Method and device for balancing surplus power during DC fault in flexible DC transmission system

Abstract

The present invention discloses a method and apparatus for balancing surplus power during a DC fault in a flexible direct current (HVDC) transmission system. This method replaces DC circuit breakers and DC energy dissipation devices with high-speed switches, and provides a strategy for balancing surplus power during a DC fault in the flexible HVDC transmission system. Surplus power balancing after a DC fault does not rely on a DC circuit breaker and DC energy dissipation device; instead, it can be achieved using a DC high-speed switch and a corresponding control strategy, significantly reducing costs. This solves the technical problem of existing offshore wind power flexible HVDC transmission systems requiring the use of DC circuit breakers and DC energy dissipation devices to achieve surplus power balancing after a DC fault, resulting in high construction costs and a disadvantage for widespread application.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) transmission, and in particular to a method and device for balancing surplus power during a DC fault in a flexible DC transmission system. Background Art

[0002] Existing offshore wind power flexible DC transmission systems such as Figure 4 As shown in the figure, the offshore wind power flexible DC transmission system includes a wind farm, a power collection system, an offshore converter station, and an onshore converter station. The offshore converter station and the onshore converter station are connected by a DC cable. After the DC cable is landed, it continues to be transmitted to the load center through the DC overhead line. Since the probability of failure of the DC overhead line is much higher than that of the DC submarine cable, it is necessary to consider the fault clearance of the DC overhead line. Figure 4 In offshore wind power flexible DC transmission systems, DC circuit breakers (DCCBs) are used for cable-to-overhead line conversion. In the event of a DC fault, the DC circuit breaker disconnects the DC overhead line, and DC energy dissipation devices are then used to balance the remaining power. However, DC circuit breakers and DC energy dissipation devices are expensive. For example, in a ±500kV / 2000MW system, the cost of two DC circuit breakers and one 2000MW DC energy dissipation device is nearly 300 million yuan, making it difficult to scale up and deploy. Summary of the Invention

[0003] The present invention provides a method and device for balancing surplus power during a DC fault in a flexible DC transmission system, which is used to solve the technical problem that the existing offshore wind power flexible DC transmission system needs to use DC circuit breakers and DC energy consumption devices to achieve surplus power balance after a DC fault, which has high construction costs and is not conducive to popularization and application.

[0004] In view of this, a first aspect of the present invention provides a method for balancing surplus power during a DC fault in a flexible DC transmission system, which is applied to an offshore wind power flexible DC transmission system. The offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station. The offshore converter station is connected to the onshore converter station via a DC cable, a DC high-speed switch, and a DC overhead line connected in series. Both the offshore converter station and the onshore converter station adopt a topology structure with DC fault clearing capability. The method for balancing surplus power during a DC fault in the flexible DC transmission system includes the following steps:

[0005] S1. When the offshore converter station detects a DC fault, it controls the grid-side converters in all wind turbine converters at the sending end to lock out, and the DC energy dissipation devices in the wind turbine converters maintain the DC voltage stability of the wind turbine converters.

[0006] S2. Controlling the DC port voltage and / or DC port current of the offshore converter station and the onshore converter station to be reduced to zero according to the topology of the offshore wind power flexible DC transmission system;

[0007] S3. After the DC fault is cleared, the DC voltage of the onshore converter station is controlled to gradually recover within a first preset time. When the DC voltage of the onshore converter station begins to recover, the wind turbine converter at the sending end is notified through the offshore converter station to gradually recover to the operating power before the DC fault within a second preset time. The second preset time is not less than the first preset time.

[0008] Optionally, after step S1 and before step S3, the method further includes:

[0009] Determine whether there is any unsuccessfully locked grid-side converter among all wind turbine converters. If so, obtain the total power output of the unsuccessfully locked grid-side converters, re-unlock a corresponding number of locked grid-side converters based on the total power output of the unsuccessfully locked grid-side converters, and control all re-unlocked grid-side converters to reversely absorb power from the collection system of the offshore wind power flexible direct current transmission system. The power reversely absorbed by the re-unlocked grid-side converters is equal to the total output of the unsuccessfully locked grid-side converters.

