Self-starting offshore wind direct-current power transmission system, and starting control method and apparatus therefor

Abstract

The present application relates to the technical field of electric power engineering. Provided are a self-starting offshore wind direct-current power transmission system, and a starting control method and apparatus therefor. The system comprises: an onshore power grid, an onshore converter station, an offshore converter station and an offshore wind farm, wherein the onshore power grid is connected to the onshore converter station; the onshore converter station is connected to the offshore converter station, and the offshore converter station comprises a first diode valve, an offshore half-bridge flexible direct-current converter valve, a second diode valve, a diesel generator-converter set and an offshore alternating-current bus; the first diode valve, the offshore half-bridge flexible direct-current converter valve and the second diode valve are connected in series on a direct-current side; the first diode valve, the offshore half-bridge flexible direct-current converter valve, the second diode valve and the diesel generator-converter set are each connected to the offshore alternating-current bus; and the offshore alternating-current bus is connected to the offshore wind farm. By means of the present application, the construction cost of an offshore wind direct-current power transmission system is reduced; moreover, a diesel generator-converter set is used to implement the self-starting of an offshore converter station and an offshore wind farm.

Description

Self-starting offshore wind power DC transmission system, startup control method and device

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 10, 2023, with application number 202311002630.8 and invention name “Self-starting offshore wind power DC transmission system, starting control method and device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electric power engineering technology, and in particular to a self-starting offshore wind power direct current transmission system, a starting control method and a device. Background Art

[0003] Currently, most offshore wind power plants in operation use flexible direct current (HVDC) transmission. However, offshore HVDC converter platforms are large, heavy, and expensive. To achieve compactness and lightweight offshore converter platforms and reduce costs, two main approaches are currently being explored: one employing pure diodes in offshore converter valves; the other employing hybrid valves composed of diodes and auxiliary modular multilevel converter valves (MMCs).

[0004] In comparison, the cost, volume and weight of the hybrid valve are lower than those of the pure flexible DC converter valve, and higher than those of the pure diode valve, but the degree of increase depends on the proportion of the auxiliary MMC. At the same time, compared with the pure diode valve, the hybrid valve can greatly reduce the investment and space occupied by the passive filter. In terms of performance, the hybrid valve has the advantages of starting offshore wind farms, active filtering, providing a certain degree of reactive power compensation and resonance suppression due to its auxiliary MMC.

[0005] In the prior art, a solution is adopted in which an auxiliary MMC is connected in parallel with a diode valve on the DC side. The DC voltage of the auxiliary MMC is the same as the system DC voltage, resulting in a large number of auxiliary MMC sub-modules and failing to effectively reduce the volume and cost of the converter valve. In the prior art, a solution is adopted in which an auxiliary full-bridge MMC is connected in series with a diode valve on the DC side. Compared with the parallel solution, the volume and weight of the full-bridge MMC can be effectively reduced. However, in order to realize the reverse transmission of the starting power from the onshore station to the offshore station, the onshore station adopts a thyristor commutated converter valve (Line Commutated Converter, LCC), which has the risk of commutation failure and reduces the power supply reliability.

[0006] Summary of the Invention

[0007] In order to reduce the construction cost of offshore wind power DC transmission systems, realize the self-starting of offshore converter stations and offshore wind farms, and ensure power supply reliability, this application proposes a self-starting offshore wind power DC transmission system, a starting control method and a device.

[0008] In a first aspect, the present application provides a self-starting offshore wind power direct current transmission system, the system comprising: an onshore power grid, an onshore converter station, an offshore converter station, and an offshore wind farm;

[0009] The onshore power grid is connected to the onshore converter station; the onshore converter station is connected to the offshore converter station, which includes a first diode valve, an offshore half-bridge flexible DC converter valve, a second diode valve, a diesel generator-converter group and an offshore AC bus; the first diode valve, the offshore half-bridge flexible DC converter valve and the second diode valve are connected in series on the DC side; the first diode valve, the offshore half-bridge flexible DC converter valve, the second diode valve and the diesel generator-converter group are respectively connected to the offshore AC bus; the offshore AC bus is connected to the offshore wind farm.

[0010] Through the above system, an offshore half-bridge flexible DC converter valve is used in the offshore converter station and is connected in series with the first diode valve and the second diode valve on the DC side. The sub-module cost of the offshore half-bridge flexible DC converter valve is lower than that of the full-bridge sub-module. At the same time, a low-cost diesel generator-converter group is used as a grid power supply in the offshore converter station to provide starting power for the offshore converter platform and wind farm. When the system cannot be started by reverse transmission of power from onshore, the self-starting function is realized, and there is no risk of commutation failure in the diesel generator-converter group, thereby ensuring power supply reliability.

[0011] In an optional embodiment, the onshore converter station includes an onshore flexible DC converter valve, the onshore flexible DC converter valve includes a three-phase bridge arm, and each bridge arm of the three-phase bridge arm includes a plurality of half-bridge sub-modules connected in series.

[0012] Through the above implementation, the use of half-bridge submodules in the onshore converter station can further reduce the construction cost of the offshore wind power DC transmission system, and at the same time improve the power supply reliability of the onshore converter station compared to the use of LLC converter valves.

