A hybrid valve network power transmission system and method for offshore wind power multi-site systems

Abstract

This invention relates to the field of offshore wind power DC transmission technology, and discloses an offshore wind power multi-site hybrid valve network transmission system and method. The system includes multiple interconnected offshore wind farm hybrid valve network transmission subsystems, each subsystem comprising: a first converter module, a second converter module, a third converter module, and an onshore converter station. This invention achieves power mutual assistance and voltage support among multiple sites through topological connection and coordinated control of the first, second, and third converter modules and the onshore converter station in the multiple interconnected subsystems. It adaptively switches between four control modes: black start, single-site near-zero, full-site near-zero, and recovery, adjusting the hybrid valve topology and power flow path to improve the system's operational continuity and reliability under all operating conditions.

Description

Technical Field

[0001] This invention relates to the field of offshore wind power DC transmission technology, specifically to an offshore wind power multi-site hybrid valve network transmission system and transmission method. Background Technology

[0002] Long-distance offshore wind power transmission typically employs high-voltage direct current (HVDC) transmission technology. Offshore converter stations convert alternating current (AC) to direct current (DC), which is then transmitted to land via DC submarine cables. Currently, most offshore converter stations utilize the MMC (Multi-Converter Valve) structure; however, the high cost, large size, and weight of MMC converter valves hinder large-scale offshore wind power transmission. In recent years, diode rectifiers (DRs) have become a research hotspot due to their low cost, small size, and light weight. However, DR solutions face the following problems in practical applications: (1) Difficulty in black start. The DR itself does not have the ability to build up voltage, and requires complex external auxiliary circuits to realize power feedback and black start, which is costly.

[0003] (2) Poor reliability of near-zero power operation. When the wind power is close to 0, the power generated by the offshore wind turbine cannot meet the power supply requirements of the wind turbine and converter station auxiliary equipment. At the same time, the low DC current of the DR will lead to the risk of current discontinuity, making it difficult for the system to operate reliably.

[0004] (3) High engineering cost in multi-channel transmission scenarios. Due to the limited capacity of submarine cables, offshore wind power bases with a capacity of tens of millions of kilowatts need to adopt multi-channel transmission methods. Existing DR solutions often need to be used in conjunction with full-power MMC in multi-site scenarios, which fails to give full play to the cost advantage of DR, and the engineering cost is still relatively high. Summary of the Invention

[0005] In view of this, the present invention provides a hybrid valve network power transmission system and method for multiple offshore wind power plants, in order to solve the problem that the hybrid valve network power transmission system for offshore wind power cannot operate continuously and reliably over a wide power range in the prior art.

[0006] In a first aspect, the present invention provides a hybrid valve network power transmission system for multiple offshore wind farms, comprising multiple interconnected hybrid valve network power transmission subsystems for offshore wind farms. Each subsystem includes: a first converter module, a second converter module, a third converter module, and an onshore converter station. The wind turbines of the offshore wind farms are connected to an offshore busbar via medium-voltage AC cables. The first converter module and the second converter module are connected in series, with one end connected to the positive terminal of the onshore converter station via a positive DC submarine cable, and the other end connected to the negative terminal of the onshore converter station via a negative DC submarine cable. The AC sides of the first converter module, the second converter module, and the third converter module are all connected to the offshore busbar. The AC side of the onshore converter station is connected to the power grid. Adjacent subsystems are connected in series via the DC side of their respective third converter modules.

[0007] The offshore wind power multi-site hybrid valve network transmission system provided by this invention connects a first converter module and a second converter module in series to a DC submarine cable, and integrates a third converter module for DC-side interconnection between adjacent subsystems, thus constructing a multi-site collaborative offshore wind power transmission topology. This topology allows each subsystem to flexibly switch power flow paths under different operating conditions, achieving power mutual assistance and voltage support among multiple sites. It effectively solves the power transmission interruption problem under near-zero power conditions, while reducing the size, weight, and engineering cost of offshore converter stations, and improving the system's operational continuity and reliability under all operating conditions.

[0008] In one optional implementation, the first converter module includes: a first transformer, a rectifier diode valve, and a first controllable switch, wherein the primary side of the first transformer is connected to the marine busbar, and the secondary side of the first transformer is connected to the AC side of the rectifier diode valve; one end of the DC side of the rectifier diode valve is connected to a DC submarine cable through the first controllable switch, and the other end of the DC side of the rectifier diode valve is connected to one end of the second converter module.

[0009] In one optional implementation, the second converter module includes: a second transformer, a first converter, a second controllable switch, and a third controllable switch, wherein the primary side of the second transformer is connected to the marine busbar, and the secondary side of the second transformer is connected to the AC side of the first converter; one end of the DC side of the first converter is connected to the positive DC submarine cable through the second controllable switch, and the other end of the DC side of the first converter is connected to the negative DC submarine cable through the third controllable switch.

[0010] In one optional implementation, the third converter module includes: a third transformer and a second converter, wherein the primary side of the third transformer is connected to the offshore busbar, and the secondary side of the third transformer is connected to the AC side of the second converter; the DC side of the second converter is connected to the DC side of the third converter module of the adjacent subsystem.

[0011] In one alternative implementation, the system further includes an energy-consuming module, wherein the energy-consuming module is connected in parallel between the DC sides of an adjacent third converter module.

[0012] Secondly, the present invention provides a method for multi-site hybrid valve network power transmission in offshore wind power, applicable to the system described in the first aspect above or any corresponding embodiment. The method includes: acquiring the current operating parameters of each offshore wind farm; determining the target offshore wind farm based on the comparison result between the current operating parameters and preset parameter thresholds, and selecting a corresponding preset control mode, including: black start mode, single-farm near-zero power operation mode, full-farm near-zero power operation mode, and normal operation recovery mode; adjusting the topological connection relationship of the first converter module, the second converter module, and / or the third converter module in the subsystem corresponding to the target offshore wind farm according to the selected control mode, and adjusting the power flow path between different offshore wind farms to maintain continuous grid-connected operation of each offshore wind farm.

[0013] The present invention provides a method for multi-site hybrid valve network transmission of offshore wind power. By real-time monitoring of the operating parameters of each offshore wind farm and comparing them with preset thresholds, it dynamically matches four control modes: black start, single-farm near-zero power operation, full-farm near-zero power operation, and restoration to normal operation. It adaptively adjusts the topological connections of the first, second, and third converter modules and the power flow paths between farms, achieving coordinated operation and seamless mode switching across multiple farms over a wide power range. This method not only solves the problem of power transmission interruption due to insufficient power under near-zero power conditions, ensuring continuous conduction of the diode rectifier valve under weak power generation conditions, but also effectively improves the system's operational continuity and reliability under all operating conditions through power mutual assistance and voltage support among multiple farms. Furthermore, this method completes black start and mode switching without increasing additional hardware costs, fully leveraging the low cost and small size advantages of diode rectifier valves, significantly reducing the overall cost of the offshore wind power transmission system, and providing an economical and efficient solution for the reliable transmission of large-scale, long-distance offshore wind power.

