Offshore wind power direct-current delivery system

Abstract

An offshore wind power direct-current delivery system, which relates to the technical field of direct-current power transmission. The system comprises an onshore direct-current switching station, multiple offshore converter stations, and multiple onshore converter units; an alternating-current side of each offshore converter station is connected to a wind turbine set, and a direct-current side of each offshore converter station is connected, by means of a direct-current cable, to an input side of a bus bar of the onshore direct-current switching station; an input side of each bus bar is configured with a direct-current switch used to connect to a direct-current cable, an output side of each bus bar is connected to a direct-current overhead line by means of a direct-current circuit breaker, each direct-current overhead line is connected to a direct-current side of an onshore converter unit by means of the direct-current circuit breaker, and each direct-current overhead line is connected to more than one onshore converter unit; a direct-current side of each onshore converter unit is configured with a direct-current high-speed parallel switch and, by means of the direct-current high-speed parallel switch, is connected to a direct-current overhead line, and an alternating-current side of each onshore converter unit is connected to one load center; and the offshore converter stations and the onshore converter units all adopt a half-bridge MMC topology. The present application can achieve reliable and low-cost super-large-capacity direct-current delivery.

Description

Offshore wind power DC transmission system

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 20, 2023, with application number 202311548726.4 and invention name “Offshore Wind Power DC Transmission System”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of direct current (DC) transmission, and in particular to an offshore wind power DC transmission system. Background Art

[0003] In recent years, to promote energy transition, my country's policies have strongly supported the development and utilization of offshore wind power. Offshore wind power development has trended from nearshore, shallow-water, small-scale demonstration projects to offshore, deep-water, large-scale, centralized development. Transmission methods for connecting offshore wind power to onshore power grids include high-voltage AC (HVAC) and high-voltage DC (HVDC). High-voltage AC is suitable for nearshore wind power. However, when offshore wind power exceeds a certain distance from shore, long-distance AC cable transmission presents challenges such as excessive charging power, resulting in voltage increases requiring compensation and overvoltage. High-voltage AC transmission is difficult to meet the needs of large-capacity, long-distance offshore wind power transmission and is also costly.

[0004] High-voltage direct current (HVDC) transmission offers advantages such as the absence of synchronization with the onshore power grid, long transmission distances, and flexible operation and regulation. This makes it particularly suitable for large-capacity, long-distance transmission scenarios. Because flexible direct current (HVDC) eliminates commutation failures, independently regulates active and reactive power, and produces low harmonic levels, it is currently the mainstream method for transmitting large-scale, offshore wind power from offshore locations to onshore power grids. To achieve ultra-high-capacity transmission, a multi-terminal flexible direct current (HVDC) transmission solution is required, but current HVDC system architectures make it difficult to achieve stable transmission of ultra-large capacities.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide an offshore wind power DC transmission system that can achieve reliable and low-cost ultra-large capacity DC transmission and improve system stability.

[0007] This application provides an offshore wind power DC transmission system.

[0008] Including: onshore DC switch station, multiple offshore converter stations and multiple onshore converter units;

[0009] The AC side of the offshore converter station is used to connect to the wind turbine generator set, and the DC side of the offshore converter station is connected to the input side of the busbar of the onshore DC switch station through a DC cable;

[0010] The input side of the busbar is provided with a DC switch for connecting to a DC cable. The output side of the busbar is connected to a DC overhead line via a DC circuit breaker. The DC overhead line is connected to the DC side of the onshore converter unit via a DC circuit breaker. Each DC overhead line is connected to more than one onshore converter unit.

[0011] The DC side of the onshore converter unit is configured with a DC high-speed parallel switch, which is connected to the DC overhead line via the DC high-speed parallel switch. The AC side of each onshore converter unit is used to connect to a load center;

[0012] Wherein, the offshore converter station and the onshore converter unit both adopt a half-bridge MMC topology structure.

[0013] In one embodiment, the DC switch configured on the input side of the busbar includes a DC high-speed parallel switch or a DC circuit breaker.

