AC three-phase short-circuit current calculation method and system considering flexible DC transmission

Abstract

The present invention relates to a method and system for calculating AC three-phase short-circuit current taking into account flexible direct current (HVDC) transmission. The method comprises: determining the system's node impedance matrix based on the power system's operating mode, as well as the transfer impedance of each power source node to a short-circuit point, the mutual impedance between the flexible direct current (DC) grid connection point and the short-circuit point, and the self-impedance of the short-circuit point; calculating a first short-circuit current at the short-circuit point based on the transfer impedance of each power source node to the short-circuit point; calculating a second short-circuit current provided by a flexible direct current (DC) equivalent current source injected solely into the flexible direct current (DC) grid connection point based on the mutual impedance between the flexible direct current (DC) grid connection point and the short-circuit point and the self-impedance of the short-circuit point; obtaining a maximum short-circuit current provided by the flexible direct current when the first short-circuit current and the second short-circuit current are in phase, and obtaining the AC three-phase short-circuit current of the flexible direct current by vectorially superimposing the first short-circuit current and the maximum short-circuit current. The present invention solves the problem of large deviation in the calculation of the AC three-phase short-circuit current provided by the flexible direct current (HVDC) and can be applied in the field of flexible direct current transmission.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current transmission, and in particular to a method and system for calculating alternating current three-phase short-circuit current taking flexible direct current transmission into account. Background Art

[0002] Compared to conventional DC transmission technology, Flexible DC transmission offers advantages such as flexible control, independent regulation of active and reactive power, no commutation failures, and a smaller footprint. It is particularly suitable for deep penetration into load centers to improve power flow distribution and enhance the overall power supply capacity of the grid. However, load centers are characterized by high system intensity and dense grid structures, often facing the problem of excessive short-circuit currents. While Flexible DC transmission enables fault ride-through, it does not block during short-circuit faults to reduce system recovery time. However, it can also inject short-circuit currents into the short-circuit point, causing short-circuit current levels to approach or exceed the circuit breaker's interrupting limit, making short-circuit faults difficult to clear and posing a serious threat to the safe and stable operation of the system. As Flexible DC transmission capacity increases, its impact on AC system short-circuit currents has become increasingly significant.

[0003] Short-circuit current calculation is fundamental to power system planning and design, electromechanical protection setting calculations, and electrical equipment selection and verification. Currently, short-circuit current calculations for systems with flexible DC connections primarily involve numerically superimposing the overcurrent capacity under flexible DC control limiting with the AC short-circuit current. This method ignores the phase difference between the short-circuit current provided by the flexible DC and the AC short-circuit current, overestimating the short-circuit current provided by the flexible DC, leading to redundant short-circuit current suppression measures and unnecessary cost increases. Another method involves simple vector superposition, which accounts for the impact of fault current limiting methods and simplifies the phase relationship between the short-circuit current provided by the flexible DC and the AC short-circuit current. However, it does not consider the impact of the flexible DC control strategy and parameters, system grid structure, and operating mode, resulting in large errors in the calculation results. Summary of the Invention

[0004] To address these issues, the present invention aims to provide a method and system for calculating three-phase AC short-circuit current, taking into account flexible direct current transmission (HVDC). This method addresses the significant deviation in the calculation of three-phase AC short-circuit current provided by HVDC. Furthermore, based on the HVDC control mode and system operation mode, this method enables reasonable calculation of the three-phase AC short-circuit current provided by HVDC.

[0005] To achieve the above-mentioned objectives, in a first aspect, the present invention adopts the following technical solutions: a method for calculating AC three-phase short-circuit current taking into account flexible direct current transmission, comprising: determining the node impedance matrix of the system, as well as the transfer impedance of each power supply node to the short-circuit point, the mutual impedance between the flexible direct current grid-connected point and the short-circuit point, and the self-impedance of the short-circuit point according to the operation mode of the power system; calculating the first short-circuit current of the short-circuit point based on the transfer impedance of each power supply node to the short-circuit point; calculating the second short-circuit current provided by the flexible direct current equivalent current source injected into the flexible direct current grid-connected point based on the mutual impedance between the flexible direct current grid-connected point and the short-circuit point and the self-impedance of the short-circuit point; when the first short-circuit current and the second short-circuit current are in phase, obtaining the maximum short-circuit current provided by the flexible direct current, and obtaining the AC three-phase short-circuit current of the flexible direct current after vector superposition of the first short-circuit current and the maximum short-circuit current.