[0014] In one optional implementation, the process of determining a target offshore wind farm and selecting a corresponding preset control mode includes: when the power generation of any offshore wind farm is zero and needs to be started, determining that offshore wind farm as the target offshore wind farm and selecting a black start mode; when the power generation of some offshore wind farms is lower than a first threshold and the power generation of other offshore wind farms is higher than a second threshold, and the wind farm is operating in black start mode, determining the offshore wind farms with power generation lower than the first threshold as the target offshore wind farms and selecting a single-farm near-zero power operation mode; when the power generation of all offshore wind farms is lower than the first threshold, determining all offshore wind farms as the target offshore wind farms and selecting a full-farm near-zero power operation mode; when the power generation of the offshore wind farms in the full-farm near-zero power operation mode recovers to above the second threshold, determining that offshore wind farm as the target offshore wind farm and selecting a restore normal operation mode; wherein, the first threshold is less than the second threshold.

[0015] The present invention provides a method for multi-site hybrid valve network power transmission in offshore wind power, which classifies the power generation of offshore wind farms by introducing a first threshold and a second threshold. This enables precise matching and adaptive switching between black start mode, single-site near-zero power operation mode, full-site near-zero power operation mode, and normal operation recovery mode. This power threshold-based hierarchical control strategy allows the system to dynamically adjust its operation mode according to the real-time power generation capacity of each wind farm. While ensuring continuous conduction of diode rectifier valves, it maximizes the synergistic and complementary capabilities between multiple wind farms, effectively solving the power transmission interruption problem under near-zero power conditions. This significantly improves the system's operational continuity, reliability, and automation level under all operating conditions, while avoiding unnecessary frequent mode switching, thus improving the system's operating efficiency and stability.

[0016] In one optional implementation, the process of maintaining continuous grid-connected operation of each offshore wind farm in black-start mode includes: controlling the onshore converter station to establish a DC-side black-start voltage and injecting it into the second converter module; controlling the second converter module to establish an AC voltage based on the black-start voltage to start wind turbine power generation; using the third converter module and energy consumption module to transfer power with the adjacent offshore wind farm, and then disconnecting the connection between the second converter module and the DC submarine cable; switching the onshore converter station to normal mode to establish a DC-side rated voltage and then putting the first converter module into operation; controlling the third converter module and energy consumption module to exit, so as to gradually increase the output power of the subsystem where the target offshore wind farm is located.

[0017] The present invention provides a method for multi-station hybrid valve network power transmission in offshore wind power. This method establishes a DC-side black-start voltage at the onshore converter station and injects it into the second converter module. The second converter module then boosts the voltage from zero to establish the offshore AC voltage to start the wind turbines, achieving reliable self-starting of the offshore wind farm from a zero-power state. Power transfer is achieved with adjacent offshore wind farms using a third converter module and energy-consuming modules. After ensuring the DC-side current of the second converter module returns to zero, it safely exits the system. The onshore converter station is then switched to normal mode to establish the rated DC-side voltage and engages the first converter module. Finally, the third converter module and energy-consuming modules are deactivated, and the transmitted power is gradually increased, completing a smooth transition from black start to normal operation. This method fully utilizes the synergistic advantages of multi-station interconnection, achieving independent black start of the offshore wind farm without relying on external power sources. Simultaneously, the transient regulation capability of the energy-consuming modules ensures stable voltage and current during mode switching, avoiding the impact of inrush currents on equipment and significantly improving the system's self-healing capability and operational safety.

[0018] In one optional implementation, after power transfer with an adjacent offshore wind farm using the third converter module and the energy dissipation module, the process of disconnecting the second converter module from the DC submarine cable includes: starting the third converter module and engaging the energy dissipation module connected in parallel with the DC side of the third converter module; adjusting the power of the third converter module so that the current flowing through the DC side of the second converter module returns to zero; when the current flowing through the DC side of the second converter module returns to zero, disconnecting the second converter module from the DC submarine cable, and switching the control target of the energy dissipation module to maintain the DC voltage of the sub-module of the second converter module less than or equal to the rated value.

[0019] In one optional implementation, the process of maintaining continuous grid-connected operation of each offshore wind farm according to the near-zero power operation mode includes: identifying offshore wind farms with power generation below a first threshold as target offshore wind farms, and identifying offshore wind farms with power generation above a second threshold as supporting offshore wind farms; activating a third converter module between the target offshore wind farm and the supporting offshore wind farm, controlling the transmission of a portion of the power from the supporting offshore wind farm to the target offshore wind farm, so that the output power of the subsystem where the target offshore wind farm is located is maintained above the first threshold; wherein, the magnitude of the portion of power is determined based on the difference between the current power generation of the target offshore wind farm and the first threshold.

[0020] The offshore wind power multi-station hybrid valve grid transmission method provided by this invention realizes on-demand power mutual assistance among multiple stations. When the target wind farm's own power generation capacity is insufficient, the supporting wind farm accurately makes up for the power gap, effectively solving the problem of current discontinuity caused by low power of diode rectifier valves, and ensuring continuous grid-connected operation of each subsystem within a wide power range. At the same time, the power transmission volume is dynamically adjusted based on real-time difference, avoiding power waste caused by over-transmission, improving the economy and accuracy of multi-station coordinated operation, and significantly enhancing the system's adaptability and operational reliability under power fluctuations in some wind farms.

[0021] In one optional implementation, the process of maintaining continuous grid-connected operation of each offshore wind farm in a near-zero power operation mode includes: identifying at least one target offshore wind farm as a supporting offshore wind farm; switching the onshore converter station corresponding to the supporting offshore wind farm to black-start mode to establish DC voltage; deactivating the first converter module of the supporting offshore wind farm and activating its second converter module, so that the supporting offshore wind farm operates as a voltage source; and transmitting the power of the supporting offshore wind farm to other target offshore wind farms through a third converter module, so that the output power of the subsystem where the other target offshore wind farms are located is maintained above a first threshold.

