Equivalent impedance calculation method and system for large-scale wind power plant power transmission line

Abstract

The invention discloses an equivalent impedance calculation method and system for a power transmission line of a large-scale wind power plant, and relates to the technical field of equivalent modeling of the large-scale wind power plant, and the method comprises the steps: judging a current unit state, and outputting a fundamental wave and each harmonic current amplitude; the cables are numbered, and equivalent current of the cables is calculated; and calculating the equivalent total impedance of each harmonic of the wind power plant port. According to the equivalent impedance calculation method for the large-scale wind power plant power transmission line, alternating current voltage and current instantaneous values of a wind turbine generator port are received in real time, the working condition of the current unit is accurately recognized, the adaptability and the real-time performance of wind power plant parameter calculation are improved, the cable equivalent current is calculated based on the circuit superposition principle, and the calculation accuracy is improved. The real-time performance and the accuracy of the calculation result are enhanced, the equivalent impedance of the wind power plant is calculated through recursive superposition of impedance parameters, the efficiency and the accuracy of impedance calculation are improved, and better effects are achieved in the aspects of accuracy, adaptability and real-time performance.

Description

Technical Field

[0001] The present invention relates to the technical field of equivalent modeling of large-scale wind farms, and specifically to a method for calculating the equivalent impedance of transmission lines in large-scale wind farms. Background Art

[0002] As an important part of modern clean energy, wind farms have developed rapidly with the adjustment of the global energy structure and the promotion of the "dual-carbon goal". By the end of 2023, China's wind power installed capacity ranks among the top in the world, with both large-scale offshore and onshore wind power. To achieve the stable operation and efficient power generation of wind farms, wind farm modeling and analysis technologies have received extensive attention. Especially for the electrical characteristics of transmission lines, existing research mainly focuses on the field of equivalent impedance modeling and calculation. By collecting the operating states, electrical parameters, and harmonic analysis of wind turbines, the dynamic characteristics of transmission lines are determined. In recent years, equivalent impedance analysis based on the PI-type circuit model has been widely used to study the frequency-domain characteristics of transmission networks. However, traditional methods are more suitable for modeling under offline conditions and cannot meet the need for real-time parameter updates under the complex dynamic conditions of wind farms.

[0003] The existing technologies have the following deficiencies in the modeling and calculation of the equivalent impedance of wind farm transmission lines. First, most methods model the transmission lines based on static conditions and can only analyze specific unit operating states or specific harmonic ranges, unable to reflect the dynamic characteristics under the complex conditions of wind farms in real time. During the operation of wind farms, the units may change frequently due to load fluctuations or outage states. Existing methods are difficult to quickly adapt to these dynamic conditions, thus affecting the accuracy of the impedance parameters of transmission lines. Second, traditional impedance calculations rely on sampling the overall electrical parameters of transmission lines. However, in distributed wind farms, the line topology is complex and the interaction effects between units are significant. Calculation methods based on linear superposition are difficult to comprehensively consider these non-linear factors, resulting in large deviations in impedance calculation results. Third, for the analysis of high-frequency harmonics, existing technologies generally rely on offline calculations and cannot obtain the equivalent impedance values at each harmonic in real time. And the high-frequency harmonic characteristics are directly related to the power quality and grid connection stability of wind farms. In addition, some technical solutions require additional hardware support, such as high-precision sensors and real-time monitoring devices, which significantly increase the operating costs of wind farms and do not meet the actual requirements of cost-benefit ratio optimization. Therefore, existing technologies are difficult to provide accurate and efficient equivalent impedance calculation methods under the comprehensive conditions of dynamic conditions, complex topologies, and real-time harmonic analysis. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed.

[0005] Therefore, the technical problem to be solved by the present invention is that the existing calculation method for the equivalent impedance of wind farm transmission lines cannot adapt to real-time updates under dynamic conditions, has insufficient handling of complex topologies and non-linear factors, has low calculation accuracy and efficiency, and how to optimize the online calculation of equivalent impedance for high efficiency and real-time.

[0006] To solve the above technical problems, the present invention provides the following technical solution: A method for calculating the equivalent impedance of transmission lines in large wind farms, including judging the current unit state and outputting the fundamental wave and the amplitudes of each harmonic current; numbering the cables and calculating the equivalent current of the cables; calculating the equivalent total impedance of each harmonic at the wind farm port.