[0014] In one embodiment, a DC energy dissipation device is configured between the positive electrode and the negative electrode of the busbar.

[0015] In one embodiment, the offshore converter station and the onshore converter unit both adopt a symmetrical monopole topology structure;

[0016] The positive pole of the busbar of the onshore DC switch station is connected to the positive terminals of two or more onshore converter units via the first DC overhead line of each loop, and the negative pole of the busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop;

[0017] The positive terminals of the onshore converter units in the same circuit are interconnected via a third DC overhead line, and the negative terminals of the onshore converter units in the same circuit are interconnected via a fourth DC overhead line.

[0018] The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, and the negative pole of the busbar is connected to the negative terminal of the offshore converter station to which the first DC cable in the same loop is connected via the second DC cable of each loop.

[0019] In one embodiment,

[0020] The offshore converter station and the onshore converter unit both adopt a symmetrical monopole topology structure;

[0021] The positive pole of the busbar of the onshore DC switch station is connected to the positive terminal of at least one onshore converter unit via the first DC overhead line of each loop, and the negative pole busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop;

[0022] The DC side of the onshore converter unit in each loop is interconnected with the DC side of the onshore converter unit in at least one different loop, wherein the positive terminals of each onshore converter unit are interconnected via a third DC overhead line, and the negative terminals are interconnected via a fourth DC overhead line;

[0023] The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, and the negative pole of the busbar is connected to the negative terminal of the offshore converter station to which the first DC cable in the same loop is connected via the second DC cable of each loop.

[0024] In one embodiment, a DC high-speed parallel switch is configured at the outlet where the onshore converter unit is connected to the third DC overhead line, and a DC high-speed parallel switch is configured at the outlet where the onshore converter unit is connected to the fourth DC overhead line.

[0025] In one embodiment, the offshore converter station and the onshore converter unit both adopt a bipolar topology structure;

[0026] The positive pole of the busbar of the onshore DC switch station is connected to the positive terminals of two or more onshore converter units via the first DC overhead line of each loop, the negative pole of the busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop, and the neutral line of the busbar is connected to the neutral line of the onshore converter unit via the fifth DC overhead line of each loop;

[0027] The neutral line of the busbar is connected to the fifth DC overhead line via an AC circuit breaker, and the neutral line of the onshore converter unit is connected to the fifth DC overhead line via an AC circuit breaker;

[0028] The positive terminals of the onshore converter units in the same circuit are interconnected via a third DC overhead line, the negative terminals of the onshore converter units in the same circuit are interconnected via a fourth DC overhead line, and the neutral lines of the onshore converter units in the same circuit are interconnected via a sixth DC overhead line.

[0029] The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, the negative pole of the busbar is connected to the negative terminal of the offshore converter station to which the first DC cable in the same loop is connected via the second DC cable of each loop, the neutral line of the busbar is connected to the neutral line of the offshore converter station to which the first DC cable in the same loop is connected via the third DC cable of each loop, and the neutral line of the busbar is connected to the third DC cable via an AC circuit breaker.

[0030] In one embodiment, the offshore converter station and the onshore converter unit both adopt a bipolar topology structure;

[0031] The positive pole of the busbar of the onshore DC switch station is connected to the positive terminal of at least one onshore converter unit via the first DC overhead line of each loop, the negative pole of the busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop, and the neutral line of the busbar is connected to the neutral line of the onshore converter unit via the fifth DC overhead line of each loop;

[0032] The neutral line of the busbar is connected to the fifth DC overhead line via an AC circuit breaker, and the neutral line of the onshore converter unit is connected to the fifth DC overhead line via an AC circuit breaker;

[0033] The DC side of the onshore converter unit in each circuit is interconnected with the DC side of the onshore converter unit in at least one different circuit, wherein the positive terminals of each onshore converter unit are interconnected via a third DC overhead line, the negative terminals are interconnected via a fourth DC overhead line, and the neutral terminals are interconnected via a sixth DC overhead line;

[0034] The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, the negative pole of the busbar is connected to the negative terminal of the offshore converter station to which the first DC cable in the same loop is connected via the second DC cable of each loop, the neutral line of the busbar is connected to the neutral line of the offshore converter station to which the first DC cable in the same loop is connected via the third DC cable of each loop, and the neutral line of the busbar is connected to the third DC cable via an AC circuit breaker.

