A method and system for offshore wind farm resonance analysis

Abstract

The application discloses a kind of offshore wind farm resonance analysis method and system, it is related to wind farm technical field, including by constructing offshore wind farm power transmission resonance equivalent mathematical characteristics, using resonance point movement method analysis offshore wind power resonance specific frequency, calculate offshore wind power equivalent parameter, build harmonic resonance simulation analysis model, design offshore wind power harmonic resonance treatment active harmonic compensation model scheme, accept harmonic resonance treatment effect.The application is by in-depth analysis resonance mechanism, compares and filters treatment method and develops station custom system, significantly improves the power quality of offshore wind farm, effectively controls harmonic pollution, not only promotes the technical progress of our country in this field, and it has important leading and demonstration effect to the development of power system power quality treatment technology.

Description

Technical Field

[0001] This invention relates to the field of wind farm technology, and in particular to a method and system for resonant analysis of offshore wind farms. Background Technology

[0002] With the rapid development of offshore wind power in China and the continuous growth of installed capacity, onshore wind power in China has become basically saturated in recent years, leading to a vigorous development of offshore wind power. By the end of 2020, the cumulative installed capacity of offshore wind power in China exceeded 26 million kilowatts, ranking first in the world. It is expected that the newly installed capacity of offshore wind power in China will exceed 30 million kilowatts, maintaining its leading position in the world. With the large-scale development of offshore wind power, the installed capacity of a single wind farm is generally over 1 million kilowatts. As wind farms develop on a large scale, power quality issues have become increasingly prominent. The grid connection of large-capacity wind turbines increases the fault current and power fluctuations of the power grid. Long-distance submarine cable transmission will generate capacitance effects. The widespread use of power electronic devices increases harmonic pollution in the power grid. These factors lead to a decline in power quality and affect the safe and stable operation of wind farms.

[0003] Currently, our understanding of the resonance mechanism in offshore wind power is not deep or comprehensive enough. Existing harmonic mitigation technologies are not ideal for offshore wind power and cannot solve the problem. The development of mitigation systems tailored to the actual conditions of domestic offshore wind farms is insufficient. Foreign countries also face similar problems in harmonic mitigation for offshore wind power, but their overall technical level is higher. Our technology conducts in-depth analysis of the resonance mechanism of offshore wind power, identifies key influencing factors, compares and studies different harmonic mitigation methods, identifies their respective applicable scenarios, and develops harmonic mitigation systems for typical offshore wind farms to effectively solve the problem. Overall, through theoretical research and comparison of mitigation methods, we have improved the shortcomings of existing technologies in terms of mechanism analysis, method selection, and practical application, thereby enhancing the harmonic mitigation effect of offshore wind farms. Summary of the Invention

[0004] In view of the problems existing in the current method and system for resonant analysis of offshore wind farms, this invention is proposed.

[0005] Therefore, the purpose of this invention is to provide a method and system for harmonic analysis of offshore wind farms, which can compare and study different harmonic control methods under the condition that the application of harmonic control technology to offshore wind power is not effective, identify their respective applicable scenarios, and carry out the research and development of harmonic control systems for typical offshore wind farms.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a method for analyzing the resonance of offshore wind farms, comprising: constructing equivalent mathematical characteristics of power transmission resonance in offshore wind farms; constructing a mathematical model based on the equivalent mathematical characteristics of the equipment; analyzing the resonance mechanism of offshore wind farms; verifying the harmonic amplification factors of offshore wind farms; analyzing specific frequencies of offshore wind farm resonance using the resonance point movement method; analyzing the passive harmonic suppression effect using the passive filtering treatment method; qualitatively analyzing the active harmonic compensation model using the active filtering compensation method; quantitatively analyzing the relationship between the active harmonic compensation model and harmonics; calculating equivalent parameters of offshore wind power; building a harmonic resonance simulation analysis model; designing an active harmonic compensation model scheme for offshore wind power harmonic resonance treatment; and accepting the harmonic resonance treatment effect.

[0008] As a preferred embodiment of the offshore wind farm resonance analysis method described in this invention, the analysis of the offshore wind farm resonance mechanism includes calculating the constant current source of harmonics, wherein the constant current source is the value of the current when the impedance changes, and the specific calculation process is as follows:

[0009]

[0010]

[0011] Among them, R Sn < <X Sn R Sn < <X Sn , For harmonic impedance, The impedance of the constant current source.

