A wind farm harmonic virtual impedance design method, system, device and medium

Abstract

This invention relates to the field of wind farm grid connection technology, and particularly to a method, system, equipment, and medium for designing harmonic virtual impedance in wind farms. The method includes: constructing an equivalent model of the entire wind farm grid connection; measuring the harmonic transmission frequency response of the wind power grid-connected system at the grid connection point based on the equivalent model; identifying harmonic amplification risk areas; introducing virtual impedance to correct the harmonic transmission frequency response for the identified harmonic amplification risk areas, obtaining the harmonic transfer function after introducing the virtual impedance, and extracting a harmonic amplification correction factor from the harmonic transfer function; establishing and solving an optimization model for harmonic virtual impedance parameters with the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, to obtain the optimized virtual impedance parameters. This invention can effectively suppress harmonic amplification at specific frequencies in offshore wind farms, improve the stability and power quality of the grid-connected system, and has the advantages of requiring no additional hardware, low cost, and strong robustness.

Description

Technical Field

[0001] This invention relates to the field of wind farm grid connection technology, and in particular to a method, system, equipment and medium for designing virtual impedance of wind farm harmonics. Background Technology

[0002] Currently, grid connection compliance requirements for offshore wind farms are becoming increasingly stringent, especially regarding voltage harmonics. The grid-connected converter of the wind turbine itself is a major source of harmonics. As the capacity of offshore wind farms continues to increase, the reactive coupling of the collector lines and transformers makes the system prone to high-frequency resonance, resulting in significant voltage harmonic amplification. This can lead to inverter overcurrent, control loop oscillation, and deterioration of grid power quality.

[0003] Traditional methods often involve installing active or passive filters at the grid connection point or on offshore platforms, but these methods suffer from high costs, limited placement, parameter uncertainties, and the risk of introducing new resonances. In recent years, some research has proposed embedding harmonic virtual impedance modules into the wind turbine converter control system to achieve harmonic suppression. However, existing virtual impedance design methods largely rely on empirical parameter tuning or precise modeling, making the design results sensitive to grid changes and difficult to guarantee stability.

[0004] Therefore, there is an urgent need for a wind farm harmonic virtual impedance design scheme that does not rely on additional equipment and balances stability and harmonic suppression performance, in order to reduce the risk of harmonic voltage amplification and improve grid connection stability. Summary of the Invention

[0005] This invention provides a method, system, device, and medium for designing virtual harmonic impedance in wind farms to solve the aforementioned technical problems in the prior art.

[0006] According to a first aspect of the present invention, a method for designing virtual harmonic impedance in a wind farm is provided.

[0007] In one embodiment, the wind farm harmonic virtual impedance design method includes:

[0008] Based on the wind farm topology, construct an equivalent model of the wind farm's overall grid connection;

[0009] Based on the overall grid-connected equivalent model of the wind farm, the harmonic transmission frequency response of the wind power grid-connected system is measured at the grid connection point; and based on the harmonic transmission frequency response, the harmonic amplification risk area is identified.

[0010] For the identified harmonic amplification risk areas, a virtual impedance is introduced to correct the harmonic transfer frequency response, resulting in the harmonic transfer function after introducing the virtual impedance, and the harmonic amplification correction factor is extracted from the harmonic transfer function.

[0011] With the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, an optimization model for harmonic virtual impedance parameters is established and solved to obtain the optimized virtual impedance parameters.

[0012] In one embodiment, constructing an equivalent model of the wind farm's overall grid connection based on the wind farm topology includes:

[0013] Based on the wind farm topology, the wind turbine inverter, step-up transformer, collector cable and external power grid are modeled as a series-parallel complex impedance network, and an equivalent model of the wind farm's overall grid connection is established.

[0014] In one embodiment, based on the overall grid-connected equivalent model of the wind farm, measuring the harmonic propagation frequency response of the wind power grid-connected system at the grid connection point includes:

[0015] Based on the electrical connection relationship between the inverter control loop and the grid connection point in the overall grid-connected equivalent model of the wind farm, the disturbance signal injection node and the grid connection point are determined.

[0016] Based on the disturbance signal injection node and grid connection point, the frequency response of the harmonic transmission of the wind power grid-connected system is measured using the frequency characteristic scanning method based on small signal disturbance injection.

[0017] In one embodiment, the frequency response scanning method based on small signal perturbation injection includes:

[0018] A small-amplitude sinusoidal disturbance signal is injected into the inverter control circuit. The frequency range of the small-amplitude sinusoidal disturbance signal is 15Hz to 2kHz.

[0019] The harmonic transmission frequency response of the wind power grid-connected system is measured by measuring the amplitude ratio and phase difference between the grid connection point voltage and the small-amplitude sinusoidal disturbance signal.

