Last Circuit Breaker Protection Method, Device and Equipment for Flexible DC Transmission Project

Abstract

The present application relates to a last breaker protection method, device and equipment for a flexible DC transmission project. The method includes obtaining the opening and closing states and tripping signals of all breakers in a flexible DC back-to-back system; determining the connection relationship between the converter unit and the AC outgoing line according to the tripping signal and the opening and closing states of the breakers, and determining whether the last breaker protection performs an action to block DC operation according to the connection relationship. The last breaker protection method for the flexible DC transmission project determines whether the last breaker protection performs an action to block DC operation through the opening and closing states and tripping signals of all breakers, avoiding the failure of the breaker protection configuration in the flexible DC back-to-back project due to the loss of power of the AC outgoing line; solving the technical problem that the breaker protection configuration method in the existing flexible DC back-to-back project will cause the failure of the breaker protection configuration due to the loss of power of the AC outgoing line.

Description

Technical Field

[0001] The present application relates to the technical field of flexible DC power transmission, and particularly to a last breaker protection method, device and equipment for a flexible DC power transmission project. Background Art

[0002] With the growth of the power grid scale, the short-circuit current of large power grids in core load areas has approached the breaking capacity of AC breakers, and the problem of excessive short-circuit current has become an important factor affecting the safe and stable operation of the power grid. To solve the problem of short-circuit current in large power grids, a flexible DC back-to-back project can be built in the core area of the power grid to divide the large power grid into two small power grids, which are interconnected through a flexible DC project in the middle, thereby reducing the short-circuit current of the power grid.

[0003] In a flexible DC back-to-back project, a last breaker protection needs to be set to identify the last breaker condition and block the safety of DC protection equipment. In addition, a blocking signal can also be generated in time for the stability control system to perform corresponding generator tripping and load shedding operations. However, when the last breaker condition occurs in the converter in the existing flexible DC back-to-back project, the loss of AC outgoing lines in the flexible DC back-to-back project will cause the converter to be unable to control normally, which will further lead to overvoltage and endanger the safety and damage of equipment, resulting in the failure of the breaker protection configuration and affecting the safety of the power grid. Summary of the Invention

[0004] Embodiments of the present application provide a last breaker protection method, device and equipment for a flexible DC power transmission project, which are used to solve the technical problem that the breaker protection configuration method in the existing flexible DC back-to-back project will cause the failure of the breaker protection configuration due to the loss of power of AC outgoing lines.

[0005] To achieve the above object, the embodiments of the present application provide the following technical solutions:

[0006] A last breaker protection method for a flexible DC power transmission project, which is applied to a flexible DC back-to-back system. The flexible DC back-to-back system includes a DC converter station and a next-level substation connected to the DC converter station through multiple AC outgoing lines. The DC converter station includes a conversion unit, a rectifier-side AC field and an inverter-side AC field connected to the conversion unit. The rectifier-side AC side and the inverter-side AC field are both connected to each AC outgoing line. Circuit breakers connected to each AC outgoing line are provided on the inverter-side AC field and the rectifier-side AC field. Last breaker protection is configured on both the rectifier-side AC field and the inverter-side AC field. The last breaker protection method includes the following steps:

[0007] Obtain the opening and closing states and tripping signals of all circuit breakers in the flexible DC back-to-back system;

[0008] Determine the connection relationship between the converter unit or the next-level substation and the AC outgoing line according to the tripping signal and the opening / closing state of the circuit breaker, and determine whether the final circuit breaker protection performs an action to block DC operation according to the connection relationship.

[0009] Preferably, determining whether the final circuit breaker protection performs an action to block DC operation according to the connection relationship includes:

[0010] If the connection relationship is that the converter unit is disconnected from the AC outgoing line and the AC voltage criterion is satisfied, then control the final circuit breaker protection to perform an action to block DC operation;

[0011] If the connection relationship is that the circuit breaker of the next-level substation is disconnected from the AC outgoing line, then control the final circuit breaker protection to perform an action to block DC operation.

[0012] Preferably, the AC voltage criterion includes: If the connection relationship is that the converter unit is disconnected from the AC outgoing line, then obtain the effective value of the AC voltage of the flexible DC back-to-back system. If the effective value of the AC voltage is greater than the voltage threshold value, then the AC voltage criterion is satisfied.