[0012] The verification of harmonic amplification factors in offshore wind farms includes calculating the total cable inductance and capacitance to ground. The specific calculation steps are as follows:

[0013] Calculate the first-stage magnification:

[0014]

[0015] Calculate the second-stage magnification:

[0016]

[0017] in, This is the magnification factor.

[0018] As a preferred embodiment of the offshore wind farm resonance analysis method described in this invention, the analysis of specific frequencies of offshore wind farm resonance includes absorbing harmonic currents using AC filtering based on proximity principles. The AC filtering includes harmonic current control and current compensation. The harmonic current control includes direct current control and indirect current control. The current compensation involves sampling the harmonic currents, extracting the harmonic current components using a harmonic extraction algorithm, and selecting the final total capacity. The specific steps are as follows:

[0019] Calculate the harmonic current components:

[0020]

[0021]

[0022] Select the final total capacity:

[0023] in, This represents the total capacity.

[0024] As a preferred embodiment of the offshore wind farm resonance analysis method described in this invention, the analysis of the passive harmonic suppression effect based on the passive filtering method includes filtering harmonics using an inductor-capacitor series connection. The passive harmonics include reactors and resistors. The active harmonic compensation model includes a harmonic main circuit supplying compensation current to the grid, with the main circuit operating in an inverter mode. The specific formula is as follows:

[0025]

[0026]

[0027]

[0028]

[0029] in, For grid current, For load current, To compensate for the current, This refers to the fundamental component of the grid current. These are harmonic components.

[0030] As a preferred embodiment of the offshore wind farm resonance analysis method described in this invention, the quantitative analysis of the relationship between the active harmonic compensation model and harmonics includes adjusting the compensation mode and harmonic frequency band, controlling the active harmonic compensation as a controlled current source, and generating a harmonic frequency band that is compatible with the harmonic frequency band. Compensation currents with the same amplitude but opposite phase The control includes employing a single-stage frequency-doubling carrier phase-shift pulse width modulation technique, by N sm In a converter with cascaded H-bridge units, a modulation wave signal V with a 180° phase difference is used, and 2N is taken. sm Columns with the same frequency and amplitude but a phase difference of 2 / N sm Carrier periodic triangular carrier signal V r The front bridge is compared with the positive modulation wave, and the rear bridge is compared with the negative modulation wave to generate 2N. smDifferent rectangular pulse sequences are used to drive the IGBT devices of each H-bridge unit to conduct.

[0031] As a preferred embodiment of the offshore wind farm resonance analysis method described in this invention, the calculation of offshore wind power equivalent parameters includes correcting the allowable value of harmonic current and allocating the ratio of the allowable harmonic current capacity to the power supply equipment capacity. The specific steps are as follows:

[0032] The formula for harmonic current correction is:

[0033]

[0034] in, For the short-circuit capacity of the common junction point, As a reference short-circuit capacity, This is the allowable value for the h-th harmonic current. For short-circuit capacity is The allowable value of the h-th harmonic current at time;

[0035] The capacity allocation formula is as follows:

[0036]

[0037] in, This is the allowable value for the nth harmonic current. Let i be the electricity consumption agreement capacity of the i-th user. The power supply capacity of the common connection point. This is the phase superposition coefficient.

[0038] As a preferred embodiment of the offshore wind farm resonance analysis method described in this invention, the following steps are included: The construction of the harmonic resonance simulation analysis model includes establishing a scatter distribution of the grid's equivalent impedance through impedance scanning and plotting the scatter distribution of the equivalent impedance. The active harmonic compensation model scheme includes dividing the boundary points of the grid's equivalent impedance into points A, B, C, D, E, and F. The equivalent impedance value at point A is 2.6542 + 10.4456j, the equivalent resistance value at point B is 2.2756 + 10.0484j, the equivalent resistance value at point C is 1.0739 + 7.1939j, the equivalent resistance value at point D is 0.6665 + 5.2089j, the equivalent resistance value at point E is 0.8747 + 5.0422j, and the equivalent resistance value at point F is 3.0055 + 9.57134j. The acceptance testing includes voltage ride-through capability, harmonic compensation capability, and the multi-task scheduling capability of the SOC platform. The voltage ride-through capability includes low-voltage ride-through capability, high-voltage ride-through capability, and continuous ride-through capability.

