Alternating current fault ride-through control method and control system for offshore wind power flexible direct current system

Abstract

The invention discloses an alternating-current fault ride-through control method and system for an offshore wind power flexible direct-current system, and the method comprises the steps: enabling each bridge arm of an onshore converter station to be connected with an energy consumption branch in parallel, and achieving the surplus power balance of a system through the cooperation of an additional energy consumption branch of the onshore converter station with a centralized energy consumption device; the switching of the energy consumption branch and the centralized energy consumption device is controlled according to the power difference between the offshore converter station and the onshore converter station, and the power of the additionally configured centralized energy consumption device is only 1 / 3 of the rated power of the system. The technical problem that according to an existing offshore wind power flexible direct current system alternating current fault ride-through control method, the power of a centralized energy consumption device additionally configured on the direct current side is the system rated power, and the energy consumption cost is high is solved.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission system technology, and in particular to an AC fault ride-through control method and control system for offshore wind power flexible DC transmission systems. Background Technology

[0002] Offshore wind power boasts advantages such as higher wind speeds and shorter calm periods, making it a key focus for future wind power development. Offshore wind power DC transmission technology does not require synchronization with the onshore power grid, has no capacitor charging effect, and offers flexible control, making it more suitable for long-distance, high-capacity transmission scenarios. Flexible DC transmission technology, in particular, offers advantages such as no commutation risk and active / reactive power decoupling, making it the mainstream method for transmitting and connecting offshore wind power to the grid.

[0003] In the area of ​​DC grid connection for deep-sea wind power, when a fault occurs in the AC system at the receiving end of the flexible DC transmission system for offshore wind power, it will cause a sudden drop in AC voltage at the grid connection point, reducing the output power of the receiving-end converter station. In severe cases, it may cause a power outage. Due to the sudden drop in AC voltage at the grid connection point, the sending-end converter station will still input the original power before the fault to the receiving-end converter station. At this time, a large amount of surplus power will be generated. The surplus power will cause the DC side voltage to rise rapidly, endangering the safety and insulation of DC equipment, and may cause the DC line to trip and the wind turbine to disconnect from the grid.

[0004] Existing offshore wind power flexible DC transmission systems typically employ an architecture of offshore converter station + submarine cable + onshore converter station. When a fault occurs in the receiving-end AC grid, it is necessary to handle the system's surplus power. Traditional AC fault ride-through control methods for offshore wind power flexible DC transmission systems include... Figure 1 As shown, an additional centralized energy consumption device needs to be configured on the DC side. The power of the centralized energy consumption device is the rated power of the system, resulting in high energy consumption costs. Summary of the Invention

[0005] This invention provides an AC fault ride-through control method and control system for offshore wind power flexible DC systems, which solves the technical problem that existing offshore wind power flexible DC system AC fault ride-through control methods require additional centralized energy consumption devices on the DC side with power equal to the system's rated power, resulting in high energy consumption costs.

[0006] In view of this, the first aspect of the present invention provides an AC fault ride-through control method for an offshore wind power flexible DC system, applied to an offshore wind power flexible DC system with a centralized energy dissipation device configured on the DC side of the onshore converter station, comprising:

[0007] S0. A power dissipation branch is connected in parallel on each bridge arm of the onshore converter station. The power dissipation branch consists of a switch and a power dissipation resistor connected in series.

[0008] S1. Check if there is an AC fault in the offshore wind power flexible DC system. If not, disconnect the centralized energy consumption device and all energy consumption branches. If yes, proceed to step S2.

[0009] S2. Determine the power difference between the offshore converter station and the onshore converter station. If the power difference is equal to the rated power of the offshore wind power flexible DC system, proceed to step S3. If the power difference is greater than or equal to 2 / 3 times the rated power of the offshore wind power flexible DC system and less than the rated power of the offshore wind power flexible DC system, proceed to step S4. If the power difference is greater than or equal to 1 / 3 times the rated power of the offshore wind power flexible DC system and less than 2 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S5. If the power difference is greater than or equal to 0 and less than 1 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S6.

[0010] S3, Activate all energy-consuming branches;

[0011] S4. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy-consuming branch of the two phase bridge arms with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy-consuming device at the same time.

[0012] S5. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy consumption branch of the bridge arm with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy consumption device at the same time.

