Offshore wind power flexible direct current transmission system wind farm smooth starting method and device

Abstract

The application relates to the technical field of new energy, and discloses a wind farm smooth starting method and device for an offshore wind power flexible direct-current power transmission system. The method is applied to the offshore wind power flexible direct-current power transmission system and comprises the following steps: a land converter station is controlled to establish a direct-current voltage for a direct-current transmission line; an offshore flexible direct-current converter valve is controlled to charge a first wind turbine in a zero-voltage step-up mode, wherein the first wind turbine is any one of at least one wind turbine; and after the first wind turbine is fully charged, the first wind turbine is started. According to the application, the offshore flexible direct-current converter valve is used to realize the smooth starting of multiple wind turbines at the same time in a zero-voltage step-up mode, the starting time of the wind farm is shortened, the starting efficiency of the wind farm is improved, the influence of a voltage step-up and excitation inrush current of the wind turbine caused by a traditional starting mode can be eliminated, and the impact on key electrical equipment during the starting process can be avoided.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, specifically to a method and apparatus for smooth startup of wind farms in offshore wind power flexible DC transmission systems. Background Technology

[0002] In current practical engineering, when starting offshore wind turbines, typically only one turbine is started at a time on a single AC transmission submarine cable. This is because closing the high-voltage side switch of the turbine's step-up transformer generates an inrush current, which is usually 6 to 7 times the rated current. If multiple turbines start simultaneously, the superimposed inrush current will exceed the current-carrying capacity of the submarine cable, leading to cable damage. Therefore, turbines connected to a single submarine cable can only be started one at a time, resulting in low efficiency. Even with this, single-turbine startup still faces the impact of inrush current. Furthermore, the DC-side capacitor voltage of the converter in the wind turbine is close to zero at startup. To avoid damage to the wind turbine from instantaneous overcurrent when closing the grid-connected circuit breaker, related technologies employ soft-start devices such as soft-start resistors and bypass switches in each wind turbine. These soft-start devices limit the inrush current to the wind turbine during the initial startup phase. Once the DC capacitor voltage rises to a certain level, the soft-start resistor is deactivated via the bypass switch. Each wind turbine takes approximately 20 seconds to charge via the soft-start resistor. With a large number of wind turbines in a wind farm, the soft-start of multiple turbines significantly increases the startup time. Even with soft-start equipment, startup shocks cannot be completely avoided. Specifically, after the DC capacitor is charged via the soft-start resistor, a large instantaneous charging current is still generated at the moment the switch on the low-voltage side of the turbine's boost converter is closed, leading to an increased equipment failure rate. Summary of the Invention

[0003] In view of this, the present invention provides a method and apparatus for smooth startup of wind farms in a flexible DC transmission system for offshore wind power, in order to solve the problem of reducing the startup cost of wind farms.

[0004] In a first aspect, the present invention provides a smooth start-up method for a wind farm in an offshore wind power flexible DC transmission system, applicable to an offshore wind power flexible DC transmission system. The system includes: an onshore power grid, an onshore converter station, an offshore converter station, and an offshore wind farm; the onshore power grid is connected to the onshore converter station; the onshore converter station is connected to the offshore converter station via a DC transmission line; the offshore converter station includes an offshore flexible DC converter valve and an offshore AC bus; the offshore wind farm includes at least one wind turbine generator, and for each wind turbine generator, the wind turbine generator is connected to the offshore flexible DC converter valve via an AC transmission submarine cable and an offshore AC bus.

[0005] The method includes:

[0006] Control the onshore converter station to establish DC voltage for DC transmission lines;

[0007] Control the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up voltage boost mode, wherein the first wind turbine is any one of at least one wind turbine.

[0008] After the first wind turbine has finished charging, start the first wind turbine.

[0009] The method provided in this embodiment addresses the following issue: Firstly, in related technologies, closing the high-voltage side switch of a wind turbine's booster transformer generates an inrush current exceeding 6 to 7 times the rated current. If multiple wind turbines start simultaneously, the superimposed inrush current exceeds the current-carrying capacity of the submarine cable, causing overheating and damage. Therefore, only one wind turbine can be started on a single AC transmission submarine cable at any given time. Taking a submarine cable connecting 10 wind turbines as an example, related technologies require starting each turbine individually, during which the wind farm can only partially generate electricity, wasting a significant amount of energy. However, in this embodiment, the offshore flexible DC converter valve charges the wind turbines using a zero-start boost method, simultaneously boosting and exciting all wind turbines on a single submarine cable, and even supporting boosting and exciting all wind turbines in the entire wind farm, without generating an inrush current. Similarly, using a submarine cable circuit with 10 wind turbines as an example, the method of this application enables simultaneous charging and synchronous starting of all 10 wind turbines. While ensuring a smooth start-up of the wind farm, this method shortens the overall start-up time of each wind farm within the farm, improves start-up efficiency, significantly reduces wind curtailment losses during the start-up phase, and indirectly increases the annual power generation and economic benefits of the wind farm. Secondly, compared to related technologies where each wind turbine requires charging of the converter's DC capacitor through soft-start devices such as soft-start resistors and bypass switches, with each turbine requiring at least approximately 20 seconds of charging time, the method provided in this embodiment charges the first wind turbine by controlling the offshore flexible DC converter valve in a zero-start voltage boost manner. During the black start process of the wind turbine, charging through soft-start devices is unnecessary; DC capacitor charging can be completed directly through a zero-start voltage boost in hundreds of milliseconds. This method is simple to operate and highly reliable, further shortening the charging time for a single wind turbine and the entire wind farm. Thirdly, even with soft-start devices, the startup impact cannot be completely avoided in related technologies. Specifically, after the DC capacitor is charged through the soft-start resistor, a large instantaneous charging current is still generated at the moment the switch of the wind turbine's step-up transformer to the low-voltage side is closed. This impact repeatedly acts on the components in the wind turbine converter, accelerating insulation aging and mechanical wear, leading to an increased equipment failure rate. In contrast, the startup process of this application features a smooth voltage and current change during the zero-start boost process of the offshore flexible DC converter valve, gradually increasing from 0 to the target value. This achieves smooth startup of each wind turbine in the wind farm, avoids damage to the core components of the wind turbine from impact loads, significantly extends equipment lifespan, reduces wind farm maintenance costs, and further enhances the long-term economic benefits of the wind farm.