[0039] Secondly, embodiments of the present invention provide an offshore wind farm resonant system, comprising: a construction module, which constructs the equivalent mathematical characteristics of power transmission resonance in an offshore wind farm, constructs a mathematical model based on the equivalent mathematical characteristics of the equipment, analyzes the resonance mechanism of the offshore wind farm, and verifies the harmonic amplification factor of the offshore wind farm; an analysis module, which uses the resonance point movement method to analyze specific frequencies of offshore wind power resonance, analyzes the passive harmonic suppression effect based on the passive filtering treatment method, qualitatively analyzes the active harmonic compensation model using the active filtering compensation method, and quantitatively analyzes the relationship between the active harmonic compensation model and harmonics; and a calculation and verification module, which calculates the equivalent parameters of offshore wind power, builds a harmonic resonance simulation analysis model, designs an active harmonic compensation model scheme for offshore wind power harmonic resonance treatment, and implements and verifies the harmonic resonance treatment effect.

[0040] Thirdly, embodiments of the present invention provide 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 any step of the above-described method for resonant analysis of offshore wind farms.

[0041] Fourthly, embodiments of the present invention provide a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, it implements any step of the above-described method for resonant analysis of an offshore wind farm.

[0042] The beneficial effects of this invention are as follows: By constructing the equivalent mathematical characteristics of power transmission resonance in offshore wind farms, analyzing specific frequencies of offshore wind power resonance using the resonance point movement method, calculating equivalent parameters of offshore wind power, building a harmonic resonance simulation analysis model, designing an active harmonic compensation model scheme for offshore wind power harmonic resonance mitigation, and verifying the harmonic resonance mitigation effect, through in-depth analysis of the resonance mechanism, comparison and selection of mitigation methods, and development of a customized system for the wind farm, the power quality of offshore wind farms has been significantly improved, and harmonic pollution has been effectively controlled. This not only promotes technological progress in this field in my country, but also plays an important leading and demonstrative role in the development of power system power quality management technology. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0044] Figure 1 A schematic diagram of an offshore wind farm, which is provided as an embodiment of the present invention, for a method and system for resonant analysis of offshore wind farms.

[0045] Figure 2Harmonic magnification diagram of a method and system for resonant analysis of offshore wind farms provided in one embodiment of the present invention.

[0046] Figure 3 An equivalent impedance scanning scatter plot of a resonance analysis method and system for offshore wind farms provided in one embodiment of the present invention. Detailed Implementation

[0047] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0048] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0049] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0050] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0051] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention 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 addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integrated connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] Example 1

[0054] Reference Figures 1-3 This is the first embodiment of the present invention, which provides a method for resonant analysis of offshore wind farms, including:

[0055] S1: Construct the equivalent mathematical characteristics of power transmission resonance in offshore wind farms, build a mathematical model based on the equivalent mathematical characteristics of the equipment, analyze the resonance mechanism of offshore wind farms, and verify the harmonic amplification factors of offshore wind farms.

[0056] The analysis of the resonance mechanism of offshore wind farms includes the calculation of the constant current source of harmonics. The constant current source is the value of the current when the impedance changes. The specific calculation process is as follows:

[0057]

[0058]

[0059] Among them, R Sn < <X Sn , For harmonic impedance, The impedance of the constant current source.

[0060] Verifying the harmonic amplification factor of offshore wind farms includes calculating the total cable inductance and capacitance to ground. The specific calculation steps are as follows:

[0061] Calculate the first-stage magnification:

[0062]

[0063] Calculate the second-stage magnification:

[0064]

[0065] in, This is the magnification factor.

