Offshore wind power harmonic suppression method and device based on virtual impedance

Abstract

The invention relates to the technical field of offshore wind power harmonic treatment, and discloses an offshore wind power harmonic treatment method and device based on virtual impedance, and the method comprises the steps: obtaining a power grid current, and carrying out the harmonic extraction of the power grid current, and obtaining a power grid current harmonic component; virtual impedance is determined based on the harmonic frequency suppression requirement, and compensation voltage is obtained through calculation according to the virtual impedance and the power grid current harmonic component; acquiring a common connection point voltage, and performing first operation processing on the common connection point voltage and the compensation voltage to obtain a reference output current; obtaining an output current of the static var generator, and performing second operation processing on the reference output current and the output current of the static var generator to obtain a reference output voltage; and performing signal conversion on the reference output voltage to obtain a modulation signal, and controlling the static var generator to perform common connection point harmonic suppression based on the modulation signal. According to the invention, suppression of a specific resonant frequency can be realized based on the virtual impedance.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power harmonic control, and in particular to an offshore wind power harmonic control method and device based on virtual impedance. Background Art

[0002] In recent years, the scale of offshore wind farms has continued to expand. With its 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-connected operation of offshore wind power, the harmonic impact it generates 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 quality of grid-connected power from wind farms, but also seriously threatens the safety of new energy station equipment and the safe and stable operation of the grid-connected power system.

[0003] At present, traditional harmonic control methods mainly rely on passive filters and active filters, but these two types of filters have obvious disadvantages in offshore wind power scenarios: the equipment is large, which increases the difficulty of deployment in the limited space of the offshore platform; the cost is high, resulting in a significant increase in the construction and operation costs of offshore wind power projects; maintenance is difficult, and the harsh natural environment and complex operating conditions at sea make equipment maintenance work high-risk and costly. In addition, the special characteristics of the offshore environment such as high humidity, strong salt spray, and complex meteorological conditions have put forward higher requirements for the reliability and adaptability of harmonic control equipment.

[0004] Therefore, it is urgent to propose a harmonic control method that is both efficient and reliable to improve the power quality of offshore wind power grid-connected power. Summary of the invention

[0005] The purpose of the present invention is to improve the harmonic suppression effect, reduce equipment costs, and enhance the stability and reliability of offshore wind power systems. In order to achieve the above purpose, the present invention provides an offshore wind power harmonic control method and device based on virtual impedance.

[0006] In a first aspect, an embodiment of the present invention provides an offshore wind power harmonic control method based on virtual impedance, wherein the offshore wind power harmonic control method is applied to an offshore wind farm grid-connected system; The offshore wind farm grid-connected system comprises: a wind farm, a public connection point, a static VAR generator and a power grid, wherein 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; The offshore wind power harmonic control method comprises: Acquiring a grid current, and performing harmonic extraction on the grid current to obtain a grid current harmonic component; 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; Acquiring a common connection point voltage, and performing a first operation process on the common connection point voltage and the compensation voltage to obtain a reference output current; Acquire a static VAR generator output current, and perform a second operation on the reference output current and the static VAR generator output current to obtain a reference output voltage; The reference output voltage is converted into a modulation signal, and the static VAR generator is controlled based on the modulation signal to suppress common connection point harmonics.

[0007] Preferably, the acquiring the grid current and performing harmonic extraction on the grid current to obtain the grid current harmonic component includes: Acquiring a grid current, and performing coordinate transformation on the grid current to obtain a two-phase static grid current; Harmonics are extracted from the two-phase static grid current to obtain grid current harmonic components.

[0008] Preferably, determining the virtual impedance based on the harmonic frequency suppression requirement comprises: If the harmonic frequency suppression requirement is to suppress the second harmonic frequency, the virtual impedance is determined by the following formula: in, represents the virtual impedance transfer function, represents the virtual impedance, represents the transfer function obtained by decoupling during the harmonic extraction process, represents the Laplace operator.

[0009] Preferably, the calculating the compensation voltage according to the virtual impedance and the grid current harmonic component includes: Based on the multiplication operation of the virtual impedance and the harmonic component of the grid current, a compensation voltage is obtained.

[0010] Preferably, the acquiring the common connection point voltage and performing a first operation process on the common connection point voltage and the compensation voltage to obtain a reference output current includes: 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; Obtaining a voltage difference based on a subtraction operation of the two-phase static common connection point voltage and the compensation voltage; The voltage difference is proportionally integrated to obtain a reference output current.

[0011] 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: 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; Obtaining a current difference based on a subtraction operation between the reference output current and the two-phase static output current; The current difference is proportionally integrated to obtain a reference output voltage.

[0012] 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: Performing 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.

[0013] 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; 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.

[0014] Preferably, 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.

