Offshore wind power direct current transmission topology circuit and system based on series-parallel converters

Abstract

The present application provides an offshore wind power direct current transmission topology circuit and system based on series-parallel converters. The topology circuit comprises an offshore wind farm, an offshore converter, a direct current submarine cable, an onshore converter, an onshore transformer, and an onshore power grid. In the topology circuit provided by the present application, the structure of the offshore converter is improved, reducing the size and costs of the offshore converter; and the improved offshore converter comprises three diode valves and one offshore auxiliary MMC, wherein direct current sides of the three diode valves are connected in series, and the offshore auxiliary MMC is connected in parallel to the direct current side of one diode valve, effectively reducing the costs of the offshore converter. In the starting process of the system provided by the present application, a first bypass switch and a second bypass switch are controlled to be switched on by means of a control device, and the onshore converter implements onshore energy reverse transmission by means of the first bypass switch and the second bypass switch, completing the black start of the offshore wind farm.

Description

A topological circuit and system for offshore wind power DC transmission based on hybrid converter valves

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 10, 2023, with application number 202311002637.X and invention name “A kind of offshore wind power DC transmission topology circuit and system based on hybrid converter valve”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of offshore wind power technology, and in particular to an offshore wind power direct current transmission topology circuit and system based on a hybrid converter valve. Background Art

[0003] Long-distance offshore wind power transmission typically utilizes high-voltage direct current (HVDC) technology. After the power generated by offshore wind turbines is collected via AC cables, offshore converter valves convert the AC into DC, which is then transmitted to an onshore converter station via the DC submarine cable. Currently, offshore converter valves in offshore wind power HVDC transmission projects all utilize modular multilevel converters (MMCs) comprised of multiple half-bridge submodules. However, MMCs are expensive, bulky, and heavy, resulting in high investment costs.

[0004] To achieve lightweight offshore converter valves and converter station platforms and reduce the cost of offshore wind power transmission systems, the current sending end of offshore wind power DC transmission systems mostly uses various aggregation transmission topologies and networking solutions, such as unidirectional current-source uncontrolled rectifier converters based on diode elements. While using unidirectional current-source uncontrolled rectifier converters based on diode elements on the sending end helps to lightweight offshore platforms, existing solutions have the disadvantage of not being able to black-start offshore wind farms.

[0005] Summary of the Invention

[0006] Therefore, the technical solution of the present application mainly solves the defects of large size and high cost of existing offshore converter valves, thereby providing an offshore wind power DC transmission topology circuit and system based on hybrid converter valves.

[0007] In a first aspect, an embodiment of the present application provides an offshore wind power DC transmission topology circuit based on a hybrid converter valve, comprising: an offshore wind farm, an offshore converter valve, a DC submarine cable, an onshore converter valve, an onshore transformer, and an onshore power grid;

[0008] The offshore converter valve is connected to the offshore wind farm via the offshore busbar and to the onshore converter valve via the DC submarine cable; the onshore converter valve is connected to the onshore power grid via the onshore transformer;

[0009] The offshore converter valve includes an offshore auxiliary modular multilevel converter valve, a first diode valve, a second diode valve and a third diode valve. The DC side of the offshore auxiliary modular multilevel converter valve is connected in parallel with the second diode valve, and the AC side of the offshore auxiliary modular multilevel converter valve is connected to the offshore busbar through a connecting transformer. The DC sides of the first diode valve, the second diode valve and the third diode valve are connected in series. The AC side of the first diode valve is connected to the offshore busbar through a first three-winding transformer, the AC side of the second diode valve is connected to the offshore busbar through a second three-winding transformer, and the AC side of the third diode valve is connected to the offshore busbar through a third three-winding transformer. The DC positive pole of the first diode valve is connected to the DC submarine cable through a first circuit breaker, and the submarine cable side of the first circuit breaker is connected to the negative pole of the first diode valve through a first bypass switch. The DC negative pole of the third diode valve is connected to the DC submarine cable through a second circuit breaker, and the submarine cable side of the second circuit breaker is connected to the positive pole of the third diode valve through a second bypass switch.

[0010] An embodiment of the present application provides an offshore wind power DC transmission topology circuit based on a hybrid converter valve. Because existing offshore converter valves use modular multi-level converter valves containing multiple half-bridge sub-modules, resulting in large size and high cost of the offshore converter valves, the structure of the offshore converter valves is improved. The improved offshore converter valve includes three groups of diode valves and one group of offshore auxiliary MMCs, wherein the three groups of diodes are connected in series on the DC side, and the offshore auxiliary MMC is connected in parallel with the DC side of a diode valve, effectively reducing the size and cost of the offshore converter valve.

[0011] In a second aspect, an embodiment of the present application provides an offshore wind power DC transmission system based on a parallel-parallel converter valve, comprising: an offshore wind power DC transmission topology circuit based on a parallel-parallel converter valve and a control device, wherein the control device is connected to the topology circuit;

[0012] a control device, configured to send a closing instruction to the first bypass switch and the second bypass switch; upon detecting that the first bypass switch and the second bypass switch are closed, obtain an onshore charging voltage of the onshore converter valve and an offshore charging voltage of the offshore converter valve; and send an unlocking and power supply instruction to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage; wherein the onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with a first working voltage output by the onshore power grid via an onshore transformer;

[0013] An offshore converter valve, configured to receive an unlocking power supply instruction and supply power to a wind turbine in an offshore wind farm based on the unlocking power supply instruction;

[0014] The control device is also used to detect the current flowing through the first bypass switch and the second bypass switch when a preset number of fans have completed startup. When the current flowing through the first bypass switch and the second bypass switch is zero, a disconnect instruction is sent to the first bypass switch and the second bypass switch respectively, and a closing instruction is sent to the first circuit breaker and the second circuit breaker respectively.