[0066] Furthermore, let the nth harmonic current of the harmonic constant current source be I. n The harmonic current entering the power system is I sn The harmonic current entering the capacitor is I cnAt this point, the external impedance of the harmonic source is the impedance resulting from the parallel connection of the inductive impedance and the capacitive reactance of the capacitor. The distribution of harmonic currents entering the power system and the capacitor will vary depending on the harmonic order, potentially resulting in I... sn >I n I may also appear cn >I n I sn >I n When I is in this state, it is called system harmonic current amplification, or harmonic current amplification. cn >I n When I is in this state, it is called capacitor harmonic current amplification. sn >I n and I cn >I n When both occur simultaneously, it is called severe harmonic current amplification. Within a certain range, the harmonic current on the system side or in the filter branch will have an amplification effect.

[0067] Furthermore, under different operating modes of the offshore wind transmission system, the total inductance and capacitance to ground of the cable change accordingly. When calculating the first-stage amplification factor and first-stage amplification factor of the harmonic current on the system side, the total inductance and capacitance to ground of the cable are directly proportional to the cable length. The cable length directly affects the cable's X... C With X L The values ​​of β1 and β2 affect the calculation results. The system impedance and impedance angle determine the degree of resonance amplification on the system side. The X value in the equivalent circuit is calculated. S The value of β affects the calculation results of β1 and β2. Based on the resonant amplification mechanism curve, the harmonic current on the system side will produce different amplification effects when the value of β is in different ranges.

[0068] S2: The resonance point movement method is used to analyze the specific frequency of offshore wind power resonance. The passive harmonic suppression effect is analyzed according to the passive filter treatment method. The active filter compensation method is used to qualitatively analyze the active harmonic compensation model and quantitatively analyze the relationship between the active harmonic compensation model and harmonics.

[0069] The analysis of specific frequencies in offshore wind power resonance addresses the issue of harmonics exceeding limits due to resonance effects at specific frequencies. This is achieved by altering impedance parameters through series reactance, shifting the frequency of harmonic exceedance, and employing AC filtering based on proximity to absorb harmonic currents. AC filtering includes harmonic current control and current compensation. Harmonic current control includes direct and indirect current control, while current compensation involves sampling the harmonic current, extracting its components using a harmonic extraction algorithm, and finally selecting the total capacity. The specific steps are as follows:

[0070] Calculate the harmonic current components:

[0071]

[0072]

[0073] Select the final total capacity:

[0074]

[0075] in, This represents the total capacity.

[0076] S2.1: The passive harmonic suppression effect is analyzed based on the passive filtering method, which includes filtering out harmonics using an inductor-capacitor series connection. Passive harmonics include reactors and resistors. The active harmonic compensation model includes the main harmonic circuit sending a compensation current to the power grid, and the main circuit operating in an inverter mode. The specific formula is as follows:

[0077]

[0078]

[0079]

[0080]

[0081] in, For grid current, For load current, To compensate for the current, This refers to the fundamental component of the grid current. These are harmonic components.

[0082] Furthermore, passive harmonic filtering typically employs an inductor-capacitor series configuration to filter out a specific harmonic. Active harmonic compensation, on the other hand, is a power electronic device that dynamically suppresses harmonics and compensates for reactive power. It allows for flexible adjustment of the compensation mode and frequency band, is less affected by grid impedance, and is less prone to grid resonance matching. A comparison of passive and active filtering is shown in Table 1 below:

[0083] In practical applications, passive filters have the following problems: fixed filtering characteristics, can only filter out single harmonics, are very sensitive to changes in grid parameters, making it difficult to guarantee the filtering effect in real time, inject a large amount of reactive power into the system while filtering, requiring the solution of reactive power balance, and under certain conditions, can easily lead to the amplification of lower harmonics, bringing potential operational risks, have low power density, and occupy a large area.

[0084] S2.2: Quantitative analysis of the relationship between the active harmonic compensation model and harmonics includes adjusting the compensation mode and harmonic frequency band, controlling the active harmonic compensation as a controlled current source, and generating harmonics... Compensation currents with the same amplitude but opposite phase The control includes employing single-stage frequency doubling carrier phase shift pulse width modulation technology, by N sm In a converter with cascaded H-bridge units, a modulation wave signal V with a 180° phase difference is used, and 2N is taken. sm Columns with the same frequency and amplitude but a phase difference of 2 / N sm Carrier periodic triangular carrier signal V r The front bridge is compared with the positive modulation wave, and the rear bridge is compared with the negative modulation wave to generate 2N. sm Different rectangular pulse sequences are used to drive the IGBT devices of each H-bridge unit to conduct.