[0006] Furthermore, the calculation of the first short-circuit current includes:

[0007] When there is only a single power source in the power grid and the potential of other power sources is zero, the third short-circuit current of the short-circuit point is calculated based on the transfer impedance of the power source node to the short-circuit point;

[0008] When all power sources in the flexible DC blocking grid are put into operation, all third short-circuit currents are superimposed and calculated to obtain the first short-circuit current.

[0009] Furthermore, the calculation of the second short-circuit current includes:

[0010] Assuming the DC output current during fault ride-through The amplitude is constant, and the short-circuit current provided by the flexible DC has been decoupled from the voltage at the flexible DC grid connection point;

[0011] Taking the voltage of the flexible DC grid connection point as the reference point, according to the flexible DC output current Limit value I max Calculate the flexible DC output current The angle δ with the voltage at the flexible DC grid connection point;

[0012] The second short-circuit current provided by the flexible DC equivalent current source is calculated based on the angle δ, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point.

[0013] Furthermore, the angle δ is:

[0014]

[0015] Where, I qmax is the limit of the output of the flexible q-axis PI link, I dmax It is the limit of the output of the flexible D-axis PI link.

[0016] Furthermore, the second short-circuit current is:

[0017]

[0018]

[0019] Where, is the second short-circuit current, Z fi is the mutual impedance between the flexible DC grid connection point and the short-circuit point, Z ff is the self-impedance of the flexible DC grid connection point and the short-circuit point, ω is the angular frequency, and α is the angle of the grid connection point voltage.

[0020] In the second aspect, the present invention adopts the following technical scheme: an AC three-phase short-circuit current calculation system taking into account flexible direct current transmission, comprising: a first processing module, which determines the node impedance matrix of the system according to the operation mode of the power system, as well as the transfer impedance of each power supply node to the short-circuit point, the mutual impedance between the flexible direct current grid-connected point and the short-circuit point, and the self-impedance of the short-circuit point; a second processing module, which calculates the first short-circuit current of the short-circuit point based on the transfer impedance of each power supply node to the short-circuit point; a third processing module, which calculates the second short-circuit current provided by the flexible direct current equivalent current source injected into the flexible direct current grid-connected point based on the mutual impedance between the flexible direct current grid-connected point and the short-circuit point and the self-impedance of the short-circuit point; a superposition calculation module, which obtains the maximum short-circuit current provided by the flexible direct current when the first short-circuit current and the second short-circuit current are in phase, and obtains the AC three-phase short-circuit current of the flexible direct current after vector superposition of the first short-circuit current and the maximum short-circuit current.

[0021] Furthermore, in the second processing module, the calculation of the first short-circuit current includes:

[0022] When there is only a single power source in the power grid and the potential of other power sources is zero, the third short-circuit current of the short-circuit point is calculated based on the transfer impedance of the power source node to the short-circuit point;

[0023] When all power sources in the flexible DC blocking grid are put into operation, all third short-circuit currents are superimposed and calculated to obtain the first short-circuit current.

[0024] Furthermore, in the third processing module, the calculation of the second short-circuit current includes:

[0025] Assuming the DC output current during fault ride-through The amplitude is constant, and the short-circuit current provided by the flexible DC has been decoupled from the voltage at the flexible DC grid connection point;

[0026] Taking the voltage of the flexible DC grid connection point as the reference point, according to the flexible DC output current Limit value I max Calculate the flexible DC output current The angle δ with the voltage at the flexible DC grid connection point;

[0027] The second short-circuit current provided by the flexible DC equivalent current source is calculated based on the angle δ, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point.

[0028] In a third aspect, the present invention adopts the following technical solution: a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, and when the instructions are executed by a computing device, the computing device executes any one of the above methods.

[0029] In a fourth aspect, the present invention adopts the following technical solution: a computing device comprising: one or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the above methods.