[0013] S6. Cut off all energy-consuming branches and connect the centralized energy-consuming device.

[0014] Optionally, the switch is a DC high-speed switch.

[0015] Optionally, the onshore converter station is a three-phase six-arm converter station.

[0016] Optionally, it also includes:

[0017] S7. After clearing the AC fault, disconnect the centralized energy consumption device and all energy consumption branches.

[0018] Optionally, it also includes:

[0019] S8, storage power difference and switching records of centralized energy consumption devices, and switching records of all energy consumption branches.

[0020] The second aspect of the present invention provides an AC fault ride-through control system for an offshore wind power flexible DC system, which is applied to an offshore wind power flexible DC system with a centralized energy dissipation device configured on the DC side of an onshore converter station, including an energy dissipation device and a control device.

[0021] The energy-consuming device includes a centralized energy-consuming device and energy-consuming branches. Each bridge arm of the onshore converter station is connected in parallel with an energy-consuming branch, which consists of a series switch and an energy-consuming resistor.

[0022] The control device is used to perform the following steps:

[0023] S1. Check if there is an AC fault in the offshore wind power flexible DC system. If not, disconnect the centralized energy consumption device and all energy consumption branches. If yes, proceed to step S2.

[0024] S2. Determine the power difference between the offshore converter station and the onshore converter station. If the power difference is equal to the rated power of the offshore wind power flexible DC system, proceed to step S3. If the power difference is greater than or equal to 2 / 3 times the rated power of the offshore wind power flexible DC system and less than the rated power of the offshore wind power flexible DC system, proceed to step S4. If the power difference is greater than or equal to 1 / 3 times the rated power of the offshore wind power flexible DC system and less than 2 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S5. If the power difference is greater than or equal to 0 and less than 1 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S6.

[0025] S3, Activate all energy-consuming branches;

[0026] S4. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy-consuming branch of the two phase bridge arms with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy-consuming device at the same time.

[0027] S5. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy consumption branch of the bridge arm with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy consumption device at the same time.

[0028] S6. Cut off all energy-consuming branches and connect the centralized energy-consuming device.

[0029] Optionally, the switch is a DC high-speed switch.

[0030] Optionally, the onshore converter station is a three-phase six-arm converter station.

[0031] Optionally, the control device is also used to perform the following steps:

[0032] S7. After clearing the AC fault, disconnect the centralized energy consumption device and all energy consumption branches.

[0033] Optionally, the control device is also used to perform the following steps:

[0034] S8, storage power difference and switching records of centralized energy consumption devices, and switching records of all energy consumption branches.

[0035] As can be seen from the above technical solutions, the AC fault ride-through control method for offshore wind power flexible DC systems provided by this invention has the following advantages:

[0036] The AC fault ride-through control method for offshore wind power flexible DC systems provided by this invention connects an energy-consuming branch in parallel on each arm of the onshore converter station. By combining the additional energy-consuming branch with a centralized energy-consuming device, the surplus power of the system is balanced. The switching of the energy-consuming branch and the centralized energy-consuming device is controlled according to the power difference between the offshore and onshore converter stations. The power of the additional centralized energy-consuming device is only 1 / 3 of the rated power of the system. This solves the technical problem of high energy consumption cost in existing offshore wind power flexible DC system AC fault ride-through control methods where the power of the additional centralized energy-consuming device on the DC side is equal to the rated power of the system. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A schematic diagram of a structure for configuring a centralized energy dissipation device on the DC side of a traditional offshore wind power flexible DC system;

[0039] Figure 2 This is a flowchart illustrating an AC fault ride-through control method for an offshore wind power flexible DC system provided in an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of a structure in which an energy-consuming branch is connected in parallel on each bridge arm of an onshore converter station, as provided in an embodiment of the present invention.

[0041] Figure 4 This is a schematic diagram of the AC fault ride-through control system for a flexible DC-DC offshore wind power system provided in an embodiment of the present invention. Detailed Implementation

[0042] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] For easier understanding, please refer to Figure 2 and Figure 3This invention provides an embodiment of an AC fault ride-through control method for offshore wind power flexible DC systems. This method is applied to offshore wind power flexible DC systems with centralized energy dissipation devices configured on the DC side of the onshore converter station. The method includes:

[0044] Step S0: Connect a power dissipation branch in parallel on each bridge arm of the onshore converter station. The power dissipation branch consists of a switch and a power dissipation resistor connected in series.

