A DC fault transient control method for symmetrical single-pole LCC-HVDC system

Abstract

The present invention discloses a DC fault transient control method for a symmetrical unipolar LCC-HVDC system, which belongs to the technical field of high-voltage direct current transmission. The method includes a fault clearing stage and a restarting stage; the fault clearing stage includes: changing the control strategy of the fault pole converter to limit the fault current, and maintaining the control strategy of the non-fault pole converter to maintain the transmission power; the restarting stage includes: rebuilding the line voltage on the inverter side, and based on the line voltage reconstructed on the inverter side, converting the fault pole converter on the rectifier side to symmetrical triggering to reduce the harmonic voltage; wherein the DC fault is a unipolar grounding fault. The method can maintain a certain DC transmission power while clearing the unipolar grounding fault, and improve the DC fault ride-through performance of the symmetrical unipolar LCC-HVDC system.

Description

Technical Field

[0001] The invention relates to a direct current fault transient control method for a symmetrical monopole LCC-HVDC system, belonging to the technical field of high-voltage direct current transmission. Background Art

[0002] The fault ride-through capability of the DC transmission line of the Line Commutated Converter-High Voltage Direct Current (LCC-HVDC) system is extremely important for ensuring equipment safety, improving power supply reliability, and maintaining the stability of the entire system.

[0003] Conventional LCC-HVDC systems with symmetrical bipolar generally use the DC line fault restart function of the pole control system to clear and restore DC line faults. It is mainly divided into three stages: phase shifting, deionization and restarting. Whether to restart, the setting of deionization time and the number of restarts need to be determined in combination with actual operating conditions. For most transient faults, DC line fault restart can quickly clear the fault and restore power supply, but for permanent faults, the failure of system recovery and shutdown will cause more serious secondary impact on the entire power supply network.

[0004] In recent years, in order to meet the needs of large-scale new energy access and improve the controllability of power grid transmission corridors, the "embedded" symmetrical monopole LCC-HVDC solution that builds converter stations at both ends inside the same AC power grid has attracted active attention and exploration by scholars. Since there is no direct connection between the neutral points at both ends of the symmetrical monopole LCC-HVDC, its DC fault characteristics are different from those of the symmetrical bipolar LCC-HVDC, and the DC fault clearing strategy used needs to be adjusted. Summary of the invention

[0005] The object of the present invention is to provide a DC fault transient control method for a symmetrical monopole LCC-HVDC system, which can maintain a certain DC transmission power while clearing a monopole grounding fault, thereby improving the DC fault ride-through performance of the symmetrical monopole LCC-HVDC system.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for controlling a DC fault transient state in a symmetrical unipolar LCC-HVDC system, including a fault clearing phase and a restarting phase;

[0008] The fault clearing stage includes: changing the control strategy of the fault pole converter to limit the fault current, and maintaining the control strategy of the non-fault pole converter to maintain the transmission power;

[0009] The restarting stage includes: rebuilding the line voltage on the inverter side, and based on the line voltage rebuilt on the inverter side, converting the fault pole converter on the rectifier side to symmetrical triggering to reduce harmonic voltage;

[0010] Wherein, the DC fault is a single-pole grounding fault.

[0011] In combination with the first aspect, further, changing the control strategy of the fault pole converter includes:

[0012] The fault-pole converter on the rectifier side is switched to constant DC current control, and the DC current of the fault-pole converter on the inverter side is controlled to be equal to the DC current of the non-fault-pole converter on the inverter side;

[0013] The DC voltage of the faulty pole converter on the rectifier side is controlled to be 0.

[0014] In combination with the first aspect, further, rebuilding the line voltage on the inverter side includes: switching the fault pole converter on the inverter side to constant DC voltage control, and rebuilding the line voltage on the inverter side.

[0015] In combination with the first aspect, further, based on the line voltage reconstructed on the inverter side, converting the fault-pole converter on the rectifier side to symmetrical triggering includes:

[0016] If the line voltage reconstructed on the inverter side is greater than the preset threshold, the rectifier side enters the bipolar converter common constant DC current mode, and the bipolar converter receives the same trigger command and operates in the 12-pulse mode;

[0017] Wherein, the bipolar converters are fault-pole converters and non-fault-pole converters.

[0018] In combination with the first aspect, further, based on the line voltage reconstructed on the inverter side, converting the fault pole converter on the rectifier side to symmetrical triggering also includes: resetting the current controller integral amount to 60°.

