Offshore wind power dc transmission system

Abstract

The application provides an offshore wind power DC transmission system. The system comprises: an onshore DC switch station, a plurality of offshore converter stations and a plurality of onshore converter units; the AC side of the offshore converter station is used for connecting a wind turbine generator, the DC side of the offshore converter station is connected to the input side of a busbar of the onshore DC switch station through a DC cable; the output side of the busbar is connected to the onshore converter unit through a DC overhead line, at least one of the input side and the output side of the busbar is provided with a DC circuit breaker; the DC side of the onshore converter unit is connected to the DC overhead line through 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 for connecting to a load center; wherein the offshore converter station adopts a half-bridge MMC topological structure, and the onshore converter unit adopts a topological structure with DC fault clearing capability. The application can realize reliable and low-cost super large capacity DC transmission.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current transmission, in particular to a direct current transmission system for offshore wind power. BACKGROUND

[0002] In recent years, in order to promote energy transformation, China's policy has vigorously supported the development and utilization of offshore wind power. Offshore wind power development shows a trend from nearshore, shallow water, small-scale demonstration to far sea, deep water, large-scale concentrated development. The transmission mode of offshore wind power to access the onshore power grid includes high-voltage alternating current transmission and high-voltage direct current transmission. Among them, the high-voltage alternating current transmission mode is suitable for the access of nearshore wind power. When the offshore wind power is more than a certain distance from the shore, the long-distance alternating current cable transmission has problems such as excessive charging power causing voltage rise needing compensation and overvoltage, and it is difficult to meet the demand of large-capacity, long-distance offshore wind power transmission by using high-voltage alternating current transmission, and the cost is high.

[0003] The high-voltage direct current transmission mode has the advantages of not needing to keep synchronization with the onshore power grid, long transmission distance, and flexible operation and regulation, and is more suitable for use in large-capacity, long-distance transmission scenarios. Among them, since the flexible direct current transmission does not have the problem of commutation failure, the active power and reactive power can be independently adjusted, and the harmonic level is low, it is the mainstream mode of large-scale offshore wind power transmission to the onshore power grid at present. In order to realize ultra-high capacity transmission, a multi-terminal flexible direct current transmission scheme needs to be used, but the current direct current transmission system architecture is difficult to realize stable transmission of ultra-large capacity. SUMMARY

[0004] The embodiment of the present application provides a direct current transmission system for offshore wind power, which can realize reliable and low-cost ultra-large capacity direct current transmission and improve system stability.

[0005] The present application provides a direct current transmission system for offshore wind power, comprising:

[0006] a land direct current switch station, a plurality of offshore converter stations and a plurality of land converter units;

[0007] The AC side of the offshore converter station is used to connect the wind turbine generator, and the DC side of the offshore converter station is connected to the input side of the busbar of the land direct current switch station through a DC cable;

[0008] The output side of the busbar is connected to the DC side of the land converter unit through a DC overhead line, and a DC circuit breaker is arranged on the pole line of at least one of the input side and the output side of the busbar;

[0009] The DC side of the land converter unit is connected to the DC overhead line through a DC high-speed parallel switch, each DC overhead line is connected to more than one land converter unit, and the AC side of each land converter unit is used to be connected to a load center.

[0010] 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.

[0011] In one of the embodiments, the offshore converter station and the onshore converter unit adopt a symmetric monopole connection, a DC circuit breaker is arranged at the input side of the busbar to connect with a DC cable, and the output side of the busbar is directly connected with a DC overhead line, connected with the DC overhead line through a DC circuit breaker, or connected with the DC overhead line through an AC circuit breaker.

[0012] In one of the embodiments, when the output side of the busbar is directly connected with the DC overhead line or connected with the DC overhead line through the AC circuit breaker, a DC energy consumption device is arranged between the positive pole and the negative pole of the busbar.

[0013] The first end of the DC energy consumption device is connected to the positive pole of the busbar through a DC cable provided with a DC circuit breaker, and the second end of the DC energy consumption device is connected to the negative pole of the busbar through a DC cable provided with a DC circuit breaker.