[0013] Preferably, the method for the final circuit breaker protection of this flexible DC transmission project includes: Using the three-out-of-one principle to determine whether the circuit breaker connected to the AC outgoing line is in the open state. The three-out-of-one principle includes: If any one phase of the circuit breaker is in the off position, then the circuit breaker is in the open state.

[0014] This application also provides a device for the final circuit breaker protection of a flexible DC transmission project, which is applied to a flexible DC back-to-back system. The flexible DC back-to-back system includes a DC converter station and a next-level substation connected to the DC converter station through multiple AC outgoing lines. The DC converter station includes a converter unit and a rectifier-side AC yard and an inverter-side AC yard connected to the converter unit. Both the rectifier-side AC side and the inverter-side AC yard are connected to each AC outgoing line. Circuit breakers connected to each AC outgoing line are provided on the inverter-side AC yard and the rectifier-side AC yard. Final circuit breaker protection is configured on both the rectifier-side AC yard and the inverter-side AC yard. This final circuit breaker protection device includes a data acquisition module and a judgment protection module;

[0015] The data acquisition module is used to acquire the opening / closing state of the circuit breaker and the tripping signal in the flexible DC back-to-back system;

[0016] The judgment protection module is used to determine the connection relationship between the converter unit or the next-level substation and the AC outgoing line according to the tripping signal and the opening / closing state of the circuit breaker, and determine whether the final circuit breaker protection performs an action to block DC operation according to the connection relationship.

[0017] Preferably, the judgment protection module is further configured to disconnect the converter unit from the AC outgoing line according to the connection relationship, and if the AC voltage criterion is satisfied, control the last breaker protection to perform an action to block DC operation; and / or disconnect the breaker of the next-level substation from the AC outgoing line according to the connection relationship, and then control the last breaker protection to perform an action to block DC operation.

[0018] Preferably, the AC voltage criterion includes: disconnect the converter unit from the AC outgoing line according to the connection relationship, then obtain the effective value of the AC voltage of the flexible DC back-to-back system, and if the effective value of the AC voltage is greater than the voltage threshold value, the AC voltage criterion is satisfied.

[0019] Preferably, the last breaker protection device of this flexible DC transmission project includes a tripping judgment module, and the tripping judgment module is used to determine whether the breaker connected to the AC outgoing line is in the tripping state by adopting the one-out-of-three principle, and the one-out-of-three principle includes: if any one phase of the breaker is in the off position, the breaker is in the tripping state.

[0020] This application also provides a storage device, in which multiple program codes are stored, and the program codes are adapted to be loaded and run by a processor to execute the above-mentioned last breaker protection method for a flexible DC transmission project.

[0021] This application also provides a terminal device, including a processor and a memory;

[0022] The memory is used to store program codes and transmit the program codes to the processor;

[0023] The processor is used to execute the above-mentioned last breaker protection method for a flexible DC transmission project according to the instructions in the program codes.

[0024] It can be seen from the above technical solutions that the embodiments of this application have the following advantages: The last breaker protection method, device and equipment for a flexible DC transmission project. The method includes obtaining the opening and closing states and tripping signals of all breakers in the flexible DC back-to-back system; determining the connection relationship between the converter unit and the AC outgoing line according to the tripping signal and the opening and closing state of the breaker, and determining whether the last breaker protection performs an action to block DC operation according to the connection relationship. The last breaker protection method for a flexible DC transmission project determines whether the last breaker protection performs an action to block DC operation through the opening and closing states and tripping signals of all breakers, avoiding the failure of the breaker protection configuration due to the loss of power of the AC outgoing line in the flexible DC back-to-back project; solving the technical problem that the breaker protection configuration method in the existing flexible DC back-to-back project will cause the failure of the breaker protection configuration due to the loss of power of the AC outgoing line. Brief Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 It is a flowchart of the steps of the last breaker protection method for a flexible DC transmission project described in an embodiment of the present application;

[0027] Figure 2 It is a framework diagram of a flexible DC back-to-back system described in an embodiment of the present application;

[0028] Figure 3 It is a framework diagram of the last breaker protection device for a flexible DC transmission project described in an embodiment of the present application. Detailed Embodiments

[0029] In order to make the invention purposes, features, and advantages of the present application more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the embodiments described below are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0030] The present application proposes a last breaker protection method, device, and equipment for a flexible DC transmission project, which are used to solve the technical problem that the breaker protection configuration method in the existing flexible DC back-to-back project will cause the failure of the breaker protection configuration due to the loss of power of the AC outgoing line.

