Method and system for determining reactive power compensation scheme of offshore wind power alternating current transmission system

Abstract

The application discloses a kind of offshore wind power AC transmission system reactive power compensation scheme determination method and system, comprising: the reactive power demand of offshore wind power AC transmission system based on the operating parameter obtained by offshore wind power AC transmission system, and the capacitance effect coefficient of single-end reactive power compensation scheme and the capacitance effect coefficient of double-end reactive power compensation scheme pre-constructed, respectively calculate the capacitance effect coefficient of wind farm under full load and light load when single-end reactive power compensation scheme and double-end reactive power compensation scheme are used;Based on the capacitance effect coefficient of wind farm under full load and light load, and offshore wind power AC transmission system stability analysis, determine the reactive power compensation scheme of offshore wind farm.The application takes the minimum as target Capacitance effect coefficient, compares the capacitance effect coefficient of offshore wind farm under different reactive power compensation schemes, and considers introducing stability analysis as a constraint condition to verify, determines the optimal offshore wind farm reactive power compensation scheme.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind farm grid connection impact analysis, and in particular to a method and system for determining a reactive power compensation scheme for an offshore wind power AC transmission system. Background Art

[0002] The world possesses vast offshore resources, and utilizing offshore wind farms for power generation holds great promise. Traditional reactive power compensation solutions for onshore wind farms struggle to adapt to the needs of offshore wind farms. Firstly, in AC transmission, offshore wind farms are connected to the onshore grid via submarine cables exceeding 110 kV. Compared to conventional lines, submarine cables have greater ground capacitance, generating significant capacitive currents and resulting in high transmission losses. This ground capacitance also creates a capacitive effect, which can increase the voltage at the end of the line. Secondly, the reactive power required for the wind farm side of the transmission line must be installed at the wind farm's booster station. However, offshore wind farm booster station platforms are expensive, and since every inch of land is valuable, their configuration requires significant consideration. For these two reasons, determining a reactive power compensation solution for offshore wind power AC transmission systems is an urgent task. Summary of the Invention

[0003] In order to address the above-mentioned deficiencies in the prior art, the present invention fully considers the impact of reactive power charging of submarine cables on offshore wind power lines, takes the minimum capacitance effect coefficient as the goal, and introduces investment and stability analysis of booster stations as constraints to determine the most cost-effective offshore wind farm reactive power compensation scheme, where the capacitance effect coefficient is the voltage ratio between the receiving end and the terminal end of the offshore wind farm transmission line.

[0004] The technical solution provided by the present invention is: a method for determining a reactive power compensation scheme for an offshore wind power AC transmission system, comprising:

[0005] Based on the obtained operating parameters of the offshore wind power AC transmission system, the reactive power demand of the offshore wind power AC transmission system is obtained;

[0006] Based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-established single-ended reactive compensation scheme and the capacitance effect coefficient of the double-ended reactive compensation scheme, respectively calculating the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are adopted;

[0007] Determining a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and stability analysis of the offshore wind power AC transmission system;

[0008] The capacitance effect coefficient is the ratio of the receiving end and terminal voltage of the offshore wind power AC transmission system.

[0009] Preferably, obtaining the reactive power demand of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system includes:

[0010] Based on the wave impedance and length of the overhead line between the confluence station and the landing point, and the wave impedance and length of the submarine cable between the landing point and the offshore booster station of the wind farm, the voltage and current of the confluence station, the landing point, and the offshore booster station of the wind farm are obtained respectively;

[0011] Based on the voltages and currents of the confluence station, landing point and offshore substation of the wind farm, calculate the capacitance effect coefficient of the entire line from end to end when the line is unloaded;

[0012] Based on the capacitance effect coefficient of the entire line from the receiving end to the terminal, the reactive power demand of the offshore wind power AC transmission system is obtained.

[0013] Preferably, the capacitance effect coefficient of the entire line from end to end is calculated as follows:

[0014]

[0015] Where: k: capacitance effect coefficient from the beginning to the end of the entire line; k 12 : Capacitive efficiency coefficient of the overhead line to the entire line; k2: Capacitive effect coefficient of the submarine cable; α1: Phase shift coefficient of the overhead line; l x : Equivalent line length of submarine cable; α2: Phase shift coefficient of submarine cable; l2: Length of submarine cable; l1: Length of overhead line.