[0014] In one of the embodiments, when the output side of the busbar is connected with the DC overhead line through the DC circuit breaker, a DC energy consumption device is arranged between the positive pole and the negative pole of the busbar.

[0015] In one of the embodiments, the offshore converter station and the onshore converter unit adopt a bipolar connection, DC circuit breakers and DC cables are arranged at the input side of the positive pole and the negative pole of the busbar, and an AC circuit breaker and a DC cable are arranged at the input side of the neutral line of the busbar.

[0016] The output side of the positive pole, the negative pole and the neutral line of the busbar are directly connected with the DC overhead line.

[0017] Or,

[0018] The positive pole and the negative pole of the busbar are respectively connected with the DC overhead line through DC circuit breakers at the output side, and the neutral line is connected with the DC overhead line through an AC circuit breaker at the output side.

[0019] In one of the embodiments, the offshore converter station and the onshore converter unit adopt a symmetric monopole connection, a DC high-speed parallel switch and a DC cable are arranged at the input side of the busbar, and a DC circuit breaker and a DC overhead line are arranged at the output side of the busbar.

[0020] In one of the embodiments, the offshore converter station and the onshore converter unit adopt bipolar connection, the positive and negative poles of the busbar are connected with the DC high-speed parallel switch and the DC cable at the input side, and the neutral line of the busbar is connected with the AC circuit breaker and the DC cable at the input side;

[0021] The positive and negative poles of the busbar are connected with the DC circuit breaker and the DC overhead line at the output side, respectively.

[0022] The neutral line of the busbar is connected with the AC circuit breaker and the DC overhead line at the output side.

[0023] In one of the embodiments, the DC energy consumption device is arranged between the positive and negative poles of the busbar.

[0024] In one of the embodiments, if any DC overhead line is connected with two or more onshore converter units, the onshore converter units connected with the DC overhead line are interconnected through the overhead line provided with the DC high-speed parallel switch.

[0025] In one of the embodiments, the AC sides of two or more onshore converter units are interconnected.

[0026] From the above technical solutions, it can be seen that the embodiments of the present application have the following advantages:

[0027] The offshore wind power DC transmission system provided by the present application comprises an onshore DC switch station, a plurality of offshore converter stations adopting a half-bridge MMC topology structure, and a plurality of onshore converter units adopting a topology structure with DC fault clearing capability. The offshore wind power DC transmission system transmits power through DC cables at the offshore side and transmits power through DC overhead lines at the onshore side. The onshore DC switch station is connected with the offshore side and the onshore side through a busbar, thereby reducing the power transmission cost of large-capacity offshore wind power, saving the power transmission corridor, supporting the transmission demand of tens of thousands of kilowatts, and configuring a DC circuit breaker on at least one of the pole lines at the input side and the output side of the busbar to realize fault isolation. When the offshore converter station does not have the DC fault clearing capability, the system can reliably isolate faults and improve the stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0029] Figure 1 In one of the embodiments, the structure schematic diagram of the offshore wind power DC transmission system;

[0030] Figure 2 Fig. 1 is a schematic diagram of a topology of a marine converter station with symmetric monopolar connection for one embodiment;

[0031] Figure 3 Fig. 2 is a schematic diagram of a topology of a land converter unit with symmetric monopolar connection for one embodiment;

[0032] Figure 4 Fig. 3 is a schematic diagram of a structure of a marine wind power DC transmission system with symmetric monopolar connection and single-circuit overhead line for one embodiment;

[0033] Figure 5 Fig. 4 is a schematic diagram of a structure of a marine wind power DC transmission system with symmetric monopolar connection and multi-circuit overhead line for one embodiment;

[0034] Figure 6 Fig. 5 is a schematic diagram of a structure of a marine wind power DC transmission system with symmetric monopolar connection and multi-circuit overhead line for another embodiment;

[0035] Figure 7 Fig. 6 is a schematic diagram of a structure of a marine wind power DC transmission system with bipolar connection and single-circuit overhead line for one embodiment;