[0007] As a preferred embodiment of the method for calculating the equivalent impedance of transmission lines in large wind farms according to the present invention, wherein: the judging the current unit state includes collecting the instantaneous value of the AC voltage, the instantaneous value of the AC current and the unit operation state information at the wind turbine port. The instantaneous value of the AC voltage is the real-time value of the voltage output at the wind turbine port changing with time. The instantaneous value of the AC current is the dynamic signal of the current output by the wind turbine, reflecting the load condition and operation stability of the unit. The unit state information is represented by the logical variables Flag 1 ~Flag n If the unit is in the operating state, mark the current unit state as logical 1 and record the AC output current of the current unit. Otherwise, mark the current unit state as logical 0 and ignore the sampled value of the current at the current unit port, and detect the state of the next unit, and loop through all wind turbines.

[0008] As a preferred embodiment of the method for calculating the equivalent impedance of transmission lines in large wind farms according to the present invention, wherein: the outputting the fundamental wave and the amplitudes of each harmonic current includes, after data collection and unit state judgment, performing Fourier transform on the current signal in the effective state of the wind turbine. The Fourier transform decomposes the time-domain signal into a frequency-domain signal to obtain the amplitudes I 1h ~I nh of the fundamental wave and each harmonic, where h is the harmonic range to be calculated. The calculation process depends on the complete power frequency cycle data collected, and clears the storage after each calculation, and outputs the calculation results of the fundamental wave and harmonic current amplitudes.

[0009] As a preferred embodiment of the method for calculating the equivalent impedance of transmission lines in large wind farms according to the present invention, wherein: the numbering the cables includes starting from the AC bus PCC at the grid connection point of the wind farm, scanning the transmission lines of the wind farm segment by segment through the binary tree traversal method, numbering each cable in sequence according to the line connection order, and corresponding the number to the connected wind turbine.

[0010] As a preferred solution of the method for calculating the equivalent impedance of the transmission line of a large-scale wind farm according to the present invention, wherein: calculating the equivalent current of the cable includes calculating the equivalent current of each cable segment numbered k based on the principle of superposition of circuits, and obtaining the equivalent current of the cable by comprehensively considering the operating state of the wind turbines connected and the amplitudes of each harmonic and the fundamental wave, which is expressed as:

[0011]

[0012] Wherein, I kh is the current value of the cable numbered k, Flag k is the operating state of the wind turbine connected to the cable numbered k, n is the number of cable segments. If the wind turbine connected to the cable is in the operating state, the output current of the wind turbine will contribute to the equivalent current of the cable, otherwise it is not included in the calculation.

[0013] As a preferred solution of the method for calculating the equivalent impedance of the transmission line of a large-scale wind farm according to the present invention, wherein: calculating the equivalent total impedance of each harmonic at the wind farm port includes obtaining the harmonic impedance value of the cable segment through the PI-type equivalent circuit model. The PI-type circuit model equivalent the cable as a combination of lumped parameters of inductance, resistance and capacitance, analyzes the electrical characteristics in the frequency domain, and sequentially solves the impedance value corresponding to each harmonic according to the input harmonic frequency range, which is expressed as:

[0014] Z cakh = Z kh * I kheq

[0015] Wherein, Z kh is the impedance value of the cable numbered k for the h-th harmonic.

[0016] As a preferred solution of the method for calculating the equivalent impedance of the transmission line of a large-scale wind farm according to the present invention, wherein: calculating the equivalent total impedance of each harmonic at the wind farm port further includes synthesizing the impedance values of all cable segments to obtain the equivalent total impedance of the h-th harmonic at the wind farm port, which is expressed as:

[0017]

[0018] Calculate the total impedance based on the principle of superposition of circuit networks and the harmonic superposition relationship, and sequentially accumulate the impedance values of each cable segment by recursion.

[0019] Another object of the present invention is to provide a system for calculating the equivalent impedance of the transmission line of a large-scale wind farm, which can deduce and obtain the equivalent total impedance of each harmonic at the wind farm port through the total impedance calculation module by a recursive calculation method, and solves the problems of low efficiency and insufficient accuracy in the current high-frequency harmonic analysis.

[0020] As a preferred solution of the system for calculating the equivalent impedance of transmission lines in large-scale wind farms according to the present invention, it includes a judgment output module, a number calculation module, and a total impedance calculation module; the judgment output module is used to judge the current unit state and output the fundamental wave and the amplitudes of each harmonic current; the number calculation module is used to number the cables and calculate the equivalent current of the cables; the total impedance calculation module is used to calculate the equivalent total impedance of each harmonic at the wind farm port.

[0021] A computer device includes a memory and a processor, the memory stores a computer program, and is characterized in that when the processor executes the computer program, the steps of the method for calculating the equivalent impedance of transmission lines in large-scale wind farms are realized.

