A method and system for SLCC fault defense and isolation based on SVF active support

Abstract

The application discloses a SLCC fault defense and isolation method and system based on SVF active support, and relates to the technical field of high-voltage direct current transmission control protection. The polar region total differential current instantaneous value of each partition, the differential current instantaneous value of the SVF branch in each partition, and the reactive power output value of the SVF in each partition are acquired in real time; for each partition, it is judged whether a fault occurs in the partition; if a fault occurs, a fault domain exclusivity identification model based on characteristic current decoupling is used to judge whether the fault occurs inside the SVF; if yes, a time sequence coordination constraint model based on a fast mechanical bypass switch is constructed to isolate the fault; otherwise, the starting threshold of the commutation failure protection is adjusted dynamically by sensing the reactive power output of the SVF. The application can avoid the full-pole blocking caused by local non-fatal faults, and guarantee the fault degradation continuous operation and power interconnection capability under the multi-partition architecture.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current transmission control and protection technology, specifically to a method and system for SLCC fault prevention and isolation based on SVF active support. Background Technology

[0002] Existing technologies include line commutated converters (LCCs) and fully controlled reactive power compensation devices (such as static var compensators and filters). In DC transmission systems with parallel coupling of devices (SVFs), the protection architecture suffers from three major bottlenecks: mismatched timing of equipment-level fault isolation, rigid commutation failure defense criteria in weak systems, and strong logical coupling in dual-zone topologies. Specifically: equipment-level isolation uses conventional AC circuit breakers, whose opening and closing times are typically greater than 30ms (60-100ms is common in engineering), which cannot complete fault clearing within the approximately 10ms voltage distortion tolerance window of the LCC converter valve; commutation failure protection (such as 87SCFP) uses a fixed voltage start threshold (typically 0.85-0.9pu), which does not adjust with the reactive power support capacity of the SVF, resulting in sensitivity redundancy in weak receiving-end systems (short-circuit ratio SCR < 3.0), making it prone to false tripping during transient processes; and dual-zone or multi-zone topologies use a unified Y-blocking (all-pole shutdown) logic, treating the entire station as a single protection unit. Failure of any auxiliary equipment (such as SVF) triggers all-pole blocking, resulting in 100% loss of power support and making it impossible to achieve fault-degraded operation and power mutual assistance between zones. This results in the system being unable to implement precise isolation and adaptive defense when a local non-fatal fault or transient voltage drop occurs, which easily triggers non-selective rectifier pole complete shutdown (Y-blocking), thus losing the fault degradation operation and dual-zone power mutual assistance capabilities expected in the hybrid topology.

[0003] Therefore, there is an urgent need for a fault defense and isolation method for SLCC DC transmission systems that can integrate real-time perception of SVF active support effectiveness, fault domain exclusive identification and millisecond-level physical time limit competition, and adaptive dynamic adjustment of protection thresholds, so as to solve the unnecessary blocking problem caused by protection isolation timing mismatch and strong logic coupling in weak receiving-end systems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method and system for SLCC fault prevention and isolation based on SVF active support.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a fault prevention and isolation method for SLCC based on SVF active support, which performs fault prevention and isolation on a multi-zone SLCC DC transmission system according to the following steps S1 to S2:

[0007] Step S1: Real-time acquisition of the instantaneous value of the total differential current of each zone, the instantaneous value of the differential current of the SVF branch in each zone, and the reactive power output value of the SVF in each zone.

[0008] Step S2: For each partition, based on the instantaneous value of the total differential current of the partition and the instantaneous value of the differential current of the SVF branch within the partition, determine whether a fault has occurred in the partition. If so, use the fault domain exclusive identification model based on characteristic current decoupling to determine the fault region. If the fault occurs inside the SVF, set the pole blocking shielding signal and perform a fast bypass isolation operation using a fast mechanical bypass switch based on timing constraints. If the fault occurs outside the SVF and the AC bus voltage drops, adjust the commutation failure protection voltage start threshold based on the reactive power output value of the SVF within the partition. Otherwise, return to step S2 until all partitions have been determined, and then return to step S1.

[0009] Furthermore, after performing the fast bypass isolation operation in step S2, the method further includes: for the faulty partition, when the polar blocking shielding signal is set for a duration that meets the preset shielding duration, the instantaneous value of the total differential current of the polar region and the instantaneous value of the differential current of the SVF branch of the partition are reacquired, and it is determined whether the fault is successfully isolated and the voltage recovers. If so, the polar blocking shielding signal is reset and the process returns to step S1; otherwise, the polar blocking shielding signal is released and Y blocking is performed.