[0010] In one optional implementation, each wind turbine unit includes a wind turbine converter; the offshore converter station also includes a connecting transformer; the wind turbine converter is connected to the AC transmission submarine cable via the low-voltage side switch and the high-voltage side switch of the wind turbine step-up transformer corresponding to the wind turbine unit, and the AC transmission submarine cable is connected to the offshore AC busbar via the AC transmission submarine cable outgoing switch; the offshore AC busbar is connected to the offshore flexible DC converter valve via the connecting transformer side switch, the connecting transformer, and the connecting valve side switch;

[0011] Before controlling the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up manner, the method also includes:

[0012] Close the low-voltage side switch of the wind turbine step-up transformer, the high-voltage side switch of the wind turbine step-up transformer, the AC power transmission submarine cable outgoing switch, the grid connection switch, and the valve connection switch corresponding to the first wind turbine unit.

[0013] In one alternative implementation, each wind turbine also includes a wind turbine step-up transformer;

[0014] Controlling the offshore flexible DC converter valve to charge the first wind turbine unit in a zero-start-up manner includes:

[0015] The system controls the offshore flexible DC converter valve to charge the wind turbine converter in the first wind turbine unit in a zero-start voltage boost mode, while simultaneously charging the AC transmission submarine cable corresponding to the first wind turbine unit and energizing the wind turbine step-up transformer in the first wind turbine unit.

[0016] In one alternative implementation, the wind turbine converter includes a turbine-side converter, a grid-side converter, and a DC capacitor.

[0017] Controlling the offshore flexible DC converter valve to charge the wind turbine converter in a zero-start-up manner includes:

[0018] The offshore flexible DC converter valve is controlled to charge the DC capacitor in a zero-start boost manner by controlling the AC voltage amplitude and frequency (V / F control).

[0019] In one alternative implementation, the method further includes:

[0020] Once the DC voltage of the DC capacitor reaches the preset DC voltage, the charging of the wind turbine converter is considered complete.

[0021] In one optional implementation, the wind turbine converter includes a grid-side converter; after the first wind turbine is fully charged, starting the first wind turbine includes:

[0022] After the wind turbine converter has finished charging, unlock the grid-side converter;

[0023] The control grid-side converter establishes the rated DC voltage corresponding to the first wind turbine unit in order to start the first wind turbine unit.

[0024] Secondly, the present invention provides a smooth start-up device for a wind farm in an offshore wind power flexible DC transmission system, which is applied to an offshore wind power flexible DC transmission system. The system includes: an onshore power grid, an onshore converter station, an offshore converter station, and an offshore wind farm; the onshore power grid is connected to the onshore converter station; the onshore converter station is connected to the offshore converter station through a DC transmission line; the offshore converter station includes an offshore flexible DC converter valve and an offshore AC bus; the offshore wind farm includes at least one wind turbine, and for each wind turbine, the wind turbine is connected to the offshore flexible DC converter valve through an AC transmission submarine cable and an offshore AC bus.

[0025] The device includes:

[0026] The first control module is used to control the onshore converter station to establish DC voltage for the DC transmission line;

[0027] The second control module is used to control the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up manner, wherein the first wind turbine is any one of at least one wind turbine.

[0028] The starting module is used to start the first wind turbine after it has finished charging.

[0029] The device provided in this embodiment addresses the following issue: Firstly, in related technologies, closing the high-voltage side switch of a wind turbine's booster transformer generates an inrush current exceeding 6 to 7 times the rated current. If multiple wind turbines start simultaneously, the superimposed inrush current exceeds the current-carrying capacity of the submarine cable, causing overheating and damage. Therefore, only one wind turbine can be started on a single AC transmission submarine cable at any given time. For example, with a submarine cable connecting 10 wind turbines, related technologies require starting each turbine individually, during which time the wind farm can only partially generate electricity, wasting a significant amount of energy. However, in this embodiment, the offshore flexible DC converter valve charges the wind turbines using a zero-start boost method, simultaneously boosting and exciting all wind turbines on a single submarine cable, and even supporting boosting and exciting all wind turbines in the entire wind farm, without generating an inrush current. Similarly, using a submarine cable circuit with 10 wind turbines as an example, the method of this application enables simultaneous charging and synchronous starting of all 10 wind turbines. While ensuring a smooth start-up of the wind farm, this method shortens the overall start-up time of each wind farm within the farm, improves start-up efficiency, significantly reduces wind curtailment losses during the start-up phase, and indirectly increases the annual power generation and economic benefits of the wind farm. Secondly, compared to related technologies where each wind turbine requires charging of the converter's DC capacitor through soft-start devices such as soft-start resistors and bypass switches, with each turbine requiring at least approximately 20 seconds of charging time, the method provided in this embodiment charges the first wind turbine by controlling the offshore flexible DC converter valve in a zero-start voltage boost manner. During the black start process of the wind turbine, charging through soft-start devices is unnecessary; DC capacitor charging can be completed directly through a zero-start voltage boost in hundreds of milliseconds. This method is simple to operate and highly reliable, further shortening the charging time for a single wind turbine and the entire wind farm. Thirdly, even with soft-start devices, the startup impact cannot be completely avoided in related technologies. Specifically, after the DC capacitor is charged through the soft-start resistor, a large instantaneous charging current is still generated at the moment the switch of the wind turbine's step-up transformer to the low-voltage side is closed. This impact repeatedly acts on the components in the wind turbine converter, accelerating insulation aging and mechanical wear, leading to an increased equipment failure rate. In contrast, the startup process of this application features a smooth voltage and current change during the zero-start boost process of the offshore flexible DC converter valve, gradually increasing from 0 to the target value. This achieves smooth startup of each wind turbine in the wind farm, avoids damage to the core components of the wind turbine from impact loads, significantly extends equipment lifespan, reduces wind farm maintenance costs, and further enhances the long-term economic benefits of the wind farm.