[0035] In one embodiment, a DC high-speed parallel switch is configured at the outlet where the onshore converter unit is connected to the third DC overhead line, a DC high-speed parallel switch is configured at the outlet where the onshore converter unit is connected to the fourth DC overhead line, and an AC circuit breaker is configured at the outlet where the onshore converter unit is connected to the sixth DC overhead line.

[0036] In one embodiment, the AC sides of two or more of the onshore converter units are interconnected.

[0037] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0038] The offshore wind power DC transmission system provided in this application includes an onshore DC switch station and multiple offshore converter stations and multiple onshore converter units, all of which adopt a half-bridge MMC topology structure. Power is transmitted via DC cables on the offshore side and via DC overhead lines on the onshore side. The offshore and onshore sides are connected by busbars of the onshore DC switch station, thereby reducing the transmission cost of large-capacity offshore wind power, saving transmission corridors, and being able to support transmission needs on a scale of tens of millions of kilowatts. DC circuit breakers are configured at both ends of the DC overhead lines to achieve fault isolation. When both the offshore converter station and the onshore converter units adopt a half-bridge MMC topology structure that does not have DC fault clearing capability, this ensures that the system can reliably achieve fault isolation in the event of a fault, thereby improving system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0040] FIG1 is a schematic structural diagram of an offshore wind power DC transmission system in one embodiment;

[0041] FIG2 is a schematic diagram of a converter station topology structure using a symmetrical monopole topology in one embodiment;

[0042] FIG3 is a schematic structural diagram of an offshore wind power DC transmission system using a symmetrical monopole topology and a single-circuit overhead line in one embodiment;

[0043] FIG4 is a schematic structural diagram of an offshore wind power DC transmission system using a symmetrical monopole topology and multiple overhead lines in one embodiment;

[0044] FIG5 is a schematic structural diagram of an offshore wind power DC transmission system using a bipolar topology and a single-circuit overhead line in one embodiment;

[0045] FIG6 is a schematic structural diagram of an offshore wind power DC transmission system using a bipolar topology and multiple overhead lines in one embodiment;

[0046] FIG7 is a schematic structural diagram of an offshore wind power DC transmission system using a bipolar topology and multiple overhead lines in another embodiment. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0048] As shown in FIG1 , an embodiment of the present application provides an offshore wind power DC transmission system, comprising: an onshore DC switch station 110 , multiple offshore converter stations 120 , and multiple onshore converter units 130 . Both the offshore converter stations 120 and the onshore converter units 130 adopt a half-bridge MMC topology structure. The AC side of the offshore converter station 120 is used to connect to the wind turbine WT, and the DC side of the offshore converter station 120 is connected to the input side of the busbar of the onshore DC switch station 110 through a DC cable. The input side of the busbar is equipped with a DC switch 111 for connecting to the DC cable. The output side of the busbar is connected to the DC overhead line via a DC circuit breaker DCCB (Direct Current Circuit Breaker). The DC overhead line is connected to the DC side of the onshore converter unit 130 via the DC circuit breaker DCCB, and the DC overhead line of each loop is connected to more than one onshore converter unit 130. The DC side of the onshore converter unit 130 is equipped with a DC high-speed parallel switch HSS, which is connected to the DC overhead line via the DC high-speed parallel switch HSS. The AC side of each onshore converter unit 130 is used to connect to a load center G.