[0010] Optionally, both the offshore converter station and the onshore converter station adopt a full half-bridge hybrid topology.

[0011] Optionally, step S2 specifically includes:

[0012] If the flexible DC transmission system adopts a symmetrical single-machine topology, the DC port voltage of the onshore converter station is controlled to drop to 0, and the DC port current of the offshore converter station is controlled to drop to 0. If the flexible DC transmission system adopts a bipolar topology, the DC port currents of both the offshore converter station and the onshore converter station are controlled to drop to 0.

[0013] A second aspect of the present invention provides a device for balancing excess power during a DC fault in a flexible DC transmission system, which is applied to an offshore wind power flexible DC transmission system. The offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station. The offshore converter station is connected to the onshore converter station via a DC cable, a DC high-speed switch, and a DC overhead line connected in series. Both the offshore converter station and the onshore converter station adopt a topology structure with DC fault clearing capability. The device for balancing excess power during a DC fault in the flexible DC transmission system includes the following modules:

[0014] The converter blocking module is used to control the grid-side converters in all wind turbine converters at the sending end to block when a DC fault is detected at the offshore converter station. The DC energy dissipation device in the wind turbine converter maintains the DC voltage stability of the wind turbine converter.

[0015] A voltage and current control module is used to control the DC port voltage and / or DC port current of the offshore converter station and the onshore converter station to be reduced to zero according to the topology of the offshore wind power flexible DC transmission system;

[0016] The recovery module is used to control the DC voltage of the onshore converter station to gradually recover within a first preset time after the DC fault is cleared. When the DC voltage of the onshore converter station begins to recover, the offshore converter station is used to notify the wind turbine converter at the sending end to gradually recover to the operating power before the DC fault within a second preset time, and the second preset time is not less than the first preset time.

[0017] Also includes:

[0018] The judgment module is used to judge whether there is any unsuccessfully locked grid-side converter among all wind turbine converters after issuing a grid-side converter locking instruction among all wind turbine converters and before the DC voltage of the onshore converter station begins to recover. If so, the total power output of the unsuccessfully locked grid-side converters is obtained, and a corresponding number of locked grid-side converters are re-unlocked according to the total power output of the unsuccessfully locked grid-side converters, and all the re-unlocked grid-side converters are controlled to reversely absorb power from the collection system of the offshore wind power flexible DC transmission system, and the power reversely absorbed by the re-unlocked grid-side converter is equal to the total output of the unsuccessfully locked grid-side converters.

[0019] Optionally, both the offshore converter station and the onshore converter station adopt a full half-bridge hybrid topology.

[0020] Optionally, the voltage and current control module is specifically used to:

[0021] If the flexible DC transmission system adopts a symmetrical single-machine topology, the DC port voltage of the onshore converter station is controlled to drop to 0, and the DC port current of the offshore converter station is controlled to drop to 0. If the flexible DC transmission system adopts a bipolar topology, the DC port currents of both the offshore converter station and the onshore converter station are controlled to drop to 0.

[0022] A third aspect of the present invention provides a device for balancing surplus power during a DC fault in a flexible DC transmission system, the device comprising a processor and a memory:

[0023] The memory is used to store program code and transmit the program code to the processor;

[0024] The processor is configured to execute, according to instructions in the program code, the method for balancing surplus power in a flexible direct current transmission system during a direct current fault according to any one of the first aspects.

[0025] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium is used to store program code, and the program code is used to execute the method for balancing surplus power during a DC fault in a flexible DC transmission system according to any one of the first aspects.