[0030] Thirdly, the present invention provides a computer device, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the smooth start-up method of the offshore wind power flexible DC transmission system wind farm described in the first aspect or any corresponding embodiment.

[0031] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to execute the smooth start-up method for a wind farm in a flexible DC transmission system for offshore wind power as described in the first aspect or any corresponding embodiment.

[0032] Fifthly, the present invention provides a computer program product, including computer instructions for causing a computer to execute the smooth start-up method for a wind farm in a flexible DC transmission system for offshore wind power as described in the first aspect or any corresponding embodiment. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the structure of a flexible DC transmission system for offshore wind power according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of a wind turbine generator connected to an offshore flexible DC converter valve in an offshore wind farm according to an embodiment of the present invention.

[0036] Figure 3 This is a flowchart illustrating a method for smooth startup of a wind farm using a flexible DC transmission system for offshore wind power, according to an embodiment of the present invention.

[0037] Figure 4(a) is a schematic diagram of the wind turbine terminal voltage when a wind farm is started using a soft-start device according to an embodiment of the present invention;

[0038] Figure 4(b) is a schematic diagram of the wind turbine terminal voltage when a wind farm is started using the starting method provided in the embodiments of this application according to an embodiment of the present invention;

[0039] Figure 5(a) is a schematic diagram of the charging current when a wind farm is started using a soft-start device according to an embodiment of the present invention;

[0040] Figure 5(b) is a schematic diagram of the charging current when starting a wind farm using the starting method provided in the embodiments of this application according to an embodiment of the present invention;

[0041] Figure 6(a) is a schematic diagram of the DC voltage of the wind turbine converter when the wind farm is started using a soft-start device according to an embodiment of the present invention;

[0042] Figure 6(b) is a schematic diagram of the DC voltage of the wind turbine converter when starting a wind farm using the starting method provided in the embodiments of this application according to an embodiment of the present invention;

[0043] Figure 7 This is a structural block diagram of a wind farm smooth start-up device for a flexible DC transmission system for offshore wind power according to an embodiment of the present invention;

[0044] Figure 8 This is a schematic diagram of the structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Figure 1 This is a schematic diagram of a flexible DC transmission system for offshore wind power. Figure 1 As shown, the system includes: onshore power grid 1, onshore converter station 2, offshore converter station 3, and offshore wind farm 4.

[0047] Among them, the onshore power grid 1 is connected to the onshore converter station 2; the onshore converter station 2 (including the onshore flexible DC converter valve) is connected to the offshore converter station 3 through the DC transmission line; the offshore converter station 3 includes the offshore flexible DC converter valve 31 and the offshore AC bus 32.

[0048] The offshore wind farm 4 includes at least one wind turbine 41. For each wind turbine 41, the wind turbine 41 is connected to the offshore flexible DC converter valve 31 via an AC transmission submarine cable 42 and an offshore AC bus 32.

[0049] Figure 2 This is a schematic diagram showing the connection between a wind turbine in an offshore wind farm and an offshore flexible DC converter valve. Figure 2 As shown, the wind turbine generator set 41 includes a wind turbine converter 411 and a wind turbine step-up transformer 412. The offshore converter station 3 also includes a connecting transformer 33; the wind turbine converter 411 is connected to the AC transmission submarine cable through the low-voltage side switch 413 of the wind turbine step-up transformer 412 and the high-voltage side switch 414 of the wind turbine step-up transformer corresponding to the wind turbine generator set 41; the AC transmission submarine cable 42 is connected to the offshore AC busbar 32 through the AC transmission submarine cable 42 outgoing switch; the offshore AC busbar 32 is connected to the offshore flexible DC converter valve 31 through the connecting transformer side switch 34, the connecting transformer 33 and the connecting valve side switch 35.

[0050] Specifically, the wind turbine converter 411 is a power electronic device used to convert the electrical energy output from the generator into AC-DC-AC converters. The wind turbine converter 411 includes a machine-side converter (MSC), a grid-side converter (GSC), and a DC capacitor C. Figure 2 In the process, the generator-side converter is connected to the grid-side converter via a DC capacitor (C).

[0051] The wind turbine step-up transformer 412 is a device within the wind turbine unit 41 that steps up low-voltage AC power to high-voltage AC power. The wind turbine converter 411 is connected to the AC transmission submarine cable 42 via the wind turbine step-up transformer low-voltage side switch 413, the wind turbine step-up transformer 412, and the wind turbine step-up transformer high-voltage side switch 414 corresponding to the wind turbine unit 41.

[0052] The generator-side converter is the part of the wind turbine converter 411 that is connected to the wind turbine generator. It is usually a rectifier, used to convert the frequency-converted AC power output by the generator into DC power to realize energy transfer and motor control.

[0053] The grid-side converter is the part of the wind turbine converter 411 that is connected to the wind turbine step-up transformer 412. It is usually an inverter used to convert DC power into AC power that is in phase and frequency with the grid, so as to realize grid-connected control.

[0054] DC capacitors are energy storage elements that connect the generator-side converter and the grid-side converter. They are usually electrolytic capacitors or film capacitors, used to stabilize the DC side voltage, buffer energy fluctuations, and suppress voltage pulsations.

[0055] In the wind turbine converter 411, the AC input terminal of the machine-side converter is connected to the stator or rotor winding of the wind turbine generator. The DC output terminal of the machine-side converter is connected to a DC capacitor via a busbar. The other end of the DC capacitor is connected to the DC input terminal of the grid-side converter via a busbar. The AC output terminal of the grid-side converter is connected via... Figure 2 The inductor shown (L) C ) and capacitance (C) f The filter, consisting of [missing information], is connected to the low-voltage side switch 413 of the wind turbine booster transformer.