[0013] In an optional embodiment, the onshore converter station further includes an onshore flexible DC transformer, and the onshore flexible DC converter valve is connected to the onshore power grid via the second circuit breaker, the onshore flexible DC transformer, and the first circuit breaker in sequence.

[0014] In an optional embodiment, the diesel generator-converter group includes a diesel generator and a converter, and the offshore converter station further includes a transformer;

[0015] The diesel generator is connected to the offshore AC busbar through the converter, the third circuit breaker, the transformer, and the fourth circuit breaker in sequence.

[0016] In an optional embodiment, the offshore converter station further includes a first rectifier transformer, an offshore flexible DC transformer, and a second rectifier transformer;

[0017] The first diode valve is connected to the offshore AC busbar through the first rectifier transformer and the fifth circuit breaker in sequence;

[0018] The offshore half-bridge flexible DC converter valve is connected to the offshore AC busbar via the sixth circuit breaker, the offshore flexible DC connecting transformer, and the seventh circuit breaker in sequence;

[0019] The second diode valve is connected to the offshore AC busbar through the second rectifier transformer and the eighth circuit breaker in sequence.

[0020] In a second aspect, the present application further provides a startup control method for a self-starting offshore wind power DC transmission system, which is used in the self-starting offshore wind power DC transmission system of the first aspect, the method comprising:

[0021] Charging the onshore converter station through the onshore power grid until the onshore converter station is fully charged;

[0022] Controlling the offshore half-bridge flexible DC converter valves and diesel generator-converter units in the offshore converter station to jointly support the AC bus voltage of the offshore AC bus to start the offshore wind farm;

[0023] The first diode valve and the second diode valve in the offshore converter station are turned on to complete the startup of the self-starting offshore wind power direct current transmission system.

[0024] Through the above method, when the offshore wind power direct current transmission system cannot be started by reverse transmission of power from onshore, a low-cost diesel generator-converter group is used as the grid power supply to achieve the self-starting function.

[0025] In an optional embodiment, the onshore converter station includes an onshore flexible DC converter valve and an onshore flexible DC connection transformer, and the onshore flexible DC converter valve is connected to the onshore power grid through the second circuit breaker, the onshore flexible DC connection transformer, and the first circuit breaker in sequence;

[0026] Charging the onshore converter station through the onshore power grid until the onshore converter station is fully charged, including:

[0027] Close the first circuit breaker and the second circuit breaker, and charge the onshore flexible DC converter valve through the onshore power grid until the onshore flexible DC converter valve is fully charged, and then unlock the onshore flexible DC converter valve.

[0028] In an optional embodiment, controlling an offshore half-bridge flexible DC converter valve and a diesel generator-converter group in an offshore converter station to jointly support an AC bus voltage of an offshore AC bus to start an offshore wind farm includes:

[0029] Control the diesel generator-converter group to establish the AC bus voltage, so that the offshore half-bridge flexible DC converter valve can be charged and unlocked;

[0030] Control the offshore half-bridge flexible DC converter valve and diesel generator-converter group to jointly support the AC bus voltage to start the offshore wind farm.

[0031] In an optional embodiment, the diesel generator-converter group includes a diesel generator and a converter; the offshore converter station further includes a transformer, a first rectifier transformer, an offshore flexible DC-connected transformer, and a second rectifier transformer; the diesel generator is connected to the offshore AC busbar via the converter, a third circuit breaker, a transformer, and a fourth circuit breaker in sequence; the first diode valve is connected to the offshore AC busbar via the first rectifier transformer and a fifth circuit breaker in sequence; the offshore half-bridge flexible DC converter valve is connected to the offshore AC busbar via a sixth circuit breaker, an offshore flexible DC-connected transformer, and a seventh circuit breaker in sequence; and the second diode valve is connected to the offshore AC busbar via the second rectifier transformer and an eighth circuit breaker in sequence.

[0032] Control the diesel generator-converter group to establish the AC bus voltage, allowing the offshore half-bridge flexible DC converter valve to complete charging and unlock the offshore half-bridge flexible DC converter valve, including:

[0033] Close the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker, the seventh circuit breaker, and the eighth circuit breaker, and control the diesel generator-converter group to establish the AC bus voltage by controlling the AC voltage amplitude and frequency in a zero-starting boost manner. During the zero-starting boost process, the offshore half-bridge flexible DC converter valve begins to be charged, and power is supplied to the first rectifier transformer, the offshore flexible DC connecting transformer, and the second rectifier transformer. After the diesel generator-converter group establishes the AC bus voltage, the offshore half-bridge flexible DC converter valve continues to be charged until the offshore half-bridge flexible DC converter valve is fully charged, and the offshore half-bridge flexible DC converter valve is unlocked.

[0034] Through the above implementation, the diesel generator-converter group is controlled to establish the AC bus voltage in a manner of boosting the AC voltage amplitude and frequency from zero, so as to charge the offshore half-bridge flexible DC converter valve smoothly and avoid charging current overcurrent. The first rectifier transformer, the offshore flexible DC link transformer and the second rectifier transformer are excited, and the current impact when the diode valve is put into operation is reduced, so as to avoid adding additional charging resistors.

