AC side fault control method and system of extra-high voltage flexible DC power transmission system, and storage medium

Abstract

The invention discloses an alternating current side fault control method and system of an extra-high voltage flexible direct current power transmission system and a storage medium. The method comprises the following steps: detecting whether the alternating current side of a receiving end converter station in the extra-high voltage flexible direct current power transmission system has a fault or not in real time; under the condition that it is detected that the alternating current side breaks down, when fault control conditions are met, the receiving end converter station is controlled to reduce the direct current voltage of the receiving end converter station to zero; wherein the fault control conditions comprise that the positive sequence component of the three-phase voltage of the alternating current side is greater than or equal to a first voltage threshold value, and the duration of the detected fault is greater than a preset duration threshold value; or, the positive-sequence component of the three-phase voltage of the alternating current side is smaller than the first voltage threshold value, so that the impact caused by surplus power on the receiving-end converter station can be avoided, and the safety and economical efficiency of the system are improved.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current transmission, and in particular to an alternating current side fault control method, system and storage medium for an ultra-high voltage flexible direct current transmission system. Background Art

[0002] At present, since the distance between the two ends of the UHV flexible DC transmission technology is generally more than 2000km, for the UHV flexible DC system with ultra-long transmission distance, when an instantaneous fault occurs in the AC system on the receiving side, it is easy to cause significant surplus power on the receiving side, which may trigger protection lockout or even shutdown of the UHV flexible DC transmission system, causing serious economic losses and safety hazards.

[0003] In the related art, a DC energy dissipation device is usually configured on the receiving side to reduce the impact on the receiving side and consume surplus power. However, the energy dissipation efficiency of the DC energy dissipation device is low, which may cause safety hazards and economic losses. Summary of the invention

[0004] In order to solve the above technical problems, the embodiments of the present application propose an AC side fault control method, system and storage medium for an ultra-high voltage flexible direct current transmission system, which can prevent the receiving end converter station from being impacted by surplus power, thereby improving the system safety and economy.

[0005] In a first aspect, an embodiment of the present application provides an AC side fault control method for an ultra-high voltage flexible direct current transmission system, comprising:

[0006] Real-time detection of whether a fault occurs on the AC side of the receiving-end converter station in the UHV flexible DC power transmission system;

[0007] In the case where a fault is detected on the AC side, when a fault control condition is met, controlling the receiving-end converter station to reduce its DC voltage to zero;

[0008] Wherein, the fault control conditions include:

[0009] The positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold;

[0010] or,

[0011] The positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold.

[0012] Optionally, controlling the receiving-end converter station to reduce its DC voltage to zero includes:

[0013] The receiving-end converter station is controlled to reduce its DC voltage to zero at a first rate, wherein the first rate is a preset constant rate.

[0014] Optionally, the method further comprises:

[0015] In the event that a fault is detected on the AC side, when the fault control condition is met, the receiving-end converter station is controlled to send a fault message to the sending-end converter station in the UHV flexible DC transmission system, so that the sending-end converter station switches its control strategy to a constant DC current control strategy, wherein the constant DC current control strategy is used to indicate operation according to a constant DC value at the sending end.

[0016] Optionally, the sending-end constant DC value is: a rated DC current value of the sending-end, or a DC current value of the sending-end converter station at a moment before receiving the fault message.

[0017] Optionally, after controlling the receiving-end converter station to reduce its DC voltage to zero, the method further includes:

[0018] When it is detected that the fault on the AC side is restored to normal, the following steps are performed:

[0019] Controlling the receiving-end converter station to increase its DC voltage to a rated DC current value of the receiving end, or to a DC current value of the receiving-end converter station at a moment before a fault occurs on the AC side, at a second rate, wherein the second rate is a preset constant rate;

[0020] The receiving-end converter station is controlled to send a recovery message to the sending-end converter station, so that the sending-end converter station switches its control strategy from the constant DC current control strategy to the control strategy before switching to the constant DC current control strategy after detecting that the voltage of the pole line to which it is connected is higher than the second voltage threshold.

[0021] Optionally, the control strategy of the sending-end converter station before switching to the fixed DC current control strategy is a fixed active power control strategy, wherein the fixed active power control strategy is used to indicate operation according to a constant power value at the sending end, and the constant power value at the sending end is the rated power value of the sending end or the power value of the sending-end converter station at a moment before receiving the fault message.