[0045] It should be noted that the onshore converter station uses a modular multilevel converter (MMC). Each bridge arm consists of several full-bridge submodules and / or half-bridge submodules cascaded together, with one bridge arm inductor L connected to each arm. An additional energy-dissipating branch is connected in parallel to each bridge arm of the onshore converter station, forming an additional energy-dissipating branch bridge arm. The energy-dissipating branch consists of a switch and an energy-dissipating resistor connected in series. Composition. The switch is a DC high-speed switch (HSS).

[0046] In one embodiment, the onshore converter station is a three-phase six-arm converter station.

[0047] Step S1: Check if there is an AC fault in the offshore wind power flexible DC system. If not, disconnect the centralized energy consumption device and all energy consumption branches. If yes, proceed to step S2.

[0048] It should be noted that existing AC fault detection equipment is used to monitor whether an AC fault has occurred in the offshore wind power flexible DC system. When no AC fault has occurred in the offshore wind power flexible DC system, all energy-consuming branches of the onshore converter station are in the off state, and the energy-consuming resistors do not consume energy; the centralized energy-consuming device is also in the off state and does not consume energy. When an AC fault occurs in the offshore wind power flexible DC system, proceed to step S2.

[0049] Step S2: Determine the power difference between the offshore converter station and the onshore converter station. If the power difference is equal to the rated power of the offshore wind power flexible DC system, proceed to step S3. If the power difference is greater than or equal to 2 / 3 times the rated power of the offshore wind power flexible DC system and less than the rated power of the offshore wind power flexible DC system, proceed to step S4. If the power difference is greater than or equal to 1 / 3 times the rated power of the offshore wind power flexible DC system and less than 2 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S5. If the power difference is greater than or equal to 0 and less than 1 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S6.

[0050] It should be noted that when an AC fault occurs in an offshore wind power flexible DC system, the power difference between the offshore converter station and the onshore converter station should be determined. .like , If the rated power of the offshore wind power flexible DC system is [value], then proceed to step S3. If [condition] Then proceed to step S4. If Then proceed to step S5. If Then proceed to step S6.

[0051] Step S3: Activate all energy-consuming branches.

[0052] It should be noted that, if In this case, the surplus power of the offshore wind power flexible DC system is consumed only by the energy-consuming branches of the onshore converter station. At this time, all the energy-consuming branches of the onshore converter station are put into operation, that is, all the energy-consuming branches of the six bridge arms of the three-phase six-bridge-arm converter station are put into operation.

[0053] Step S4: Detect the voltage of all bridge arms of the onshore converter station, connect the energy-consuming branch of the two phase bridge arms with the closest voltage between the upper and lower bridge arms, and simultaneously connect the centralized energy-consuming device.

[0054] It should be noted that, if The surplus power of the offshore wind power flexible DC system is consumed by the energy-consuming branches of the onshore converter station and the centralized energy-consuming device. The voltage of all bridge arms of the onshore converter station is monitored, and the two phases with the closest voltages are selected. The energy-consuming branches of both phases are then activated; simultaneously, the centralized energy-consuming device is activated to consume the surplus power.

[0055] Step S5: Detect the voltage of all bridge arms of the onshore converter station, connect the energy-consuming branch of the bridge arm with the closest voltage between the upper and lower bridge arms, and simultaneously connect the centralized energy-consuming device.

[0056] It should be noted that, if The surplus power of the offshore wind power flexible DC system is consumed by the onshore additional energy consumption branches and the centralized energy consumption device. The voltage of all bridge arms of the onshore converter station is detected, and the phase with the closest voltage between the upper and lower bridge arms is selected. The additional energy consumption branches of the upper and lower bridge arms of this phase are put into operation. At the same time, the centralized energy consumption device is put into operation to consume the surplus power.

[0057] Step S6: Cut off all energy-consuming branches and connect them to the centralized energy-consuming device.

[0058] It should be noted that, if In this case, the surplus power of the offshore wind power flexible DC system is consumed only by the centralized energy consumption device.