[0026] From the above technical solutions, it can be seen that the method for balancing surplus power during a DC fault in a flexible HVDC transmission system provided by the present invention has the following advantages:

[0027] The method for balancing surplus power during a DC fault in a flexible DC transmission system provided by the present invention replaces a DC circuit breaker and a DC energy dissipation device with a DC high-speed switch, and provides a surplus power balancing strategy during a DC fault in the flexible DC transmission system. When an offshore converter station detects a DC fault, the grid-side converters in all wind turbine converters are controlled to be locked, and the DC energy dissipation devices in the wind turbine converters maintain the DC voltage stability of the wind turbine converters. The DC port voltage and / or DC port current of the offshore converter station and the onshore converter station are controlled to be reduced to zero according to the topology of the flexible DC transmission system. After the DC fault is cleared, the DC voltage of the onshore converter station is controlled to gradually recover within a first preset time. When the DC voltage of the onshore converter station begins to recover, the offshore converter station notifies the sending-end wind turbine converter to gradually recover to the operating power before the DC fault within a second preset time, and the second preset time is not less than the first preset time. The surplus power balance after a DC fault does not need to rely on DC circuit breakers and DC energy dissipation devices. The surplus power balance after a DC fault can be achieved by using DC high-speed switches and corresponding control strategies, which greatly reduces the cost. This solves the technical problem that the existing offshore wind power flexible DC transmission system needs to use DC circuit breakers and DC energy dissipation devices to achieve surplus power balance after a DC fault, which has high construction costs and is not conducive to promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A schematic flow chart of a method for balancing surplus power during a DC fault in a flexible DC transmission system provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the circuit structure of the offshore wind power flexible direct current transmission system provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic structural diagram of a surplus power balancing device during a DC fault in a flexible DC transmission system provided in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the circuit structure of the existing offshore wind power flexible direct current transmission system. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0034] For easier understanding, see Figure 1 and Figure 2 The present invention provides an embodiment of a method for balancing surplus power during a DC fault in a flexible direct current (HVDC) transmission system. The method is applied to an offshore wind power flexible direct current (HVDC) transmission system, wherein the offshore wind power flexible direct current (HVDC) transmission system includes an offshore converter station and an onshore converter station. The offshore converter station is connected to the onshore converter station via a DC cable, a DC high-speed switch (HSS), and a DC overhead line connected in series. Both the offshore converter station and the onshore converter station adopt a topology with DC fault clearing capability, which can be a full half-bridge hybrid topology. The method includes the following steps:

[0035] Step S1: When the offshore converter station detects a DC fault, the grid-side converters in all wind turbine converters at the sending end are controlled to be locked, and the DC energy consumption devices in the wind turbine converters maintain the DC voltage of the wind turbine converters stable.

[0036] It's important to note that the offshore converter station and the wind turbine converters have a direct, fast communication channel, enabling the activation of the DC energy dissipation devices within the wind turbine converters within 1ms. When the offshore converter station detects a DC fault, it issues a command to the wind turbine converters via fast communication. All wind turbine converters on the sending end lock their grid-side converters, and the DC energy dissipation devices within the wind turbine converters maintain DC voltage stability. In an offshore wind power flexible DC transmission system, the sending end is the offshore converter station, and the receiving end is the onshore converter station.

[0037] Step S2: controlling the DC port voltage and / or DC port current of the offshore converter station and the onshore converter station to drop to 0 according to the topology of the offshore wind power flexible DC transmission system.

[0038] It should be noted that after or simultaneously with the offshore converter station controlling the grid-side converters in all wind turbine converters to lock out, the Flexible DC transmission system, based on its adopted topology, controls the DC port voltage and / or DC port current of the offshore and onshore converter stations to drop to zero. Specifically, if the Flexible DC transmission system adopts a symmetrical single-machine topology, the DC port voltage of the onshore converter station and the DC port current of the offshore converter station are controlled to drop to zero. If the Flexible DC transmission system adopts a bipolar topology, the DC port currents of the offshore and onshore converter stations are controlled to be zero.

[0039] Step S3: After the DC fault is cleared, the DC voltage of the onshore converter station is controlled to gradually recover within a first preset time. When the DC voltage of the onshore converter station begins to recover, the offshore converter station is used to notify the wind turbine converter at the sending end to gradually recover to the operating power before the DC fault within a second preset time, and the second preset time is not less than the first preset time.