[0020] In one embodiment, identifying harmonic amplification risk areas based on the harmonic propagation frequency response includes:

[0021] Based on the frequency response of harmonic propagation, the location of amplified peaks is analyzed to identify areas of harmonic amplification risk.

[0022] In one embodiment, when a virtual impedance is introduced for the identified harmonic amplification risk region, the virtual impedance is introduced into the inverter control loop via a complex bandpass filter;

[0023] The expression for the complex bandpass filter is:

[0024]

[0025] In the formula, Q(s) represents the transfer function of the complex bandpass filter; ω b ω represents the filter bandwidth frequency, b represents the bandwidth;h represents the center frequency of the bandpass filter, h represents harmonics; s represents complex frequency variables; j represents the imaginary unit;

[0026] The expression for the virtual impedance control voltage is as follows:

[0027] U v (s)=Z V (s)Q(s)i(s)

[0028] Z V (s)=R V +jX V

[0029] In the formula, U V (s) represents the harmonic virtual impedance control voltage; Z V (s) represents the harmonic virtual impedance; i(s) represents the fan output current; R V Indicates virtual resistance; X V V represents virtual inductive impedance; j represents the imaginary unit.

[0030] In one embodiment, the harmonic transfer frequency response is corrected to obtain the harmonic transfer function after introducing virtual impedance, including:

[0031] Based on virtual impedance, the harmonic transfer frequency response is corrected according to the extra element theorem to obtain the harmonic transfer function after introducing virtual impedance.

[0032] The expression for the harmonic transfer function is:

[0033]

[0034] In the formula, H(jω / Z) V Z represents the harmonic transfer function; V (jω) represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; H0(jω) represents the harmonic propagation frequency response of the system before the introduction of the virtual harmonic impedance; Z o (jω), Z s (jω) represents the open-circuit drive impedance and short-circuit drive impedance of the network port, respectively; o and s represent open circuit and short circuit, respectively; jω represents the frequency variable.

[0035] In one embodiment, the expression for the harmonic virtual impedance parameter optimization model is:

[0036]

[0037] In the formula, F(Z) V ) represents the objective function; jω represents the frequency variable; ω represents the angular frequency; Ω represents the frequency range; This represents the system phase margin when considering the virtual impedance Zv; This represents the minimum stability margin of the system.

[0038] In one embodiment, when solving the harmonic virtual impedance parameter optimization model, a multi-objective genetic algorithm or particle swarm optimization algorithm is used to solve for the optimized virtual impedance parameters.

[0039] In one embodiment, the wind farm harmonic virtual impedance design method further includes:

[0040] The optimized virtual impedance parameters were substituted into the overall grid-connected equivalent model of the wind farm, and the system characteristics were tested based on the frequency characteristic scanning method of small signal disturbance injection to verify the harmonic amplification suppression effect and system stability.

[0041] In one embodiment, the optimized virtual impedance parameters are substituted into the overall grid-connected equivalent model of the wind farm, and the harmonic amplification suppression effect is verified using a frequency response scanning method based on small-signal disturbance injection, including:

[0042] The optimized virtual impedance parameters are loaded into the wind farm converter controller. The harmonic transfer function is measured by the frequency characteristic scanning method based on small signal disturbance injection. The harmonic amplification peak value is then verified based on the harmonic transfer function.

[0043] When the peak value of harmonic amplification is reduced, determine whether the harmonic amplification suppression effect meets the grid connection standard. If it does not meet the standard, increase the resistive component of the virtual impedance.

[0044] In one embodiment, the optimized virtual impedance parameters are substituted into the overall grid-connected equivalent model of the wind farm, and the system stability is verified using the frequency response scanning method based on small-signal disturbance injection, including:

[0045] The optimized virtual impedance parameters are loaded into the wind farm converter controller to calculate the real-time stability margin; and the real-time stability margin is compared with the minimum stability margin.

[0046] If the comparison result shows that the real-time stability margin is greater than the minimum stability margin, the system is determined to be stable; if the comparison result shows that the real-time stability margin is less than the minimum stability margin, the minimum stability margin of the system is increased and the virtual impedance is solved again.

[0047] In one embodiment, the formula for calculating the real-time stability margin is:

[0048]

[0049] In the formula, This represents the system phase margin when considering the virtual impedance Zv; Z VRepresents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; Z s (jω) represents the frequency characteristic of the port short-circuit drive impedance; ω represents the angular frequency; Ω represents the frequency range; jω represents the frequency variable.

[0050] According to a second aspect of the present invention, a wind farm harmonic virtual impedance design system is provided.