[0030] The present invention has the following advantages due to the adoption of the above technical solution:

[0031] This paper presents a calculation method and system for AC three-phase short-circuit current taking into account flexible direct current transmission. Aiming at the situation where flexible direct current is connected to the power grid, the paper comprehensively considers the influence of flexible direct current control mode and control parameters, and system operation mode on AC short-circuit current, and obtains reasonable short-circuit current by calculation. This solves the problem of high and inaccurate calculation results of short-circuit current in power grids with flexible direct current, and provides a basis for power system planning and design, electromechanical protection setting calculation, and electrical equipment selection and verification. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 2. It is a control schematic diagram of a flexible direct current transmission system according to an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of a short circuit fault in a multi-power AC network with flexible DC transmission access in an embodiment of the present invention;

[0034] Figure 3 This is a flow chart of a method for calculating AC three-phase short-circuit current taking into account flexible DC transmission in an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of a single power supply providing short-circuit current in an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of short-circuit current provided by multiple power sources without flexible direct current transmission in an embodiment of the present invention;

[0037] Figure 6 Schematic diagram of flexible DC providing short-circuit current in an embodiment of the present invention;

[0038] Figure 7This is a diagram showing the calculation principle of the maximum short-circuit current provided by the flexible DC system in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] In order to solve the problem of large deviation in the calculation of AC three-phase short-circuit current provided by the existing flexible direct current, the present invention provides a method and system for calculating AC three-phase short-circuit current taking into account flexible direct current transmission. The present invention is applicable to power systems connected to flexible direct current transmission, including: determining the node impedance matrix of the system according to the operation mode of the power system, determining the transfer impedance of each power supply node to the short-circuit point, the mutual impedance between the flexible direct current grid-connected point and the short-circuit point, and the self-impedance of the short-circuit point, calculating the short-circuit current provided by all power supply nodes and the flexible direct current grid-connected point voltage according to the superposition principle, calculating the short-circuit current provided by the flexible direct current equivalent current source injected into the flexible direct current grid-connected point, and determining the AC three-phase short-circuit current taking into account the flexible direct current. The present invention can reasonably calculate the short-circuit current level of the power system connected to the flexible direct current transmission, and further provide a reference for considering the influence of the flexible direct current on the short-circuit current and analyzing the influence of the flexible direct current on the system short-circuit current under different operation modes under different control modes.

[0042] In one embodiment of the present invention, a method for calculating AC three-phase short-circuit current taking flexible direct current transmission into account is provided. In this embodiment, the overall control structure of the flexible direct current converter is as follows: Figure 1 As shown in the figure, the main method adopted is the dual closed-loop decoupling control in the dq coordinate system, which is divided into an inner loop controller and an outer loop controller. The inner loop control belongs to direct current control and can obtain excellent dynamic response performance. The outer loop can be set to fixed active power control or fixed DC voltage control on the d-axis according to the control target, and the q-axis can be set to fixed reactive power control or fixed AC voltage control. The PI links of the d and q axes are both set to limit, and a current limiting link is set to avoid overcurrent. Among them, I dmax is the limit of the d-axis PI link output, Iqmax is the limit of the q-axis PI link output, I max It is the limit of the output of the current limiting link.

[0043] The calculation of three-phase short-circuit in a power system mainly involves the calculation of the periodic component of the short-circuit current. When the power source potential is given, it is actually the solution of the steady-state AC circuit. The node equation can be used for fault calculation. First, the equivalent circuit of the system is formulated according to the given power system operation mode to form the node impedance matrix Z without the generator. The equivalent circuit of the system after a short-circuit fault in a multi-source AC network with flexible DC transmission access is as follows: Figure 2 shown.

[0044] Specifically, such as Figure 3 As shown, the method for calculating AC three-phase short-circuit current taking into account flexible direct current transmission of the present invention includes the following steps:

[0045] 1) Determine the node impedance matrix of the system according to the operation mode of the power system, as well as the transfer impedance of each power node to the short-circuit point, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point;

[0046] 2) calculating a first short-circuit current of the short-circuit point based on the transfer impedance of each power supply node to the short-circuit point;

[0047] 3) Based on the mutual impedance between the flexible DC grid connection point and the short-circuit point and the self-impedance of the short-circuit point, calculate the second short-circuit current provided by the flexible DC equivalent current source injected into the flexible DC grid connection point alone;

[0048] 4) When the first short-circuit current and the second short-circuit current are in phase, the maximum short-circuit current provided by the flexible DC is obtained. After vector superposition of the first short-circuit current and the maximum short-circuit current, the AC three-phase short-circuit current of the flexible DC is obtained.

[0049] In the above step 2), the calculation of the first short-circuit current includes the following steps:

[0050] 2.1) When there is only a single power source i in the power grid and the potential of other power sources is zero (such as Figure 4 As shown), the third short-circuit current of the short-circuit point is calculated based on the transfer impedance of the power supply node to the short-circuit point

[0051]

[0052] Where z fi is the transfer impedance of power source i to short-circuit point f, which can be obtained using the node impedance matrix Z; It is a separate power source in the power grid.

