Offshore wind power DC transmission system and startup control method thereof

Abstract

The present invention relates to the technical field of flexible direct current transmission, and provides an offshore wind power direct current transmission system and a startup control method thereof. The system comprises: some wind turbines are connected to an offshore booster station through an offshore AC busbar, connected to a DRU converter valve of a diode uncontrolled rectifier unit, then connected to the offshore DC busbar through a first switch, connected to an onshore converter valve of an onshore converter station through a DC line, and finally connected to an onshore AC power grid; some wind turbines are connected to a DC transformer through an offshore DC busbar, then connected to the offshore DC busbar, connected to an onshore converter valve of an onshore converter station through a DC line, and finally connected to an onshore AC power grid. The offshore wind power direct current transmission system proposed by the present invention adopts a DRU converter valve and a DC transformer. The DRU does not need to adopt a series / parallel MMC structure. The black start problem of the DRU converter valve is solved by the bidirectional power flow characteristic of the DC transformer, and the DC transformer can transmit power.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) transmission, and in particular to an offshore wind power DC transmission system and a startup control method thereof. Background Art

[0002] At present, the current solutions for offshore wind power transmission projects are industrial frequency AC transmission and DC transmission. With the construction of offshore wind power transmission, the future will focus on the development of offshore wind power resources. Industrial frequency AC transmission is limited by the capacitance effect of submarine cables and can no longer meet the application requirements in scenarios beyond 70km offshore. The use of flexible DC transmission is the most practical solution under current technical conditions. At present, the flexible DC transmission system based on the Modular Multilevel Converter (MMC) is a typical solution for offshore wind power grid connection. The use of diode uncontrolled rectifier units (DRU) can further improve the economy and reliability of the transmission system. The DRU converter valve requires the help of an external power supply for phase change and the power transmission is unidirectional. Therefore, neither the DRU rectifier station nor the onshore power grid can start the offshore wind farm. The DRU converter valve has the problem of being unable to independently achieve black start.

[0003] A hybrid DC transmission scheme with DRU and MMC in parallel is adopted. This scheme requires that the DC side voltage of DRU and MMC is equal, resulting in a large number of MMC sub-modules; a hybrid offshore wind power transmission scheme with DRU and MMC in series is adopted. The AC grid on the MMC wind turbine side adopts an AC aggregation method. Multiple rectification, inversion and boosting of electric energy in the path increase the loss. By increasing the voltage level of the submarine cable, black start is achieved but the system insulation requirements are increased; a scheme with DRU and full-bridge MMC in series on the DC side is adopted, and the DC line power is regulated by the full-bridge MMC, but the problem of black start of offshore wind farms is not solved. Summary of the Invention

[0004] The purpose of the present invention is to solve at least one technical problem in the background technology and provide an offshore wind power direct current transmission system and a control method thereof.

[0005] To achieve the above-mentioned object, the present invention provides an offshore wind power DC transmission system, comprising: a wind turbine, an offshore AC busbar, an offshore DC busbar, an offshore booster station, a DRU converter valve, a DC transformer, an offshore DC busbar, a DC line, an onshore converter station, and an onshore AC power grid;

[0006] Among them, some wind turbines are connected to the offshore booster station through the offshore AC busbar, connected to the DRU converter valve, and then connected to the offshore DC busbar through the first switch. They are connected to the onshore converter valve of the onshore converter station through the DC line and finally connected to the onshore AC power grid.

[0007] Some wind turbines are connected to the DC transformer through the offshore DC busbar, and then to the offshore DC busbar. They are then connected to the onshore converter valves of the onshore converter station through DC lines and finally to the onshore AC grid.

[0008] The DC transformer is connected to the DC capacitors of some wind turbine generator sets through the second switch and the third switch respectively;

[0009] The DC transformer is directly connected to the DC capacitors of some wind turbine generator sets.