[0031] Embodiment 1:

[0032] Figure 1 It is a flowchart of the steps of the last breaker protection method for a flexible DC transmission project described in an embodiment of the present application, Figure 2 It is a framework diagram of a flexible DC back-to-back system described in an embodiment of the present application.

[0033] As Figure 2As shown in the figure, the present application provides a last breaker protection method for a flexible DC transmission project, which is applied to a flexible DC back-to-back system. The flexible DC back-to-back system includes a DC converter station 10 and a next-level substation 20 connected to the DC converter station through multiple AC outgoing lines. The DC converter station 10 includes a conversion unit and a rectifier-side AC field 12 and an inverter-side AC field 13 connected to the conversion unit. Circuit breakers connected to each of the AC outgoing lines are provided on the inverter-side AC field 12 and the rectifier-side AC field 12. The inverter-side AC field 13 and the rectifier-side AC field 12 are also connected to each AC outgoing line. The rectifier-side AC field 12 and the inverter-side AC field 13 are both configured with last breaker protection.

[0034] It should be noted that circuit breakers 5011, 5021, 5012, 5023, 5013, and 5024 are provided on the rectifier-side AC field 12. Circuit breaker 5011 and circuit breaker 5012 are connected in series and are respectively connected to the rectifier side of the first conversion unit 11. Circuit breaker 5012 and circuit breaker 5013 are connected in series and are respectively grounded. Circuit breaker 5023 and circuit breaker 5024 are connected in series and are respectively connected to the rectifier side of the second conversion unit 14. Circuit breaker 5021 and circuit breaker 5022 are connected in series and are respectively grounded. Circuit breakers 5031, 5032, 5033, 5041, 5042, and 5043 are provided on the inverter-side AC field 13. Circuit breaker 5031 and circuit breaker 5032 are connected in series and are respectively connected to the inverter side of the first conversion unit 11. Circuit breaker 5032 and circuit breaker 5033 are connected in series and are respectively connected to the next-level substation 20 through the second AC outgoing line 32. Circuit breaker 5041 and circuit breaker 5042 are connected in series and are respectively connected to the next-level substation 20 through the first AC outgoing line 31. Circuit breaker 5042 and circuit breaker 5043 are connected in series and are respectively connected to the inverter side of the second AC unit 14. Circuit breakers 5051, 5051, 5053, 5061, 5062, 5063, 5071, 5072, and 5073 are provided on the next-level substation 20. Circuit breaker 5051 and circuit breaker 5052 are connected in series and are respectively connected to the first AC outgoing line 3. Circuit breaker 5052 and circuit breaker 5053 are connected in series and are respectively grounded. Circuit breaker 5062 and circuit breaker 5063 are connected in series and are respectively connected to the second AC outgoing line 32. Circuit breaker 5061 and circuit breaker 5062 are connected in series and are respectively grounded; Circuit breakers 5071, 5072, and 5073 are connected in series in this way and are respectively grounded.

[0035] As Figure 1 shown, the last breaker protection method for this flexible DC transmission project includes the following steps:

[0036] S10. Obtain the opening and closing states and tripping signals of the circuit breakers in the flexible DC back-to-back system.

[0037] It should be noted that in step S10, it is mainly to obtain the opening and closing states of all the circuit breakers on the DC converter station and the tripping signals of the circuit breakers, AC outgoing lines, etc.

[0038] S20. Determine the connection relationship between the converter unit or the next-level substation and the AC outgoing line according to the tripping signal and the opening and closing states of the circuit breakers, and determine whether the final circuit breaker protection executes an action to block DC operation according to the connection relationship.

[0039] It should be noted that in step S20, it is mainly to judge the connection relationship between each converter unit on the flexible DC back-to-back system and each AC outgoing line according to whether each circuit breaker on the DC converter station trips or is in the open state, so as to determine whether to execute the action of the final circuit breaker protection on the DC converter station to block DC operation.

[0040] In the embodiment of the present application, the final circuit breaker protection method of this flexible DC transmission project executes the final circuit breaker protection work in the DC converter station according to the judgment in step S20, avoiding the failure of the circuit breaker protection configuration in the flexible DC back-to-back project due to the loss of power of the AC outgoing line.