[0022] The offshore wind power multi-site hybrid valve grid transmission method provided by this invention, when all wind farms are in a weak power generation state, converts one wind farm into a voltage source mode as a power aggregation hub to provide stable voltage support for the entire system, while concentrating the dispersed power of other wind farms for transmission. This effectively solves the problem that each wind farm cannot independently maintain transmission due to insufficient power under extreme weak power generation conditions. By introducing the voltage source mode, the risk of current discontinuity of diode rectifier valves under extremely low power is avoided, ensuring continuous and reliable operation of the system under near-zero power conditions across the entire site. This significantly improves the system's adaptability and survivability in extreme weather or low wind speed scenarios across the entire sea area.

[0023] In one optional implementation, the process of maintaining continuous grid-connected operation of each offshore wind farm in accordance with the normal operation restoration mode includes: switching the onshore converter station corresponding to the target offshore wind farm to normal mode to establish the DC side rated voltage; disconnecting the connection between the second converter module of the target offshore wind farm and the DC submarine cable, and putting its first converter module into operation, so that the target offshore wind farm operates as a power source; and gradually adjusting the power transmitted from the adjacent offshore wind farm to the target offshore wind farm through the third converter module until the power output of the subsystem where the target offshore wind farm is located is maintained above the second threshold.

[0024] The hybrid valve network method for offshore wind power multi-site transmission provided by this invention achieves a smooth and seamless transition from near-zero mode to normal power generation. After the target wind farm's own power generation capacity recovers, it gradually withdraws external power support to avoid system shocks caused by power fluctuations. Through a tiered withdrawal mechanism, it ensures stable power and voltage during mode switching, enabling wind farms to independently undertake power transmission tasks while releasing power resources supporting wind farms, providing conditions for the recovery of other wind farms, and significantly improving the system's stability and self-healing capability during dynamic recovery.

[0025] In one optional implementation, the process of disconnecting the second converter module of the target offshore wind farm from the DC submarine cable and activating its first converter module includes: limiting the power generation of the wind turbine generators of the target offshore wind farm to zero; adjusting the power of the third converter module between the target offshore wind farm and the adjacent offshore wind farm so that the DC side current flowing through the second converter module of the target offshore wind farm returns to zero, and then disconnecting the second converter module from the DC submarine cable; switching the power command reference value of the third converter module to maintain the DC side capacitor voltage of the second converter module submodule of the target offshore wind farm at the rated value; switching the onshore converter station corresponding to the target offshore wind farm to normal mode to establish the rated DC side voltage, and then activating the first and second converter modules of the target offshore wind farm.

[0026] In one optional implementation, the process of gradually adjusting the power transmitted from an adjacent offshore wind farm to a target offshore wind farm through a third converter module includes: controlling the power transmitted from the adjacent offshore wind farm to the target offshore wind farm through the third converter module, so that the power output of the subsystem to which the target offshore wind farm is located is maintained above a first threshold and the power generation of the target offshore wind farm is gradually increased; when the power generation of the target offshore wind farm is stable above a second threshold, the power command of the third converter module is set to zero and the operation of the third converter module is stopped. Attached Figure Description

[0027] 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.

[0028] Figure 1 This is a composition diagram of a multi-station hybrid valve network power transmission system for offshore wind power according to an embodiment of the present invention; Figure 2 This is a detailed circuit diagram of a multi-station hybrid valve network power transmission system for offshore wind power according to an embodiment of the present invention; Figure 3 This is a flowchart illustrating the offshore wind power multi-station hybrid valve network power transmission method according to an embodiment of the present invention; Figure 4 This is a diagram showing the composition of the control device for a multi-station hybrid valve network power transmission system for offshore wind power according to an embodiment of the present invention. Figure 5 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0029] 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.

[0030] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0031] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0032] Long-distance offshore wind power transmission typically employs high-voltage direct current (HVDC) transmission technology. Offshore wind turbines generate electricity, which is then collected via AC cables. Offshore converter stations convert this AC power into DC power, which is then transmitted to onshore converter stations via DC submarine cables. Currently, the converter valves in offshore wind power HVDC transmission projects all utilize the MMC (Multi-Mechanical Controlled Conversion) structure. However, MMC converter valves are costly and bulky, thus requiring further optimization for large-scale offshore wind power transmission schemes.

[0033] Due to the unidirectional transmission characteristic of offshore wind power, diode rectifier (DR) DC transmission has become a focus of attention in recent years. Compared with MMC (Multi-mode Converter), DR has advantages such as lower cost, smaller size, and lighter weight. During the normal operation of DR and its hybrid converter methods, if wind power approaches zero, the power generated by the offshore wind turbines cannot meet the power requirements for the turbines, auxiliary equipment of the converter station, and the main equipment losses. Furthermore, excessively low DR DC current poses a risk of current interruption due to ripple. Therefore, for DR and its hybrid converters, not only the black start process needs to be considered, but also the near-zero power operation capability of offshore wind farms is required.

[0034] Due to limitations in the voltage levels and capacity of submarine cables, the current single-channel transmission capacity typically does not exceed 2000MW. For ultra-large-scale offshore wind power bases with capacities in the tens of millions of kilowatts, multi-channel transmission is inevitable. The contiguous development of offshore wind farms and multi-channel transmission also provide more possibilities for the coordinated operation of multiple offshore converters. To fully utilize the DR (Diverterless Transmission) method to achieve low-cost, compact offshore converters, while simultaneously addressing the black start problem of the DR method and the near-zero power issue in offshore wind farms, a multi-terminal DC transmission technology for offshore wind power based on DC-assisted weak interconnection lines has been proposed.

[0035] However, existing DC transmission schemes using DR and hybrid converters are complex to implement, difficult to achieve black start, and costly to implement. When offshore wind power generation is close to zero, the power generated by the offshore wind turbines cannot meet the power requirements for power supply to the turbines and converter station auxiliary equipment, as well as the power required for main equipment losses, making reliable operation difficult in practical engineering. For existing offshore wind farms with contiguous development and multi-channel transmission, DR and hybrid converters often need to be used in conjunction with full-power MMC mixing valves, resulting in high engineering costs.

[0036] This embodiment provides a hybrid valve network power transmission system for multiple offshore wind power stations, such as... Figure 1 As shown, it includes multiple interconnected offshore wind farm hybrid valve network transmission subsystems, each subsystem including: a first converter module 1, a second converter module 2, a third converter module 3, and an onshore converter station 4.

[0037] Figure 1 In this system, the wind turbines of the offshore wind farm are connected to the offshore busbar via medium-voltage AC cables; after the first converter module 1 and the second converter module 2 are connected in series, one end is connected to the positive end of the onshore converter station 4 via a positive DC submarine cable, and the other end is connected to the negative end of the onshore converter station 4 via a negative DC submarine cable; the AC side of the first converter module 1, the AC side of the second converter module 2, and the AC side of the third converter module 3 are all connected to the offshore busbar; the AC side of the onshore converter station 4 is connected to the power grid; adjacent subsystems are connected in series via the DC side of their respective third converter modules 3.

