A method, device, terminal and medium for calculating short-circuit current in a power system

Abstract

The present application discloses a method, device, terminal and medium for calculating short-circuit current in a power system. According to the characteristics of node electrical signals in a power system without synchronous generators after a short circuit, the present application constructs a short-circuit current calculation equation and a node voltage calculation equation, and then, based on the calculation equation, calculates the node voltage through cyclic calculation and updates the injected current. Through iterative optimization of the calculation equation, when the optimization is completed, the short-circuit point current of the power system without synchronous generators is calculated using the optimized short-circuit current calculation equation. Compared with the traditional scheme, it is more in line with the characteristics of the power system without synchronous generators, the calculation result is more accurate, and it can solve the technical problem of low accuracy of short-circuit current calculation caused by the inapplicability of the traditional short-circuit current calculation method to the new power system.

Description

Technical Field

[0001] The present application relates to the technical field of electric power, and in particular, to a method, device, terminal and medium for calculating short-circuit current in an electric power system. Background Art

[0002] In the design and operation of electric power systems and electrical equipment, short-circuit calculation is an essential calculation for solving a series of technical problems. One of the main problems is to select electrical equipment with sufficient mechanical and thermal stability, such as circuit breakers, instrument transformers, busbars, cables, etc., which must be based on short-circuit calculation. This includes calculating the impact current to check the electrodynamic stability of the equipment; calculating the periodic component of the short-circuit current at several moments to check the thermal stability of the equipment; calculating the effective value of the short-circuit current at a specified moment to check the breaking capacity of the circuit breaker, etc.

[0003] Calculating the effective value of the short-circuit current at a specified moment to check the breaking capacity of the circuit breaker is the main content of short-circuit analysis in modern large-scale AC / DC power systems. The commonly used short-circuit current calculation methods currently consider synchronous generators, transmission networks, and loads. Among them, synchronous generators are considered as a parallel combination of a constant current source and admittance, transmission networks are considered as a combination of resistance and reactance, and loads are considered as grounded branches and represented by constant impedance.

[0004] However, with the development of new energy technologies in recent years, new power systems without synchronous generators have begun to be widely applied. Since such power electronic node systems are only composed of new energy power generation systems such as wind power and photovoltaic power generation, and equipment such as flexible DC transmission, through the grid-forming control strategy of flexible DC, a constant voltage amplitude and frequency are provided for the system. However, the traditional short-circuit current calculation methods are not applicable to the new power systems, resulting in the technical problem of low accuracy in short-circuit current calculation. Summary of the Invention

[0005] The present application provides a method, device, terminal and medium for calculating short-circuit current in an electric power system, which is used to solve the technical problem of low accuracy in short-circuit current calculation caused by the inapplicability of traditional short-circuit current calculation methods to new power systems.

[0006] To solve the above technical problems, a first aspect of the present application provides a method for calculating short-circuit current in an electric power system, including:

[0007] Obtain the basic information of the electric power system, and construct a system node electrical energy parameter relationship equation for the electric power system when a short-circuit fault occurs, where the basic information includes: node impedance information;

[0008] Based on the system node electrical energy parameter relationship equation, construct a short-circuit current calculation equation and a node voltage calculation equation;

[0009] Based on the short-circuit current calculation equation and the node voltage calculation formula, combined with a preset initial injection current, calculate the node voltages of each non-short-circuit node in the power system, and update the injection current of the non-short-circuit node according to the node voltages;

[0010] Based on the updated injection current, recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltages. Then, compare the node voltages obtained in this calculation with the node voltages obtained in the previous calculation. If the comparison result does not meet the preset error threshold condition, recalculate the node voltages of each non-short-circuit node according to the current injection current and update the injection current according to the node voltages, and then compare the node voltages obtained in this calculation with the node voltages obtained in the previous calculation until the comparison result meets the error threshold condition;

[0011] Compare the node voltages with a preset low-voltage ride-through threshold. If there are nodes with voltages exceeding the low-voltage ride-through threshold, adjust the injection current of the nodes, and then return to recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltages. If there are no nodes with voltages exceeding the low-voltage ride-through threshold, calculate the short-circuit current of the power system according to the current injection current and the short-circuit current calculation equation.