[0085] S3: Calculate the equivalent parameters of offshore wind power, build a harmonic resonance simulation analysis model, design an active harmonic compensation model scheme for offshore wind power harmonic resonance mitigation, and accept the harmonic resonance mitigation effect.

[0086] The calculation of equivalent parameters for offshore wind power includes correcting for the allowable harmonic current value and allocating the ratio of the allowable harmonic current capacity to the power supply equipment capacity. The specific steps are as follows:

[0087] The formula for harmonic current correction is:

[0088]

[0089] in, For the short-circuit capacity of the common junction point, As a reference short-circuit capacity, This is the allowable value for the h-th harmonic current. For short-circuit capacity is The allowable value of the h-th harmonic current at time;

[0090] The capacity allocation formula is as follows:

[0091]

[0092] in, This is the allowable value for the nth harmonic current. Let i be the electricity consumption agreement capacity of the i-th user. The power supply capacity of the common connection point. This is the phase superposition coefficient.

[0093] S3.1: The harmonic resonance simulation analysis model is built by establishing the scatter distribution of the equivalent impedance of the power grid through impedance scanning and drawing the scatter distribution of the equivalent impedance. The active harmonic compensation model scheme includes dividing the boundary points of the equivalent impedance of the power grid into points A, B, C, D, E and F. The equivalent impedance value of point A is 2.6542+10.4456j, the equivalent resistance value of point B is 2.2756+10.0484j, the equivalent resistance value of point C is 1.0739+7.1939j, the equivalent resistance value of point D is 0.6665+5.2089j, the equivalent resistance value of point E is 0.8747+5.0422j, and the equivalent resistance value of point F is 3.0055+9.57134j.

[0094] Preferably, the impedance value at point A is 2.6542 + 10.4456j. The real part of 2.6542 ohms indicates that the resistive component of the equivalent impedance at this point is relatively small, while the imaginary part of 10.4456 ohms is relatively large. This point mainly reflects the reactive nature of the equivalent impedance of the power grid and is located in the upper right of the equivalent impedance distribution, representing the maximum value of the equivalent impedance. The impedance value at point B is 2.2756 + 10.0484j. Similar to point A, it mainly reflects the equivalent reactance of the power grid. Its impedance value is slightly smaller than that at point A and is located in the middle of the equivalent impedance distribution. In the upper region, the impedance value at point C is 1.0739 + 7.1939j. Compared with the previous two points, the imaginary part of point C decreases more, and the proportion of resistance increases. This indicates that the equivalent impedance of the power grid at this point changes from being dominated by reactance to having both resistance and reactance being significant, representing the inflection point of the equivalent impedance of the power grid. The parameters of points D and E show that the equivalent impedance of the power grid near these two points is dominated by resistance, reflecting the characteristics of the typical impedance range in the power grid. Point F, as a boundary point, shows that the reactance component in this region increases again, indicating an intermediate state.

[0095] Furthermore, the impedance scan establishes the scatter plot distribution of the equivalent impedance of the power grid, as shown in Table 2 below:

[0096] The background harmonic levels under different grid operation modes (i.e., the harmonic voltage level of the 220kV busbar of the shared substation before the wind farm is put into operation) are as follows: For operating conditions 5.1 and 5.2, due to significant changes in the equivalent impedance of the grid, the background harmonic levels exceed the national standard limit by 1.6%. Therefore, under these two operating conditions, it is no longer required that the control device control the harmonic voltage at the grid connection point below the national standard limit. Instead, it is required that after control by the device, the harmonic voltage at the grid connection point should not be higher than the background harmonic level before the wind farm is put into operation. The background harmonic levels of the grid under different grid operation modes are shown in Table 3 below.