[0053] 2.2) When all the power sources in the flexible DC blocking grid are put into operation (such as Figure 5As shown), according to the superposition principle, all the third short-circuit currents Perform superposition calculation to obtain the first short-circuit current

[0054]

[0055] Where n is the total number of power supplies.

[0056] At the same time, the voltage at the flexible DC grid connection point and the AC short-circuit current can be calculated as follows:

[0057]

[0058]

[0059] Where, is the voltage at node m when all power sources in the flexible DC blocking grid are put into operation, ω is the angular frequency, α is the angle of the grid connection point voltage, and β is the angle between the short-circuit current and the flexible DC grid connection point voltage.

[0060] In the above step 3), during the short circuit fault period, the flexible DC enters the low voltage ride-through control. When the short circuit point f occurs close to the flexible DC grid connection point m, the grid connection point voltage drops more deeply, and the flexible DC output current Amplitude reaches limit I max When the short-circuit point f occurs far from the flexible DC grid connection point m, the grid connection point voltage drop is not much, or the flexible DC output current is small before the fault, the flexible DC output current during the fault period is Amplitude does not reach limit I max , but in this case the short-circuit current provided by the flexible DC is limited. At the same time, the output current of the flexible DC during the fault It is closely related to the flexible DC low voltage control strategy, pre-fault control mode, control parameter settings, etc., and it is difficult to calculate exhaustively. Therefore, when calculating the short-circuit current, Amplitude is set to limit I max , the results obtained are conservative and reasonable.

[0061] Therefore, the calculation of the second short-circuit current includes the following steps:

[0062] 3.1) Assuming the flexible DC output current during fault ride-through The amplitude is constant, and the short-circuit current provided by the flexible DC has been decoupled from the voltage at the flexible DC grid connection point;

[0063] 3.2) The voltage at the flexible DC grid connection point m (The flexible DC grid-connected point is node m, and the voltage at this node is like Figure 2As shown in the figure, the short-circuit current is calculated by superposition method, which is to sum the short-circuit current vectors under different working conditions. In order to distinguish the m-node voltage under different working conditions so that it can be expressed more clearly in the formula, the voltage of the flexible DC grid connection point under different working conditions is summed. Respectively expressed as Respectively as Figures 4-6 As shown. It can be understood as The specific expression under different working conditions) is the reference point, according to the flexible DC output current Limit value I max Calculate the flexible DC output current Voltage at the flexible DC grid connection point The angle δ;

[0064] Although the flexible DC converter is a voltage source converter, it must rely on the grid voltage as a reference due to the use of dq decoupling control. In the short-circuit current calculation process, it is assumed that the flexible DC output current during the fault ride-through period is After the amplitude is constant, the short-circuit current provided by it is calculated to have been decoupled from the voltage at the flexible DC grid connection point. Therefore, the flexible DC can be equivalent to an ideal current source, specifically:

[0065]

[0066] Among them, δ is determined according to the fault ride-through strategy and the setting of the current limiting link. The current limiting link can adopt geometric limiting, active power priority, reactive power priority, etc. Taking the current limiting link adopting geometric limiting as an example, the angle δ is:

[0067]

[0068] Where, I qmax is the limit of the output of the flexible q-axis PI link, I dmax It is the limit of the output of the flexible D-axis PI link.

[0069] 3.3) Calculate the second short-circuit current provided by the flexible DC equivalent current source based on the angle δ, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point;

[0070] Among them, such as Figure 6 As shown, the second short-circuit current is:

[0071]

[0072]

[0073] Where, is the second short-circuit current, Z fi is the mutual impedance between the flexible DC grid connection point and the short-circuit point, Z ff is the self-impedance of the flexible DC grid connection point and the short-circuit point, which can be obtained using the node impedance matrix Z.

[0074] And there are:

[0075]

[0076]

[0077] In step 4) above, the short-circuit current at point f when the flexible DC is taken into account should be the vector superposition of the short-circuit current provided by the flexible DC and the short-circuit current provided by all power sources, specifically:

[0078]

[0079] when and When the phase is the same, the short-circuit current provided by the flexible DC is the largest, which is the current Valid values, such as Figure 7 As shown. At this time, there are:

[0080] δ Ifmax =β-α-γ.

[0081] Where, δ Ifmax The phase angle between the grid connection point voltage and the flexible DC line when providing the maximum short-circuit current.