[0015] Preferably, the compensation voltage determination module includes: 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.

[0016] Compared with the prior art, the offshore wind power harmonic control method and device based on virtual impedance in the embodiment of the present invention has the following beneficial effects: by accurately acquiring the grid current and using the harmonic extraction technology, the harmonic components of the grid current can be clearly identified, 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, and 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of a method for controlling harmonics of offshore wind power based on virtual impedance according to an embodiment of the present invention; Figure 2 is a schematic structural diagram of an offshore wind farm grid-connected system according to an embodiment of the present invention; Figure 3 It is a schematic diagram of simulation verification results of an embodiment of the present invention; 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; Reference numerals: 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

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] Combine the following Figure 2 Explain the offshore wind farm grid connection system: 1) Wind farm 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.

[0024] 2) Boosting and transmission part 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.

[0025] 3) Power grid 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.

[0026] This topology enables offshore wind farms to efficiently and stably integrate the generated electricity into the power grid, while at the same time ensuring the quality of power and reliable operation of the system through the synergy of various devices.

[0027] The offshore wind power harmonic control method comprises the following steps: S1. Obtaining the grid current and performing harmonic extraction on the grid current to obtain the grid current harmonic component; Specifically, step S1 includes: 1) Obtain the grid current and perform coordinate transformation on the grid current to obtain the two-phase static grid current; 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.

[0028] 2) Extract the harmonics of the two-phase static grid current to obtain the harmonic components of the grid current.

[0029] 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.

[0030] S2. Determine the virtual impedance based on the harmonic frequency suppression requirement, and calculate the compensation voltage based on the virtual impedance and the harmonic component of the grid current; 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 of different frequency domains. By selecting appropriate virtual impedance and setting the harmonic frequency in harmonic extraction, the present invention can suppress the harmonic frequency of any frequency domain.

[0031] Specifically, step S2 includes: 1) If the harmonic frequency suppression requirement is to suppress the second harmonic frequency, the following formula is used to determine the virtual impedance: in, represents the virtual impedance transfer function, represents the virtual impedance, represents the transfer function obtained by decoupling during the harmonic extraction process, It should be noted that the derivation process of the above formula will be explained after the remaining steps are expanded.

[0032] 2) Based on the multiplication of the virtual impedance and the harmonic components of the grid current, the compensation voltage is obtained.

[0033] The compensation voltage is the compensation voltage of the static VAR generator, which is the product of the virtual impedance and the harmonic component of the grid current.

[0034] S3, obtaining a common connection point voltage, and performing a first operation process on the common connection point voltage and the compensation voltage to obtain a reference output current; Specifically, step S3 includes: 1) Obtain the common connection point voltage and perform coordinate transformation on the common connection point voltage to obtain the two-phase static common connection point voltage; The common connection point voltage obtained is a three-phase voltage. The common connection point voltage is converted from the three-phase stationary coordinate system (abc) to the two-phase stationary coordinate system ( ), the two-phase static common connection point voltage is obtained to facilitate subsequent calculation and processing.

[0035] 2) Based on the subtraction operation of the two-phase static common connection point voltage and the compensation voltage, the voltage difference is obtained; 3) Perform proportional integration on the voltage difference to obtain the reference output current.

[0036] Specifically, the deviation is quickly responded to through the proportional link, and the steady-state error is eliminated through the integral link, so as to finally obtain the reference output current, that is, the reference output current of the static VAR generator.

[0037] S4, obtaining 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; Specifically, step S4 includes: 1) Obtain 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; The obtained static VAR generator output current is a three-phase current. The static VAR generator output current is converted from the three-phase stationary coordinate system (abc) to the two-phase stationary coordinate system ( ), and obtain the two-phase static output current, which is convenient for subsequent calculation and processing.

[0038] 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).

[0039] 2) Based on the subtraction operation between the reference output current and the two-phase static output current, the current difference is obtained; 3) Perform proportional integration on the current difference to obtain the reference output voltage.

[0040] Specifically, the deviation is quickly responded to through the proportional link, and the steady-state error is eliminated through the integral link, so as to finally obtain the reference output voltage, that is, the reference output voltage of the static VAR generator.

[0041] S5. Convert the reference output voltage into a modulation signal, and control the static VAR generator to suppress common connection point harmonics based on the modulation signal.

[0042] Specifically, step S5 includes: 1) Pulse width modulation is performed on the reference output voltage to obtain a pulse width modulation signal; 2) Controlling 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 common connection point.

[0043] 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 grid or adjust the voltage as required, thereby achieving the goal of suppressing harmonic voltage and improving the grid voltage quality.

