A method for harmonic suppression of offshore wind farm based on voltage harmonic injection

Abstract

The application provides a harmonic suppression method for offshore wind farm based on voltage harmonic injection, 1, comprising the following steps: S1, applying voltage harmonic to three-phase voltage reference value generation link of wind turbine generator converter control system; S2, calculating current harmonic component of power quality examination point of wind turbine generator converter control system when voltage harmonic component is not applied, and obtaining amplitude and phase information thereof; S3, injecting first voltage harmonic component, and correspondingly calculating current harmonic component amplitude and phase of current power quality examination point; S4, injecting second voltage harmonic component, and correspondingly calculating current harmonic component amplitude and phase of current power quality examination point; S5, determining transfer function amplitude-frequency characteristic between injected voltage harmonic component and power quality examination point according to calculation results of steps S3 and S4; S6, determining voltage harmonic component amplitude and phase required to be applied to injection point according to amplitude and phase information of current harmonic component when voltage harmonic is not applied, and combining transfer function amplitude-frequency characteristic. The suppression measure of the application can carry out harmonic suppression by using the ability of wind turbine generator converter control itself without increasing primary equipment, and problems caused by inputting primary equipment are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of offshore wind power generation, in particular to a method for suppressing harmonics of offshore wind farms based on voltage harmonic injection. BACKGROUND

[0002] The offshore wind power transmission system may have a resonance problem under certain conditions, thereby amplifying the current components of a specific frequency, resulting in excessive harmonic current at the system grid connection point, and high-amplitude harmonic components may threaten the safety of the grid connection system and affect the grid connection operation of the wind farm. The active and passive filtering devices applied to the primary system can solve the problem of excessive harmonic current in the system to some extent. However, the primary equipment has problems such as high investment and large floor area. The variable flow control system of the wind turbine has the characteristics of flexibility and controllability, and is affected by the characteristics of wind resources, so offshore wind turbines usually do not operate at full capacity, and therefore the converter has redundant capacity for use. More importantly, for the case of cable amplification of the harmonic current at the wind farm side, the source side treatment measures, i.e. the harmonic injection device applied at the wind farm side, require a smaller capacity than the harmonic injection device applied at the onshore grid connection point. Therefore, the harmonic suppression device can be applied in the variable flow control link to suppress the existing harmonic current components in the system by using the control effect of the converter. SUMMARY

[0003] In view of the problems in the prior art, the present application aims to provide a method for suppressing harmonics of offshore wind farms based on voltage harmonic injection. The suppression measures of the present application can utilize the ability of the variable flow control of the wind turbine to suppress harmonics without increasing the primary equipment, thereby avoiding the problems caused by the primary equipment.

[0004] To solve the above technical problems, the present application realizes the following technical scheme:

[0005] A method for suppressing harmonics of offshore wind farms based on voltage harmonic injection, characterized in that it comprises the following steps:

[0006] S1, applying a voltage harmonic to the three-phase voltage reference value generation link of the variable flow control system of the wind turbine;

[0007] S2, calculating the current harmonic component of the power quality examination point of the wind turbine grid connection system without applying the voltage harmonic component, and obtaining the amplitude and phase information thereof;

[0008] S3, injecting a first voltage harmonic component and calculating the amplitude and phase of the current harmonic component of the current power quality examination point;

[0009] S4, injecting a second voltage harmonic component and calculating the amplitude and phase of the current harmonic component of the current power quality examination point:

[0010] S5. Based on the two calculation results in steps S3 and S4, determine the amplitude-frequency characteristics of the transfer function between the injected voltage harmonic component and the power quality assessment point.

[0011] S6. Based on the amplitude and phase information of the current harmonic components when no voltage harmonics are applied, and combined with the amplitude-frequency characteristics of the transfer function, determine the amplitude and phase of the voltage harmonic components that need to be applied at the injection point.