[0012] Preferably, the system node electrical energy parameter relationship equation is specifically:

[0013]

[0014] In the formula, V' is the node voltage of the node equipment after the fault, I' is the injection current vector of the node equipment after the fault, Z is the node impedance matrix, and v f is the node voltage of the short-circuit point.

[0015] Preferably, the short-circuit current calculation equation and the node voltage calculation equation are specifically:

[0016]

[0017] V i = Z ni I n + Z fi I f

[0018] In the formula, I n is the injection current of the nth node, Z ni is the transfer impedance between the node and node i, Zfi is the transfer impedance between the short-circuit node and node i, Z nf is the transfer impedance between the node and the short-circuit node, Zff is the self - impedance of the short - circuit node.

[0019] Preferably, the basic information further specifically includes: node type information.

[0020] Preferably, the updating of the injection current of the non - short - circuit nodes according to the node voltage specifically includes:

[0021] Based on the updated injection current, recalculate the node voltages of each non - short - circuit node, and according to the node voltages, combined with the node types, update the injection currents of the first - type non - short - circuit nodes, the second - type non - short - circuit nodes, and the third - type non - short - circuit nodes, where the first - type non - short - circuit nodes are flexible direct - current with grid - following control, the second - type non - short - circuit nodes are new - energy units with grid - following control, and the third - type non - short - circuit nodes are new - energy units with constant reactive - power control.

[0022] Preferably, the comparing of the node voltage with a preset low - voltage ride - through threshold specifically includes:

[0023] According to the node voltage and the preset low - voltage ride - through threshold, combined with the node types, compare the node voltages of the second - type non - short - circuit nodes, the third - type non - short - circuit nodes, and the fourth - type non - short - circuit nodes with the preset low - voltage ride - through threshold, where the fourth - type non - short - circuit nodes are specifically new - energy units with constant reactive - current control.

[0024] Preferably, after calculating the short - circuit current of the power system, it further includes:

[0025] According to a preset short - circuit current maximum - minimum value verification formula, for the maximum value and the minimum value of the short - circuit current.

[0026] Meanwhile, a second aspect of the present application provides a power - system short - circuit current calculation device, including:

[0027] An electrical - energy parameter relationship construction unit, configured to obtain the basic information of the power system and construct a system - node electrical - energy parameter relationship equation of the power system when a short - circuit fault occurs, where the basic information includes: node impedance information;

[0028] A current - voltage calculation equation construction unit, configured to construct a short - circuit current calculation equation and a node - voltage calculation equation based on the system - node electrical - energy parameter relationship equation;

[0029] An injection - current update unit, configured to calculate the node voltages of each non - short - circuit node in the power system through the short - circuit current calculation equation and the node - voltage calculation formula, combined with a preset initial injection current, and update the injection currents of the non - short - circuit nodes according to the node voltages;

[0030] An injection current iterative update unit is configured to recalculate the node voltages of each non-short-circuit node based on the updated injection current, update the injection current according to the node voltages, then compare the node voltages obtained in this calculation with the node voltages obtained in the previous calculation. If the comparison result does not meet the preset error threshold condition, recalculate the node voltages of each non-short-circuit node based on the current injection current, update the injection current according to the node voltages, and then compare the node voltages obtained in this calculation with the node voltages obtained in the previous calculation until the comparison result meets the error threshold condition;

[0031] A low voltage ride-through determination unit is configured to compare the node voltages with a preset low voltage ride-through threshold. If there is a node whose voltage exceeds the low voltage ride-through threshold, adjust the injection current of the node, and then return to recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltages. If there is no node whose voltage exceeds the low voltage ride-through threshold, calculate the short-circuit current of the power system according to the current injection current and the short-circuit current calculation equation.

[0032] A third aspect of the present application provides a power system short-circuit current calculation terminal, including: a memory and a processor;

[0033] The memory is used to store program codes, and the program codes correspond to a power system short-circuit current calculation method provided in the first aspect of the present application;

[0034] The processor is used to execute the program codes.

