Offshore wind power collecting and sending-out system and method based on multi-port multi-frequency alternating current and direct current hybrid integrated platform

Abstract

The invention discloses an offshore wind power collecting and sending-out system and method based on a multi-port multi-frequency alternating current and direct current hybrid integrated platform, and belongs to the field of power transmission and distribution of power systems. The system comprises an intermediate-frequency, power-frequency and low-frequency wind power collection subsystem, an offshore integrated platform, a direct-current sending-out submarine cable, a low-frequency sending-out submarine cable, an onshore converter station and an onshore frequency conversion station. The various wind power collection subsystems respectively collect wind turbine generator group outputs with corresponding frequencies and send the wind turbine generator group outputs to the offshore integrated platform; the offshore integrated platform converts intermediate-frequency, power-frequency and partial low-frequency electric energy into direct current and then transmits the direct current to the onshore converter station through the direct-current sending-out submarine cable, and the converter station converts the direct current into power-frequency alternating current; and after being boosted, the other low-frequency electric energy is sent to a land frequency conversion station through a low-frequency sending-out submarine cable to be converted into power-frequency alternating current, so that efficient collection and grid-connected sending-out of multi-frequency wind power resources are realized. According to the invention, the problem that a plurality of independent platforms need to be built in a complex multi-point grid-connected scene in the prior art can be solved.

Description

Technical Field

[0001] This invention relates to the field of power system transmission and distribution technology, specifically to an offshore wind power collection and transmission system and method based on a multi-port, multi-frequency AC / DC hybrid integrated platform. Background Technology

[0002] Large-scale offshore wind farms are a key component in achieving energy structure transformation and carbon neutrality goals, and their development trend is increasingly moving towards deeper waters, larger scale, and clustering. Offshore wind power collection and transmission systems, as the "energy arteries" connecting offshore wind farms to the onshore power grid, directly determine whether large-scale offshore wind energy resources can be efficiently and stably developed and utilized due to the advancement, reliability, and economic efficiency of their technological solutions. Therefore, researching and developing new offshore wind power collection and transmission systems adapted to future complex application scenarios is of paramount importance for promoting the development of the entire new energy industry.

[0003] However, in complex multi-point grid connection scenarios, existing technologies face two major bottlenecks. First, traditional transmission methods typically require the construction of multiple independent platforms for different wind farm clusters or landing points, such as independent offshore booster stations or offshore converter stations. This "one-to-one" approach not only leads to high engineering costs and operational difficulties but also makes the coordination between multiple systems exceptionally complex. Second, although various advanced technologies such as medium-frequency collection, power frequency transmission, low-frequency transmission, and DC transmission have been developed, these technologies are usually applied as independent systems in existing solutions. Existing technologies generally lack a unified framework to integrate these different technologies, preventing their collaborative application within a unified system and thus limiting the flexibility and economy of developing wind energy resources in complex offshore areas. Summary of the Invention

[0004] This invention provides an offshore wind power collection and transmission system and method based on a multi-port, multi-frequency AC / DC hybrid integrated platform, which can solve the problem of needing to build multiple independent platforms in complex multi-point grid connection scenarios in the prior art.

[0005] One embodiment of the present invention provides an offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform, comprising:

[0006] The system includes an offshore medium-frequency wind power collection subsystem comprising a group of medium-frequency wind turbines, an offshore power frequency wind power collection subsystem comprising a group of power frequency wind turbines, an offshore low-frequency wind power collection subsystem comprising a group of low-frequency wind turbines, an offshore integrated platform, a DC transmission submarine cable, a low-frequency transmission submarine cable, an onshore converter station, and an onshore frequency converter station.

[0007] The offshore medium-frequency wind power collection subsystem is used to collect the medium-frequency AC power generated by the medium-frequency wind turbine group and transmit the medium-frequency AC power to the offshore integrated platform.

[0008] The offshore industrial frequency wind power collection subsystem is used to collect the industrial frequency AC power generated by the industrial frequency wind turbine group and transmit the industrial frequency AC power to the offshore integrated platform.

[0009] The offshore low-frequency wind power collection subsystem is used to collect low-frequency AC power generated by a group of low-frequency wind turbines and transmit the low-frequency AC power to the offshore integrated platform; wherein, the low-frequency AC power includes a first low-frequency AC component and a second low-frequency AC component.

[0010] The offshore integrated platform is used to convert all of the received medium-frequency AC power and power frequency AC power, as well as the first low-frequency AC portion of the low-frequency AC power, into DC power, and to transmit all the converted DC power to the onshore converter station via the DC transmission submarine cable.

[0011] The offshore integrated platform is also used to boost the second low-frequency AC component of the low-frequency AC power and transmit the boosted low-frequency AC power to the onshore frequency converter station via the low-frequency transmission submarine cable.

[0012] The onshore converter station is used to convert the DC power transmitted from the offshore integrated platform into first-frequency AC power.

[0013] The onshore frequency converter station is used to convert the boosted low-frequency AC power supplied by the offshore integrated platform into a second power frequency AC power.

[0014] Furthermore, the AC collection bus of the offshore medium-frequency wind power collection subsystem is connected to the medium-frequency input terminal of the offshore integrated platform;

[0015] The AC collection bus of the offshore power frequency wind power collection subsystem is connected to the power frequency input terminal of the offshore integrated platform;

[0016] The AC collection bus of the offshore low-frequency wind power collection subsystem is connected to the low-frequency input terminal of the offshore integrated platform.

[0017] The DC output terminal of the offshore integrated platform is connected to the DC input terminal of the onshore converter station via the DC transmission submarine cable.

[0018] The low-frequency AC output terminal of the offshore integrated platform is connected to the low-frequency AC input terminal of the onshore frequency converter station via the low-frequency transmission submarine cable.

[0019] Furthermore, the offshore medium-frequency wind power collection subsystem includes an offshore medium-frequency wind turbine group and a medium-frequency AC collection network;

[0020] The offshore medium-frequency wind turbine group includes at least one offshore medium-frequency wind farm, and the offshore medium-frequency wind farm is composed of several medium-frequency wind turbines;

[0021] The medium-frequency AC aggregation network includes several medium-frequency AC aggregation submarine cables and a set of medium-frequency AC aggregation buses; the medium-frequency AC aggregation buses are the AC aggregation buses of the offshore medium-frequency wind power aggregation subsystem.

[0022] The medium-frequency AC collecting submarine cable is used to connect the medium-frequency wind turbines in the offshore medium-frequency wind farm to each other and collect electrical energy to the medium-frequency AC collecting bus.

[0023] Furthermore, the offshore power frequency wind power aggregation subsystem includes an offshore power frequency wind turbine group and a power frequency AC aggregation network;

[0024] The offshore industrial frequency wind turbine group includes at least one offshore industrial frequency wind farm, and the offshore industrial frequency wind farm is composed of several industrial frequency wind turbines.