[0051] In one embodiment, the wind farm harmonic virtual impedance design system includes:

[0052] The equivalent modeling module is used to construct an equivalent model of the entire grid connection of the wind farm based on the wind farm topology.

[0053] The frequency sweep analysis module is used to measure the harmonic transmission frequency response of the wind power grid-connected system at the grid connection point based on the overall grid-connected equivalent model of the wind farm; and to identify the harmonic amplification risk area based on the harmonic transmission frequency response.

[0054] The harmonic correction module is used to introduce virtual impedance to correct the harmonic transfer frequency response for the identified harmonic amplification risk areas, obtain the harmonic transfer function after introducing virtual impedance, and extract the harmonic amplification correction factor from the harmonic transfer function.

[0055] The model optimization module is used to establish an optimization model for harmonic virtual impedance parameters with the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, and to solve the optimization model to obtain the optimized virtual impedance parameters.

[0056] In one embodiment, when constructing an equivalent model of the wind farm's overall grid connection based on the wind farm's topology, the equivalent modeling module models the wind turbine inverter, step-up transformer, collector cable, and external power grid as a series-parallel complex impedance network to establish an equivalent model of the wind farm's overall grid connection.

[0057] In one embodiment, when the frequency sweep analysis module measures the harmonic propagation frequency response of the wind power grid-connected system at the grid connection point based on the overall grid-connected equivalent model of the wind farm, it determines the disturbance signal injection node and the grid connection point based on the electrical connection relationship between the inverter control loop and the grid connection point in the overall grid-connected equivalent model of the wind farm; according to the disturbance signal injection node and the grid connection point, it measures the harmonic propagation frequency response of the wind power grid-connected system using a frequency characteristic scanning method based on small signal disturbance injection.

[0058] In one embodiment, the frequency response scanning method based on small signal perturbation injection includes:

[0059] A small-amplitude sinusoidal disturbance signal is injected into the inverter control circuit. The frequency range of the small-amplitude sinusoidal disturbance signal is 15Hz to 2kHz.

[0060] The harmonic transmission frequency response of the wind power grid-connected system is measured by measuring the amplitude ratio and phase difference between the grid connection point voltage and the small-amplitude sinusoidal disturbance signal.

[0061] In one embodiment, when the frequency sweep analysis module identifies the harmonic amplification risk area based on the harmonic propagation frequency response, it analyzes the amplification peak position and identifies the harmonic amplification risk area based on the harmonic propagation frequency response.

[0062] In one embodiment, when the harmonic correction module introduces a virtual impedance for the identified harmonic amplification risk area, the virtual impedance is introduced into the inverter control loop through a complex bandpass filter.

[0063] The expression for the complex bandpass filter is:

[0064]

[0065] In the formula, Q(s) represents the transfer function of the complex bandpass filter; ω b ω represents the filter bandwidth frequency, b represents the bandwidth; h represents the center frequency of the bandpass filter, h represents harmonics; s represents complex frequency variables; j represents the imaginary unit;

[0066] The expression for the virtual impedance control voltage is as follows:

[0067] U V (s)=Z V (s)Q(s)i(s)

[0068] Z V (s)=R V +jX V

[0069] In the formula, U V (s) represents the harmonic virtual impedance control voltage; Z V (s) represents the harmonic virtual impedance; i(s) represents the fan output current; R V Indicates virtual resistance; X V V represents virtual inductive impedance; j represents the imaginary unit.

[0070] In one embodiment, when the harmonic correction module corrects the harmonic transmission frequency response to obtain the harmonic transfer function after introducing virtual impedance, it corrects the harmonic transmission frequency response based on the virtual impedance and the extra element theorem to obtain the harmonic transfer function after introducing virtual impedance.

[0071] The expression for the harmonic transfer function is:

[0072]

[0073] In the formula, H(jω / Z) V Z represents the harmonic transfer function; V (jω) represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; H0(jω) represents the harmonic propagation frequency response of the system before the introduction of the virtual harmonic impedance; Z o (jω), Z s (jω) represents the open-circuit drive impedance and short-circuit drive impedance of the network port, respectively; o and s represent open circuit and short circuit, respectively; jω represents the frequency variable.

[0074] In one embodiment, the expression for the harmonic virtual impedance parameter optimization model is:

[0075]

[0076] In the formula, F(Z) V ) represents the objective function; jω represents the frequency variable; ω represents the angular frequency; Ω represents the frequency range; This represents the system phase margin when considering the virtual impedance Zv; This represents the minimum stability margin of the system.

[0077] In one embodiment, the model optimization module employs a multi-objective genetic algorithm or a particle swarm optimization algorithm to solve the optimized virtual impedance parameters when solving the harmonic virtual impedance parameter optimization model.