[0056] by Figure 2Taking the startup process of a wind turbine (hereinafter referred to as a wind turbine) as an example, in related technologies, firstly, the rated AC bus voltage is established through the offshore flexible DC converter valve 31. Then, the AC transmission submarine cable outgoing switch 43 is closed to charge the AC transmission submarine cable. Next, the high-voltage side switch 414 and the low-voltage side switch 413 of the wind turbine step-up transformer 412 are closed, and the AC voltage charges the DC capacitor through the anti-parallel diodes of the grid-side converter. To avoid damage to the wind turbine caused by the instantaneous overcurrent surge when the high-voltage side switch 414 of the wind turbine step-up transformer is closed, a soft-start device (including a soft-start resistor and a corresponding contactor) is connected in series to charge the DC capacitor during wind turbine startup. Finally, when the DC capacitor is charged to a certain preset DC voltage, the circuit is closed. Figure 2 The contactor connected in parallel with the soft start resistor in the soft start device bypasses the branch where the soft start resistor is located, thus completing the start of the fan.

[0057] In related technologies, such as Figure 2 As shown, to avoid damage to equipment from instantaneous overcurrent surges when closing the grid-connected circuit breaker, a set of soft-start equipment, including soft-start resistors, bypass switches, and their controls, is configured. Each wind turbine takes approximately 20 seconds to charge through the soft-start resistor. With a large number of wind turbines in a wind farm, the soft-starting of multiple turbines significantly increases the startup time. Furthermore, even with the soft-start equipment, startup shocks cannot be completely avoided. Specifically, after charging the DC capacitor through the soft-start resistor, a large instantaneous charging current is still generated when closing the low-voltage side switch of the turbine's step-up transformer, leading to an increased equipment failure rate. Therefore, how to achieve a smooth startup of the wind farm during the black start phase without using soft-start equipment is a current focus.

[0058] In view of this, this application provides a method for smooth startup of a wind farm in an offshore wind power flexible DC transmission system. The method includes: first, controlling the onshore converter station 2 to establish DC voltage for the DC transmission line; then, controlling the offshore flexible DC converter valve 31 to charge a first wind turbine in a zero-start voltage boost manner, wherein the first wind turbine is any one of at least one wind turbine 41; finally, after the first wind turbine has been charged, starting the first wind turbine.

[0059] The method provided in this embodiment addresses the following issue: Firstly, in related technologies, closing the high-voltage side switch of a wind turbine's booster transformer generates an inrush current exceeding 6 to 7 times the rated current. If multiple wind turbines start simultaneously, the superimposed inrush current exceeds the current-carrying capacity of the submarine cable, causing overheating and damage. Therefore, only one wind turbine can be started on a single AC transmission submarine cable at any given time. Taking a submarine cable connecting 10 wind turbines as an example, related technologies require starting each turbine individually, during which the wind farm can only partially generate electricity, wasting a significant amount of energy. However, in this embodiment, the offshore flexible DC converter valve charges the wind turbines using a zero-start boost method, simultaneously boosting and exciting all wind turbines on a single submarine cable, and even supporting boosting and exciting all wind turbines in the entire wind farm, without generating an inrush current. Similarly, using a submarine cable circuit with 10 wind turbines as an example, the method of this application enables simultaneous charging and synchronous starting of all 10 wind turbines. While ensuring a smooth start-up of the wind farm, this method shortens the overall start-up time of each wind farm within the farm, improves start-up efficiency, significantly reduces wind curtailment losses during the start-up phase, and indirectly increases the annual power generation and economic benefits of the wind farm. Secondly, compared to related technologies where each wind turbine requires charging of the converter's DC capacitor through soft-start devices such as soft-start resistors and bypass switches, with each turbine requiring at least approximately 20 seconds of charging time, the method provided in this embodiment charges the first wind turbine by controlling the offshore flexible DC converter valve in a zero-start voltage boost manner. During the black start process of the wind turbine, charging through soft-start devices is unnecessary; DC capacitor charging can be completed directly through a zero-start voltage boost in hundreds of milliseconds. This method is simple to operate and highly reliable, further shortening the charging time for a single wind turbine and the entire wind farm. Thirdly, even with soft-start devices, the startup impact cannot be completely avoided in related technologies. Specifically, after the DC capacitor is charged through the soft-start resistor, a large instantaneous charging current is still generated at the moment the switch of the wind turbine's step-up transformer to the low-voltage side is closed. This impact repeatedly acts on the components in the wind turbine converter, accelerating insulation aging and mechanical wear, leading to an increased equipment failure rate. In contrast, the startup process of this application features a smooth voltage and current change during the zero-start boost process of the offshore flexible DC converter valve, gradually increasing from 0 to the target value. This achieves smooth startup of each wind turbine in the wind farm, avoids damage to the core components of the wind turbine from impact loads, significantly extends equipment lifespan, reduces wind farm maintenance costs, and further enhances the long-term economic benefits of the wind farm.

[0060] It should be noted that the method for smooth startup of a wind farm in an offshore wind power flexible DC transmission system provided in this embodiment of the invention can be executed by a device for smooth startup of the offshore wind power flexible DC transmission system. This device can be implemented as part or all of an electronic device through software, hardware, or a combination of both. The electronic device can be a server or a terminal. In this embodiment, the server can be a single server or a server cluster composed of multiple servers. The terminal in this embodiment can be a smartphone, personal computer, tablet computer, wearable device, or other intelligent hardware device such as a smart robot. The following method embodiments will use an electronic device as an example for explanation.

[0061] According to an embodiment of the present invention, a method for smooth startup of a wind farm in a flexible DC transmission system for offshore wind power is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0062] This embodiment provides a method for smooth startup of a wind farm using a flexible DC transmission system for offshore wind power, which can be used in the aforementioned electronic devices, such as servers. Figure 3 This is a flowchart of a smooth start-up method for a wind farm in an offshore wind power flexible DC transmission system according to an embodiment of the present invention, such as... Figure 3 As shown, the process includes the following steps:

[0063] S101 controls the onshore converter station to establish DC voltage for the DC transmission line.