[0015] An embodiment of the present application provides an offshore wind power DC transmission system based on a hybrid converter valve. By improving the structure of the offshore converter valve, the volume and cost of the offshore converter valve are reduced. The improved offshore converter valve includes three groups of diode valves and a group of offshore auxiliary MMCs, wherein the three groups of diodes are connected in series on the DC side, and the offshore auxiliary MMC is connected in parallel with the DC side of a diode valve. During system startup, the onshore converter valve realizes onshore energy reverse transmission through the first bypass switch and the second bypass switch, completing the black start of the offshore wind farm.

[0016] In combination with the second aspect, in a possible implementation manner, the offshore converter valve further includes a third circuit breaker, a fourth circuit breaker, a fifth circuit breaker, a sixth circuit breaker, and a seventh circuit breaker;

[0017] The AC side of the offshore auxiliary modular multilevel converter valve is connected to the offshore busbar via the third circuit breaker, the connecting transformer, and the fourth circuit breaker in sequence; the AC side of the first diode valve is connected to the offshore busbar via the first three-winding transformer and the fifth circuit breaker in sequence; the AC side of the second diode valve is connected to the offshore busbar via the second three-winding transformer and the sixth circuit breaker in sequence; and the AC side of the third diode valve is connected to the offshore busbar via the third three-winding transformer and the seventh circuit breaker in sequence;

[0018] The control device is further configured to, when detecting that the offshore converter valve is unlocked, send closing instructions to the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker, and the seventh circuit breaker, respectively, so that the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker, and the seventh circuit breaker are closed.

[0019] In combination with the second aspect, in one possible embodiment, when the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker and the seventh circuit breaker are closed, the offshore converter valve is also used to establish a preset voltage on the offshore busbar in a zero-starting manner. The preset voltage is less than the rated voltage of the offshore busbar. The preset voltage makes the first diode valve, the second diode valve and the third diode valve non-conductive, and the preset voltage is higher than the preset grid-connected voltage threshold of the offshore wind turbine.

[0020] In conjunction with the second aspect, in another possible implementation, the onshore transformer includes a starting transformer, the starting transformer is connected on a valve side to the onshore converter valve via an eighth circuit breaker, and is connected on a grid side to the onshore power grid via a ninth circuit breaker.

[0021] The control device is further used to send control instructions to the eighth circuit breaker and the ninth circuit breaker respectively, and the control instructions are used to control the closing of the eighth circuit breaker and the ninth circuit breaker. After the eighth circuit breaker and the ninth circuit breaker are closed, the onshore power grid outputs a first working voltage through the starting transformer and then charges the onshore converter valve and the offshore converter valve.

[0022] In conjunction with the second aspect, in another possible implementation, the onshore transformer further includes a steady-state operation transformer, wherein the valve side of the steady-state operation transformer is connected to the onshore converter valve through a tenth circuit breaker, and the grid side is connected to the onshore power grid through an eleventh circuit breaker;

[0023] The control device is further configured to, upon detecting that the first bypass switch and the second bypass switch are disconnected, send disconnect instructions to the eighth circuit breaker and the ninth circuit breaker, respectively, and send closing instructions to the tenth circuit breaker and the eleventh circuit breaker; wherein, after the tenth circuit breaker and the eleventh circuit breaker are closed, the onshore power grid outputs the second operating voltage through the steady-state operating transformer to charge the onshore converter valve.

[0024] In combination with the second aspect, in another possible implementation, the control device is further used to detect in real time the onshore charging voltage of the onshore converter valve and the offshore charging voltage of the offshore converter valve, and when the onshore charging voltage reaches a first voltage threshold and the offshore charging voltage reaches a second voltage threshold, send an unlocking power supply instruction to the offshore converter valve.

[0025] In combination with the second aspect, in another possible implementation, the control device is further used to send an uncontrolled charging instruction to the onshore converter valve when obtaining the closed state of the eighth circuit breaker and the ninth circuit breaker, and obtain the DC side capacitor voltage of the onshore converter valve, and send a controllable charging instruction to the onshore converter valve based on the capacitor voltage.

[0026] In combination with the second aspect, in another possible implementation, the control device is further configured to, when detecting that the first circuit breaker and the second circuit breaker are closed, obtain the rated voltage value of the offshore busbar, the voltage reference value of the AC side of the offshore converter valve, and the current value of the connecting line between the DC side of the offshore auxiliary modular multilevel converter valve and the second diode valve, and input the rated voltage value of the offshore busbar, the voltage reference value of the AC side of the offshore converter valve, and the current value of the connecting line between the DC side of the offshore auxiliary modular multilevel converter valve and the second diode valve into a pre-built voltage control model to obtain a voltage adjustment value of the AC side of the offshore converter valve, and adjust the voltage to send to the offshore converter valve, so that the offshore converter valve adjusts the AC side voltage.

[0027] In a third aspect, an embodiment of the present application further provides a method for starting an offshore wind power DC transmission system based on a hybrid converter valve, which is applied to an offshore wind power DC transmission system based on a hybrid converter valve. The method includes: sending a closing instruction to a first bypass switch and a second bypass switch; when it is detected that the first bypass switch and the second bypass switch are closed, obtaining an onshore charging voltage of the onshore converter valve and an offshore charging voltage of the offshore converter valve, and sending an unlocking power supply instruction to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage; wherein the onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with the first working voltage output by the onshore transformer from the onshore power grid; when a preset number of wind turbines are started, sending a no-load operation instruction to the offshore auxiliary modular multi-level converter valve, and sending a disconnection instruction to the first bypass switch and the second bypass switch respectively, and sending a closing instruction to the first circuit breaker and the second circuit breaker respectively.