[0078] In one embodiment, the wind farm harmonic virtual impedance design system further includes:

[0079] The system verification module is used to substitute the optimized virtual impedance parameters into the overall grid-connected equivalent model of the wind farm, and to test the system characteristics using the frequency characteristic scanning method based on small signal disturbance injection, thereby verifying the harmonic amplification suppression effect and system stability.

[0080] In one embodiment, when the system verification module substitutes the optimized virtual impedance parameters into the overall grid-connected equivalent model of the wind farm and uses the frequency characteristic scanning method based on small-signal disturbance injection to verify the harmonic amplification suppression effect, it loads the optimized virtual impedance parameters into the wind farm converter controller, measures the harmonic transfer function using the frequency characteristic scanning method based on small-signal disturbance injection, and verifies whether the harmonic amplification peak value has decreased based on the harmonic transfer function. If the harmonic amplification peak value has decreased, it determines whether the harmonic amplification suppression effect meets the grid connection standard. If it does not meet the standard, it increases the resistance component of the virtual impedance.

[0081] In one embodiment, when the system verification module substitutes the optimized virtual impedance parameters into the overall grid-connected equivalent model of the wind farm and verifies the system stability based on the frequency characteristic scanning method of small-signal disturbance injection, it loads the optimized virtual impedance parameters into the wind farm converter controller and calculates the real-time stability margin; then it compares the real-time stability margin with the minimum stability margin; if the comparison result shows that the real-time stability margin is greater than the minimum stability margin, the system is determined to be stable; if the comparison result shows that the real-time stability margin is less than the minimum stability margin, the minimum system stability margin is increased and the virtual impedance is solved again.

[0082] In one embodiment, the formula for calculating the real-time stability margin is:

[0083]

[0084] In the formula, This represents the system phase margin when considering the virtual impedance Zv; Z V Represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; Z s (jω) represents the frequency characteristic of the port short-circuit drive impedance; ω represents the angular frequency; Ω represents the frequency range; jω represents the frequency variable.

[0085] According to a third aspect of the present invention, a computer device is provided.

[0086] In one embodiment, the computer device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the method described above.

[0087] According to a fourth aspect of the present invention, a computer-readable storage medium is provided.

[0088] In one embodiment, a computer program is stored on the computer-readable storage medium, which, when executed by a processor, implements the steps of the method described above.

[0089] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0090] This invention achieves quantitative correction and accurate modeling of harmonic propagation frequency characteristics by treating virtual impedance as an equivalent additional component, thereby effectively suppressing harmonic amplification in offshore wind farms without adding extra active filtering devices. This method achieves adaptive identification of wind farm harmonic risks through small-signal injection, allowing for online application without affecting the normal operation of the wind farm. Furthermore, by solving for virtual impedance parameters using a multi-objective genetic algorithm or particle swarm optimization algorithm, the system significantly improves harmonic suppression and dynamic response performance while meeting stability margin constraints. Compared to traditional empirical parameter tuning or fixed impedance control strategies, this invention enables rapid adaptation to dynamic power grids and multi-machine interconnection conditions, providing a new commissioning method for high-quality operation of offshore wind farm grid-connected systems.

[0091] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0092] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0093] Figure 1 This is a flowchart illustrating a wind farm harmonic virtual impedance design method according to an exemplary embodiment;

[0094] Figure 2 This is a structural block diagram of a wind farm harmonic virtual impedance design system according to an exemplary embodiment;

[0095] Figure 3 This is a schematic diagram illustrating an application scenario of a harmonic virtual impedance design method for offshore wind farm inverters based on the additional element theorem, according to an exemplary embodiment.

[0096] Figure 4 This is an equivalent modeling diagram of a wind farm in an offshore wind farm inverter harmonic virtual impedance design method based on the additional element theorem, according to an exemplary embodiment.

[0097] Figure 5 This is a schematic diagram illustrating the principle of measuring the harmonic transmission frequency characteristics of an offshore wind farm based on the additional element theorem, according to an exemplary embodiment.

[0098] Figure 6 This is a schematic diagram illustrating the calculation of drive impedance in a harmonic virtual impedance design method for offshore wind farm inverters based on the additional element theorem, according to an exemplary embodiment.

[0099] Figure 7 This is a schematic diagram of the structure of a computer device according to an exemplary embodiment.