[0010] Further, in step S1, the instantaneous voltage of the AC bus, the polar current signal of each zone, and the SVF branch current signal in each zone are collected in real time. By performing vector summation on the polar current signal and the SVF branch current signal in each zone, the instantaneous value of the total differential current of each zone and the instantaneous value of the differential current of the SVF branch in each zone are obtained. The reactive power output value of the SVF in each zone is obtained through instantaneous reactive power theory.

[0011] Furthermore, the fault domain exclusive identification model based on characteristic current decoupling is specifically as follows:

[0012] ;

[0013] in, This is the partition index number, used to identify different independent transformation units or compensation units; For the first The fault identification status bit of the partition, where 1 indicates that the fault is strictly limited to the first partition. Within the SVF device of the partition, 0 indicates a fault involving the converter valve body or the external AC system; For the first The instantaneous value of the total differential current in the polar region of the partition is used to characterize the first... Overall current imbalance in the partition; For the first The instantaneous value of the differential current of the SVF branch within the partition is used to characterize the fault characteristics inside the compensation equipment. This is an anti-saturation correction factor used to compensate for the measurement reduction of current transformers under severe fault transients; Set the startup value for equipment-level faults. This is the threshold for blocking system-level faults.

[0014] Furthermore, the timing constraints are specifically as follows:

[0015] ;

[0016] in, The total isolation delay from the moment a fault occurs until the physical branch is completely disconnected; The hardware response time required for signal acquisition, data filtering, and feature mapping; The time required for the controller to perform logical operations and issue instructions based on the fault domain exclusive identification model based on characteristic current decoupling; The physical action time of a fast mechanical bypass switch from receiving a command to the complete closure of the mechanical contacts; The physical critical time window for commutation failure to evolve into system-level all-pole blocking.

[0017] Furthermore, when the total isolation delay is not less than the physical critical time window, the pole blocking shielding signal is released, and the all-pole Y blocking is directly executed.

[0018] Further, step S2 adjusts the commutation failure protection voltage activation threshold according to the following formula:

[0019] ;

[0020] in, The protection voltage threshold for commutation failure is set as the activation threshold. This is the uncorrected reference voltage threshold. For the first Real-time reactive power output of the partitioned SVF converter; This represents the upper limit of the rated reactive power support capacity of the SVF equipment under strong excitation mode. The modality sensing factor is used when the SVF is in the conventional filtering mode. When the SVF senses an AC voltage drop and switches to the strong excitation support mode... ; This represents the immune boundary limit value for phase transition failure.

[0021] Another aspect of the present invention provides an SLCC fault prevention and isolation system based on SVF active support, used to implement the SLCC fault prevention and isolation method based on SVF active support, comprising:

[0022] The data collaborative acquisition module is used to collect electrical characteristic quantities on both AC and DC sides in real time in multiple dimensions. The electrical characteristic quantities include the instantaneous value of the total differential current of each zone, the instantaneous value of the differential current of the SVF branch in each zone, and the reactive power output value of the SVF in each zone.

[0023] The fault domain identification and isolation decision module is used to distinguish between device-level local faults and system-level global faults based on exclusive identification logic, and to independently issue fast bypass pulses and polar blocking shielding signals when there is a device-level fault.

[0024] The setpoint adaptive and limit control module is used to convert the active reactive power support efficiency of SVF into protection tolerance based on the reactive power output value of SVF in each zone, and dynamically calculate and update the voltage start threshold of commutation failure protection.

[0025] The fast isolation execution module includes a fast mechanical bypass switch connected in series in the SVF branch, which is used to execute fast bypass isolation operations in response to instructions from the fault domain identification and isolation decision module.

[0026] The beneficial effects of adopting the above technical solution are as follows:

[0027] (1) This invention constructs a timing coordination constraint model based on a fast mechanical bypass switch, which coordinates fault feature perception, logical decision-making and switch mechanical action in the entire link timing, realizes the advanced physical blocking of internal faults in SVF branches, effectively avoids unexpected rectifier pole shutdown (Y blocking), greatly improves the operation continuity of DC system, and solves the problem that the traditional AC circuit breaker has a delayed action, which causes equipment-level fault isolation to lag behind the evolution window of irreversible commutation failure of converter valve, thus forcing the full pole shutdown.