[0035] In an optional embodiment, controlling the offshore half-bridge flexible DC converter valve and the diesel generator-converter group to jointly support the AC bus voltage to start the offshore wind farm includes:

[0036] The offshore half-bridge flexible DC converter valves are controlled using AC voltage amplitude and frequency, and together with the diesel generator-converter group, they support the AC bus voltage to start a preset number of wind turbines in the offshore wind farm.

[0037] When a preset number of wind turbines in the offshore wind farm are started and transmit power to the offshore converter station, the diesel generator is switched to fixed active power and fixed reactive power control.

[0038] In an optional embodiment, the first diode valve and the second diode valve in the offshore converter station are turned on to complete the startup of the self-starting offshore wind power direct current transmission system, including:

[0039] Controlling the offshore half-bridge flexible DC converter valve to increase the AC bus voltage to turn on the first diode valve and the second diode valve;

[0040] Control the diesel generator to stop running and start other wind turbines in the offshore wind farm to complete the system startup.

[0041] In an optional embodiment, controlling the diesel generator to stop running includes:

[0042] Reduce the active power and reactive power of the diesel generator until both the active power and reactive power are 0, and then disconnect the third and fourth circuit breakers.

[0043] In a third aspect, the present application further provides a self-starting offshore wind power DC transmission system startup control device, which is used in the self-starting offshore wind power DC transmission system of the first aspect, and the device comprises:

[0044] a first control module, configured to charge the onshore converter station through the onshore power grid until the onshore converter station completes charging;

[0045] The second control module is used to control the offshore half-bridge flexible DC converter valve and the diesel generator-converter group in the offshore converter station to jointly support the AC bus voltage of the offshore AC bus to start the offshore wind farm;

[0046] The conduction module is used to conduct the first diode valve and the second diode valve in the offshore converter station to complete the startup of the self-starting offshore wind power direct current transmission system.

[0047] In a fourth aspect, the present application also provides a computer device comprising a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the computer instructions to thereby execute the steps of the self-starting offshore wind power direct current transmission system startup control method of the second aspect or any embodiment of the second aspect.

[0048] In a fifth aspect, the present application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the self-starting offshore wind power direct current transmission system startup control method of the second aspect or any embodiment of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0050] FIG1 is a circuit diagram of a self-starting offshore wind power direct current transmission system according to an exemplary embodiment;

[0051] FIG2 is a flow chart of a method for controlling the startup of a self-starting offshore wind power direct current transmission system according to an exemplary embodiment;

[0052] FIG3 is a schematic structural diagram of a self-starting offshore wind power direct current transmission system startup control device according to an exemplary embodiment;

[0053] FIG4 is a schematic diagram of a hardware structure of a computer device according to an exemplary embodiment. DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solution of this application in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0055] In order to reduce the construction cost of offshore wind power DC transmission systems, realize the self-starting of offshore converter stations and offshore wind farms, and ensure power supply reliability, this application proposes a self-starting offshore wind power DC transmission system, a starting control method and a device.

[0056] Figure 1 is a circuit diagram of a self-starting offshore wind power direct current transmission system according to an exemplary embodiment. The system includes: an onshore power grid 1, an onshore converter station 2, an offshore converter station 3, and an offshore wind farm 4;

[0057] The onshore power grid 1 is connected to the onshore converter station 2 .

[0058] The onshore converter station 2 is connected to the offshore converter station 3. For example, the onshore converter station 2 is connected to the offshore converter station 3 via a DC submarine cable.

[0059] The offshore converter station 3 includes a first diode valve 31, an offshore half-bridge flexible DC converter valve 32, a second diode valve 33, a diesel generator-converter group 34 and an offshore AC bus 35; the first diode valve 31, the offshore half-bridge flexible DC converter valve 32, and the second diode valve 33 are connected in series on the DC side; the first diode valve 31, the offshore half-bridge flexible DC converter valve 32, the second diode valve 33, and the diesel generator-converter group 34 are respectively connected to the offshore AC bus 35; the offshore AC bus 35 is connected to the offshore wind farm 4.

[0060] Through the above system, an offshore half-bridge flexible DC converter valve 32 is used in the offshore converter station 3 and is connected in series with the first diode valve 31 and the second diode valve 33 on the DC side. The sub-module cost of the offshore half-bridge flexible DC converter valve 32 is lower than the full-bridge sub-module cost. At the same time, a low-cost diesel generator-converter group 34 is used as a grid power supply in the offshore converter station 3 to provide starting power for the offshore converter station 3 and the offshore wind farm 4. When the system cannot start the power supply through reverse transmission from land, the self-starting function is realized, and there is no risk of commutation failure in the diesel generator-converter group 34, thereby ensuring the power supply reliability.

[0061] In FIG1 , the onshore converter station 2 includes an onshore flexible DC converter valve 21 , which includes a three-phase bridge arm. Each bridge arm of the three-phase bridge arm includes a plurality of half-bridge sub-modules connected in series.