[0022] In a second aspect, an embodiment of the present application provides an AC side fault control system for an ultra-high voltage flexible direct current transmission system, comprising:

[0023] A detection module, used for detecting in real time whether a fault occurs on the AC side of the receiving-end converter station in the UHV flexible DC power transmission system;

[0024] A first control module is used to control the receiving-end converter station to reduce its DC voltage to zero when a fault is detected on the AC side and a fault control condition is met;

[0025] Wherein, the fault control conditions include:

[0026] The positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold;

[0027] or,

[0028] The positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold.

[0029] Optionally, controlling the receiving-end converter station to reduce its DC voltage to zero includes:

[0030] The receiving-end converter station is controlled to reduce its DC voltage to zero at a first rate, wherein the first rate is a preset constant rate.

[0031] Optionally, the first control module is further used to control the receiving-end converter station to send a fault message to the sending-end converter station in the UHV flexible DC transmission system when a fault is detected on the AC side and the fault control condition is met, so that the sending-end converter station switches its control strategy to a constant DC current control strategy, wherein the constant DC current control strategy is used to indicate operation according to a constant DC value at the sending end.

[0032] Optionally, the system further comprises:

[0033] The second control module is configured to, after controlling the receiving-end converter station to reduce its DC voltage to zero, execute the following steps when detecting that the fault on the AC side returns to normal:

[0034] Controlling the receiving-end converter station to increase its DC voltage to a rated DC current value of the receiving end, or to a DC current value of the receiving-end converter station at a moment before a fault occurs on the AC side, at a second rate, wherein the second rate is a preset constant rate;

[0035] The receiving-end converter station is controlled to send a recovery message to the sending-end converter station, so that the sending-end converter station switches its control strategy from the constant DC current control strategy to the control strategy before switching to the constant DC current control strategy after detecting that the voltage of the pole line to which it is connected is higher than the second voltage threshold.

[0036] In a third aspect, an embodiment of the present application provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps of any of the methods described above are implemented.

[0037] In summary, the embodiments of the present application have at least the following beneficial effects:

[0038] By adopting the embodiment of the present application, whether a fault occurs on the AC side of the receiving-end converter station in the ultra-high voltage flexible direct current transmission system is detected in real time; when a fault is detected on the AC side, when the fault control condition is met, the receiving-end converter station is controlled to reduce its DC voltage to zero; wherein the fault control condition includes: the positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold; or the positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold, which can avoid the receiving-end converter station from being impacted by surplus power, thereby improving system safety and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of an AC side fault control method of an ultra-high voltage flexible direct current transmission system provided in an embodiment of the present application;

[0040] Figure 2 It is a structural schematic diagram of an AC side fault control system of an ultra-high voltage flexible DC power transmission system provided in an embodiment of the present application;

[0041] Figure 3 is a schematic diagram of electrical information on a DC pole line when a fault occurs provided by an embodiment of the present application;

[0042] Figure 4 It is a schematic diagram of the maximum voltage of the receiving-end converter valve submodule when a fault occurs provided in an embodiment of the present application. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0044] In the description of the present application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "multiple" is two or more. In the description of the present application, the term "including" and its variations are open inclusions, i.e., "including but not limited to". The term "based on" means "at least partially based on". The term "according to" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments".

[0045] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0046] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0047] First, see Figure 1 , shows a flow chart of an AC side fault control method of a UHV flexible DC transmission system provided in an embodiment of the present application, the method comprising steps S101-S102, which are as follows:

[0048] S101, detecting in real time whether a fault occurs on the AC side of a receiving-end converter station in the ultra-high voltage flexible direct current power transmission system;

[0049] S102, when a fault is detected on the AC side and a fault control condition is met, controlling the receiving-end converter station to reduce its DC voltage to zero.

[0050] Wherein, the fault control conditions include:

[0051] The positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold;

[0052] or,

[0053] The positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold.

[0054] It should be noted that the ultra-high voltage flexible direct current transmission system in this embodiment refers to a typical ±800kV / 8GW ultra-high voltage flexible direct current transmission system, and its main circuit parameters are as follows: submodule rated working voltage 2.0kV, submodule capacitance 24mF, bridge arm reactor 25mH, current limiting reactor 300mH. The length of the DC transmission line is 2400km, using 6 split conductors, and the line resistance is about 10Ω. The ultra-high voltage flexible direct current transmission system adopts a true bipolar wiring scheme, each pole is cascaded by two valve groups, and the DC voltage of each valve group is 400kV. The valve group adopts a full half-bridge hybrid module, and the full bridge ratio is 60%. The AC side of the sending end converter station is a networking mode, the sending end adopts a fixed active power and fixed reactive power control strategy, and the receiving end adopts a fixed DC voltage and fixed reactive power control strategy. There is no need to configure a DC energy consumption device in the ultra-high voltage flexible direct current transmission system of this embodiment.