[0038] Specifically, Figure 1 In this system, the wind turbines of the offshore wind farm are connected to the offshore busbar via medium-voltage AC cables, forming a unified AC collection point. The first converter module 1 and the second converter module 2 are connected in series, with one end connected to the positive end of the onshore converter station 4 via a positive DC submarine cable, and the other end connected to the negative end of the onshore converter station 4 via a negative DC submarine cable, forming the DC transmission main circuit of the subsystem. The AC side of the first converter module 1, the AC side of the second converter module 2, and the AC side of the third converter module 3 are all connected to the offshore busbar, enabling the three converter modules to draw power from or send power to the same AC busbar. The AC side of the onshore converter station 4 is connected to the power grid, realizing the grid connection of offshore wind power. Adjacent subsystems are connected in series via the DC side of their respective third converter modules 3, forming an interconnection channel between multiple stations. Based on the above structure, each subsystem can transmit power through the first converter module 1, regulate voltage through the second converter module 2, and exchange power with other subsystems through the third converter module 3. Multiple subsystems together constitute a reconfigurable and mutually supportive multi-terminal DC transmission network.

[0039] For example, Figure 1 In order to ensure the continuous and reliable operation of the multi-station hybrid valve network power transmission system of offshore wind power under any operating conditions, adaptive control is achieved in the following four scenarios through coordinated control and topology reconfiguration of the first converter module, the second converter module, the third converter module, and the onshore converter station: (1) When the offshore wind farm is in a zero-power state and needs to be started, the black start voltage is established through the onshore converter station and injected into the second converter module. The second converter module establishes AC voltage to start the wind turbine. After the wind turbine generates electricity, the power is transferred through the third converter module. The connection between the second converter module and the DC submarine cable is disconnected and the first converter module is put into operation to complete the black start.

[0040] (2) When the power generation of some offshore wind farms is insufficient while the power generation of other wind farms is sufficient, the power is transmitted from the high-power wind farm to the low-power wind farm through the third converter module, so that the power output of the subsystem where the low-power wind farm is located is maintained above the minimum operating requirements.

[0041] (3) When the power generation of all offshore wind farms is insufficient, select at least one wind farm as the supporting wind farm, switch its onshore converter station to black start mode, deactivate its first converter module and put in the second converter module to make it operate as a voltage source, and at the same time transmit the remaining power of other wind farms to the supporting wind farm for unified output through the third converter module.

[0042] (4) When the power generation returns to normal, switch the onshore converter station of the corresponding wind farm to normal mode, disconnect the connection between the second converter module and the DC submarine cable and put the first converter module into operation. Gradually reduce the external power injection through the third converter module until it operates independently.

[0043] Optionally, the first converter module 1 can be composed of multiple diode rectifier valves. The number of first converter modules 1 can be set to multiple according to the actual transmission capacity requirements. Multiple first converter modules 1 are connected in series, and the second converter module 2 is connected in series in the middle position of multiple first converter modules 1.

[0044] The offshore wind power multi-site hybrid valve network transmission system provided in this embodiment connects to a DC submarine cable via a first converter module and a second converter module connected in series. Combined with a third converter module for DC-side interconnection between adjacent subsystems, a multi-site collaborative offshore wind power transmission topology is constructed. This topology allows each subsystem to flexibly switch power flow paths under different operating conditions, achieving power mutual assistance and voltage support among multiple sites. It effectively solves the power transmission interruption problem under near-zero power conditions, while reducing the size, weight, and engineering cost of the offshore converter station, and improving the system's operational continuity and reliability under all operating conditions.

[0045] In some alternative implementations, such as Figure 2 As shown, taking the No. 1 offshore wind farm as an example: The first converter module includes: a first transformer T1A (or T3A), a rectifier diode valve DR, and a first controllable switch Bp3A (or Bp4A). The primary side of the first transformer is connected to the marine busbar, and the secondary side of the first transformer is connected to the AC side of the rectifier diode valve. One end of the DC side of the rectifier diode valve is connected to the DC submarine cable through the first controllable switch, and the other end of the DC side of the rectifier diode valve is connected to one end of the second converter module.

[0046] The second converter module includes: a second transformer T2A, a first converter MMC1A, a second controllable switch Bp1A, and a third controllable switch Bp2A. The primary side of the second transformer is connected to the marine busbar, and the secondary side of the second transformer is connected to the AC side of the first converter. One end of the DC side of the first converter is connected to the positive DC submarine cable through the second controllable switch, and the other end of the DC side of the first converter is connected to the negative DC submarine cable through the third controllable switch.

[0047] The third converter module includes a third transformer T6A and a second converter MMC3. The primary side of the third transformer is connected to the offshore busbar, and the secondary side of the third transformer is connected to the AC side of the second converter. The DC side of the second converter is connected to the DC side of the third converter module of the adjacent subsystem.

[0048] Specifically, Figure 2 Taking the No. 1 offshore wind farm as an example, the wind turbines are connected to the offshore busbar via medium-voltage AC cables. The offshore busbar is connected to two 12-pulse rectifier diode valves (DR) via switches Brk6A and Brk7A and a rectifier transformer. At the same time, the offshore busbar is also connected to the offshore MMC converter valve (MMC1A) via switch Brk5A, a connecting transformer, and switch Brk4. The upper 12-pulse rectifier diode valve, MMC1A, and the lower 12-pulse rectifier diode valve are directly connected in series on their DC sides. The positive terminal of the upper 12-pulse rectifier diode valve is connected to the positive terminal of the DC submarine cable via switch Bp3A, and the negative terminal of the lower 12-pulse rectifier diode valve is connected to the negative terminal of the DC submarine cable via switch Bp4A. The positive terminal of the DC side of the MMC converter valve is connected to the positive terminal of the DC submarine cable via switch Bp1A, and the negative terminal of the DC side of the MMC converter valve is connected to the negative terminal of the DC submarine cable via switch Bp2A. The onshore converter station adopts a half-bridge MMC topology. The AC outgoing lines of the onshore converter station are connected to the main grid via switch Brk2A and large transformer TA4, switch Brk3A and small transformer T5A.

[0049] Specifically, Figure 2 In this system, the connection structure between the two offshore wind farms and their transmission systems is as follows: the DC sides of the two MMC converters (i.e., MMC3 and MMC4) are interconnected, and the AC sides are connected to the corresponding offshore wind farms through transformers.