[0012] Furthermore: In step S1, the mathematical model of the injected voltage harmonic components is as follows:

[0013]

[0014] Among them, U am U bm and U cm These represent the positive sequence voltage amplitudes of each phase; U amx U bmx and U cmx These represent the negative sequence voltage magnitudes of each phase; ω s1 ω s2 and ω sn These are the angular frequencies of each harmonic; and These are the phases of each positive sequence harmonic of phase a; and Let be the phase values ​​of each phase of the nth positive sequence harmonic; and These are the phases of each negative sequence harmonic of phase a; and The phase values ​​of each phase of the nth negative sequence harmonic;

[0015] The above U ah U bh and U ch The vector expression for the voltage signal is shown below:

[0016]

[0017] Based on the frequency of the current harmonic components present in the wind turbine converter control system, the target voltage harmonic components can be selectively injected. Based on the current harmonics in the wind turbine converter control system, the amplitude and phase of each of the above voltage signals can be adjusted.

[0018] Furthermore: In step S2, the harmonics of the current in each phase at the power quality assessment point are respectively and Through vector transformation, the positive and negative sequence harmonic components of each phase current harmonic can be calculated:

[0019]

[0020] To suppress the positive and negative sequence harmonic components of each phase current harmonic, it is necessary to inject reverse positive and negative sequence current harmonic components, respectively I, at the power quality assessment point. xc+ and I xc- :

[0021]

[0022] Furthermore: In step S5, the transfer function between the current harmonic component injected at the power quality assessment point and the voltage harmonic component injected by the voltage disturbance value is as follows:

[0023]

[0024] Furthermore: In step S2, when no voltage harmonic components are injected into the voltage reference value, i.e. and When all values ​​are 0, record and calculate the current harmonic values ​​at the power quality assessment point. and In step S3, only the positive sequence voltage component is injected. Record and calculate the current harmonic values ​​at the power quality assessment point at this time. and In step S4, only the negative sequence voltage is injected. Record and calculate the current harmonic values ​​at the power quality assessment point at this time. and

[0025] Combining this with equation (4), we can obtain:

[0026]

[0027] Therefore, the transfer admittance matrix is ​​obtained as follows:

[0028]

[0029] Furthermore: In step S6, the formulas for the positive and negative sequence components of the voltage harmonics to be injected at the injection point are as follows:

[0030]

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] This invention relates to the research on harmonic suppression measures for offshore wind farms, and in particular to the use of wind turbine converter control systems to suppress excessive harmonic amplitudes. This method does not require the addition of new primary equipment, but only the improvement of the secondary converter control system of the wind turbine. The proposed suppression measures can effectively suppress the problem of excessive harmonic currents in offshore wind farms, while also saving the land area of ​​offshore booster stations and onshore control centers, thus reducing construction costs.

[0033] The voltage harmonics of this invention only need to be added to the secondary converter control system of the wind turbine. By adding them to the voltage reference value link as voltage source harmonic disturbances, a reverse harmonic current is generated in the system by adjusting the voltage amplitude and phase to suppress the original harmonic current. This method only requires improvements to the secondary converter control system and has the advantages of flexibility and controllability. Attached Figure Description

[0034] Fig. 1 This is a schematic diagram of the wind turbine converter control system and the voltage harmonic signal application position of the present invention;

[0035] Fig. 2 This is a schematic diagram of the generation of positive / negative sequence harmonic voltage components according to the present invention;

[0036] Fig. 3 This is the wind farm grid connection topology diagram of the present invention; Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present invention. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present invention.

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0039] like Figs. 1 to 3 As shown, a method for harmonic suppression in offshore wind farms based on voltage harmonic injection includes the following steps:

[0040] S1. Apply voltage harmonics to the three-phase voltage reference value generation stage of the wind turbine converter control system;

[0041] S2. Calculate the current harmonic components at the power quality assessment point of the wind turbine grid-connected system when no voltage harmonic components are applied, and obtain their amplitude and phase information.

[0042] S3. Inject the first voltage harmonic component, and calculate the amplitude and phase of the current harmonic component at the current power quality assessment point.

[0043] S4. Inject the second voltage harmonic component, and calculate the amplitude and phase of the current harmonic component at the current power quality assessment point:

[0044] S5. Based on the two calculation results in steps S3 and S4, determine the amplitude-frequency characteristics of the transfer function between the injected voltage harmonic component and the power quality assessment point.

[0045] S6. Based on the amplitude and phase information of the current harmonic components when no voltage harmonics are applied, and combined with the amplitude-frequency characteristics of the transfer function, determine the amplitude and phase of the voltage harmonic components that need to be applied at the injection point.