[0028] (2) This invention transforms the active support performance of SVF into the action tolerance of the protection system, significantly broadens the immune boundary of the converter valve to AC faults, enhances the continuous ride-through capability of the system under non-fatal disturbances, and solves the problem that the traditional commutation failure protection adopts a fixed high voltage start threshold, which is prone to over-reaction and unnecessary tripping when encountering slight transient voltage drops in a weak power grid environment.

[0029] (3) This invention achieves hierarchical control for multi-zone architecture by using a fault domain exclusive identification (FDI) strategy based on electrical node characteristic current decoupling and combined with pole blocking shielding logic. That is, when a local equipment failure occurs, only the damaged zone is precisely isolated, while the healthy zone and the main converter equipment can still maintain a high proportion of power transmission, maximizing the maintenance of the system's degraded continuous operation capability. This solves the problem that traditional DC protection in complex parallel topologies is prone to causing the healthy zone and converter valve body to stop due to the intertwining of defense lines and strong logic coupling. Attached Figure Description

[0030] Figure 1 This is a flowchart of the fault prevention and isolation method of the present invention;

[0031] Figure 2 This is a schematic diagram of the dual-partition SLCC system architecture and control module connection of the present invention;

[0032] Figure 3 This is a flowchart of the fixed-value adaptive and polar-blocking shielding process based on SVF reactive power support efficiency in this invention.

[0033] Figure 4 This is a block diagram of the exclusive identification logic based on characteristic current decoupling in this invention.

[0034] Figure 5 The diagram shows the characteristic current and isolation timing waveforms of FDI under equipment-level faults according to the present invention.

[0035] Figure 6 This is a comparison diagram of adaptive threshold following and DC current waveform under weak network transient conditions according to the present invention;

[0036] Figure 7 This is a comparison chart of the station's power continuity under dual-zone equipment failure according to the present invention;

[0037] Figure 8 This is a bar chart comparing the comprehensive defense performance indicators under different control strategies of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] Example 1:

[0040] refer to Figure 1 and Figure 2 A fault prevention and isolation method for SLCC based on SVF active support is proposed, which performs fault prevention and isolation on a dual-zone SLCC DC transmission system according to the following steps S1 to S2:

[0041] In this embodiment, each partition includes a grid-commutated converter (LCC), a static var compensator and filter (SVF), a fast mechanical bypass switch (MBS), a high-frequency current transformer (CT), and an AC bus voltage transformer (PT). The fast mechanical bypass switch comprises... Its ability to rapidly close or remove objects mechanically.

[0042] Specifically, the first The LCC converter valves and SVF converters in each zone are connected in parallel to the same AC bus of the receiving-end converter station through their respective converter transformers or connecting reactors, forming a strong electrical coupling and sharing the bus voltage. A fast mechanical bypass switch is configured in series in the AC access branch of the SVF, its physical location defining the electrical separation point between the equipment-level fault domain and the system-level fault domain. Furthermore, the LCC and SVF combined units in each zone are independent of each other, achieving power aggregation only through the upstream AC main network segment or DC pole bus.

[0043] Step S1: Real-time acquisition of instantaneous AC bus voltage, polar current signals of each zone, and SVF branch current signals within each zone; and mathematical conversion to obtain the instantaneous value of total differential current of each zone, the instantaneous value of differential current of SVF branches within each zone, and the reactive power output value of SVF within each zone.

[0044] Specifically, by performing vector summation on the polar current signals of each partition and the SVF branch current signals within each partition, the instantaneous values ​​of the total differential current of each partition and the instantaneous values ​​of the differential current of the SVF branches within each partition are obtained; and the reactive power output value of the SVF within each partition is obtained through instantaneous reactive power theory.

[0045] Furthermore, in a multi-zone SLCC DC transmission system, by simply expanding the number of global sensing nodes in step S1, each zone can independently perform the exclusive identification and hierarchical isolation actions based on its own differential current characteristics, thereby achieving degraded continuous operation in a more complex system.

