A method and device for harmonic control of offshore wind power based on virtual impedance

Abstract

The present invention relates to the technical field of harmonic governance for offshore wind power, and discloses a method and device for harmonic governance of offshore wind power based on virtual impedance. The method includes: obtaining grid current, and extracting harmonics from the grid current to obtain grid current harmonic components; determining virtual impedance based on harmonic frequency suppression requirements, and calculating a compensation voltage according to the virtual impedance and the grid current harmonic components; obtaining the voltage at the point of common coupling, and performing a first arithmetic process on the voltage at the point of common coupling and the compensation voltage to obtain a reference output current; obtaining the output current of the static var generator, and performing a second arithmetic process on the reference output current and the output current of the static var generator to obtain a reference output voltage; performing signal conversion on the reference output voltage to obtain a modulation signal, and controlling the static var generator based on the modulation signal to suppress harmonics at the point of common coupling. The present invention can achieve the suppression of specific resonant frequencies based on virtual impedance.

Description

Technical Field

[0001] The present invention relates to the technical field of harmonic governance for offshore wind power, and particularly to a method and device for harmonic governance of offshore wind power based on virtual impedance. Background Art

[0002] In recent years, the scale of offshore wind farms has been continuously expanding. With the advantages of being clean and renewable, offshore wind power has occupied an increasingly important position in the energy structure. However, with the large-scale development and grid connection operation of offshore wind power, its harmonic impact on the power system has become increasingly prominent, and the harmonic resonance problem has become a key factor restricting the development of offshore wind power. This problem not only affects the power quality of the grid-connected electric energy of the wind farm, but also seriously threatens the safety of new energy station equipment and the safe and stable operation of the grid-connected power system.

[0003] Currently, traditional harmonic governance methods mainly rely on passive filters and active filters. However, these two types of filters have obvious drawbacks in the offshore wind power scenario: large equipment volume, increasing the deployment difficulty in the limited space of the offshore platform; high cost, resulting in a significant increase in the construction and operation costs of offshore wind power projects; difficult maintenance, and the harsh natural environment and complex operation conditions at sea make the equipment maintenance work risky and costly. In addition, the particularities of the offshore environment such as high humidity, strong salt fog, and complex meteorological conditions have put forward higher requirements for the reliability and adaptability of harmonic governance equipment.

[0004] Therefore, there is an urgent need to propose a harmonic governance method with both high efficiency and high reliability to improve the power quality of grid-connected offshore wind power. Summary of the Invention

[0005] The purpose of the present invention is to improve the harmonic suppression effect, reduce the equipment cost, and enhance the stability and reliability of the offshore wind power system. To achieve the above purpose, the present invention provides a method and device for harmonic governance of offshore wind power based on virtual impedance.

[0006] In the first aspect, an embodiment of the present invention provides a method for harmonic governance of offshore wind power based on virtual impedance, and the method for harmonic governance of offshore wind power is applied to an offshore wind farm grid-connected system;

[0007] The offshore wind farm grid-connected system includes: a wind farm, a point of common coupling, a static var generator, and a power grid. Among them, the wind farm and the power grid are connected to the point of common coupling, and the static var generator is connected to the point of common coupling;

[0008] The method for harmonic governance of offshore wind power includes:

[0009] Obtain the grid current, and perform harmonic extraction on the grid current to obtain the grid current harmonic components;

[0010] Determine the virtual impedance based on the harmonic frequency suppression requirement, and calculate the compensation voltage according to the virtual impedance and the harmonic component of the grid current;

[0011] Obtain the voltage at the point of common coupling, and perform a first arithmetic processing on the voltage at the point of common coupling and the compensation voltage to obtain the reference output current;

[0012] Obtain the output current of the static var generator, and perform a second arithmetic processing on the reference output current and the output current of the static var generator to obtain the reference output voltage;

[0013] Perform signal conversion on the reference output voltage to obtain a modulation signal, and control the static var generator to suppress the harmonics at the point of common coupling based on the modulation signal.