[0035] A fourth aspect of the present application provides a computer-readable storage medium, in which program codes are stored, and the program codes correspond to a power system short-circuit current calculation method provided in the first aspect of the present application.

[0036] From the above technical solutions, it can be seen that the embodiments of the present application have the following advantages:

[0037] Based on the node electrical signal characteristics of a power system without a synchronous generator after a short circuit, the present application constructs a short-circuit current calculation equation and a node voltage calculation equation. Then, according to the calculation equation, the node voltages are calculated in a loop, the injection current is updated, and through iterative optimization of the calculation equation, when the optimization is completed, the short-circuit point current of the power system without a synchronous generator is calculated using the optimized short-circuit current calculation equation. Compared with the traditional solution, it is more in line with the characteristics of the power system without a synchronous generator, the calculation result is more accurate, and it can solve the technical problem of low accuracy of short-circuit current calculation caused by the inapplicability of the traditional short-circuit current calculation method to a new type of power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 It is a schematic flowchart of an embodiment of a method for calculating short-circuit current in a power system provided by the present application.

[0040] Figure 2 It is a schematic flowchart of another embodiment of a method for calculating short-circuit current in a power system provided by the present application.

[0041] Figure 3 It is a schematic structural diagram of an embodiment of a device for calculating short-circuit current in a power system provided by the present application. Detailed implementation manners

[0042] The applicant has found through research that in the commonly used short-circuit current calculation method, synchronous generators, transmission networks, and loads are considered. Among them, the synchronous generator is considered as a parallel combination of a constant current source and admittance, the transmission network is considered as a combination of resistance and reactance, and the load is considered as a grounded branch and represented by a constant impedance. After considering the above methods, the nodal equation of the power system can be expressed as:

[0043] YV = I (1)

[0044] where Y is the nodal admittance matrix, V is the nodal voltage vector, I is the nodal injection current vector, Only the current at the generator terminal node in I is not zero, and the currents at the remaining nodes are all zero.

[0045] By transforming Equation (1), Equation (2) can be obtained:

[0046] V = ZI (2)

[0047] where Z is the nodal impedance matrix, which is the inverse matrix of the nodal admittance matrix and can be obtained from the nodal admittance matrix, Z = Y -1 。

[0048] Assume that a direct grounding short circuit occurs at node f in the system, which is equivalent to adding an injection current i at node f f . Since the injection current of the constant current source of the synchronous generator remains unchanged before and after the fault, the nodal equation of the network after the short circuit becomes Equation (3):

[0049] V' = ZI + ZIf = V + ZI f (3)

[0050] Wherein, I f is the vector of the change value of the node injection current, only the value at node f is not zero, and the rest of the values are all zero.

[0051] After the short circuit, the voltage at node f becomes 0. Therefore, the voltage equation of node f in Equation (3) can be expressed as:

[0052] 0 = v f + z ff i f (4)

[0053] Therefore, the short-circuit current at node f is:

[0054]

[0055] Wherein, v f is the voltage at node f before the short circuit. All the above voltage, current, admittance or impedance values are complex numbers.

[0056] After the short-circuit current at node f is obtained, the voltages of the remaining nodes in the network can be obtained by Equation (3).

[0057] The above calculation method only considers the generator as a constant injection current source, and this method is applicable when there are only generators, AC transmission networks and loads in the calculated power system. However, in a power electronic node system without synchronous generators, for the calculation method of the short-circuit current of a power electronic node network without synchronous generators, considering that flexible DC, wind power and photovoltaic new energy power generation systems, loads, etc. are retained in the system, the processing steps according to the traditional method (described in the first part) are as follows.

[0058] (1) Under the normal operation state, establish the node voltage equation of the system as follows:

[0059] V = ZI (6)

[0060] Equation (6) has exactly the same form as Equation (2), the difference being that the node injection current vector I does not include the injection current of the synchronous generation node, and only includes the injection currents of the flexible converter node, wind turbine node, and photovoltaic power generation system node. Assume that the number of the injection current node is m, then i m = i d + ji q , wherein, i d , i qThey are the d-axis current and q-axis current injected into the system under normal operating conditions. The node can be a flexible DC converter station, a wind farm, or a photovoltaic power station. Since the flexible DC, wind turbines, or photovoltaic power generation systems all adopt direct current control strategies, i d and i q can be calculated from the control strategy of the device.