[0055] In one example, the first voltage threshold is 0.6 pu.

[0056] In one example, the preset duration threshold is 100 ms.

[0057] In one example, if the fault control condition is not met, there is no need to control the receiving-end converter station, that is, there is no need to intervene in the operation of the receiving-end converter station.

[0058] In an optional implementation manner, controlling the receiving-end converter station to reduce its DC voltage to zero includes:

[0059] The receiving-end converter station is controlled to reduce its DC voltage to zero at a first rate, wherein the first rate is a preset constant rate.

[0060] In one example, the first rate is 1 kV / μs.

[0061] In an optional embodiment, the method further includes:

[0062] In the event that a fault is detected on the AC side, when the fault control condition is met, the receiving-end converter station is controlled to send a fault message to the sending-end converter station in the UHV flexible DC transmission system, so that the sending-end converter station switches its control strategy to a constant DC current control strategy, wherein the constant DC current control strategy is used to indicate operation according to a constant DC value at the sending end.

[0063] In an optional implementation, the sending-end constant DC value is: the sending-end rated DC current value, or the DC current value of the sending-end converter station at a moment before receiving the fault message.

[0064] In an optional implementation manner, after controlling the receiving-end converter station to reduce its DC voltage to zero, the method further includes:

[0065] When it is detected that the fault on the AC side is restored to normal, the following steps are performed:

[0066] Controlling the receiving-end converter station to increase its DC voltage to a rated DC current value of the receiving end, or to a DC current value of the receiving-end converter station at a moment before a fault occurs on the AC side, at a second rate, wherein the second rate is a preset constant rate;

[0067] The receiving-end converter station is controlled to send a recovery message to the sending-end converter station, so that the sending-end converter station switches its control strategy from the constant DC current control strategy to the control strategy before switching to the constant DC current control strategy after detecting that the voltage of the pole line to which it is connected is higher than the second voltage threshold.

[0068] In one example, the second rate may be 100 V / μs.

[0069] In one example, the second voltage threshold may be 0.8 pu.

[0070] In an optional embodiment, the control strategy of the sending-end converter station before switching to the fixed DC current control strategy is a fixed active power control strategy, wherein the fixed active power control strategy is used to indicate operation according to a constant power value at the sending end, and the constant power value at the sending end is the rated power value of the sending end or the power value of the sending-end converter station at the moment before receiving the fault message.

[0071] On the second aspect, accordingly, the embodiment of the present application also provides an AC side fault control system of an ultra-high voltage flexible direct current transmission system, which can implement all processes of the AC side fault control method of the ultra-high voltage flexible direct current transmission system provided in the above embodiment.

[0072] See also Figure 2 , shows a schematic structural diagram of an AC side fault control system of an ultra-high voltage flexible direct current transmission system provided in an embodiment of the present application, the AC side fault control system comprising:

[0073] The detection module 201 is used to detect in real time whether a fault occurs on the AC side of the receiving end converter station in the UHV flexible DC power transmission system;

[0074] The first control module 202 is used to control the receiving-end converter station to reduce its DC voltage to zero when a fault is detected on the AC side and a fault control condition is met;

[0075] Wherein, the fault control conditions include:

[0076] The positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold;

[0077] or,

[0078] The positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold.

[0079] In an optional implementation manner, controlling the receiving-end converter station to reduce its DC voltage to zero includes:

[0080] The receiving-end converter station is controlled to reduce its DC voltage to zero at a first rate, wherein the first rate is a preset constant rate.

[0081] In an optional embodiment, the first control module is further used to control the receiving-end converter station to send a fault message to the sending-end converter station in the UHV flexible DC transmission system when a fault is detected on the AC side and the fault control condition is met, so that the sending-end converter station switches its control strategy to a constant DC current control strategy, wherein the constant DC current control strategy is used to indicate operation according to a constant DC value at the sending end.

[0082] In an optional implementation, the sending-end constant DC value is: the sending-end rated DC current value, or the DC current value of the sending-end converter station at a moment before receiving the fault message.

[0083] In an optional embodiment, the system further includes:

[0084] The second control module is configured to, after controlling the receiving-end converter station to reduce its DC voltage to zero, execute the following steps when detecting that the fault on the AC side returns to normal:

[0085] Controlling the receiving-end converter station to increase its DC voltage to a rated DC current value of the receiving end, or to a DC current value of the receiving-end converter station at a moment before a fault occurs on the AC side, at a second rate, wherein the second rate is a preset constant rate;

[0086] The receiving-end converter station is controlled to send a recovery message to the sending-end converter station, so that the sending-end converter station switches its control strategy from the constant DC current control strategy to the control strategy before switching to the constant DC current control strategy after detecting that the voltage of the pole line to which it is connected is higher than the second voltage threshold.