[0049] The core components of the modular multilevel converter (MMC) are the sub-modules connected in series in the bridge arms. The half-bridge MMC topology is a topology in which the sub-modules adopt half-bridge sub-modules. The half-bridge MMC topology is widely used in offshore wind power DC transmission systems due to its low cost and wide application range. However, the half-bridge sub-modules do not have the ability to clear DC faults. Once a fault occurs in the DC line of the flexible DC transmission system, the converter and DC-side energy storage elements will discharge rapidly, causing the fault current to reach the upper tolerance limit of the power electronic devices within milliseconds, threatening the safety of equipment and system operation. Referring to Figure 2 (taking a symmetrical single-pole topology as an example), in this embodiment, both the offshore converter and the onshore converter adopt a half-bridge MMC topology and do not have the ability to clear DC faults. DC circuit breakers (DCCBs) are configured on both sides of the DC overhead line. The DC circuit breakers (DCCBs) can achieve rapid disconnection and isolation of DC faults. When a DC fault occurs, the DC circuit breakers (DCCBs) on both sides of the DC overhead line can achieve fault isolation, improving the stability of system operation.

[0050] In addition, this embodiment proposes a transmission method using DC cables on the offshore side and DC overhead lines on the onshore side. Compared with the method of using DC land cables for the onshore transmission portion in Europe, this can significantly reduce costs. Compared with the method of using AC overhead lines for the onshore transmission portion currently adopted in my country, the number of transmission corridors can be reduced in large-scale offshore wind power transmission. The DC overhead line of each loop can be connected to multiple onshore converter units 130 within the capacity allowable range, further saving transmission corridors and reducing costs. In this embodiment, an onshore DC switch station 110 is set on land to connect the DC cable and the DC overhead line, thereby realizing conversion between the offshore cable and the overhead line. In long-distance transmission, the DC switch 111 of the onshore DC switch station 110 is used to achieve fault clearance of the faulty line portion, avoiding the impact on the entire transmission line when the fault is cleared, thereby improving the flexibility of the system power supply.

[0051] Among them, the DC cable includes a DC submarine cable and / or a DC land cable. Since the busbar may be located in an onshore area at a certain distance from the coastline, the DC submarine cable is used for the offshore transmission part, and the DC land cable is used for transmission between the coastline and the busbar.

[0052] In some embodiments, an onshore converter unit refers to an onshore converter station. In other embodiments, an onshore converter unit refers to a single converter unit in a single onshore converter station.

[0053] In some embodiments, the load center to which different onshore converter units are connected may be the same load center, or may be connected to different load centers.

[0054] The offshore wind power DC transmission system provided in this application includes an onshore DC switch station 110, multiple offshore converter stations 120, and multiple onshore converter units 130, all of which adopt a half-bridge MMC topology. Power is transmitted via DC cables on the offshore side and via DC overhead lines on the onshore side. The offshore and onshore sides are connected via busbars of the onshore DC switch station 110, thereby reducing the transmission cost of large-capacity offshore wind power, saving transmission corridors, and being able to support transmission needs of tens of millions of kilowatts. DC circuit breakers (DCCBs) are configured at both ends of the DC overhead lines to achieve fault isolation. When both the offshore converter station 120 and the onshore converter units 130 adopt a half-bridge MMC topology that does not have DC fault clearing capabilities, this ensures that the system can reliably achieve fault isolation in the event of a fault, thereby improving system stability.

[0055] In one embodiment, the DC switch 111 configured on the input side of the busbar is a DC circuit breaker DCCB.

[0056] A DC circuit breaker DCCB is configured on the input side of the busbar to connect to the DC cable. When a DC fault occurs, the DC circuit breaker DCCB can cut off the short-circuit current in the DC cable to achieve fault isolation.

[0057] In one embodiment, the DC switch 111 configured at the input side of the busbar is a DC high-speed parallel switch HSS.

[0058] Deploying a high-speed DC paralleling switch (HSS) on the input side of the busbar and connected to the DC cable isolates faults, improving the reliability and availability of the entire DC system. Using the HSS prevents DC system power interruptions during the commissioning and decommissioning of converter stations. While HSSs cannot interrupt high DC currents, they offer lower cost, smaller size, and simpler structure than DC circuit breakers (DCCBs). When used in conjunction with DC circuit breakers on DC overhead lines, they can also provide reliable fault isolation.