[0059] The AC fault ride-through control method for offshore wind power flexible DC systems provided in this invention allows surplus power in the offshore wind power flexible DC system to be consumed by the energy-consuming branches of the onshore converter station and the centralized energy-consuming device. After all the energy-consuming branches of the upper and lower arms of one phase of the onshore converter station are put into operation, one-third of the surplus power can be consumed. Different numbers of energy-consuming branches are selected for operation depending on the surplus power; for example, when the system surplus power is 1.5... / 3, at this point, the energy-consuming branches of both the upper and lower bridge arms of one phase can be put into operation. The energy-consuming branches of the onshore converter station can then consume [energy]. / 3 of the power, with 0.5 remaining. One-third of the power can be consumed by centralized energy-consuming devices.

[0060] The AC fault ride-through control method for offshore wind power flexible DC systems provided by this invention connects an energy-consuming branch in parallel on each arm of the onshore converter station. By combining the additional energy-consuming branch with a centralized energy-consuming device, the surplus power of the system is balanced. The switching of the energy-consuming branch and the centralized energy-consuming device is controlled according to the power difference between the offshore and onshore converter stations. The power of the additional centralized energy-consuming device is only 1 / 3 of the rated power of the system. This solves the technical problem of high energy consumption cost in existing offshore wind power flexible DC system AC fault ride-through control methods where the power of the additional centralized energy-consuming device on the DC side is equal to the rated power of the system.

[0061] In one embodiment, after steps S3 to S6, the method further includes:

[0062] Step S7: After clearing the AC fault, disconnect the centralized energy consumption device and all energy consumption branches.

[0063] It should be noted that, in order to reduce the impact of the energy-consuming devices on the offshore wind power flexible DC transmission system when the receiving end is operating normally, and to reduce the waste of power of the energy-consuming devices on the sending end when the receiving end is operating normally, in this embodiment of the invention, after the AC fault is cleared, the centralized energy-consuming devices and all energy-consuming branches are cut off.

[0064] In one embodiment, after steps S3 to S7, the method further includes:

[0065] Step S8: Record the power difference and switching of centralized energy-consuming devices, as well as the switching records of all energy-consuming branches.

[0066] It should be noted that the power difference storage and the switching records of centralized energy consumption devices, as well as the switching records of all energy consumption branches, are recorded to facilitate subsequent analysis of the operation of the offshore wind power flexible DC system.

[0067] For easier understanding, please refer to Figures 3 to 4 This invention provides an embodiment of an AC fault ride-through control system for an offshore wind power flexible DC system. The control system is applied to an offshore wind power flexible DC system with a centralized energy dissipation device configured on the DC side of an onshore converter station, and includes an energy dissipation device and a control device.

[0068] The energy-consuming device includes a centralized energy-consuming device and energy-consuming branches. Each bridge arm of the onshore converter station is connected in parallel with an energy-consuming branch, which consists of a series switch and an energy-consuming resistor.

[0069] The control device is used to perform the following steps:

[0070] S1. Check if there is an AC fault in the offshore wind power flexible DC system. If not, disconnect the centralized energy consumption device and all energy consumption branches. If yes, proceed to step S2.

[0071] It should be noted that the onshore converter station adopts a modular multilevel converter. Each bridge arm consists of several full-bridge submodules and / or half-bridge submodules cascaded together and connected to a bridge arm inductor L. An additional energy-dissipating branch is connected in parallel to each bridge arm of the onshore converter station, forming an additional energy-dissipating branch bridge arm. The energy-dissipating branch consists of a switch and an energy-dissipating resistor connected in series. Composition. The switch is a DC high-speed switch (HSS). Existing AC fault detection equipment is used to monitor whether an AC fault has occurred in the offshore wind power flexible DC system. When no AC fault has occurred in the offshore wind power flexible DC system, all energy-consuming branches of the onshore converter station are in the off-state, and the energy-consuming resistors do not consume energy; the centralized energy-consuming device is also in the off-state and does not consume energy. When an AC fault occurs in the offshore wind power flexible DC system, proceed to step S2.

[0072] S2. Determine the power difference between the offshore converter station and the onshore converter station. If the power difference is equal to the rated power of the offshore wind power flexible DC system, proceed to step S3. If the power difference is greater than or equal to 2 / 3 times the rated power of the offshore wind power flexible DC system and less than the rated power of the offshore wind power flexible DC system, proceed to step S4. If the power difference is greater than or equal to 1 / 3 times the rated power of the offshore wind power flexible DC system and less than 2 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S5. If the power difference is greater than or equal to 0 and less than 1 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S6.