[0014] Preferably, the obtaining the grid current and performing harmonic extraction on the grid current to obtain the harmonic component of the grid current includes:

[0015] Obtain the grid current, and perform coordinate transformation on the grid current to obtain two-phase static grid currents;

[0016] Perform harmonic extraction on the two-phase static grid currents to obtain the harmonic component of the grid current.

[0017] Preferably, the determining the virtual impedance based on the harmonic frequency suppression requirement includes:

[0018] If the harmonic frequency suppression requirement is to suppress the second harmonic frequency, the virtual impedance is determined by using the following formula:

[0019]

[0020] Wherein, represents the virtual impedance transfer function, represents the virtual impedance, represents the transfer function obtained through decoupling processing during harmonic extraction, represents the Laplace operator.

[0021] Preferably, the calculating the compensation voltage according to the virtual impedance and the harmonic component of the grid current includes:

[0022] Based on the multiplication operation of the virtual impedance and the harmonic component of the grid current, obtain the compensation voltage.

[0023] Preferably, the obtaining the voltage at the point of common coupling and performing a first arithmetic processing on the voltage at the point of common coupling and the compensation voltage to obtain the reference output current includes:

[0024] Acquiring a common connection point voltage and performing coordinate transformation on the common connection point voltage to obtain a two-phase static common connection point voltage;

[0025] Obtaining a voltage difference based on a subtraction operation of the two-phase static common connection point voltage and the compensation voltage;

[0026] The voltage difference is proportionally integrated to obtain a reference output current.

[0027] Preferably, the step of acquiring the output current of the static VAR generator and performing a second operation on the reference output current and the output current of the static VAR generator to obtain a reference output voltage comprises:

[0028] Acquire the output current of the static VAR generator, and perform coordinate transformation on the output current of the static VAR generator to obtain a two-phase static output current;

[0029] Obtaining a current difference based on a subtraction operation between the reference output current and the two-phase static output current;

[0030] The current difference is proportionally integrated to obtain a reference output voltage.

[0031] Preferably, the converting the reference output voltage into a modulation signal, and controlling the static VAR generator to suppress common connection point harmonics based on the modulation signal, comprises:

[0032] Performing pulse width modulation on the reference output voltage to obtain a pulse width modulation signal;

[0033] An output current of the static VAR generator is controlled based on the pulse width modulation signal so that the output current weakens the harmonic voltage of the common connection point.

[0034] In a second aspect, an embodiment of the present invention provides an offshore wind power harmonic control device based on virtual impedance, wherein the offshore wind power harmonic control device is applied to the offshore wind farm grid-connected system as described above;

[0035] The offshore wind power harmonic control device comprises:

[0036] A harmonic extraction module is used to obtain the grid current and perform harmonic extraction on the grid current to obtain the grid current harmonic component;

[0037] A compensation voltage determination module, used to determine a virtual impedance based on a harmonic frequency suppression requirement, and calculate a compensation voltage based on the virtual impedance and the harmonic component of the grid current;

[0038] The first operation processing module is used to obtain the voltage of the common connection point, and perform a first operation processing on the voltage of the common connection point and the compensation voltage to obtain a reference output current;

[0039] The second operation processing module is used to obtain the output current of the static var generator, and perform a second operation processing on the reference output current and the output current of the static var generator to obtain a reference output voltage;

[0040] The harmonic suppression module is used to perform signal conversion on the reference output voltage to obtain a modulation signal, and control the static var generator to perform harmonic suppression at the common connection point based on the modulation signal.

[0041] Preferably, the harmonic extraction module includes:

[0042] The coordinate transformation unit is used to obtain the grid current and perform coordinate transformation on the grid current to obtain two-phase static grid currents;

[0043] The harmonic component determination unit is used to perform harmonic extraction on the two-phase static grid currents to obtain the grid current harmonic components.

[0044] Preferably, the compensation voltage determination module includes:

[0045] The operation processing unit is used to obtain the compensation voltage based on the multiplication operation of the virtual impedance and the grid current harmonic components.