[0046] Step S2, refer to Figure 3For each partition, based on the instantaneous value of the total differential current of the partition and the instantaneous value of the differential current of the SVF branch within the partition, it is determined whether a fault has occurred in the partition. If so, the fault domain exclusive identification model based on characteristic current decoupling is used to determine the fault region. If the fault occurs inside the SVF, it is determined to be a device-level fault, and the pole blocking shielding signal is set. At the same time, according to the timing constraints, a fast bypass isolation operation is performed using a fast mechanical bypass switch. If the fault occurs outside the SVF and the AC bus voltage drops, it is determined to be a system-level fault, and the commutation failure protection voltage start threshold is adjusted based on the reactive power output value of the SVF within the partition. If the fault occurs outside the SVF and the AC bus voltage does not drop, the process directly returns to step S2; otherwise, it returns to step S2 until all partitions have been determined, and then returns to step S1.

[0047] In this embodiment, the pole blocking shielding signal adds a "NAND" gate constraint to the system-level Y blocking logic output, forcibly suppressing all blocking requests during the shielding period. This prevents unnecessary all-pole shutdowns during physical isolation operations and ensures the power maintenance of healthy partitions where no faults have occurred.

[0048] Furthermore, when performing fast bypass isolation using a fast mechanical bypass switch, logic reset and protection operations are also included. Specifically, for the fault zone, when the polar blocking shield signal is set for a duration that meets the preset shield duration, the instantaneous value of the total differential current of the polar zone and the instantaneous value of the differential current of the SVF branch of that zone are reacquired, and it is determined whether the fault has been successfully isolated and the voltage has recovered. If so, the polar blocking shield signal is reset; otherwise, the polar blocking shield signal is released and Y blocking is performed.

[0049] Meanwhile, when a fault occurs outside the SVF and the bus voltage drops, the SLCC DC transmission system dynamically lowers the commutation failure protection activation threshold by sensing the reactive power output of the SVF, enabling the SLCC DC transmission system to withstand a larger voltage drop without blocking, thus achieving active defense, i.e., preventing blocking.

[0050] Further, refer to Figure 4 The fault domain exclusive identification model based on characteristic current decoupling is specifically as follows:

[0051] ;

[0052] in, This is the partition index number, used to identify different independent transformation units or compensation units; For the first The fault identification status bit of the partition, where 1 indicates that the fault is strictly limited to the first partition. Within the SVF device of the partition, 0 indicates a fault involving the converter valve body or the external AC system; For the first The instantaneous value of the total differential current in the polar region of the partition is used to characterize the first... Overall current imbalance in the partition; For the first The instantaneous value of the differential current of the SVF branch within the partition is used to characterize the fault characteristics inside the compensation equipment. This is an anti-saturation correction factor used to compensate for the measurement reduction of current transformers under severe fault transients; Set the startup value for equipment-level faults. This is the threshold for blocking system-level faults.

[0053] In this embodiment, the anti-saturation correction factor is 0.9; the equipment-level fault start-up setting is based on the equipment's rated current. The settings are adjusted to take sensitivity into account; the system-level fault blocking threshold is set according to the background unbalanced current during normal system operation to prevent malfunction.

[0054] Furthermore, by precisely decomposing the total fault handling time into three independent time delay components—sensor preprocessing, logical decision-making, and switch mechanical displacement—the following timing constraints are constructed to ensure that the removal of local faults precedes the removal of system-level global faults:

[0055] ;

[0056] in, The total isolation delay from the moment a fault occurs until the physical branch is completely disconnected; The hardware response time required for signal acquisition, data filtering, and feature mapping; The time required for the controller to perform logical operations and issue instructions based on the fault domain exclusive identification model based on characteristic current decoupling; The physical action time of a fast mechanical bypass switch from receiving a command to the complete closure of the mechanical contacts; The physical critical time window for commutation failure to evolve into system-level all-pole blocking.

[0057] In this embodiment, when the total isolation delay is less than the physical critical time window, it indicates that the equipment-level advanced isolation is successful and effective, meaning that the physical cutoff is faster than the fault evolution. The SLCC DC transmission system will continue to maintain the pole blocking shield signal to ensure the continuous operation of the fault-free sections. When the total isolation delay is not less than the physical critical time window due to mechanical failure of the switch or communication link abnormality, the local fault is determined to be a system-level fault, the pole blocking shield signal is released, and full-pole Y blocking is directly executed.