[0062] Considering that in the related art, the onshore converter station 2 uses flexible DC converter valves with a wide range of adjustable DC voltage, which requires the configuration of a large number of full-bridge submodules, significantly increasing the cost of the onshore flexible DC converter valves 21. In the embodiment of the present application, the onshore converter station 2 uses half-bridge submodules. Since half-bridge submodules have two fewer expensive power semiconductor devices than full-bridge submodules, the construction cost of the offshore wind power DC transmission system is further reduced. At the same time, compared with the use of LLC converter valves, the power supply reliability of the onshore converter station 2 is improved.

[0063] In Figure 1, the onshore converter station 2 also includes an onshore flexible DC transformer 22. The three phases A, B, and C of the onshore flexible DC converter valve 21 are connected to the onshore power grid 1 through the second circuit breaker 24, the onshore flexible DC transformer 22, and the first circuit breaker 23 in sequence.

[0064] In FIG1 , the diesel generator-converter group 34 includes a diesel generator 341 and a converter 342 , and the offshore converter station 3 further includes a transformer 36 .

[0065] The diesel generator 341 is connected to the offshore AC bus 35 via the converter 342 , the third circuit breaker 37 , the transformer 36 , and the fourth circuit breaker 38 in sequence.

[0066] In FIG1 , the offshore converter station 3 further includes a first rectifier transformer 39 , an offshore flexible DC transformer 40 , and a second rectifier transformer 41 .

[0067] The first diode valve 31 is connected to the offshore AC bus 35 via the first rectifier transformer 39 and the fifth circuit breaker 42 in sequence.

[0068] The offshore half-bridge flexible DC converter valve 32 is connected to the offshore AC bus 35 via the sixth circuit breaker 43 , the offshore flexible DC connection transformer 40 , and the seventh circuit breaker 44 in sequence.

[0069] The second diode valve 33 is connected to the offshore AC bus 35 via the second rectifier transformer 41 and the eighth circuit breaker 45 in sequence.

[0070] FIG2 is a flow chart of a method for controlling the startup of a self-starting offshore wind power DC transmission system according to an exemplary embodiment, which is applicable to the self-starting offshore wind power DC transmission system in the above embodiment. As shown in FIG2 , the method includes the following steps S201 to S203 .

[0071] Step S201: charging the onshore converter station 2 through the onshore power grid 1 until the onshore converter station 2 completes charging.

[0072] In an optional embodiment, the onshore flexible DC converter valve in the onshore converter station 2 is charged through the onshore power grid 1 until the onshore flexible DC converter valve is completely charged.

[0073] Step S202 : controlling the offshore half-bridge flexible DC converter valve 32 and the diesel generator-converter group 34 in the offshore converter station 3 to jointly support the AC bus voltage of the offshore AC bus 35 , so as to start the offshore wind farm 4 .

[0074] Step S203: The first diode valve 31 and the second diode valve 33 in the offshore converter station 3 are turned on to complete the startup of the self-starting offshore wind power direct current transmission system.

[0075] Through the startup control method provided in the embodiment of the present application, the offshore wind power DC transmission system uses a low-cost diesel generator-converter group 34 as a grid power supply to achieve a self-starting function when it is impossible to start the power supply through onshore reverse transmission.

[0076] In one example, the onshore converter station 2 includes an onshore flexible DC converter valve 21 and an onshore flexible DC connection transformer 22. The onshore flexible DC converter valve 21 is connected to the onshore power grid 1 through a second circuit breaker 24, an onshore flexible DC connection transformer 22, and a first circuit breaker 23 in sequence.

[0077] In the above step S201, the specific contents of charging the onshore converter station 2 through the onshore power grid 1 include:

[0078] Close the first circuit breaker 23 and the second circuit breaker 24, and charge the onshore flexible DC converter valve 21 through the onshore power grid 1 until the onshore flexible DC converter valve 21 is fully charged, and then unlock the onshore flexible DC converter valve 21.

[0079] In an optional embodiment, after the onshore flexible DC converter valve 21 is charged, the onshore flexible DC converter valve 21 is unlocked and the DC voltage of the onshore flexible DC converter valve 21 is set to the rated DC voltage.

[0080] In one example, in step S202, the following steps are performed to control the offshore half-bridge flexible DC converter valve 32 and the diesel generator-converter group 34 in the offshore converter station 3 to jointly support the AC bus voltage of the offshore AC bus 35, including:

[0081] Step a1: Control the diesel generator-converter group 34 to establish an AC bus voltage, so that the offshore half-bridge flexible DC converter valve 32 completes charging and unlocks the offshore half-bridge flexible DC converter valve 32.

[0082] In an optional embodiment, the voltage value of the AC bus voltage established by the diesel generator-converter group 34 can be slightly lower than the rated AC bus voltage. For example, it can be set to 0.95 times the AC bus voltage. The purpose is to make the station DC voltage of the offshore converter station 3 lower than the DC voltage of the onshore converter station 2 before the offshore half-bridge flexible DC converter valve 32 is unlocked, so as to prevent the diode valve from conducting.

