Offshore wind power direct current transmission system

Abstract

An offshore wind power direct current transmission system, relating to the technical field of direct current power transmission. The system comprises an onshore direct current switch station, a plurality of offshore converter stations, and a plurality of onshore converter units; alternating current sides of the offshore converter stations are connected to wind turbine generators, and direct current sides of the offshore converter stations are connected to an input side of a bus bar of the onshore direct current switch station by means of direct current cables; an output side of the bus bar is connected to the onshore converter units by means of direct current overhead lines, and direct current circuit breakers are arranged on at least one of the input side and the output side of the bus bar; and direct current sides of the onshore converter units are connected to the direct current overhead lines by means of direct current high-speed parallel switches, each direct current overhead line is connected to one or more onshore converter units, and an alternating current side of each onshore converter unit is connected to one load center, wherein each offshore converter station uses a half-bridge MMC topological structure, and each onshore converter unit uses a topological structure having direct current fault clearing capability. The present application can realize reliable and low-cost ultra-large capacity direct current transmission.

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 202311554951.9 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, comprising:

[0008] Onshore DC switch stations, 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 output side of the busbar is connected to the DC side of the onshore converter unit via a DC overhead line, and a DC circuit breaker is configured on the pole line of at least one of the input side and the output side of the busbar;

[0011] The DC side of the onshore converter unit is connected to the DC overhead line via a DC high-speed parallel switch. Each DC overhead line is connected to more than one onshore converter unit. The AC side of each onshore converter unit is used to connect to a load center.

[0012] The offshore converter station adopts a half-bridge MMC topology structure, and the onshore converter unit adopts a topology structure with DC fault clearing capability.

[0013] In one embodiment, the offshore converter station and the onshore converter unit adopt symmetrical monopole connection, the input side of the busbar is configured with a DC circuit breaker connected to a DC cable, and the output side of the busbar is directly connected to a DC overhead line, connected to a DC overhead line via a DC circuit breaker, or connected to a DC overhead line via an AC circuit breaker.

[0014] In one embodiment, when the output side of the busbar is directly connected to the DC overhead line or connected to the DC overhead line via an AC circuit breaker, a DC energy dissipation device is arranged between the positive and negative poles of the busbar;

[0015] The first end of the DC energy consuming device is connected to the positive pole of the busbar via a DC cable equipped with a DC circuit breaker, and the second end of the DC energy consuming device is connected to the negative pole of the busbar via a DC cable equipped with a DC circuit breaker.

[0016] In one embodiment, when the output side of the busbar is connected to the DC overhead line via a DC circuit breaker, a DC energy dissipation device is disposed between the positive and negative poles of the busbar.

[0017] In one embodiment, the offshore converter station and the onshore converter unit adopt bipolar wiring, the positive and negative poles of the busbar are both equipped with DC circuit breakers and connected to DC cables on the input side, and the neutral line of the busbar is equipped with an AC circuit breaker and connected to the DC cable on the input side;

[0018] The output sides of the positive pole, negative pole and neutral line of the busbar are directly connected to the DC overhead line;

[0019] or,

[0020] The positive and negative poles of the busbar are connected to the DC overhead line via DC circuit breakers on the output side, and the neutral line is connected to the DC overhead line via an AC circuit breaker on the output side.

[0021] In one embodiment, the offshore converter station and the onshore converter unit adopt symmetrical single-pole connection, the input side of the busbar is configured with a DC high-speed parallel switch connected to a DC cable, and the output side of the busbar is configured with a DC circuit breaker connected to a DC overhead line.

[0022] In one embodiment, the offshore converter station and the onshore converter unit adopt bipolar wiring, the positive and negative poles of the busbar are both equipped with DC high-speed parallel switches on the input side and connected to the DC cable, and the neutral line of the busbar is equipped with an AC circuit breaker on the input side and connected to the DC cable;

[0023] The positive and negative poles of the busbar are connected to the DC overhead line via DC circuit breakers on the output side;

[0024] The neutral line of the busbar is connected to the DC overhead line through an AC circuit breaker at the output side.