[0010] According to one aspect of the present invention, a reactive power compensation device is configured in the offshore boost station to filter out harmonics and provide reactive power support to the DRU converter valve.

[0011] According to one aspect of the present invention, the wind turbine generator set includes a first wind turbine converter and a second wind turbine converter;

[0012] The first wind turbine converter connected to the offshore boost station through the offshore AC busbar is an AC-DC-AC converter, and the second wind turbine converter connected to the DC transformer through the offshore DC busbar is an AC-DC converter.

[0013] According to one aspect of the present invention, some of the first wind turbine converters adopt a grid-type control strategy to obtain grid-type wind turbine characteristic control results, which are used to maintain the AC bus voltage and transmit electric energy; some of the first wind turbine converters adopt a grid-following control strategy to obtain grid-following wind turbine characteristic control results, which are used to transmit electric energy.

[0014] According to one aspect of the present invention, the second wind turbine converter adopts maximum power point tracking and constant AC voltage control.

[0015] According to one aspect of the present invention, the DC transformer is connected to the DC capacitor of the first wind turbine converter via a second switch and a third switch respectively;

[0016] The DC transformer is directly connected to the DC capacitor of the second wind turbine converter.

[0017] To achieve the above-mentioned object, the present invention further provides a startup control method for an offshore wind power DC transmission system, comprising:

[0018] Switch the onshore converter station to operating state and charge the offshore DC bus;

[0019] Start and configure the wind turbine generator set of the first grid-type wind turbine converter;

[0020] Start the wind turbine generator set configured with the first grid-following wind turbine converter;

[0021] Start the wind turbine generator set equipped with the grid-following second wind turbine converter;

[0022] Start the DRU converter valve and switch the DC transformer to the system operation state.

[0023] According to one aspect of the present invention, starting a wind turbine generator set configured with a first grid-connected wind turbine converter and a wind turbine generator set configured with a first grid-following wind turbine converter includes:

[0024] The onshore converter station switches to operation, and the onshore AC grid charges the offshore DC busbar via the DC line through the onshore converter station.

[0025] When the offshore DC bus voltage U dc_offshore =1p.u., close the second switch and the third switch, start the DC transformer, and charge the DC capacitor of the first wind turbine converter through the DC transformer;

[0026] When the DC capacitor voltage U cap_conI When ≥0.8 pu, start the grid-type wind turbine side converter and wait for the DC capacitor voltage U cap_conI =1p.u., the second switch is disconnected, the grid-side converter of the grid-connected wind turbine is started, and the offshore AC busbar is charged;

[0027] Waiting for offshore AC bus voltage U acp_offshore =1p.u., disconnect the third switch, start the first wind turbine converter on the grid side of the grid-following wind turbine, and connect the first wind turbine converter on the grid side to the offshore AC busbar.

[0028] According to one aspect of the present invention, starting a wind turbine generator set with a grid-connected second wind turbine converter includes:

[0029] The onshore converter station switches to operation, and the onshore AC grid charges the offshore DC busbar via the DC line through the onshore converter station.

[0030] When the offshore DC bus voltage U dc_offshore =1p.u., start the DC transformer and charge the DC capacitor of the second wind turbine converter through the DC transformer;

[0031] When the DC capacitor voltage U cap_conII When the power consumption is ≥0.8pu, the generator-side converter is started. When the second wind turbine converter enters the operating state, the DC transformer switches to the power supply state.

[0032] According to one aspect of the present invention, the method for starting a DRU converter valve includes:

[0033] The onshore converter station switches to the operating state, and the onshore AC grid converts the DC bus voltage U dc_offshoreCharge to 1 p.u.;

[0034] After the grid-type first wind turbine converter is started, the offshore AC bus voltage is established. When the offshore AC bus voltage U acp_offshore =1p.u., close the first switch and the DRU converter valve is started.