[0083] In an optional embodiment, the offshore half-bridge flexible DC converter valve 32 can be either uncontrolled charging or controllable charging, which is not specifically limited here.

[0084] Step a2: Control the offshore half-bridge flexible DC converter valve 32 and the diesel generator-converter group 34 to jointly support the AC bus voltage to start the offshore wind farm 4.

[0085] In an example, the diesel generator-converter group 34 includes a diesel generator 341 and a converter 342; the offshore converter station 3 also includes a transformer 36, a first rectifier transformer 39, an offshore flexible DC connection transformer 40, and a second rectifier transformer 41; the diesel generator 341 is connected to the offshore AC bus 35 through the converter 342, the third circuit breaker 37, the transformer 36, and the fourth circuit breaker 38 in sequence; the first diode valve 31 is connected to the offshore AC bus 35 through the first rectifier transformer 39 and the fifth circuit breaker 42 in sequence; the offshore half-bridge flexible DC converter valve 32 is connected to the offshore AC bus 35 through the sixth circuit breaker 43, the offshore flexible DC connection transformer 40, and the seventh circuit breaker 44 in sequence; the second diode valve 33 is connected to the offshore AC bus 35 through the second rectifier transformer 41 and the eighth circuit breaker 45 in sequence.

[0086] In step a1 above, the diesel generator-converter group 34 is controlled to establish the AC bus voltage in the following manner, so that the offshore half-bridge flexible DC converter valve 32 is fully charged:

[0087] Close the third circuit breaker 37, the fourth circuit breaker 38, the fifth circuit breaker 42, the sixth circuit breaker 43, the seventh circuit breaker 44, and the eighth circuit breaker 45, and control the diesel generator-converter group 34 to establish the AC bus voltage by means of zero-starting boosting through AC voltage amplitude and frequency control (V / F control). During the zero-starting boosting process, the offshore half-bridge flexible DC converter valve 32 begins to be charged, and power is supplied to the first rectifier transformer 39, the offshore flexible DC connecting transformer 40, and the second rectifier transformer 41. After the diesel generator-converter group 34 establishes the AC bus voltage, the offshore half-bridge flexible DC converter valve 32 continues to be charged until the offshore half-bridge flexible DC converter valve 32 is fully charged, and the offshore half-bridge flexible DC converter valve 32 is unlocked.

[0088] Through the embodiment of the present application, the diesel generator-converter group 34 is controlled to establish the AC bus voltage in a zero-starting and voltage-boosting manner by controlling the AC voltage amplitude and frequency, so as to charge the offshore half-bridge flexible DC converter valve 32 smoothly and avoid charging current overcurrent, excite the first rectifier transformer 39, the offshore flexible DC connection transformer 40 and the second rectifier transformer 41, reduce the current impact when the diode valve is put into operation, and avoid adding additional charging resistors.

[0089] In one example, in step a2 above, the offshore half-bridge flexible DC converter valve 32 and the diesel generator-converter group 34 are controlled to jointly support the AC bus voltage in the following manner:

[0090] Controlling the offshore half-bridge flexible DC converter valve 32 using AC voltage amplitude and frequency control (V / F control), together with the diesel generator-converter group 34, supports the AC bus voltage to start a preset number of wind turbines in the offshore wind farm 4;

[0091] When a preset number of wind turbines in the offshore wind farm 4 are started and transmit power to the offshore converter station 3 , the diesel generator 341 is switched to constant active power and constant reactive power control (P / Q control).

[0092] In an optional embodiment, the number of starting wind turbines of the offshore wind farm 4 can be set according to actual needs and is not specifically limited here.

[0093] In one example, in the above step S203, the specific steps of conducting the first diode valve 31 and the second diode valve 33 in the offshore converter station 3 include:

[0094] First, the offshore half-bridge flexible DC converter valve 32 is controlled to increase the AC bus voltage to turn on the first diode valve 31 and the second diode valve 33 .

[0095] In an alternative embodiment, after establishing the DC voltage, the onshore flexible DC converter valve 21 charges the DC submarine cable. The offshore half-bridge flexible DC converter valve 32 increases the AC bus voltage, increasing the DC voltage at the offshore converter station 3 to a value greater than the DC voltage at the connection between the DC submarine cable and the offshore converter station 3. At this point, the first diode valve 31 and the second diode valve 33 conduct. The power delivered by the wind turbines in the offshore wind farm 4 to the offshore converter station 3 is then transmitted to the onshore converter station 2 via the DC submarine cable.

[0096] Then, the diesel generator 341 is controlled to stop running, and the other wind turbines of the offshore wind farm 4 are started to complete the system startup. At this time, the offshore wind power direct current transmission system is converted to a normal operating state.

[0097] In an optional embodiment, the diesel generator 341 is controlled to stop running in the following manner:

[0098] The active power and reactive power of the diesel generator 341 are reduced until both the active power and reactive power of the diesel generator 341 are 0, and then the third circuit breaker 37 and the fourth circuit breaker 38 are opened.