[0061] (2) After a short-circuit fault occurs, because the node voltage changes, all the node injection currents in Equation (6) mutate, and the injection current after the short circuit is determined by the node voltage after the fault. i m = i d '+ ji q ', where i d ' and

[0062] i q ' are the d-axis current and q-axis current injected into the system after the fault, respectively.

[0063] (3) After the short-circuit fault, the node equation (3) of the network becomes

[0064] V' = ZI' + ZI f (7)

[0065] In the formula, I' is the injection current vector of the node equipment after the fault. Compared with I in Equation (6), all the currents have changed. Therefore, V in Equation (3) cannot be used to represent ZI' anymore. Therefore, the calculation process after Equation (3) in the first part is no longer applicable.

[0066] It can be seen that the basic conditions of the above calculation method no longer exist, that is, the condition that "the injection current of the constant current source of the synchronous generator remains unchanged before and after the fault" does not exist. As a result, Equations (3) and (4) do not exist either. This causes the calculation process after Equation (3) to be no longer applicable to the short-circuit current calculation of a power system without a synchronous generator.

[0067] In view of this, the embodiments of the present application provide a power system short-circuit current calculation method, device, terminal, and medium, which are used to solve the technical problem of low accuracy of short-circuit current calculation caused by the inapplicability of the traditional short-circuit current calculation method to the new power system.

[0068] To make the invention purpose, features, and advantages of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the embodiments described below are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present application.

[0069] Please refer to Figure 1 , a method for calculating short-circuit current of a power system provided by the first embodiment of this application includes:

[0070] Step 101: Obtain the basic information of the power system, and construct a system node electrical energy parameter relationship equation of the power system when a short-circuit fault occurs according to the basic information.

[0071] Among them, the basic information includes: node impedance information.

[0072] It should be noted that first, obtain the basic information of the power system. According to the basic information, combined with the node equation of the power system in the short-circuit state, that is, formula (7), construct a system node electrical energy parameter relationship equation of the power system when a short-circuit fault occurs.

[0073] Step 102: Based on the system node electrical energy parameter relationship equation, construct a short-circuit current calculation equation and a node voltage calculation equation.

[0074] Step 103: Through the short-circuit current calculation equation and the node voltage calculation formula, combined with the preset initial injection current, calculate the node voltages of each non-short-circuit node in the power system, and update the injection current of the non-short-circuit node according to the node voltage.

[0075] It should be noted that based on the short-circuit current calculation equation and the node voltage calculation equation constructed in the previous step, combined with the preset initial value of the injection current, generally assign values according to the maximum current of each node, calculate the node voltages of each non-short-circuit node in the power system, and reversely update the injection current of the non-short-circuit node at the current voltage according to the calculated node voltage.

[0076] Step 104: Based on the updated injection current, recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltage. Then compare the node voltage obtained in this calculation with the node voltage obtained in the previous calculation. If the comparison result does not meet the preset error threshold condition, recalculate the node voltages of each non-short-circuit node according to the current injection current and update the injection current according to the node voltage. Then compare the node voltage obtained in this calculation with the node voltage obtained in the previous calculation until the comparison result meets the error threshold condition.

[0077] It should be noted that based on the injection current updated in step 103, the node voltage calculation and injection current update are performed again. The specific calculation and update methods are the same as those in the previous step, which will not be elaborated here. After the update, the node voltages calculated before and after are compared, and a judgment is made according to the comparison result. If the preset error threshold condition is not met, the node voltage calculation, injection current update, and node voltage comparison are performed again until the comparison result meets the error threshold condition. When the condition is met, step 105 can be entered.

[0078] Step 105: Compare the node voltage with the preset low-voltage ride-through threshold. If there is a node whose voltage exceeds the low-voltage ride-through threshold, adjust the injection current of the node, and then return to recalculate the node voltages of all non-short-circuit nodes and update the injection current according to the node voltages. If there is no node whose voltage exceeds the low-voltage ride-through threshold, execute the next step.