[0028] In a fourth aspect, an embodiment of the present application further provides a starting device for an offshore wind power DC transmission system based on a parallel-parallel converter valve, which is applied to an offshore wind power DC transmission system based on a parallel-parallel converter valve. The device includes: a first sending module, used to send a closing instruction to a first bypass switch and a second bypass switch; an acquisition module, used to obtain an onshore charging voltage of the onshore converter valve and an offshore charging voltage of the offshore converter valve after detecting that the first bypass switch and the second bypass switch are closed, and send an unlocking power supply instruction to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage; wherein the onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with the first working voltage output by the onshore transformer from the onshore power grid; a second sending module, used to send a no-load operation instruction to the offshore auxiliary modular multi-level converter valve when a preset number of wind turbines have completed startup, and send a disconnection instruction to the first bypass switch and the second bypass switch respectively, and send a closing instruction to the first circuit breaker and the second circuit breaker respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] FIG1 is a circuit diagram of an offshore wind power DC transmission topology circuit based on a parallel-parallel converter valve according to an embodiment of the present application;

[0031] FIG2 is a schematic diagram of a control strategy for a specific example of an offshore wind power DC transmission system based on a parallel-parallel converter valve according to an embodiment of the present application;

[0032] FIG3 is a flow chart of a method for starting an offshore wind power DC transmission system based on a parallel-parallel converter valve according to an embodiment of the present application;

[0033] FIG4 is a functional block diagram of a starting device for an offshore wind power DC transmission system based on a parallel-parallel converter valve according to an embodiment of the present application;

[0034] FIG5 is a specific example diagram of an electronic device in an embodiment of the present application. DETAILED DESCRIPTION

[0035] 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.

[0036] In the description of this application, it should be noted that the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a mechanical connection, or an electrical connection; or it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two components, or it can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0037] The embodiment of the present application provides an offshore wind power DC transmission topology circuit based on a hybrid converter valve, as shown in FIG1 , including: an offshore wind farm 3, an offshore converter valve 4, a DC submarine cable 5, an onshore converter valve 6, an onshore transformer 7, and an onshore power grid 8;

[0038] The offshore converter valve 4 is connected to the offshore wind farm 3 via the offshore busbar, and is connected to the onshore converter valve 6 via the DC submarine cable 5; the onshore converter valve 6 is connected to the onshore power grid 8 via the onshore transformer 7;

[0039] The offshore converter valve 4 includes an offshore auxiliary modular multi-level converter valve 9, a first diode valve 10, a second diode valve 11 and a third diode valve 12. The DC side of the offshore auxiliary modular multi-level converter valve 9 is connected in parallel with the second diode valve 11. The AC side of the offshore auxiliary modular multi-level converter valve 9 is connected to the offshore busbar through a connecting transformer 13. The DC sides of the first diode valve 10, the second diode valve 11 and the third diode valve 12 are connected in series. The AC side of the first diode valve 10 is connected to the offshore busbar through a first three-winding transformer 14. The second diode valve 11 is connected to the offshore busbar through a first three-winding transformer 15. The AC side of the third diode valve 12 is connected to the offshore busbar through a second three-winding transformer 15, the AC side of the third diode valve 12 is connected to the offshore busbar through a third three-winding transformer 16, the DC positive pole of the first diode valve 10 is connected to the DC submarine cable 5 through a first circuit breaker 17, the submarine cable side of the first circuit breaker 17 is connected to the negative pole of the first diode valve 10 through a first bypass switch 18, the DC negative pole of the third diode valve 12 is connected to the DC submarine cable 5 through a second circuit breaker 19, and the submarine cable side of the second circuit breaker 19 is connected to the positive pole of the third diode valve 12 through a second bypass switch 20.

[0040] This embodiment proposes a topology circuit for offshore wind power DC transmission based on a hybrid converter valve. Because existing offshore converter valves use modular multi-level converter valves containing multiple half-bridge sub-modules, resulting in large size and high cost, the topology circuit in this embodiment improves the structure of the offshore converter valve. The improved offshore converter valve includes three groups of diode valves and one group of offshore auxiliary MMCs. The three groups of diodes are connected in series on the DC side, and the offshore auxiliary MMC is connected in parallel with the DC side of a diode valve, effectively reducing the size and cost of the offshore converter valve.

[0041] The embodiment of the present application provides an offshore wind power DC transmission system based on a parallel-parallel converter valve, comprising: an offshore wind power DC transmission topology circuit based on a parallel-parallel converter valve and a control device, wherein the control device is connected to the topology circuit;

[0042] The control device is configured to send a closing instruction to the first bypass switch 18 and the second bypass switch 20. Upon detecting that the first bypass switch 18 and the second bypass switch 20 are closed, the control device obtains the onshore charging voltage of the onshore converter valve 6 and the offshore charging voltage of the offshore converter valve 4, and sends an unlocking power supply instruction to the offshore converter valve 4 based on the onshore charging voltage and the offshore charging voltage. The onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve 6 and the offshore converter valve 4 with the first operating voltage output by the onshore power grid 8 via the onshore transformer 7.

[0043] Exemplarily, when the control device detects that the first bypass switch 18 (Bp1) and the second bypass switch 20 (Bp2) are in the closed state, the onshore charging voltage of the onshore converter valve 6 and the offshore charging voltage of the offshore converter valve 4 are obtained, and an unlocking instruction is sent to the offshore converter valve 4 based on the onshore charging voltage of the onshore converter valve 6 and the offshore charging voltage of the offshore converter valve 4, so that the offshore converter valve is unlocked, providing a starting voltage for the wind turbines in the offshore wind farm 3.

[0044] Specifically, the control device is further configured to detect, in real time, the onshore charging voltage of the onshore converter valve 6 and the offshore charging voltage of the offshore converter valve 4. When the onshore charging voltage reaches a first voltage threshold and the offshore charging voltage reaches a second voltage threshold, the control device sends an unlocking power supply instruction to the offshore converter valve 4. In the embodiments of the present application, the specific contents of the first and second voltage thresholds are not limited and can be determined by those skilled in the art as needed.

[0045] The offshore converter valve 4 is configured to receive an unlocking power supply instruction and supply power to the wind turbines in the offshore wind farm 3 based on the unlocking power supply instruction.