[0035] According to one aspect of the present invention, during the startup of the offshore wind power DC transmission system, the DC transformer sequentially completes the following control steps:

[0036] Before the wind turbine is started, the DC transformer is started first and receives the power from the offshore DC bus to charge the DC capacitors of the first wind turbine converter and the second wind turbine converter. The DC capacitor voltages of the first wind turbine converter and the second wind turbine converter are U cap_con Increased to 0.8 pu;

[0037] When the wind turbine set configured with the first grid-forming wind turbine converter is started, the second switch is turned on; when the wind turbine set configured with the first grid-following wind turbine converter is started, the third switch is turned on; when the wind turbine set configured with the second grid-following wind turbine converter is started, the DC transformer is switched to the power supply state.

[0038] To achieve the above objectives, the present invention also provides an electronic device, comprising a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein the computer program implements the startup control method described above when executed by the processor.

[0039] To achieve the above object, the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the startup control method described above is implemented.

[0040] According to the solution of the present invention, the offshore wind power DC transmission system proposed in the present invention adopts a DRU converter valve and a DC transformer, wherein the DRU does not need to adopt a series / parallel MMC structure, and the black start problem of the DRU converter valve is solved by the bidirectional power flow characteristics of the DC transformer. At the same time, the DC transformer can also transmit power.

[0041] According to the solution of the present invention, a DC transformer is introduced into the topology to charge the DC capacitor of the grid-type wind turbine converter during the startup phase, so that the grid-type wind turbine converter can establish a collective AC voltage, solve the black start problem, and eliminate the need for a diesel engine to be configured on the offshore platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The system structure diagram of an offshore wind power DC transmission system according to one embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0043] The present invention will now be discussed with reference to exemplary embodiments. It should be understood that the embodiments discussed are only intended to enable those skilled in the art to better understand and implement the present invention, rather than to imply any limitation on the scope of the present invention.

[0044] As used herein, the term "including" and variations thereof are to be interpreted as open-ended terms meaning "including, but not limited to." The term "based on" is to be interpreted as "based, at least in part, on." The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment."

[0045] Figure 1 The following schematically shows the system structure of an offshore wind power DC transmission system according to an embodiment of the present invention. Figure 1 As shown, in this embodiment, the offshore wind power DC transmission system includes: a wind turbine, an offshore AC busbar 1, an offshore DC busbar 2, an offshore booster station 3, a diode uncontrolled rectifier unit 4, a DC transformer 5, an offshore DC busbar 6, a DC line 7, an onshore converter station 8, and an onshore AC power grid 9;

[0046] Among them, some wind turbines are connected to the offshore booster station through the offshore AC busbar, connected to the DRU converter valve, and then connected to the offshore DC busbar through the first switch 10. They are connected to the onshore converter valve of the onshore converter station through the DC line and finally connected to the onshore AC power grid.

[0047] Some wind turbines are connected to the DC transformer through the offshore DC busbar, and then to the offshore DC busbar. They are then connected to the onshore converter valves of the onshore converter station through DC lines and finally to the onshore AC grid.

[0048] The DC transformer is connected to the DC capacitors of some wind turbine generator sets through the second switch 11 and the third switch 12 respectively;

[0049] The DC transformer is directly connected to the DC capacitors of some wind turbines.

[0050] Furthermore, according to one embodiment of the present invention, a reactive power compensation device is configured in the offshore boost station to filter out harmonics and provide reactive power support to the DRU converter valve.

[0051] Further, according to an embodiment of the present invention, the wind turbine generator set includes a first wind turbine converter 13 and a second wind turbine converter 14;

[0052] The first wind turbine converter connected to the offshore boost station through the offshore AC busbar is an AC-DC-AC converter, and the second wind turbine converter connected to the DC transformer through the offshore DC busbar is an AC-DC converter.

[0053] Furthermore, according to one embodiment of the present invention, some of the first wind turbine converters adopt a grid-forming control strategy to obtain grid-forming wind turbine characteristic control results, which are used to maintain the AC bus voltage and transmit electric energy; some of the first wind turbine converters adopt a grid-following control strategy to obtain grid-following wind turbine characteristic control results, which are used to transmit electric energy.