[0079] It should be noted that check the node voltage of the node to determine whether there is a node whose voltage exceeds the low-voltage ride-through threshold. If there is, adjust the injection current of the node. The adjustment method can be that the injection current of this unit is constantly 0, and then return to the previous step to perform the node voltage calculation, injection current update, and node voltage comparison again. If there is no such node, execute the next step.

[0080] Step 106: Calculate the short-circuit current of the power system according to the current injection current in combination with the short-circuit current calculation equation.

[0081] In the embodiment of the present application, according to the node electrical signal characteristics of the power system without synchronous generators after a short circuit, a short-circuit current calculation equation and a node voltage calculation equation are constructed. Then, according to this calculation equation, the node voltage is calculated in a loop and the injection current is updated. Through iterative optimization of this calculation equation, when the optimization ends, the short-circuit point current of the power system without synchronous generators is calculated using the optimized short-circuit current calculation equation. Compared with the traditional scheme, it is more in line with the characteristics of the power system without synchronous generators, the calculation result is more accurate, and it can solve the technical problem of low accuracy of short-circuit current calculation caused by the inapplicability of the traditional short-circuit current calculation method to the new power system.

[0082] The above content is the detailed description of the basic embodiment of a power system short-circuit current calculation method provided by the present application. The following is the detailed description of a specific embodiment of a power system short-circuit current calculation method provided by the present application.

[0083] Please refer to Figure 2 , based on the content of the previous embodiment, a power system short-circuit current calculation method provided by the second embodiment of the present application specifically includes the following content:

[0084] Furthermore, the specific equation for the relationship of power parameters of system nodes is as follows:

[0085]

[0086] In the formula, V' is the node voltage of the node equipment after the fault, I' is the injection current vector of the node equipment after the fault, Z is the node impedance matrix, and v f is the node voltage at the short - circuit point.

[0087] Suppose there are n nodes in total. Among them, the terminal node n is generally the power supply node, there are m power access points, and there are a total of n + m variables, which are the node voltages of n - 1 nodes, the injection currents of m voltage access points, and the short - circuit current at the short - circuit point. There are also a total of n + m equations. The number of variables and equations is the same, so they can be solved.

[0088] Suppose the short - circuit point is numbered f. By extracting the equation of node f in Equation (8), the short - circuit current calculation equation and the node voltage calculation equation can be obtained, which are specifically as follows:

[0089]

[0090] V i = Z ni I n + Z fi I f

[0091] In the formula, I n is the injection current of the nth node, Z ni is the transfer impedance between the node and node i, Zfi is the transfer impedance between the short - circuit node and node i, Z nf is the transfer impedance between the node and the short - circuit node, and Z ff is the self - impedance of the short - circuit node.

[0092] Furthermore, the basic information specifically also includes: node type information.

[0093] The specific node types can be divided into: flexible DC with Vf control, flexible DC with grid - following control, new - energy units with grid - following control, new - energy units with constant reactive - power control, and new - energy units with constant reactive - current control.

[0094] It should be noted that if a fine calculation of the actual short-circuit current in a certain mode is required, it is also possible to further consider that in this type of system, flexible DC generally adopts Vf control and grid-following control. Under Vf control, flexible DC will output the limit current to support the voltage of the access node as much as possible, while grid-following control refers to the VI curve obtained from the manufacturer's tests and controls the externally output current according to the voltage of the access node. Wind power and photovoltaic new energy power generation systems generally adopt grid-following control, constant reactive power control or constant reactive current control during low-voltage ride-through. In the engineering calculation of short-circuit current, it can be considered that wind power and photovoltaic new energy power generation systems only contribute to the short-circuit current when the voltage of the access node drops to the low-voltage ride-through threshold value (generally 0.9 p.u.). Among them, grid-following control generally calculates the output short-circuit current according to parameters such as the reactive power regulation coefficient given by the manufacturer's tests based on the voltage of the access node.