[0022] A computer-readable storage medium stores a computer program thereon, and is characterized in that when the computer program is executed by a processor, the steps of the method for calculating the equivalent impedance of transmission lines in large-scale wind farms are realized.

[0023] The beneficial effects of the present invention: The method for calculating the equivalent impedance of transmission lines in large-scale wind farms provided by the present invention receives the instantaneous values of AC voltage and current at the wind turbine generator port in real time, accurately identifies the working conditions of the current unit, improves the adaptability and real-time performance of wind farm parameter calculation, processes the sampled data through Fourier transform, improves the resolution of the data, enhances the accuracy and integrity of harmonic analysis, establishes the wind farm topology through the binary tree traversal method, improves the real-time performance and system adaptability of impedance calculation, calculates the equivalent current of the cable based on the circuit superposition principle, enhances the real-time performance and accuracy of the calculation result, calculates the harmonic impedance through the PI-type equivalent circuit model, realizes the accurate modeling of grid parameters in the high-frequency band, calculates the equivalent impedance of the wind farm through the recursive superposition of impedance parameters, improves the efficiency and accuracy of impedance calculation, and the present invention achieves better effects in terms of accuracy, adaptability and real-time performance. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. Among them:

[0025] Figure 1 It is the overall flowchart of a method for calculating the equivalent impedance of transmission lines in large-scale wind farms provided by the first embodiment of the present invention.

[0026] Figure 2 It is the simplified wind farm topology diagram of a method for calculating the equivalent impedance of transmission lines in large-scale wind farms provided by the first embodiment of the present invention.

[0027] Figure 3 This is the overall module diagram of a system for calculating the equivalent impedance of transmission lines in a large-scale wind farm provided by the third embodiment of the present invention. Detailed implementation manners

[0028] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0029] Embodiment 1

[0030] Refer to Figure 1 - Figure 2 , which is an embodiment of the present invention, and provides a method for calculating the equivalent impedance of transmission lines in a large-scale wind farm, including:

[0031] S1: Judge the current unit state and output the amplitudes of the fundamental wave and each harmonic current.

[0032] Furthermore, judging the current unit state includes collecting the instantaneous value of the AC voltage, the instantaneous value of the AC current, and the unit operation state information at the port of the wind turbine generator.

[0033] It should be noted that the instantaneous value of the AC voltage is the real-time value of the voltage output at the port of the wind turbine generator changing with time, the instantaneous value of the AC current is the dynamic signal of the current output by the wind turbine generator, reflecting the load condition and operation stability of the unit. The unit state information is represented by the logical variables Flag 1 ~Flag n . If the unit is in the operating state, mark the current unit state as logical 1 and record the AC output current of the current unit. Otherwise, mark the current unit state as logical 0 and ignore the sampled value of the current at the port of the current unit, detect the next unit state, and loop through all wind turbine generators.

[0034] Furthermore, outputting the amplitudes of the fundamental wave and each harmonic current includes after data acquisition and unit state judgment.

[0035] It should be noted that the current signal in the effective state of the wind turbine generator is subjected to Fourier transform. The Fourier transform decomposes the time-domain signal into a frequency-domain signal to obtain the amplitudes I 1h ~I nh of the fundamental wave and each harmonic, where h is the harmonic range to be calculated. The calculation process depends on the complete power frequency cycle data collected and clears the storage after each calculation, and outputs the calculation results of the amplitudes of the fundamental wave and harmonic currents.

[0036] S2: Number the cables and calculate the equivalent current of the cables.

[0037] Furthermore, numbering the cables includes starting from the AC bus PCC at the grid connection point of the wind farm.

[0038] It should be noted that by using the binary tree traversal method to scan the transmission lines of the wind farm section by section, each cable is numbered in sequence according to the line connection order, and the number is corresponding to the connected wind turbine.

[0039] Furthermore, calculating the equivalent current of the cables includes based on the principle of superposition of circuits.

[0040] It should be noted that to calculate the equivalent current of each cable section numbered l, the equivalent current of the cable is obtained by comprehensively considering the operating status of the connected wind turbines and the amplitudes of each harmonic and fundamental wave, expressed as:

[0041]

[0042] where, I kh is the current value of the cable numbered k, Flag k is the operating status of the fan connected to the cable numbered k, n is the number of cable segments. If the fan connected to the cable is in the operating state, the output current of the fan will contribute to the equivalent current of the cable, otherwise it is not included in the calculation.

[0043] S3: Calculate the equivalent total impedance of each harmonic at the port of the wind farm.

[0044] Furthermore, calculating the equivalent total impedance of each harmonic at the port of the wind farm includes obtaining the harmonic impedance value of the cable section through the PI-type equivalent circuit model.