[0046] For example, when the offshore converter valve 4 receives the unlock power supply instruction and performs the unlock power supply operation, the offshore auxiliary modular multi-level converter valve 9 (offshore auxiliary MMC) uses a zero-start boost method to provide grid-connected voltage to the AC side of the offshore wind farm 3, so that the wind turbines in the offshore wind farm 3 are started.

[0047] The control device is also used to detect the current flowing through the first bypass switch 18 and the second bypass switch 20 when a preset number of fans have completed startup. When the current flowing through the first bypass switch 18 and the second bypass switch 20 is zero, an opening instruction is sent to the first bypass switch 18 and the second bypass switch 20 respectively, and a closing instruction is sent to the first circuit breaker 17 and the second circuit breaker 19 respectively.

[0048] For example, the preset number can be any number that can be determined by those skilled in the art as needed. In the embodiment of the present application, the preset number can be 10% of the number of wind turbines in the offshore wind farm 3. When the preset number of wind turbines are started and the power generation gradually increases, and when the current flowing through the first bypass switch 18 (Bp1) and the second bypass switch 20 (Bp2) gradually decreases to zero, the first bypass switch 18 (Bp1) and the second bypass switch 20 (Bp2) are controlled to be opened; and closing instructions are sent to the first circuit breaker 17 (Brk8) and the second circuit breaker 19 (Brk9), respectively. When the first circuit breaker 17 and the second circuit breaker 19 are closed, and the diode valve in the offshore converter valve 4 meets the conduction condition and is turned on, the offshore wind power DC output system operates normally.

[0049] This embodiment proposes an offshore wind power DC transmission system based on a hybrid converter valve. By improving the structure of the offshore converter valve, the size and cost of the offshore converter valve are reduced. The improved offshore converter valve includes three groups of diode valves and one group of offshore auxiliary MMCs. The three groups of diodes are connected in series on the DC side, and the offshore auxiliary MMC is connected in parallel with the DC side of a diode valve. During system startup, the onshore converter valve realizes onshore energy feedback through the first bypass switch and the second bypass switch, completing the black start of the offshore wind farm.

[0050] As an optional embodiment of the present application, the offshore converter valve further includes a third circuit breaker 21, a fourth circuit breaker 22, a fifth circuit breaker 23, a sixth circuit breaker 24 and a seventh circuit breaker 25;

[0051] The AC side of the offshore auxiliary modular multilevel converter valve 9 is connected to the offshore busbar via the third circuit breaker 21, the connecting transformer 13, and the fourth circuit breaker 22 in sequence. The AC side of the first diode valve 10 is connected to the offshore busbar via the first three-winding transformer 14 and the fifth circuit breaker 23 in sequence. The AC side of the second diode valve 11 is connected to the offshore busbar via the second three-winding transformer 15 and the sixth circuit breaker 24 in sequence. The AC side of the third diode valve 12 is connected to the offshore busbar via the third three-winding transformer 16 and the seventh circuit breaker 25 in sequence.

[0052] The control device is further configured to, when detecting that the offshore converter valve 4 is unlocked, send closing instructions to the third circuit breaker 21, the fourth circuit breaker 22, the fifth circuit breaker 23, the sixth circuit breaker 24, and the seventh circuit breaker 25, respectively, so that the third circuit breaker 21, the fourth circuit breaker 22, the fifth circuit breaker 23, the sixth circuit breaker 24, and the seventh circuit breaker 25 are closed.

[0053] For example, when the control device detects that the offshore converter valve 4 is unlocked, it sends a closing instruction to the third circuit breaker 21 (Brk10), the fourth circuit breaker 22 (Brk11), the fifth circuit breaker 23 (Brk6), the sixth circuit breaker 24 (Brk5) and the seventh circuit breaker 25 (Brk7). After the third circuit breaker 21 (Brk10), the fourth circuit breaker 22 (Brk11), the fifth circuit breaker 23 (Brk6), the sixth circuit breaker 24 (Brk5) and the seventh circuit breaker 25 (Brk7) are closed, the offshore auxiliary modular multilevel converter valve 9 (offshore auxiliary MMC) in the offshore converter valve 4 provides the grid-connected voltage to the AC side of the offshore wind farm 3 through the connecting transformer 13.

[0054] As an optional embodiment of the present application, the third circuit breaker 21, the fourth circuit breaker 22, the fifth circuit breaker 23, the sixth circuit breaker 24 and the seventh circuit breaker 25, the offshore converter valve is also used to establish a preset voltage on the offshore busbar in a zero-starting manner, the preset voltage is lower than the rated voltage of the offshore busbar, the preset voltage makes the first diode valve 10, the second diode valve 11 and the third diode valve 12 non-conductive, and the preset voltage is higher than the preset grid-connected voltage threshold of the offshore wind turbine.

[0055] For example, in this embodiment of the present application, the offshore converter valve 4 is unlocked based on the unlock power supply command and operates in AC voltage source control mode. The offshore auxiliary MMC in the offshore converter valve uses a zero-start voltage step-up method to provide grid-connected voltage to the AC side of the offshore wind farm. This grid-connected voltage amplitude is controlled to a preset voltage, which can be 95% of the rated voltage amplitude of the offshore busbar. This ensures that the first diode valve 10, the second diode valve 11, and the third diode valve 12 in the offshore converter valve do not suddenly conduct when the fifth circuit breaker 23, the sixth circuit breaker 24, and the seventh circuit breaker 25 are closed. The preset grid-connected voltage threshold may include, but is not limited to, 90% of the rated voltage amplitude of the offshore busbar.

[0056] As an optional embodiment of the present application, the onshore transformer 7 includes a starting transformer 26 , the valve side of the starting transformer 26 is connected to the onshore converter valve 6 through an eighth circuit breaker 27 , and the grid side is connected to the onshore power grid 8 through a ninth circuit breaker 28 ;

[0057] The control device is further used to send control instructions to the eighth circuit breaker 27 and the ninth circuit breaker 28 respectively, and the control instructions are used to control the closing of the eighth circuit breaker 27 and the ninth circuit breaker 28. After the eighth circuit breaker 27 and the ninth circuit breaker 28 are closed, the onshore power grid 8 outputs the first working voltage through the starting transformer 26, and then charges the onshore converter valve 6 and the offshore converter valve 4.