[0054] Furthermore, according to an embodiment of the present invention, the second wind turbine converter adopts maximum power point tracking and constant AC voltage control.

[0055] Furthermore, according to an embodiment of the present invention, the DC transformer is connected to the DC capacitor of the first wind turbine converter via the second switch and the third switch respectively;

[0056] The DC transformer is directly connected to the DC capacitor of the second wind turbine converter.

[0057] According to the above solution of the present invention, the offshore wind power DC transmission system proposed in the present invention adopts a DRU converter valve and a DC transformer, wherein the DRU does not need to adopt a series / parallel MMC structure, and the black start problem of the DRU converter valve is solved by the bidirectional power flow characteristics of the DC transformer. At the same time, the DC transformer can also transmit power.

[0058] Furthermore, in order to achieve the above-mentioned purpose, the present invention also provides a startup control method for an offshore wind power DC transmission system, Figure 1 As shown, the method includes:

[0059] Switch the onshore converter station to operating state and charge the offshore DC bus;

[0060] Start and configure the wind turbine generator set of the first grid-type wind turbine converter;

[0061] Start the wind turbine generator set configured with the first grid-following wind turbine converter;

[0062] Start the wind turbine generator set equipped with the grid-following second wind turbine converter;

[0063] Start the DRU converter valve and switch the DC transformer to the system operation state.

[0064] Furthermore, according to an embodiment of the present invention, starting a wind turbine generator set configured with a first grid-forming wind turbine converter and a wind turbine generator set configured with a first grid-following wind turbine converter includes:

[0065] The onshore converter station switches to operation, and the onshore AC grid charges the offshore DC busbar via the DC line through the onshore converter station.

[0066] When the offshore DC bus voltage U dc_offshore=1p.u., close the second switch and the third switch, start the DC transformer, and charge the DC capacitor of the first wind turbine converter through the DC transformer;

[0067] When the DC capacitor voltage U cap_conI When ≥0.8 pu, start the grid-type wind turbine side converter and wait for the DC capacitor voltage U cap_conI =1 p.u., the second switch is opened, the grid-type wind turbine grid-side converter is started, and the offshore AC collection bus is charged. In this embodiment, the AC collection wind turbine converter is an AC-DC-AC structure. The AC-DC close to the wind turbine side is called the wind turbine side converter, and the DC-AC close to the grid side is called the wind turbine grid-side converter.

[0068] Waiting for offshore AC bus voltage U acp_offshore =1p.u., disconnect the third switch, start the first wind turbine converter on the grid side of the grid-following wind turbine, and connect the first wind turbine converter on the grid side to the offshore AC busbar.

[0069] Furthermore, according to an embodiment of the present invention, starting a wind turbine generator set with a second wind turbine converter includes:

[0070] The onshore converter station switches to operation, and the onshore AC grid charges the offshore DC busbar via the DC line through the onshore converter station.

[0071] When the offshore DC bus voltage U dc_offshore =1p.u., start the DC transformer and charge the DC capacitor of the second wind turbine converter through the DC transformer;

[0072] When the DC capacitor voltage U cap_conII When the power consumption is ≥0.8pu, the generator-side converter is started. When the second wind turbine converter enters the operating state, the DC transformer switches to the power supply state.

[0073] Furthermore, according to one embodiment of the present invention, the method for starting the DRU converter valve includes:

[0074] The onshore converter station switches to the operating state, and the onshore AC grid converts the DC bus voltage U dc_offshore Charge to 1 p.u.;

[0075] After the grid-type first wind turbine converter is started, the offshore AC bus voltage is established. When the offshore AC bus voltage U acp_offshore =1p.u., close the first switch and the DRU converter valve is started.