[0025] The power frequency AC aggregation network includes several power frequency AC aggregation submarine cables and a set of power frequency AC aggregation buses; the power frequency AC aggregation buses are the AC aggregation buses of the offshore power frequency wind power aggregation subsystem.

[0026] The power frequency AC collecting submarine cable is used to connect the power frequency wind turbines in the offshore power frequency wind farm to each other and collect electrical energy to the power frequency AC collecting bus.

[0027] Furthermore, the offshore low-frequency wind power collection subsystem includes an offshore low-frequency wind turbine group and a low-frequency AC collection network;

[0028] The offshore low-frequency wind turbine group includes at least one offshore low-frequency wind farm, and the offshore low-frequency wind farm is composed of several low-frequency wind turbines.

[0029] The low-frequency AC aggregation network includes several low-frequency AC aggregation submarine cables and a set of low-frequency AC aggregation buses; the low-frequency AC aggregation buses are the AC aggregation buses of the offshore low-frequency wind power aggregation subsystem.

[0030] The low-frequency AC collecting submarine cable is used to connect the low-frequency wind turbines in the offshore low-frequency wind farm to each other and collect electrical energy to the low-frequency AC collecting bus.

[0031] Furthermore, the marine integrated platform internally includes an intermediate frequency converter, a power frequency converter, a low frequency converter, an intermediate frequency transformer, a power frequency transformer, and a low frequency transformer;

[0032] The input terminal of the intermediate frequency transformer is the intermediate frequency input terminal of the offshore integrated platform;

[0033] The output terminal of the intermediate frequency transformer is connected to the AC side of the intermediate frequency converter;

[0034] The input terminal of the power frequency transformer is the power frequency input terminal of the offshore integrated platform;

[0035] The output terminal of the power frequency transformer is connected to the AC side of the power frequency converter.

[0036] The input terminal of the low-frequency transformer is the low-frequency input terminal of the offshore integrated platform;

[0037] The voltage matching output terminal of the low-frequency transformer is connected to the AC side of the low-frequency converter.

[0038] The step-up output terminal of the low-frequency transformer is the low-frequency AC output terminal of the offshore integrated platform;

[0039] The positive DC terminal of the intermediate frequency converter, the positive DC terminal of the power frequency converter, and the positive DC terminal of the low frequency converter are interconnected to form a positive DC bus.

[0040] The negative DC terminal of the intermediate frequency converter, the negative DC terminal of the power frequency converter, and the negative DC terminal of the low frequency converter are interconnected to form a negative DC bus.

[0041] The positive DC bus and the negative DC bus together constitute the DC output terminal of the offshore integrated platform.

[0042] Furthermore, the power frequency AC output terminal of the onshore converter station is connected to the first land power grid through a first connecting transformer;

[0043] The power frequency AC output terminal of the land-based frequency converter station is connected to the second land power grid through a second connecting transformer.

[0044] Furthermore, the intermediate frequency converter, the power frequency converter, and the low frequency converter all operate using a constant AC voltage and frequency control method.

[0045] The onshore converter station operates using a constant DC output voltage control method;

[0046] The onshore frequency converter station operates using a constant power control method.

[0047] Furthermore, the offshore medium-frequency wind power collection subsystem operates at a medium-frequency frequency greater than a preset Hertz value;

[0048] The offshore power frequency wind power collection subsystem operates at a power frequency equal to a preset Hertz value;

[0049] The offshore low-frequency wind power collection subsystem operates at a low frequency less than a preset Hertz value.

[0050] The second low-frequency AC section, output from the marine integrated platform to the low-frequency transmission submarine cable, operates at a transmission frequency lower than a preset Hertz value;

[0051] The onshore converter station is used to control the frequency of the first power frequency AC power it generates at a preset Hertz value;

[0052] The onshore frequency converter station is used to control the frequency of the second power frequency AC power it generates at a preset Hertz value.

[0053] Based on the above-described method embodiments, the present invention provides corresponding method embodiments.

[0054] One embodiment of the present invention provides a method for offshore wind power collection and transmission based on a multi-port multi-frequency AC / DC hybrid integrated platform, applicable to the offshore integrated platform of the offshore wind power collection and transmission system based on the multi-port multi-frequency AC / DC hybrid integrated platform, comprising: receiving medium-frequency AC power transmitted from the offshore medium-frequency wind power collection subsystem;

[0055] Receives AC power transmitted from the offshore power frequency wind power collection subsystem;

[0056] Receive low-frequency AC power transmitted from the offshore low-frequency wind power collection subsystem;

[0057] The intermediate frequency AC power is converted into the first DC power.

[0058] The power frequency AC power is converted into a second DC power.

[0059] The first low-frequency AC component of the low-frequency AC power is converted into a third DC power.

[0060] The second low-frequency AC component of the low-frequency AC power is boosted to generate boosted low-frequency AC power.

[0061] The first DC power, the second DC power, and the third DC power are combined to generate combined DC power.

[0062] The collected DC power is transmitted via the DC transmission submarine cable;

[0063] The boosted low-frequency AC power is transmitted via the low-frequency transmission submarine cable.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] This invention provides an offshore wind power collection and transmission system and method based on a multi-port, multi-frequency AC / DC hybrid integrated platform. The system includes three types of wind power collection subsystems: medium-frequency, power-frequency, and low-frequency; an offshore integrated platform; DC transmission submarine cables; low-frequency transmission submarine cables; an onshore converter station; and an onshore frequency converter station. Each wind power collection subsystem collects the output of wind turbine groups at its corresponding frequency and sends it to the offshore integrated platform. The offshore integrated platform converts the medium-frequency, power-frequency, and some low-frequency power into DC and transmits it to the onshore converter station via the DC transmission submarine cables. The converter station then converts it into power-frequency AC. The remaining low-frequency power is boosted and transmitted to the onshore frequency converter station via the low-frequency transmission submarine cables, where it is converted into power-frequency AC, thereby achieving efficient collection and grid connection of multi-frequency wind power resources.

[0066] This invention integrates the offshore voltage boosting and converter functions required for various offshore wind power transmission schemes by constructing a unified offshore integrated platform. This solves the problem of existing technologies requiring the construction of multiple independent platforms in complex multi-point grid connection scenarios, significantly reducing engineering costs and operation and maintenance difficulties. Simultaneously, this system is the first to achieve the coordinated aggregation of wind power energy from different technology systems, including medium-frequency, power-frequency, and low-frequency, and uses the most efficient DC or low-frequency AC hybrid mode for transmission. This solves the problem of existing advanced technologies being independent and unable to be applied collaboratively in a unified system, greatly improving the flexibility and economy of the overall development of wind energy resources in complex offshore areas. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the overall structure of an offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform, according to an embodiment of the present invention.

