A method and system for SLCC fault discrimination and recovery based on SVF state perception

Abstract

The application discloses a kind of based on SVF state perception SLCC fault discrimination and recovery method and system, the running state of static var generator is acquired in real time and converter turn-off angle, and reactive power support margin and commutation margin are calculated;According to the preset adaptive correction rule, the protection threshold correction coefficient and time window correction coefficient are determined, and the protection threshold and time window are corrected;Based on the protection threshold and time window after correction, according to the voltage, current instantaneous value of ac side and dc side, it is judged whether SLCC direct current transmission system exists fault, and then according to the spatial distribution of electrical quantity and SVF state change time sequence, the function area of fault is determined, and the fault recovery is carried out using hierarchical response strategy or restart coordination strategy.The application can adaptively dynamically adjust the protection threshold correction coefficient and time window correction coefficient, and through the function partition fault processing logic and phased stage restart strategy, the recovery speed and success rate of direct current system are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current transmission and relay protection technology, specifically to a method and system for SLCC fault identification and recovery based on SVF state awareness. Background Technology

[0002] Based on the assumption of a constant system structure, the existing protection and recovery strategies for SLCC DC transmission systems do not use the switching, mode switching, and current limiting of the SVF (Signal Variable Voltage Regulator) as criteria for judgment. When dynamic adjustment of the SVF causes transient changes in voltage / current, the protection device is prone to misinterpreting it as a system fault, leading to unnecessary pole blocking or system shutdown, which seriously weakens the operational reliability.

[0003] Furthermore, existing solutions mostly adopt uniform system-level protection actions, without differentiating responses based on the importance of the fault location (SVF auxiliary area, converter core area, DC line). Non-fatal faults in SVF branches often directly trigger pole blocking, making it impossible to achieve local isolation and derating ride-through, thus expanding the scope of the fault impact.

[0004] Meanwhile, traditional restart strategies rely on passive phase shifting of LCC converters, failing to utilize the grid-building capabilities of SVF during the deionization phase or the STATCOM capability to support AC voltage. In weak AC systems or high-capacity sending-end scenarios, AC voltage fluctuations can easily lead to restart failures, and the lack of a phased, rollback-capacity extreme restart mechanism results in a high risk of long-term lockout.

[0005] Therefore, there is an urgent need for a fault identification and recovery method for DC transmission systems that can integrate real-time sensing of the operating status of static var generators, differentiated fault handling for functional zones, and adaptive control of commutation margin, and provide graded responses to the severity of faults and the attenuation of support capacity in different regions, so as to achieve dynamic adaptation of protection settings and coordinated enhancement of pole restart in symmetrical unipolar SLCC systems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method and system for SLCC fault identification and recovery based on SVF state awareness.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for fault identification and recovery of SLCC based on SVF state awareness. In each control cycle, fault identification and recovery of the SLCC DC transmission system are performed according to the following steps S1 to S3:

[0009] Step S1: Real-time acquisition of the operating status of the static var generator and calculation of the reactive power support margin; simultaneously, acquisition of the converter turn-off angle and calculation of the commutation margin.

[0010] Step S2: Based on the operating status and reactive power support margin of the static var generator, and according to the preset adaptive correction rule and combined with the commutation margin, determine the protection threshold correction coefficient and the time window correction coefficient, and use the protection threshold correction coefficient and the time window correction coefficient to correct the protection threshold and time window of the polarity protection device setpoint area.

[0011] Step S3: Based on the corrected protection threshold and time window, determine whether there is a fault in the SLCC DC transmission system according to the instantaneous values ​​of AC and DC side voltage and current. If so, determine the functional area to which the fault belongs according to the spatial distribution of electrical quantities and the timing of SVF state changes, and use a graded response strategy or restart coordination strategy to restore the fault; otherwise, proceed to step S1.

[0012] Furthermore, the operating state includes control mode, health state, and reactive power command value; wherein the control state includes voltage support mode, filter-dominated mode, and hybrid mode, and the health state includes normal, current limiting, loop exit, and bypass.

[0013] Further, step S1 calculates the reactive power support margin according to the following formula:

[0014] ;

[0015] in, Indicates reactive power support margin. This refers to the rated reactive power capacity of the static var generator. This is the reactive power command value.

[0016] Further, step S1 calculates the commutation margin according to the following formula:

[0017] ;

[0018] in, For commutation margin, and This indicates that the commutation margin is sufficient; The converter turn-off angle. For reference shut-off angle.