[0041] The final circuit breaker protection method of the flexible DC transmission project provided by the present application includes obtaining the opening and closing states and tripping signals of the circuit breakers in the flexible DC back-to-back system; determining the connection relationship between the converter unit and the AC outgoing line according to the tripping signal and the opening and closing states of the circuit breakers, and determining whether the final circuit breaker protection executes an action to block DC operation according to the connection relationship. The final circuit breaker protection method of this flexible DC transmission project judges whether the final circuit breaker protection executes an action to block DC operation through the opening and closing states of the circuit breakers and the tripping signals, avoiding the failure of the circuit breaker protection configuration in the flexible DC back-to-back project due to the loss of power of the AC outgoing line; solving the technical problem that the existing circuit breaker protection configuration method in the flexible DC back-to-back project will cause the failure of the circuit breaker protection configuration due to the loss of power of the AC outgoing line.

[0042] In an embodiment of the present application, determining whether the final circuit breaker protection executes an action to block DC operation according to the connection relationship includes:

[0043] If the connection relationship is that the converter unit is disconnected from the AC outgoing line and the AC voltage criterion is satisfied, then control the final circuit breaker protection to execute an action to block DC operation;

[0044] If the connection relationship is that the next-level substation is disconnected from all AC outgoing lines, then control the final circuit breaker protection to execute an action to block DC operation.

[0045] It should be noted that asFigure 2 As shown, if the circuit breakers 5031 and 5033 trip and open, then the inverter side of the first converter unit and the second AC outgoing line are only connected through the circuit breaker 5032, that is, the connection relationship is that the converter unit is connected to at least one AC outgoing line, which does not meet the operating conditions of the last circuit breaker, so the control of the last circuit breaker protection does not execute the action to block the DC operation. For example Figure 2 As shown, if both the first AC outgoing line and the second AC outgoing line are disconnected from the next-level substation, then the control of the last circuit breaker protection executes the action to block the DC operation. It can also be based on the series connection situation of the first AC outgoing line and the second AC outgoing line in the next-level substation. For example: if the circuit breakers 5051, 5052, and 5053 all trip or are in the open state, and the circuit breakers 5061, 5062, and 5063 all trip or are in the open state, that is, both the first AC outgoing line and the second AC outgoing line lose the electrical connection with the next-level substation, then a blocking signal is sent to control the last circuit breaker protection to execute the action to block the DC operation.

[0046] In an embodiment of the present application, the AC voltage criterion includes: if the connection relationship is that the converter unit is disconnected from the AC outgoing line, then the effective value of the AC voltage of the flexible DC back-to-back system is obtained. If the effective value of the AC voltage is greater than the voltage fixed threshold value, then the AC voltage criterion is met.

[0047] It should be noted that the voltage fixed threshold value can be set according to the requirements of the flexible DC back-to-back system, and no detailed limitation is made here. The last circuit breaker protection method for this flexible DC transmission project realizes the prevention of misoperation by configuring the last circuit breaker protection on both the rectifier-side AC field and the inverter-side AC field. The last circuit breaker protection method for this flexible DC transmission project judges whether to control the last circuit breaker protection to execute the action to block the DC operation through the effective value of the AC voltage, and realizes the overvoltage protection of the flexible DC back-to-back system.

[0048] In an embodiment of the present application, the last circuit breaker protection method for this flexible DC transmission project can also determine whether the last circuit breaker protection executes the action to block the DC operation according to the opening and closing states of the circuit breakers, that is, if all the circuit breakers connected to the AC outgoing line are in the open state, then the control of the last circuit breaker protection executes the action to block the DC operation. Among them, the three-out-of-one principle is adopted to determine whether the circuit breaker connected to the AC outgoing line is in the open state. The three-out-of-one principle includes: if any one phase of the circuit breaker is in the off position, then the circuit breaker is in the open state

[0049] It should be noted that the three-out-of-one means that the circuit breaker is configured with three phases A, B, and C. As long as any one phase of the circuit breaker is open, it is judged that the circuit breaker is in the open state. For example Figure 2As shown, if the second AC outgoing line stops working and only the first AC outgoing line is operating, and if a line phase A fault (also known as single-phase tripping) occurs in the first AC outgoing line at this time, the AC protection acts, and the phase A of the circuit breakers 5041 and 5042 connected to the first AC outgoing line are in the off position. At this time, the flexible DC back-to-back system is in a single-phase operation state. According to the one-out-of-three criterion principle, if the circuit breakers 5041 and 5042 are in the open state, then the control finally makes the circuit breaker protection execute an action to block the DC operation.