[0016] Preferably, the capacitance benefit coefficient k of the overhead line to the entire line is 12 , calculated as follows:

[0017]

[0018] Where: Voltage at landing point; Voltage of offshore booster station at wind farm; Voltage at the junction station.

[0019] Preferably, the capacitance effect coefficient k2 of the submarine cable is calculated as follows:

[0020]

[0021] Preferably, the capacitance effect coefficient of the single-ended reactive power compensation scheme is calculated as follows:

[0022]

[0023] Where: k 单: capacitance effect coefficient of single-ended reactive power compensation scheme; C1: capacitance per unit length of overhead line; C2: capacitance per unit length of submarine cable; L2: reactance per unit length of submarine cable; Q: compensation capacity; ω: angular velocity; U: rated voltage of high-voltage reactive power compensation device; α1: phase shift coefficient of overhead line; α2: phase shift coefficient of submarine cable; l2: length of submarine cable; l1: length of overhead line.

[0024] Preferably, the capacitance effect coefficient of the two-terminal reactive power compensation scheme is calculated as follows:

[0025]

[0026] Where: k 双 : Capacitive effect coefficient of the two-terminal reactive power compensation scheme.

[0027] Preferably, determining the reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and the stability analysis of the offshore wind power AC transmission system, includes:

[0028] S301: Compare the capacitance effect coefficients of the wind farm under full load and light load, and use the reactive power compensation scheme with the smallest capacitance effect coefficient as the preliminary compensation scheme;

[0029] S302: Verifying the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints;

[0030] S303: When the preliminary compensation scheme meets the stability constraint of the offshore wind power AC transmission system, the current preliminary compensation scheme is determined to be the reactive power compensation scheme of the offshore wind farm; otherwise, the preliminary compensation scheme is re-determined among the remaining compensation schemes based on the capacitance effect coefficient and S2 is executed.

[0031] Preferably, the verification of the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints further includes:

[0032] The preliminary compensation scheme is verified using offshore wind power AC transmission system stability analysis and investment minimization as constraints.

[0033] Based on the same inventive concept, the present invention also provides a system for determining a reactive power compensation scheme for an offshore wind power AC transmission system, comprising:

[0034] an acquisition module, configured to obtain reactive power requirements of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system;

[0035] a calculation module for calculating, based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-established single-ended reactive compensation scheme and the capacitance effect coefficient of the pre-established double-ended reactive compensation scheme, the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are respectively adopted;

[0036] a determination module, configured to determine a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and a stability analysis of the offshore wind power AC transmission system;

[0037] The capacitance effect coefficient is the ratio of the receiving end and terminal voltage of the offshore wind power AC transmission system.

[0038] Preferably, the acquisition module includes:

[0039] an operation parameter acquisition unit, configured to respectively obtain the voltage and current of the converging station, the landing point, and the offshore booster station of the wind farm based on the wave impedance and length of the overhead line between the converging station and the landing point, and the wave impedance and length of the submarine cable between the landing point and the offshore booster station of the wind farm;

[0040] A capacitance effect coefficient obtaining unit is used to calculate the capacitance effect coefficient of the entire line from the receiving end to the terminal when the line is unloaded based on the voltage and current of the confluence station, the landing point and the offshore substation of the wind farm;

[0041] The reactive power demand obtaining unit is used to obtain the reactive power demand of the offshore wind power AC transmission system based on the capacitance effect coefficient of the entire line from the receiving end to the terminal.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The technical solution provided by the present invention obtains the reactive power demand of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system; based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-constructed single-end reactive compensation scheme and the capacitance effect coefficient of the double-end reactive compensation scheme, the capacitance effect coefficients of the wind farm under full load and light load when the single-end reactive compensation scheme and the double-end reactive compensation scheme are respectively calculated; based on the capacitance effect coefficients of the wind farm under full load and light load and the stability analysis of the offshore wind power AC transmission system, the reactive power compensation scheme of the offshore wind farm is determined; the present invention determines the most cost-effective offshore wind farm reactive power compensation scheme based on the capacitance effect coefficient and the stability analysis of the offshore wind power AC transmission system.

[0044] The technical solution provided by the present invention fully takes into account the requirements for reactive power configuration of offshore wind farms, takes minimizing the capacitance effect coefficient as the goal, compares the capacitance effect coefficients under different reactive power compensation schemes adopted by offshore wind farms, and considers introducing stability analysis as a constraint condition for verification, thereby providing a method for determining a reactive power compensation scheme for offshore wind power AC transmission systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of offshore wind power grid connection in the prior art;

[0046] Figure 2 A flow chart of a method for determining a reactive power compensation scheme for an offshore wind power AC transmission system provided by the present invention;

[0047] Figure 3 This is a detailed flow chart of a method for determining a reactive power compensation scheme for an offshore wind power AC transmission system in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to better understand the present invention, the present invention is further described below with reference to the accompanying drawings and examples.