[0068] Figure 2 This is a schematic diagram of a control method using constant AC voltage and frequency control provided by the present invention;

[0069] Figure 3 This is a schematic diagram of a control method using constant DC voltage and reactive power control provided by the present invention;

[0070] Figure 4 This is a schematic diagram of a control method using constant power control provided by the present invention;

[0071] Figure 5 This invention provides an offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform, which has two DC transmission submarine cables, two onshore converter stations and two connected land power grids.

[0072] Figure 6This is a flowchart illustrating a method for collecting and transmitting offshore wind power based on a multi-port, multi-frequency AC / DC hybrid integrated platform, according to an embodiment of the present invention. Attached image description:

[0074] 1 represents the offshore medium-frequency wind power collection subsystem; 11 represents the offshore medium-frequency wind farm; 12 represents the medium-frequency AC collection submarine cable; 13 represents the medium-frequency AC collection busbar; 111 represents the medium-frequency wind turbine string; and 112 represents the medium-frequency wind turbine unit. 2 represents the offshore industrial frequency wind power collection subsystem; 21 represents the offshore industrial frequency wind farm; 22 represents the industrial frequency AC collection submarine cable; 23 represents the industrial frequency AC collection busbar; 211 represents the industrial frequency wind turbine string; and 212 represents the industrial frequency wind turbine unit. 3 represents the offshore low-frequency wind power collection subsystem; and 31 represents the offshore low-frequency wind power... 32 is a low-frequency AC collection submarine cable, 33 is a low-frequency AC collection bus, 311 is a low-frequency wind turbine string, 312 is a low-frequency wind turbine; 4 is an offshore integrated platform, 41 is a medium-frequency transformer, 42 is converter I, 43 is a power frequency transformer, 44 is converter II, 45 is a low-frequency transformer, 46 is converter III; 5 is a DC transmission submarine cable; 6 is an onshore converter station; 7 is a land power grid node I; 8 is a low-frequency transmission submarine cable; 9 is an onshore frequency converter station; 10 is a land power grid node II. Detailed Implementation

[0075] 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, and 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.

[0076] It should be noted that, for ease of understanding of the present invention, it is necessary to explain in advance that, in the accompanying drawings and descriptions of the present invention, for the sake of simplicity and clarity, some components are referred to by reference numerals or abbreviations, and their correspondence with the specific technical terms used in the claims and description of the present invention is as follows. Specifically, converter I (42), converter II (44), and converter III (46) mentioned in the accompanying drawings correspond to the medium-frequency converter, power frequency converter, and low-frequency converter mentioned in the claims, respectively. Similarly, land grid node I (7) and land grid node II (10) mentioned in the accompanying drawings, and the transformers located between the land converter station (6) and land grid node I (7), and between the land frequency converter station (9) and land grid node II (10) mentioned in the drawings, correspond to the first connecting transformer and the second connecting transformer mentioned in the claims, respectively. They correspond to the first land grid and the second land grid mentioned in the claims, respectively. Those skilled in the art can understand the above names by referring to the accompanying drawings when reading the embodiments of the present invention.

[0077] Figure 1 , Figure 5 The abbreviation PCC in this context stands for Point of Common Coupling. Figure 2 , Figure 3 , Figure 4 U in d U q P and Q are the d-axis and q-axis components of the AC voltage of the common AC bus, respectively; P and Q are the active and reactive power of the onshore DC grid and / or the onshore AC grid, respectively; P ref Q ref These are reference values ​​for active power and reactive power, respectively; U dc DC voltage; U dcref This is the reference value for DC voltage; I dref and I qref These are the reference values ​​for the d-axis and q-axis components of the alternating current, respectively; M d and M q These are the d-axis and q-axis components of the AC modulation ratio, respectively; θ is the reference phase angle of the converter; V PCC is the voltage at point PCC; f is the frequency.

[0078] like Figure 1 As shown, to address the problem of needing to construct multiple independent platforms in complex multi-point grid connection scenarios in existing technologies, an embodiment of the present invention provides an offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform, comprising: an offshore medium-frequency wind power collection subsystem containing a group of medium-frequency wind turbines, an offshore power frequency wind power collection subsystem containing a group of power frequency wind turbines, an offshore low-frequency wind power collection subsystem containing a group of low-frequency wind turbines, an offshore integrated platform, a DC transmission submarine cable, a low-frequency transmission submarine cable, an onshore converter station, and an onshore frequency converter station;

[0079] The offshore medium-frequency wind power collection subsystem is used to collect the medium-frequency AC power generated by the medium-frequency wind turbine group and transmit the medium-frequency AC power to the offshore integrated platform.

[0080] The offshore industrial frequency wind power collection subsystem is used to collect the industrial frequency AC power generated by the industrial frequency wind turbine group and transmit the industrial frequency AC power to the offshore integrated platform.

[0081] The offshore low-frequency wind power collection subsystem is used to collect low-frequency AC power generated by a group of low-frequency wind turbines and transmit the low-frequency AC power to the offshore integrated platform; wherein, the low-frequency AC power includes a first low-frequency AC component and a second low-frequency AC component.

[0082] The offshore integrated platform is used to convert all of the received medium-frequency AC power and power frequency AC power, as well as the first low-frequency AC portion of the low-frequency AC power, into DC power, and to transmit all the converted DC power to the onshore converter station via the DC transmission submarine cable.

[0083] The offshore integrated platform is also used to boost the second low-frequency AC component of the low-frequency AC power and transmit the boosted low-frequency AC power to the onshore frequency converter station via the low-frequency transmission submarine cable.

[0084] The onshore converter station is used to convert the DC power transmitted from the offshore integrated platform into first-frequency AC power.

[0085] The onshore frequency converter station is used to convert the boosted low-frequency AC power supplied by the offshore integrated platform into a second power frequency AC power.

[0086] Specifically, one embodiment of the present invention provides an offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform. Here, "multi-port" means that the system can receive electrical energy from different wind farms from multiple input ports and transmit it to land from multiple output ports; "multi-frequency" means that the system can simultaneously receive and process AC power of three different frequency systems: medium frequency, power frequency, and low frequency; "AC / DC hybrid" means that the system uses both DC and AC modes in parallel for long-distance power transmission to land; and "integrated platform" refers to the physical integration of all the core functions of the above-mentioned multi-port, multi-frequency processing, and AC / DC hybrid transmission onto a unified offshore platform. The system completely includes: an offshore medium-frequency wind power collection subsystem, an offshore power frequency wind power collection subsystem, an offshore low-frequency wind power collection subsystem, an offshore integrated platform, a DC transmission submarine cable, a low-frequency transmission submarine cable, an onshore converter station, and an onshore frequency converter station.