[0100] In the picture:

[0101] Z inv Z represents the inverter impedance. T1 Filter inductor impedance, Z g Z represents the impedance of the filter capacitor. T2 Z represents the total impedance of the filter inductor and the step-up transformer. cable Z represents the cable impedance. S The system impedance is represented by Vs. Figure 4 Electrical symbol for China's power grid; V dk (h) represents the harmonic voltage obtained on the output side of the wind turbine, where h represents the harmonic order, V pcck (h) represents the harmonic voltage measured at the grid connection point, V d V represents the injected disturbance voltage. pcc Represents the grid connection point voltage; Q(s) Z v This represents the equivalent impedance at the fan output after introducing virtual impedance (obtained through mathematical analysis of the circuit). Detailed Implementation

[0102] The following description and accompanying drawings fully illustrate specific embodiments described herein to enable those skilled in the art to practice them. Some embodiments may include or substitute parts and features of other embodiments. The scope of the embodiments herein encompasses the entire scope of the claims and all available equivalents thereof. Throughout this document, the terms “first,” “second,” etc., are used only to distinguish one element from another without requiring or implying any actual relationship or order between the elements. Indeed, a first element can also be referred to as a second element, and vice versa. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure, apparatus, or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a structure, apparatus, or device. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the structure, apparatus, or device that includes said element. The various embodiments described herein are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0103] The terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" used in this document to indicate orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings. They are used solely for the convenience of describing the document and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description herein, unless otherwise specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two elements; they can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0104] In this document, unless otherwise stated, the term "multiple" means two or more.

[0105] In this article, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0106] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0107] It should be understood that although the steps in the flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order constraint on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0108] The modules in the apparatus or system of this application can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0109] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0110] Figure 1An embodiment of a wind farm harmonic virtual impedance design method according to the present invention is shown.

[0111] In this optional embodiment, the wind farm harmonic virtual impedance design method includes:

[0112] Step S101: Based on the wind farm topology, construct an equivalent model of the wind farm's overall grid connection.

[0113] Step S102: Based on the overall grid-connected equivalent model of the wind farm, measure the harmonic transmission frequency response of the wind power grid-connected system at the grid connection point; and based on the harmonic transmission frequency response, identify the harmonic amplification risk area.

[0114] Step S103: For the identified harmonic amplification risk area, a virtual impedance is introduced to correct the harmonic transmission frequency response, and the harmonic transfer function after introducing the virtual impedance is obtained. The harmonic amplification correction factor is then extracted from the harmonic transfer function.

[0115] Step S104: With the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, establish an optimization model for the harmonic virtual impedance parameters, and solve the optimization model to obtain the optimized virtual impedance parameters.

[0116] Figure 2 An embodiment of a wind farm harmonic virtual impedance design system according to the present invention is shown.

[0117] In this optional embodiment, the wind farm harmonic virtual impedance design system includes:

[0118] The equivalent modeling module 201 is used to construct an equivalent model of the overall grid connection of the wind farm based on the wind farm topology.

[0119] The frequency sweep analysis module 202 is used to measure the harmonic transmission frequency response of the wind power grid connection system at the grid connection point based on the overall grid connection equivalent model of the wind farm; and to identify the harmonic amplification risk area based on the harmonic transmission frequency response.

[0120] The harmonic correction module 203 is used to introduce virtual impedance for the identified harmonic amplification risk area, correct the harmonic transmission frequency response, obtain the harmonic transfer function after introducing virtual impedance, and extract the harmonic amplification correction factor from the harmonic transfer function.

[0121] The model optimization module 204 is used to establish an optimization model for harmonic virtual impedance parameters with the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, and to solve the optimization model to obtain the optimized virtual impedance parameters.

[0122] In the above optional embodiments, when constructing the overall grid-connected equivalent model of the wind farm based on the wind farm topology, the wind turbine inverter, step-up transformer, collector cable and external power grid can be modeled as a series-parallel complex impedance network to establish the overall grid-connected equivalent model of the wind farm.

[0123] Specifically, refer to Figure 3 The basic topology of an offshore wind farm includes: wind turbine inverters, step-up transformers, submarine collection cables, and transmission lines connecting to the onshore power grid. The output side of a single wind turbine inverter is connected to the submarine cable via an LCL filter. Multiple turbines are combined via a collection bus and connected to the offshore step-up transformer, from where the power is transmitted to the onshore grid connection point via a long-distance submarine cable.

[0124] In this structure, the inverter and its LCL filter are modeled as the wind turbine output impedance Z. inv (jω), submarine cable impedance Z cable By connecting the transformer impedance to construct a system according to topology, the wind farm as a whole is ultimately equivalent to a complex impedance network with an inverter connected to the grid, such as... Figure 4 As shown.