[0049] Example 1

[0050] With the continuous deepening of the large-scale development of offshore wind power, the reactive voltage regulation of wind farms and the coordinated control of reactive voltage between wind farms and access systems have received widespread attention. Due to the particularity of the distribution characteristics of offshore wind resources, offshore wind farms are generally distributed in areas far away from the coastline, with weak electrical connections to the power grid. In addition, the power grids to which wind farms are connected are mostly distribution networks of regional load characteristics, with fewer local power sources and weak voltage support capabilities. At the same time, offshore wind power is mostly transmitted through submarine cables. Submarine cables with large capacitance (abbreviated as: submarine cables) will generate large capacitive currents to the ground, causing a significant drop in line voltage. Since the voltage deviation of the power supply system is generally controlled within 10%, the static constraint of voltage has become an important factor limiting wind power transmission. The patent of this invention defines the capacitance effect coefficient by the ratio of the receiving and terminal voltages of the offshore wind farm transmission line. With the goal of minimizing the capacitance effect coefficient, the capacitance effect coefficients of offshore wind farms under different reactive compensation schemes are compared, and the investment and stability analysis are considered as constraints for verification, so as to determine the most cost-effective offshore wind farm reactive compensation scheme.

[0051] Depend on Figure 1 From the offshore wind power grid connection diagram, we can see that the common way to transmit offshore wind power is as follows: the wind energy of each wind farm is boosted by a transformer and then transmitted via submarine cables. All wind power is collected at the landing point and then sent to the grid.

[0052] like Figure 2As shown, the present invention provides a method for determining a reactive power compensation scheme for an offshore wind power AC transmission system, comprising:

[0053] Step S1: obtaining reactive power demand of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system;

[0054] Step S2: Based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-established single-ended reactive compensation scheme and the capacitance effect coefficient of the pre-established double-ended reactive compensation scheme, respectively calculating the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are adopted;

[0055] Step S3: determining a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and stability analysis of the offshore wind power AC transmission system;

[0056] The capacitance effect coefficient is the ratio of the receiving end and terminal voltage of the offshore wind power AC transmission system.

[0057] Step S1: Obtaining reactive power demand of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system, including:

[0058] Since there is an overhead line between the confluence station 3 and the landing point 2, and a submarine cable between the landing point 2 and the offshore booster station 1 of the wind farm, when there are two different wave impedances in the line, it can be deduced that:

[0059]

[0060]

[0061] Where, are the voltage and current of offshore booster station 1, landing point 2, and confluence station 3 of the wind farm respectively; α1 is the phase shift coefficient of the overhead line between confluence station 3 and landing point 2; α2 is the phase shift coefficient of the submarine cable between landing point 2 and offshore booster station 1 of the wind farm; Z c1 is the wave impedance of the overhead line between the confluence station 3 and the landing point 2; Z c2 is the wave impedance of the submarine cable between landing point 2 and offshore booster station 1 of the wind farm; l1 is the length of the overhead line between confluence station 3 and landing point 2; l2 is the length of the submarine cable between landing point 2 and offshore booster station 1 of the wind farm.

[0062] Formula (1) and Formula (2) reflect the relationship between the voltage and current at the receiving and terminal ends of the entire line. When the receiving voltage is greater than the terminal voltage, a reactive power compensation scheme needs to be configured. The reactive power demand of the offshore wind power AC transmission system can be reflected through the capacitance effect coefficient of the receiving end to the terminal end of the entire line.

[0063] Step S2: Based on the reactive power demand of the offshore wind power AC transmission system and the pre-established capacitance effect coefficient of the single-ended reactive compensation scheme and the capacitance effect coefficient of the double-ended reactive compensation scheme, respectively calculating the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are adopted, including:

[0064] When the line is unloaded, The capacitance effect coefficient of the entire line from receiving end to terminal end can be obtained as follows:

[0065]

[0066] Wave impedance Z of overhead line c1 Greater than the wave impedance Z of the submarine cable c2 Therefore, when the overhead line is the front section, When the submarine cable is the front section, From this, it can be seen that the capacitance effect coefficient of the first section to the end when the front section is an overhead line is greater than the capacitance effect coefficient of the first section to the end when the front section is a submarine cable.