[0046] Voltage harmonics are injected by a harmonic injection module, such as... Fig. 1 middle "U abch The block diagram shows a three-phase harmonic injection device, where the block diagram for the a-phase harmonic signal is as follows. Fig. 2 As shown, the mathematical model of the injected voltage harmonic components in step S1 is as follows:

[0047]

[0048] Among them, U am U bm and U cm These represent the positive sequence voltage amplitudes of each phase; U amx U bmx and U cmx These represent the negative sequence voltage magnitudes of each phase; ω s1 ω s2 and ω sn These are the angular frequencies of each harmonic; and These are the phases of each positive sequence harmonic of phase a; and Let be the phase values ​​of each phase of the nth positive sequence harmonic; and These are the phases of each negative sequence harmonic of phase a; and The phase values ​​of each phase of the nth negative sequence harmonic;

[0049] The above U ah U bh and U ch The vector expression for the voltage signal is shown below:

[0050]

[0051] Based on the frequency of the current harmonic components present in the wind turbine converter control system, the target voltage harmonic components can be selectively injected. Based on the current harmonics in the wind turbine converter control system, the amplitude and phase of each of the above voltage signals can be adjusted.

[0052] To effectively suppress harmonic current components at the power quality assessment point of the wind farm, it is necessary to calculate their positive and negative sequence components separately. In step S2, the harmonic currents of each phase at the power quality assessment point are as follows: and Through vector transformation, the positive and negative sequence harmonic components of each phase current harmonic can be calculated:

[0053]

[0054] To suppress the positive and negative sequence harmonic components of each phase current harmonic, it is necessary to inject reverse positive and negative sequence current harmonic components, respectively I, at the power quality assessment point. xc+ and I xc- :

[0055]

[0056] In step S5, the transfer function between the current harmonic component injected at the power quality assessment point and the voltage harmonic component superimposed on the voltage reference value is as follows:

[0057]

[0058] In the above formula, the transfer admittance as well as The transfer function of the positive and negative sequence voltage disturbance at the voltage injection point with respect to the positive and negative sequence harmonic current at the power quality assessment point can be obtained analytically.

[0059] In step S2, when no voltage harmonic components are injected into the voltage reference value, i.e. and When all values ​​are 0, record and calculate the current harmonic values ​​at the power quality assessment point. and In step S3, only the positive sequence voltage component is injected. Record and calculate the current harmonic values ​​at the power quality assessment point at this time. and In step S4, only the negative sequence voltage is injected. Record and calculate the current harmonic values ​​at the power quality assessment point at this time. and

[0060] Combining this with equation (4), we can obtain:

[0061]

[0062] Therefore, the transfer admittance matrix is ​​obtained as follows:

[0063]

[0064] Therefore, the harmonic current component required at the power quality assessment point is: and In step S6, according to equation (4), the formulas for the positive and negative sequence components of the voltage harmonics to be injected at the injection point are as follows:

[0065]

[0066] The design process of harmonic injection is illustrated using the example of a 650Hz harmonic amplitude exceeding the standard under a certain operating condition of the system.

[0067] (1) Harmonic Injection Module Design

[0068] The harmonic injection module identified for the 13th harmonic exceeding the limit is shown below:

[0069]

[0070] (2) Injection Component Analysis

[0071] Under a certain operating condition, there is a problem of the 650Hz harmonic amplitude exceeding the standard. The harmonic components of each phase at the power quality assessment point are:

[0072]

[0073] According to equation (3), the values ​​of the positive and negative sequence components of the current are calculated:

[0074]

[0075] Therefore, the harmonic components that need to be injected are determined. and The values ​​are 22.5858∠178.9921 and 78.8018∠177.833.

[0076] (3) Solving for transfer admittance

[0077] Inject only the positive sequence voltage component With a voltage of 2V and a ∠60°, record and calculate the harmonic current value at the power quality assessment point. and The values ​​are 34.3A∠99.16° and 67.35A∠-6.92°, respectively. Only negative-sequence harmonic voltage values ​​are injected. Record and calculate the harmonic current value at the power quality assessment point at this time. and The angles are 32.26A∠21.53° and 22.27A∠-58.42°, respectively.