[0040] It should be noted that after the DC fault is reliably cleared, the onshore converter station controls the DC voltage to gradually recover within a first preset time. When the DC voltage begins to recover, the offshore converter station notifies the wind turbine converter at the sending end to gradually restore its pre-fault operating power within a second preset time, which is no less than the first preset time.

[0041] In one embodiment, the flexible DC transmission system needs to communicate with hundreds of wind turbines simultaneously. During actual project execution, some wind turbines may not be able to respond to the request to lock the grid-side converter due to communication interruption, internal equipment abnormality, etc., and there will still be some surplus power to charge the offshore converter station, which may cause module overvoltage. Therefore, it is necessary to call on wind turbine converters that can communicate normally to absorb additional surplus power. Specifically, after step S1 and before step S3, it also includes:

[0042] Determine whether there is any unsuccessfully locked grid-side converter among all wind turbine converters. If so, obtain the total power output of the unsuccessfully locked grid-side converters, re-unlock the corresponding number of locked grid-side converters based on the total power output of the unsuccessfully locked grid-side converters, and control all re-unlocked grid-side converters to reversely absorb power from the collection system of the offshore wind power flexible direct current transmission system. The power reversely absorbed by the re-unlocked grid-side converters is equal to the total output of the unsuccessfully locked grid-side converters. The collection system of the offshore wind power flexible direct current transmission system is a collection device used to transmit the AC power output from the wind farm to the offshore converter station. Figure 4 The center shows the left side of the offshore converter station, which includes AC / DC and DC / AC. A wind farm consists of several wind turbines (WTs), which output AC power and transmit it to a collection system. The collection system converts the received AC power into a voltage before transmitting it to the offshore converter station.

[0043] The method for balancing surplus power during a DC fault in a flexible DC transmission system provided by the present invention replaces a DC circuit breaker and a DC energy dissipation device with a DC high-speed switch, and provides a surplus power balancing strategy during a DC fault in the flexible DC transmission system. When an offshore converter station detects a DC fault, the grid-side converters in all wind turbine converters are controlled to be locked, and the DC energy dissipation devices in the wind turbine converters maintain the DC voltage stability of the wind turbine converters. The DC port voltage and / or DC port current of the offshore converter station and the onshore converter station are controlled to be reduced to zero according to the topology of the flexible DC transmission system. After the DC fault is cleared, the DC voltage of the onshore converter station is controlled to gradually recover within a first preset time. When the DC voltage of the onshore converter station begins to recover, the offshore converter station notifies the sending-end wind turbine converter to gradually recover to the operating power before the DC fault within a second preset time, and the second preset time is not less than the first preset time. The surplus power balance after a DC fault does not need to rely on DC circuit breakers and DC energy dissipation devices. The surplus power balance after a DC fault can be achieved by using DC high-speed switches and corresponding control strategies, which greatly reduces the cost. This solves the technical problem that the existing offshore wind power flexible DC transmission system needs to use DC circuit breakers and DC energy dissipation devices to achieve surplus power balance after a DC fault, which has high construction costs and is not conducive to promotion and application.

[0044] For easier understanding, see Figure 3 The present invention provides an embodiment of a device for balancing surplus power during a DC fault in a flexible DC transmission system. The device is applied to an offshore wind power flexible DC transmission system, wherein the offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station. The offshore converter station is connected to the onshore converter station via a DC cable, a DC high-speed switch, and a DC overhead line connected in series. Both the offshore converter station and the onshore converter station adopt a topology with DC fault clearing capability, which can be a full half-bridge hybrid topology. The device includes the following modules:

[0045] The converter blocking module is used to control the grid-side converters in all wind turbine converters to block when a DC fault is detected at the offshore converter station, so that the DC energy dissipation devices in the wind turbine converters maintain the DC voltage stability of the wind turbine converters;

[0046] A voltage and current control module, configured to control the DC port voltage and / or DC port current of the offshore converter station and the onshore converter station to be reduced to zero according to the topology of the flexible DC transmission system;

[0047] The recovery module is used to control the DC voltage of the onshore converter station to gradually recover within a first preset time after the DC fault is cleared. When the DC voltage of the onshore converter station begins to recover, the offshore converter station is used to notify the wind turbine converter at the sending end to gradually recover to the operating power before the DC fault within a second preset time, and the second preset time is not less than the first preset time.