[0036] Figure 8 Fig. 7 is a schematic diagram of a structure of a marine wind power DC transmission system with bipolar connection and multi-circuit overhead line for one embodiment;

[0037] Figure 9 Fig. 8 is a schematic diagram of a structure of a marine wind power DC transmission system with bipolar connection and multi-circuit overhead line for another embodiment;

[0038] Figure 10 Fig. 9 is a schematic diagram of a structure of a marine wind power DC transmission system with symmetric monopolar connection and multi-circuit overhead line for another embodiment;

[0039] Figure 11 Fig. 10 is a schematic diagram of a structure of a marine wind power DC transmission system with bipolar connection and multi-circuit overhead line for another embodiment. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0041] As Figure 1As shown, the embodiment of the present application provides a kind of offshore wind power DC transmission system, comprising: land DC switch station 101, multiple offshore converter stations 102 and multiple land converter units 103.Wherein, the AC side of offshore converter station 102 is used to connect wind turbine WT, the DC side of offshore converter station 102 is connected to the input side of busbar of land DC switch station 101 by DC cable;The output side of busbar is connected with the DC side of land converter unit 103 through DC overhead line, and at least one side (i.e. switch 1 and / or switch 2) of the input side and the output side of busbar is configured with direct current circuit breaker DCCB (Direct Current Circuit Breaker);The DC side of land converter unit 103 is connected with DC overhead line through DC high-speed parallel switch HSS (High Speed Switch), and each DC overhead line is connected with more than one land converter unit 103;The AC side of each land converter unit 103 is used to connect with a load center G;Wherein, offshore converter station 102 is half-bridge MMC topology structure, and land converter unit 103 is the topology structure with DC fault clearing capability.

[0042] Wherein, DC cable includes DC submarine cable and / or DC land cable, since busbar can be arranged in land area away from coastline, part of transmission in sea adopts DC submarine cable, and DC land cable is used for transmission between coastline and busbar.

[0043] In some embodiments, one land converter unit refers to one land converter station.In other embodiments, one land converter unit refers to single converter unit in single land converter station.

[0044] Modular multilevel converter MMC is voltage source converter, and the core component is sub-module (Sub-module) in bridge arm in series, and half-bridge MMC topology structure is the topology structure of half-bridge sub-module used by sub-module.Half-bridge MMC topology structure is widely used in offshore wind power DC transmission system due to its low cost and wide application range, but half-bridge sub-module does not have DC fault clearing capability, once fault occurs in DC line of flexible DC transmission system, converter and DC side energy storage element will discharge quickly, leading to that fault current reaches the upper limit of power electronic device in several milliseconds, which threatens the safety of equipment and system operation.Direct current circuit breaker DCCB can realize rapid removal and isolation of DC fault.Reference Figure 2 As shown (for example, in symmetric monopolar wiring), in the embodiment, offshore converter adopts half-bridge MMC topology structure, and does not have DC fault clearing capability, by configuring direct current circuit breaker DCCB on at least one side of the input side and the output side of busbar of land DC switch station 101, when DC fault occurs, fault isolation can be realized through direct current circuit breaker DCCB, and the stability of system operation is improved.

[0045] In addition, in the embodiment, the DC cable is used on the sea side, and the DC overhead line is used on the land side, which can greatly reduce the cost compared with the mode that the DC land cable is used on the land side in the European region. Compared with the mode that the AC overhead line is used on the land side in China, in the large-capacity offshore wind power transmission, the number of transmission corridors can be reduced, the single-return DC overhead line can be connected to multiple land converter units 103 within the capacity range, the transmission corridor is further saved, and the cost is reduced. In the embodiment, the land DC switch station 101 is arranged on the land to connect the DC cable and the DC overhead line. The DC circuit breaker DCCB is arranged on at least one of the input side and the output side of the bus bar, which can reliably remove the fault. Therefore, in order to reduce the cost, the DC overhead line is connected to the DC side of the land converter unit 103 through the high-speed parallel switch HSS, and the DC circuit breaker DCCB with high cost needs not to be additionally arranged at the land converter unit 103.