[0019] In combination with the first aspect, further, the fault clearing stage also includes: changing the arc extinction angle prediction control strategy of the non-fault pole on the inverter side to suppress the commutation failure of the converter of the non-fault pole on the inverter side.

[0020] In combination with the first aspect, further, changing the inverter-side non-fault pole arc extinction angle prediction control strategy includes: modifying the current control command value in the original arc extinction angle prediction control strategy to a measured value of the DC current.

[0021] In a second aspect, the present invention provides a symmetrical single-pole LCC-HVDC system DC fault transient control device, comprising:

[0022] Fault clearing module: used to change the control strategy of the fault pole converter to limit the fault current and maintain the control strategy of the non-fault pole converter to maintain the transmission power;

[0023] Restart module: used to rebuild the line voltage on the inverter side. Based on the rebuilt line voltage on the inverter side, the faulty pole converter on the rectifier side is switched to symmetrical triggering to reduce harmonic voltage.

[0024] Wherein, the DC fault is a single-pole grounding fault.

[0025] In a third aspect, the present invention provides a symmetrical single-pole LCC-HVDC system DC fault transient control system, comprising:

[0026] Storage medium: used to store computer programs;

[0027] Processor: used to execute the computer program to implement the steps of any method described in the first aspect.

[0028] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the methods described in the first aspect.

[0029] In a fifth aspect, the present invention provides a computer program product, comprising a computer program, which, when executed by a processor, implements the steps of any one of the methods described in the first aspect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The DC fault transient control method of the symmetrical monopole LCC-HVDC system provided by the present invention limits the fault current by changing the control strategy of the fault pole converter in the fault clearing stage, and maintains the output power by maintaining the control strategy of the non-fault pole converter, so that a certain DC transmission power can be maintained while clearing the monopole grounding fault; in the restarting stage, based on the line voltage reconstructed on the inverter side, the harmonic voltage can be reduced by converting the fault pole converter on the rectifier side to symmetrical triggering, so as to reduce the impact of the restarting stage of the symmetrical monopole LCC-HVDC system on the AC power grid. In the fault clearing stage, the commutation failure of the non-fault pole converter on the inverter side is suppressed by changing the non-fault pole arc extinction angle prediction control strategy on the inverter side, so as to improve the DC fault ride-through performance of the symmetrical monopole LCC-HVDC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of a DC fault transient control method for a symmetrical single-pole LCC-HVDC system provided by an embodiment of the present invention;

[0033] Figure 2 is a DC side equivalent circuit diagram of a symmetrical single-pole LCC-HVDC system in a fault clearing stage provided by an embodiment of the present invention;

[0034] Figure 3: is a DC side equivalent circuit diagram of a symmetrical monopolar LCC-HVDC system in the restart phase provided by an embodiment of the present invention;

[0035] Figure 4 is a voltage and current response waveform diagram of a symmetrical unipolar LCC-HVDC system under a unipolar grounding fault after adopting a symmetrical unipolar LCC-HVDC system DC fault transient control method provided by an embodiment of the present invention, Figure 4 In the figure, (a) is the waveform of the DC current on the inverter side, (b) is the waveform of the fault current, (c) is the waveform of the DC voltage on the inverter side, and (d) is the waveform of the DC voltage on the rectifier side;

[0036] Figure 5 It is a schematic diagram of modifying the inverter side non-fault pole extinction angle prediction control strategy provided by an embodiment of the present invention;

[0037] Figure 6 is a schematic diagram of the test effect of the inverter side non-fault pole extinction angle prediction control strategy before and after modification provided by an embodiment of the present invention, Figure 6 In the figure, (a) is the test effect of the non-fault pole extinction angle prediction control strategy on the inverter side before modification, and (b) is the test effect of the non-fault pole extinction angle prediction control strategy on the inverter side after modification;

[0038] Figure 7 It is a DC side equivalent circuit diagram of a symmetrical unipolar LCC-HVDC system after the rectifier side adopts a symmetrical triggering mode in the fault clearing stage provided by an embodiment of the present invention;

[0039] Figure 8 It is an AC voltage waveform diagram after the rectifier side adopts a symmetrical triggering mode in the restart phase provided by an embodiment of the present invention;

[0040] Fig. 9 It is a schematic diagram of harmonic content on the AC side after the rectifier side adopts a symmetrical triggering method during the restart phase provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present application is further described in detail below in conjunction with specific implementation methods.