[0099] Based on the same inventive concept, an embodiment of the present application further provides a self-starting offshore wind power DC transmission system startup control device, which is used in the self-starting offshore wind power DC transmission system in the above embodiment. As shown in FIG3 , the device includes:

[0100] The first control module 301 is used to charge the onshore converter station through the onshore power grid until the onshore converter station completes charging. For details, please refer to the description of step S201 in the above embodiment, which will not be repeated here.

[0101] The second control module 302 is used to control the offshore half-bridge flexible DC converter valve and the diesel generator-converter group in the offshore converter station to jointly support the AC bus voltage of the offshore AC bus to start the offshore wind farm; for details, please refer to the description of step S202 in the above embodiment and will not be repeated here.

[0102] The conduction module 303 is used to conduct the first diode valve and the second diode valve in the offshore converter station to complete the startup of the self-starting offshore wind power direct current transmission system. For details, please refer to the description of step S203 in the above embodiment and will not be repeated here.

[0103] In one example, the onshore converter station includes an onshore flexible DC converter valve and an onshore flexible DC connection transformer. The onshore flexible DC converter valve is connected to the onshore power grid through the second circuit breaker, the onshore flexible DC connection transformer, and the first circuit breaker in sequence. The first control module 301 includes:

[0104] The first control submodule is configured to close the first and second circuit breakers, charge the onshore flexible DC converter valve via the onshore power grid, and unlock the onshore flexible DC converter valve after charging is complete. For details, refer to the description in the above embodiment and will not be repeated here.

[0105] In one example, the second control module 302 includes:

[0106] The second control submodule is used to control the diesel generator-converter group to establish the AC bus voltage, so that the offshore half-bridge flexible DC converter valve can complete charging and unlock the offshore half-bridge flexible DC converter valve; for details, please refer to the description in the above embodiment and will not be repeated here.

[0107] The third control submodule is used to control the offshore half-bridge flexible DC converter valve and the diesel generator-converter group to jointly support the AC bus voltage to start the offshore wind farm. Detailed descriptions are given in the above embodiments and will not be repeated here.

[0108] In one example, the diesel generator-converter group includes a diesel generator and a converter; the offshore converter station also includes a transformer, a first rectifier transformer, an offshore flexible DC-connected transformer, and a second rectifier transformer; the diesel generator is connected to the offshore AC busbar through the converter, the third circuit breaker, the transformer, and the fourth circuit breaker in sequence; the first diode valve is connected to the offshore AC busbar through the first rectifier transformer and the fifth circuit breaker in sequence; the offshore half-bridge flexible DC converter valve is connected to the offshore AC busbar through the sixth circuit breaker, the offshore flexible DC-connected transformer, and the seventh circuit breaker in sequence; the second diode valve is connected to the offshore AC busbar through the second rectifier transformer and the eighth circuit breaker in sequence. The second control submodule includes:

[0109] The first control unit is configured to close the third, fourth, fifth, sixth, seventh, and eighth circuit breakers, controlling the diesel generator-converter assembly to establish an AC bus voltage by controlling the AC voltage amplitude and frequency in a zero-start step-up manner. During the zero-start step-up process, the offshore half-bridge flexible DC converter valve begins to charge, and power is supplied to the first rectifier transformer, the offshore flexible DC link transformer, and the second rectifier transformer. After the diesel generator-converter assembly establishes the AC bus voltage, the offshore half-bridge flexible DC converter valve continues to charge until the offshore half-bridge flexible DC converter valve is fully charged, thereby unlocking the offshore half-bridge flexible DC converter valve. For details, please refer to the description in the above embodiment and will not be repeated here.

[0110] In one example, the third control submodule includes:

[0111] The second control unit is used to control the offshore half-bridge flexible DC converter valve to adopt AC voltage amplitude and frequency control, and jointly support the AC bus voltage with the diesel generator-converter group to start a preset number of wind turbines in the offshore wind farm; for details, please refer to the description in the above embodiment and will not be repeated here.

[0112] The third control unit is configured to switch the diesel generator to fixed active power and fixed reactive power control after a preset number of wind turbines in the offshore wind farm are started and transmit power to the offshore converter station. For details, please refer to the description in the above embodiment and will not be repeated here.

[0113] In one example, the conducting module 303 includes:

[0114] The fourth control submodule is used to control the offshore half-bridge flexible DC converter valve to increase the AC bus voltage to turn on the first diode valve and the second diode valve; for details, please refer to the description in the above embodiment and will not be repeated here.

[0115] The fifth control submodule is used to control the diesel generator to stop running and start other wind turbines in the offshore wind farm to complete the system startup. The details are described in the above embodiment and will not be repeated here.

[0116] In one example, the fifth control submodule includes:

[0117] The fourth control unit is configured to reduce the active power and reactive power of the diesel generator until both the active power and reactive power of the diesel generator are 0, and then disconnect the third and fourth circuit breakers. For details, refer to the description in the above embodiment and will not be repeated here.

[0118] The specific limitations and beneficial effects of the above-mentioned device can be found in the above-mentioned limitations on the startup control method for a self-starting offshore wind power DC transmission system, and will not be repeated here. Each of the above-mentioned modules can be implemented in whole or in part through software, hardware, or a combination thereof. Each of the above-mentioned modules can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the memory of the computer device in software form, so that the processor can call and execute the corresponding operations of each of the above modules.