[0125] In the above optional embodiments, when measuring the harmonic transmission frequency response of the wind power grid-connected system at the grid connection point based on the overall grid-connected equivalent model of the wind farm, the disturbance signal injection node and the grid connection point can be determined based on the electrical connection relationship between the inverter control loop and the grid connection point in the overall grid-connected equivalent model of the wind farm. Based on the disturbance signal injection node and the grid connection point, a frequency characteristic scanning method based on small-signal disturbance injection is used to measure the harmonic transmission frequency response of the wind power grid-connected system. The frequency characteristic scanning method based on small-signal disturbance injection includes: injecting a small-amplitude sinusoidal disturbance signal into the inverter control loop, the frequency coverage range of the small-amplitude sinusoidal disturbance signal being 15Hz to 2kHz in the harmonic frequency band; measuring the amplitude ratio and phase difference between the grid connection point voltage and the small-amplitude sinusoidal disturbance signal, and the harmonic transmission frequency response of the wind power grid-connected system; and when identifying the harmonic amplification risk area based on the harmonic transmission frequency response, analyzing the amplification peak position based on the harmonic transmission frequency response to identify the harmonic amplification risk area.

[0126] Specifically, refer to Figure 5 To identify the amplification characteristics of the system in the harmonic frequency band, a series of small-amplitude sinusoidal disturbance signals V are injected into the voltage control circuit of the inverter. d The disturbance frequency range covers the main harmonic frequency band from 15Hz to 2kHz; by measuring the grid connection point voltage V PCC With a small sinusoidal disturbance signal V d The amplitude ratio and phase difference are used to obtain the transmission frequency response H(jω) of the system. The potential harmonic amplification risk domain Ω is obtained by analyzing the amplification peak location. h .

[0127] In the above optional embodiments, when a virtual impedance is introduced for the identified harmonic amplification risk area, the virtual impedance is introduced into the inverter control loop through a complex bandpass filter.

[0128] The expression for the complex bandpass filter is:

[0129]

[0130] In the formula, Q(s) represents the transfer function of the complex bandpass filter; ω b ω represents the filter bandwidth frequency, b represents the bandwidth; h represents the center frequency of the bandpass filter, h represents harmonics; s represents complex frequency variables; j represents the imaginary unit;

[0131] The expression for the virtual impedance control voltage is as follows:

[0132] U V (s)=Z V (s)Q(s)i(s)

[0133] Z V (s)=R V +jX V

[0134] In the formula, U V (s) represents the harmonic virtual impedance control voltage; Z V (s) represents the harmonic virtual impedance; i(s) represents the fan output current; R V Indicates virtual resistance; X V V represents virtual inductive impedance; j represents the imaginary unit.

[0135] In the above optional embodiments, when correcting the harmonic transmission frequency response to obtain the harmonic transfer function after introducing virtual impedance, the harmonic transmission frequency response is corrected based on the virtual impedance and the extra element theorem to obtain the harmonic transfer function after introducing virtual impedance; the calculation process is as follows: Figure 6 The expression for the harmonic transfer function is:

[0136]

[0137] In the formula, H(jω / Z) V Z represents the harmonic transfer function; V (jω) represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; H0(jω) represents the harmonic propagation frequency response of the system before the introduction of the virtual harmonic impedance; Z o (jω), Z s(jω) represents the open-circuit drive impedance and short-circuit drive impedance of the network port, respectively; o and s represent open circuit and short circuit, respectively; jω represents the frequency variable.

[0138] Based on the above, it can be seen that the harmonic virtual impedance module Z... V (jω)Q(jω) directly affects the degree of harmonic amplification and the damping characteristics of the system.

[0139] In the above optional embodiments, the stability domain meets the system design requirements, so that the amplification factor at the harmonic frequency is |H(jωh|Z). V The goal is to minimize the virtual impedance parameter Z. V =R V +jX V , where R V X is the virtual impedance resistance. V For virtual sensory resistance.

[0140] Specifically, the harmonic virtual impedance optimization process is as follows:

[0141] The amplification factor at the harmonic frequency is |H(jωh|Z V With the objective of minimizing || and the system stability margin as a constraint, an optimization model is established:

[0142]

[0143] In the formula, F(Z) V ) represents the objective function; jω represents the frequency variable; ω represents the angular frequency; Ω represents the frequency range; This represents the system phase margin when considering the virtual impedance Zv; This represents the minimum stability margin of the system.

[0144] Based on this optimization model, a multi-objective genetic algorithm or particle swarm optimization algorithm is used to solve for the optimized virtual impedance parameter Z. V =R V +jX V .

[0145] In the above optional embodiments, the optimized harmonic virtual impedance parameter Z V The voltage control loop is introduced into the grid-side inverter control system of the wind farm. The frequency characteristic scanning method based on small signal disturbance injection is used to test the system characteristics, verify the harmonic amplification suppression effect and system stability.

