impedance of the grid-forming device, is the self-impedance of the compensation point k.

[0021] From the formula , it can be seen that the solution of the capacity of the grid-forming device that needs to be configured to meet the short-circuit ratio standard of multiple power stations can be reduced to the solution of a unary algebraic equation, and only the following variables need to be obtained: the short-circuit ratio of multiple power stations at the assessment point before the grid-forming device is connected , the short-circuit ratio of multiple power stations at the compensation point before the grid-forming device is connected , the self-impedance of the compensation point k , the mutual impedance between the assessment point i and the compensation point k , and the equivalent impedance z of the grid-forming device.

[0022] Figure 2 is the structural schematic diagram of the grid-forming device directly connected to the system provided by the embodiment of the present invention. Refer to Figure 2 , when the grid-forming device is directly connected to the compensation point k, solve respectively: (1) Self-impedance of compensation point k ; The new energy power station access report will provide the short-circuit capacity of the new energy power station at the grid connection point and the short-circuit capacity of the equipment compensation point before the grid-forming equipment is connected , the short-circuit capacity of the equipment compensation point , where is the short-circuit capacity of the new energy power station at the grid connection point before the grid-forming equipment is connected is the percentage of the short-circuit voltage of the transformer is the rated capacity of the transformer. It can be known from the definition of self-impedance that the self-impedance of a certain node is equal to the equivalent impedance of the node. After simplification using per-unit values, the self-impedance of the compensation point is obtained , where is the base capacity

[0023] (2) Mutual impedance between compensation point k and assessment point i; When the new energy is connected to the grid through the typical unit wiring form shown in Figure 2 , combining the definition of node mutual impedance, when 1 per-unit current is injected at the compensation point k, the new energy power station is regarded as a current source (i.e., open circuit), the voltages of the compensation point k and the assessment point i are equal, and the mutual impedance between the assessment point i and the compensation point k

[0024] (3) Multi-station short-circuit ratio of the compensation point before the grid-forming equipment is connected ; If the access report gives the multi-station short-circuit ratio of the compensation point k, directly use the multi-station short-circuit ratio of the compensation point before the grid-forming equipment is connected; When the access report only provides the new energy machine terminal and the multi-station short-circuit ratio of the grid connection point, the multi-station short-circuit ratio of the compensation point before the grid-forming equipment is connected : In the formula, is the per-unit value of the impedance of the main transformer of the step-up transformer of the new energy power station

[0025] (4) Equivalent impedance of the grid-forming equipment ; The equivalent impedance of the grid-forming equipment , is the over-current multiple is the base capacity is the rated capacity of the equipment

[0026] Figure 3 is the schematic diagram of the structure of the grid-forming equipment connected to the system through a step-up transformer provided by the embodiment of the present invention. Referring to Figure 3 , when the grid-forming equipment is connected to the compensation point k through a step-up transformer, the self-impedance of the compensation point k, the mutual impedance between the compensation point k and the assessment point i, and the multi-station short-circuit ratio The solution of the compensation point k directly connected to the network-forming device is the same as that described above and will not be elaborated here.

[0027] When the network-forming device is connected to the system through a step-up transformer, the network-forming device step-up transformer and the network-forming device can be regarded as a whole, so its equivalent impedance , where is the overcurrent multiple, and the transformer impedance , where is the percentage of the short-circuit voltage of the transformer, is the rated capacity of the transformer, is the base capacity. By adjusting the capacity of the network-forming device, the equivalent impedance of the network-forming device is changed to meet the short-circuit ratio of multiple new energy power stations at the assessment point i after connecting the network-forming device. The short-circuit ratio of multiple new energy power stations at the assessment point i after connecting the network-forming device , if the short-circuit ratio of multiple new energy power stations at the assessment point i after connecting the network-forming device is a fixed value, the capacity of the network-forming device is deduced.

[0028] In the embodiments of the present invention, all impedances refer to the per-unit values under the system base capacity, and the network-forming device may also refer to a synchronous condenser.

[0029] In the Power System Analysis Software Package (PSASP), taking a certain regional power grid as an example to verify the reliability of the proposed calculation method, the boundary conditions are as follows: before the network-forming device is connected, the assessment point =1.68, the capacity of the network-forming device is 100 MVA; the overcurrent multiple is 3 pu.

[0030] The calculated values and simulation values of the assessment point i for the direct connection of the network-forming device to the system are shown in Table 1 Table 1 Calculated value of assessment point i after the network construction device is connected Simulated value of assessment point i after the network construction device is connected MRSCR 3.37 3.39 The calculated values and simulation values of the assessment point i for the connection of the network-forming device to the system through a step-up transformer are shown in Table 2 Table 2 Calculated value of assessment point i after the network construction device is connected Simulated value of assessment point i after the network construction device is connected MRSCR 2.15 2.377 From Table 1 and Table 2, the calculated values of the assessment point i and the simulation values of the assessment point i are close, and the error is within the allowable range.