[0046] Compared with the prior art, the method and device for harmonic governance of offshore wind power based on virtual impedance in the embodiments of the present invention have the following beneficial effects: By accurately obtaining the grid current and relying on harmonic extraction technology, the grid current harmonic components can be clearly identified, providing strong support for the formulation of subsequent governance strategies; On this basis, according to the grid harmonic characteristics and governance requirements, the parameters of the virtual impedance are optimized, so that the virtual impedance exhibits high impedance characteristics at specific harmonic frequencies, and the harmonic current corresponding to the frequency can be effectively suppressed; Key parameters such as the voltage of the common connection point and the output current of the static var generator are incorporated into the operation process. The first operation comprehensively considers the voltage of the common connection point and the compensation voltage, making the reference output current closely fit the real-time state of the grid. The second operation combines the reference output current with the output current of the static var generator to achieve precise regulation of the output of the static var generator; The harmonic governance method using virtual impedance does not require additional installation of physical filters, effectively reducing the hardware equipment cost. Description of the Drawings

[0047] Figure 1 is a schematic flowchart of a method for harmonic governance of offshore wind power based on virtual impedance in the embodiments of the present invention;

[0048] Figure 2 is a schematic structural diagram of an offshore wind farm grid-connected system according to an embodiment of the present invention;

[0049] Figure 3 It is a schematic diagram of simulation verification results of an embodiment of the present invention;

[0050] Figure 4 It is a structural schematic diagram of an offshore wind power harmonic control device based on virtual impedance according to an embodiment of the present invention;

[0051] Reference numerals:

[0052] RSC, rotor-side converter; GSC, grid-side converter; L, reactor; , the first grounding reactor; , second grounding reactor; PCC, common connection point; SVG, static VAR generator. DETAILED DESCRIPTION

[0053] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0054] In the description of the present invention, it should be understood that the terms "first" and "second" etc. are used in the present invention to distinguish different objects rather than to describe a specific order.

[0055] In the description of the present invention, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0056] like Figure 1 As shown, an embodiment of the present invention provides an offshore wind power harmonic control method based on virtual impedance, which is applied to an offshore wind farm grid-connected system.

[0057] like Figure 2 As shown, the offshore wind farm grid-connected system includes: a wind farm, a public connection point, a static VAR generator and a power grid. The wind farm and the power grid are connected to the public connection point, and the static VAR generator is connected to the public connection point.

[0058] Combine the following Figure 2 Explain the offshore wind farm grid connection system:

[0059] 1) Wind farm

[0060] Wind turbines capture wind energy and convert it into electrical energy. The output electrical energy is controlled and converted by RSC (rotor-side converter) and GSC (grid-side converter). RSC controls the excitation of the generator rotor, and GSC realizes the connection with the grid and power transmission. L (reactor) is connected in series in the circuit to suppress current changes and filter out some harmonics.

[0061] 2) Boosting and transmission part

[0062] The step-up transformer increases the low voltage electricity output by the wind farm to high voltage electricity, which is convenient for long-distance transmission to reduce power loss. The submarine cable is used as an offshore transmission line to transmit the electricity of the offshore wind farm to the land. The first grounding reactor ( ) and the second grounding reactor ( ) can limit the ground fault current and improve the safety and stability of system operation.

[0063] 3) Power grid

[0064] PCC (Point of Common Connection) is the connection point between the wind farm and the grid, where parameters such as power quality can be monitored. SVG (Static VAR Generator) is connected near the PCC point to quickly compensate for reactive power, regulate voltage, and improve power quality. Step-down transformers reduce high voltage electricity to the grid.

[0065] This topology enables offshore wind farms to efficiently and stably integrate the generated electricity into the power grid, while ensuring the quality of power and reliable operation of the system through the synergy of various devices.

[0066] The offshore wind power harmonic control method comprises the following steps:

[0067] S1. Obtaining the grid current and performing harmonic extraction on the grid current to obtain the grid current harmonic component;

[0068] Specifically, step S1 includes:

[0069] 1) Obtain the grid current and perform coordinate transformation on the grid current to obtain the two-phase static grid current;

[0070] The grid current obtained is a three-phase current. The grid current is converted from the three-phase stationary coordinate system (abc) to the two-phase stationary coordinate system ( ), and obtain the two-phase static grid current, which is convenient for subsequent harmonic extraction.