[0087] In this system, the offshore medium-frequency, power-frequency, and low-frequency wind power aggregation subsystems serve as three power input sources. Each subsystem independently collects the AC power of its respective frequency generated by the medium-frequency, power-frequency, or low-frequency wind turbine groups and stably transmits this power to the offshore integrated platform. Specifically, the low-frequency AC power collected and transmitted by the offshore low-frequency wind power aggregation subsystem is defined in this embodiment as including a first low-frequency AC portion for subsequent first processing methods and a second low-frequency AC portion for subsequent second processing methods.

[0088] The offshore integrated platform is the core processing hub of this system. On one hand, it converts all received medium-frequency AC power, power-frequency AC power, and the first low-frequency AC portion of the low-frequency AC power into DC power, and then collects all the converted DC power before transmitting it to the onshore converter station via the DC transmission submarine cable. On the other hand, it also boosts the voltage of the second low-frequency AC portion of the low-frequency AC power and independently transmits the boosted low-frequency AC power to the onshore frequency converter station via the low-frequency transmission submarine cable.

[0089] The onshore converter station and the onshore frequency converter station are two grid-connected terminals of this system located on the land side. The onshore converter station receives DC power transmitted from the offshore integrated platform via a DC submarine cable and converts it into first-frequency AC power. Simultaneously, the onshore frequency converter station receives boosted low-frequency AC power transmitted from the offshore integrated platform via a low-frequency submarine cable and converts it into second-frequency AC power. It should be noted that both the first-frequency and second-frequency AC power here are standard AC power in physical properties. The use of ordinal numbers such as "first" and "second" to distinguish them is merely for clear textual reference to two independent power sources generated by two different technical paths, and does not constitute a further limitation on the physical characteristics of the power itself.

[0090] Through the above structure and process, the embodiments of the present invention integrate the collection and transmission functions of multiple different technical systems into a single platform, realizing the unified, flexible and efficient development and utilization of wind energy resources in complex marine areas.

[0091] In a preferred embodiment, the AC collection bus of the offshore medium-frequency wind power collection subsystem is connected to the medium-frequency input terminal of the offshore integrated platform;

[0092] The AC collection bus of the offshore power frequency wind power collection subsystem is connected to the power frequency input terminal of the offshore integrated platform;

[0093] The AC collection bus of the offshore low-frequency wind power collection subsystem is connected to the low-frequency input terminal of the offshore integrated platform.

[0094] The DC output terminal of the offshore integrated platform is connected to the DC input terminal of the onshore converter station via the DC transmission submarine cable.

[0095] The low-frequency AC output terminal of the offshore integrated platform is connected to the low-frequency AC input terminal of the onshore frequency converter station via the low-frequency transmission submarine cable.

[0096] Specifically, the specific connection relationships of the system described in this invention are further elaborated. The AC collection bus of the offshore medium-frequency wind power collection subsystem is connected to the medium-frequency input terminal of the offshore integrated platform; the AC collection bus of the offshore power-frequency wind power collection subsystem is connected to the power-frequency input terminal of the offshore integrated platform; and the AC collection bus of the offshore low-frequency wind power collection subsystem is connected to the low-frequency input terminal of the offshore integrated platform. This multi-port input connection structure provides the physical basis for the offshore integrated platform to simultaneously receive and process AC power of three different frequency systems.

[0097] Meanwhile, in the system's energy output path, the DC output terminal of the offshore integrated platform is connected to the DC input terminal of the onshore converter station via the DC transmission submarine cable; and the low-frequency AC output terminal of the offshore integrated platform is connected to the low-frequency AC input terminal of the onshore frequency converter station via the low-frequency transmission submarine cable. These two independent output connection paths constitute the system's DC power transmission channel and low-frequency AC power transmission channel, respectively, and are the key physical links for realizing the AC / DC hybrid power transmission mode described in this invention.

[0098] Through the clear and explicit connection relationships described above, this system has constructed a complete topology in terms of physical structure, from the collection of multi-source heterogeneous energy to the transmission of dual-mode hybrid energy, thus providing a reliable guarantee for the stable and efficient operation of the entire system.

[0099] In a preferred embodiment, the offshore medium-frequency wind power collection subsystem includes an offshore medium-frequency wind turbine group and a medium-frequency AC collection network;

[0100] The offshore medium-frequency wind turbine group includes at least one offshore medium-frequency wind farm, and the offshore medium-frequency wind farm is composed of several medium-frequency wind turbines;

[0101] The medium-frequency AC aggregation network includes several medium-frequency AC aggregation submarine cables and a set of medium-frequency AC aggregation buses; the medium-frequency AC aggregation buses are the AC aggregation buses of the offshore medium-frequency wind power aggregation subsystem.

[0102] The medium-frequency AC collecting submarine cable is used to connect the medium-frequency wind turbines in the offshore medium-frequency wind farm to each other and collect electrical energy to the medium-frequency AC collecting bus.

[0103] In a preferred embodiment, the offshore power frequency wind power aggregation subsystem includes an offshore power frequency wind turbine group and a power frequency AC aggregation network;

[0104] The offshore industrial frequency wind turbine group includes at least one offshore industrial frequency wind farm, and the offshore industrial frequency wind farm is composed of several industrial frequency wind turbines.

[0105] The power frequency AC aggregation network includes several power frequency AC aggregation submarine cables and a set of power frequency AC aggregation buses; the power frequency AC aggregation buses are the AC aggregation buses of the offshore power frequency wind power aggregation subsystem.

[0106] The power frequency AC collecting submarine cable is used to connect the power frequency wind turbines in the offshore power frequency wind farm to each other and collect electrical energy to the power frequency AC collecting bus.

[0107] In a preferred embodiment, the offshore low-frequency wind power collection subsystem includes an offshore low-frequency wind turbine group and a low-frequency AC collection network.

[0108] The offshore low-frequency wind turbine group includes at least one offshore low-frequency wind farm, and the offshore low-frequency wind farm is composed of several low-frequency wind turbines.

[0109] The low-frequency AC aggregation network includes several low-frequency AC aggregation submarine cables and a set of low-frequency AC aggregation buses; the low-frequency AC aggregation buses are the AC aggregation buses of the offshore low-frequency wind power aggregation subsystem.

[0110] The low-frequency AC collecting submarine cable is used to connect the low-frequency wind turbines in the offshore low-frequency wind farm to each other and collect electrical energy to the low-frequency AC collecting bus.