[0046] In one of the embodiments, the land converter unit 103 adopts a full-bridge half-bridge hybrid MMC topology (for example, a symmetric monopole connection, as shown in FIG. 11), or other topologies with DC fault clearing capability. Figure 3

[0047] The offshore wind power DC transmission system provided in the application includes the land DC switch station 101, the plurality of offshore converter stations 102 adopting the half-bridge MMC topology, and the plurality of land converter units 103 adopting the topology with the DC fault clearing capability. The DC cable is used on the sea side, the DC overhead line is used on the land side, the bus bar of the land DC switch station 101 is connected to the sea side and the land side, the transmission cost of the large-capacity offshore wind power is reduced, the transmission corridor is saved, the transmission demand of the order of ten million kilowatts can be supported, the DC circuit breaker DCCB is arranged on at least one of the input side and the output side of the bus bar, the fault isolation is realized, the system reliability is ensured, and the system stability is improved when the offshore converter station 102 does not have the DC fault clearing capability.

[0048] As shown in FIG. 12 (for example, a single-return DC overhead line), in one of the embodiments, the offshore converter station 102 and the land converter unit 103 adopt the symmetric monopole connection. The DC circuit breaker DCCB is arranged on the input side of the bus bar and connected to the DC cable. The output side of the bus bar is directly connected to the DC overhead line. Figure 4

[0049] ​​In the embodiment, the offshore converter station 102 does not have the DC fault clearing capability, the DC circuit breaker DCCB configured at the input side of the busbar can clear the DC fault by cutting off the short-circuit current in the DC cable line where the DC circuit breaker DCCB is located when a fault occurs, ensuring the stability of the power transmission system, and the onshore converter unit 103 itself has the DC fault clearing capability, the output side of the busbar can be directly connected with the DC overhead line, reducing the investment of the DC circuit breaker DCCB and lowering the system cost.

[0050] As shown in FIG. 1 (taking a multi-circuit DC overhead line as an example), in one of the embodiments, the offshore converter station 102 and the onshore converter unit 103 adopt the symmetric monopole connection, the input side of the busbar is connected with the DC cable through the DC circuit breaker DCCB, and the output side of the busbar is connected with the DC overhead line through the AC circuit breaker BRK. Figure 5 In the embodiment, the offshore converter station 102 does not have the DC fault clearing capability, the DC circuit breaker DCCB configured at the input side of the busbar can clear the DC fault by cutting off the short-circuit current in the DC cable line where the DC circuit breaker DCCB is located when a fault occurs, ensuring the stability of the power transmission system, and the onshore converter unit 103 itself has the DC fault clearing capability, the output side of the busbar is connected with the DC overhead line through the AC circuit breaker BRK with lower cost, reducing the investment of the DC circuit breaker DCCB and lowering the system cost.

[0051] As shown in FIG. 2 (taking a single-circuit DC overhead line as an example), in one of the embodiments, the offshore converter station 102 and the onshore converter unit 103 adopt the symmetric monopole connection, the input side of the busbar is connected with the DC cable through the DC circuit breaker DCCB, and the output side of the busbar is connected with the DC overhead line through the DC circuit breaker DCCB.

[0052] Figure 6 In the embodiment, the DC circuit breakers DCCB are configured on the pole lines at the input side and the output side of the busbar, which can cut off the DC cable line or the DC overhead line through the DC circuit breaker DCCB when a fault occurs, and the flexibility and reliability of fault clearing are higher.

[0053] In the embodiment, the DC circuit breakers DCCB are configured on the pole lines at the input side and the output side of the busbar, which can cut off the DC cable line or the DC overhead line through the DC circuit breaker DCCB when a fault occurs, and the flexibility and reliability of fault clearing are higher.