[0071] 2) Extract the harmonics of the two-phase static grid current to obtain the harmonic components of the grid current.

[0072] A specific harmonic can be extracted from the two-phase static grid current to obtain the grid current harmonic component. In this embodiment, the second harmonic component of the two-phase static grid current is obtained by extracting the second harmonic.

[0073] S2. Determine the virtual impedance based on the harmonic frequency suppression requirement, and calculate the compensation voltage according to the virtual impedance and the harmonic component of the grid current;

[0074] It should be noted that the present invention is not limited to suppressing a single specific harmonic frequency, but can adapt to the harmonic frequency suppression requirements in different frequency domains. By selecting an appropriate virtual impedance and setting the harmonic frequency in the harmonic extraction, the present invention can suppress the harmonic frequency in any frequency domain.

[0075] Specifically, step S2 includes:

[0076] 1) If the harmonic frequency suppression requirement is to suppress the second harmonic frequency, the virtual impedance is determined by the following formula:

[0077]

[0078] Among them, represents the virtual impedance transfer function, represents the virtual impedance, represents the transfer function obtained through decoupling processing in the harmonic extraction process, represents the Laplace operator. It should be noted that the derivation process of the above formula will be described after the remaining steps are expanded.

[0079] 2) Based on the multiplication operation of the virtual impedance and the harmonic component of the grid current, the compensation voltage is obtained.

[0080] The compensation voltage is the compensation voltage of the static var generator, that is, the product of the virtual impedance and the harmonic component of the grid current.

[0081] S3. Obtain the voltage at the point of common coupling, and perform a first arithmetic processing on the voltage at the point of common coupling and the compensation voltage to obtain the reference output current;

[0082] Specifically, step S3 includes:

[0083] 1) Obtain the voltage at the point of common coupling, and perform a coordinate transformation on the voltage at the point of common coupling to obtain the two-phase stationary voltage at the point of common coupling;

[0084] The obtained voltage at the point of common coupling is a three-phase voltage. The voltage at the point of common coupling is transformed from the three-phase stationary coordinate system (abc) to the two-phase stationary coordinate system ( ), and the two-phase stationary voltage at the point of common coupling is obtained, which is convenient for subsequent arithmetic processing.

[0085] 2) Based on the subtraction operation of the two-phase stationary voltage at the point of common coupling and the compensation voltage, the voltage difference is obtained;

[0086] 3) Perform proportional-integral on the voltage difference to obtain the reference output current.

[0087] Specifically, the proportional link quickly responds to the deviation, and the integral link eliminates the steady-state error, and finally the reference output current is obtained, that is, the reference output current of the static var generator.

[0088] S4. Obtain the output current of the static var generator, and perform a second arithmetic process on the reference output current and the output current of the static var generator to obtain the reference output voltage;

[0089] Specifically, step S4 includes:

[0090] 1) Obtain the output current of the static var generator, and perform a coordinate transformation on the output current of the static var generator to obtain the two-phase stationary output current;

[0091] The obtained output current of the static var generator is a three-phase current, and the output current of the static var generator is converted from the three-phase stationary coordinate system (abc) to the two-phase stationary coordinate system ( ), to obtain the two-phase stationary output current, which is convenient for subsequent arithmetic processing.

[0092] It should be noted that the grid current in step S1 is actually the current after the output current of the static var generator is filtered by an LC filter (composed of a filter inductor, an equivalent resistor, and a filter capacitor).

[0093] 2) Based on the subtraction operation of the reference output current and the two-phase stationary output current, obtain the current difference;

[0094] 3) Perform proportional-integral on the current difference to obtain the reference output voltage.

[0095] Specifically, the proportional link quickly responds to the deviation, and the integral link eliminates the steady-state error, and finally the reference output voltage is obtained, that is, the reference output voltage of the static var generator.