[0045] It should be noted that the PI-type circuit model equivalent the cable as a combination of lumped parameters of inductance, resistance and capacitance, analyzes the electrical characteristics in the frequency domain, and solves the impedance value corresponding to each harmonic in sequence according to the input harmonic frequency range, expressed as:

[0046] Z cakh = Z kh * I kheq

[0047] where, Z kh is the impedance value of the cable numbered k for the hth harmonic.

[0048] Furthermore, calculating the equivalent total impedance of each harmonic at the port of the wind farm also includes synthesizing the impedance values of all cable segments.

[0049] It should be noted that the equivalent total impedance of the hth harmonic at the port of the wind farm is obtained, expressed as:

[0050]

[0051] Calculate the total impedance based on the superposition principle of the circuit network and the harmonic superposition relationship, and accumulate the impedance values of each section of the cable in turn by a recursive method.

[0052] Embodiment 2

[0053] An embodiment of the present invention provides a method for calculating the equivalent impedance of a transmission line for a large-scale wind farm. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0054] The test scenario includes 10 wind turbines, and the topology of the transmission line is complex. The transmission line connecting each turbine to the AC bus (PCC) point consists of 5 sections of cables. The test data collection and calculation are completed in two stages: the data collection stage and the impedance calculation stage.

[0055] In the data collection stage, the instantaneous port voltage value, the instantaneous AC current value, and the unit operation status (logical flag Flag) of each wind turbine are collected. During the test, the unit operation status changes dynamically. Some units switch from the operation status to the shutdown status in different cycles. The unit status is judged in real time and only the valid data of the operating units are recorded. The collected valid current signal is accumulated for one power frequency cycle and then subjected to Fourier transform (FFT) to obtain the fundamental wave and the amplitudes of the first 20 harmonics of the current, which are stored to provide basic data for subsequent impedance calculation.

[0056] In the impedance calculation stage, starting from the PCC point, traverse the transmission line topology by the binary tree method, number each section of the cable one by one, and calculate the equivalent current of the cable by using the superposition principle according to the harmonic current amplitude corresponding to the number and the unit. Subsequently, use the PI-type equivalent circuit model to calculate the impedance values of each cable under the fundamental wave and harmonic conditions, recursively superimpose the impedance of each section of the cable, and obtain the total impedance of the wind farm port. The entire calculation process is dynamically updated. The test simulates 3 typical working conditions: all units are running at full load, some units are shut down, and dynamic adjustment under load fluctuation conditions.

[0057] As shown in Table 1, when some units are out of service, the present invention dynamically judges the unit status through logical flags to ensure that only the valid signals of the operating units are calculated. Under the condition that some units are out of service, the fundamental wave impedance calculated by the present invention (such as 0.16 Ω for Unit 2 and 0.16 Ω for Unit 4) can accurately reflect the actual working condition. The present invention extracts harmonic characteristics through Fourier transform and can accurately calculate the harmonic impedance of each order under different working conditions. In the working condition of load fluctuation, the amplitude of the 5th harmonic current shows a dynamic distribution due to the change of the working condition (such as 1.12 A for Unit 2 and 1.09 A for Unit 6), while the traditional method cannot accurately capture these high-order harmonic characteristics, which affects the accuracy of power grid harmonic control. The present invention adopts binary tree traversal and recursive superposition calculation, and the total impedance value can be accurately output in real-time dynamic update. Compared with the traditional method, the present invention not only avoids data redundancy in the complex calculation process, but also improves the calculation efficiency. Under the working condition of load fluctuation, the impedance values of Unit 3 and Unit 7 (0.13 Ω and 0.13 Ω respectively) can quickly respond to changes, while the traditional method cannot achieve the same real-time update ability.

[0058] Table 1 Experimental data table

[0059]

[0060] Example 3

[0061] Refer to Figure 3 , which is an embodiment of the present invention, and provides a system for calculating the equivalent impedance of a transmission line in a large-scale wind farm, including: a judgment and output module, a number calculation module, and a total impedance calculation module.

[0062] Among them, the judgment and output module is used to judge the current unit status and output the fundamental wave and the amplitude of each harmonic current; the number calculation module is used to number the cables and calculate the equivalent current of the cables; the total impedance calculation module is used to calculate the equivalent total impedance of each harmonic at the wind farm port.

[0063] If the function 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 such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing 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 methods of the various embodiments of the present invention. The aforementioned storage medium includes: various media 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 that can store program codes.

[0064] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a definitional sequence list of executable instructions for implementing logical functions, and can be embodied specifically in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, a system including a processor, or other systems that can fetch instructions from and execute the instructions of the instruction execution system, apparatus, or device. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in connection with the instruction execution system, apparatus, or device.