[0054] Reference is made to FIG. 3 (taking a multi-circuit DC overhead line as an example), in one of the embodiments, the offshore converter station 102 and the onshore converter unit 103 adopt the symmetric monopole connection, the input side of the busbar is connected with the DC cable through the DC circuit breaker DCCB, and the output side of the busbar is connected with the DC overhead line through the DC circuit breaker DCCB. Figure 4 Figure 5 ​​In one of the embodiments, when the output side of the busbar is directly connected with the DC overhead line or connected with the DC overhead line through the AC circuit breaker BRK, a DC energy consumption device 104 is arranged between the positive pole and the negative pole of the busbar; wherein the first end of the DC energy consumption device 104 is connected with the positive pole DC+ of the busbar through the DC cable provided with the DC circuit breaker DCCB, and the second end of the DC energy consumption device 104 is connected with the negative pole DC- of the busbar through the DC cable provided with the DC circuit breaker DCCB.

[0055] To further ensure the fault removal capability of the system when a DC fault occurs, a DC energy consumption device 104 can be arranged on the offshore side, and after the DC circuit breaker DCCB removes the DC fault, the DC energy consumption device 104 can work at full voltage to achieve the surplus power balance during the DC fault.

[0056] In one of the embodiments, if the offshore converter station 102 or the wind turbine is provided with an energy consumption device, the DC energy consumption device 104 can also not be arranged, and the surplus power balance can be achieved through the energy consumption device of the offshore converter station 102 or the energy consumption device of the wind turbine, but this way requires higher configuration of the offshore converter station 102 or the wind turbine, and has larger cost investment.

[0057] Reference Figure 6 In one of the embodiments, when the output side of the busbar is connected with the DC overhead line through the DC circuit breaker DCCB, a DC energy consumption device 104 is arranged between the positive pole and the negative pole of the busbar; wherein the first end of the DC energy consumption device 104 is connected with the positive pole DC+ of the busbar through the DC overhead line, and the second end of the DC energy consumption device 104 is connected with the negative pole DC- of the busbar through the DC overhead line.

[0058] In this embodiment, the DC circuit breaker DCCB for removing the DC fault is arranged on the DC overhead line side, to further ensure the fault removal capability of the system when a DC fault occurs, a DC energy consumption device 104 can be arranged between the positive pole and the negative pole of the busbar, and after the DC circuit breaker DCCB removes the DC fault, the DC energy consumption device 104 can work at full voltage to achieve the surplus power balance during the DC fault.

[0059] Reference Figure 7 , Figure 8As shown, in one of the embodiments, the offshore converter station 102 and the onshore converter unit 103 adopt bipolar connection, the positive DC+ and the negative DC- of the bus bar are connected with the DC cable through the DC circuit breaker DCCB at the input side, and the neutral line N of the bus bar is connected with the DC cable through the AC circuit breaker BRK at the input side; the positive DC+ and the negative DC- of the bus bar are directly connected with the DC cable, and the output side of the neutral line N of the bus bar is directly connected with the DC overhead line. In some embodiments, the positive and the negative of the bus bar are connected with the DC overhead line through the DC circuit breaker DCCB at the output side, and the neutral line N of the bus bar is connected with the DC overhead line through the AC circuit breaker BRK at the output side.

[0060] When bipolar connection is adopted, the loop fault current can be isolated through the pole line DCCB action, so the neutral pole of the output side of the bus bar can be connected with the DC overhead line through the AC circuit breaker BRK, the cost of the AC circuit breaker BRK is lower, and the cost of the system can be reduced.

[0061] Reference Figure 9 As shown, in one of the embodiments, when the offshore converter station 102 and the onshore converter unit 103 adopt bipolar connection, one neutral line can be shared on the offshore side to reduce the cost, and one neutral line can be shared on the onshore side to reduce the cost.

[0062] Reference Figure 10 As shown, in one of the embodiments, the offshore converter station 102 and the onshore converter unit 103 adopt symmetric monopole connection, the input side of the bus bar is connected with the DC cable through the DC high-speed parallel switch HSS, and the output side of the bus bar is connected with the DC overhead line through the DC circuit breaker DCCB.