[0082] In one embodiment of the present invention, a system for calculating AC three-phase short-circuit current taking into account flexible direct current transmission is provided, comprising:

[0083] The first processing module determines the system's node impedance matrix, as well as the transfer impedance of each power node to the short-circuit point, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point, based on the power system operation mode.

[0084] A second processing module calculates a first short-circuit current of the short-circuit point based on the transfer impedance of each power supply node to the short-circuit point;

[0085] The third processing module calculates the second short-circuit current provided by the flexible DC grid-connected point alone injecting the flexible DC equivalent current source based on the mutual impedance between the flexible DC grid-connected point and the short-circuit point and the self-impedance of the short-circuit point;

[0086] The superposition calculation module obtains the maximum short-circuit current provided by the flexible DC when the first short-circuit current and the second short-circuit current are in phase. After vector superposition of the first short-circuit current and the maximum short-circuit current, the AC three-phase short-circuit current of the flexible DC is obtained.

[0087] In the second processing module, the calculation of the first short-circuit current includes:

[0088] When there is only a single power source in the power grid and the potential of other power sources is zero, the third short-circuit current of the short-circuit point is calculated based on the transfer impedance of the power source node to the short-circuit point;

[0089] When all power sources in the flexible DC blocking grid are put into operation, all third short-circuit currents are superimposed and calculated to obtain the first short-circuit current.

[0090] In the third processing module, the calculation of the second short-circuit current includes:

[0091] Assuming the DC output current during fault ride-through The amplitude is constant, and the short-circuit current provided by the flexible DC has been decoupled from the voltage at the flexible DC grid connection point;

[0092] Taking the voltage of the flexible DC grid connection point as the reference point, according to the flexible DC output current Limit value I max Calculate the flexible DC output current The angle δ with the voltage at the flexible DC grid connection point;

[0093] The second short-circuit current provided by the flexible DC equivalent current source is calculated based on the angle δ, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point.

[0094] The angle δ is:

[0095]

[0096] Where, I qmax is the limit of the output of the flexible q-axis PI link, I dmax It is the limit of the output of the flexible D-axis PI link.

[0097] The second short-circuit current is:

[0098]

[0099]

[0100] Where, is the second short-circuit current, Z fi is the mutual impedance between the flexible DC grid connection point and the short-circuit point, Z ff is the self-impedance of the flexible DC grid connection point and the short-circuit point, ω is the angular frequency, and α is the angle of the grid connection point voltage.

[0101] The system provided in this embodiment is used to execute the above-mentioned method embodiments. Please refer to the above-mentioned embodiments for specific processes and detailed contents, which will not be repeated here.

[0102] In one embodiment of the present invention, a computing device structure is provided. The computing device may be a terminal and may include: a processor, a communications interface, a memory, a display, and an input device. The processor, communications interface, and memory communicate with each other via a communications bus. The processor is configured to provide computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and a computer program. When executed by the processor, the computer program implements a method for calculating AC three-phase short-circuit current taking into account flexible direct current transmission. The internal memory provides an environment for the operating system and computer program in the non-volatile storage medium to run. The communications interface is configured to communicate with an external terminal via wired or wireless communication, where wireless communication may be achieved via Wi-Fi, a network management provider, NFC (near-field communication), or other technologies. The display may be a liquid crystal display or an electronic ink display. The input device may be a touchscreen covering the display, a keypad, a trackball, or a touchpad provided on the computing device housing, or an external keyboard, touchpad, or mouse. The processor may invoke logic instructions from the memory.

[0103] In addition, the logical instructions in the above-mentioned memory can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the 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 enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0104] In one embodiment of the present invention, a computer program product is provided, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the methods provided by the above-mentioned method embodiments.

[0105] In one embodiment of the present invention, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium stores server instructions. The computer instructions enable a computer to execute the methods provided in the above embodiments.

[0106] The above embodiment provides a computer-readable storage medium, whose implementation principle and technical effects are similar to those of the above method embodiment, and will not be repeated here.