[0073] It should be noted that when an AC fault occurs in an offshore wind power flexible DC system, the power difference between the offshore converter station and the onshore converter station should be determined. .like , If the rated power of the offshore wind power flexible DC system is [value], then proceed to step S3. If [condition] Then proceed to step S4. If Then proceed to step S5. If Then proceed to step S6.

[0074] S3, Activate all energy-consuming branches.

[0075] It should be noted that, if In this case, the surplus power of the offshore wind power flexible DC system is consumed only by the energy-consuming branches of the onshore converter station. At this time, all the energy-consuming branches of the onshore converter station are put into operation, that is, all the energy-consuming branches of the six bridge arms of the three-phase six-bridge-arm converter station are put into operation.

[0076] S4. Detect the voltage of all bridge arms of the onshore converter station, connect the energy-consuming branch of the two bridge arms with the closest voltage between the upper and lower bridge arms, and simultaneously connect the centralized energy-consuming device.

[0077] It should be noted that, if The surplus power of the offshore wind power flexible DC system is consumed by the energy-consuming branches of the onshore converter station and the centralized energy-consuming device. The voltage of all bridge arms of the onshore converter station is monitored, and the two phases with the closest voltages are selected. The energy-consuming branches of both phases are then activated; simultaneously, the centralized energy-consuming device is activated to consume the surplus power.

[0078] S5. Detect the voltage of all bridge arms of the onshore converter station, connect the energy-consuming branch of the bridge arm with the closest voltage between the upper and lower bridge arms, and simultaneously connect the centralized energy-consuming device.

[0079] It should be noted that, if The surplus power of the offshore wind power flexible DC system is consumed by the onshore additional energy consumption branches and the centralized energy consumption device. The voltage of all bridge arms of the onshore converter station is detected, and the phase with the closest voltage between the upper and lower bridge arms is selected. The additional energy consumption branches of the upper and lower bridge arms of this phase are put into operation. At the same time, the centralized energy consumption device is put into operation to consume the surplus power.

[0080] S6. Cut off all energy-consuming branches and connect the centralized energy-consuming device.

[0081] It should be noted that, if In this case, the surplus power of the offshore wind power flexible DC system is consumed only by the centralized energy consumption device.

[0082] In one embodiment, the control device is further configured to perform the following steps:

[0083] S7. After clearing the AC fault, disconnect the centralized energy consumption device and all energy consumption branches.

[0084] It should be noted that, in order to reduce the impact of the energy-consuming devices on the offshore wind power flexible DC transmission system when the receiving end is operating normally, and to reduce the waste of power of the energy-consuming devices on the sending end when the receiving end is operating normally, in this embodiment of the invention, after the AC fault is cleared, the centralized energy-consuming devices and all energy-consuming branches are cut off.

[0085] In one embodiment, the control device is further configured to perform the following steps:

[0086] S8, storage power difference and switching records of centralized energy consumption devices, and switching records of all energy consumption branches.

[0087] It should be noted that the power difference storage and the switching records of centralized energy consumption devices, as well as the switching records of all energy consumption branches, are recorded to facilitate subsequent analysis of the operation of the offshore wind power flexible DC system.

[0088] The AC fault ride-through control system for offshore wind power flexible DC systems provided by this invention connects an energy-consuming branch in parallel on each arm of the onshore converter station. By combining the additional energy-consuming branch with a centralized energy-consuming device, the system's surplus power is balanced. The switching of the energy-consuming branch and the centralized energy-consuming device is controlled according to the power difference between the offshore and onshore converter stations. The power of the additional centralized energy-consuming device is only 1 / 3 of the system's rated power. This solves the technical problem of high energy consumption costs in existing offshore wind power flexible DC system AC fault ride-through control methods where the power of the additional centralized energy-consuming device on the DC side is equal to the system's rated power.

[0089] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0090] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0091] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0092] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0093] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media capable of storing program code.