[0096] S5. Perform signal conversion on the reference output voltage to obtain a modulation signal, and control the static var generator to suppress the harmonic at the point of common coupling based on the modulation signal.

[0097] Specifically, step S5 includes:

[0098] 1) Perform pulse-width modulation on the reference output voltage to obtain a pulse-width modulation signal;

[0099] 2) Control the output current of the static var generator based on the pulse-width modulation signal, so that the output current weakens the harmonic voltage at the point of common coupling.

[0100] The pulse-width modulation signal controls the output current of the static var generator so that the static var generator can inject reactive current into the power grid or regulate the voltage as required, thereby achieving the goal of suppressing harmonic voltage and improving the power grid voltage quality.

[0101] The derivation process of the formula in step S2 will be described below in conjunction with steps S1, S3 to S5:

[0102] The transfer function for extracting the second harmonic in step S1 can be expressed by the following formula:

[0103]

[0104] Among them, and represent the transfer function for extracting the second harmonic, is mainly used to extract harmonic signals of specific frequencies, and are orthogonal signals to each other, represents the transfer function parameter, represents the harmonic frequency.

[0105] To extract the second harmonic, the harmonic frequency can be set to , is the fundamental frequency, and then the decoupling principle can be obtained as follows:

[0106]

[0107] Among them, and represent the transfer functions obtained based on the decoupling principle, and correspond to and respectively.

[0108] Finally, through derivation, the transfer function of the secondary virtual impedance is obtained as follows:

[0109]

[0110] By selecting an appropriate virtual impedance , methods such as the impedance method and the Nyquist curve can be used to evaluate the stability of the system. To ensure the system stability, first, the stability requirements of the system need to be met, and on this basis, select the virtual impedance that can achieve the best suppression effect. Based on the above selection requirements, in a specific embodiment, select and take the grid-connected system of the offshore wind farm shown in Figure 2 as an example for simulation verification. The simulation verification results are as shown in Figure 3As shown in the figure, from Figure 3 it can be seen that after adding the virtual impedance control, the system is reshaped into a low-impedance path under the second harmonic at 100 Hz. Comparing the impedances before and after introducing the virtual impedance, the impedance amplitude at specific harmonic frequencies is significantly reduced, verifying the effectiveness of the above method.

[0111] In an embodiment of the present invention, a method for harmonic governance of offshore wind power based on virtual impedance can accurately obtain the grid current and clearly identify the harmonic components of the grid current with the help of harmonic extraction technology, providing strong support for the formulation of subsequent governance strategies; on this basis, according to the harmonic characteristics of the grid and the governance requirements, the parameters of the virtual impedance are optimized so that the virtual impedance exhibits high-impedance characteristics at specific harmonic frequencies, effectively suppressing the harmonic current at the corresponding frequencies; key parameters such as the voltage at the point of common coupling and the output current of the static var generator are incorporated into the calculation process. The first calculation comprehensively considers the voltage at the point of common coupling and the compensation voltage, making the reference output current closely fit the real-time state of the grid. The second calculation combines the reference output current with the output current of the static var generator to achieve precise control of the output of the static var generator; the harmonic governance method using virtual impedance does not require additional installation of physical filters, effectively reducing the hardware equipment cost.

[0112] As Figure 4 shown, an embodiment of the present invention provides a device for harmonic governance of offshore wind power based on virtual impedance, which is applied to an offshore wind farm grid-connected system as shown in Figure 2 the figure.

[0113] The device for harmonic governance of offshore wind power includes:

[0114] A harmonic extraction module 1, configured to obtain the grid current and perform harmonic extraction on the grid current to obtain the harmonic components of the grid current;

[0115] Specifically, the harmonic extraction module includes:

[0116] A coordinate transformation unit, configured to obtain the grid current and perform coordinate transformation on the grid current to obtain two-phase stationary grid currents;

[0117] A harmonic component determination unit, configured to perform harmonic extraction on the two-phase stationary grid currents to obtain the harmonic components of the grid current.

[0118] Specifically, the harmonic component determination unit in this embodiment is a second-order generalized integral orthogonal signal generator (SOGI-QSG).