[0058] Furthermore, traditional commutation failure protection trips immediately if the bus voltage drops to 0.85. However, when grid disturbances occur, the dynamic reactive power actively injected by the SVF device supports the converter bus voltage, effectively compensating for the transient commutation margin of the converter valve. Therefore, referring to... Figure 3 In this embodiment, the active support effectiveness is equivalently converted into a quantitative compensation term for the protection threshold according to the following formula for correcting the protection voltage start threshold for commutation failure. Under the premise of ensuring that the physical tolerance limit of the equipment is not exceeded, the protection action conditions are dynamically relaxed, thereby maximizing the expansion of the degraded continuous operation boundary of the system. This allows the SLCC DC transmission system to continue operating by adjusting the protection sensitivity when a non-fatal disturbance occurs in the system, rather than directly blocking the trip.

[0059] ;

[0060] in, The protection voltage threshold for commutation failure is set as the activation threshold. This is the uncorrected reference voltage threshold. For the first Real-time reactive power output of the partitioned SVF converter; This represents the upper limit of the rated reactive power support capacity of the SVF equipment under strong excitation mode. The modality sensing factor is used when the SVF is in the conventional filtering mode. When the SVF senses an AC voltage drop and switches to the strong excitation support mode... ; This represents the immune boundary limit value for phase transition failure.

[0061] In this embodiment, the reference voltage threshold is set to 0.85, and the commutation failure immune boundary limit value is set to 0.60.

[0062] The following section will use a complete SLCC DC transmission simulation model built based on MATLAB / Simulink R2025a, with traditional fixed criterion protection as the control group, and comparative experiments to further explain the technical effects of this embodiment.

[0063] In this embodiment, the physical topology adopts a symmetrical unipolar dual-partition architecture based on the CIGRE HVDC Benchmark first standard model. The receiving-end AC system simulates a weak system condition (SCR=2.5). The key parameters are as follows:

[0064] The rated power of the DC main circuit of the system is set to 1000MW, the rated voltage is ±500kV, the LCC converter is equipped with a converter transformer with a capacity of 2×600MVA and a leakage reactance of 0.18pu, and the operating control parameters are set to the rectifier side firing angle α of 15° and the inverter side lead angle β of 140°.

[0065] The SLCC DC transmission system adopts a dual-zone topology architecture, with each zone equipped with a ±150Mvar SVF compensation unit. The SLCC DC transmission system's commutation failure protection voltage setting is 12, with a time window of 100ms, a verification time of 200ms, and a dead zone of 0.1. The start-up threshold is 0.15 pu, and the blocking threshold is 0.10 pu.

[0066] Figure 5 This is a waveform diagram showing the characteristic current and isolation timing of FDI under equipment-level faults according to the present invention. From Figure 5 It can be observed that, When a device-level partial fault occurs, the total differential current in the polar region and the differential current in the SVF branch oscillate violently. This invention addresses this by calculating the exclusive residual. ,exist The residual value is quickly converged to the device-level start-up setpoint, and the status bit is accurately output. The fault was identified as being strictly located within the SVF. The system immediately set the latch-up shielding signal and triggered the fast mechanical bypass switch (MBS). The waveform shows that the MBS... Complete isolation is achieved in a short time, and this isolation delay is much shorter than the critical time for commutation failure to evolve into full-polarity blockage. This successfully achieved proactive physical blocking of local faults.

[0067] Figure 6 This is a comparison diagram of the adaptive threshold following and DC current waveform under weak network transient conditions according to the present invention. From Figure 6 It can be observed that when the receiving-end power grid is in a weak grid condition (SCR=2.2) and the AC bus voltage is low... Under severe disturbances such as a drop to approximately 0.45 pu, if a traditional fixed-value strategy (baseline setpoint) is adopted... The voltage drops rapidly below the threshold, triggering the commutation failure protection, resulting in a surge of DC current. When the value is zero (as shown by the red line), the system is forced to shut down. However, using the adaptive setpoint strategy of this invention (as shown by the blue line), the system senses that the SVF has entered the strong excitation support mode and dynamically adjusts the protection threshold according to the real-time reactive power output. (and higher than the limit) Throughout the entire transient process, it remains unchanged. This successfully avoided false triggering of the commutation failure protection and ensured that the DC current quickly recovered to a higher steady-state level after a short period of fluctuation.