[0042] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limitations on the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0043] Embodiment 1:

[0044] The present embodiment provides a symmetrical monopole LCC-HVDC system DC fault transient control method, which can be applied to a terminal and can be executed by a symmetrical monopole LCC-HVDC system DC fault transient control device, which can be implemented by software and / or hardware, and can be integrated in a terminal, for example: any tablet computer or computer device with communication function.

[0045] The DC fault transient control method for a symmetrical monopole LCC-HVDC system provided in this embodiment includes a fault clearing phase and a restarting phase.

[0046] The fault clearing stage includes: changing the control strategy of the fault pole converter to limit the fault current and maintaining the control strategy of the non-fault pole converter to maintain the transmission power.

[0047] The restart phase includes: rebuilding the line voltage on the inverter side, and based on the rebuilt line voltage on the inverter side, converting the fault pole converter on the rectifier side to symmetrical triggering to reduce the harmonic voltage.

[0048] In this embodiment, the DC fault is a single-pole grounding fault.

[0049] Changing the control strategy of the faulty pole converter specifically includes the following steps:

[0050] Step 1: convert the fault-pole converter on the rectifier side to constant DC current control, and control the DC current of the fault-pole converter on the inverter side to be equal to the DC current of the non-fault-pole converter on the inverter side;

[0051] In this embodiment, Figure 2 As shown in FIG. 1 , the fault-pole converter on the rectifier side is switched to constant DC current control, and the DC current of the fault-pole converter on the inverter side is controlled to be equal to the DC current of the non-fault-pole converter on the inverter side, so that Figure 2 The currents in loop 1 and loop 2 are equal, thus limiting the fault current.

[0052] Step 2: Control the DC voltage of the fault-pole converter on the rectifier side to be 0.

[0053] In this embodiment, Figure 2 As shown, controlling the DC voltage of the fault-pole converter on the rectifier side to 0 can limit the neutral point voltage and the overall voltage on the rectifier side.

[0054] Rebuilding the line voltage on the inverter side and converting the fault-pole converter on the rectifier side to symmetrical triggering to reduce the harmonic voltage based on the line voltage reconstructed on the inverter side specifically include the following steps:

[0055] Step ①: Switch the inverter-side fault-pole converter to constant DC voltage control and rebuild the line voltage on the inverter side;

[0056] In this embodiment, Figure 3As shown, during the restart phase, the faulty pole converter on the inverter side is switched to constant DC voltage control, and an attempt is made to rebuild the line voltage on the inverter side.

[0057] Step ②: If the line voltage reconstructed on the inverter side is greater than the preset threshold, the rectifier side enters the bipolar converter common constant DC current mode, and the bipolar converter receives the same trigger instruction and operates in the 12-pulse mode.

[0058] In this embodiment, Figure 3 As shown, the bipolar converters are a fault pole converter and a non-fault pole converter.

[0059] During the restart phase, due to the asymmetric operation of the bipolar converter, the converter stations at both ends of the symmetrical unipolar LCC-HVDC system have relatively prominent 5th and 7th harmonics in a short period of time, which have a certain impact on the reliable operation of the AC power grid.

[0060] Therefore, the current of loop 1 is symmetrically controlled by the bipolar converter on the rectifier side, that is, the symmetrical triggering mode is adopted on the rectifier side. Then, after the fault clearing stage, the equivalent circuit of the DC side of the symmetrical unipolar LCC-HVDC system adopts the symmetrical triggering mode on the rectifier side as follows: Figure 7 As shown in the figure, the AC voltage waveform after the rectifier side adopts the symmetrical triggering method during the restart phase is as follows Figure 8 As shown in the figure, after the rectifier side adopts the symmetrical contact method during the restart phase, the harmonic content on the AC side is as follows: Fig. 9 shown. Figure 7 middle, , Indicates the positive and negative DC current on the rectifier side. , Indicates the positive and negative DC currents on the inverter side. , Indicates the current of loop 1 and loop 2. Indicates the DC voltage of the negative converter on the inverter side, , Indicates constant DC current and constant DC voltage. Indicates the fault current, Indicates the inductance of the smoothing reactor.