[0058] Exemplarily, the starting transformer 26 is used in the system startup phase. In the embodiment of the present application, when the eighth circuit breaker 27 (Brk4) and the ninth circuit breaker 28 (Brk3) are closed, the onshore power grid 8 outputs the first working voltage through the starting transformer 26 and charges the onshore converter valve 6 and the offshore converter valve 4.

[0059] As an optional embodiment of the present application, the onshore transformer 7 further includes a steady-state operation transformer 29 , the valve side of the steady-state operation transformer 29 is connected to the onshore converter valve 6 via a tenth circuit breaker 30 , and the grid side is connected to the onshore power grid 8 via an eleventh circuit breaker 31 ;

[0060] The control device is further configured to, upon detecting that the first bypass switch 18 and the second bypass switch 20 are disconnected, send disconnect instructions to the eighth circuit breaker 27 and the ninth circuit breaker 28, respectively, and send closing instructions to the tenth circuit breaker 30 and the eleventh circuit breaker 31; wherein, after the tenth circuit breaker 30 and the eleventh circuit breaker 31 are closed, the onshore power grid 8 outputs the second operating voltage through the steady-state operation transformer 29 to charge the onshore converter valve 6.

[0061] For example, when it is monitored that the first bypass switch 18 (Bp1) and the second bypass switch 20 (Bp2) are disconnected, a disconnection instruction is sent to the eighth circuit breaker 27 (Brk4) and the ninth circuit breaker 28 (Brk3), and a closing instruction is sent to the tenth circuit breaker 30 (Brk2) and the eleventh circuit breaker 31 (Brk1). After the tenth circuit breaker 30 and the eleventh circuit breaker 31 are closed, the onshore power grid 8 charges the onshore converter valve 6 through the steady-state operating transformer, so that the onshore converter valve 6 completes uncontrolled charging at the rated voltage and is unlocked, and the rated voltage of the DC side is established.

[0062] As an optional embodiment of the present application, the control device is further used to send an uncontrolled charging instruction to the onshore converter valve 6 when obtaining the closed state of the eighth circuit breaker 27 and the ninth circuit breaker 28, and obtain the DC side capacitor voltage of the onshore converter valve 6, and send a controllable charging instruction to the onshore converter valve 6 based on the capacitor voltage.

[0063] For example, the onshore power grid 8 uses the startup transformer 26 to perform uncontrolled charging on the onshore converter valve 6. Typically, when the capacitor voltage of the onshore converter valve reaches 30% of its rated voltage, the control device issues a controlled charging command, switching the onshore converter valve 6 from uncontrolled charging to controlled charging. After uncontrolled charging is complete, the onshore converter valve 6 is unlocked, and controlled charging begins. A constant DC voltage and constant reactive power control are used to establish a DC voltage. During startup, only a low DC voltage is output (e.g., 10% of the rated voltage, in which case the DC voltage command value is 10% of the rated value, and the reactive power command is zero).

[0064] As an optional embodiment of the present application, the control device is further used to obtain the rated voltage value of the offshore busbar, the AC side voltage reference value of the offshore converter valve 4, and the current value of the connecting line between the DC side of the offshore auxiliary modular multi-level converter valve 9 and the second diode valve 11 when detecting that the first circuit breaker 17 and the second circuit breaker 19 are closed, and input the rated voltage value of the offshore busbar, the AC side voltage reference value of the offshore converter valve 4, and the current value of the connecting line between the DC side of the offshore auxiliary modular multi-level converter valve 9 and the second diode valve 9 into a pre-constructed voltage control model to obtain the AC side voltage adjustment value of the offshore converter valve 4, and adjust the voltage to send to the offshore converter valve 4, so that the offshore converter valve 4 adjusts the AC side voltage.

[0065] Exemplarily, a pre-built voltage control model is used to control the AC side voltage of the offshore converter valve 4. In an embodiment of the present application, when the first circuit breaker 17 (Brk8) and the second circuit breaker 19 (Brk9) are closed, the voltage on the offshore busbar is 95% of the rated voltage, so the diode valve in the offshore converter valve 4 will not be turned on. At this time, the offshore converter valve 4 AC side voltage adjustment value is obtained based on the rated voltage value of the offshore busbar, the offshore converter valve 4 AC side voltage reference value, the current value of the connecting line between the DC side of the offshore auxiliary modular multi-level converter valve 9 and the second diode valve 9, and the pre-built voltage control model, and the voltage is adjusted and sent to the offshore converter valve 4, so that the offshore converter valve 4 adjusts the AC side voltage. The control strategy of the pre-built voltage control model is shown in FIG2, where I dc _MMC represents the current in the connection line between the offshore auxiliary MMC and its parallel diode valve; 66kV represents the rated amplitude of the offshore wind power AC collection voltage (66kV for general projects), ω ref Indicates the angular frequency reference value. 100πrad / s indicates the control angular frequency is 100πrad / s. V ref Indicates the voltage amplitude reference value; -5% × 66kV is mainly to set the voltage amplitude reference value of the AC side of the offshore auxiliary MMC to 95% of 66kV. The role of the PI controller is to ensure that I dc The value of _MMC is kept at 0, so that the offshore auxiliary MMC does not need to transmit active power and only needs to provide reactive power, which reduces the overall capacity demand and further saves the cost of offshore converter valves. The PI controller is generally composed of a proportional control link and an integral control link in parallel. Specifically, the PI controller first obtains I dc The difference between _MMC and 0 is then processed through the proportional link and the integral link to obtain the correction value of the voltage amplitude reference value of the AC side of the offshore auxiliary MMC. The correction value is then added to the 66kV rated value to obtain the final required voltage amplitude reference value of the AC side of the offshore auxiliary MMC.

[0066] The following describes the working process of an offshore wind power DC transmission system based on a parallel-parallel converter valve through a specific embodiment.