[0064] The following is combined Figure 1 , Figure 2 The smooth start-up method of the offshore wind power flexible DC transmission system provided in this application embodiment is illustrated by way of example. When the onshore converter station 2 includes an onshore flexible DC converter valve, the DC voltage output by the onshore flexible DC converter valve is gradually increased by controlling the firing angle of the insulated gate bipolar transistor (IGBT) in the onshore flexible DC converter valve. During the voltage increase process, the DC voltage of the DC transmission line is collected in real time and compared with the target DC voltage. The firing angle is adjusted according to the deviation until the collected DC voltage is stable at the target DC voltage.

[0065] S102 controls the offshore flexible DC converter valve to charge the first wind turbine unit in a zero-start-up voltage boost mode.

[0066] The first wind turbine unit is any one of the at least one wind turbine unit 41.

[0067] Specifically, zero-start boost refers to gradually and smoothly increasing the voltage from an initial state of zero voltage until a preset DC voltage is reached.

[0068] For example, the control of the offshore flexible DC converter valve 31 gradually increases the AC output voltage according to the preset voltage increase rate, and transmits it to the first wind turbine through the offshore AC bus 32 and the AC power transmission submarine cable 42.

[0069] S103, after the first wind turbine unit has finished charging, start the first wind turbine unit.

[0070] For example, after the first wind turbine is charged, the process of starting the first wind turbine includes: First, controlling the pitch system to gradually adjust the blade pitch from the standby angle (e.g., 90°, at which point the blade is almost not facing the wind) to the optimal windward angle (e.g., 30°). Then, as the wind speed drives the blades to rotate, the generator speed gradually increases. When the speed reaches the grid connection speed (e.g., 1500 r / min, corresponding to 50Hz AC), the grid connection switch is closed to connect the first wind turbine to the offshore AC bus 32. After grid connection, the blade angle and generator excitation current are adjusted according to the wind speed to gradually increase the output power of the first wind turbine to the rated power.

[0071] For example, during the voltage boosting process, the DC voltage of the DC capacitor in the first wind turbine is monitored in real time until the DC voltage of the DC capacitor reaches the preset DC voltage. At this point, it is determined that the first wind turbine is fully charged and the first wind turbine is started.

[0072] In some embodiments, before controlling the offshore flexible DC converter valve 31 to charge the first wind turbine in a zero-start-up manner, the method provided in this application embodiment further includes the following:

[0073] Close the low-voltage side switch 413 of the wind turbine step-up transformer corresponding to the first wind turbine unit, the high-voltage side switch 414 of the wind turbine step-up transformer, the AC power transmission submarine cable outgoing switch 43, the grid connection switch 34, and the valve connection switch 35.

[0074] This application embodiment does not limit the closing sequence of the above-mentioned switches. For example, the following switches are closed sequentially: the connecting transformer valve side switch 35, the connecting transformer grid side switch 34, the AC transmission submarine cable outgoing switch 43, the wind turbine booster transformer high-voltage side switch 414, and the wind turbine booster transformer low-voltage side switch 413. After each switch is closed, auxiliary contacts or sensors installed at each switch can detect whether the switch is fully closed. In this way, by closing the switches sequentially, a complete charging circuit is established from the offshore flexible DC converter valve 31 to the wind turbine 41, ensuring that the current generated during subsequent zero-start voltage boost can smoothly reach the wind turbine 41 to charge it. This avoids charging failure due to a single unclosed switch, improving the reliability of the startup process. Furthermore, completing all switch closing operations before zero-start voltage boost avoids operational shocks that may occur during switching operations during charging, ensuring the smoothness of the subsequent zero-start voltage boost process and further protecting the wind turbine equipment.

[0075] In an optional implementation, in S102 above, controlling the offshore flexible DC converter valve 31 to charge the first wind turbine in a zero-start-up voltage boost manner specifically includes the following:

[0076] The offshore flexible DC converter valve 31 is controlled to charge the wind turbine converter 411 in the first wind turbine unit in a zero-start voltage boost mode, while charging the AC transmission submarine cable 42 corresponding to the first wind turbine unit and energizing the wind turbine step-up transformer 412 in the first wind turbine unit.

[0077] Specifically, with Figure 2 For example, the charging path for the wind turbine converter 411 in the first wind turbine unit is as follows: offshore flexible DC converter valve 31 → connecting valve side switch 35 → connecting transformer 33 → connecting grid side switch 34 → offshore AC bus 32 → AC transmission submarine cable outgoing switch 43 → AC transmission submarine cable 42 → wind turbine step-up transformer high voltage side switch 414 → wind turbine step-up transformer 412 → wind turbine step-up transformer low voltage side switch 413 → wind turbine converter 411 DC capacitor.

[0078] The charging process for the wind turbine converter 411 also includes charging the AC transmission submarine cable and energizing the step-up transformer. Charging the AC transmission submarine cable involves gradually charging its distributed capacitance as the converter valve output voltage increases, with the voltage gradually rising from 0 to a preset DC voltage. Energizing the step-up transformer refers to the process where, when the voltage reaches the required voltage for transformer energization (e.g., 5% of the rated voltage), the transformer core begins to establish a magnetic field, and the energizing current gradually stabilizes at the rated energizing current (e.g., 0.5A).

[0079] For example, during the charging process of the first wind turbine, the DC side voltage of the wind turbine converter 411 can be monitored in real time, such as through the converter's built-in sensor. When the voltage reaches 95% of the preset DC voltage (e.g., 1045V), the boost rate is reduced. Simultaneously, the charging current of the AC transmission cable is monitored (through the current transformer at the cable's inlet) to ensure it does not exceed the limit, and the excitation current of the wind turbine's step-up transformer is monitored (through the transformer's neutral point current transformer) to prevent inrush current.