[0019] Furthermore, the functional area to which the fault belongs in step S3 includes the SVF area, the converter area, and the DC line area; when the fault occurs in the SVF area or the converter area, a hierarchical response strategy is used for fault recovery; when the fault occurs in the DC line area, a restart coordination strategy is used for fault recovery.

[0020] Furthermore, the hierarchical response strategy includes a Level I response strategy, a Level II response strategy, and a Level III response strategy;

[0021] Among them, the Level I response strategy is local isolation, that is, SVF branch isolation or bypass operation is performed, and the LCC converter continues to operate; the Level II response strategy is derating ride-through, that is, the SLCC DC transmission system enters derating operation; the Level III response strategy is pole blocking, that is, pole blocking operation or pole isolation operation is performed.

[0022] Specifically, when the fault is located in the SVF region and the fault can be locally handled, the Level I response strategy is used for fault recovery. After the Level I response strategy is completed, it is determined whether the reactive power support margin is not less than the minimum reactive power support margin allowable threshold and whether the commutation margin is not less than the preset threshold. If so, the Level II response strategy is executed; otherwise, the Level III response strategy is executed.

[0023] When the fault is located in the converter area, the Level III response strategy is executed directly.

[0024] Furthermore, the restart coordination strategy is divided into regular restart operation and de-voltage restart operation;

[0025] When a fault occurs in the DC line area, the fault is first restored by the conventional restart operation. If the conventional restart operation fails, the fault is restored by the reduced voltage restart operation. If the reduced voltage restart operation still fails, the pole is locked.

[0026] Specifically, when performing fault recovery using a conventional restart operation, it is determined whether the SVF health status is normal and whether the reactive power support margin is not less than a preset threshold. If so, the rated transmission power of the DC system is used as the restart power. ,in The rated transmission power of the DC system. To restart power; simultaneously, SVF enters grid-connected or static synchronous compensator mode, providing dynamic reactive power support to the AC bus; otherwise ;

[0027] When using a reduced-voltage restart operation for fault recovery , .

[0028] Another aspect of the present invention provides an SLCC fault identification and recovery system based on SVF state awareness, comprising:

[0029] The status monitoring module is used to acquire the operating status of the static var generator in real time and calculate the reactive power support margin; at the same time, it monitors the converter turn-off angle and calculates the commutation margin.

[0030] The protection threshold adaptive module is used to generate protection threshold correction coefficients and time window correction coefficients based on reactive power support margin and commutation margin.

[0031] The fault zone identification module is used to integrate protection action signals, electrical quantity spatial distribution and SVF state change timing to determine whether a fault has occurred and to identify the functional area to which the fault belongs.

[0032] The graded response module is used to generate fault recovery instructions according to the graded response strategy, wherein the fault recovery instructions include partial isolation, derating pass-through or extreme blocking.

[0033] The extreme restart coordination module is used to select between regular restart operations or buck restart operations for fault recovery based on SVF availability, and to generate restart power commands.

[0034] The beneficial effects of adopting the above technical solution are as follows:

[0035] (1) By establishing a correlation mechanism between the operating status and fault characteristics of SVF, this invention dynamically adjusts the protection threshold correction coefficient and time window correction coefficient during normal dynamic processes such as SVF mode switching, reactive power regulation or current limiting, effectively distinguishes disturbances from real faults, significantly reduces the risk of protection maloperation, and improves the operational continuity of SLCC DC transmission system.

[0036] (2) The present invention constructs a functional zoning fault handling framework for SLCC DC transmission system, which can implement hierarchical response according to the fault occurrence area. When a locally handleable fault occurs in the SVF area, the SLCC DC transmission system only isolates the SVF branch, and the LCC converter continues to operate at reduced rate without triggering pole blocking. This realizes fault zoning and avoids the expansion of non-fatal faults.

[0037] (3) This invention uses an enhanced pole restart strategy based on SVF active support to control SVF to enter the grid / STATCOM mode during the deionization stage, providing dynamic reactive power support to the AC bus and suppressing overvoltage caused by the phase shift process. At the same time, it introduces a phased power restart and rollback mechanism to ensure that the SLCC DC transmission system has a definite and gradually conservative recovery path under uncertain conditions in the step-by-step degradation process from high power to low power and then to blocking. This greatly improves the restart success rate after DC line faults and accelerates the recovery of SLCC DC transmission system.