[0097] When the power grid operates under condition 5.1, after treatment, the 5th harmonic current of the grid-connected line decreased from 42.1A to 4.2A, and the 7th harmonic current decreased from 17.5A to 1.2A. When the power grid operates under condition 5.2, after treatment, the 5th harmonic current of the grid-connected line decreased from 44.5A to 0.7A, and the 7th harmonic current decreased from 17.6A to 0.8A. When the power grid operates under condition 5.3, after treatment, the 5th harmonic current of the grid-connected line decreased from 40.0A to 2.2A, and the 7th harmonic current decreased from 16.6A to 0.7A. When the power grid operates under condition 5.4, after treatment, the 5th harmonic current of the grid-connected line decreased from 22.5A to 2.0A, and the 7th harmonic current decreased from 15.5A to 0.6A. When the power grid operates under condition 5.5, after treatment, the 5th harmonic current of the grid-connected line decreased from 15.8A to 1.9A, and the 7th harmonic current decreased from 15.0A to 1.1A. When the power grid operates under condition 5.6, after treatment, the 5th harmonic current of the grid-connected line decreased from 42.1A to 4.2A, and the 7th harmonic current decreased from 17.5A to 1.2A.

[0098] S3.2: Acceptance includes voltage ride-through capability, harmonic compensation capability, and multi-task scheduling capability of the SOC platform. Voltage ride-through capability includes low-voltage ride-through capability, high-voltage ride-through capability, and continuous ride-through capability.

[0099] Furthermore, in terms of low-voltage ride-through capability, harmonic mitigation responds rapidly from the moment the voltage drop occurs during low-voltage ride-through, supporting voltage recovery by injecting capacitive reactive current. The response time of dynamic capacitive reactive current control is no more than 75ms from the moment the voltage drop occurs at the grid connection point, and capacitive reactive current can be continuously injected during voltage faults. In terms of high-voltage ride-through capability, when a three-phase symmetrical voltage rise occurs at the grid connection point of the harmonic mitigation system, it should respond rapidly from the moment the voltage rise occurs, supporting voltage recovery by injecting inductive reactive current. The response time of dynamic inductive reactive current control is no more than 40ms from the moment the voltage rise occurs at the grid connection point, and inductive reactive current can be continuously injected during voltage faults. In terms of continuous ride-through capability, to cope with low-voltage-high-voltage cascading faults, harmonic mitigation also has continuous fault ride-through capability, which can achieve continuous ride-through from low to high to low to high.

[0100] Furthermore, the harmonic compensation capability enables harmonic mitigation to possess high-precision harmonic detection and compensation capabilities. By employing methods such as sliding window DFT and rotating coordinate transformation, it is possible to extract harmonics from the 2nd to the 50th order with a detection accuracy of over 97%. During the harmonic compensation process, a composite control method combining PI control and PR control is used to achieve open-loop or closed-loop compensation for specified harmonics from the 2nd to the 25th order, with a comprehensive compensation accuracy of up to 80%.

[0101] The SOC platform's multi-task scheduling capability utilizes industry-leading SOC (ARM+FPGA) processing chips, featuring a dual-core processor with a clock speed of up to 800MHz and a large-capacity FPGA. Its computing speed and scalability far exceed those of existing DSP+FPGA architectures.

[0102] In a preferred embodiment, an offshore wind farm resonant system includes a construction module, which constructs the equivalent mathematical characteristics of power transmission resonance in the offshore wind farm, builds a mathematical model based on the equivalent mathematical characteristics of the equipment, analyzes the resonance mechanism of the offshore wind farm, and verifies the harmonic amplification factor of the offshore wind farm; an analysis module, which analyzes the specific frequency of offshore wind power resonance using the resonance point movement method, analyzes the passive harmonic suppression effect according to the passive filtering treatment method, qualitatively analyzes the active harmonic compensation model using the active filtering compensation method, and quantitatively analyzes the relationship between the active harmonic compensation model and harmonics; and a calculation and verification module, which calculates the equivalent parameters of offshore wind power, builds a harmonic resonance simulation analysis model, designs an active harmonic compensation model scheme for offshore wind power harmonic resonance treatment, and implements and verifies the harmonic resonance treatment effect.

[0103] The above-mentioned unit modules can be embedded in the processor of the computer device in hardware form or independent of it, or they can be stored in the memory of the computer device in software form, so that the processor can call and execute the corresponding operations of the above modules.

[0104] In one embodiment, a computer device is provided, which may be a terminal. The computer device includes a processor, memory, a communication interface, a display screen, and an input device connected via a system bus. The processor of the computer device provides computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage medium. The communication interface of the computer device is used for wired or wireless communication with external terminals. Wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen of the computer device may be an LCD screen or an e-ink display screen. The input device of the computer device may be a touch layer covering the display screen, or buttons, a trackball, or a touchpad located on the casing of the computer device, or an external keyboard, touchpad, or mouse, etc.