[0050] As Figure 2 shown, according to the obtained opening and closing states and tripping signals of the circuit breakers in the rectifier-side AC substation, the inverter-side AC substation, and the next-level substation, the rectifier-side DC controller corresponding to the rectifier-side AC substation and the inverter-side DC controller corresponding to the inverter-side AC substation respectively control whether the corresponding final circuit breaker executes the protection action to block the DC according to the final circuit breaker protection method of this flexible DC transmission project. The inverter-side DC controller also analyzes the opening and closing states and tripping signals of the circuit breakers in the next-level substation according to the final circuit breaker protection method of this flexible DC transmission project to obtain the blocking signal for controlling whether the final circuit breaker protection executes the action to block the DC operation.

[0051] Embodiment 2:

[0052] Figure 3 It is a framework diagram of the final circuit breaker protection device for the flexible DC transmission project described in the embodiments of this application.

[0053] As Figure 3 shown, this application also provides a final circuit breaker protection device for a flexible DC transmission project, which is applied to a flexible DC back-to-back system. The flexible DC back-to-back system includes a DC converter station and a next-level substation connected to the DC converter station through multiple AC outgoing lines. The DC converter station includes a conversion unit and a rectifier-side AC substation and an inverter AC substation connected to the conversion unit. The rectifier-side AC side and the inverter AC substation are each connected to each AC outgoing line. Circuit breakers connected to each AC outgoing line are provided on the inverter AC substation and the rectifier-side AC substation. Final circuit breaker protection is configured for both the rectifier-side AC substation and the inverter AC substation. The final circuit breaker protection device includes a data acquisition module 10 and a judgment protection module 20;

[0054] The data acquisition module 10 is used to acquire the opening and closing states and tripping signals of the circuit breakers in the flexible DC back-to-back system;

[0055] The judgment protection module 20 is used to determine the connection relationship between the conversion unit or the next-level substation and the AC outgoing line according to the tripping signal and the opening and closing states of the circuit breakers, and to determine whether the final circuit breaker protection executes the action to block the DC operation according to the connection relationship.

[0056] In the embodiment of the present application, the judgment protection module 20 is further configured to disconnect the converter unit from the AC outgoing line according to the connection relationship, and when the AC voltage criterion is satisfied, control the last breaker protection to perform an action to block DC operation; and / or disconnect the breaker of the next-level substation from the AC outgoing line according to the connection relationship, and then control the last breaker protection to perform an action to block DC operation.

[0057] In the embodiment of the present application, the AC voltage criterion includes: when the converter unit is disconnected from the AC outgoing line according to the connection relationship, obtain the effective value of the AC voltage of the flexible DC back-to-back system. If the effective value of the AC voltage is greater than the voltage threshold value, the AC voltage criterion is satisfied.

[0058] In the embodiment of the present application, the last breaker protection device of the flexible DC transmission project includes a tripping judgment module. The tripping judgment module is used to determine whether the breaker connected to the AC outgoing line is in the tripping state by using the one-out-of-three principle. The one-out-of-three principle includes: if any one phase of the breaker is in the off position, the breaker is in the tripping state.

[0059] It should be noted that the content of the module in Embodiment 2 corresponds to the steps in the method of Embodiment 1. The content of the method steps in Embodiment 1 has been elaborated in detail in Embodiment 1, and the content of the module in the system will not be repeated in Embodiment 2.

[0060] Embodiment 3:

[0061] The present application also provides a storage device, in which multiple program codes are stored. The program codes are suitable for being loaded and run by a processor to execute the above-mentioned last breaker protection method for a flexible DC transmission project.

[0062] Embodiment 4:

[0063] The present application also provides a terminal device, including a processor and a memory;

[0064] The memory is used to store program codes and transmit the program codes to the processor;

[0065] The processor is used to execute the above-mentioned last breaker protection method for a flexible DC transmission project according to the instructions in the program codes.

[0066] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described system, device, and unit can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein again.

[0067] In several embodiments provided by the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling, direct coupling, or communication connection between each other can be through some interfaces, and the indirect coupling or communication connection of the device or unit can be in electrical, mechanical, or other forms.

[0068] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0069] In addition, each functional unit in various embodiments of the present application can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0070] If the above-mentioned integrated unit is implemented in the form of 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 application, in essence, or the part that contributes to the prior art, or all or part of this 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 enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present application. The foregoing storage medium includes: USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs and other various media that can store program codes.

[0071] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of various embodiments of the present application.