[0119] Figure 4 is a schematic diagram of the hardware structure of a computer device according to an exemplary embodiment. As shown in Figure 4 , the device includes one or more processors 410 and memory 420. Memory 420 includes persistent memory, volatile memory, and a hard disk. Figure 4 uses one processor 410 as an example. The device may also include an input device 430 and an output device 440.

[0120] The processor 410 , the memory 420 , the input device 430 , and the output device 440 may be connected via a bus or other means. FIG. 4 takes the bus connection as an example.

[0121] The processor 410 may be a central processing unit (CPU). The processor 410 may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or a combination of the above chips. The general-purpose processor may be a microprocessor or any conventional processor.

[0122] Memory 420, as a non-transitory computer-readable storage medium, includes persistent memory, volatile memory, and a hard disk, and can be used to store non-transitory software programs, non-transitory computer executable programs, and modules, such as the program instructions / modules corresponding to the self-starting offshore wind power DC transmission system startup control method in the embodiments of the present application. Processor 410 executes the non-transitory software programs, instructions, and modules stored in memory 420 to execute various server functional applications and data processing, thereby implementing any of the aforementioned self-starting offshore wind power DC transmission system startup control methods.

[0123] The memory 420 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data required for use, etc. In addition, the memory 420 may include a high-speed random access memory, and may also include a non-volatile memory, such as at least one disk storage device, a flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory 420 may optionally include a memory remotely located relative to the processor 410, and these remote memories may be connected to the data processing device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0124] The input device 430 can receive input digital or character information and generate signal input related to user settings and function control. The output device 440 can include a display device such as a display screen.

[0125] One or more modules are stored in the memory 420 , and when executed by one or more processors 410 , the method shown in FIG. 2 is performed.

[0126] The above-mentioned product can execute the method provided in the embodiment of this application, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not fully described in this embodiment, please refer to the relevant description in the embodiment shown in Figure 2.

[0127] The present application also provides a non-transitory computer storage medium, which stores computer-executable instructions that can execute the control method in any of the above method embodiments. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), a random access memory (RAM), a flash memory, a hard disk drive (HDD), or a solid-state drive (SSD); the storage medium can also include a combination of the above types of memory.

[0128] It should be noted that, in this document, relational terms such as "first" and "second" 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, so that a process, method, article, or device that includes 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 other identical elements in the process, method, article, or device that includes the element.

[0129] The above are merely specific embodiments of the present application to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those 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 will not be limited to the embodiments shown herein, but rather is intended to conform to the widest scope consistent with the principles and novel features of the present application.

Claims

1. A self-starting offshore wind power direct current transmission system, characterized in that: The system comprises: an onshore power grid, an onshore converter station, an offshore converter station and an offshore wind farm; The onshore power grid is connected to the onshore converter station; The onshore converter station is connected to the offshore converter station, and the offshore converter station includes a first diode valve, an offshore half-bridge flexible DC converter valve, a second diode valve, a diesel generator-converter group and an offshore AC busbar; The first diode valve, the offshore half-bridge flexible DC converter valve, and the second diode valve are connected in series on the DC side; The first diode valve, the offshore half-bridge flexible DC converter valve, the second diode valve, and the diesel generator-converter group are respectively connected to the offshore AC bus; The offshore AC busbar is connected to the offshore wind farm.

2. The system according to claim 1, characterized in that The onshore converter station includes an onshore flexible DC converter valve, which includes a three-phase bridge arm, and each bridge arm of the three-phase bridge arm includes a plurality of half-bridge sub-modules connected in series.

3. The system according to claim 2, characterized in that The onshore converter station also includes an onshore flexible DC connection transformer, and the onshore flexible DC converter valve is connected to the onshore power grid via a second circuit breaker, the onshore flexible DC connection transformer, and a first circuit breaker in sequence.

4. The system according to claim 1, characterized in that The diesel generator-converter group includes a diesel generator and a converter, and the offshore converter station also includes a transformer; The diesel generator is connected to the offshore AC busbar via the converter, the third circuit breaker, the transformer and the fourth circuit breaker in sequence.

5. The system according to claim 4, characterized in that The offshore converter station also includes a first rectifier transformer, an offshore flexible DC connection transformer, and a second rectifier transformer; The first diode valve is connected to the offshore AC busbar via the first rectifier transformer and the fifth circuit breaker in sequence; The offshore half-bridge flexible DC converter valve is connected to the offshore AC busbar via the sixth circuit breaker, the offshore flexible DC connection transformer, and the seventh circuit breaker in sequence; The second diode valve is connected to the offshore AC busbar via the second rectifier transformer and the eighth circuit breaker in sequence.

6. A self-starting offshore wind power DC transmission system startup control method, characterized in that: For the self-starting offshore wind power direct current transmission system according to claim 1, the method comprises: Charging the onshore converter station through the onshore power grid until the onshore converter station completes charging; Control the offshore half-bridge flexible DC converter valve and diesel generator-converter group in the offshore converter station to jointly support the AC bus voltage of the offshore AC bus to start the offshore wind farm; The first diode valve and the second diode valve in the offshore converter station are turned on to complete the startup of the self-starting offshore wind power direct current transmission system.