[0050] In some alternative implementations, such as Figure 2 As shown, it also includes: an energy-consuming module, wherein the energy-consuming module is connected in parallel between the DC side of the adjacent third converter module, and the energy-consuming module is composed of a DC energy-consuming resistor and a control switch connected in series.

[0051] This embodiment provides a method for multi-site hybrid valve network power transmission in offshore wind power, applicable to systems described in the above embodiment or any corresponding implementation, such as... Figure 3As shown, the method includes: Step S1: Obtain the current operating parameters for each offshore wind farm.

[0052] Specifically, by deploying monitoring devices in each offshore wind farm subsystem, key parameters reflecting the system's operating status are collected in real time, including at least the power generation of each offshore wind farm, the DC-side current and voltage of each converter module, and the on / off status of each controllable switch.

[0053] Step S2: Based on the comparison results between the current operating parameters and the preset parameter thresholds, determine the target offshore wind farm and select the corresponding preset control mode. The control modes include: black start mode, single field near-zero power operation mode, full field near-zero power operation mode and normal operation recovery mode.

[0054] Specifically, the operating parameters obtained in step S1 are compared and analyzed with the first and second preset thresholds in the system. Based on the matching relationship between power generation and the thresholds, the system automatically identifies the current operating condition: when a wind farm's power generation is zero and it needs to be started, it is identified as the target wind farm and the black start mode is selected; when some wind farms' power generation is below the first threshold while other wind farms' power generation is above the second threshold, the low-power wind farm is identified as the target and the single-farm near-zero mode is selected; when all wind farms' power generation is below the first threshold, all wind farms are identified as the target and the whole-farm near-zero mode is selected; when the power generation of a wind farm in the whole-farm near-zero mode recovers to above the second threshold, that wind farm is identified as the target and the normal recovery mode is selected. Through this hierarchical judgment mechanism, accurate matching and adaptive switching of operating modes are achieved.

[0055] Step S3: According to the selected control mode, adjust the topology connection relationship of the first converter module, the second converter module, and / or the third converter module in the subsystem corresponding to the target offshore wind farm, and adjust the power flow path between different offshore wind farms to maintain continuous grid-connected operation of each offshore wind farm.

[0056] Specifically, based on the control mode selected in step S2, the converter modules in the corresponding subsystem of the target offshore wind farm are controlled collaboratively: In black-start mode, a black-start voltage is injected into the second converter module through the onshore converter station to start the wind turbine. After power transfer using the third converter module, the connection between the second converter module and the DC submarine cable is disconnected, and the first converter module is put into operation. In single-farm near-zero mode, part of the power from the high-power wind farm is transmitted to the low-power wind farm through the third converter module, ensuring that its output power remains above the minimum operating requirements. In full-farm near-zero mode, the second converter module of the selected supporting wind farm is put into operation as a voltage source, and the remaining power from other wind farms is collected and transmitted uniformly through the third converter module. In normal recovery mode, the power injection of the third converter module is gradually reduced, the connection between the second converter module and the DC submarine cable is disconnected, and the first converter module is put into operation, allowing the wind farm to independently bear the power transmission. Through dynamic adjustment of the switching status of each converter module and the power flow path, continuous and reliable operation of the system under all operating conditions is achieved.

[0057] The hybrid valve network transmission method for multiple offshore wind farms provided in this embodiment dynamically matches four control modes—black start, single-farm near-zero power operation, full-farm near-zero power operation, and restoration to normal operation—by real-time monitoring of the operating parameters of each offshore wind farm and comparing them with preset thresholds. It adaptively adjusts the topology connections of the first, second, and third converter modules and the power flow paths between farms, achieving coordinated operation and seamless mode switching across multiple farms over a wide power range. This method not only solves the problem of power transmission interruption due to insufficient power under near-zero power conditions, ensuring continuous conduction of the diode rectifier valve under weak power generation conditions, but also effectively improves the system's operational continuity and reliability under all operating conditions through power mutual assistance and voltage support among multiple farms. Furthermore, this method completes black start and mode switching without increasing additional hardware costs, fully leveraging the low cost and small size advantages of diode rectifier valves, significantly reducing the overall cost of the offshore wind power transmission system, and providing an economical and efficient solution for the reliable transmission of large-scale, long-distance offshore wind power.

[0058] In some optional implementations, the process of determining the target offshore wind farm and selecting the corresponding preset control mode includes: (1) When the power generation of any offshore wind farm is zero and it needs to be started, determine the offshore wind farm as the target offshore wind farm and select the black start mode.

[0059] When any offshore wind farm has zero power generation and needs to be started, the system determines that it is in a zero-power waiting-to-start state, identifies it as the target offshore wind farm, selects the black start mode, establishes the initial voltage, and starts the wind turbine to generate electricity.

[0060] (2) When the power generation of some offshore wind farms is lower than the first threshold and the power generation of other offshore wind farms is higher than the second threshold, and the wind farm is operating in black start mode, the offshore wind farm with power generation lower than the first threshold is identified as the target offshore wind farm, and the single farm near zero power operation mode is selected.

[0061] When the power generation of some offshore wind farms is lower than the first threshold while the power generation of other offshore wind farms is higher than the second threshold, the system identifies the wind farms with insufficient power generation as having a near-zero operation risk, identifies them as target offshore wind farms, selects a single-farm near-zero power operation mode, and maintains their continuous operation by introducing external power support.

[0062] (3) When the power generation of all offshore wind farms is lower than the first threshold, all offshore wind farms are identified as target offshore wind farms, and the near-zero power operation mode of the entire farm is selected.

[0063] When the power generation of all offshore wind farms is below the first threshold, the system determines that the entire group of farms is in a weak power generation state, identifies all wind farms as targets and selects a near-zero power operation mode for the entire farm, and provides voltage support to the system by converting some wind farms to voltage source mode.

[0064] (4) When the power generation of an offshore wind farm in a near-zero power operation mode recovers to a level higher than the second threshold, the offshore wind farm is identified as the target offshore wind farm and the normal operation mode is selected; wherein the first threshold is less than the second threshold.

[0065] When the power generation of an offshore wind farm operating in near-zero power mode recovers to above the second threshold, the system determines that it has the ability to operate independently, identifies it as the target offshore wind farm, selects the normal operation mode, gradually withdraws external support, and switches back to power source mode operation.

[0066] The first threshold is set below the second threshold, forming a power level judgment range from low to high. This ensures a reasonable order and stable boundary for mode switching, avoids frequent mode switching caused by small power fluctuations, and improves the stability of system operation and the reliability of control strategy.