[0061] Depend on Figure 8 , Fig. 9 It can be seen that after the symmetrical triggering method is adopted on the rectifier side, the harmonic voltage level of the converter station is greatly reduced. During the fault clearing stage, the 5th and 7th harmonic voltage contents are reduced from 6.41% and 5.66% to 0.012% and 0.028%, respectively, reducing the impact of the symmetrical monopolar LCC-HVDC system on the AC power grid during the restart stage.

[0062] Step 3: Reset the current controller integral to 60°.

[0063] In this embodiment, Figure 3 As shown, resetting the current controller integral to 60° can avoid a sudden increase in the DC voltage on the rectifier side.

[0064] The symmetrical unipolar LCC-HVDC system DC fault transient control method provided in this embodiment limits the fault current by changing the control strategy of the fault pole converter in the fault clearing stage, and maintains the output power by maintaining the control strategy of the non-fault pole converter, so that a certain DC transmission power can be maintained while clearing the unipolar grounding fault; in the restarting stage, based on the line voltage reconstructed on the inverter side, the harmonic voltage is reduced by converting the fault pole converter on the rectifier side to symmetrical triggering, so as to reduce the impact of the restarting stage of the symmetrical unipolar LCC-HVDC system on the AC power grid.

[0065] Embodiment 2:

[0066] The DC fault transient control method for a symmetrical single-pole LCC-HVDC system provided in this embodiment is based on Embodiment 1, and the fault clearing stage further includes: changing the arc extinction angle prediction control strategy of the non-fault pole on the inverter side to suppress the commutation failure of the converter of the non-fault pole on the inverter side.

[0067] In this embodiment, changing the inverter-side non-fault pole arc extinction angle prediction control strategy specifically includes: modifying the current control command value in the original arc extinction angle prediction control strategy to the actual measured value of the DC current.

[0068] In the DC fault transient control method for a symmetrical unipolar LCC-HVDC system provided in Example 1, since the rectifier side does not perform rapid phase shifting during the fault clearing stage, the non-fault pole current is not immediately limited, and there is a large peak current in a short period of time, resulting in a commutation failure in the non-fault pole converter on the inverter side.

[0069] In order to suppress the commutation failure of the non-fault pole converter on the inverter side, the arc extinction angle prediction control strategy of the non-fault pole on the inverter side is modified during the fault clearing stage, such as Figure 5 As shown, the current control command value in the original arc extinction angle prediction control strategy is modified to the actual measured value of the DC current. Figure 5 middle, Indicates the DC current reference value, Indicates the measured value of DC current, Indicates the DC current rating, Indicates the ideal DC no-load voltage rating, Indicates the measured value of the ideal DC no-load voltage, represents the equivalent commutation reactance, represents the gain, represents the arc extinction angle, Indicates the turn-off angle.

[0070] After the current control command value in the original arc extinction angle prediction control strategy is modified to the actual DC current measured value, the inverter side non-fault pole converter will adjust the arc extinction angle prediction control command in time according to the DC current to suppress the inverter side non-fault pole converter commutation failure. The test results of the inverter side non-fault pole arc extinction angle prediction control strategy before and after the modification are shown in the figure. Figure 6 As shown, Figure 6 In the figure, (a) is the test effect of the non-fault pole extinction angle prediction control strategy on the inverter side before modification, and (b) is the test effect of the non-fault pole extinction angle prediction control strategy on the inverter side after modification.

[0071] Depend on Figure 6 It can be seen that after modifying the arc extinction angle prediction control strategy of the non-fault pole on the inverter side, the non-fault pole converter on the inverter side no longer fails to commutate during the fault clearing stage, and the goals of limiting the fault current and clearing the DC fault can also be achieved.

[0072] The DC fault transient control method for a symmetrical monopole LCC-HVDC system provided in this embodiment can improve the DC fault ride-through performance of the symmetrical monopole LCC-HVDC system by changing the arc extinction angle prediction control strategy of the non-fault pole on the inverter side to suppress the commutation failure of the converter of the non-fault pole on the inverter side during the fault clearing stage.

[0073] Embodiment 3:

[0074] The DC fault transient control method for a symmetrical single-pole LCC-HVDC system provided in this embodiment is based on Embodiment 1 or 2. Figure 1 As shown, the specific steps include:

[0075] S1: Determine whether the DC fault is a single-pole grounding fault. If so, enter S2;

[0076] In this embodiment, after detecting that a DC fault occurs in the symmetrical monopolar LCC-HVDC system, the converter station first determines the type of the DC fault. If the type of the DC fault is determined to be a monopolar grounding fault, the process proceeds to S2.