[0067] Since it is difficult to solve the capacitance effect coefficient after reactive power compensation in equation (3), it is simplified into a practical model. The submarine cable line is converted into an equivalent line with the same wave impedance as the overhead line according to the capacitive reactance. The line capacitive reactance is So the equivalent line length is C1 and C2 are the capacitance per unit length of overhead line and submarine cable respectively. After conversion, the capacitance benefit coefficient k of overhead line to the whole line is calculated. 12

[0068]

[0069]

[0070] Where, is the end of the line after equalization.

[0071] From formula (4) and (5), we can get:

[0072]

[0073] When the submarine cable itself produces capacitance effect, the capacitance effect coefficient is:

[0074]

[0075] In summary, the capacitance effect coefficient of the entire circuit is:

[0076]

[0077] In order to ensure the voltage stability of the wind farm, corresponding reactive equipment will be configured in the wind farm. In order to ensure the stability of the entire AC transmission system, it is considered to add reactive compensation devices to the transmission channel.

[0078] When one end of the submarine cable is compensated, that is, a high-resistance compensation device is connected in parallel at the landing point, and the compensation capacity is Q, then the inductive reactance U is the rated voltage of the high-voltage compensation device. The capacitive reactance of the submarine cable line after compensation is:

[0079]

[0080] Convert it into an equivalent line with the same capacitive reactance as the overhead line wave impedance:

[0081]

[0082] We can obtain l y for:

[0083]

[0084] Substituting into formula (11), the capacitance effect coefficient of the entire line after reactive power compensation is obtained as follows:

[0085]

[0086] The same compensation is applied at both ends, that is, equal reactive power is applied at both ends of the submarine cable line. The compensation capacity at each end is Q / 2, and the compensation inductive reactance at each end is: Compared with the one-end compensation, the capacitance effect coefficient of the front overhead line on the entire line is still k 12 Because of the capacitance effect of the submarine cable line itself, the high impedance is connected in parallel at the end, which is equivalent to offsetting part of the capacitance effect of the submarine cable line. Therefore, the high impedance can be converted into an equivalent submarine cable line length l according to the equivalent capacitance impedance. z ,but:

[0087]

[0088] Find l z for:

[0089]

[0090] Substituting into formula (6), the capacitance effect coefficient of the submarine cable itself is:

[0091]

[0092] Substituting equation (15) into equation (8), we can obtain that after reactive power is compensated at both ends, the capacitance effect coefficient of the entire line is:

[0093]

[0094] Step S3, determining a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and stability analysis of the offshore wind power AC transmission system, including:

[0095] S301: Compare the capacitance effect coefficients of the wind farm under full load and light load, and use the reactive power compensation scheme with the smallest capacitance effect coefficient as the preliminary compensation scheme;

[0096] S302: Verifying the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints;

[0097] S303: When the preliminary compensation scheme meets the stability constraint of the offshore wind power AC transmission system, the current preliminary compensation scheme is determined to be the reactive power compensation scheme of the offshore wind farm; otherwise, the preliminary compensation scheme is re-determined among the remaining compensation schemes based on the capacitance effect coefficient and S2 is executed.

[0098] The verification of the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints further includes:

[0099] The preliminary compensation scheme is verified using offshore wind power AC transmission system stability analysis and investment minimization as constraints.

[0100] The present invention proposes a method for determining a reactive compensation scheme for an offshore wind power AC transmission system based on capacitance effect coefficient comparison. Figure 3 As shown, the method includes the following steps:

[0101] Ⅰ. Arrangement of transmission line parameters and calculation of reactive power demand;

[0102] II. Calculate the capacitance effect coefficient based on single-ended and two-ended reactive power compensation schemes;

[0103] III. Compare capacitance effect coefficients and conduct economic and stability analysis and verification.

[0104] Furthermore, in step I, the transmission line parameter arrangement and reactive power demand calculation include:

[0105] For offshore wind power systems, the relevant parameters of the submarine cables are sorted out and the related reactive power requirements are calculated and analyzed.

[0106] Furthermore, in step II, the capacitance effect coefficient is calculated based on the single-ended and two-ended reactive power compensation schemes, including:

[0107] Configure the reactor capacity for no-load and the capacitor capacity for full-load, set the no-load boundary conditions and the full-load boundary conditions, and see if the capacity can be reduced while ensuring stability. Based on the reactor capacity configured for no-load or the capacitor capacity configured for full-load, calculate the capacitance effect coefficient of the wind farm under full and light load respectively using formulas (12) and (16).