[0067] Example:

[0068] Step 1: First, close switches Bp1 and Bp2, and then close switches Brk3 and Brk4 in sequence. The onshore MMC converter valve completes uncontrolled charging and unlocks. The onshore MMC converter valve controls its DC side voltage to low-voltage startup mode and charges the offshore auxiliary MMC DC side capacitor.

[0069] Step 2: Close switches Brk10, Brk11, Brk5, Brk6, and Brk7, then unlock the offshore auxiliary MMC and operate in AC voltage source control mode. The offshore auxiliary MMC uses a zero-start boost method to provide grid-connected voltage for the AC side of the offshore wind farm. The amplitude of this grid-connected voltage is controlled at 95% of the rated voltage to ensure that the offshore diode converter valve will not suddenly turn on after Brk8 and Brk9 are closed.

[0070] Step 3: After the offshore wind farm wind turbine detects that the grid voltage has reached 95% of the rated value, it begins to gradually start generating electricity, and the power generation power gradually increases. When the current flowing through Bp1 and Bp2 gradually decreases and reaches zero, the Bp1 and Bp2 switches are disconnected, and the offshore wind turbine power generation power is controlled to remain unchanged.

[0071] Step 4: Open Brk4 and Brk3 in sequence, then close Brk1 and Brk2. The onshore MMC converter valve completes uncontrolled charging at rated voltage and unlocks, and establishes its DC side rated voltage.

[0072] Step 5: Close switches Brk8 and Brk9. Since the grid-connected voltage of the offshore wind farm is 95% of the rated value at this time, the diode valve of the offshore converter valve will not be turned on. At this time, the voltage amplitude control reference value of the AC side of the offshore auxiliary MMC is switched. The specific control strategy is shown in Figure 2. Then, the power generation of the offshore wind farm is no longer restricted, and the offshore wind turbine operates in the Maximum Power Point Tracking (MPPT) mode. At this point, the entire offshore wind power DC transmission system operates normally.

[0073] The present application also discloses a method for starting an offshore wind power DC transmission system based on a parallel-parallel converter valve. The method is applied to the offshore wind power DC transmission system based on a parallel-parallel converter valve in the above embodiment. As shown in FIG3 , the method includes:

[0074] Step S301: Send a closing instruction to the first bypass switch and the second bypass switch.

[0075] Specifically, when the onshore charging voltage reaches a first voltage threshold and the offshore charging voltage reaches a second voltage threshold, an unlocking power supply instruction is sent to the offshore converter valve.

[0076] Step S302: Upon detecting that the first and second bypass switches are closed, the onshore charging voltage of the onshore converter valve and the offshore charging voltage of the offshore converter valve are obtained, and an unlocking power supply instruction is sent to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage. The onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve using the first operating voltage output by the onshore power grid via the onshore transformer. For example, please refer to the description of the relevant portions of the embodiment shown in FIG. 1 , which will not be repeated here.

[0077] Step S303: When the preset number of wind turbines have completed startup, a no-load operation instruction is sent to the offshore auxiliary modular multi-level converter valve, an opening instruction is sent to the first bypass switch and the second bypass switch, and a closing instruction is sent to the first circuit breaker and the second circuit breaker. For example, please refer to the description of the relevant parts of the embodiment shown in FIG. 1 for details, which will not be repeated here.

[0078] The present application provides a startup method for an offshore wind power DC transmission system based on a hybrid converter valve. During the system startup process, the onshore converter valve is controlled to realize onshore energy reverse transmission through a first bypass switch and a second bypass switch, thereby completing a black start of the offshore wind farm.

[0079] As an optional embodiment of the present application, it also includes:

[0080] When it is detected that the offshore converter valve is unlocked, closing instructions are sent to the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker and the seventh circuit breaker respectively, so that the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker and the seventh circuit breaker are closed.

[0081] As an optional embodiment of the present application, it also includes:

[0082] Control instructions are sent to the eighth circuit breaker and the ninth circuit breaker respectively, where the control instructions are used to control the closing of the eighth circuit breaker and the ninth circuit breaker. After the eighth circuit breaker and the ninth circuit breaker are closed, the onshore power grid outputs a first working voltage through the starting transformer, and then charges the onshore converter valve and the offshore converter valve.

[0083] As an optional embodiment of the present application, it also includes:

[0084] When it is detected that the first bypass switch and the second bypass switch are disconnected, disconnect commands are sent to the eighth circuit breaker and the ninth circuit breaker, respectively, and closing commands are sent to the tenth circuit breaker and the eleventh circuit breaker. After the tenth circuit breaker and the eleventh circuit breaker are closed, the onshore power grid outputs the second operating voltage through the steady-state operating transformer to charge the onshore converter valve.

[0085] As an optional embodiment of the present application, it also includes:

[0086] When the closing states of the eighth circuit breaker and the ninth circuit breaker are obtained, an uncontrolled charging instruction is sent to the onshore converter valve, and the DC side capacitor voltage of the onshore converter valve is obtained, and a controlled charging instruction is sent to the onshore converter valve based on the capacitor voltage.

[0087] As an optional embodiment of the present application, it also includes:

[0088] When it is detected that the first circuit breaker and the second circuit breaker are closed, the rated voltage value of the offshore busbar, the voltage reference value of the AC side of the offshore converter valve, and the current value of the connecting line between the DC side of the offshore auxiliary modular multilevel converter valve and the second diode valve are obtained, and the rated voltage value of the offshore busbar, the voltage reference value of the AC side of the offshore converter valve, and the current value of the connecting line between the DC side of the offshore auxiliary modular multilevel converter valve and the second diode valve are input into a pre-built voltage control model to obtain an AC side voltage adjustment value of the offshore converter valve, and the voltage is adjusted and sent to the offshore converter valve, so that the offshore converter valve adjusts the AC side voltage.