[0038] (4) Through state perception and coordinated control, the present invention enables the SLCC DC transmission system to maintain good operating characteristics under weak AC system (low short-circuit ratio), significantly improves the operating stability and fault recovery capability of DC system under harsh grid conditions, enhances the adaptability to weak AC grid, and expands the engineering application scenarios. Attached Figure Description

[0039] Figure 1 This is a flowchart of the fault diagnosis and recovery method of the present invention;

[0040] Figure 2 This is a block diagram of the adaptive correction logic for the protection threshold of this invention;

[0041] Figure 3 This is a flowchart of the fault partitioning and hierarchical response decision-making process of the present invention;

[0042] Figure 4 This is a flowchart illustrating the enhanced high-level restart coordination process of the present invention;

[0043] Figure 5 This is a comparison curve of the misjudgment rate under the SVF state change conditions of the present invention;

[0044] Figure 6 This is a comparison chart of the success rate of DC line fault restart in this invention;

[0045] Figure 7 This is a comparison chart showing the probability of a local fault being misjudged as a system fault in this invention. Detailed Implementation

[0046] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0047] Example 1:

[0048] refer to Figure 1 A fault identification and recovery method for SLCC based on SVF state awareness is proposed. In each control cycle, fault identification and recovery are performed on the SLCC DC transmission system according to the following steps S1 to S3:

[0049] In this embodiment, the SLCC DC transmission system includes an AC bus, a DC line, a static var generator, an LCC converter, and protection and measurement devices.

[0050] The system includes one AC bus on each of the rectifier and inverter sides, connecting the AC system power supply, converter transformer, and static var generator (SVF) respectively. Voltage and current transformers are installed on the AC buses for measuring three-phase voltage and current. The DC lines are overhead lines, with the positive and negative terminals independently erected. Both ends are connected to the DC side of the converter via smoothing reactors. Traveling wave measurement and voltage / current transformers are installed on the DC lines.

[0051] The static var generator (SVF) is connected in parallel to the AC bus on the rectifier side and is directly electrically connected to the AC bus via a three-phase line. The SVF internally contains a voltage source converter, DC capacitors, and connecting reactors. Its control mode (voltage-supported mode, filter-dominated mode, and hybrid mode) and health status (normal, current limiting, loop disconnection, and bypass) can be obtained in real time through the controller interface.

[0052] The LCC converter consists of two sets of 6-pulse thyristor converter bridges connected in series to form a 12-pulse converter, which is connected to the AC bus through a converter transformer (Y / Y and Y / Δ connection).

[0053] The protection and measurement devices include converter differential protection, commutation failure protection, and DC line traveling wave protection. Each protection device obtains electrical quantities from the instrument transformer through hard wiring or process bus.

[0054] Step S1: Obtain the operating status of the static var generator and the converter turn-off angle in real time, and calculate the reactive power support margin and commutation margin according to the following formulas:

[0055] ;

[0056] ;

[0057] in, Indicates reactive power support margin. This refers to the rated reactive power capacity of the static var generator, i.e., its maximum reactive power output capability. This is the reactive power command value. For commutation margin, and This indicates that the commutation margin is sufficient; The converter turn-off angle. For reference shut-off angle.

[0058] Step S2, refer to Figure 2 Based on the operating status and reactive power support margin of the static var generator, the protection threshold correction coefficient and time window correction coefficient are determined according to the preset adaptive correction rules. It is then determined whether the static var generator is normal and whether the reactive power support margin is not greater than the preset reactive power support margin. If so, the protection threshold correction coefficient and time window correction coefficient are reduced; otherwise, the protection threshold correction coefficient and time window correction coefficient remain unchanged. Furthermore, the protection threshold correction coefficient and time window correction coefficient are updated according to the commutation margin and the preset dead time.

[0059] Specifically, when the preset dead time is ,in The dead zone is set to 0.1. It is determined whether the commutation margin is not greater than the preset dead zone time. If so, transient forced tightening is performed, and the protection threshold correction coefficient and time window correction coefficient are multiplied by the preset transient tightening coefficient, respectively, to update the protection threshold correction coefficient and time window correction coefficient; otherwise, the protection threshold correction coefficient and time window correction coefficient remain unchanged. In this embodiment, the preset transient tightening coefficient is 0.8.