[0048] Also includes:

[0049] The judgment module is used to judge whether there is any unsuccessfully locked grid-side converter among all wind turbine converters after issuing a grid-side converter locking instruction among all wind turbine converters and before the DC voltage of the onshore converter station begins to recover. If so, the total power output of the unsuccessfully locked grid-side converters is obtained, and a corresponding number of locked grid-side converters are re-unlocked according to the total power output of the unsuccessfully locked grid-side converters, and all re-unlocked grid-side converters are controlled to absorb reverse power from the collection system, and the reverse power absorbed by the re-unlocked grid-side converters is equal to the total output of the unsuccessfully locked grid-side converters.

[0050] The voltage and current control module is specifically used for:

[0051] If the flexible DC transmission system adopts a symmetrical single-machine topology, the DC port voltage of the onshore converter station is controlled to drop to 0, and the DC port current of the offshore converter station is controlled to drop to 0. If the flexible DC transmission system adopts a bipolar topology, the DC port currents of the offshore converter station and the onshore converter station are controlled to be 0.

[0052] The present invention also provides an embodiment of a surplus power balancing device during a DC fault in a flexible DC transmission system.

[0053] The device includes a processor and a memory:

[0054] The memory is used to store program code and transmit the program code to the processor;

[0055] The processor is configured to execute the method for balancing surplus power during a DC fault in a flexible DC transmission system according to the instructions in the program code.

[0056] The present invention also provides an embodiment of a computer-readable storage medium, wherein the computer-readable storage medium is used to store program code, and the program code is used to execute the method for balancing surplus power during a DC fault in a flexible DC transmission system described in the present invention.

[0057] The device, apparatus, and computer-readable storage medium for balancing surplus power during a DC fault in a flexible DC transmission system provided in the present invention are used to execute the method for balancing surplus power during a DC fault in a flexible DC transmission system provided in the present invention. The principles and technical effects achieved are the same as those of the method for balancing surplus power during a DC fault in a flexible DC transmission system provided in the present invention, and are not further described here.

[0058] The terms "first," "second," "third," "fourth," and the like in the description of the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present invention described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0059] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for balancing surplus power during a DC fault in a flexible HVDC transmission system, applied to an offshore wind power flexible HVDC transmission system, characterized in that: The offshore wind power flexible DC transmission system includes an offshore converter station and an onshore converter station. The offshore converter station is connected to the onshore converter station via a DC cable, a DC high-speed switch, and a DC overhead line connected in series. Both the offshore converter station and the onshore converter station adopt a topology with DC fault clearing capability. The method for balancing surplus power during a DC fault in the flexible DC transmission system includes the following steps: S1. When the offshore converter station detects a DC fault, it controls the grid-side converters in all wind turbine converters at the sending end to lock out, and the DC energy dissipation devices in the wind turbine converters maintain the DC voltage stability of the wind turbine converters. S2. Controlling the DC port voltage and / or DC port current of the offshore converter station and the onshore converter station to be reduced to zero according to the topology of the offshore wind power flexible DC transmission system; S3. After the DC fault is cleared, the DC voltage of the onshore converter station is controlled to gradually recover within a first preset time. When the DC voltage of the onshore converter station begins to recover, the wind turbine converter at the sending end is notified through the offshore converter station to gradually recover to the operating power before the DC fault within a second preset time. The second preset time is not less than the first preset time.

2. The method for balancing surplus power during a DC fault in a flexible DC transmission system according to claim 1, characterized in that: After step S1 and before step S3, the method further includes: Determine whether there is any unsuccessfully locked grid-side converter among all wind turbine converters. If so, obtain the total power output of the unsuccessfully locked grid-side converters, re-unlock a corresponding number of locked grid-side converters based on the total power output of the unsuccessfully locked grid-side converters, and control all re-unlocked grid-side converters to reversely absorb power from the collection system of the offshore wind power flexible direct current transmission system. The power reversely absorbed by the re-unlocked grid-side converters is equal to the total output of the unsuccessfully locked grid-side converters.