[0067] In some alternative implementations, the process of maintaining continuous grid-connected operation of each offshore wind farm in black-start mode includes: (1) After the onshore converter station establishes the DC side black start voltage, it is injected into the second converter module.

[0068] (2) Control the second converter module to establish AC voltage based on the black start voltage to start the wind turbine to generate electricity.

[0069] (3) After using the third converter module and energy consumption module to transfer power to the adjacent offshore wind farm, disconnect the connection between the second converter module and the DC submarine cable.

[0070] The process of disconnecting the second converter module from the DC submarine cable after power transfer with the adjacent offshore wind farm using the third converter module and the energy dissipation module includes: starting the third converter module and engaging the energy dissipation module connected in parallel with the DC side of the third converter module; adjusting the power of the third converter module so that the current flowing through the DC side of the second converter module returns to zero; when the current flowing through the DC side of the second converter module returns to zero, disconnecting the second converter module from the DC submarine cable and switching the control target of the energy dissipation module to maintain the DC voltage of the sub-module of the second converter module less than or equal to the rated value.

[0071] (4) After switching the onshore converter station to normal mode to establish the rated voltage on the DC side, the first converter module is put into operation.

[0072] (5) Control the third converter module and energy consumption module to shut down, so as to gradually increase the output power of the subsystem where the target offshore wind farm is located. Specifically, refer to Figure 2 Each individual offshore wind farm and its transmission system can be individually black-started sequentially. Taking the black start of offshore wind farm #1 as an example: First, close switches Brk1A and Brk3A, then close switches Bp1A and Bp2A. The onshore converter station #1 is unlocked and put into operation, establishing the DC-side black-start voltage. Then, close switches Brk4A, Brk5A, Brk6A, and Brk7A. After the DC-side black-start voltage is established, MMC1A is unlocked, and the AC voltage of the offshore wind farm is established from zero using the voltage / frequency (V / F) control method. The offshore wind turbines are started, and their output power is controlled so that the current flowing through Bp1A slightly exceeds zero. MMC3 is activated, and the DC power consumption resistor is put into operation. The control target for DC power consumption is that the current flowing through Bp1A is 0. When the current flowing through Bp1A is 0, Bp1A and Bp2A are disconnected. Then, the control target for DC power consumption is switched to maintain the DC voltage of the submodule of the offshore MMC not exceeding the rated value. At this time, the onshore MMC first locks and disconnects Brk3A, then closes Brk2A. The onshore MMC unlocks and establishes the rated voltage on the DC side. After the rated voltage on the DC side reaches stability, switches Bp3A and Bp4A are closed. The control MMC3 and the DC power consumption resistor stop operating, and the power generation of the offshore wind turbine is gradually increased. The No. 1 offshore wind farm completes the black start.

[0073] In some alternative implementations, the process of maintaining continuous grid-connected operation of each offshore wind farm in a near-zero power operation mode includes: (1) Offshore wind farms with power generation below the first threshold are identified as target offshore wind farms, and offshore wind farms with power generation above the second threshold are identified as supporting offshore wind farms.

[0074] (2) Activate the third converter module between the target offshore wind farm and the supporting offshore wind farm to control part of the power of the supporting offshore wind farm to be transmitted to the target offshore wind farm, so that the power output of the subsystem where the target offshore wind farm is located is maintained above the first threshold; wherein, the size of part of the power output is determined according to the difference between the current power generation of the target offshore wind farm and the first threshold.

[0075] Specifically, refer to Figure 2 Assuming that the power generation of offshore wind farm #1 is 10% greater than its installed capacity, while the power generation of offshore wind farm #2 is less than 5% of its installed capacity, the power generation of offshore wind farm #2 is close to zero, facing the risk of intermittent current in the diode rectifier valve and power loss on the offshore AC voltage bus. At this time, MMC3 connected to offshore wind farm #1 is unlocked and its DC voltage UdcC is controlled to the rated value, and the DC energy-consuming resistor is not activated; MMC4 is unlocked and outputs power to offshore wind farm #2 to ensure that the total power output of the subsystem where offshore wind farm #2 is located is not less than 5%.

[0076] In some alternative implementations, the process of maintaining continuous grid-connected operation of each offshore wind farm in a near-zero power operation mode includes: (1) Identify at least one target offshore wind farm as a supporting offshore wind farm.

[0077] (2) Switch the onshore converter station corresponding to the offshore wind farm to black start mode to establish DC voltage.

[0078] (3) The first converter module supporting the offshore wind farm is deactivated and its second converter module is activated, so that the offshore wind farm can operate in the form of a voltage source.

[0079] (4) The power supporting the offshore wind farm is transmitted to other target offshore wind farms through the third converter module, so that the power output of the subsystem where the other target offshore wind farms are located is maintained above the first threshold.

[0080] Specifically, refer to Figure 2If the power generation of both offshore wind farm #1 and offshore wind farm #2 is difficult to maintain above 5% of the installed capacity, assuming that before this moment, offshore wind farm #1 was transmitting power to offshore wind farm #2 through the power exchange channel composed of MMC3 and MMC4, and at this time the total power generation of offshore wind farm #1 also falls below 5% of the installed capacity, then it is necessary to switch the topology and control mode of the power transmission system of offshore wind farm #2. First, control the power transmission command of MMC4 to make the current of Bp3B and Bp4B reach zero crossing, and disconnect Bp3B and Bp4B at the zero crossing moment. Then switch the power command reference value of MMC4 to keep the DC side capacitor voltage of the MMC1B submodule at the rated value. The converter valve of the No. 2 onshore converter station is first locked and Brk2B is disconnected, then Brk3B is closed, and the converter valve of the No. 2 onshore converter station is unlocked again to establish the DC side black start voltage. Then fine-tune the DC side voltage of MMC1B to keep it consistent with the DC side black start voltage. Then close Bp1B and Bp2B. At this time, the DC side voltage of MMC1B is clamped by the DC side voltage of the converter valve of the No. 2 onshore converter station. The power transmission command control of MMC4 can ensure that the total transmission power of the No. 1 offshore wind farm is not less than 5% of the installed capacity.

[0081] In some alternative implementations, the process of maintaining continuous grid-connected operation of each offshore wind farm according to the normal operation restoration mode includes: (1) Switch the onshore converter station corresponding to the target offshore wind farm to normal mode to establish the DC side rated voltage.

[0082] (2) Disconnect the second converter module of the target offshore wind farm from the DC submarine cable and put its first converter module into operation so that the target offshore wind farm can operate as a power source.