[0111] Specifically, the internal structure of the offshore medium-frequency wind power aggregation subsystem, the offshore power-frequency wind power aggregation subsystem, and the offshore low-frequency wind power aggregation subsystem is described in detail. These three aggregation subsystems are structurally consistent, each including a group of wind turbines of its respective frequency and an AC aggregation network. Specifically, each wind turbine group contains at least one wind farm, and each wind farm consists of several wind turbines of corresponding frequencies. The AC aggregation network, working in conjunction with the wind turbine group, includes several AC aggregation submarine cables of corresponding frequencies and a set of AC aggregation buses of corresponding frequencies. In this structure, the function of the AC aggregation submarine cables is to electrically connect the various wind turbines within the same wind farm and to uniformly aggregate the electrical energy they generate to the AC aggregation bus, which is the final port for the entire aggregation subsystem to output electrical energy.

[0112] This modular and hierarchical aggregation subsystem structure enables the reliable and efficient collection of electrical energy generated by wind turbine generators of different technologies distributed over a wide area, providing a stable multi-source energy input for the unified processing of subsequent offshore integrated platforms.

[0113] In a preferred embodiment, the marine integrated platform internally includes an intermediate frequency converter, a power frequency converter, a low frequency converter, an intermediate frequency transformer, a power frequency transformer, and a low frequency transformer;

[0114] The input terminal of the intermediate frequency transformer is the intermediate frequency input terminal of the offshore integrated platform;

[0115] The output terminal of the intermediate frequency transformer is connected to the AC side of the intermediate frequency converter;

[0116] The input terminal of the power frequency transformer is the power frequency input terminal of the offshore integrated platform;

[0117] The output terminal of the power frequency transformer is connected to the AC side of the power frequency converter.

[0118] The input terminal of the low-frequency transformer is the low-frequency input terminal of the offshore integrated platform;

[0119] The voltage matching output terminal of the low-frequency transformer is connected to the AC side of the low-frequency converter.

[0120] The step-up output terminal of the low-frequency transformer is the low-frequency AC output terminal of the offshore integrated platform;

[0121] The positive DC terminal of the intermediate frequency converter, the positive DC terminal of the power frequency converter, and the positive DC terminal of the low frequency converter are interconnected to form a positive DC bus.

[0122] The negative DC terminal of the intermediate frequency converter, the negative DC terminal of the power frequency converter, and the negative DC terminal of the low frequency converter are interconnected to form a negative DC bus.

[0123] The positive DC bus and the negative DC bus together constitute the DC output terminal of the offshore integrated platform.

[0124] Specifically, the internal structure and connections of the marine integrated platform, which is the core of this system, are described. The marine integrated platform includes core equipment such as an intermediate frequency converter, a power frequency converter, a low-frequency converter, an intermediate frequency transformer, a power frequency transformer, and a low-frequency transformer. These devices are connected within the platform through clearly defined paths to achieve coordinated processing of three different frequency electrical energy sources. Specifically, the intermediate frequency input of the platform is first connected to the input of the intermediate frequency transformer, and the output of the intermediate frequency transformer is connected to the AC side of the intermediate frequency converter, forming the intermediate frequency power processing path. Similarly, the power frequency input of the platform is connected to the input of the power frequency transformer, and the output of the power frequency transformer is connected to the AC side of the power frequency converter, forming the power frequency power processing path. For low-frequency power, the platform's low-frequency input is connected to the input of a low-frequency transformer, which has two independent outputs: a voltage matching output, which is connected to the AC side of the low-frequency converter for power conversion; and a boost output, which is directly used as the platform's low-frequency AC output for direct power transmission.

[0125] On the DC collection path after all AC power has been processed, the positive DC terminals of the intermediate frequency converter, power frequency converter, and low frequency converter are interconnected to form a single positive DC bus. Simultaneously, the negative DC terminals of these three converters are also interconnected to form a single negative DC bus. Ultimately, this positive and negative DC bus together constitute the unified DC output terminal of the entire offshore integrated platform.

[0126] Through the aforementioned internal structural layout, the marine integrated platform of this embodiment clearly realizes the reception, conversion, splitting, and aggregation of three different frequency AC power sources within a single platform, laying a solid hardware foundation for subsequent AC / DC hybrid long-distance transmission.

[0127] In a preferred embodiment, the power frequency AC output terminal of the onshore converter station is connected to the first land power grid through a first connecting transformer;

[0128] The power frequency AC output terminal of the land-based frequency converter station is connected to the second land power grid through a second connecting transformer.

[0129] Specifically, in a preferred embodiment, the grid connection interface of the system on the land side is described in detail. The power frequency AC output terminal of the onshore converter station is connected to the first land power grid through a first connecting transformer. Similarly, the power frequency AC output terminal of the onshore frequency converter station is connected to the second land power grid through a second connecting transformer. The connecting transformers here function to transform the voltage level of the power frequency AC power generated by the onshore station to ensure that its voltage matches the voltage level of the land power grid to be connected.

[0130] It should be noted that the "first connecting transformer" and "second connecting transformer" mentioned here are only used to clearly distinguish two independent physical devices serving two different transmission paths in the text, and do not constitute a limitation on their specific specifications or models. Similarly, the "first land power grid" and "second land power grid" are intended to refer to two independent grid connection points, which can be different nodes of the same AC power grid or belong to two different AC power grids.

[0131] Through the above grid connection structure, this system can perform final voltage adaptation of the electrical energy transmitted from the sea, realizing safe and reliable feeding into one or more land power grids.

[0132] In a preferred embodiment, the intermediate frequency converter, the power frequency converter, and the low frequency converter all operate using a constant AC voltage and frequency control method.

[0133] The onshore converter station operates using a constant DC output voltage control method;

[0134] The onshore frequency converter station operates using a constant power control method.

[0135] In a preferred embodiment, the offshore medium-frequency wind power collection subsystem operates at a medium-frequency frequency greater than a preset Hertz value;

[0136] The offshore power frequency wind power collection subsystem operates at a power frequency equal to a preset Hertz value;

[0137] The offshore low-frequency wind power collection subsystem operates at a low frequency less than a preset Hertz value.

[0138] The second low-frequency AC section, output from the marine integrated platform to the low-frequency transmission submarine cable, operates at a transmission frequency lower than a preset Hertz value;

[0139] The onshore converter station is used to control the frequency of the first power frequency AC power it generates at a preset Hertz value;

[0140] The onshore frequency converter station is used to control the frequency of the second power frequency AC power it generates at a preset Hertz value.

[0141] Specifically, in a preferred embodiment, the system employs a well-defined and coordinated collaborative control method to ensure the stable operation of the entire complex system. Specifically, the intermediate frequency converter, power frequency converter, and low-frequency converter located within the offshore integrated platform all operate using a constant AC voltage and frequency control mode. The purpose of this is to proactively establish and maintain a constant frequency and voltage AC grid environment for their respective connected offshore wind power aggregation subsystems, providing a stable and reliable grid connection point for the wind turbine cluster. At the receiving end of the DC transmission path, the onshore converter station operates using a constant DC output voltage control mode, responsible for maintaining voltage stability throughout the DC transmission link. Simultaneously, at the receiving end of the low-frequency AC transmission path, the onshore frequency converter station operates using a constant power control mode to precisely control the power ultimately fed into the onshore power grid.