[0080] In related technologies, an inrush current of 6-7 times the rated current is still generated when the transformer switch is closed. Long-term impact can lead to transformer winding deformation and insulation aging. The starting method provided in this application achieves smooth transformer excitation through zero-start voltage boost, without inrush current generation, enabling simultaneous starting of multiple wind turbines on the entire submarine cable. This significantly improves starting efficiency, greatly shortens wind farm start-up time, and increases power generation duration. Simultaneously, by controlling the voltage rise rate through zero-start voltage boost, the charging current of the submarine cable changes smoothly, reducing the risk of submarine cable failure. Furthermore, compared to related technologies where charging a single wind turbine takes at least 30 seconds, this application's embodiment completes the charging of a wind turbine through a sequential zero-start voltage boost process in just 500 milliseconds, shortening the charging time for a single turbine and the entire wind farm. In addition, the voltage and current changes smoothly during the zero-start voltage boost process of the offshore flexible DC converter valve, gradually increasing from 0 to the target value. This reduces the closing inrush current and voltage during the charging phase without the need for soft-start equipment to achieve black start of the wind turbine.

[0081] In one possible implementation, the offshore flexible DC converter valve 31 is controlled to charge the wind turbine converter 411 in a zero-start-up manner by controlling the offshore flexible DC converter valve 31 to charge the DC capacitor in a zero-start-up manner through AC voltage amplitude and frequency control (V / F control).

[0082] Parameters in AC voltage amplitude and frequency control include, but are not limited to, boost time, frequency variation range, and maximum charging current limit. This application does not impose specific limitations on the parameters in AC voltage amplitude and frequency control; they can be set according to actual conditions.

[0083] For example, during the process of charging the DC capacitor in a zero-start-up manner, the charging current, the ratio of AC voltage to frequency, the temperature of the grid-side converter (to avoid overheating) and its insulation status, and the DC voltage of the DC capacitor are monitored to ensure a smooth start-up of the wind turbine. Specifically, the charging current is monitored in real time, such as by detecting the charging current through a DC-side current sensor; if the charging current exceeds a preset charging current, the voltage boost is paused. The ratio of AC voltage to frequency is monitored to ensure it strictly conforms to the preset V / F curve.

[0084] In this way, by controlling the DC voltage of the zero-start boost DC capacitor using AC voltage amplitude and frequency control, the charging current is always kept within a safe range, the capacitor temperature rise does not exceed the preset temperature difference, and the capacitor lifespan is extended. In the embodiments of this application, AC voltage amplitude and frequency control can achieve stable charging without complex phase synchronization or current closed-loop control, and the control algorithm is simple and reliable.

[0085] In this embodiment of the application, the charging of the wind turbine converter is determined to be complete after the DC voltage of the DC capacitor reaches the preset DC voltage.

[0086] The preset DC voltage can be set according to the rated power of the first wind turbine and the design parameters of the converter (such as the rated voltage of the capacitor and the withstand voltage of the switching device). This application embodiment does not specifically limit this.

[0087] For example, a voltage sensor (such as a Hall voltage sensor) is connected in parallel across the positive and negative terminals of a DC capacitor to acquire the voltage value of the DC capacitor in real time.

[0088] In some embodiments, in S103 above, after the first wind turbine is charged, the first wind turbine is started, which specifically includes the following steps:

[0089] First, after the wind turbine converter has finished charging, unlock the grid-side converter.

[0090] Specifically, unlocking the grid-side converter refers to unlocking the standby lockout state of the grid-side converter, allowing it to switch from a non-operating mode to an operating mode for conversion, voltage regulation, and other operations. Before unlocking, the power switching devices (such as IGBTs) of the grid-side converter are in the off state and cannot perform power conversion; after unlocking, the devices can switch on and off normally and enter the operating state.

[0091] Then, the grid-side converter establishes the rated DC voltage corresponding to the first wind turbine to start the first wind turbine.

[0092] Specifically, the rated DC voltage refers to the standard operating voltage that the DC side of the wind turbine converter 411 (mainly the two ends of the DC capacitor) should maintain, as specified in the design of the first wind turbine unit. It is the core voltage parameter for normal operation of the wind turbine and needs to be matched with the power rating of the converter, the withstand voltage of the IGBT device, and the power generation capacity of the wind turbine.

[0093] Figures 4(a), 5(a), and 6(a) are schematic diagrams of the turbine terminal voltage, charging current, and turbine converter DC voltage when starting a wind farm using a soft-start device. Figures 4(b), 5(b), and 6(b) are schematic diagrams of the turbine terminal voltage, charging current, and turbine converter DC voltage when starting a wind farm using the starting method provided in this application. A comparison of the figures shows that after charging the wind farm using the soft-start device and the Wanheng DC capacitor, a significant instantaneous increase in turbine terminal voltage, charging current, and turbine converter DC voltage still occurs when the low-voltage side switch of the wind turbine step-up transformer is closed. However, when starting a wind farm using the method provided in this application, the turbine terminal voltage, charging current, and turbine converter DC voltage change smoothly and remain within a preset range, avoiding damage to the core components of the wind turbine from impact loads. Therefore, it can be concluded that the startup method provided in this application is far superior to the startup method using soft start devices in related technologies. While smoothly starting the wind farm, it can start multiple wind turbines in parallel through a simple and reliable control strategy, thereby shortening the overall startup time of the wind farm, improving startup efficiency, and reducing the cost of the wind farm.

[0094] The above mainly describes the solution provided by the embodiments of this application from a methodological perspective.

[0095] This application also provides a wind farm smooth start-up device for a flexible DC transmission system for offshore wind power. This device is used to implement the above embodiments and preferred embodiments, and details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0096] This embodiment provides a smooth start-up device for a wind farm in an offshore wind power flexible DC transmission system. The system includes: an onshore power grid, an onshore converter station, an offshore converter station, and an offshore wind farm. The onshore power grid is connected to the onshore converter station. The onshore converter station is connected to the offshore converter station via a DC transmission line. The offshore converter station includes an offshore flexible DC converter valve and an offshore AC bus. The offshore wind farm includes at least one wind turbine generator. For each wind turbine generator, the wind turbine generator is connected to the offshore flexible DC converter valve via an AC transmission submarine cable and an offshore AC bus.