[0068] Figure 7 This is a comparison chart of the station's power continuity under dual-zone equipment failure conditions according to the present invention. From Figure 7As can be observed, taking a system with a rated power of 2500MW as an example, when an internal SVF fault occurs in zone 1 at 0 seconds, the traditional Y-blocking strategy leads to a complete shutdown, with a power retention rate of 0%; the traditional AC circuit breaker isolation strategy causes severe system transients due to delayed action, resulting in a deep power drop and slow recovery, ultimately with a power retention rate of only about 60%. In contrast, the strategy of this invention, through the coordinated defense of equipment-level isolation and adaptive setting, ensures that the system only experiences a slight power drop during fault clearing and weak network transients, followed by a rapid recovery and stabilization of DC transmission power at approximately 2250MW, achieving a station-wide power retention rate of approximately 90%, greatly improving the degraded continuous operation capability under the dual-zone architecture.

[0069] Figure 8 This is a bar chart comparing the comprehensive defense performance indicators under different control strategies of this invention. For intuitive comparison, all indicators have been normalized (value range 0~1), with higher values ​​indicating better performance. Figure 8 As can be observed, the strategy of this invention outperforms other strategies in key dimensions such as unnecessary blocking rate, fault isolation time, power retention rate, maximum voltage drop tolerance, and system recovery time. The overall defense effectiveness index of this invention is 0.93, which is higher than that of traditional AC circuit breaker isolation strategies and traditional Y-blocking strategies. The above quantitative comparative simulation data fully demonstrate that this invention possesses extremely superior fault-tolerant ride-through capability and security defense effectiveness when dealing with transient disturbances in complex multi-zone DC transmission systems.

[0070] In one embodiment variation, the static var compensator and filter can be replaced with a flexible AC transmission device with rapid dynamic reactive power regulation capabilities, such as a static synchronous compensator, a static var generator, or a unified power flow controller. Furthermore, when using the equivalent replacement device, only the real-time reactive power output data of the corresponding device needs to be acquired.

[0071] In another implementation variant of this embodiment, the total isolation delay is less than the physical critical time window (i.e., Under the time-coordination constraints, other types of fast switching devices such as solid-state switches (SSC) and hybrid DC / AC fast circuit breakers can be used to achieve advanced physical blocking of equipment-level faults.

[0072] Example 2:

[0073] This embodiment provides an SLCC fault prevention and isolation system based on SVF active support, used to implement the SLCC fault prevention and isolation method based on SVF active support, including:

[0074] The data collaborative acquisition module is used to collect electrical characteristic quantities on both AC and DC sides in real time in multiple dimensions. The electrical characteristic quantities include the instantaneous value of the total differential current of each zone, the instantaneous value of the differential current of the SVF branch in each zone, and the reactive power output value of the SVF in each zone.

[0075] The fault domain identification and isolation decision module is used to distinguish between device-level local faults and system-level global faults based on exclusive identification logic, and to independently issue fast bypass pulses and polar blocking shielding signals when there is a device-level fault.

[0076] The setpoint adaptive and limit control module is used to convert the active reactive power support efficiency of SVF into protection tolerance based on the reactive power output value of SVF in each zone, and dynamically calculate and update the voltage start threshold of commutation failure protection.

[0077] The fast isolation execution module includes a fast mechanical bypass switch connected in series in the SVF branch, which is used to execute fast bypass isolation operations in response to instructions from the fault domain identification and isolation decision module.

[0078] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for SLCC fault prevention and isolation based on SVF active support, characterized in that, Follow steps S1 to S2 below to perform fault prevention and isolation for the multi-zone SLCC DC transmission system: Step S1: Real-time acquisition of the instantaneous value of the total differential current of each zone, the instantaneous value of the differential current of the SVF branch in each zone, and the reactive power output value of the SVF in each zone. Step S2: For each partition, based on the instantaneous value of the total differential current of the partition and the instantaneous value of the differential current of the SVF branch in the partition, determine whether a fault has occurred in the partition. If so, use the fault domain exclusive identification model based on characteristic current decoupling to determine the area to which the fault belongs. If the fault occurs inside the SVF, set the pole blocking shielding signal and perform a fast bypass isolation operation using a fast mechanical bypass switch based on timing constraints. If the fault occurs outside the SVF and the AC bus voltage drops, adjust the commutation failure protection voltage start threshold based on the reactive power output value of the SVF in that zone; otherwise, return to step S2 until all zones have been judged, and then return to step S1.