[0105] In summary, this invention constructs equivalent mathematical characteristics of power transmission resonance in offshore wind farms, analyzes specific frequencies of offshore wind power resonance using the resonance point movement method, calculates equivalent parameters of offshore wind power, builds a harmonic resonance simulation analysis model, designs an active harmonic compensation model scheme for offshore wind power harmonic resonance mitigation, and verifies the effectiveness of harmonic resonance mitigation. Through in-depth analysis of the resonance mechanism, comparison and selection of mitigation methods, and development of a customized system for wind farms, this invention significantly improves the power quality of offshore wind farms and effectively controls harmonic pollution. This not only promotes technological progress in this field in my country but also plays a significant leading and demonstrative role in the development of power system power quality management technology.

[0106] Example 2

[0107] Reference Figures 1-3 This is the second embodiment of the present invention, which provides a method for analyzing the resonance of offshore wind farms. In order to verify the beneficial effects of the present invention, a simulation experiment is conducted for scientific demonstration.

[0108] The results of the mitigation effects of the 5th and 7th harmonics under changes in power grid background harmonics show that when the background harmonics increase by 20%, after the designed active filter treatment, the 5th harmonic voltage content at the grid connection point decreases from 1.89% to 1.42%, the 5th harmonic current in the grid-connected line decreases from 33.90A to 2.64A, and the 7th harmonic current decreases from 15.26A to 2.03A. When the background harmonics increase by 40%, after treatment, the 5th harmonic voltage content at the grid connection point decreases from 2.18% to 1.58%, the 5th harmonic current in the grid-connected line decreases from 39.09A to 0.94A, and the 7th harmonic current decreases from 17.42A to 1.23A. The mitigation results of the 5th and 7th harmonics under changes in power grid operation mode are shown in Tables 4 and 5 below:

[0109]

[0110] Considering the actual changes in power grid operation, after the designed active filter treatment, the 5th and 7th harmonic current indicators at the grid connection point of Huaneng Hehai Wind Farm can meet the national standard requirements. When the background harmonic voltage before the wind farm is put into operation does not exceed the national standard limit, after treatment, the 5th and 7th harmonic voltages at the grid connection point can meet the national standard requirements. When the background harmonic voltage exceeds the national standard limit, after treatment, the 5th and 7th harmonic voltages at the grid connection point can be restored to the background harmonic level before the wind farm is put into operation.

[0111] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for resonant analysis of offshore wind farms, characterized in that: include, Construct equivalent mathematical characteristics of power transmission resonance in offshore wind farms, build mathematical models based on the equivalent mathematical characteristics of equipment, analyze the resonance mechanism of offshore wind farms, and verify the harmonic amplification factors of offshore wind farms; The analysis of the resonance mechanism of offshore wind farms includes calculating the constant current source of harmonics. The constant current source is the value of the current when the impedance changes. The specific calculation process is as follows: ; ; Among them, R Sn < <X Sn , For harmonic impedance, The impedance of the constant current source is used; the verification of the harmonic amplification factor of the offshore wind farm includes calculating the total inductance of the cable and the capacitance to ground, and the specific calculation steps are as follows: Calculate the first-stage magnification: ; Calculate the second-stage magnification: ; In the formula, β1 is the first-stage magnification factor, and β2 is the second-stage magnification factor; In particular, the total inductance and capacitance to ground of the cable change depending on the operating mode of the offshore wind transmission system. When calculating the first and second stage amplification factors of the cable's harmonic current to the system side, the total inductance and capacitance to ground of the cable are directly proportional to the cable length. The cable length directly affects the cable's X... C With X L The values ​​of β1 and β2 affect the calculation results. The system impedance and impedance angle determine the degree of resonance amplification on the system side. The X value in the equivalent circuit is calculated. S The value of β affects the calculation results of β1 and β2. Based on the resonant amplification mechanism curve, the harmonic current on the system side will produce different amplification effects when the value of β is in different ranges. β is the amplification factor. The resonance point shifting method is used to analyze the specific frequency of offshore wind power resonance. The passive harmonic suppression effect is analyzed according to the passive filtering treatment method. The active harmonic compensation model is qualitatively analyzed using the active filtering compensation method. The relationship between the active harmonic compensation model and harmonics is quantitatively analyzed. The analysis of specific frequencies of offshore wind power resonance includes absorbing harmonic currents using AC filtering based on proximity. The AC filtering includes harmonic current control and current compensation. The harmonic current control includes direct current control and indirect current control. The current compensation involves sampling the harmonic current, extracting the harmonic current components using a harmonic extraction algorithm, and selecting the final total capacity. Calculate the equivalent parameters of offshore wind power and build a harmonic resonance simulation analysis model. The construction of the harmonic resonance simulation analysis model includes establishing the scatter distribution of the equivalent impedance of the power grid through impedance scanning and drawing the scatter distribution of the equivalent impedance. The active harmonic compensation model scheme includes dividing the boundary points of the equivalent impedance of the power grid into points A, B, C, D, E and F. Design an active harmonic compensation model scheme for offshore wind power harmonic resonance mitigation, and verify the effectiveness of harmonic resonance mitigation.