[0087] In an optional embodiment, the control strategy of the sending-end converter station before switching to the fixed DC current control strategy is a fixed active power control strategy, wherein the fixed active power control strategy is used to indicate operation according to a constant power value at the sending end, and the constant power value at the sending end is the rated power value of the sending end or the power value of the sending-end converter station at the moment before receiving the fault message.

[0088] A specific embodiment is given below to explain the fault control provided by this application and how to achieve the effect of fault ride-through (a key technology in the power system, fault ride-through capability refers to the ability of the power system to maintain stable operation and quickly recover to normal state when a fault occurs).

[0089] Based on a typical ±800kV / 8GW ultra-high voltage flexible direct current transmission system, its main circuit parameters are as follows: submodule rated working voltage 2.0kV, submodule capacitance 24mF, bridge arm reactor 25mH, current limiting reactor 300mH. The length of the direct current transmission line is 2400km, using 6 split conductors, and the line resistance is about 10Ω. The ultra-high voltage flexible direct current transmission system adopts a true bipolar wiring scheme, each pole is cascaded by two valve groups, and the DC voltage of each valve group is 400kV. The valve group adopts a full half-bridge hybrid module, and the full bridge ratio is 60%. The AC side of the sending end converter station is in networking mode, the sending end adopts a fixed active power and fixed reactive power control strategy, and the receiving end adopts a fixed DC voltage and fixed reactive power control strategy. The flexible direct current system is not equipped with a DC energy consumption device.

[0090] Before the fault occurs, the UHV flexible DC transmission system operates at full capacity. Figure 35.1s), a two-phase metallic grounding fault occurs on the AC side of the receiving-end converter, and the positive sequence component of the three-phase voltage on the AC side drops to 0.33pu. About 10ms after the fault, the receiving-end converter station detects the fault and immediately reduces the DC voltage to zero at a rate of 1kV / μs. At the same time, through inter-station communication, the sending-end converter station is informed to change the fixed active power control strategy to the fixed DC current control strategy, and the DC current command value is set to 1pu. About 40ms after the fault, after receiving the command from the receiving-end converter station, the sending-end converter station immediately changes the fixed active power control strategy to the fixed DC current control strategy, and sets the DC current command value to 1pu. About 100ms after the fault, the fault on the AC side of the receiving-end converter is cleared. About 110ms after the fault, after the receiving-end converter station detects that the fault on the AC side has been cleared, it immediately increases the DC voltage to the previous value at a rate of 100V / μs, and at the same time informs the sending-end converter station through inter-station communication that it will change the fixed DC current control strategy to a fixed active power control strategy, and the power command value is 1pu. After the sending-end converter station receives the command from the receiving-end converter station and detects that the pole line voltage is higher than 0.8pu (about 150ms after the fault), it immediately changes the fixed DC current control strategy to a fixed active power control strategy, and the power command value is 1pu. Figure 3 As shown, about 150ms after the fault is cleared, the power on the DC pole line basically returns to the state before the fault, and about 300ms after the fault is cleared, the voltage, current and power on the DC pole line basically return to the stable operating state before the fault. Figure 4 is the maximum voltage of the converter valve submodule of the receiving station during the fault ride-through period, which does not exceed 2.7 kV and is lower than the overvoltage protection setting of the submodule. It can be seen that the AC side fault ride-through method of the ultra-high voltage flexible direct current transmission system with rapid recovery after a fault provided by the embodiment of the present invention can realize system fault ride-through after a fault occurs on the AC side of the receiving end converter transformer.

[0091] In a third aspect, an embodiment of the present application provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps of any of the methods described above are implemented.

[0092] In summary, the embodiments of the present application have at least the following beneficial effects:

[0093] By adopting the embodiment of the present application, whether a fault occurs on the AC side of the receiving-end converter station in the ultra-high voltage flexible direct current transmission system is detected in real time; when a fault is detected on the AC side, when the fault control condition is met, the receiving-end converter station is controlled to reduce its DC voltage to zero; wherein the fault control condition includes: the positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold; or the positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold, which can avoid the receiving-end converter station from being impacted by surplus power, thereby improving system safety and economy.