[0025] In one embodiment, a DC energy dissipation device is disposed between the positive electrode and the negative electrode of the busbar.

[0026] In one embodiment, if any DC overhead line is connected to two or more onshore converter units, the onshore converter units connected to the DC overhead line are interconnected via the overhead line equipped with DC high-speed parallel switches.

[0027] In one embodiment, the AC sides of two or more of the onshore converter units are interconnected.

[0028] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0029] The offshore wind power DC transmission system provided in this application includes an onshore DC switch station, multiple offshore converter stations adopting a half-bridge MMC topology, and multiple onshore converter units adopting a topology with DC fault clearing capability. 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 a busbar 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 on the pole lines on at least one of the input and output sides of the busbar to achieve fault isolation. When the offshore converter station does not have DC fault clearing capability, reliable fault isolation of the system is ensured, thereby improving system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] FIG1 is a schematic structural diagram of an offshore wind power DC transmission system in one embodiment;

[0032] FIG2 is a schematic diagram of the topological structure of an offshore converter station using symmetrical monopole connection in one embodiment;

[0033] FIG3 is a schematic diagram of a topological structure of an onshore converter unit using symmetrical monopole connection in one embodiment;

[0034] FIG4 is a schematic structural diagram of an offshore wind power DC transmission system using symmetrical monopole connection and a single-circuit overhead line in one embodiment;

[0035] FIG5 is a schematic structural diagram of an offshore wind power DC transmission system using symmetrical monopole wiring and multiple overhead lines in one embodiment;

[0036] FIG6 is a schematic structural diagram of an offshore wind power DC transmission system using symmetrical monopole connection and a single-circuit overhead line in another embodiment;

[0037] FIG7 is a schematic structural diagram of an offshore wind power DC transmission system using a bipolar connection and a single-circuit overhead line in one embodiment;

[0038] FIG8 is a schematic structural diagram of an offshore wind power DC transmission system using bipolar wiring and multiple overhead lines in one embodiment;

[0039] FIG9 is a schematic structural diagram of an offshore wind power DC transmission system using bipolar wiring and multiple overhead lines in another embodiment;

[0040] FIG10 is a schematic structural diagram of an offshore wind power DC transmission system using symmetrical monopole wiring and multiple overhead lines in another embodiment;

[0041] FIG11 is a structural diagram of an offshore wind power DC transmission system using bipolar wiring and multiple overhead lines in another embodiment. DETAILED DESCRIPTION

[0042] 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.

[0043] As shown in FIG1 , an embodiment of the present application provides an offshore wind power DC transmission system, comprising: an onshore DC switch station 101 , multiple offshore converter stations 102 , and multiple onshore converter units 103 . The AC side of the offshore converter station 102 is used to connect to the wind turbine WT, and the DC side of the offshore converter station 102 is connected to the input side of the busbar of the onshore DC switch station 101 via a DC cable. The output side of the busbar is connected to the DC side of the onshore converter unit 103 via a DC overhead line, and at least one of the input and output sides of the busbar (i.e., switch 1 and / or switch 2) is equipped with a DC circuit breaker (DCCB). The DC side of the onshore converter unit 103 is connected to the DC overhead line via a DC high-speed parallel switch (HSS). Each DC overhead line is connected to more than one onshore converter unit 103, and the AC side of each onshore converter unit 103 is used to connect to a load center G. The offshore converter station 102 has a half-bridge MMC topology, and the onshore converter unit 103 has a topology with DC fault clearing capability.

[0044] 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.

[0045] 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.