[0142] Through the implementation of the above-mentioned collaborative control method, the system exhibits clear and stable frequency characteristics at each key node. The preset Hertz value can be 50 Hertz; the offshore medium-frequency wind power collection subsystem operates at a medium-frequency frequency greater than 50 Hertz; the offshore power frequency wind power collection subsystem operates at a power frequency equal to 50 Hertz; and the offshore low-frequency wind power collection subsystem operates at a low-frequency frequency less than 50 Hertz. The second low-frequency AC component, output from the offshore integration platform and transmitted via a low-frequency submarine cable, also has a transmission frequency less than 50 Hertz. Ultimately, regardless of whether it is through a DC path or a low-frequency AC path, the frequencies of the first and second power frequency AC power generated by the onshore converter station and the onshore frequency converter station are precisely controlled at 50 Hertz. It should be noted that the first and second power frequency AC power here are both standard power frequency AC power in terms of physical properties. The use of ordinal numbers such as "first" and "second" to distinguish them is only to clearly refer to the two independent power sources generated by two different technical paths in the text, and does not make any further limitation on the physical characteristics of the power itself.

[0143] This complete strategy, from source frequency construction to terminal frequency control, ensures that clean energy from multiple sources and different frequencies can be stably and efficiently collected and ultimately unified into standard electrical energy for safe feeding into the terrestrial power grid.

[0144] Example 1:

[0145] Please see Figure 1 A preferred embodiment of the present invention discloses an offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform. The system includes an offshore section and an onshore section, specifically including: an offshore medium-frequency wind power collection subsystem 1, an offshore power frequency wind power collection subsystem 2, an offshore low-frequency wind power collection subsystem 3, an offshore integrated platform 4, a DC transmission submarine cable 5, an onshore converter station 6, a first onshore power grid 7, a low-frequency transmission submarine cable 8, an onshore frequency converter station 9, and a second onshore power grid 10.

[0146] Specifically, the offshore medium-frequency wind power collection subsystem 1 includes an offshore medium-frequency wind farm 11, a medium-frequency AC collection submarine cable 12, and a medium-frequency AC collection bus 13. Similarly, the offshore power frequency wind power collection subsystem 2 includes an offshore power frequency wind farm 21, a power frequency AC collection submarine cable 22, and a power frequency AC collection bus 23; the offshore low-frequency wind power collection subsystem 3 includes an offshore low-frequency wind farm 31, a low-frequency AC collection submarine cable 32, and a low-frequency AC collection bus 33. The interior of the offshore integrated platform 4 includes a medium-frequency transformer 41, a medium-frequency converter 42, a power frequency transformer 43, a power frequency converter 44, a low-frequency transformer 45, and a low-frequency converter 46.

[0147] In this embodiment, the offshore medium-frequency, power-frequency, and low-frequency wind farms collect electrical energy through their respective AC collection networks (composed of submarine cables 12, 22, 32 and busbars 13, 23, 33, respectively). The collection method is flexible; it can involve collecting the AC ports of multiple individual medium-frequency, power-frequency, or low-frequency wind turbine units 112, 212, 312, or it can involve forming a single medium-frequency, power-frequency, or low-frequency wind turbine string 111, 211, 311 and then grouping and collecting the energy. The medium-frequency, power-frequency, or low-frequency AC collection submarine cables 12, 22, 32 can be used to connect individual wind turbine units or strings within the wind farm, or to connect the offshore wind farm to the corresponding AC collection busbars 13, 23, 33.

[0148] As the core of this embodiment, the intermediate frequency converter 42, power frequency converter 44, and low frequency converter 46 within the offshore integrated platform 4 can be internally composed of one or more sub-converters. When composed of multiple sub-converters, each sub-converter includes a DC port and an AC port. The DC ports of all sub-converters can be connected in series to form the DC output terminal of the converter; the AC ports of all sub-converters can be connected in parallel to form the AC input terminal of the converter. The specific circuit topology can be a voltage source converter with network construction capability. Similarly, the onshore converter station 6 and the onshore frequency converter station 9 can also contain multiple sub-converters, and modular multilevel converters with bidirectional current flow capability can be selected.

[0149] In this embodiment, a collaborative control method is also designed to ensure the stable operation of the entire system. Please refer to [link / reference]. Figure 2 The intermediate frequency converter 42, power frequency converter 44, and low frequency converter 46 located within the offshore integrated platform 4 all operate using a constant AC voltage and frequency control mode. This control mode aims to actively maintain a grid environment with constant AC voltage amplitude and frequency for each of the connected offshore intermediate frequency, power frequency, and low frequency wind power aggregation subsystems, thereby ensuring the safe and stable aggregation of large-scale offshore wind power.

[0150] Along the DC transmission path, since the three converters on the offshore side all employ the aforementioned constant AC voltage and frequency control, the DC voltage of the offshore integrated platform 4 and the DC transmission submarine cable 5 needs to be maintained stable by the control of the onshore converter station 6. For details on achieving this function, please refer to [link to relevant documentation]. Figure 3 The onshore converter station 6 operates using a constant DC voltage control mode. Furthermore, the onshore converter station 6 can also simultaneously control the reactive power on its AC side, so as to provide a certain degree of voltage support in the event of a system fault in the first onshore power grid 7.

[0151] On the low-frequency AC transmission path, the onshore frequency converter 9 is responsible for receiving low-frequency AC power transmitted from the low-frequency submarine cable 8. To ensure that the power fed into the grid is controllable, please refer to [reference needed]. Figure 4 The onshore frequency converter 9 operates using a constant power control mode. This control mode allows it to maintain a constant active power value delivered to the second land power grid 10, while also controlling the reactive power on its AC side, so that it can still provide voltage support when a system fault occurs in the second land power grid 10.

[0152] Specifically, please refer to Figure 2 The figure details the control block diagram for constant AC voltage and frequency control applied to the intermediate frequency converter 42, power frequency converter 44, and low frequency converter 46 within the offshore integrated platform 4. This control strategy employs a dual closed-loop structure, with the outer loop being the AC voltage control loop. This control is achieved by comparing the d-axis components U of the AC voltage. d and q-axis component U q Its reference value U dcref and U qref The deviation, the current reference value I required to generate the inner loop. dref and I qref Its inner loop is a current tracking control loop, responsible for accurately tracking the current reference value given by the outer loop and outputting a modulation signal M. d and M q These signals, along with the reference phase angle θ generated by the phase-locked loop, are fed into the modulation strategy module. Finally, after passing through the capacitor equalization control and triggering logic of the submodule, they generate pulse signals to drive the converter. This control method aims to actively maintain a grid environment with constant AC voltage amplitude and frequency for each connected offshore wind power aggregation subsystem, ensuring the safe and stable aggregation of large-scale offshore wind power.