[0059] As shown in FIG3 , in one embodiment, a DC energy dissipation device 140 is disposed between the positive and negative poles of the busbar; wherein a first end of the DC energy dissipation device 140 is connected to the positive pole DC+ of the busbar, and a second end of the DC energy dissipation device 140 is connected to the negative pole DC- of the busbar.

[0060] To further ensure the system's fault clearing capability when a DC fault occurs, a DC energy dissipation device 140 can be configured between the positive and negative poles of the busbar. After the DC circuit breaker DCCB clears the DC fault, the DC energy dissipation device 140 can operate at full voltage to achieve surplus power balance during the DC fault.

[0061] In one embodiment, if the offshore converter station 120 or the wind turbine is equipped with an energy dissipation device, the DC energy dissipation device 140 may not be configured, and surplus power balance can be achieved through the energy dissipation device of the offshore converter station 120 or the energy dissipation device of the wind turbine. However, this method has higher requirements on the configuration of the offshore converter station 120 or the wind turbine and the cost investment is relatively large.

[0062] 3 , in one embodiment, the offshore converter station 120 and the onshore converter unit 130 both have a symmetrical monopole topology. The positive DC+ busbar of the onshore DC switch station 110 is connected to the positive terminals of two or more onshore converter units 130 via the first DC overhead line of each circuit, and the negative DC- busbar is connected to the negative terminal of the onshore converter unit 130 connected to the first DC overhead line in the same circuit via the second DC overhead line. The positive terminals of the onshore converter units 130 in the same circuit are interconnected via the third DC overhead line, and the negative terminals of the onshore converter units 130 in the same circuit are interconnected via the fourth DC overhead line. The positive DC+ busbar is connected to the positive terminal of one offshore converter station 120 via the first DC cable of each circuit, and the negative DC- busbar is connected to the negative terminal of the offshore converter station 120 connected to the first DC cable in the same circuit via the second DC cable of each circuit.

[0063] In this embodiment, a converter station with a symmetrical monopole topology is used. For converter stations in large-scale offshore wind power transmission systems, the symmetrical monopole topology can employ an odd or even number of flexible DC transformers, allowing for greater room for optimization of system equipment configuration. The capacity of a single onshore converter unit 130 is greater than that of a single offshore converter station 120. Within the permitted capacity range, a single overhead line can simultaneously connect to multiple converter stations. In one embodiment, a high-speed DC parallel switch (HSS) is configured on the third DC overhead line, and a high-speed DC parallel switch (HSS) is configured on the fourth DC overhead line. When fault isolation is required on the third or fourth DC overhead line, especially when the electrical distance between the third and fourth DC overhead lines reaches a certain distance, isolation can be achieved using the high-speed DC parallel switch (HSS), thereby improving system stability.

[0064] As shown in FIG4 , in one embodiment, the offshore converter station 120 and the onshore converter unit 130 both adopt a symmetrical monopole topology, and the DC overhead line adopts a multi-circuit connection; the positive pole DC+ of the busbar of the onshore DC switch station 110 is connected to the positive terminal of at least one onshore converter unit 130 via the first DC overhead line of each single circuit, and the negative pole DC- of the busbar is connected to the negative terminal of the onshore converter unit 130 connected to the first DC overhead line in the same circuit via the second DC overhead line of each single circuit; the onshore DC line in each circuit The DC side of the upper converter unit 130 is interconnected with the DC side of at least one onshore converter unit 130 of a different circuit, wherein the positive terminal of each onshore converter unit 130 is interconnected through a third DC overhead line, and the negative terminal is interconnected through a fourth DC overhead line; the positive pole DC+ of the busbar is connected to the positive terminal of an offshore converter station 120 via the first DC cable of each single circuit, and the negative pole DC- of the busbar is connected to the negative terminal of the offshore converter station 120 connected to the first DC cable in the same circuit via the second DC cable of each single circuit.