[0046] A modular multilevel converter (MMC) is a voltage-source converter whose core components are the sub-modules connected in series within the bridge arms. A half-bridge MMC topology employs half-bridge sub-modules. This topology is widely used in offshore wind power DC transmission systems due to its low cost and wide applicability. However, the half-bridge sub-modules lack DC fault clearing capabilities. If a fault occurs in the DC line of a flexible DC transmission system, the converter and DC-side energy storage elements will rapidly discharge, causing the fault current to reach the tolerance limit of power electronic devices within milliseconds, threatening the safe operation of equipment and systems. A DC circuit breaker (DCCB) can quickly clear and isolate DC faults. Referring to FIG. 2 (taking symmetrical single-pole connection as an example), in this embodiment, the offshore converter adopts a half-bridge MMC topology and does not have a DC fault clearing capability. By configuring a DC circuit breaker DCCB on the pole line on at least one side of the input side and the output side of the busbar of the onshore DC switch station 101, when a DC fault occurs, the DC circuit breaker DCCB can be used to achieve fault isolation, thereby improving the stability of system operation.

[0047] Furthermore, this embodiment proposes a transmission method using DC cables on the offshore side and DC overhead lines on the onshore side. This significantly reduces costs compared to the European method of using DC cables for all onshore transmission. Compared to the current Chinese method of using AC overhead lines for onshore transmission, this method can reduce the number of transmission corridors in large-scale offshore wind power transmission. Within the permitted capacity, a single DC overhead line can connect to multiple onshore converter units 103, further conserving transmission corridors and reducing costs. In this embodiment, an onshore DC switch station 101 is installed onshore to connect the DC cables and DC overhead lines. By configuring a DC circuit breaker (DCCB) on at least one of the poles on the input and output sides of the busbar, faults can be reliably cleared. Therefore, to reduce costs, the DC overhead line is connected to the DC side of the onshore converter unit 103 via a DC high-speed parallel switch (HSS), eliminating the need for an additional, costly DC circuit breaker (DCCB) at the onshore converter unit 103.

[0048] In one embodiment, the onshore converter unit 103 adopts a full-bridge / half-bridge hybrid MMC topology (see FIG3 , taking symmetrical single-pole connection as an example), or other topologies with DC fault clearing capability.

[0049] The offshore wind power DC transmission system provided in this application includes an onshore DC switch station 101, multiple offshore converter stations 102 using a half-bridge MMC topology, and multiple onshore converter units 103 using a topology with DC fault clearing capability. 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 a busbar of the onshore DC switch station 101, thereby reducing the transmission cost of large-capacity offshore wind power, saving transmission corridors, and supporting transmission needs on the scale of tens of millions of kilowatts. A DC circuit breaker (DCCB) is configured on at least one of the pole lines on the input and output sides of the busbar to achieve fault isolation. When the offshore converter station 102 does not have DC fault clearing capability, reliable fault isolation of the system is ensured, thereby improving system stability.

[0050] As shown in FIG4 (taking a single-circuit DC overhead line as an example), in one embodiment, the offshore converter station 102 and the onshore converter unit 103 adopt a symmetrical monopole connection. A DC circuit breaker DCCB is configured on the input side of the busbar and connected to the DC cable, and the output side of the busbar is directly connected to the DC overhead line.

[0051] In this embodiment, since the offshore converter station 102 does not have a DC fault clearing capability, the DC circuit breaker DCCB configured on the input side of the busbar can be used to cut off the short-circuit current in the DC cable line where the DC circuit breaker DCCB is located when a fault occurs, thereby cutting off the DC fault and ensuring the stability of the power transmission system. The onshore converter unit 103 itself has a DC fault clearing capability, and the output side of the busbar can be directly connected to the DC overhead line, thereby reducing the investment in the DC circuit breaker DCCB and lowering the system cost.

[0052] As shown in Figure 5 (taking a multi-circuit DC overhead line as an example), in one embodiment, the offshore converter station 102 and the onshore converter unit 103 adopt a symmetrical single-pole connection. The input side of the busbar is configured with a DC circuit breaker DCCB connected to the DC cable, and the output side of the busbar is connected to the DC overhead line via an AC circuit breaker BRK (Breaker).

[0053] In this embodiment, since the offshore converter station 102 does not have the ability to clear DC faults, the DC circuit breaker DCCB configured on the input side of the busbar can be used to clear the DC fault by disconnecting the DC cable line where the DC circuit breaker DCCB is located when a fault occurs, thereby ensuring the stability of the power transmission system. The onshore converter unit 103 itself has the ability to clear DC faults. The output side of the busbar uses a low-cost AC circuit breaker BRK to connect the output side of the busbar to the DC overhead line, thereby reducing the investment in DC circuit breakers DCCB and lowering system costs.