[0044] The derivation process of the formula in step S2 is described below in combination with steps S1, S3 to S5: The transfer function of the second harmonic extracted in step S1 can be expressed by the following formula: in, and represents the transfer function used to extract the second harmonic, Mainly used to extract harmonic signals of specific frequencies. and They are orthogonal signals. Indicates the transfer of function parameters, Indicates harmonic frequency.

[0045] To extract the second harmonic, the harmonic frequency Can be set to , is the fundamental frequency, and the decoupling principle is as follows: in, and represents the transfer function obtained based on the decoupling principle, and Corresponding to and .

[0046] Finally, the transfer function of the secondary virtual impedance is derived: as follows: By selecting a suitable virtual impedance , the impedance method, Nyquist curve and other methods can be used to evaluate the stability of the system. In order to ensure the stability of the system, it is necessary to first meet the stability requirements of the system, 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 Figure 2The offshore wind farm grid-connected system shown in the figure is used as an example for simulation verification. The simulation verification results are shown in Figure 3 As shown. Figure 3 It can be seen that after adding virtual impedance control, the system is reshaped into a low impedance path under the second harmonic at 100Hz. Comparing the impedance before and after the introduction of virtual impedance, the impedance amplitude of the specific harmonic frequency is significantly reduced, verifying the effectiveness of the above method.

[0047] The embodiment of the present invention is a method for offshore wind power harmonic control based on virtual impedance. By accurately acquiring the grid current and using the 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, and the second calculation combines the reference output current with the static VAR generator output current to achieve precise regulation 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.

[0048] like Figure 4 As shown, the embodiment of the present invention provides an offshore wind power harmonic control device based on virtual impedance, which is applied to Figure 2 The offshore wind farm grid-connected system shown.

[0049] The offshore wind power harmonic control device comprises: The harmonic extraction module 1 is used to obtain the grid current and perform harmonic extraction on the grid current to obtain the grid current harmonic component; Specifically, the harmonic extraction module includes: A coordinate transformation unit is used to obtain the grid current and perform 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.

[0050] Specifically, the harmonic component determination unit of this embodiment is a second-order generalized integral orthogonal signal generator (SOGI-QSG).

[0051] The compensation voltage determination module 2 is used 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 component of the grid current; Specifically, the compensation voltage determination module includes: 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.

[0052] 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; Specifically, the first operation processing module in this embodiment is a voltage loop.

[0053] 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; Specifically, the second operation processing module in this embodiment is a current loop.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 controlling offshore wind power harmonics based on virtual impedance, characterized in that: The offshore wind power harmonic control method is applied to offshore wind farm grid-connected systems; The offshore wind farm grid-connected system comprises: a wind farm, a public connection point, a static VAR generator and a power grid, wherein 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; The offshore wind power harmonic control method comprises: Acquiring a grid current, and performing harmonic extraction on the grid current to obtain a grid current harmonic component; Determine a virtual impedance based on the harmonic frequency suppression requirement, and calculate a compensation voltage based on the virtual impedance and the harmonic component of the grid current; Acquiring a common connection point voltage, and performing a first operation process on the common connection point voltage and the compensation voltage to obtain a reference output current; Acquire a static VAR generator output current, and perform a second operation on the reference output current and the static VAR generator output current to obtain a reference output voltage; The reference output voltage is converted into a modulation signal, and the static VAR generator is controlled based on the modulation signal to suppress common connection point harmonics.

2. The offshore wind power harmonic control method according to claim 1 is characterized in that: The obtaining of the grid current and performing harmonic extraction on the grid current to obtain the grid current harmonic component includes: Acquiring a grid current, and performing coordinate transformation on the grid current to obtain a two-phase static grid current; Harmonics are extracted from the two-phase static grid current to obtain grid current harmonic components.

3. The offshore wind power harmonic control method according to claim 1 is characterized in that: The determining of the virtual impedance based on the harmonic frequency suppression requirement comprises: If the harmonic frequency suppression requirement is to suppress the second harmonic frequency, the virtual impedance is determined by the following formula: in, represents the virtual impedance transfer function, represents the virtual impedance, represents the transfer function obtained by decoupling during the harmonic extraction process, represents the Laplace operator.

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

5. The offshore wind power harmonic control method according to claim 1, characterized in that: The acquiring the common connection point voltage and performing a first operation process on the common connection point voltage and the compensation voltage to obtain a reference output current includes: 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; Obtaining a voltage difference based on a subtraction operation of the two-phase static common connection point voltage and the compensation voltage; The voltage difference is proportionally integrated to obtain a reference output current.

6. The offshore wind power harmonic control method according to claim 1, characterized in that: The step of obtaining 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 includes: 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; Obtaining a current difference based on a subtraction operation between the reference output current and the two-phase static output current; The current difference is proportionally integrated to obtain a reference output voltage.

7. The offshore wind power harmonic control method according to claim 1, characterized in that: The step of 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: Performing 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.

Images