[0089] The present application also discloses a startup device for an offshore wind power DC transmission system based on a parallel-parallel converter valve. The startup device is applied to the offshore wind power DC transmission system based on a parallel-parallel converter valve in the above embodiment. As shown in FIG4 , the startup device includes:

[0090] The first sending module 401 is used to send a closing instruction to the first bypass switch and the second bypass switch. For details, please refer to the description of the relevant parts of the embodiment shown in FIG3 , which will not be repeated here.

[0091] The acquisition module 402 is configured to, upon detecting that the first bypass switch and the second bypass switch are closed, acquire an onshore charging voltage of the onshore converter valve and an offshore charging voltage of the offshore converter valve, and send an unlocking and power supply instruction to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage. The onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with a first operating voltage output by the onshore power grid via an onshore transformer. For details, see the description of the relevant portions of the embodiment shown in FIG. 3 , which will not be repeated here.

[0092] The second sending module 403 is used to send a no-load operation instruction to the offshore auxiliary modular multi-level converter valve when a preset number of wind turbines have completed startup, and to send a disconnection instruction to the first bypass switch and the second bypass switch, and to send a closing instruction to the first circuit breaker and the second circuit breaker, respectively. For details, please refer to the description of the relevant parts of the embodiment shown in Figure 1, which will not be repeated here.

[0093] In addition, an embodiment of the present application further provides an electronic device, as shown in FIG5 , which may include a processor 110 and a memory 120, wherein the processor 110 and the memory 120 may be connected via a bus or other means, with FIG5 taking a bus connection as an example. Furthermore, the electronic device also includes at least one interface 130, which may be a communication interface or other interface, and is not limited in this embodiment.

[0094] The processor 110 may be a central processing unit (CPU). The processor 110 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.

[0095] Memory 120, as a non-transitory computer-readable storage medium, 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 video synthesis method in the embodiments of the present application. Processor 110 executes the non-transitory software programs, instructions, and modules stored in memory 120 to perform various processor functions and data processing, thereby implementing the startup method for an offshore wind power DC transmission system based on a parallel-parallel converter valve in the above-mentioned method embodiment.

[0096] The memory 120 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 created by the processor 110, etc. In addition, the memory 120 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 120 may optionally include a memory remotely located relative to the processor 110, and these remote memories may be connected to the processor 110 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.

[0097] In addition, at least one interface 130 is used for communication between the electronic device and external devices, such as communication with a server, etc. Optionally, at least one interface 130 can also be used to connect to external input and output devices, such as a keyboard, a display screen, etc.

[0098] One or more modules are stored in the memory 120 , and when executed by the processor 110 , perform a method for starting an offshore wind power direct current transmission system based on a parallel-parallel converter valve in the embodiment shown in FIG3 .

[0099] The specific details of the above electronic device can be understood by referring to the corresponding descriptions and effects in the embodiment shown in FIG3 , which will not be repeated here.

[0100] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. 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-mentioned types of memory.

[0101] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A topological circuit for direct current transmission of offshore wind power based on a hybrid converter valve, characterized in that: include: Offshore wind farms, offshore converter valves, DC submarine cables, onshore converter valves, onshore transformers and onshore power grids; The offshore converter valve is connected to the offshore wind farm via an offshore busbar, and is connected to the onshore converter valve via the DC submarine cable; the onshore converter valve is connected to the onshore power grid via the onshore transformer; The offshore converter valve comprises an offshore auxiliary modular multilevel converter valve, a first diode valve, a second diode valve and a third diode valve. The DC side of the offshore auxiliary modular multilevel converter valve is connected in parallel with the second diode valve, and the AC side of the offshore auxiliary modular multilevel converter valve is connected to the offshore busbar through a connecting transformer. The DC sides of the first diode valve, the second diode valve and the third diode valve are connected in series. The AC side of the first diode valve is connected to the offshore busbar through a first three-winding transformer, the AC side of the second diode valve is connected to the offshore busbar through a second three-winding transformer, and the AC side of the third diode valve is connected to the offshore busbar through a third three-winding transformer. The DC positive pole of the first diode valve is connected to the DC submarine cable through a first circuit breaker, and the submarine cable side of the first circuit breaker is connected to the negative pole of the first diode valve through a first bypass switch. The DC negative pole of the third diode valve is connected to the DC submarine cable through a second circuit breaker, and the submarine cable side of the second circuit breaker is connected to the positive pole of the third diode valve through a second bypass switch.

2. An offshore wind power DC transmission system based on a hybrid converter valve, characterized in that: include: The offshore wind power DC transmission topology circuit and control device based on the hybrid converter valve according to claim 1, wherein the control device is connected to the topology circuit; The control device is used to send a closing instruction to the first bypass switch and the second bypass switch, and when detecting that the first bypass switch and the second bypass switch are closed, obtain an onshore charging voltage of the onshore converter valve and an offshore charging voltage of the offshore converter valve, and send an unlocking power supply instruction to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage; wherein the onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with the first working voltage output by the onshore transformer from the onshore power grid; The offshore converter valve is used to receive the unlocking power supply instruction and supply power to the wind turbines in the offshore wind farm based on the unlocking power supply instruction; The control device is also used to detect the current flowing through the first bypass switch and the second bypass switch when a preset number of fans have completed startup, and when the current flowing through the first bypass switch and the second bypass switch is zero, send a disconnection instruction to the first bypass switch and the second bypass switch respectively, and send a closing instruction to the first circuit breaker and the second circuit breaker respectively.

3. The offshore wind power DC transmission system based on a parallel-parallel converter valve according to claim 2 is characterized in that: The offshore converter valve further includes a third circuit breaker, a fourth circuit breaker, a fifth circuit breaker, a sixth circuit breaker and a seventh circuit breaker; The AC side of the offshore auxiliary modular multilevel converter valve is connected to the offshore busbar through the third circuit breaker, the connecting transformer, and the fourth circuit breaker in sequence, the AC side of the first diode valve is connected to the offshore busbar through the first three-winding transformer and the fifth circuit breaker in sequence, the AC side of the second diode valve is connected to the offshore busbar through the second three-winding transformer and the sixth circuit breaker in sequence, and the AC side of the third diode valve is connected to the offshore busbar through the third three-winding transformer and the seventh circuit breaker in sequence; The control device is also used to send closing instructions to the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker and the seventh circuit breaker respectively when it is detected that the offshore converter valve is unlocked, so that the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker and the seventh circuit breaker are closed.