[0095] Further, updating the injection current of non-short-circuit nodes according to the node voltage specifically includes:

[0096] Based on the updated injection current, recalculate the node voltages of each non-short-circuit node and update the injection currents of the first type of non-short-circuit nodes, the second type of non-short-circuit nodes, and the third type of non-short-circuit nodes according to the node voltage and in combination with the node type. Among them, the first type of non-short-circuit nodes are flexible DCs adopting grid-following control, the second type of non-short-circuit nodes are new energy units adopting grid-following control, and the third type of non-short-circuit nodes are new energy units adopting constant reactive power control.

[0097] It should be noted that based on the short-circuit current calculation equation and the node voltage calculation equation mentioned in the above steps, according to the calculated node voltages of each node, calculate and update the injection currents of flexible DCs adopting grid-following control, new energy units adopting grid-following control, and new energy units adopting constant reactive power control at the current voltage.

[0098] Return to the previous step and substitute the obtained injection current into the aforementioned equation to recalculate the short-circuit node current and the node voltages of each node, and update the injection current of specific nodes according to the calculated node voltage. Compare the node voltages obtained from the two calculations. If the differences in all node voltages obtained from the two calculations are less than a certain threshold value (usually taken as 0.001 p.u.), enter step 105. If not satisfied, substitute the obtained injection current into the short-circuit current calculation equation and the node voltage calculation equation to recalculate until the threshold condition is met.

[0099] Further, comparing the node voltage with the preset low-voltage ride-through threshold value specifically includes:

[0100] Compare the node voltages of the second - type non - short - circuit nodes, third - type non - short - circuit nodes, and fourth - type non - short - circuit nodes with the preset low - voltage ride - through threshold according to the node voltage and the preset low - voltage ride - through threshold, in combination with the node type. Among them, the fourth - type non - short - circuit nodes are specifically new - energy units adopting constant reactive - current control.

[0101] It should be noted that check whether the access node voltages of all new - energy units adopting grid - following control, new - energy units adopting constant reactive - power control, and new - energy units adopting constant reactive - current control exceed the low - voltage ride - through threshold (usually 0.9 p.u.). If there is a new - energy unit whose node voltage exceeds the low - voltage ride - through threshold, set the injection current of this unit to be constantly 0 and return to the steps of calculating the node voltage and updating the injection current. If there is no new - energy unit whose node voltage exceeds the low - voltage ride - through threshold, enter step 106.

[0102] Furthermore, after step 106, it also includes:

[0103] Step 107: According to the preset short - circuit current maximum - minimum value verification formula, verify the maximum value and minimum value of the short - circuit current.

[0104] Among them, short - circuit current calculation is mainly used for checking the switching breaking capacity of switches. At this time, the maximum short - circuit current needs to be checked; for checking protection devices, the minimum short - circuit current needs to be concerned at the same time.

[0105] It can be seen from Equation (9) that the larger the injection current I' of each power source, the larger the short - circuit current at the short - circuit point. Therefore, when verifying the maximum short - circuit current, it can be calculated using the following formula:

[0106]

[0107] In the formula, I nmax is the maximum injection current of power source n.

[0108] (5) If it is necessary to verify the minimum short - circuit current, it can be considered that new - energy power generation systems such as wind power and photovoltaic power generation in the system do not provide short - circuit current, keep the output current at 0 during the fault, and only consider the injection current of the flexible DCs connected to the system.

[0109]

[0110] In the formula, I vscnmax is the maximum injection current of the nth flexible converter node.

[0111] The above content is the detailed description of the second embodiment of a power - system short - circuit current calculation method provided by this application. Next is the detailed description of the embodiments of a power - system short - circuit current calculation device, a terminal, and a storage medium provided by this application.