[0065] In this embodiment, "multiple circuits" can be two or more circuits. Multi-circuit wiring ensures that when one circuit fails, the other circuits can maintain the normal operation of the onshore converter unit 130 and the corresponding load center G, thereby ensuring power reliability. In one embodiment, a DC high-speed parallel switch (HSS) is configured at the outlet where the onshore converter unit connects to the third DC overhead line, and a DC high-speed parallel switch (HSS) is configured at the outlet where the onshore converter unit connects to the fourth DC overhead line. When fault isolation is required on the third or fourth DC overhead line, especially when the electrical distance between the third and fourth DC overhead lines reaches a certain distance, isolation can be achieved using the DC high-speed parallel switch (HSS), thereby improving system stability.

[0066] As shown in FIG5 , in one embodiment, the offshore converter station 120 and the onshore converter unit 130 both adopt a bipolar topology structure; the positive pole DC+ of the busbar of the onshore DC switch station 110 is connected to the positive terminals of two or more onshore converter units 130 via the first DC overhead line of each loop, the negative pole DC- of the busbar is connected to the negative terminal of the onshore converter unit 130 connected to the first DC overhead line in the same loop via the second DC overhead line of each loop, and the neutral line N of the busbar is connected to the neutral line of the onshore converter unit 130 via the fifth DC overhead line of each loop; the neutral line N of the busbar is connected to the fifth DC overhead line via the AC circuit breaker BRK (Breaker), and the neutral line of the onshore converter unit 130 is connected to the fifth DC overhead line via the AC circuit breaker BRK; the same The positive terminals of the onshore converter units 130 in the loop are interconnected via a third DC overhead line, the negative terminals of the onshore converter units 130 in the same loop are interconnected via a fourth DC overhead line, and the neutral lines of the onshore converter units 130 in the same loop are interconnected via a sixth DC overhead line. The positive pole DC+ of the busbar is connected to the positive pole of an offshore converter station 120 via the first DC cable of each loop, the negative pole DC- of the busbar is connected to the negative pole of the offshore converter station 120 connected to the first DC cable in the same loop via the second DC cable of each loop, the neutral line of the busbar is connected to the neutral line of the offshore converter station 120 connected to the first DC cable in the same loop via the third DC cable of each loop, and the neutral line N of the busbar is connected to the third DC cable via an AC circuit breaker BRK.

[0067] When a bipolar topology is adopted, the DC circuit breaker DCCB on the pole line can be operated to isolate the loop fault current. The neutral line N of the busbar is configured with an AC circuit breaker BRK and connected to the fifth DC overhead line. The neutral line of the onshore converter unit 130 is also configured with an AC circuit breaker BRK and connected to the fifth DC overhead line. The AC circuit breaker BRK has a low cost and can reduce the cost of the system. Similarly, on the offshore side, the neutral line N of the busbar is configured with an AC circuit breaker BRK and connected to the third DC cable.

[0068] As shown in FIG6 , in one embodiment, the offshore converter station 120 and the onshore converter unit 130 both adopt a bipolar topology structure; the positive pole DC+ of the busbar of the onshore DC switch station 110 is connected to the positive terminal of at least one onshore converter unit 130 via the first DC overhead line of each loop, the negative pole DC- of the busbar is connected to the negative terminal of the onshore converter unit 130 connected to the first DC overhead line in the same loop via the second DC overhead line of each loop, and the neutral line N of the busbar is connected to the neutral line of the onshore converter unit 130 via the fifth DC overhead line of each loop; the neutral line N of the busbar is connected to the fifth DC overhead line via the AC circuit breaker BRK, and the neutral line of the onshore converter unit 130 is connected to the fifth DC overhead line via the AC circuit breaker BRK; the onshore converter unit in each loop The DC side of the unit 130 is interconnected with the DC side of at least one onshore converter unit 130 of a different circuit, wherein the positive terminal of each onshore converter unit 130 is interconnected via a third DC overhead line, the negative terminal is interconnected via a fourth DC overhead line, and the neutral line is interconnected via a sixth DC overhead line; the positive pole DC+ of the busbar is connected to the positive terminal of an offshore converter station 120 via the first DC cable of each circuit, the negative pole DC- of the busbar is connected to the negative terminal of the offshore converter station 120 connected to the first DC cable in the same circuit via the second DC cable of each circuit, the neutral line N of the busbar is connected to the neutral line of the offshore converter station 120 connected to the first DC cable in the same circuit via the third DC cable of each circuit, and the neutral line N of the busbar is connected to the third DC cable via an AC circuit breaker BRK.