Claims

1. A final breaker protection method for a flexible DC transmission project, which is applied to a flexible DC back-to-back system. The flexible DC back-to-back system includes a DC converter station and a next-level substation connected to the DC converter station through multiple AC outgoing lines. The DC converter station includes a conversion unit, a rectifier-side AC yard and an inverter-side AC yard connected to the conversion unit. Both the rectifier-side AC side and the inverter-side AC yard are connected to each AC outgoing line. Circuit breakers connected to each AC outgoing line are provided on the inverter-side AC yard and the rectifier-side AC yard. It is characterized in that, Both the rectifier - side AC substation and the inverter - side AC substation are equipped with final breaker protection, and the final breaker protection method includes the following steps: Obtain the opening - closing state and tripping signal of the breaker in the flexible DC back - to - back system; Determine the connection relationship between the converter unit or the next - level substation and the AC outgoing line according to the tripping signal and the breaker opening - closing state, and determine whether the final breaker protection performs an action to block DC operation according to the connection relationship; Determining whether the final breaker protection performs an action to block DC operation according to the connection relationship includes: If the connection relationship is that the converter unit is disconnected from the AC outgoing line and the AC voltage criterion is met, then control the final breaker protection to perform an action to block DC operation; If the connection relationship is that the next - level substation is disconnected from all the AC outgoing lines, then control the final breaker protection to perform an action to block DC operation.

2. The final breaker protection method for a flexible DC transmission project according to claim 1, characterized in that, The AC voltage criterion includes: If the connection relationship is that the converter unit is disconnected from the AC outgoing line, then obtain the effective value of the AC voltage of the flexible DC back - to - back system. If the effective value of the AC voltage is greater than the voltage threshold value, then the AC voltage criterion is met.

3. The final breaker protection method for a flexible DC transmission project according to claim 1, characterized in that, Includes: Adopt the three - out - of - one principle to determine whether the breaker connected to the AC outgoing line is in the open state. The three - out - of - one principle includes: If any one phase of the breaker is in the off - position, then the breaker is in the open state.

4. A final breaker protection device for a flexible DC transmission project, which is applied to a flexible DC back-to-back system. The flexible DC back-to-back system includes a DC converter station and a next-level substation connected to the DC converter station through multiple AC outgoing lines. The DC converter station includes a conversion unit, a rectifier-side AC yard and an inverter-side AC yard connected to the conversion unit. Both the rectifier-side AC side and the inverter-side AC yard are connected to each AC outgoing line. Circuit breakers connected to each AC outgoing line are provided on the inverter-side AC yard and the rectifier-side AC yard. It is characterized in that, Both the rectifier - side AC substation and the inverter - side AC substation are equipped with final breaker protection. The final breaker protection device includes a data acquisition module and a protection judgment module; The data acquisition module is used to obtain the opening - closing state and tripping signal of the breaker in the flexible DC back - to - back system; The protection judgment module is used to determine the connection relationship between the converter unit or the next - level substation and the AC outgoing line according to the tripping signal and the breaker opening - closing state, and determine whether the final breaker protection performs an action to block DC operation according to the connection relationship; The protection judgment module is also used to control the final breaker protection to perform an action to block DC operation if the connection relationship is that the converter unit is disconnected from the AC outgoing line and the AC voltage criterion is met; and / or control the final breaker protection to perform an action to block DC operation if the connection relationship is that the breaker of the next - level substation is disconnected from the AC outgoing line.

5. The final breaker protection device for a flexible DC transmission project according to claim 4, characterized in that, The AC voltage criterion includes: If the connection relationship is that the converter unit is disconnected from the AC outgoing line, then obtain the effective value of the AC voltage of the flexible DC back - to - back system. If the effective value of the AC voltage is greater than the voltage threshold value, then the AC voltage criterion is met.

6. The final breaker protection device for a flexible DC transmission project according to claim 4, characterized in that, Includes a tripping judgment module. The tripping judgment module is used to adopt the three - out - of - one principle to determine whether the breaker connected to the AC outgoing line is in the open state. The three - out - of - one principle includes: If any one phase of the breaker is in the off - position, then the breaker is in the open state.

7. A storage device, in which multiple program codes are stored, characterized in that, The program code is suitable for being loaded and run by a processor to execute the final breaker protection method of the flexible DC transmission project as described in any one of claims 1 - 3.

8. A terminal device, characterized in that, Includes a processor and a memory; The memory is configured to store program code and transmit the program code to the processor; The processor is configured to execute the last breaker protection method for a flexible DC transmission project according to any one of claims 1-3 based on the instructions in the program code.

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