[0146] Specifically, the optimized virtual impedance parameters are loaded into the wind farm converter controller. The harmonic transfer function is measured by the frequency characteristic scanning method based on small signal disturbance injection, and the harmonic amplification peak value is verified based on the harmonic transfer function. If the harmonic amplification peak value is reduced, it is determined whether the harmonic amplification suppression effect meets the grid connection standard. If the standard is not met, the resistance component of the virtual impedance is increased.

[0147] The optimized virtual impedance parameters are loaded into the wind farm converter controller to calculate the real-time stability margin. The real-time stability margin is then compared with the minimum stability margin. If the real-time stability margin is greater than the minimum stability margin, the system is considered stable. If the real-time stability margin is less than the minimum stability margin, the minimum stability margin is increased and the virtual impedance is solved again.

[0148] The formula for calculating the real-time stability margin is as follows:

[0149]

[0150] In the formula, This represents the system phase margin when considering the virtual impedance Zv; Z V Represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; Z s (jω) represents the frequency characteristic of the port short-circuit drive impedance; ω represents the angular frequency; Ω represents the frequency range; jω represents the frequency variable.

[0151] Based on the above technical solution, this invention performs frequency sweep analysis by analyzing the harmonic transmission frequency characteristics of wind farms, constructs a transfer function with virtual impedance by combining additional component theory, and optimizes parameters with the goal of minimizing the harmonic correction factor and the constraint of stability margin, thereby achieving voltage amplification suppression at specific harmonic frequencies while ensuring system stability and feasibility.

[0152] Figure 7 An embodiment of a computer device according to the present invention is shown. This computer device may be a server and includes a processor, memory, and a network interface connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database stores static and dynamic information data. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements the steps in the above-described method embodiment.

[0153] Those skilled in the art will understand that Figure 7 The structure shown is merely a block diagram of a portion of the structure related to the present invention and does not constitute a limitation on the computer device to which the present invention is applied. A specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0154] In addition, the present invention also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0155] In addition, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the above method embodiments.

[0156] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided by this invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0157] This invention is not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this invention is limited only by the appended claims.

Claims

1. A method for designing virtual harmonic impedance in a wind farm, characterized in that, include: Based on the wind farm topology, construct an equivalent model of the wind farm's overall grid connection; Based on the overall grid-connected equivalent model of the wind farm, the harmonic transmission frequency response of the wind power grid-connected system is measured at the grid connection point; and based on the harmonic transmission frequency response, the harmonic amplification risk area is identified. For the identified harmonic amplification risk areas, a virtual impedance is introduced to correct the harmonic transfer frequency response, resulting in the harmonic transfer function after introducing the virtual impedance, and the harmonic amplification correction factor is extracted from the harmonic transfer function. With the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, an optimization model for harmonic virtual impedance parameters is established and solved to obtain the optimized virtual impedance parameters.

2. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, Based on the wind farm topology, the equivalent model of the wind farm's overall grid connection is constructed as follows: Based on the wind farm topology, the wind turbine inverter, step-up transformer, collector cable and external power grid are modeled as a series-parallel complex impedance network, and an equivalent model of the wind farm's overall grid connection is established.

3. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, Based on the equivalent model of the overall grid connection of the wind farm, the measurement of the harmonic transmission frequency response of the wind power grid-connected system at the grid connection point includes: Based on the electrical connection relationship between the inverter control loop and the grid connection point in the overall grid-connected equivalent model of the wind farm, the disturbance signal injection node and the grid connection point are determined. Based on the disturbance signal injection node and grid connection point, the frequency response of the harmonic transmission of the wind power grid-connected system is measured using the frequency characteristic scanning method based on small signal disturbance injection.

4. The wind farm harmonic virtual impedance design method according to claim 3, characterized in that, The frequency response scanning method based on small signal perturbation injection includes: A small sinusoidal disturbance signal is injected into the inverter control circuit. The frequency range of the small sinusoidal disturbance signal is 15Hz to 2kHz. The harmonic transmission frequency response of the wind power grid-connected system is measured by measuring the amplitude ratio and phase difference between the grid connection point voltage and the small-amplitude sinusoidal disturbance signal.

5. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, Based on the harmonic propagation frequency response, the areas at risk of harmonic amplification include: Based on the frequency response of harmonic propagation, the location of amplified peaks is analyzed to identify areas of harmonic amplification risk.

6. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, When introducing virtual impedance to target the identified harmonic amplification risk area, the virtual impedance is introduced into the inverter control loop through a complex bandpass filter. The expression for the complex bandpass filter is: In the formula, Q(s) represents the transfer function of the complex bandpass filter; ω b ω represents the filter bandwidth frequency, b represents the bandwidth; h represents the center frequency of the bandpass filter, h represents harmonics; s represents complex frequency variables; j represents the imaginary unit; The expression for the virtual impedance control voltage is as follows: U V (s)=Z V (s)Q(s)i(s) Z V (s)=R V +jX V In the formula, U V (s) represents the harmonic virtual impedance control voltage; Z V (s) represents the harmonic virtual impedance; i(s) represents the fan output current; R V Indicates virtual resistance; X V V represents virtual inductive impedance; j represents the imaginary unit.

7. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, After correcting the harmonic transfer frequency response, the harmonic transfer function after introducing virtual impedance is obtained as follows: Based on virtual impedance, the harmonic transfer frequency response is corrected according to the extra element theorem to obtain the harmonic transfer function after introducing virtual impedance. The expression for the harmonic transfer function is: In the formula, H(jω / Z) V Z represents the harmonic transfer function; V (jω) represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; H0(jω) represents the harmonic propagation frequency response of the system before the introduction of the virtual harmonic impedance; Z o (jω), Z s (jω) represents the open-circuit drive impedance and short-circuit drive impedance of the network port, respectively; o and s represent open circuit and short circuit, respectively; jω represents the frequency variable.

8. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, The expression for the harmonic virtual impedance parameter optimization model is as follows: In the formula, F(Z) V ) represents the objective function; jω represents the frequency variable; ω represents the angular frequency; Ω represents the frequency range; This represents the system phase margin when considering the virtual impedance Zv; This represents the minimum stability margin of the system.

9. The method for designing virtual impedance of wind farm harmonics according to claim 1, characterized in that, When solving the optimization model of harmonic virtual impedance parameters, a multi-objective genetic algorithm or particle swarm optimization algorithm is used to solve the optimization virtual impedance parameters.

10. The method for designing virtual harmonic impedance in a wind farm according to claim 1, characterized in that, Also includes: The optimized virtual impedance parameters were substituted into the overall grid-connected equivalent model of the wind farm, and the system characteristics were tested using the frequency characteristic scanning method based on small signal disturbance injection to verify the harmonic amplification suppression effect and system stability.

11. The method for designing virtual impedance of wind farm harmonics according to claim 10, characterized in that, By substituting optimized virtual impedance parameters into the overall grid-connected equivalent model of the wind farm, and employing a frequency response scanning method based on small-signal disturbance injection, the harmonic amplification suppression effect was verified, including: The optimized virtual impedance parameters are loaded into the wind farm converter controller. The harmonic transfer function is measured by the frequency characteristic scanning method based on small signal disturbance injection. The harmonic amplification peak value is then verified based on the harmonic transfer function. When the peak value of harmonic amplification is reduced, determine whether the harmonic amplification suppression effect meets the grid connection standard. If it does not meet the standard, increase the resistive component of the virtual impedance.

12. The method for designing virtual impedance of wind farm harmonics according to claim 10, characterized in that, By substituting optimized virtual impedance parameters into the overall grid-connected equivalent model of the wind farm, and using the frequency response scanning method based on small-signal disturbance injection, the system stability was verified, including: The optimized virtual impedance parameters are loaded into the wind farm converter controller to calculate the real-time stability margin; and the real-time stability margin is compared with the minimum stability margin. If the comparison result shows that the real-time stability margin is greater than the minimum stability margin, the system is determined to be stable; if the comparison result shows that the real-time stability margin is less than the minimum stability margin, the minimum stability margin of the system is increased and the virtual impedance is solved again.

13. The method for designing virtual harmonic impedance in a wind farm according to claim 12, characterized in that, The formula for calculating the real-time stability margin is: In the formula, This represents the system phase margin when considering the virtual impedance Zv; Z V Represents the virtual impedance; Q(jω) represents the frequency response of the complex bandpass filter; Z s (jω) represents the frequency characteristic of the port short-circuit drive impedance; ω represents the angular frequency; Ω represents the frequency range; jω represents the frequency variable.

14. A wind farm harmonic virtual impedance design system, characterized in that, include: The equivalent modeling module is used to construct an equivalent model of the entire grid connection of the wind farm based on the wind farm topology. The frequency sweep analysis module is used to measure the harmonic transmission frequency response of the wind power grid-connected system at the grid connection point based on the overall grid-connected equivalent model of the wind farm; and to identify the harmonic amplification risk area based on the harmonic transmission frequency response. The harmonic correction module is used to introduce virtual impedance to correct the harmonic transfer frequency response for the identified harmonic amplification risk areas, obtain the harmonic transfer function after introducing virtual impedance, and extract the harmonic amplification correction factor from the harmonic transfer function. The model optimization module is used to establish an optimization model for harmonic virtual impedance parameters with the goal of minimizing the harmonic amplification correction factor and the system stability margin as a constraint, and to solve the optimization model to obtain the optimized virtual impedance parameters.

15. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 13.

16. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 13.

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