7. The method according to claim 6, characterized in that The onshore converter station comprises an onshore flexible DC converter valve and an onshore flexible DC connection transformer, and the onshore flexible DC converter valve is connected to the onshore power grid via a second circuit breaker, the onshore flexible DC connection transformer and a first circuit breaker in sequence; The charging of the onshore converter station through the onshore power grid until the onshore converter station completes charging includes: The first circuit breaker and the second circuit breaker are closed, and the onshore flexible DC converter valve is charged through the onshore power grid until the onshore flexible DC converter valve is completely charged, and the onshore flexible DC converter valve is unlocked.

8. The method according to claim 6, characterized in that The method of controlling the offshore half-bridge flexible DC converter valve and the diesel generator-converter group in the offshore converter station to jointly support the AC bus voltage of the offshore AC bus to start the offshore wind farm includes: Controlling the diesel generator-converter group to establish the AC bus voltage, so that the offshore half-bridge flexible DC converter valve completes charging, and unlocking the offshore half-bridge flexible DC converter valve; The offshore half-bridge flexible DC converter valve and the diesel generator-converter group are controlled to jointly support the AC bus voltage to start the offshore wind farm.

9. The method according to claim 8, characterized in that The diesel generator-converter group includes a diesel generator and a converter; the offshore converter station also includes a transformer, a first rectifier transformer, an offshore flexible DC connection transformer, and a second rectifier transformer; the diesel generator is connected to the offshore AC busbar through the converter, the third circuit breaker, the transformer, and the fourth circuit breaker in sequence; the first diode valve is connected to the offshore AC busbar through the first rectifier transformer and the fifth circuit breaker in sequence; the offshore half-bridge flexible DC converter valve is connected to the offshore AC busbar through the sixth circuit breaker, the offshore flexible DC connection transformer, and the seventh circuit breaker in sequence; the second diode valve is connected to the offshore AC busbar through the second rectifier transformer and the eighth circuit breaker in sequence; The controlling the diesel generator-converter group to establish the AC bus voltage so that the offshore half-bridge flexible DC converter valve completes charging and unlocks the offshore half-bridge flexible DC converter valve includes: Close the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker, the seventh circuit breaker and the eighth circuit breaker, control the diesel generator-converter group to establish the AC bus voltage by controlling the AC voltage amplitude and frequency in a zero-starting boosting manner, start charging the offshore half-bridge flexible DC converter valve during the zero-starting boosting process, and supply power to the first rectifier transformer, the offshore flexible DC connecting transformer and the second rectifier transformer, continue to charge the offshore half-bridge flexible DC converter valve after the diesel generator-converter group establishes the AC bus voltage, until the offshore half-bridge flexible DC converter valve is fully charged, and unlock the offshore half-bridge flexible DC converter valve.

10. The method according to claim 9, characterized in that The controlling the offshore half-bridge flexible DC converter valve and the diesel generator-converter group to jointly support the AC bus voltage to start the offshore wind farm includes: Controlling the offshore half-bridge flexible DC converter valve to adopt AC voltage amplitude and frequency control, and jointly supporting the AC bus voltage with the diesel generator-converter group to start a preset number of wind turbines in the offshore wind farm; When a preset number of wind turbines in the offshore wind farm are started and transmit power to the offshore converter station, the diesel generator is switched to fixed active power and fixed reactive power control.

11. The method according to claim 10, characterized in that The step of conducting the first diode valve and the second diode valve in the offshore converter station to complete the startup of the self-starting offshore wind power direct current transmission system includes: Controlling the offshore half-bridge flexible DC converter valve to increase the AC bus voltage to turn on the first diode valve and the second diode valve; The diesel generator is controlled to stop running, and other wind turbines of the offshore wind farm are started to complete the startup of the system.

12. The method according to claim 11, characterized in that Controlling the diesel generator to stop running includes: The active power and reactive power of the diesel generator are reduced until the active power and reactive power of the diesel generator are both 0, and then the third circuit breaker and the fourth circuit breaker are disconnected.

13. A self-starting offshore wind power DC transmission system startup control device, characterized in that: The self-starting offshore wind power direct current transmission system according to claim 1, the device comprising: A first control module is used to charge the onshore converter station through the onshore power grid until the onshore converter station completes charging; The second control module is used to control the offshore half-bridge flexible DC converter valve and the diesel generator-converter group in the offshore converter station to jointly support the AC bus voltage of the offshore AC bus to start the offshore wind farm; The conduction module is used to conduct the first diode valve and the second diode valve in the offshore converter station to complete the start-up of the self-starting offshore wind power direct current transmission system.

14. A computer device, characterized in that: It comprises a memory and a processor, the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the steps of the self-starting offshore wind power direct current transmission system startup control method described in any one of claims 6 to 12 by executing the computer instructions.

15. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the self-starting offshore wind power direct current transmission system startup control method as described in any one of claims 6 to 12 are implemented.

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