[0077] S2: Maintain the control strategy of the non-fault pole converter, control the DC current of the inverter-side fault pole converter to be equal to the DC current of the inverter-side non-fault pole converter, and control the DC voltage of the rectifier-side fault pole converter to be 0, and enter S3;

[0078] In this embodiment, S2 is a fault clearing stage. Taking a positive pole grounding fault in a symmetrical single-pole LCC-HVDC system as an example, the fault clearing stage lasts for 400 ms.

[0079] In the fault clearing stage, the control strategy of the non-fault pole converter is maintained, and the control strategy of the fault pole converter is changed, such as Figure 2As shown, the fault-pole converter on the rectifier side is switched to constant DC current control, that is, , and control the DC current of the inverter-side fault pole converter to be equal to the DC current of the inverter-side non-fault pole converter, that is, , which can make Figure 2 The currents of loop 1 and loop 2 are equal, thus limiting the fault current and controlling the DC voltage of the fault-pole converter on the rectifier side to 0, that is, , which can limit the neutral point voltage and overall voltage on the rectifier side. Figure 2 middle, , Indicates the positive and negative DC current on the rectifier side. , Indicates the positive and negative DC currents on the inverter side. , Indicates the current of loop 1 and loop 2. , Indicates the DC voltage of the positive and negative converters on the rectifier side. , Indicates the DC voltage of the positive and negative converters on the inverter side. , Indicates constant DC current and constant DC voltage. Indicates the fault current, Indicates the inductance of the smoothing reactor.

[0080] S3: Maintain bipolar current, restore fault pole voltage, and enter S4;

[0081] In this embodiment, S3 is a restart phase. Taking a positive pole grounding fault in a symmetrical monopolar LCC-HVDC system as an example, the restart phase lasts for 200ms.

[0082] During the restart phase, Figure 3 As shown, the inverter side fault pole converter is switched to constant DC voltage control, that is, , try to rebuild the line voltage on the inverter side. If the line voltage rebuilt on the inverter side is greater than the preset threshold, that is, , the rectifier side enters the bipolar converter common constant DC current mode, and the bipolar converter receives the same trigger command and operates in the 12-pulse mode, that is, , the bipolar converter is the fault pole converter and the non-fault pole converter, and the current controller integral is reset to about 60°, that is, , which can avoid the sudden increase of DC voltage on the rectifier side. Figure 3 middle, , Indicates the positive and negative DC current on the rectifier side. , Indicates the positive and negative DC currents on the inverter side. Represents the DC voltage of the positive converter on the rectifier side, , Indicates the DC voltage of the positive and negative converters on the inverter side. , Indicates constant DC current and constant DC voltage. Indicates the fault current, represents the inductance of the smoothing reactor, represents the direct current, Indicates the integral amount of the current controller.

[0083] S4: Determine whether the restart is successful, if so, go to S7, otherwise go to S5;

[0084] S5: Determine whether the number of restarts exceeds the upper limit. If so, proceed to S6; otherwise, return to S2;

[0085] S6: Lock each converter, start stabilization control, and enter S7;

[0086] S7: End.

[0087] After adopting the DC fault transient control method for the symmetrical unipolar LCC-HVDC system provided in this embodiment, the voltage and current response waveforms of the symmetrical unipolar LCC-HVDC system under a unipolar grounding fault are as follows: Figure 4 As shown, Figure 4 In the figure, (a) is the waveform of the DC current on the inverter side, (b) is the waveform of the fault current, (c) is the waveform of the DC voltage on the inverter side, and (d) is the waveform of the DC voltage on the rectifier side.

[0088] Embodiment 4:

[0089] This embodiment provides a symmetrical single-pole LCC-HVDC system DC fault transient control device, including:

[0090] Fault clearing module: used to change the control strategy of the fault pole converter to limit the fault current and maintain the control strategy of the non-fault pole converter to maintain the transmission power;

[0091] Restart module: used to rebuild the line voltage on the inverter side. Based on the rebuilt line voltage on the inverter side, the faulty pole converter on the rectifier side is switched to symmetrical triggering to reduce harmonic voltage.

[0092] Among them, the DC fault is a single-pole grounding fault.

[0093] In this embodiment, the fault clearing module is further used to change the inverter-side non-fault pole arc extinction angle prediction control strategy to suppress the inverter-side non-fault pole converter commutation failure.