[0065] More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection (electronic device) having one or more wirings, a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which a program can be printed, as the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or other suitable processing as necessary, and then stored in a computer memory.

[0066] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc. It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

[0067] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for calculating equivalent impedance of transmission lines in large wind farms, characterized in that: include: Determine the current state of the unit and output the amplitude of the fundamental wave and each harmonic current; Number the cables and calculate the equivalent current of the cables; Calculate the equivalent total impedance of each harmonic at the wind farm port.

2. The method for calculating equivalent impedance of a large wind farm transmission line according to claim 1, characterized in that: The current unit state determination includes collecting the instantaneous value of the AC voltage and the AC current at the wind turbine port and the unit operation state information. The instantaneous value of the AC voltage is the real-time value of the voltage output by the wind turbine port over time. The instantaneous value of the AC current is the dynamic signal of the wind turbine output current, which reflects the load condition and operation stability of the unit. The unit state information is represented by the logical variables Flag1 to Flag n It means that if the unit is in operation, the current unit state is marked as logic 1 and the current unit AC output AC current is recorded. Otherwise, the current unit state is marked as logic 0 and the sampling value of the current unit port current is ignored. The next unit state is detected and all wind turbines are looped through.

3. The method for calculating equivalent impedance of a large wind farm transmission line according to claim 2, characterized in that: The output fundamental wave and each harmonic current amplitude includes performing Fourier transform on the current signal of the wind turbine in the effective state after data collection and unit state judgment. The Fourier transform decomposes the time domain signal into the frequency domain signal to obtain the amplitude I of the fundamental wave and each harmonic current. 1h ~I nh , h is the harmonic range to be calculated. The calculation process relies on the collected complete power frequency cycle data, and the storage is cleared after each calculation is completed, and the calculation results of the fundamental and harmonic current amplitudes are output.

4. The method for calculating equivalent impedance of a large wind farm transmission line according to claim 3, characterized in that: The cable numbering includes taking the AC busbar PCC of the wind farm grid connection point as the starting point, scanning the wind farm's transmission lines section by section through a binary tree traversal method, numbering each cable in sequence according to the line connection order, and corresponding the number to the connected wind turbine set.

5. The method for calculating equivalent impedance of a large wind farm transmission line according to claim 4, characterized in that: The calculation of the cable equivalent current includes calculating the equivalent current of each cable segment numbered k based on the circuit superposition principle, and obtaining the cable equivalent current by comprehensively connecting the operating status of the wind turbine generator set and the amplitudes of each harmonic and fundamental wave, which is expressed as: Among them, I kh is the current value of the cable numbered k, Flag k is the operating status of the fan connected to the cable numbered k, n is the number of cable segments. If the fan connected to the cable is in operation, the fan output current will contribute to the cable equivalent current, otherwise it will not be included in the calculation.

6. The method for calculating equivalent impedance of a large wind farm transmission line according to claim 5, characterized in that: The calculation of the equivalent total impedance of each harmonic at the wind farm port includes obtaining the harmonic impedance value of the cable section through a PI-type equivalent circuit model. The PI-type circuit model equates the cable to a combination of lumped parameters of inductance, resistance and capacitance, analyzes the electrical characteristics in the frequency domain, and solves the impedance value corresponding to each harmonic in turn according to the input harmonic frequency range, which is expressed as: WITH cakh =Z kh *AND kheq Among them, Z kh is the impedance value of the cable numbered l to the hth harmonic.

7. The method for calculating equivalent impedance of a large wind farm transmission line according to claim 6, characterized in that: The calculation of the equivalent total impedance of each harmonic at the wind farm port also includes integrating the impedance values ​​of all cable segments to obtain the jth harmonic equivalent total impedance of the wind farm port, which is expressed as: The total impedance is calculated based on the superposition principle of the circuit network and the superposition relationship of harmonics, and the impedance value of each cable section is accumulated in turn in a recursive manner.

8. A system using the method for calculating equivalent impedance of a large wind farm transmission line according to any one of claims 1 to 7, characterized in that: It includes a judgment output module, a number calculation module, and a total impedance calculation module; The judgment output module is used to judge the current state of the unit and output the fundamental wave and each harmonic current amplitude; The numbering calculation module is used to number the cables and calculate the cable equivalent current; The total impedance calculation module is used to calculate the equivalent total impedance of each harmonic at the wind farm port.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for calculating equivalent impedance of a large wind farm transmission line according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for calculating equivalent impedance of a large wind farm transmission line according to any one of claims 1 to 7 are implemented.

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