[0031] The network-forming equipment capacity evaluation method for improving the short-circuit ratio index of multiple substations provided by the present invention derives a quantitative calculation formula for the improvement value of the short-circuit ratio of multiple substations by network-forming equipment with different capacities and structures under the condition of the short-circuit ratio of multiple substations before the new energy substation is known to be configured with network-forming equipment. It can be used to quickly evaluate the capacity of network-forming equipment that needs to be configured to meet the short-circuit ratio standard under the condition of lacking whole-network data, simplifies the data input requirements for calculating the short-circuit ratio of multiple substations, does not rely on the whole-network node impedance matrix, and can realize the rapid calculation of the short-circuit ratio of multiple substations based on the short-circuit ratio of multiple substations at the assessment point before the compensation equipment is connected, the short-circuit capacity at the grid connection point, and parameters such as transformers and lines in the substation in the new energy substation access report. By replacing the simulation calculation with an analytical formula, the rapid evaluation of the capacity of network-forming equipment to meet the improvement of the short-circuit ratio of new energy power stations is realized; the network-forming equipment capacity evaluation method for improving the short-circuit ratio index of multiple substations provided by the present invention is applicable to the power grid planning in the new energy high-penetration scenario, especially provides rapid decision-making support for the early planning stage, and reduces the trial-and-error cost and data acquisition threshold.

[0032] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for evaluating the capacity of network-forming equipment to improve the short-circuit ratio index for multiple substations, characterized in that, including: Let the currents injected by each new energy grid-connected bus into the AC system be , then the node voltages of each grid-connected bus , . The MRSCR at the i-th new energy grid-connected bus in the system is , where is the nominal voltage of the i-th grid-connected bus node, is the current injected by the i-th new energy power generation equipment / power station, is the mutual impedance between node i and node k; Connect the network-forming compensation device to the k-th node of the system. After the network-forming compensation device is connected, the impedance matrix of the i-th row in the new impedance matrix is , , where is the impedance matrix of the i-th row in the original impedance matrix before the network-forming device is connected, and is the impedance matrix of the k-th row in the original impedance matrix before the network-forming device is connected; Substitute into the MRSCR at the i-th new energy grid-connected busbar, and obtain the short-circuit ratio of the multi-station new energy at the assessment point i after the grid-forming equipment is connected : , where is the mutual impedance between the assessment point i and the compensation point k, is the equivalent impedance of the grid-forming equipment, is the self-impedance of the compensation point k 2. The method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index for multiple substations according to claim 1, wherein When the network-forming device is directly connected to the system, the short-circuit capacity of the compensation point , where is the short-circuit capacity of the grid connection point of the new energy power station before the network-forming device is connected, is the percentage of the short-circuit voltage of the transformer, is the rated capacity of the transformer. When the network-forming device is connected to the system through a step-up transformer, the short-circuit capacity of the compensation point is . After simplification using per-unit values, the self-impedance of the compensation point is , where is the base capacity.

3. The grid-forming equipment capacity evaluation method for improving the short-circuit ratio index for multiple substations according to claim 2, characterized in that, When the network-forming device is directly connected to the system or the network-forming device is connected to the system through a step-up transformer, when 1 per-unit current is injected at the compensation point k, the new energy power station is regarded as a current source, the voltage at the compensation point k is equal to the voltage at the assessment point i, and the mutual impedance between the assessment point i and the compensation point k .

4. The capacity evaluation method of network-forming equipment for improving the short-circuit ratio index facing multiple substations according to claim 1, characterized in that When the network-forming device is directly connected to the system or the network-forming device is connected to the system through 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 network-forming device is connected is directly used.

5. The method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index for multiple substations according to claim 4, wherein When the access report only provides the new energy machine terminal and the short-circuit ratio of multiple substations at the grid connection point the short-circuit ratio of multiple substations at the compensation point before the grid-forming equipment is connected is In the formula is the per-unit value of the main transformer impedance of the step-up transformer of the new energy substation is the per-unit value of the unit transformer impedance of the new energy substation 6. The method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index for multiple substations according to claim 1, wherein When the network-forming device is directly connected to the system, the equivalent impedance of the network-forming device is , is the overcurrent multiple, is the base capacity, is the rated capacity of the device.

7. The method for evaluating the capacity of network-forming equipment for improving the short-circuit ratio index for multiple substations according to claim 1, wherein When the network-forming device is connected to the system through a step-up transformer, the step-up transformer of the network-forming device and the network-forming device are regarded as a whole, and its equivalent impedance is , where is the overcurrent multiple, and the transformer impedance is , where is the percentage of the short-circuit voltage of the transformer, is the rated capacity of the transformer, is the base capacity. By adjusting the capacity of the network-forming device, the equivalent impedance of the network-forming device is changed to meet the requirement that the short-circuit ratio of multiple new energy stations at the assessment point i after connecting the network-forming device reaches the standard.

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