[0076] Furthermore, according to one embodiment of the present invention, during the startup of the offshore wind power DC transmission system, the DC transformer sequentially completes the following control steps:

[0077] Before the wind turbine is started, the DC transformer is started first and receives the power from the offshore DC bus to charge the DC capacitors of the first wind turbine converter and the second wind turbine converter. The DC capacitor voltages of the first wind turbine converter and the second wind turbine converter are U cap_con Increased to 0.8 pu;

[0078] When the wind turbine set configured with the first grid-forming wind turbine converter is started, the second switch is turned on; when the wind turbine set configured with the first grid-following wind turbine converter is started, the third switch is turned on; when the wind turbine set configured with the second grid-following wind turbine converter is started, the DC transformer is switched to the power supply state.

[0079] According to the above solution of the present invention, the offshore wind power DC transmission system proposed in the present invention adopts a DRU converter valve and a DC transformer, wherein the DRU does not need to adopt a series / parallel MMC structure, and the black start problem of the DRU converter valve is solved by the bidirectional power flow characteristics of the DC transformer. At the same time, the DC transformer can also transmit power.

[0080] Furthermore, to achieve the above objectives, the present invention also provides an electronic device, comprising a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein the computer program implements the startup control method described above when executed by the processor.

[0081] Furthermore, to achieve the above-mentioned purpose, the present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the startup control method described above is implemented.

[0082] Those skilled in the art will appreciate that the modules and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented using electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0083] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described devices and equipment can refer to the corresponding processes in the aforementioned method implementation methods and will not be repeated here.

[0084] In the embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the modules is merely a logical function division. In actual implementation, there may be other division methods, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0085] The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the objectives of the embodiments of the present invention.

[0086] In addition, each functional module in the embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0087] If the functions are implemented as software modules and sold or used as standalone products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the energy-saving signal transmission / reception method according to various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a mobile hard drive, ROM, RAM, a magnetic disk, or an optical disk.

[0088] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the inventive concept. For example, a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0089] It should be understood that the size of the serial numbers of each step in the content of the invention and the implementation methods of the present invention does not absolutely mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation methods of the present invention.

Claims

1. A startup control method for an offshore wind power DC transmission system, wherein the offshore wind power DC transmission system comprises: Wind turbines, offshore AC busbars, offshore DC busbars, offshore booster stations, diode uncontrolled rectifier units, DC transformers, offshore DC busbars, DC lines, onshore converter stations, and onshore AC power grids; Among them, some wind turbines are connected to the offshore booster station through the offshore AC busbar, connected to the DRU converter valve of the diode uncontrolled rectifier unit, and then connected to the offshore DC busbar through the first switch. They are connected to the onshore converter valve of the onshore converter station through the DC line and finally connected to the onshore AC power grid. Some wind turbines are connected to the DC transformer through the offshore DC busbar, and then to the offshore DC busbar. They are then connected to the onshore converter valves of the onshore converter station through DC lines and finally to the onshore AC grid. The DC transformer is connected to the DC capacitors of some wind turbine generator sets through the second switch and the third switch respectively; The DC transformer is directly connected to the DC capacitors of some wind turbines; It is characterized in that the startup control method includes: Switch the onshore converter station to operating state and charge the offshore DC bus; Start and configure the wind turbine generator set of the first grid-type wind turbine converter; Start the wind turbine generator set configured with the first grid-following wind turbine converter; Start the wind turbine generator set equipped with the grid-following second wind turbine converter; Start the DRU converter valve and switch the DC transformer to the system operation state; Starting a wind turbine generator set configured with a grid-forming first wind turbine converter and a wind turbine generator set configured with a grid-following first wind turbine converter includes: The onshore converter station switches to operation, and the onshore AC grid charges the offshore DC busbar via the DC line through the onshore converter station. When the offshore DC bus voltage U dc_offshore =1p.u., close the second switch and the third switch, start the DC transformer, and charge the DC capacitor of the first wind turbine converter through the DC transformer; When the DC capacitor voltage U cap_conI When ≥0.8 pu, start the grid-type wind turbine side converter and wait for the DC capacitor voltage U cap_conI =1p.u., the second switch is disconnected, the grid-side converter of the grid-connected wind turbine is started, and the offshore AC busbar is charged; Waiting for offshore AC bus voltage U acp_offshore =1p.u., disconnect the third switch, start the first wind turbine converter on the grid side of the grid-following wind turbine, and connect the first wind turbine converter to the offshore AC busbar; Start the wind turbine generator set with the grid-following second wind turbine converter, including: The onshore converter station switches to operation, and the onshore AC grid charges the offshore DC busbar via the DC line through the onshore converter station. When the offshore DC bus voltage U dc_offshore =1p.u., start the DC transformer and charge the DC capacitor of the second wind turbine converter through the DC transformer; When the DC capacitor voltage U cap_conII When the power consumption is ≥0.8pu, the generator-side converter is started. When the second wind turbine converter enters the operating state, the DC transformer switches to the power supply state.