[0094] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for AC fault ride-through control of an offshore wind power flexible DC system, applied to an offshore wind power flexible DC system with a centralized energy dissipation device configured on the DC side of the onshore converter station, characterized in that, include: S0. A power dissipation branch is connected in parallel on each bridge arm of the onshore converter station. The power dissipation branch consists of a switch and a power dissipation resistor connected in series. S1. Check if there is an AC fault in the offshore wind power flexible DC system. If not, disconnect the centralized energy consumption device and all energy consumption branches. If yes, proceed to step S2. S2. Determine the power difference between the offshore converter station and the onshore converter station. If the power difference is equal to the rated power of the offshore wind power flexible DC system, proceed to step S3. If the power difference is greater than or equal to 2 / 3 times the rated power of the offshore wind power flexible DC system and less than the rated power of the offshore wind power flexible DC system, proceed to step S4. If the power difference is greater than or equal to 1 / 3 times the rated power of the offshore wind power flexible DC system and less than 2 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S5. If the power difference is greater than or equal to 0 and less than 1 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S6. S3, Activate all energy-consuming branches; S4. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy-consuming branch of the two phase bridge arms with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy-consuming device at the same time. S5. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy consumption branch of the bridge arm with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy consumption device at the same time. S6. Cut off all energy-consuming branches and connect the centralized energy-consuming device.

2. The AC fault ride-through control method for offshore wind power flexible DC systems according to claim 1, characterized in that, The switch is a high-speed DC switch.

3. The AC fault ride-through control method for offshore wind power flexible DC systems according to claim 1, characterized in that, The onshore converter station is a three-phase, six-bridge converter station.

4. The AC fault ride-through control method for offshore wind power flexible DC systems according to claim 1, characterized in that, Also includes: S7. After clearing the AC fault, disconnect the centralized energy consumption device and all energy consumption branches.

5. The AC fault ride-through control method for offshore wind power flexible DC systems according to any one of claims 1-4, characterized in that, Also includes: S8, storage power difference and switching records of centralized energy consumption devices, and switching records of all energy consumption branches.

6. An AC fault ride-through control system for an offshore wind power flexible DC system, applied to an offshore wind power flexible DC system with a centralized energy dissipation device configured on the DC side of an onshore converter station, characterized in that, Includes energy-consuming devices and control devices; The energy-consuming device includes a centralized energy-consuming device and energy-consuming branches. Each bridge arm of the onshore converter station is connected in parallel with an energy-consuming branch, which consists of a series switch and an energy-consuming resistor. The control device is used to perform the following steps: S1. Check if there is an AC fault in the offshore wind power flexible DC system. If not, disconnect the centralized energy consumption device and all energy consumption branches. If yes, proceed to step S2. S2. Determine the power difference between the offshore converter station and the onshore converter station. If the power difference is equal to the rated power of the offshore wind power flexible DC system, proceed to step S3. If the power difference is greater than or equal to 2 / 3 times the rated power of the offshore wind power flexible DC system and less than the rated power of the offshore wind power flexible DC system, proceed to step S4. If the power difference is greater than or equal to 1 / 3 times the rated power of the offshore wind power flexible DC system and less than 2 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S5. If the power difference is greater than or equal to 0 and less than 1 / 3 times the rated power of the offshore wind power flexible DC system, proceed to step S6. S3, Activate all energy-consuming branches; S4. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy-consuming branch of the two phase bridge arms with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy-consuming device at the same time. S5. Detect the voltage of all bridge arms of the onshore converter station, put into operation the energy consumption branch of the bridge arm with the closest voltage between the upper and lower bridge arms, and put into operation the centralized energy consumption device at the same time. S6. Cut off all energy-consuming branches and connect the centralized energy-consuming device.

7. The AC fault ride-through control system for offshore wind power flexible DC system according to claim 6, characterized in that, The switch is a high-speed DC switch.

8. The AC fault ride-through control system for offshore wind power flexible DC system according to claim 6, characterized in that, The onshore converter station is a three-phase, six-bridge converter station.

9. The AC fault ride-through control system for offshore wind power flexible DC system according to claim 1, characterized in that, The control device is also used to perform the following steps: S7. After clearing the AC fault, disconnect the centralized energy consumption device and all energy consumption branches.

10. The AC fault ride-through control system for offshore wind power flexible DC systems according to any one of claims 6-9, characterized in that, The control device is also used to perform the following steps: S8, storage power difference and switching records of centralized energy consumption devices, and switching records of all energy consumption branches.

Images