4. The offshore wind power DC transmission system based on a hybrid converter valve according to claim 3 is characterized in that: When the third circuit breaker, the fourth circuit breaker, the fifth circuit breaker, the sixth circuit breaker and the seventh circuit breaker are closed, the offshore converter valve is also used to establish a preset voltage on the offshore busbar in a starting voltage manner, wherein the preset voltage is less than the rated voltage of the offshore busbar, and the preset voltage makes the first diode valve, the second diode valve and the third diode valve non-conductive, and the preset voltage is higher than the preset grid-connected voltage threshold of the offshore wind turbine.

5. The offshore wind power DC transmission system based on a hybrid converter valve according to claim 2 is characterized in that: The onshore transformer comprises a starting transformer, the valve side of the starting transformer is connected to the onshore converter valve through an eighth circuit breaker, and the grid side is connected to the onshore power grid through a ninth circuit breaker; The control device is further used to send control instructions to the eighth circuit breaker and the ninth circuit breaker respectively, and the control instructions are used to control the closing of the eighth circuit breaker and the ninth circuit breaker. After the eighth circuit breaker and the ninth circuit breaker are closed, the onshore power grid outputs the first working voltage through the starting transformer and then charges the onshore converter valve and the offshore converter valve.

6. The offshore wind power DC transmission system based on a hybrid converter valve according to claim 5, characterized in that: The onshore transformer further comprises a steady-state operation transformer, wherein the valve side of the steady-state operation transformer is connected to the onshore converter valve through a tenth circuit breaker, and the grid side is connected to the onshore power grid through an eleventh circuit breaker; The control device is further used to send a disconnection instruction to the eighth circuit breaker and the ninth circuit breaker respectively, and send a closing instruction to the tenth circuit breaker and the eleventh circuit breaker when it is detected that the first bypass switch and the second bypass switch are disconnected; wherein, after the tenth circuit breaker and the eleventh circuit breaker are closed, the onshore power grid outputs a second working voltage through the steady-state operation transformer to charge the onshore converter valve.

7. The offshore wind power DC transmission system based on a hybrid converter valve according to claim 2, characterized in that: The control device is also used to detect in real time the onshore charging voltage of the onshore converter valve and the offshore charging voltage of the offshore converter valve, and send an unlocking power supply instruction to the offshore converter valve when the onshore charging voltage reaches a first voltage threshold and the offshore charging voltage reaches a second voltage threshold.

8. The offshore wind power DC transmission system based on a hybrid converter valve according to claim 5, characterized in that: The control device is further used to send an uncontrolled charging instruction to the onshore converter valve when obtaining the closing states of the eighth circuit breaker and the ninth circuit breaker, and to obtain the DC side capacitor voltage of the onshore converter valve, and to send a controllable charging instruction to the onshore converter valve based on the capacitor voltage.

9. The offshore wind power DC transmission system based on a hybrid converter valve according to claim 2, characterized in that: The control device is also used to obtain the rated voltage value of the offshore busbar, the voltage reference value of the AC side of the offshore converter valve, and the current value of the connecting line between the DC side of the offshore auxiliary modular multi-level converter valve and the second diode valve when it is detected that the first circuit breaker and the second circuit breaker are closed, and input the rated voltage value of the offshore busbar, the voltage reference value of the AC side of the offshore converter valve, and the current value of the connecting line between the DC side of the offshore auxiliary modular multi-level converter valve and the second diode valve into a pre-constructed voltage control model to obtain the voltage adjustment value of the AC side of the offshore converter valve, and adjust the voltage to send it to the offshore converter valve, so that the offshore converter valve adjusts the AC side voltage.

10. A method for starting an offshore wind power DC transmission system based on a hybrid converter valve, characterized in that: Applied to the offshore wind power DC transmission system based on the hybrid converter valve according to any one of claims 2 to 9, the method comprises: Sending a closing instruction to the first bypass switch and the second bypass switch; When it is detected that the first bypass switch and the second bypass switch are closed, the onshore charging voltage of the onshore converter valve and the offshore charging voltage of the offshore converter valve are obtained, and a solution is sent to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage. Lock power supply instruction; wherein the onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with the first working voltage output by the onshore transformer through the onshore power grid; When the preset number of wind turbines complete startup, a no-load operation instruction is sent to the offshore auxiliary modular multi-level converter valve, and a disconnection instruction is sent to the first bypass switch and the second bypass switch respectively, and a closing instruction is sent to the first circuit breaker and the second circuit breaker respectively.

11. A starting device for an offshore wind power DC transmission system based on a hybrid converter valve, characterized in that: Applicable to the offshore wind power DC transmission system based on the hybrid converter valve according to any one of claims 2 to 9, the device comprises: A first sending module, used for sending a closing instruction to the first bypass switch and the second bypass switch; an acquisition module, configured to acquire an onshore charging voltage of an onshore converter valve and an offshore charging voltage of an offshore converter valve, and send an unlocking power supply instruction to the offshore converter valve based on the onshore charging voltage and the offshore charging voltage, after detecting that the first bypass switch and the second bypass switch are closed; wherein the onshore charging voltage and the offshore charging voltage are generated by charging the onshore converter valve and the offshore converter valve with the first working voltage output by the onshore transformer from the onshore power grid; The second sending module is used to send a no-load operation instruction to the offshore auxiliary modular multi-level converter valve when the preset number of wind turbines have completed startup, and to send a disconnection instruction to the first bypass switch and the second bypass switch respectively, and to send a closing instruction to the first circuit breaker and the second circuit breaker respectively.

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