2. The SLCC fault prevention and isolation method based on SVF active support according to claim 1, characterized in that, After performing the fast bypass isolation operation in step S2, the method further includes: for the faulty partition, when the polar blocking shielding signal is set for a duration that meets the preset shielding duration, the instantaneous value of the total differential current of the polar region and the instantaneous value of the differential current of the SVF branch of the partition are reacquired, and it is determined whether the fault is successfully isolated and the voltage recovers. If so, the polar blocking shielding signal is reset and the process returns to step S1; otherwise, the polar blocking shielding signal is released and Y blocking is performed.

3. The SLCC fault prevention and isolation method based on SVF active support according to claim 1, characterized in that, Step S1 involves real-time acquisition of the instantaneous AC bus voltage, the polar current signal of each zone, and the SVF branch current signal within each zone. By performing vector summation on the polar current signal and the SVF branch current signal of each zone, the instantaneous value of the total differential current of each zone and the instantaneous value of the differential current of the SVF branch within each zone are obtained. The reactive power output value of the SVF within each zone is obtained through instantaneous reactive power theory.

4. The SLCC fault prevention and isolation method based on SVF active support according to claim 1, characterized in that, The fault domain exclusive identification model based on characteristic current decoupling is specifically as follows: ； in, This is the partition index number, used to identify different independent transformation units or compensation units; For the first The fault identification status bit of the partition, where 1 indicates that the fault is strictly limited to the first partition. Within the SVF device of the partition, 0 indicates a fault involving the converter valve body or the external AC system; For the first The instantaneous value of the total differential current in the polar region of the partition is used to characterize the first... Overall current imbalance in the partition; For the first The instantaneous value of the differential current of the SVF branch within the partition is used to characterize the fault characteristics inside the compensation equipment. This is an anti-saturation correction factor used to compensate for the measurement reduction of current transformers under severe fault transients; Set the startup value for equipment-level faults. This is the threshold for blocking system-level faults.

5. The SLCC fault prevention and isolation method based on SVF active support according to claim 4, characterized in that, The timing constraints are specifically as follows: ； in, The total isolation delay from the moment a fault occurs until the physical branch is completely disconnected; The hardware response time required for signal acquisition, data filtering, and feature mapping; The time required for the controller to perform logical operations and issue instructions based on the fault domain exclusive identification model based on characteristic current decoupling; The physical action time of a fast mechanical bypass switch from receiving a command to the complete closure of the mechanical contacts; The physical critical time window for commutation failure to evolve into system-level all-pole blocking.

6. The SLCC fault prevention and isolation method based on SVF active support according to claim 5, characterized in that, When the total isolation delay is not less than the physical critical time window, the pole blocking shielding signal is released, and the all-pole Y blocking is directly executed.

7. The SLCC fault prevention and isolation method based on SVF active support according to claim 1, characterized in that, In step S2, the commutation failure protection voltage activation threshold is adjusted according to the following formula: ； in, The protection voltage threshold for commutation failure is set as the activation threshold. This is the uncorrected reference voltage threshold. For the first Real-time reactive power output of the partitioned SVF converter; This represents the upper limit of the rated reactive power support capacity of the SVF equipment under strong excitation mode. The modality sensing factor is used when the SVF is in the conventional filtering mode. When the SVF senses an AC voltage drop and switches to the strong excitation support mode... ; This represents the immune boundary limit value for phase transition failure.

8. A fault prevention and isolation system for SLCC based on SVF active support, used to implement the fault prevention and isolation method for SLCC based on SVF active support as described in any one of claims 1-7, characterized in that, include: The data collaborative acquisition module is used to collect electrical characteristic quantities on both AC and DC sides in real time in multiple dimensions. The electrical characteristic quantities include the instantaneous value of the total differential current of each zone, the instantaneous value of the differential current of the SVF branch in each zone, and the reactive power output value of the SVF in each zone. The fault domain identification and isolation decision module is used to distinguish between device-level local faults and system-level global faults based on exclusive identification logic, and to independently issue fast bypass pulses and polar blocking shielding signals when there is a device-level fault. The setpoint adaptive and limit control module is used to convert the active reactive power support efficiency of SVF into protection tolerance based on the reactive power output value of SVF in each zone, and dynamically calculate and update the voltage start threshold of commutation failure protection. The fast isolation execution module includes a fast mechanical bypass switch connected in series in the SVF branch, which is used to execute fast bypass isolation operations in response to instructions from the fault domain identification and isolation decision module.

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