2. The startup control method of the offshore wind power DC transmission system according to claim 1, characterized in that: The offshore booster station is equipped with a reactive power compensation device to filter out harmonics and provide reactive power support to the DRU converter valve.

3. The startup control method of the offshore wind power DC transmission system according to claim 1, characterized in that: The wind turbine generator set includes a first wind turbine converter and a second wind turbine converter; The first wind turbine converter connected to the offshore boost station through the offshore AC busbar is an AC-DC-AC converter, and the second wind turbine converter connected to the DC transformer through the offshore DC busbar is an AC-DC converter.

4. The startup control method of the offshore wind power DC transmission system according to claim 3, characterized in that: Some of the first wind turbine converters adopt a grid-forming control strategy to obtain grid-forming wind turbine characteristic control results, which are used to maintain the AC bus voltage and transmit electric energy; some of the first wind turbine converters adopt a grid-following control strategy to obtain grid-following wind turbine characteristic control results, which are used to transmit electric energy.

5. The startup control method of the offshore wind power DC transmission system according to claim 3, characterized in that: The second wind turbine converter adopts maximum power point tracking and constant AC voltage control.

6. The startup control method of the offshore wind power DC transmission system according to claim 1, characterized in that: The DC transformer is connected to the DC capacitor of the first wind turbine converter via a second switch and a third switch respectively; The DC transformer is directly connected to the DC capacitor of the second wind turbine converter.

7. The startup control method of the offshore wind power DC transmission system according to claim 1, characterized in that: The method for starting the DRU converter valve includes: The onshore converter station switches to the operating state, and the onshore AC grid converts the DC bus voltage U dc_offshore Charge to 1 p.u.; After the grid-type first wind turbine converter is started, the offshore AC bus voltage is established. When the offshore AC bus voltage U acp_offshore =1p.u., close the first switch and the DRU converter valve is started.

8. The startup control method of the offshore wind power DC transmission system according to claim 1, characterized in that: During the startup of the offshore wind power DC transmission system, the DC transformer completes the following control steps in sequence: Before the wind turbine is started, the DC transformer is started first and receives the power from the offshore DC bus to charge the DC capacitors of the first wind turbine converter and the second wind turbine converter. The DC capacitor voltages of the first wind turbine converter and the second wind turbine converter are U cap_con Increased to 0.8 pu; After the wind turbine generator set configured with the first grid-type wind turbine converter is started, the second switch is turned on; When the wind turbine set configured with the first grid-following wind turbine converter is started, the third switch is turned on; when the wind turbine set configured with the second grid-following wind turbine converter is started, the DC transformer is switched to the power supply state.

9. An electronic device, characterized in that The invention comprises a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the startup control method of the offshore wind power direct current transmission system according to any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by the processor, the startup control method of the offshore wind power direct current transmission system according to any one of claims 1 to 8 is implemented.

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