[0112] Please refer toFigure 3 , the third embodiment of the present application provides a device for calculating short-circuit current in a power system, including:

[0113] An electric energy parameter relationship construction unit 201, configured to obtain basic information of the power system, and construct a system node electric energy parameter relationship equation of the power system when a short-circuit fault occurs according to the basic information, where the basic information includes: node impedance information;

[0114] A current-voltage calculation equation construction unit 202, configured to construct a short-circuit current calculation equation and a node voltage calculation equation based on the system node electric energy parameter relationship equation;

[0115] An injection current update unit 203, configured to calculate the node voltages of each non-short-circuit node in the power system through the short-circuit current calculation equation and the node voltage calculation formula, and combine with a preset initial injection current, and update the injection current of the non-short-circuit node according to the node voltage;

[0116] An injection current iterative update unit 204, configured to recalculate the node voltages of each non-short-circuit node based on the updated injection current and update the injection current according to the node voltage, and then compare the node voltage obtained in this calculation with the node voltage obtained in the previous calculation. If the comparison result does not meet the preset error threshold condition, recalculate the node voltages of each non-short-circuit node according to the current injection current and update the injection current according to the node voltage, and then compare the node voltage obtained in this calculation with the node voltage obtained in the previous calculation until the comparison result meets the error threshold condition;

[0117] A low-voltage ride-through determination unit 205, configured to compare the node voltage with a preset low-voltage ride-through threshold. If there is a node whose voltage exceeds the low-voltage ride-through threshold, adjust the injection current of the node, and then return to recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltage. If there is no node whose voltage exceeds the low-voltage ride-through threshold, calculate the short-circuit current of the power system according to the current injection current and the short-circuit current calculation equation.

[0118] In addition, the fourth embodiment of the present application provides a terminal for calculating short-circuit current in a power system, including: a memory and a processor, and the memory and the processor can be communicatively connected through a data bus;

[0119] The memory is used to store program codes, and the program codes correspond to a method for calculating short-circuit current in a power system provided in the first embodiment or the second embodiment of the present application;

[0120] The processor is used to execute the program codes to implement a method for calculating short-circuit current in a power system provided by the present application.

[0121] The fifth embodiment of the present application provides a computer-readable storage medium, in which program code is stored, and the program code corresponds to a method for calculating short-circuit current of a power system provided in the first embodiment or the second embodiment of the present application.

[0122] Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the above-described terminal, device, and unit can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein.

[0123] In several embodiments provided by the present application, it should be understood that the disclosed terminal, device, and method can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed mutual coupling, direct coupling, or communication connection can be through some interfaces, and the indirect coupling or communication connection of the device or unit can be in electrical, mechanical, or other forms.

[0124] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and do not have to be used to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0125] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0126] In addition, each functional unit in various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0127] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0128] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present application.

Claims

1. A method for calculating short-circuit current in a power system, characterized in that, Including: Obtain the basic information of the power system, and construct a system node electrical energy parameter relationship equation of the power system when a short-circuit fault occurs according to the basic information, where the basic information includes: node impedance information; Based on the system node electrical energy parameter relationship equation, construct a short-circuit current calculation equation and a node voltage calculation equation; Through the short-circuit current calculation equation and the node voltage calculation formula, combined with a preset initial injection current, calculate the node voltages of each non-short-circuit node in the power system, and update the injection current of the non-short-circuit node according to the node voltages; Based on the updated injection current, recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltages, and then compare the node voltages obtained in this calculation with the node voltages obtained in the previous calculation. If the comparison result does not meet the preset error threshold condition, recalculate the node voltages of each non-short-circuit node according to the current injection current and update the injection current according to the node voltages, and then compare the node voltages obtained in this calculation with the node voltages obtained in the previous calculation until the comparison result meets the error threshold condition; Compare the node voltages with a preset low-voltage ride-through threshold. If there is a node with a voltage exceeding the low-voltage ride-through threshold, adjust the injection current of the node, and then return to recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltages. If there is no node with a voltage exceeding the low-voltage ride-through threshold, calculate the short-circuit current of the power system according to the current injection current and the short-circuit current calculation equation; The specific form of the system node electrical energy parameter relationship equation is: ； Wherein, is the node voltage of the node device after the fault, is the injection current vector of the node device after the fault, Z is the node impedance matrix, is the node voltage at the short-circuit point; The specific forms of the short-circuit current calculation equation and the node voltage calculation equation are: ； ； wherein, is the injection current of the nth node, is the transfer impedance between node n and node i, is the transfer impedance between the short - circuit node and node i, is the transfer impedance between node n and the short - circuit node, is the self - impedance of the short - circuit node.