[0119] A compensation voltage determination module 2, configured to determine the virtual impedance based on the harmonic frequency suppression requirement and calculate the compensation voltage according to the virtual impedance and the harmonic components of the grid current;

[0120] Specifically, the compensation voltage determination module includes:

[0121] The operation processing unit is used to obtain the compensation voltage based on the multiplication operation of the virtual impedance and the harmonic component of the grid current.

[0122] A first operation processing module 3 is used to obtain a common connection point voltage, and perform a first operation processing on the common connection point voltage and a compensation voltage to obtain a reference output current;

[0123] Specifically, the first operation processing module in this embodiment is a voltage loop.

[0124] The second operation processing module 4 is used to obtain the output current of the static VAR generator, and perform a second operation processing on the reference output current and the output current of the static VAR generator to obtain a reference output voltage;

[0125] Specifically, the second operation processing module in this embodiment is a current loop.

[0126] The harmonic suppression module 5 is used to perform signal conversion on the reference output voltage to obtain a modulation signal, and control the static VAR generator to suppress common connection point harmonics based on the modulation signal.

[0127] Specifically, the harmonic suppression module of this embodiment includes a modulation signal generator, which performs signal conversion on a reference output voltage to obtain a modulation signal.

[0128] It should be noted that each module in the above-mentioned offshore wind power harmonic control device based on virtual impedance can be embedded in or independent of the processor in the computer device in the form of hardware, so that the processor can call and execute the operations corresponding to the above modules. For the specific definition of an offshore wind power harmonic control device based on virtual impedance, please refer to the definition of an offshore wind power harmonic control method based on virtual impedance above. The two have the same functions and effects, which will not be repeated here.

[0129] In summary, the embodiment of the present invention is a method and device for offshore wind power harmonic control based on virtual impedance. By accurately acquiring the grid current and using harmonic extraction technology, it can clearly identify the harmonic components of the grid current, providing strong support for the formulation of subsequent control strategies; on this basis, according to the harmonic characteristics and control requirements of the grid, the parameters of the virtual impedance are optimized, so that the virtual impedance presents high impedance characteristics at a specific harmonic frequency, which can effectively suppress the harmonic current of the corresponding frequency; key parameters such as the common connection point voltage and the static VAR generator output current are integrated into the calculation process. The first calculation comprehensively considers the common connection point voltage and the compensation voltage, so that the reference output current is closely matched to the real-time state of the grid. The second calculation combines the reference output current with the static VAR generator output current to achieve precise control of the static VAR generator output; the harmonic control method using virtual impedance does not require the installation of additional physical filters, effectively reducing the cost of hardware equipment.

[0130] Each embodiment in this specification is described in a progressive manner, and the same or similar parts of each embodiment can be directly referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. It should be noted that the technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0131] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A method for harmonic governance of offshore wind power based on virtual impedance, characterized in that, The above-mentioned method for harmonic control of offshore wind power is applied to the grid-connected system of an offshore wind farm; The grid-connected system of the offshore wind farm includes: a wind farm, a point of common coupling, a static var generator, and a power grid. Among them, the wind farm and the power grid are connected to the point of common coupling, and the static var generator is connected to the point of common coupling; The method for harmonic control of offshore wind power includes: Obtain the grid current and perform harmonic extraction on the grid current to obtain the grid current harmonic components; Determine the virtual impedance based on the harmonic frequency suppression requirement, and calculate the compensation voltage according to the virtual impedance and the grid current harmonic components; Obtain the voltage at the point of common coupling, and perform a first arithmetic operation on the voltage at the point of common coupling and the compensation voltage to obtain the reference output current; Obtain the output current of the static var generator, and perform a second arithmetic operation on the reference output current and the output current of the static var generator to obtain the reference output voltage; Perform signal conversion on the reference output voltage to obtain a modulation signal, and control the static var generator to suppress harmonics at the point of common coupling based on the modulation signal.