[0054] As shown in FIG6 (taking a single-circuit DC overhead line as an example), in one embodiment, the offshore converter station 102 and the onshore converter unit 103 adopt a symmetrical monopole connection. A DC circuit breaker DCCB is configured on the input side of the busbar to connect to the DC cable, and the output side of the busbar is connected to the DC overhead line via the DC circuit breaker DCCB.

[0055] In this embodiment, DC circuit breakers DCCB are configured on the pole lines on both the input and output sides of the busbar. When a fault occurs, the DC cable line or DC overhead line can be disconnected by the DC circuit breaker DCCB, which increases the flexibility and reliability of fault disconnection.

[0056] 4 and 5 , in one embodiment, when the output side of the busbar is directly connected to the DC overhead line or connected to the DC overhead line via an AC circuit breaker BRK, a DC energy dissipation device 104 is disposed between the positive and negative poles of the busbar. A first end of the DC energy dissipation device 104 is connected to the positive pole DC+ of the busbar via a DC cable equipped with a DC circuit breaker DCCB, and a second end of the DC energy dissipation device 104 is connected to the negative pole DC- of the busbar via a DC cable equipped with a DC circuit breaker DCCB.

[0057] To further ensure the system's fault clearing capability when a DC fault occurs, a DC energy dissipation device 104 may be configured on the offshore side. After the DC circuit breaker DCCB clears the DC fault, the DC energy dissipation device 104 may operate at full voltage to achieve surplus power balance during the DC fault.

[0058] In one embodiment, if the offshore converter station 102 or the wind turbine is equipped with an energy dissipation device, the DC energy dissipation device 104 may not be configured, and surplus power balance can be achieved through the energy dissipation device of the offshore converter station 102 or the energy dissipation device of the wind turbine. However, this method has higher requirements on the configuration of the offshore converter station 102 or the wind turbine and the cost investment is relatively large.

[0059] Referring to FIG. 6 , in one embodiment, when the output side of the busbar is connected to the DC overhead line via a DC circuit breaker DCCB, a DC energy dissipation device 104 is configured at the positive and negative poles of the busbar. A first end of the DC energy dissipation device 104 is connected to the positive pole DC+ of the busbar via the DC overhead line, and a second end of the DC energy dissipation device 104 is connected to the negative pole DC- of the busbar via the DC overhead line.

[0060] In this embodiment, a DC circuit breaker DCCB is configured on the DC overhead line side for clearing DC faults. To further ensure the system's fault clearing capability when a DC fault occurs, a DC energy dissipation device 104 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 104 can operate at full voltage to achieve surplus power balance during the DC fault.

[0061] Referring to Figures 7 and 8 , in one embodiment, the offshore converter station 102 and the onshore converter unit 103 utilize bipolar wiring. The positive DC+ and negative DC- poles of the busbar are both connected to the DC cable via a DC circuit breaker DCCB on the input side, while the neutral line N of the busbar is connected to the DC cable via an AC circuit breaker BRK on the input side. The positive DC+ and negative DC- poles of the busbar are both directly connected to the DC cable, while the neutral line N of the busbar is directly connected to the DC overhead line on the output side. In some embodiments, the positive and negative poles of the busbar are connected to the DC overhead line via a DC circuit breaker DCCB on the output side, respectively, while the neutral line N of the busbar is connected to the DC overhead line via an AC circuit breaker BRK on the output side.

[0062] When bipolar wiring is used, the fault current in the circuit can be isolated by operating the pole line DCCB. Therefore, the neutral pole on the output side of the busbar can be configured with an AC circuit breaker BRK to connect to the DC overhead line. The AC circuit breaker BRK is relatively low in cost and can reduce system costs.

[0063] Referring to FIG9 , in one embodiment, when the offshore converter station 102 and the onshore converter unit 103 adopt bipolar connection, the offshore side can share a neutral line to reduce costs; the onshore side can share a neutral line to reduce costs.