[0107] The present invention is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products of the above-mentioned embodiments. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0108] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0109] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for calculating AC three-phase short-circuit current taking into account flexible direct current transmission, characterized in that: include: Determine the node impedance matrix of the system according to the operation mode of the power system, as well as the transfer impedance of each power node to the short-circuit point, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point; Calculating a first short-circuit current of the short-circuit point based on the transfer impedance of each power supply node to the short-circuit point; Based on the mutual impedance between the flexible DC grid connection point and the short-circuit point and the self-impedance of the short-circuit point, the second short-circuit current provided by the flexible DC equivalent current source injected into the flexible DC grid connection point is calculated; When the first short-circuit current and the second short-circuit current are in phase, the maximum short-circuit current provided by the flexible DC is obtained. After vector superposition of the first short-circuit current and the maximum short-circuit current, the AC three-phase short-circuit current of the flexible DC is obtained. The calculation of the second short-circuit current includes: Assuming the DC output current during fault ride-through The amplitude is constant, and the short-circuit current provided by the flexible DC has been decoupled from the voltage at the flexible DC grid connection point; Taking the voltage of the flexible DC grid connection point as the reference point, according to the flexible DC output current Limit I max Calculate the flexible DC output current Angle with the voltage at the flexible DC grid connection point δ ; According to the angle δ As well as the mutual impedance between the flexible DC grid connection point and the short-circuit point and the self-impedance of the short-circuit point, calculate the second short-circuit current provided by the flexible DC equivalent current source; The angle δ for: Where, is the limit of the output of the flexible direct current q-axis PI link, It is the limit of the output of the flexible straight d-axis PI link; The second short-circuit current is: Where, is the second short-circuit current, Z fi is the mutual impedance between the flexible DC grid connection point and the short-circuit point, Z ff is the self-impedance of the flexible DC grid connection point and the short-circuit point, is the angular frequency, is the angle of the grid connection point voltage.

2. The method for calculating AC three-phase short-circuit current taking into account flexible direct current transmission as claimed in claim 1, characterized in that: The calculation of the first short-circuit current includes: When there is only a single power source in the power grid and the potential of other power sources is zero, the third short-circuit current of the short-circuit point is calculated based on the transfer impedance of the power source node to the short-circuit point; When all power sources in the flexible DC blocking grid are put into operation, all third short-circuit currents are superimposed and calculated to obtain the first short-circuit current.

3. An AC three-phase short-circuit current calculation system taking into account flexible direct current transmission, used to implement the AC three-phase short-circuit current calculation method taking into account flexible direct current transmission as claimed in any one of claims 1 to 2, characterized in that: include: The first processing module determines the system's node impedance matrix, as well as the transfer impedance of each power node to the short-circuit point, the mutual impedance between the flexible DC grid connection point and the short-circuit point, and the self-impedance of the short-circuit point, based on the power system operation mode. A second processing module calculates a first short-circuit current of the short-circuit point based on the transfer impedance of each power supply node to the short-circuit point; The third processing module calculates the second short-circuit current provided by the flexible DC grid-connected point alone injecting the flexible DC equivalent current source based on the mutual impedance between the flexible DC grid-connected point and the short-circuit point and the self-impedance of the short-circuit point; The superposition calculation module obtains the maximum short-circuit current provided by the flexible DC when the first short-circuit current and the second short-circuit current are in phase. After vector superposition of the first short-circuit current and the maximum short-circuit current, the AC three-phase short-circuit current of the flexible DC is obtained.

4. The AC three-phase short-circuit current calculation system taking flexible DC transmission into account as claimed in claim 3, characterized in that: In the second processing module, the calculation of the first short-circuit current includes: When there is only a single power source in the power grid and the potentials of other power sources are equal to zero, the third short-circuit current of the short-circuit point is calculated based on the transfer impedance of the power source node to the short-circuit point; When all power sources in the flexible DC blocking grid are put into operation, all third short-circuit currents are superimposed and calculated to obtain the first short-circuit current.

5. The AC three-phase short-circuit current calculation system taking flexible DC transmission into account as claimed in claim 3, characterized in that: In the third processing module, the calculation of the second short-circuit current includes: Assuming the DC output current during fault ride-through The amplitude is constant, and the short-circuit current provided by the flexible DC has been decoupled from the voltage at the flexible DC grid connection point; Taking the voltage of the flexible DC grid connection point as the reference point, according to the flexible DC output current Limit I max Calculate the flexible DC output current Angle with the voltage at the flexible DC grid connection point δ ; According to the angle δ As well as the mutual impedance between the flexible DC grid connection point and the short-circuit point and the self-impedance of the short-circuit point, the second short-circuit current provided by the flexible DC equivalent current source is calculated.

6. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any one of the methods of claims 1 to 2 .

7. A computing device, characterized in that include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the methods according to claims 1 to 2.

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