[0097] like Figure 7 As shown, the device includes:

[0098] The first control module 701 is used to control the onshore converter station to establish DC voltage for the DC transmission line;

[0099] The second control module 702 is used to control the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up manner, wherein the first wind turbine is any one of at least one wind turbine.

[0100] The starting module 703 is used to start the first wind turbine after the first wind turbine has finished charging.

[0101] The device provided in this embodiment addresses the following issue: Firstly, in related technologies, closing the high-voltage side switch of a wind turbine's booster transformer generates an inrush current exceeding 6 to 7 times the rated current. If multiple wind turbines start simultaneously, the superimposed inrush current exceeds the current-carrying capacity of the submarine cable, causing overheating and damage. Therefore, only one wind turbine can be started on a single AC transmission submarine cable at any given time. For example, with a submarine cable connecting 10 wind turbines, related technologies require starting each turbine individually, during which time the wind farm can only partially generate electricity, wasting a significant amount of energy. However, in this embodiment, the offshore flexible DC converter valve charges the wind turbines using a zero-start boost method, simultaneously boosting and exciting all wind turbines on a single submarine cable, and even supporting boosting and exciting all wind turbines in the entire wind farm, without generating an inrush current. Similarly, using a submarine cable circuit with 10 wind turbines as an example, the method of this application enables simultaneous charging and synchronous starting of all 10 wind turbines. While ensuring a smooth start-up of the wind farm, this method shortens the overall start-up time of each wind farm within the farm, improves start-up efficiency, significantly reduces wind curtailment losses during the start-up phase, and indirectly increases the annual power generation and economic benefits of the wind farm. Secondly, compared to related technologies where each wind turbine requires charging of the converter's DC capacitor through soft-start devices such as soft-start resistors and bypass switches, with each turbine requiring at least approximately 20 seconds of charging time, the method provided in this embodiment charges the first wind turbine by controlling the offshore flexible DC converter valve in a zero-start voltage boost manner. During the black start process of the wind turbine, charging through soft-start devices is unnecessary; DC capacitor charging can be completed directly through a zero-start voltage boost in hundreds of milliseconds. This method is simple to operate and highly reliable, further shortening the charging time for a single wind turbine and the entire wind farm. Thirdly, even with soft-start devices, the startup impact cannot be completely avoided in related technologies. Specifically, after the DC capacitor is charged through the soft-start resistor, a large instantaneous charging current is still generated at the moment the switch of the wind turbine's step-up transformer to the low-voltage side is closed. This impact repeatedly acts on the components in the wind turbine converter, accelerating insulation aging and mechanical wear, leading to an increased equipment failure rate. In contrast, the startup process of this application features a smooth voltage and current change during the zero-start boost process of the offshore flexible DC converter valve, gradually increasing from 0 to the target value. This achieves smooth startup of each wind turbine in the wind farm, avoids damage to the core components of the wind turbine from impact loads, significantly extends equipment lifespan, reduces wind farm maintenance costs, and further enhances the long-term economic benefits of the wind farm.

[0102] In one possible implementation, each wind turbine unit includes a wind turbine converter; the offshore converter station also includes a connecting transformer; the wind turbine converter is connected to the AC transmission submarine cable via the low-voltage side switch and the high-voltage side switch of the wind turbine step-up transformer corresponding to the wind turbine unit; the AC transmission submarine cable is connected to the offshore AC busbar via the AC transmission submarine cable outgoing switch; the offshore AC busbar is connected to the offshore flexible DC converter valve via the connecting transformer side switch, the connecting transformer, and the connecting valve side switch.

[0103] The second control module 702 is specifically used to close the low-voltage side switch of the wind turbine step-up transformer, the high-voltage side switch of the wind turbine step-up transformer, the AC power transmission submarine cable outgoing switch, the connection transformer side switch, and the connection transformer valve side switch corresponding to the first wind turbine unit.

[0104] In one possible implementation, each wind turbine also includes a wind turbine step-up transformer; the second control module 702 is specifically used to control the offshore flexible DC converter valve to charge the wind turbine converter in the first wind turbine in a zero-start voltage boost manner, while charging the AC transmission submarine cable corresponding to the first wind turbine, and energizing the wind turbine step-up transformer in the first wind turbine.

[0105] In one possible implementation, the wind turbine converter includes a turbine-side converter, a grid-side converter, and a DC capacitor; the second control module 702 is specifically used to control the offshore flexible DC converter valve to charge the DC capacitor in a zero-start-up manner through AC voltage amplitude and frequency control (V / F control).

[0106] In one possible implementation, the startup module 703 is also used to determine that the wind turbine converter is fully charged after the DC voltage of the DC capacitor reaches a preset DC voltage.

[0107] In one possible implementation, the wind turbine converter includes a grid-side converter; the startup module 703 is also used to unlock the grid-side converter after the wind turbine converter has finished charging.

[0108] The control grid-side converter establishes the rated DC voltage corresponding to the first wind turbine unit in order to start the first wind turbine unit.

[0109] Further functional descriptions of the above modules and units are the same as those in the corresponding embodiments described above, and will not be repeated here.

[0110] In this embodiment, the wind farm smooth start-up device of the offshore wind power flexible DC transmission system is presented in the form of a functional unit. Here, a unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that execute one or more software or fixed programs, and / or other devices that can provide the above functions.

[0111] This invention also provides a computer device having the above-described features. Figure 7 The image shows a wind farm smooth start-up device for a flexible DC transmission system for offshore wind power.

[0112] Please see Figure 8 , Figure 8 This is a schematic diagram of the structure of a computer device provided in an optional embodiment of the present invention, such as... Figure 8 As shown, the computer device includes one or more processors 10, memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on external input / output devices (such as display devices coupled to the interfaces). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 8 Take a processor 10 as an example.

[0113] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GDA), or any combination thereof.

[0114] The memory 20 stores instructions executable by at least one processor 10 to cause at least one processor 10 to perform the method shown in the above embodiments.