3. The method for balancing surplus power during a DC fault in a flexible DC transmission system according to claim 1, characterized in that: Both the offshore converter station and the onshore converter station adopt a full half-bridge hybrid topology.

4. The method for balancing surplus power during a DC fault in a flexible HVDC transmission system according to claim 1, wherein step S2 specifically comprises: If the flexible DC transmission system adopts a symmetrical single-machine topology, the DC port voltage of the onshore converter station is controlled to drop to 0, and the DC port current of the offshore converter station is controlled to drop to 0. If the flexible DC transmission system adopts a bipolar topology, the DC port currents of both the offshore converter station and the onshore converter station are controlled to drop to 0.

5. A device for balancing surplus power during a DC fault in a flexible DC transmission system, applied to an offshore wind power flexible DC transmission system, characterized in that: The offshore wind power HVDC Flexible transmission system includes an offshore converter station and an onshore converter station. The offshore converter station is connected to the onshore converter station via a DC cable, a DC high-speed switch, and a DC overhead line connected in series. Both the offshore and onshore converter stations adopt a topology with DC fault clearing capabilities. The surplus power balancing device during a DC fault in the HVDC Flexible transmission system includes the following modules: The converter blocking module is used to control the grid-side converters in all wind turbine converters at the sending end to block when a DC fault is detected at the offshore converter station. The DC energy dissipation device in the wind turbine converter maintains the DC voltage stability of the wind turbine converter. A voltage and current control module is used to control the DC port voltage and / or DC port current of the offshore converter station and the onshore converter station to be reduced to zero according to the topology of the offshore wind power flexible DC transmission system; The recovery module is used to control the DC voltage of the onshore converter station to gradually recover within a first preset time after the DC fault is cleared. When the DC voltage of the onshore converter station begins to recover, the offshore converter station is used to notify the wind turbine converter at the sending end to gradually recover to the operating power before the DC fault within a second preset time, and the second preset time is not less than the first preset time.

6. The device for balancing surplus power during a DC fault in a flexible DC transmission system according to claim 5, characterized in that: Also includes: The judgment module is used to judge whether there is any unsuccessfully locked grid-side converter among all wind turbine converters after issuing a grid-side converter locking instruction among all wind turbine converters and before the DC voltage of the onshore converter station begins to recover. If so, the total power output of the unsuccessfully locked grid-side converters is obtained, and a corresponding number of locked grid-side converters are re-unlocked according to the total power output of the unsuccessfully locked grid-side converters, and all the re-unlocked grid-side converters are controlled to reversely absorb power from the collection system of the offshore wind power flexible DC transmission system, and the power reversely absorbed by the re-unlocked grid-side converter is equal to the total output of the unsuccessfully locked grid-side converters.

7. The device for balancing surplus power during a DC fault in a flexible DC transmission system according to claim 5, characterized in that: Both the offshore converter station and the onshore converter station adopt a full half-bridge hybrid topology.

8. In the device for balancing surplus power during a DC fault in a flexible DC transmission system according to claim 5, the voltage and current control module is specifically configured to: If the flexible DC transmission system adopts a symmetrical single-machine topology, the DC port voltage of the onshore converter station is controlled to drop to 0, and the DC port current of the offshore converter station is controlled to drop to 0. If the flexible DC transmission system adopts a bipolar topology, the DC port currents of both the offshore converter station and the onshore converter station are controlled to drop to 0.

9. A device for balancing surplus power during a DC fault in a flexible DC transmission system, characterized in that: The device includes a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the method for balancing surplus power during a DC fault in a flexible DC transmission system according to any one of claims 1 to 4 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium is used to store program code, and the program code is used to execute the method for balancing surplus power during a DC fault in a flexible DC transmission system according to any one of claims 1 to 4.

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