[0069] In this embodiment, a multi-circuit interconnected wiring scheme is employed. If one circuit fails, the remaining circuits can maintain normal operation of the onshore converter unit 130 and the corresponding load center G, ensuring power reliability. In a bipolar topology, since there is no need for fault isolation in the event of a neutral line fault, the neutral line N of the busbar is connected to the fifth DC overhead line with an AC circuit breaker BRK. The neutral line of the onshore converter unit 130 is also connected to the fifth DC overhead line with an AC circuit breaker BRK. The AC circuit breaker BRK is relatively low-cost, reducing system costs. Similarly, on the offshore side, the neutral line N of the busbar is connected to the third DC cable with an AC circuit breaker BRK. In one embodiment, a DC high-speed paralleling switch (HSS) is configured at the onshore converter unit's exit from the third DC overhead line, a DC high-speed paralleling switch (HSS) is configured at the onshore converter unit's exit from the fourth DC overhead line, and an AC circuit breaker BRK is configured at the onshore converter unit's exit from the sixth DC overhead line.

[0070] 7 , in one embodiment, when the offshore converter station 120 and the onshore converter unit 130 adopt a bipolar topology, the offshore side can share a neutral line to reduce costs; the onshore side can share a neutral line to reduce costs.

[0071] 4 to 7 , in one embodiment, the AC sides of two or more onshore converter units 130 are interconnected.

[0072] In this embodiment, the AC sides of two or more onshore converter units 130 are interconnected to enable the onshore converter units 130 to participate in the construction of the load center G power grid. The onshore converter units 130 do not need to perform load allocation. The interconnected onshore converter units 130 on the AC side and the load centers G to which they are respectively connected together constitute a large power grid, which can automatically coordinate the load internally and improve the safe and stable operation level of the power grid.

[0073] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0074] Furthermore, 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 the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0075] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediate element. In addition, the "connection" in the embodiments of the present application should be understood as "electrical connection", "communication connection", etc., if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0076] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referenced to each other.

[0077] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An offshore wind power DC transmission system, characterized in that: include: Onshore DC switch station, multiple offshore converter stations and multiple onshore converter units; The AC side of the offshore converter station is used to connect the wind turbines, and the DC side of the offshore converter station is connected to the input side of the busbar of the onshore DC switch station through a DC cable; The input side of the busbar is provided with a DC switch for connecting to a DC cable, the output side of the busbar is connected to a DC overhead line via a DC circuit breaker, the DC overhead line is connected to the DC side of the onshore converter unit via a DC circuit breaker, and each DC overhead line is connected to more than one onshore converter unit; The DC side of the onshore converter unit is equipped with a DC high-speed parallel switch, which is connected to the DC overhead line through the DC high-speed parallel switch. The AC side of each onshore converter unit is used to connect to a load center; Wherein, the offshore converter station and the onshore converter unit both adopt a half-bridge MMC topology structure.

2. The offshore wind power DC transmission system according to claim 1, characterized in that: The DC switch configured at the input side of the busbar includes a DC high-speed parallel switch or a DC circuit breaker.

3. The offshore wind power DC transmission system according to claim 1 or 2, characterized in that: A DC energy dissipation device is arranged between the positive pole and the negative pole of the busbar.

4. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit both adopt a symmetrical monopole topology structure; The positive pole of the busbar of the onshore DC switch station is connected to the positive terminals of two or more onshore converter units via the first DC overhead line of each loop, and the negative pole of the busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop; The positive terminals of the onshore converter units in the same circuit are interconnected through a third DC overhead line, and the negative terminals of the onshore converter units in the same circuit are interconnected through a fourth DC overhead line; The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, and the negative pole of the busbar is connected to the negative terminal of the offshore converter station connected to the first DC cable in the same loop via the second DC cable of each loop.

5. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit both adopt a symmetrical monopole topology structure; The positive pole of the busbar of the onshore DC switch station is connected to the positive terminal of at least one onshore converter unit via the first DC overhead line of each loop, and the negative pole busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop; The DC side of the onshore converter unit in each loop is interconnected with the DC side of the onshore converter unit of at least one different loop, wherein the positive terminal of each onshore converter unit is interconnected through a third DC overhead line, and the negative terminal is interconnected through a fourth DC overhead line; The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, and the negative pole of the busbar is connected to the negative terminal of the offshore converter station connected to the first DC cable in the same loop via the second DC cable of each loop.

6. The offshore wind power DC transmission system according to claim 4 or 5, characterized in that: A DC high-speed parallel switch is configured at an outlet where the onshore converter unit is connected to the third DC overhead line, and a DC high-speed parallel switch is configured at an outlet where the onshore converter unit is connected to the fourth DC overhead line.

7. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit both adopt a bipolar topology structure; The positive pole of the busbar of the onshore DC switch station is connected to the positive terminals of more than two onshore converter units via the first DC overhead line of each loop, the negative pole of the busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop, and the neutral line of the busbar is connected to the neutral line of the onshore converter unit via the fifth DC overhead line of each loop; The neutral line of the busbar is connected to the fifth DC overhead line via an AC circuit breaker, and the neutral line of the onshore converter unit is connected to the fifth DC overhead line via an AC circuit breaker; The positive terminals of the onshore converter units in the same circuit are interconnected through the third DC overhead line, the negative terminals of the onshore converter units in the same circuit are interconnected through the fourth DC overhead line, and the neutral lines of the onshore converter units in the same circuit are interconnected through the sixth DC overhead line; The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, and the negative pole of the busbar is connected to the positive terminal of the offshore converter station via the second DC cable of each loop. The neutral line of the busbar is connected to the negative terminal of an offshore converter station connected to a DC cable, the neutral line of the busbar is connected to the neutral line of the offshore converter station connected to the first DC cable in the same circuit via the third DC cable of each circuit, and the neutral line of the busbar is connected to the third DC cable via an AC circuit breaker.

8. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit both adopt a bipolar topology structure; The positive pole of the busbar of the onshore DC switch station is connected to the positive terminal of at least one onshore converter unit via the first DC overhead line of each loop, the negative pole of the busbar is connected to the negative terminal of the onshore converter unit connected to the first DC overhead line in the same loop via the second DC overhead line of each loop, and the neutral line of the busbar is connected to the neutral line of the onshore converter unit via the fifth DC overhead line of each loop; The neutral line of the busbar is connected to the fifth DC overhead line via an AC circuit breaker, and the neutral line of the onshore converter unit is connected to the fifth DC overhead line via an AC circuit breaker; The DC side of the onshore converter unit in each loop is interconnected with the DC side of the onshore converter unit of at least one different loop, wherein the positive terminal of each onshore converter unit is interconnected through a third DC overhead line, the negative terminal is interconnected through a fourth DC overhead line, and the neutral line is interconnected through a sixth DC overhead line; The positive pole of the busbar is connected to the positive terminal of an offshore converter station via the first DC cable of each loop, the negative pole of the busbar is connected to the negative terminal of the offshore converter station connected to the first DC cable in the same loop via the second DC cable of each loop, the neutral line of the busbar is connected to the neutral line of the offshore converter station connected to the first DC cable in the same loop via the third DC cable of each loop, and the neutral line of the busbar is connected to the third DC cable via an AC circuit breaker.

9. The offshore wind power DC transmission system according to claim 7 or 8, characterized in that: A DC high-speed parallel switch is configured at the outlet where the onshore converter unit is connected to the third DC overhead line, a DC high-speed parallel switch is configured at the outlet where the onshore converter unit is connected to the fourth DC overhead line, and an AC circuit breaker is configured at the outlet where the onshore converter unit is connected to the sixth DC overhead line.

10. The offshore wind power DC transmission system according to claim 1, characterized in that: The AC sides of two or more of the above-mentioned onshore converter units are interconnected.

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