[0083] The process of disconnecting the second converter module of the target offshore wind farm from the DC submarine cable and activating its first converter module includes: limiting the power generation of the wind turbines of the target offshore wind farm to zero; adjusting the power of the third converter module between the target offshore wind farm and the adjacent offshore wind farm so that the DC side current flowing through the second converter module of the target offshore wind farm returns to zero, and then disconnecting the second converter module from the DC submarine cable; switching the power command reference value of the third converter module to maintain the DC side capacitor voltage of the second converter module submodule of the target offshore wind farm at the rated value; switching the onshore converter station corresponding to the target offshore wind farm to normal mode to establish the rated DC side voltage, and then activating the first and second converter modules of the target offshore wind farm.

[0084] (3) Through the third converter module, the power transmitted from the adjacent offshore wind farm to the target offshore wind farm is gradually adjusted until the power transmitted from the subsystem where the target offshore wind farm is located is maintained above the second threshold.

[0085] The process of gradually adjusting the power transmitted from the adjacent offshore wind farm to the target offshore wind farm through the third converter module includes: controlling the power transmitted from the adjacent offshore wind farm to the target offshore wind farm through the third converter module, so that the power output of the subsystem to which the target offshore wind farm is located is maintained above the first threshold and the power generation of the target offshore wind farm is gradually increased; when the power generation of the target offshore wind farm is stable above the second threshold, the power command of the third converter module is set to zero and the operation of the third converter module is stopped.

[0086] Specifically, refer to Figure 2 If the No. 2 offshore wind farm has switched to near-zero operating mode, but the power generation of both the No. 1 and No. 2 offshore wind farms has rebounded to more than 10% of their respective total installed capacity, then the No. 2 offshore wind farm needs to exit the near-zero operating mode and return to normal power generation. The specific procedure is as follows: First, limit the power generation of the wind turbines in the No. 2 offshore wind farm to 0. Then, control the MMC4 to transmit power commands, making the current flowing through Bp1B and Bp2B zero. Disconnect the switches when the current flowing through Bp1B and Bp2B is zero. Then, switch the power command reference value of the MMC4 to maintain the DC-side capacitor voltage of the MMC1B submodule. Maintain the rated value; the converter valve of the No. 2 onshore converter station is first locked and Brk3B is opened, then Brk2B is closed, and the converter valve of the No. 2 onshore converter station is unlocked again to establish the rated voltage UdcB on the DC side, and then Bp3B and Bp4B are closed; at this time, the power transmission command of MMC4 is used to ensure that the total transmission power of the No. 2 offshore wind farm is not less than 5% of the installed capacity, and then the power generation power of the No. 2 offshore wind farm is gradually increased. When the power output of the subsystem where the No. 2 offshore wind farm is located is increased to more than 10% of the rated installed capacity, the power transmission command of MMC4 is set to zero, MMC4 and MMC3 stop operating, and all wind farms return to normal power generation state.

[0087] This embodiment also provides a control device for a multi-site hybrid valve network power 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.

[0088] This embodiment provides a control device for a multi-site hybrid valve network power transmission system for offshore wind power, such as... Figure 4 As shown, it includes: The parameter acquisition module 401 is used to acquire the current operating parameters of each offshore wind farm.

[0089] The mode decision module 402 is used to determine the target offshore wind farm based on the comparison results between the current operating parameters and the preset parameter thresholds, and select the corresponding preset control mode. The control modes include: black start mode, single field near zero power operation mode, full field near zero power operation mode and normal operation recovery mode.

[0090] The collaborative control module 403 is used to adjust the topological connection relationship of the first converter module, the second converter module, and / or the third converter module in the subsystem corresponding to the target offshore wind farm according to the selected control mode, and to adjust the power flow path between different offshore wind farms in order to maintain the continuous grid-connected operation of each offshore wind farm.

[0091] The control device for the offshore wind power multi-site hybrid valve network power transmission system provided in this embodiment of the invention can execute the method provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects for executing the method. Further functional descriptions of the above modules and units are the same as in the corresponding embodiments described above, and will not be repeated here. Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0092] The following is a detailed reference. Figure 5 The diagram illustrates a structural schematic suitable for implementing an electronic device according to embodiments of the present invention. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 001, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 002 or a program loaded from memory 008 into random access memory (RAM) 003. The RAM 003 also stores various programs and data required for the operation of the electronic device. The processor 001, ROM 002, and RAM 003 are interconnected via bus 004. An input / output (I / O) interface 005 is also connected to bus 004.

[0093] Typically, the following devices can be connected to I / O interface 005: input devices 006 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 007 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 008 including, for example, magnetic tapes, hard disks, etc.; and communication devices 009. Communication device 009 allows electronic devices to exchange data via wireless or wired communication with other devices. Although Figure 5 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0094] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication device 009, or installed from memory 008, or installed from ROM 002. When the computer program is executed by processor 001, it performs the functions defined in the methods of the embodiments of the present invention.

[0095] Figure 5 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0096] 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.

[0097] 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.

[0098] 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. An offshore wind farm multi-station hybrid valve networking export system, characterized in that, It includes multiple interconnected offshore wind farm hybrid valve network transmission subsystems, each subsystem comprising: a first converter module, a second converter module, a third converter module, and an onshore converter station, wherein, The wind turbines of the offshore wind farm are connected to the offshore busbar via medium-voltage AC cables; After the first converter module and the second converter module are connected in series, one end is connected to the positive end of the onshore converter station through a positive DC submarine cable, and the other end is connected to the negative end of the onshore converter station through a negative DC submarine cable. The AC side of the first converter module, the AC side of the second converter module, and the AC side of the third converter module are all connected to the marine busbar. The AC side of the onshore converter station is connected to the power grid; The adjacent subsystems are connected in series on the DC side of their respective third converter modules.

2. The system of claim 1, wherein, The first converter module includes: a first transformer, a rectifier diode valve, and a first controllable switch, wherein, The primary side of the first transformer is connected to the marine busbar, and the secondary side of the first transformer is connected to the AC side of the rectifier diode valve. One end of the DC side of the rectifier diode valve is connected to the DC submarine cable through the first controllable switch, and the other end of the DC side of the rectifier diode valve is connected to one end of the second converter module.

3. The system of claim 1, wherein, The second converter module includes: a second transformer, a first converter, a second controllable switch, and a third controllable switch, wherein, The primary side of the second transformer is connected to the marine busbar, and the secondary side of the second transformer is connected to the AC side of the first converter. One end of the DC side of the first converter is connected to the positive DC submarine cable via the second controllable switch, and the other end of the DC side of the first converter is connected to the negative DC submarine cable via the third controllable switch.