2. The offshore wind farm resonance analysis method as described in claim 1, characterized in that: The analysis of the passive harmonic suppression effect based on the passive filtering method includes filtering harmonics using an inductor-capacitor series configuration. The passive filter includes a reactor and a capacitor. The active harmonic compensation model includes a harmonic main circuit that sends a compensation current to the power grid. The main circuit operates in inverter mode. The specific formula is as follows: ; ; ; ; in, For grid current, For load current, To compensate for the current, This refers to the fundamental component of the grid current. These are harmonic components.

3. The offshore wind farm resonance analysis method as described in claim 2, characterized in that: The calculation of equivalent parameters for offshore wind power includes correcting for the allowable harmonic current value and allocating the ratio of the allowable harmonic current capacity to the power supply equipment capacity. The specific steps are as follows: The formula for harmonic current correction is: ; in, For the short-circuit capacity of the common junction point, As a reference short-circuit capacity, This is the allowable value for the h-th harmonic current. For short-circuit capacity is The allowable value of the h-th harmonic current at time; The capacity allocation formula is as follows: ; in, This is the allowable value for the nth harmonic current. Let i be the electricity consumption agreement capacity of the i-th user. denoted as the power supply capacity of the common connection point, and 'a' as the phase superposition coefficient.

4. The offshore wind farm resonance analysis method as described in claim 3, characterized in that: The equivalent resistance values ​​at point A are 2.6542 + 10.4456 J, at point B are 2.2756 + 10.0484 J, at point C are 1.0739 + 7.1939 J, at point D are 0.6665 + 5.2089 J, at point E are 0.8747 + 5.0422 J, and at point F are 3.0055 + 9.57134 J. The acceptance test includes voltage ride-through capability, harmonic compensation capability, and the multi-task scheduling capability of the SOC platform. The voltage ride-through capability includes low-voltage ride-through capability, high-voltage ride-through capability, and continuous ride-through capability.

5. A resonant system for an offshore wind farm, used to implement the resonant analysis method for an offshore wind farm as described in any one of claims 1 to 4, characterized in that: include, The module constructs the equivalent mathematical characteristics of power transmission resonance in offshore wind farms, builds a mathematical model based on the equivalent mathematical characteristics of the equipment, analyzes the resonance mechanism of offshore wind farms, and verifies the harmonic amplification factors of offshore wind farms. The analysis module uses the resonant point movement method to analyze specific frequencies of offshore wind power resonance, analyzes the passive harmonic suppression effect based on the passive filter treatment method, uses the active filter compensation method to qualitatively analyze the active harmonic compensation model, and quantitatively analyzes the relationship between the active harmonic compensation model and harmonics. The calculation and verification module calculates the equivalent parameters of offshore wind power, builds a harmonic resonance simulation analysis model, designs an active harmonic compensation model scheme for offshore wind power harmonic resonance mitigation, and implements and accepts the harmonic resonance mitigation effect.

6. 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 offshore wind farm resonance analysis method according to any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the offshore wind farm resonance analysis method according to any one of claims 1 to 4.

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