[0094] The symmetrical monopole LCC-HVDC system DC fault transient control device provided in the embodiment of the present application can execute the symmetrical monopole LCC-HVDC system DC fault transient control method provided in any embodiment of the present application, and has the corresponding functional modules and beneficial effects of the execution method.

[0095] Embodiment 5:

[0096] This embodiment provides a symmetrical single-pole LCC-HVDC system DC fault transient control system, including:

[0097] Storage medium: used to store computer programs;

[0098] Processor: used to execute computer programs to implement the steps of the method in Example 1.

[0099] Embodiment 6:

[0100] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method in Embodiment 1 are implemented.

[0101] Embodiment 7:

[0102] This embodiment provides a computer program product, including a computer program, which implements the steps of the method in Embodiment 1 when executed by a processor.

[0103] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0104] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0105] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0106] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0107] The above are only preferred implementations 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 technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A DC fault transient control method for a symmetrical single-pole LCC-HVDC system, characterized in that: It includes the fault clearing phase and the restart phase; The fault clearing stage includes: changing the control strategy of the fault pole converter to limit the fault current, and maintaining the control strategy of the non-fault pole converter to maintain the transmission power; The restarting stage includes: rebuilding the line voltage on the inverter side, and based on the line voltage rebuilt on the inverter side, converting the fault pole converter on the rectifier side to symmetrical triggering to reduce harmonic voltage; Wherein, the DC fault is a single-pole grounding fault; The control strategy for changing the fault pole converter includes: The fault-pole converter on the rectifier side is switched to constant DC current control, and the DC current of the fault-pole converter on the inverter side is controlled to be equal to the DC current of the non-fault-pole converter on the inverter side; The DC voltage of the faulty pole converter on the rectifier side is controlled to be 0.

2. The DC fault transient control method for a symmetrical single-pole LCC-HVDC system according to claim 1, characterized in that: Rebuilding the line voltage on the inverter side includes: converting the faulty pole converter on the inverter side to constant DC voltage control, and rebuilding the line voltage on the inverter side.

3. The DC fault transient control method for a symmetrical single-pole LCC-HVDC system according to claim 1, characterized in that: Based on the reconstructed line voltage on the inverter side, the fault-pole converter on the rectifier side is converted to symmetrical triggering, including: If the line voltage reconstructed on the inverter side is greater than the preset threshold, the rectifier side enters the bipolar converter common constant DC current mode, and the bipolar converter receives the same trigger command and operates in the 12-pulse mode; Wherein, the bipolar converters are fault-pole converters and non-fault-pole converters.

4. The DC fault transient control method for a symmetrical single-pole LCC-HVDC system according to claim 3 is characterized in that: Based on the line voltage reconstructed on the inverter side, converting the fault pole converter on the rectifier side to symmetrical triggering also includes: resetting the current controller integral amount to 60°.

5. The DC fault transient control method of a symmetrical single-pole LCC-HVDC system according to claim 1, characterized in that: The fault clearing stage also includes: changing the inverter side non-fault pole arc extinction angle prediction control strategy to suppress the inverter side non-fault pole converter commutation failure.

6. The DC fault transient control method for a symmetrical single-pole LCC-HVDC system according to claim 5, characterized in that: Changing the inverter side non-fault pole extinction angle prediction control strategy includes: modifying the current control command value in the original extinction angle prediction control strategy to the actual measured value of the DC current.

7. A symmetrical single-pole LCC-HVDC system DC fault transient control device, characterized in that: include: Fault clearing module: used to change the control strategy of the fault pole converter to limit the fault current and maintain the control strategy of the non-fault pole converter to maintain the transmission power; Restart module: used to rebuild the line voltage on the inverter side. Based on the rebuilt line voltage on the inverter side, the faulty pole converter on the rectifier side is switched to symmetrical triggering to reduce harmonic voltage. Wherein, the DC fault is a single-pole grounding fault; The control strategy for changing the fault pole converter includes: The fault-pole converter on the rectifier side is switched to constant DC current control, and the DC current of the fault-pole converter on the inverter side is controlled to be equal to the DC current of the non-fault-pole converter on the inverter side; The DC voltage of the faulty pole converter on the rectifier side is controlled to be 0.

8. A symmetrical single-pole LCC-HVDC system DC fault transient control system, characterized in that: include: Storage medium: used to store computer programs; Processor: used to execute the computer program to implement the steps of any one of claims 1 to 6.

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

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