4. The system according to claim 1, characterized in that, The third converter module includes: a third transformer and a second converter, wherein... The primary side of the third transformer is connected to the marine busbar, and the secondary side of the third transformer is connected to the AC side of the second converter. The DC side of the second converter is connected to the DC side of the third converter module of the adjacent subsystem.

5. The system according to claim 1, characterized in that, Also includes: Energy-consuming modules, among which, The energy-consuming module is connected in parallel between the DC side of the adjacent third converter module.

6. A method for transmitting power from multiple offshore wind power stations via a hybrid valve network, characterized in that, Applied to the system according to any one of claims 1 to 5, the method comprises: Obtain the current operating parameters for each of the offshore wind farms; Based on the comparison results between the current operating parameters and the preset parameter thresholds, the target offshore wind farm is determined, and the corresponding preset control mode is selected. The control modes include: black start mode, single field near-zero power operation mode, full field near-zero power operation mode, and normal operation recovery mode. According to the selected control mode, adjust the topological connection relationship of the first converter module, the second converter module, and / or the third converter module in the subsystem corresponding to the target offshore wind farm, and adjust the power flow path between different offshore wind farms to maintain continuous grid-connected operation of each offshore wind farm.

7. The method according to claim 6, characterized in that, The process of determining the target offshore wind farm and selecting the corresponding preset control mode includes: When the power generation capacity of any offshore wind farm is zero and it needs to be started, the offshore wind farm is identified as the target offshore wind farm, and the black start mode is selected. When the power generation of some offshore wind farms is lower than the first threshold and the power generation of other offshore wind farms is higher than the second threshold, the offshore wind farms with power generation lower than the first threshold are identified as target offshore wind farms, and a single farm near-zero power operation mode is selected. When the power generation of all offshore wind farms is lower than the first threshold, all offshore wind farms are identified as target offshore wind farms, and the near-zero power operation mode of the entire farm is selected. When the power generation of an offshore wind farm operating in near-zero power mode recovers to above the second threshold, and the wind farm is operating in black start mode, the offshore wind farm is identified as the target offshore wind farm, and the normal operation mode is selected. Wherein, the first threshold is less than the second threshold.

8. The method according to claim 7, characterized in that, The process of maintaining continuous grid connection for each offshore wind farm under the black start mode includes: After establishing the DC-side black start voltage at the onshore converter station, the voltage is injected into the second converter module. The second converter module is controlled to establish an AC voltage based on the black start voltage to start the wind turbine for power generation; After transferring power with the adjacent offshore wind farm using the third converter module and energy consumption module, the connection between the second converter module and the DC submarine cable is disconnected. After switching the onshore converter station to normal mode to establish the rated voltage on the DC side, the first converter module is put into operation. The third converter module and energy consumption module are deactivated to gradually increase the output power of the target offshore wind farm's on-site subsystem.

9. The method according to claim 8, characterized in that, The process of disconnecting the second converter module from the DC submarine cable after power transfer with the adjacent offshore wind farm using the third converter module and energy dissipation module includes: Start the third converter module and put into operation the energy-consuming module connected in parallel with the DC side of the third converter module; Adjust the power of the third converter module so that the current flowing through the DC side of the second converter module returns to zero; When the current flowing through the DC side of the second converter module returns to zero, the connection between the second converter module and the DC submarine cable is disconnected, and the control target of the energy-consuming module is switched to maintain the DC voltage of the sub-module of the second converter module equal to the rated value.

10. The method according to claim 7, characterized in that, The process of maintaining continuous grid-connected operation of each offshore wind farm in a near-zero power operation mode includes: Offshore wind farms with power generation below the first threshold are identified as target offshore wind farms, and offshore wind farms with power generation above the second threshold are identified as supporting offshore wind farms. The third converter module between the target offshore wind farm and the supporting offshore wind farm is deployed to control a portion of the power of the supporting offshore wind farm to be transmitted to the target offshore wind farm, so that the output power of the subsystem where the target offshore wind farm is located is maintained above the first threshold. The magnitude of the power component is determined based on the difference between the current power generation of the target offshore wind farm and a first threshold.

11. The method according to claim 7, characterized in that, The process of maintaining continuous grid connection for each offshore wind farm under a near-zero power operation mode includes: Identify at least one target offshore wind farm as a supporting offshore wind farm; Switch the onshore converter station corresponding to the offshore wind farm to black start mode to establish DC voltage; The first converter module supporting the offshore wind farm is deactivated, and its second converter module is activated, so that the offshore wind farm supports the voltage source mode. The power supporting the offshore wind farm is transmitted to other target offshore wind farms through the third converter module, so that the output power of the subsystem where the other target offshore wind farms are located is maintained above the first threshold.

12. The method according to claim 7, characterized in that, The process of maintaining continuous grid connection for each offshore wind farm in accordance with the normal operation restoration mode includes: Switch the onshore converter station corresponding to the target offshore wind farm to normal mode to establish the rated voltage on the DC side; Disconnect the second converter module of the target offshore wind farm from the DC submarine cable and put its first converter module into operation, so that the target offshore wind farm can operate in normal operation mode. The third converter module gradually adjusts the power transmitted from the adjacent offshore wind farm to the target offshore wind farm until the power output of the subsystem where the target offshore wind farm is located is maintained above the second threshold.

13. The method according to claim 12, characterized in that, The process of disconnecting the second converter module of the target offshore wind farm from the DC submarine cable and engaging its first converter module includes: The power generation capacity of the wind turbines in the target offshore wind farm is limited to zero. Adjust the power of the third converter module between the target offshore wind farm and the adjacent offshore wind farm, so that the DC side current flowing through the second converter module of the target offshore wind farm returns to zero, and then disconnect the connection between the second converter module and the DC submarine cable. The power command reference value of the third converter module is switched to maintain the DC side capacitor voltage of the second converter module submodule of the target offshore wind farm at the rated value. After switching the onshore converter station corresponding to the target offshore wind farm to normal mode to establish the rated DC voltage, the first converter module and the second converter module of the target offshore wind farm are put into operation.

14. The method according to claim 12, characterized in that, The process of gradually adjusting the power transmitted from the adjacent offshore wind farm to the target offshore wind farm through the third converter module includes: The third converter module controls the power transmission from the adjacent offshore wind farm to the target offshore wind farm, so that the power output of its subsystem is maintained above the first threshold. Gradually increase the power generation capacity of the target offshore wind farm; When the power generation of the target offshore wind farm stabilizes above the second threshold, the power command of the third converter module is set to zero, and the operation of the third converter module is stopped.

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