[0063] In the embodiment, because the offshore converter station 102 does not have DC fault clearing capability, the DC circuit breaker DCCB needs to be configured in the DC transmission line to remove the DC fault, it is difficult to configure the DC circuit breaker DCCB on the offshore side, and the cost is higher, the DC circuit breaker DCCB configured at the output side of the bus bar can be used to remove the DC fault by cutting off the DC overhead line when a fault occurs, to ensure the stability of the power transmission system, and the input side of the bus bar can be configured with the DC high-speed parallel switch HSS with lower cost to cooperate with the DC circuit breaker DCCB at the output side to switch the line, to reduce the investment of the DC circuit breaker DCCB and reduce the cost of the system.

[0064] Reference Figure 11As shown, in one of the embodiments, the offshore converter station 102 and the onshore converter unit 103 are connected in bipolar connection, the positive and negative poles of the busbar are connected with the DC cable through the DC high-speed shunt switch HSS at the input side, and the neutral line N of the busbar is connected with the DC cable through the AC circuit breaker BRK at the input side; the positive and negative poles of the busbar are connected with the DC overhead line through the DC circuit breaker DCCB at the output side; and the neutral line N of the busbar is connected with the DC overhead line through the AC circuit breaker BRK at the output side.

[0065] In the embodiment, when the converter station is connected in bipolar connection, there is no need for fault isolation for the neutral line, the neutral line N of the busbar can be connected with the DC cable through the AC circuit breaker BRK at the input side, and the neutral line N of the busbar can be connected with the DC overhead line through the AC circuit breaker BRK at the output side, so that the cost of the system can be reduced. Since the offshore converter station 102 does not have the DC fault clearing capability, the DC circuit breaker DCCB needs to be configured in the DC transmission line to remove the DC fault, it is difficult to configure the DC circuit breaker DCCB on the offshore side, and the cost is higher. The DC circuit breaker DCCB configured at the output side of the busbar can cut off the DC overhead line to remove the DC fault and ensure the stability of the power transmission system when a fault occurs. The input side of the busbar can be configured with the DC high-speed shunt switch HSS with lower cost to cooperate with the DC circuit breaker DCCB at the output side to switch the line, so as to reduce the investment of the DC circuit breaker DCCB and reduce the cost of the system.

[0066] Reference Figure 10 In one of the embodiments, a DC energy consumption device 104 is configured between the positive pole and the negative pole of the busbar; the first end of the DC energy consumption device 104 is connected with the positive pole of the busbar, and the second end is connected with the negative pole of the busbar.

[0067] In the embodiment, the DC circuit breaker DCCB for removing the DC fault is configured at the DC overhead line side. In order to further ensure the fault removal capability of the system when the DC fault occurs, the DC energy consumption device 104 can be configured between the positive pole and the negative pole of the busbar. After the DC circuit breaker DCCB removes the DC fault, the DC energy consumption device 104 can work at full voltage to balance the surplus power during the DC fault.

[0068] Reference Figures 4 to 11 In one of the embodiments, if any DC overhead line is connected with two or more onshore converter units 103, the onshore converter units 103 connected with the DC overhead line are interconnected through the overhead line configured with the DC high-speed shunt switch HSS.

[0069] 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 the power transmission corridor, the DC overhead line can adopt multi-loop connection, 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 overhead line are interconnected through the overhead line configured with a DC high-speed parallel switch HSS. The DC high-speed parallel switch HSS configured between any interconnected onshore converter units 103 is used for fault isolation in cooperation with the DC circuit breaker DCCB.

[0070] In one embodiment, the AC sides of two or more onshore converter units 103 are interconnected.

[0071] In this embodiment, the AC sides of two or more onshore converter units 103 are interconnected to participate in the construction of the load center G power grid. The onshore converter units 103 do not need to perform load allocation, and the interconnected onshore converter units 103 on the AC side and the load centers G connected thereto jointly form a large power grid, which can automatically coordinate the load inside to improve the safe and stable operation level of the power grid.

[0072] Finally, it should be noted that in this document, the terms such as first and second are merely used to distinguish one entity or operation from another, and do not necessarily require or imply that there is any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or device including the element.

[0073] In addition, the terms "first", "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise specifically limited. At the same time, the term "and / or" used in the specification includes any and all combinations of the related listed items.