2. The method for calculating short-circuit current of a power system according to claim 1, wherein The basic information specifically further includes: node type information.

3. A method for calculating short-circuit current of a power system according to claim 2, characterized in that, The updating the injection current of the non-short-circuit node according to the node voltages specifically includes: Based on the updated injection current, recalculate the node voltages of each non-short-circuit node and update the injection currents of the first type of non-short-circuit node, the second type of non-short-circuit node, and the third type of non-short-circuit node according to the node voltages and in combination with the node type, where the first type of non-short-circuit node is a flexible DC with grid-following control, the second type of non-short-circuit node is a new energy unit with grid-following control, and the third type of non-short-circuit node is a new energy unit with constant reactive power control.

4. A method for calculating short-circuit current of a power system according to claim 3, characterized in that, The comparing the node voltages with a preset low-voltage ride-through threshold specifically includes: According to the node voltages and the preset low-voltage ride-through threshold, and in combination with the node type, compare the node voltages of the second type of non-short-circuit node, the third type of non-short-circuit node, and the fourth type of non-short-circuit node with the preset low-voltage ride-through threshold, where the fourth type of non-short-circuit node is specifically a new energy unit with constant reactive current control.

5. A method for calculating short-circuit current of a power system according to claim 1, characterized in that, After calculating the short-circuit current of the power system, it further includes: According to a preset short-circuit current maximum and minimum value verification formula, verify the maximum and minimum values of the short-circuit current.

6. A device for calculating short-circuit current in a power system, characterized in that, Including: The electric energy parameter relationship construction unit is used to obtain the basic information of the power system and construct the system node electric energy parameter relationship equation of the power system when a short-circuit fault occurs according to the basic information, where the basic information includes: node impedance information; The current-voltage calculation equation construction unit is used to construct a short-circuit current calculation equation and a node voltage calculation equation based on the system node electric energy parameter relationship equation; The injection current update unit is used to calculate the node voltages of each non-short-circuit node in the power system through the short-circuit current calculation equation and the node voltage calculation formula, combined with a preset initial injection current, and update the injection current of the non-short-circuit node according to the node voltage; The injection current iterative update unit is used to recalculate the node voltages of each non-short-circuit node based on the updated injection current, update the injection current according to the node voltage, and then compare the node voltage obtained in this calculation with the node voltage obtained in the previous calculation. If the comparison result does not meet the preset error threshold condition, recalculate the node voltages of each non-short-circuit node according to the current injection current, update the injection current according to the node voltage, and then compare the node voltage obtained in this calculation with the node voltage obtained in the previous calculation until the comparison result meets the error threshold condition; The low-voltage ride-through determination unit is used to compare the node voltage with a preset low-voltage ride-through threshold. If there is a node with a voltage exceeding the low-voltage ride-through threshold, adjust the injection current of the node, and then return to recalculate the node voltages of each non-short-circuit node and update the injection current according to the node voltage. If there is no node with a voltage exceeding the low-voltage ride-through threshold, calculate the short-circuit current of the power system according to the current injection current and the short-circuit current calculation equation; The specific form of the system node electric energy parameter relationship equation is: ； Wherein, is the node voltage of the node device after the fault, is the injection current vector of the node device after the fault, Z is the node impedance matrix, is the node voltage at the short - circuit point; The specific forms of the short-circuit current calculation equation and the node voltage calculation equation are: ； ； wherein, is the injection current of the nth node, is the transfer impedance between node n and node i, is the transfer impedance between the short - circuit node and node i, is the transfer impedance between node n and the short - circuit node, is the self - impedance of the short - circuit node.

7. A short-circuit current calculation terminal for a power system, characterized in that, Including: A memory and a processor; The memory is used to store program code, and the program code corresponds to a power system short-circuit current calculation method as described in any one of claims 1 to 5; The processor is used to execute the program code.

8. A computer-readable storage medium, characterized in that, Program code is stored in the computer-readable storage medium, and the program code corresponds to a power system short-circuit current calculation method as described in any one of claims 1 to 5.

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