2. The method for harmonic control of offshore wind power according to claim 1, characterized in that, The obtaining the grid current and performing harmonic extraction on the grid current to obtain the grid current harmonic components includes: Obtain the grid current and perform coordinate transformation on the grid current to obtain two-phase stationary grid currents; Perform harmonic extraction on the two-phase stationary grid currents to obtain the grid current harmonic components.

3. The method for harmonic control of offshore wind power according to claim 1, wherein, The determining the virtual impedance based on the harmonic frequency suppression requirement includes: If the harmonic frequency suppression requirement is to suppress the second harmonic frequency, the following formula is used to determine the virtual impedance: Among them, represents the virtual impedance transfer function, represents the virtual impedance, represents the transfer function obtained through decoupling processing during the harmonic extraction process, represents the Laplace operator.

4. The method for harmonic governance of offshore wind power according to claim 1, characterized in that, The calculating the compensation voltage according to the virtual impedance and the grid current harmonic components includes: Based on the multiplication operation of the virtual impedance and the grid current harmonic components, the compensation voltage is obtained.

5. The method for suppressing harmonics in offshore wind power according to claim 1, wherein The obtaining the voltage at the point of common coupling and performing a first arithmetic operation on the voltage at the point of common coupling and the compensation voltage to obtain the reference output current includes: Obtain the voltage at the point of common coupling and perform coordinate transformation on the voltage at the point of common coupling to obtain two-phase stationary voltages at the point of common coupling; Based on the subtraction operation of the two-phase stationary voltages at the point of common coupling and the compensation voltage, obtain the voltage difference; Perform proportional integral on the voltage difference to obtain the reference output current.

6. The method for harmonic governance of offshore wind power according to claim 1, characterized in that The obtaining the output current of the static var generator and performing a second arithmetic operation on the reference output current and the output current of the static var generator to obtain the reference output voltage includes: Obtain the output current of the static var generator and perform coordinate transformation on the output current of the static var generator to obtain two-phase stationary output currents; Based on the subtraction operation of the reference output current and the two-phase stationary output currents, obtain the current difference; Perform proportional integral on the current difference to obtain the reference output voltage.

7. The method for harmonic governance of offshore wind power according to claim 1, characterized in that, The performing signal conversion on the reference output voltage to obtain a modulation signal and controlling the static var generator to suppress harmonics at the point of common coupling based on the modulation signal includes: Perform pulse width modulation on the reference output voltage to obtain a pulse width modulation signal; An output current of the static VAR generator is controlled based on the pulse width modulation signal so that the output current weakens the harmonic voltage of the common connection point.

8. An offshore wind power harmonic control device based on virtual impedance, characterized in that: The offshore wind power harmonic control device is applied to the offshore wind farm grid-connected system as claimed in any one of claims 1 to 7; The offshore wind power harmonic control device comprises: A harmonic extraction module is used to obtain the grid current and perform harmonic extraction on the grid current to obtain the grid current harmonic component; A compensation voltage determination module, used to determine a virtual impedance based on a harmonic frequency suppression requirement, and calculate a compensation voltage based on the virtual impedance and the harmonic component of the grid current; A first operation processing module, used for acquiring a common connection point voltage, and performing a first operation processing on the common connection point voltage and the compensation voltage to obtain a reference output current; A second operation processing module is used to obtain the output current of the static VAR generator, and perform a second operation processing on the reference output current and the output current of the static VAR generator to obtain a reference output voltage; The harmonic suppression module is used to perform signal conversion on the reference output voltage to obtain a modulation signal, and control the static VAR generator to perform common connection point harmonic suppression based on the modulation signal.

9. The offshore wind power harmonic control device according to claim 8, characterized in that: The harmonic extraction module comprises: A coordinate transformation unit, used for acquiring a grid current and performing coordinate transformation on the grid current to obtain a two-phase static grid current; The harmonic component determination unit is used to extract harmonics from the two-phase static grid current to obtain the grid current harmonic components.

10. The offshore wind power harmonic control device according to claim 8, characterized in that: The compensation voltage determination module comprises: The operation processing unit is used to obtain a compensation voltage based on a multiplication operation of the virtual impedance and the harmonic component of the grid current.

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