[0064] Referring to FIG. 10 , in one embodiment, the offshore converter station 102 and the onshore converter unit 103 adopt a symmetrical single-pole connection. A DC high-speed parallel switch HSS is configured on the input side of the busbar to connect to the DC cable, and a DC circuit breaker DCCB is configured on the output side of the busbar to connect to the DC overhead line.

[0065] In this embodiment, since the offshore converter station 102 does not have the ability to clear DC faults, a DC circuit breaker (DCCB) needs to be configured in the DC transmission line to clear the DC fault. Configuring the DC circuit breaker (DCCB) on the offshore side is more difficult and more expensive. The DC circuit breaker (DCCB) configured on the output side of the busbar can be used to clear the DC fault by disconnecting the DC overhead line when a fault occurs, thereby ensuring the stability of the transmission system. A lower-cost DC high-speed parallel switch (HSS) can be configured on the input side of the busbar to cooperate with the DC circuit breaker (DCCB) on the output side to switch the line, thereby reducing the investment in DC circuit breakers (DCCB) and lowering system costs.

[0066] Referring to FIG. 11 , in one embodiment, the offshore converter station 102 and the onshore converter unit 103 adopt bipolar wiring. The positive and negative poles of the busbar are both configured with a DC high-speed parallel switch HSS on the input side and connected to the DC cable. The neutral line N of the busbar is configured with an AC circuit breaker BRK on the input side and connected to the DC cable. The positive and negative poles of the busbar are respectively connected to the DC overhead line via a DC circuit breaker DCCB on the output side. The neutral line N of the busbar is configured with an AC circuit breaker BRK on the output side and connected to the DC overhead line.

[0067] In this embodiment, when bipolar wiring is used at the converter station, since neutral line faults do not require fault isolation, the neutral line N of the busbar can be configured with an AC circuit breaker BRK on the input side to connect to the DC cable, and with an AC circuit breaker BRK on the output side to connect to the DC overhead line. The AC circuit breaker BRK is relatively low-cost and can reduce system costs. Because the offshore converter station 102 does not have DC fault clearing capabilities, a DC circuit breaker DCCB must be configured in the DC transmission line to clear the DC fault. Deploying a DC circuit breaker DCCB on the offshore side is more difficult and more expensive. The DC circuit breaker DCCB configured on the output side of the busbar can be used to clear the DC fault by disconnecting the DC overhead line in the event of a fault, thereby ensuring the stability of the transmission system. A lower-cost DC high-speed parallel switch HSS can be configured on the input side of the busbar to cooperate with the DC circuit breaker DCCB on the output side to switch the line, reducing the investment in DC circuit breakers DCCB and lowering system costs.

[0068] 10 , in one embodiment, a DC energy dissipation device 104 is disposed between the positive and negative poles of the busbar; wherein a first end of the DC energy dissipation device 104 is connected to the positive pole of the busbar, and a second end thereof is connected to the negative pole of the busbar.

[0069] In this embodiment, a DC circuit breaker DCCB is configured on the DC overhead line side for clearing DC faults. To further ensure the system's fault clearing capability when a DC fault occurs, a DC energy dissipation device 104 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 104 can operate at full voltage to achieve surplus power balance during the DC fault.

[0070] 4 to 11 , in one embodiment, if any DC overhead line is connected to two or more onshore converter units 103 , the onshore converter units 103 connected to the DC overhead line are interconnected via an overhead line configured with a DC high-speed parallel switch HSS.

[0071] Since the capacity of a single onshore converter unit 103 is greater than that of a single offshore converter station 102, one overhead line loop can be connected to multiple offshore converter stations 102 at the same time. In order to further save transmission corridors, the DC overhead line can adopt multi-circuit wiring, that is, one overhead line loop is connected to multiple onshore converter units 103 at the same time, and the multiple onshore converter units 103 connected to the DC overhead line of the loop are interconnected via overhead lines equipped with DC high-speed parallel switches HSS. The DC high-speed parallel switches HSS configured between any interconnected onshore converter units 103 are used to cooperate with the DC circuit breaker DCCB for fault isolation.