[0108] Furthermore, in step III, the capacitance effect coefficients are compared, and economic and stability analysis and verification are performed to ultimately determine the compensation plan.

[0109] By comparing the capacitance effect coefficients under full load and light load, a preliminary compensation scheme is determined with the goal of minimizing the capacitance effect coefficient. On this basis, investment and stability constraints are introduced for verification.

[0110] Assume that after analysis, the two-terminal configuration scheme is superior to the single-terminal configuration in terms of capacitance effect coefficient. However, after the introduction of investment constraints, the two-terminal configuration scheme does not meet the requirements. At this time, it is necessary to verify whether the stability meets the relevant standards and grid requirements. If so, the single-ended configuration scheme is determined.

[0111] The investment and stability constraints adopted in the present invention are commonly used technical means in this field.

[0112] When the stability check fails or the economy is too high, the configured capacitor or inductor needs to have its capacity adjusted, that is, the boundary conditions need to be updated.

[0113] Example 2

[0114] Based on the same inventive concept, an embodiment of the present invention further provides a system for determining a reactive power compensation scheme for an offshore wind power AC transmission system, comprising:

[0115] an acquisition module, configured to obtain reactive power requirements of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system;

[0116] a calculation module for calculating, based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-established single-ended reactive compensation scheme and the capacitance effect coefficient of the pre-established double-ended reactive compensation scheme, the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are respectively adopted;

[0117] a determination module, configured to determine a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and a stability analysis of the offshore wind power AC transmission system;

[0118] The capacitance effect coefficient is the ratio of the receiving end and terminal voltage of the offshore wind power AC transmission system.

[0119] In an embodiment, the acquisition module includes:

[0120] an operation parameter acquisition unit, configured to respectively obtain the voltage and current of the converging station, the landing point, and the offshore booster station of the wind farm based on the wave impedance and length of the overhead line between the converging station and the landing point, and the wave impedance and length of the submarine cable between the landing point and the offshore booster station of the wind farm;

[0121] A capacitance effect coefficient obtaining unit is used to calculate the capacitance effect coefficient of the entire line from the receiving end to the terminal when the line is unloaded based on the voltage and current of the confluence station, the landing point and the offshore substation of the wind farm;

[0122] The reactive power demand obtaining unit is used to obtain the reactive power demand of the offshore wind power AC transmission system based on the capacitance effect coefficient of the entire line from the receiving end to the terminal.

[0123] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0124] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0125] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0126] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0127] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A method for determining a reactive power compensation scheme for an offshore wind power AC transmission system, characterized in that: include: Based on the obtained operating parameters of the offshore wind power AC transmission system, the reactive power demand of the offshore wind power AC transmission system is obtained; Based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-established single-ended reactive compensation scheme and the capacitance effect coefficient of the double-ended reactive compensation scheme, respectively calculating the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are adopted; Determining a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and stability analysis of the offshore wind power AC transmission system; The capacitance effect coefficient is the ratio of the receiving end and terminal voltage of the offshore wind power AC transmission system; The determining of a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and the stability analysis of the offshore wind power AC transmission system, includes: S301: Compare the capacitance effect coefficients of the wind farm under full load and light load, and use the reactive power compensation scheme with the smallest capacitance effect coefficient as the preliminary compensation scheme; S302: Verifying the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints; S303: When the preliminary compensation scheme satisfies the stability constraint of the offshore wind power AC transmission system, the current preliminary compensation scheme is determined to be the reactive power compensation scheme of the offshore wind farm; otherwise, the preliminary compensation scheme is re-determined from the remaining compensation schemes based on the capacitance effect coefficient and S2 is executed; Verifying the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints also includes: The preliminary compensation scheme is verified using offshore wind power AC transmission system stability analysis and investment minimization as constraints.

2. The method according to claim 1, wherein Obtaining the reactive power demand of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system includes: Based on the wave impedance and length of the overhead line between the confluence station and the landing point, and the wave impedance and length of the submarine cable between the landing point and the offshore booster station of the wind farm, the voltage and current of the confluence station, the landing point, and the offshore booster station of the wind farm are obtained respectively; Based on the voltages and currents of the confluence station, landing point and offshore substation of the wind farm, calculate the capacitance effect coefficient of the entire line from end to end when the line is unloaded; Based on the capacitance effect coefficient of the entire line from the receiving end to the terminal, the reactive power demand of the offshore wind power AC transmission system is obtained.