[0074] It should be noted that when one element is referred to as being "connected" to another element, it can be directly connected to the other element or connected through an intermediate element. Also, "connection" in the embodiments of the present application, if the circuit, module, unit and the like connected to each other have the transmission of electrical signals or data, should be understood as "electrical connection", "communication connection" and the like.

[0075] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The various embodiments can be combined as needed, and the same or similar parts refer to each other.

[0076] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will 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, The application relates to a DC power transmission system. The DC power transmission system comprises: a land DC switching station, a plurality of offshore converter stations and a plurality of land converter units; the AC side of the offshore converter station is used for connecting wind turbine generators, and the DC side of the offshore converter station is connected to the input side of a busbar of the land DC switching station through a DC cable; the output side of the busbar is connected to the DC side of the land converter unit through a DC overhead line, and a DC circuit breaker is arranged on the pole line of at least one of the input side and the output side of the busbar; the DC side of the land converter unit is connected to the DC overhead line through a DC high-speed parallel switch, and each DC overhead line is connected to more than one land converter unit, and the AC side of each land converter unit is used for connecting to a load center; wherein the offshore converter station adopts a half-bridge MMC topological structure, and the land converter unit adopts a topological structure with DC fault clearing capability; wherein the offshore converter station and the land converter unit adopt symmetric monopole wiring, a DC circuit breaker is arranged on the input side of the busbar and connected to the DC cable, the output side of the busbar is directly connected to the DC overhead line, connected to the DC overhead line through a DC circuit breaker, or connected to the DC overhead line through an AC circuit breaker; and when the output side of the busbar is directly connected to the DC overhead line or connected to the DC overhead line through an AC circuit breaker, a DC energy consumption device is arranged between the positive pole and the negative pole of the busbar; wherein the first end of the DC energy consumption device is connected to the positive pole of the busbar through a DC cable provided with a DC circuit breaker, and the second end of the DC energy consumption device is connected to the negative pole of the busbar through a DC cable provided with a DC circuit breaker; 2. The offshore wind power DC transmission system according to claim 1, characterized in that, and when the output side of the busbar is connected to the DC overhead line through a DC circuit breaker, a DC energy consumption device is arranged between the positive pole and the negative pole of the busbar. The offshore converter station and the land converter unit adopt bipolar wiring, the positive pole and the negative pole of the busbar are connected to the DC cable through the DC circuit breaker at the input side, and the neutral line of the busbar is connected to the DC cable through the AC circuit breaker at the input side; the output side of the positive pole, the negative pole and the neutral line of the busbar are directly connected to the DC overhead line; 3. The offshore wind power DC transmission system of claim 1, wherein, or the positive pole and the negative pole of the busbar are respectively connected to the DC overhead line through the DC circuit breaker at the output side, and the neutral line of the busbar is connected to the DC overhead line through the AC circuit breaker at the output side.

4. The offshore wind power DC transmission system of claim 1, wherein, The offshore converter station and the land converter unit adopt symmetric monopole wiring, the input side of the busbar is connected to the DC cable through the DC high-speed parallel switch, and the output side of the busbar is connected to the DC overhead line through the DC circuit breaker. The offshore converter station and the land converter unit adopt bipolar wiring, the positive pole and the negative pole of the busbar are connected to the DC cable through the DC high-speed parallel switch at the input side, and the neutral line of the busbar is connected to the DC cable through the AC circuit breaker at the input side; the positive pole and the negative pole of the busbar are respectively connected to the DC overhead line through the DC circuit breaker at the output side; and the neutral line of the busbar is connected to the DC overhead line through the AC circuit breaker at the output side.

5. Offshore wind power DC transmission system according to any of claims 2 to 4, characterized in that A direct current energy consumption device is arranged between the positive pole and the negative pole of the busbar.

6. Offshore wind power DC transmission system according to any of claims 1 to 4, characterized in that If any direct current overhead line is connected with two or more onshore converter units, overhead line interconnections with direct current high speed parallel switches are arranged between each onshore converter unit connected with the direct current overhead line.

7. The offshore wind power DC transmission system according to claim 6, characterized in that, The AC sides of two or more onshore converter units are interconnected.

Images