[0115] The memory 20 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the computer device. Furthermore, the memory 20 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some alternative embodiments, the memory 20 may optionally include memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0116] The memory 20 may include volatile memory, such as random access memory; the memory may also include non-volatile memory, such as flash memory, hard disk or solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0117] The computer device also includes a communication interface 30 for communicating with other devices or communication networks.

[0118] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code, which, when accessed and executed by the computer, processor, or hardware, implements the methods shown in the above embodiments.

[0119] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0120] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for smooth startup of a wind farm in an offshore wind power flexible DC transmission system, characterized in that, An application is made to a flexible DC transmission system for offshore wind power. The system includes: an onshore power grid, an onshore converter station, an offshore converter station, and an offshore wind farm; the onshore power grid is connected to the onshore converter station; the onshore converter station is connected to the offshore converter station via a DC transmission line; the offshore converter station includes an offshore flexible DC converter valve and an offshore AC bus; the offshore wind farm includes at least one wind turbine, and for each wind turbine, the wind turbine is connected to the offshore flexible DC converter valve via an AC transmission submarine cable and the offshore AC bus. The method includes: Control the onshore converter station to establish DC voltage for the DC transmission line; The offshore flexible DC converter valve is controlled to charge the first wind turbine in a zero-start-up voltage boost mode, wherein the first wind turbine is any one of at least one wind turbine. After the first wind turbine has finished charging, start the first wind turbine. Each of the aforementioned wind turbine units includes a wind turbine converter; the offshore converter station also includes a connecting transformer; the wind turbine converter is connected to the AC transmission submarine cable via the low-voltage side switch and the high-voltage side switch of the wind turbine step-up transformer corresponding to the wind turbine unit; the AC transmission submarine cable is connected to the offshore AC busbar via the AC transmission submarine cable outgoing switch; the offshore AC busbar is connected to the offshore flexible DC converter valve via the connecting transformer side switch, the connecting transformer, and the connecting valve side switch; Before controlling the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up manner, the method further includes: Close the low-voltage side switch of the wind turbine step-up transformer, the high-voltage side switch of the wind turbine step-up transformer, the AC power transmission submarine cable outgoing switch, the grid connection switch, and the valve connection switch corresponding to the first wind turbine unit; Each of the aforementioned wind turbine units also includes a wind turbine step-up transformer; The control of the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up voltage boost manner includes: The offshore flexible DC converter valve is controlled to charge the wind turbine converter in the first wind turbine in a zero-start voltage boost mode, while simultaneously charging the AC transmission submarine cable corresponding to the first wind turbine and energizing the wind turbine step-up transformer in the first wind turbine.

2. The method according to claim 1, characterized in that, The wind turbine converter includes a machine-side converter, a grid-side converter, and a DC capacitor; Controlling the offshore flexible DC converter valve to charge the wind turbine converter in a zero-start-up voltage-boosting manner includes: The offshore flexible DC converter valve is controlled to charge the DC capacitor in a zero-start voltage boost manner by controlling the AC voltage amplitude and frequency.

3. The method according to claim 2, characterized in that, The method further includes: Once the DC voltage of the DC capacitor reaches the preset DC voltage, the charging of the wind turbine converter is considered complete.

4. The method according to any one of claims 1-3, characterized in that, The wind turbine converter includes a grid-side converter; the step of starting the first wind turbine after charging is completed includes: After the wind turbine converter has finished charging, the grid-side converter is unlocked. The grid-side converter is controlled to establish the rated DC voltage corresponding to the first wind turbine to start the first wind turbine.

5. A smooth start-up device for a wind farm in an offshore wind power flexible DC transmission system, characterized in that, An application is made to a flexible DC transmission system for offshore wind power. The system includes: an onshore power grid, an onshore converter station, an offshore converter station, and an offshore wind farm; the onshore power grid is connected to the onshore converter station; the onshore converter station is connected to the offshore converter station via a DC transmission line; the offshore converter station includes an offshore flexible DC converter valve and an offshore AC bus; the offshore wind farm includes at least one wind turbine, and for each wind turbine, the wind turbine is connected to the offshore flexible DC converter valve via an AC transmission submarine cable and the offshore AC bus. The device includes: The first control module is used to control the onshore converter station to establish DC voltage for the DC transmission line; The second control module is used to control the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up voltage boost mode, wherein the first wind turbine is any one of at least one wind turbine. The starting module is used to start the first wind turbine after the first wind turbine has finished charging; Each of the aforementioned wind turbine units includes a wind turbine converter; the offshore converter station also includes a connecting transformer; the wind turbine converter is connected to the AC transmission submarine cable via the low-voltage side switch and the high-voltage side switch of the wind turbine step-up transformer corresponding to the wind turbine unit; the AC transmission submarine cable is connected to the offshore AC busbar via the AC transmission submarine cable outgoing switch; the offshore AC busbar is connected to the offshore flexible DC converter valve via the connecting transformer side switch, the connecting transformer, and the connecting valve side switch; Before controlling the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up manner, the method further includes: Close the low-voltage side switch of the wind turbine step-up transformer, the high-voltage side switch of the wind turbine step-up transformer, the AC power transmission submarine cable outgoing switch, the grid connection switch, and the valve connection switch corresponding to the first wind turbine unit; Each of the aforementioned wind turbine units also includes a wind turbine step-up transformer; The control of the offshore flexible DC converter valve to charge the first wind turbine in a zero-start-up voltage boost manner includes: The offshore flexible DC converter valve is controlled to charge the wind turbine converter in the first wind turbine in a zero-start voltage boost mode, while simultaneously charging the AC transmission submarine cable corresponding to the first wind turbine and energizing the wind turbine step-up transformer in the first wind turbine.

6. A computer device, characterized in that, include: The system includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes the computer instructions to perform the smooth start-up method for offshore wind power flexible DC transmission system wind farms as described in any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to execute the smooth start-up method of the offshore wind power flexible DC transmission system for wind farms as described in any one of claims 1 to 4.

8. A computer program product, characterized in that, The system includes computer instructions for causing a computer to execute the smooth startup method for a wind farm in a flexible DC transmission system for offshore wind power, as described in any one of claims 1 to 4.

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