[0153] Along the DC transmission path, since all three converters on the offshore side employ the aforementioned control strategy, the DC voltage of the offshore integrated platform 4 and the DC transmission submarine cable 5 needs to be maintained stable by the control of the onshore converter station 6. Please refer to... Figure 3 The figure shows the control block diagram of constant DC voltage and reactive power control used in the onshore converter station 6. This control strategy also employs a dual closed-loop structure, with the outer loop being the power control loop. One loop compares the DC voltage U... dc Its reference value U dcref The deviation generates the d-axis current reference value I. dref To stabilize the DC voltage; another loop compares the reactive power Q with its reference value Q. ref The deviation generates the q-axis current reference value I. qref To control reactive power. Its inner loop and subsequent modulation and triggering sections are related to... Figure 2The control structure shown is similar. This not only stabilizes the DC transmission link, but also provides voltage support by adjusting reactive power when a system fault occurs in the first terrestrial power grid 7.

[0154] On the low-frequency AC transmission path, the onshore frequency converter 9 is responsible for receiving low-frequency AC power transmitted from the low-frequency outgoing submarine cable 8. To ensure controllable power input to the grid, please refer to [reference needed]. Figure 4 The figure shows the control block diagram of the constant power control used in the onshore frequency converter station 9. Its outer loop power control circuit compares the active power P and reactive power Q with their reference values ​​P. ref and Q ref The deviation is used to generate current reference values ​​I for the d-axis and q-axis. dref and I qref This control method can keep the active power delivered to the second land power grid 10 constant, and can also control the reactive power on its AC side so that it can still provide voltage support when the second land power grid 10 experiences a system fault.

[0155] Example 2:

[0156] Please see Figure 5 The present invention also discloses another preferred embodiment, which demonstrates a system structure with multi-terminal DC transmission capability. The offshore portion of the system is essentially the same as the aforementioned embodiment, including an offshore medium-frequency wind power collection subsystem 1, an offshore power-frequency wind power collection subsystem 2, an offshore low-frequency wind power collection subsystem 3, and an offshore integration platform 4. The difference lies in that the system is configured with two parallel DC transmission paths and one independent low-frequency AC transmission path. Specifically, the system includes a first DC transmission submarine cable 5, a first onshore converter station 6, a first onshore power grid 7; a low-frequency transmission submarine cable 8, an onshore frequency converter station 9, a second onshore power grid 10; and newly added second DC transmission submarine cable 51, a second onshore converter station 61, and a third onshore power grid 71.

[0157] In this embodiment, the DC output terminal of the offshore integrated platform 4 is simultaneously connected to the first DC transmission submarine cable 5 and the second DC transmission submarine cable 51, thereby splitting the collected DC power into two paths and transmitting them to the first onshore converter station 6 and the second onshore converter station 61, respectively. These two onshore converter stations can employ different converter structures and capacity configurations, and the first and third land power grids 7 and 71 they are connected to can also have different AC voltage levels or network topologies. However, for stable system operation, the DC side voltage levels of the first onshore converter station 6 and the second onshore converter station 61 should remain the same and consistent with the voltage levels of the two DC transmission submarine cables 5 and 51.

[0158] To adapt to this multi-terminal DC transmission structure, the control method in this embodiment has also been adjusted accordingly. On the offshore integrated platform side, its internal intermediate frequency converter, power frequency converter, and low frequency converter all continue to use... Figure 2 The control method shown is a constant AC voltage and frequency control. On the land side, to maintain voltage stability throughout the entire DC transmission network, the first land-based converter station 6 plays a leading regulatory role, employing the following method: Figure 3 The constant DC voltage control method is shown. The second onshore converter station 61 is used to receive the remaining DC power transmitted from the offshore platform after regulation by the first onshore converter station 6; therefore, it adopts the following... Figure 4 The constant power control method shown is used to precisely control the power fed into the third land power grid 71. For low-frequency AC transmission paths, the control method of the onshore frequency converter 9 remains unchanged, continuing to employ the method shown below. Figure 4 The constant power control method shown.

[0159] like Figure 6 As shown, an embodiment of the present invention provides a method for offshore wind power collection and transmission based on a multi-port, multi-frequency AC / DC hybrid integrated platform, applicable to the offshore integrated platform of the offshore wind power collection and transmission system based on the multi-port, multi-frequency AC / DC hybrid integrated platform, and includes at least the following steps:

[0160] Step S1: Receive medium-frequency AC power transmitted from the offshore medium-frequency wind power collection subsystem; receive power frequency AC power transmitted from the offshore power frequency wind power collection subsystem; receive low-frequency AC power transmitted from the offshore low-frequency wind power collection subsystem.

[0161] Step S2: Convert the medium-frequency AC power into first DC power; convert the power frequency AC power into second DC power; convert the first low-frequency AC portion of the low-frequency AC power into third DC power;

[0162] Step S3: Boost the second low-frequency AC portion of the low-frequency AC power to generate boosted low-frequency AC power.

[0163] Step S4: Combine the first DC power, the second DC power, and the third DC power to generate combined DC power.

[0164] Step S5: The collected DC power is transmitted via the DC transmission submarine cable; the boosted low-frequency AC power is transmitted via the low-frequency transmission submarine cable.

Claims

1. A marine wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform, characterized in that, include: The system includes an offshore medium-frequency wind power collection subsystem comprising a group of medium-frequency wind turbines, an offshore power frequency wind power collection subsystem comprising a group of power frequency wind turbines, an offshore low-frequency wind power collection subsystem comprising a group of low-frequency wind turbines, an offshore integrated platform, a DC transmission submarine cable, a low-frequency transmission submarine cable, an onshore converter station, and an onshore frequency converter station. The offshore medium-frequency wind power collection subsystem is used to collect the medium-frequency AC power generated by the medium-frequency wind turbine group and transmit the medium-frequency AC power to the offshore integrated platform. The offshore industrial frequency wind power collection subsystem is used to collect the industrial frequency AC power generated by the industrial frequency wind turbine group and transmit the industrial frequency AC power to the offshore integrated platform. The offshore low-frequency wind power collection subsystem is used to collect low-frequency AC power generated by a group of low-frequency wind turbines and transmit the low-frequency AC power to the offshore integrated platform; wherein, the low-frequency AC power includes a first low-frequency AC component and a second low-frequency AC component. The offshore integrated platform is used to convert all of the received medium-frequency AC power and power frequency AC power, as well as the first low-frequency AC portion of the low-frequency AC power, into DC power, and to transmit all the converted DC power to the onshore converter station via the DC transmission submarine cable. The offshore integrated platform is also used to boost the second low-frequency AC component of the low-frequency AC power and transmit the boosted low-frequency AC power to the onshore frequency converter station via the low-frequency transmission submarine cable. The onshore converter station is used to convert the DC power transmitted from the offshore integrated platform into first-frequency AC power. The onshore frequency converter station is used to convert the boosted low-frequency AC power transmitted from the offshore integrated platform into a second power frequency AC power.

2. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 1, characterized in that, The AC collection bus of the offshore medium-frequency wind power collection subsystem is connected to the medium-frequency input terminal of the offshore integrated platform; The AC collection bus of the offshore power frequency wind power collection subsystem is connected to the power frequency input terminal of the offshore integrated platform; The AC collection bus of the offshore low-frequency wind power collection subsystem is connected to the low-frequency input terminal of the offshore integrated platform. The DC output terminal of the offshore integrated platform is connected to the DC input terminal of the onshore converter station via the DC transmission submarine cable. The low-frequency AC output terminal of the offshore integrated platform is connected to the low-frequency AC input terminal of the onshore frequency converter station via the low-frequency transmission submarine cable.

3. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 2, characterized in that, The offshore medium-frequency wind power collection subsystem includes an offshore medium-frequency wind turbine group and a medium-frequency AC collection network; The offshore medium-frequency wind turbine group includes at least one offshore medium-frequency wind farm, and the offshore medium-frequency wind farm is composed of several medium-frequency wind turbines; The medium-frequency AC aggregation network includes several medium-frequency AC aggregation submarine cables and a set of medium-frequency AC aggregation buses; the medium-frequency AC aggregation buses are the AC aggregation buses of the offshore medium-frequency wind power aggregation subsystem. The medium-frequency AC collecting submarine cable is used to connect the medium-frequency wind turbines in the offshore medium-frequency wind farm to each other and collect electrical energy to the medium-frequency AC collecting bus.

4. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 3, characterized in that, The offshore power frequency wind power aggregation subsystem includes an offshore power frequency wind turbine group and a power frequency AC aggregation network. The offshore industrial frequency wind turbine group includes at least one offshore industrial frequency wind farm, and the offshore industrial frequency wind farm is composed of several industrial frequency wind turbines. The power frequency AC aggregation network includes several power frequency AC aggregation submarine cables and a set of power frequency AC aggregation buses; the power frequency AC aggregation buses are the AC aggregation buses of the offshore power frequency wind power aggregation subsystem. The power frequency AC collecting submarine cable is used to connect the power frequency wind turbines in the offshore power frequency wind farm to each other and collect electrical energy to the power frequency AC collecting bus.

5. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 4, characterized in that, The offshore low-frequency wind power collection subsystem includes a group of offshore low-frequency wind turbine units and a low-frequency AC collection network. The offshore low-frequency wind turbine group includes at least one offshore low-frequency wind farm, and the offshore low-frequency wind farm is composed of several low-frequency wind turbines. The low-frequency AC aggregation network includes several low-frequency AC aggregation submarine cables and a set of low-frequency AC aggregation buses; the low-frequency AC aggregation buses are the AC aggregation buses of the offshore low-frequency wind power aggregation subsystem. The low-frequency AC collecting submarine cable is used to connect the low-frequency wind turbines in the offshore low-frequency wind farm to each other and collect electrical energy to the low-frequency AC collecting bus.

6. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 5, characterized in that, The marine integrated platform includes an intermediate frequency converter, a power frequency converter, a low frequency converter, an intermediate frequency transformer, a power frequency transformer, and a low frequency transformer. The input terminal of the intermediate frequency transformer is the intermediate frequency input terminal of the offshore integrated platform; The output terminal of the intermediate frequency transformer is connected to the AC side of the intermediate frequency converter; The input terminal of the power frequency transformer is the power frequency input terminal of the offshore integrated platform; The output terminal of the power frequency transformer is connected to the AC side of the power frequency converter. The input terminal of the low-frequency transformer is the low-frequency input terminal of the offshore integrated platform; The voltage matching output terminal of the low-frequency transformer is connected to the AC side of the low-frequency converter. The step-up output terminal of the low-frequency transformer is the low-frequency AC output terminal of the offshore integrated platform; The positive DC terminal of the intermediate frequency converter, the positive DC terminal of the power frequency converter, and the positive DC terminal of the low frequency converter are interconnected to form a positive DC bus. The negative DC terminal of the intermediate frequency converter, the negative DC terminal of the power frequency converter, and the negative DC terminal of the low frequency converter are interconnected to form a negative DC bus. The positive DC bus and the negative DC bus together constitute the DC output terminal of the offshore integrated platform.

7. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 6, characterized in that, The power frequency AC output terminal of the onshore converter station is connected to the first land power grid through the first connecting transformer; The power frequency AC output terminal of the land-based frequency converter station is connected to the second land power grid through a second connecting transformer.

8. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 7, characterized in that, The intermediate frequency converter, the power frequency converter, and the low frequency converter all operate using a constant AC voltage and frequency control method. The onshore converter station operates using a constant DC output voltage control method; The onshore frequency converter station operates using a constant power control method.

9. The offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in claim 8, characterized in that, The offshore medium-frequency wind power collection subsystem operates at a medium-frequency frequency greater than a preset Hertz value; The offshore power frequency wind power collection subsystem operates at a power frequency equal to a preset Hertz value; The offshore low-frequency wind power collection subsystem operates at a low frequency less than a preset Hertz value. The second low-frequency AC section, output from the marine integrated platform to the low-frequency transmission submarine cable, operates at a transmission frequency lower than a preset Hertz value; The onshore converter station is used to control the frequency of the first power frequency AC power it generates at a preset Hertz value; The onshore frequency converter station is used to control the frequency of the second power frequency AC power it generates at a preset Hertz value.

10. A method for offshore wind power collection and transmission based on a multi-port, multi-frequency AC / DC hybrid integrated platform, applicable to the offshore integrated platform of the offshore wind power collection and transmission system based on a multi-port, multi-frequency AC / DC hybrid integrated platform as described in any one of claims 1-9, characterized in that, include: Receives medium-frequency AC power transmitted from the offshore medium-frequency wind power collection subsystem; Receives AC power transmitted from the offshore power frequency wind power collection subsystem; Receive low-frequency AC power transmitted from the offshore low-frequency wind power collection subsystem; The intermediate frequency AC power is converted into the first DC power. The power frequency AC power is converted into a second DC power. The first low-frequency AC component of the low-frequency AC power is converted into a third DC power. The second low-frequency AC component of the low-frequency AC power is boosted to generate boosted low-frequency AC power. The first DC power, the second DC power, and the third DC power are combined to generate combined DC power. The collected DC power is transmitted via the DC transmission submarine cable; The boosted low-frequency AC power is transmitted via the low-frequency transmission submarine cable.

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