3. The method according to claim 2, wherein The capacitance effect coefficient of the entire line from the receiving end to the terminal is calculated as follows: Where: k: capacitance effect coefficient from the beginning to the end of the entire line; k 12 : Capacitive efficiency coefficient of the overhead line to the entire line; k2: Capacitive effect coefficient of the submarine cable; α1: Phase shift coefficient of the overhead line; l x : Equivalent line length of submarine cable; α2: Phase shift coefficient of submarine cable; l2: Length of submarine cable; l1: Length of overhead line.

4. The method according to claim 3, wherein The capacitance benefit coefficient k of the overhead line to the entire line 12 , calculated as follows: Where: Voltage at landing point; Voltage of offshore booster station at wind farm; Voltage at the junction station.

5. The method according to claim 3, wherein The capacitance effect coefficient k2 of the submarine cable is calculated as follows:

6. The method according to claim 1, wherein The capacitance effect coefficient of the single-ended reactive power compensation scheme is calculated as follows: Where: k 单 : capacitance effect coefficient of the single-ended reactive power compensation scheme; C1: capacitance per unit length of overhead line; C2: capacitance per unit length of submarine cable; L2: reactance per unit length of submarine cable; Q: compensation capacity; ω: angular velocity; U: rated voltage of high-voltage compensator; α1: phase shift coefficient of overhead line; α2: phase shift coefficient of submarine cable; l2: length of submarine cable; l1: length of overhead line.

7. The method according to claim 6, wherein The capacitance effect coefficient of the two-terminal reactive power compensation scheme is calculated as follows: Where: k 双 : Capacitive effect coefficient of the two-terminal reactive power compensation scheme.

8. A system for determining reactive power compensation schemes for offshore wind power AC transmission systems, characterized in that: include: an acquisition module, configured to obtain reactive power requirements of the offshore wind power AC transmission system based on the acquired operating parameters of the offshore wind power AC transmission system; a calculation module for calculating, based on the reactive power demand of the offshore wind power AC transmission system and the capacitance effect coefficient of the pre-established single-ended reactive compensation scheme and the capacitance effect coefficient of the pre-established double-ended reactive compensation scheme, the capacitance effect coefficient of the wind farm under full load and light load when the single-ended reactive compensation scheme and the double-ended reactive compensation scheme are respectively adopted; a determination module, configured to determine a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and a stability analysis of the offshore wind power AC transmission system; The capacitance effect coefficient is the ratio of the receiving end and terminal voltage of the offshore wind power AC transmission system; The determining of a reactive power compensation scheme for the offshore wind farm based on the capacitance effect coefficient of the wind farm under full load and light load, and the stability analysis of the offshore wind power AC transmission system, includes: S301: Compare the capacitance effect coefficients of the wind farm under full load and light load, and use the reactive power compensation scheme with the smallest capacitance effect coefficient as the preliminary compensation scheme; S302: Verifying the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints; S303: When the preliminary compensation scheme satisfies the stability constraint of the offshore wind power AC transmission system, the current preliminary compensation scheme is determined to be the reactive power compensation scheme of the offshore wind farm; otherwise, the preliminary compensation scheme is re-determined from the remaining compensation schemes based on the capacitance effect coefficient and S2 is executed; Verifying the preliminary compensation scheme using offshore wind power AC transmission system stability analysis constraints also includes: The preliminary compensation scheme is verified using offshore wind power AC transmission system stability analysis and investment minimization as constraints.

9. The system according to claim 8, wherein The acquisition module includes: an operation parameter acquisition unit, configured to respectively obtain the voltage and current of the converging station, the landing point, and the offshore booster station of the wind farm based on the wave impedance and length of the overhead line between the converging station and the landing point, and the wave impedance and length of the submarine cable between the landing point and the offshore booster station of the wind farm; A capacitance effect coefficient obtaining unit is used to calculate the capacitance effect coefficient of the entire line from the receiving end to the terminal when the line is unloaded based on the voltage and current of the confluence station, the landing point and the offshore substation of the wind farm; The reactive power demand obtaining unit is used to obtain the reactive power demand of the offshore wind power AC transmission system based on the capacitance effect coefficient of the entire line from the receiving end to the terminal.

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