[0078] Then, the transfer function matrix is ​​calculated according to equation (8):

[0079]

[0080] (4) Injected harmonic voltage and suppression effect

[0081] According to equation (9), the positive and negative sequence components of the harmonic voltage to be injected are calculated to be 1.6922∠126.1399° and 2.3161∠-23.4581°, respectively.

[0082] Taking phase a current as an example, the amplitudes before and after applying suppression are:

[0083]

[0084] Based on the description and accompanying drawings of this invention, those skilled in the art can readily manufacture or use the offshore wind farm harmonic suppression method based on voltage harmonic injection of this invention, and can produce the positive effects described in this invention.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for suppressing harmonics in offshore wind farms based on voltage harmonic injection, characterized in that: Includes the following steps: S1. Apply voltage harmonics to the three-phase voltage reference value generation stage of the wind turbine converter control system; S2. Calculate the current harmonic components at the power quality assessment point of the wind turbine grid-connected system when no voltage harmonic components are applied, and obtain their amplitude and phase information. S3. Inject the first voltage harmonic component, and calculate the amplitude and phase of the current harmonic component at the current power quality assessment point. S4. Inject the second voltage harmonic component, and calculate the amplitude and phase of the current harmonic component at the current power quality assessment point: S5. Based on the two calculation results in steps S3 and S4, determine the amplitude-frequency characteristics of the transfer function between the injected voltage harmonic component and the power quality assessment point. S6. Based on the amplitude and phase information of the current harmonic components when no voltage harmonics are applied, and combined with the amplitude-frequency characteristics of the transfer function, determine the amplitude and phase of the voltage harmonic components that need to be applied at the injection point. (1) Transfer admittance calculation When no voltage harmonic components are injected into the voltage reference value, i.e. and When all values ​​are 0, record and calculate the current harmonic values ​​at the power quality assessment point. and Inject only positive sequence component voltage Record and calculate the current harmonic values ​​at the power quality assessment point at this time. and Only inject negative sequence voltage Record and calculate the current harmonic values ​​at the power quality assessment point at this time. and Based on the relationship between the harmonic injection amount of the voltage reference value and the harmonic amplitude at the grid connection point, we can obtain: as well as To obtain the transfer admittance, the transfer admittance matrix is ​​as follows: (2) Determination of harmonic voltage injection amount The amount of harmonics that needs to be injected at the power quality assessment point is I. xc+ and I xc- Given that the transfer function admittance matrix has been calculated, the formulas for the positive and negative sequence components of the voltage harmonics to be injected at the injection point are as follows:

2. The method for suppressing harmonics in offshore wind farms based on voltage harmonic injection according to claim 1, characterized in that: The mathematical model for the injected voltage harmonic components in step S1 is as follows: Among them, U am U bm and U cm These represent the positive sequence voltage amplitudes of each phase; U amx U bmx and U cmx These represent the negative sequence voltage magnitudes of each phase; ω s1 ω s2 and ω sn These are the angular frequencies of each harmonic; and These are the phases of each positive sequence harmonic of phase a; and Let be the phase values ​​of each phase of the nth positive sequence harmonic; and These are the phases of each negative sequence harmonic of phase a; and The phase values ​​of each phase of the nth negative sequence harmonic; The above U ah U bh and U ch The vector expression for the voltage signal is shown below: Based on the frequency of the current harmonic components present in the wind turbine converter control system, the target voltage harmonic components can be selectively injected. Based on the current harmonics in the wind turbine converter control system, the amplitude and phase of each of the above voltage signals can be adjusted.

3. The method for suppressing harmonics in offshore wind farms based on voltage harmonic injection according to claim 1, characterized in that: In step S2, the harmonics of the current in each phase at the power quality assessment point are respectively and Through vector transformation, the positive and negative sequence harmonic components of each phase current harmonic can be calculated: To suppress the positive and negative sequence harmonic components of each phase current harmonic, it is necessary to inject reverse positive and negative sequence current harmonic components, respectively I, at the power quality assessment point. xc+ and I xc- :

4. The method for suppressing harmonics in offshore wind farms based on voltage harmonic injection according to claim 3, characterized in that: In step S5, the transfer functions between the injected current harmonic component and the injected voltage harmonic component at the power quality assessment point are as follows:

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