[0094] Through the description of the above implementation methods, those skilled in the art can clearly understand that the present application can be implemented by means of software plus the necessary hardware platform, and of course, it can also be implemented entirely by hardware. Based on such an understanding, all or part of the contribution of the technical solution of the present application to the background technology can be embodied in the form of a software product, and the computer software product can be stored in a storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present application or some parts of the embodiments.

[0095] The above is a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A method for controlling AC side faults in a UHV flexible DC transmission system, characterized in that: include: Real-time detection of whether a fault occurs on the AC side of the receiving-end converter station in the UHV flexible DC power transmission system; In the case where a fault is detected on the AC side, when a fault control condition is met, controlling the receiving-end converter station to reduce its DC voltage to zero; Wherein, the fault control conditions include: The positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold; or, The positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold.

2. The method according to claim 1, characterized in that The controlling the receiving-end converter station to reduce its DC voltage to zero comprises: The receiving-end converter station is controlled to reduce its DC voltage to zero at a first rate, wherein the first rate is a preset constant rate.

3. The method according to claim 1 or 2, characterized in that The method further comprises: In the event that a fault is detected on the AC side, when the fault control condition is met, the receiving-end converter station is controlled to send a fault message to the sending-end converter station in the UHV flexible DC transmission system, so that the sending-end converter station switches its control strategy to a constant DC current control strategy, wherein the constant DC current control strategy is used to indicate operation according to a constant DC value at the sending end.

4. The method according to claim 3, characterized in that The sending-end constant DC value is: the sending-end rated DC current value, or the DC current value of the sending-end converter station at a moment before receiving the fault message.

5. The method according to claim 3, characterized in that After controlling the receiving-end converter station to reduce its DC voltage to zero, the method further includes: When it is detected that the fault on the AC side is restored to normal, the following steps are performed: Control the receiving-end converter station to increase its DC voltage to a rated DC current value of the receiving end, or to a DC current value of the receiving-end converter station at a moment before a fault occurs on the AC side, at a second rate, wherein the second rate is a preset constant rate; The receiving-end converter station is controlled to send a recovery message to the sending-end converter station, so that the sending-end converter station switches its control strategy from the constant DC current control strategy to the control strategy before switching to the constant DC current control strategy after detecting that the voltage of the pole line to which it is connected is higher than the second voltage threshold.

6. The method according to claim 5, characterized in that The control strategy of the sending-end converter station before switching to the fixed DC current control strategy is a fixed active power control strategy, wherein the fixed active power control strategy is used to indicate operation according to a constant power value at the sending end, and the constant power value at the sending end is the rated power value of the sending end or the power value of the sending-end converter station at the moment before receiving the fault message.

7. An AC side fault control system for a UHV flexible DC transmission system, characterized in that: include: A detection module, used for detecting in real time whether a fault occurs on the AC side of the receiving-end converter station in the UHV flexible DC power transmission system; A first control module is used to control the receiving-end converter station to reduce its DC voltage to zero when a fault is detected on the AC side and a fault control condition is met; Wherein, the fault control conditions include: The positive sequence component of the three-phase voltage on the AC side is greater than or equal to a first voltage threshold, and the detected fault duration is greater than a preset duration threshold; or, The positive sequence component of the three-phase voltage on the AC side is less than the first voltage threshold.

8. The system according to claim 7, characterized in that The controlling the receiving-end converter station to reduce its DC voltage to zero comprises: The receiving-end converter station is controlled to reduce its DC voltage to zero at a first rate, wherein the first rate is a preset constant rate.

9. The system according to claim 7 or 8, characterized in that The first control module is also used to control the receiving-end converter station to send a fault message to the sending-end converter station in the UHV flexible DC transmission system when a fault is detected on the AC side and the fault control condition is met, so that the sending-end converter station switches its control strategy to a constant DC current control strategy, wherein the constant DC current control strategy is used to indicate operation according to a constant DC value at the sending end.

10. The system according to claim 9, characterized in that The system further comprises: The second control module is configured to, after controlling the receiving-end converter station to reduce its DC voltage to zero, execute the following steps when detecting that the fault on the AC side returns to normal: Control the receiving-end converter station to increase its DC voltage to a rated DC current value of the receiving end, or to a DC current value of the receiving-end converter station at a moment before a fault occurs on the AC side, at a second rate, wherein the second rate is a preset constant rate; The receiving-end converter station is controlled to send a recovery message to the sending-end converter station, so that the sending-end converter station switches its control strategy from the constant DC current control strategy to the control strategy before switching to the constant DC current control strategy after detecting that the voltage of the pole line to which it is connected is higher than the second voltage threshold.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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