[0072] In one embodiment, the AC sides of two or more onshore converter units 103 are interconnected.

[0073] In this embodiment, the AC sides of two or more onshore converter units 103 are interconnected to enable the onshore converter units 103 to participate in the construction of the load center G power grid. The onshore converter units 103 do not need to perform load allocation. The interconnected onshore converter units 103 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.

[0074] 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.

[0075] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined. At the same time, the term "and / or" used in this specification includes any and all combinations of the relevant listed items.

[0076] 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.

[0077] 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.

[0078] 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 output side of the busbar is connected to the DC side of the onshore converter unit via a DC overhead line, and a DC circuit breaker is arranged on the pole line of at least one side of the input side and the output side of the busbar; The DC side of the onshore converter unit is connected to the DC overhead line via a DC high-speed parallel switch, each DC overhead line is connected to more than one onshore converter unit, and the AC side of each onshore converter unit is used to connect to a load center; The offshore converter station adopts a half-bridge MMC topology structure, and the onshore converter unit adopts a topology structure with a DC fault clearing capability.

2. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit adopt symmetrical single-pole connection, the input side of the busbar is configured with a DC circuit breaker connected to a DC cable, and the output side of the busbar is directly connected to a DC overhead line, connected to a DC overhead line via a DC circuit breaker, or connected to a DC overhead line via an AC circuit breaker.

3. The offshore wind power DC transmission system according to claim 2, characterized in that: When the output side of the busbar is directly connected to the DC overhead line or connected to the DC overhead line via an AC circuit breaker, a DC energy dissipation device is arranged between the positive and negative poles of the busbar; Wherein, the first end of the DC energy dissipation device is connected to the positive pole of the busbar via a DC cable equipped with a DC circuit breaker, and the second end of the DC energy dissipation device is connected to the negative pole of the busbar via a DC cable equipped with a DC circuit breaker.

4. The offshore wind power DC transmission system according to claim 2, characterized in that: When the output side of the busbar is connected to the DC overhead line via a DC circuit breaker, a DC energy dissipation device is arranged between the positive pole and the negative pole of the busbar.

5. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit adopt bipolar wiring, the positive and negative poles of the busbar are both equipped with a DC circuit breaker and connected to a DC cable on the input side, and the neutral line of the busbar is equipped with an AC circuit breaker and connected to a DC cable on the input side; The output sides of the positive pole, negative pole and neutral line of the busbar are directly connected to the DC overhead line; Alternatively, the positive and negative electrodes of the busbar are connected to the DC overhead line via DC circuit breakers at the output side, and the neutral line is connected to the DC overhead line via an AC circuit breaker at the output side.

6. The offshore wind power DC transmission system according to claim 1, characterized in that: The offshore converter station and the onshore converter unit adopt symmetrical single-pole connection, the input side of the busbar is equipped with a DC high-speed parallel switch connected to a DC cable, and the output side of the busbar is equipped with a DC circuit breaker connected to a 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 adopt bipolar wiring, the positive and negative poles of the busbar are both equipped with DC high-speed parallel switches on the input side and connected to the DC cable, and the neutral line of the busbar is equipped with an AC circuit breaker on the input side and connected to the DC cable; The positive and negative electrodes of the busbar are connected to the DC overhead line via DC circuit breakers at the output side; The neutral line of the busbar is connected to the DC overhead line through an AC circuit breaker at the output side.

8. The offshore wind power DC transmission system according to any one of claims 5 to 7, characterized in that: A DC energy dissipation device is arranged between the positive pole and the negative pole of the busbar.

9. The offshore wind power DC transmission system according to any one of claims 1 to 7, characterized in that: If any DC overhead line is connected to more than two onshore converter units, the onshore converter units connected to the DC overhead line are interconnected via the overhead line equipped with DC high-speed parallel switches.

10. The offshore wind power DC transmission system according to claim 9, characterized in that: The AC sides of two or more of the above-mentioned onshore converter units are interconnected.

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