[0060] When based on the preset dead time The system determines whether the commutation margin is not less than the preset dead time. If so, it performs transient relaxation by multiplying the protection threshold correction coefficient and the time window correction coefficient by the preset transient relaxation coefficient, and then updating the protection threshold correction coefficient and the time window correction coefficient. Otherwise, the protection threshold correction coefficient and the time window correction coefficient remain unchanged. In this embodiment, the preset transient relaxation coefficient is 1.1.

[0061] In this embodiment, the adaptive correction rule is as follows:

[0062] Table 1 Adaptive Correction Rules

[0063]

[0064] Among them, the standard support state indicates that the SVF health state is normal and the reactive power support margin is sufficient, which can provide full rated support; the limited support margin indicates that the SVF health state is normal but the reactive power support margin is insufficient, that is, the SVF function is intact but close to the output limit, and the ability to cope with disturbances is weakened; the output limited state indicates that the SVF health state is current limiting and the reactive power support margin is close to the limit; the control degradation state indicates that the SVF health state is loop disconnection and bypass and the reactive power support margin is close to the limit; the unavailable state indicates that the SVF health state is loop disconnection and bypass and the reactive power support margin is zero.

[0065] Further utilize the protection threshold correction factor and time window correction factor to correct the protection threshold and time window of the polarity protection device's setting range:

[0066] ;

[0067] ;

[0068] in, The corrected protection threshold. To protect the threshold correction coefficient, This is the corrected time window. This is a time window correction factor. and This is the nominal value.

[0069] Step S3: Based on the corrected protection threshold and time window, determine whether there is a fault in the SLCC DC transmission system according to the instantaneous values ​​of AC and DC side voltage and current. If so, determine the functional area to which the fault belongs according to the spatial distribution of electrical quantities and the timing of SVF state changes, and use a graded response strategy or restart coordination strategy to restore the fault; otherwise, proceed to step S1.

[0070] In this embodiment, when any electrical quantity exceeds the corresponding preset threshold and continues to exceed the time window, the protection device generates a corresponding action flag, i.e., a protection action signal. The protection action signal is directly obtained through the binary output of the protection device and is used to preliminarily determine the approximate range of the fault. The faults include commutation failure, internal short circuit of the converter, DC line grounding or inter-electrode short circuit, and SVF branch overcurrent or short circuit.

[0071] The spatial distribution of electrical quantities refers to the differences in voltage and current amplitudes and phases at different measurement points (such as AC busbars, SVF branches, converter valve sides, and both ends of DC lines). By comparing the degree of abnormality in electrical quantities at each measurement point (e.g., voltage drop amplitude, current change direction), the physical location of the fault can be determined. Specifically, this is achieved by deploying voltage / current transformers at key nodes of the SLCC DC transmission system, and then performing real-time calculations by the protection device after analog-to-digital conversion.

[0072] SVF state change timing refers to the temporal sequence of changes in the internal state of the SVF (such as control mode switching, current limiting action, loop exit, etc.) and the occurrence of electrical anomalies. By comparing the order of SVF state change moments and electrical quantity abrupt changes, it is possible to distinguish whether the fault is caused by the SVF's own dynamics or by an external fault. Specifically, this timing is obtained through the SVF controller's internal control mode, health status, and timestamps. The timestamps are provided by the SVF controller's internal clock and are used to record the precise moment of state changes, typically with microsecond precision.

[0073] Furthermore, the functional areas to which the fault belongs include the SVF area, the converter area, and the DC line area; when the fault occurs in the SVF area or the converter area, a hierarchical response strategy is used for fault recovery; when the fault occurs in the DC line area, a restart coordination strategy is used for fault recovery.

[0074] The fault determination principle for the SVF area is as follows: the voltage transformer at the SVF connection bus detects an abnormal voltage drop, and the SVF branch current suddenly increases. At the same time, the status change sequence reported by the SVF controller (such as current limiting or circuit exit) occurs before or at the same time as the electrical quantity abnormality; the differential protection of the SVF connection transformer is activated.

[0075] The fault judgment principle for the converter area is as follows: the difference between the converter valve side voltage and the grid side voltage exceeds the differential protection threshold, and the converter differential protection is activated; the commutation failure protection detects that the shut-off angle is continuously lower than the threshold, and no abnormal SVF state is detected.

[0076] The principle for determining faults in DC line areas is as follows: the voltage at both ends of the DC line drops suddenly at the same time, and the DC line traveling wave protection or undervoltage protection operates; the direction of the transient traveling wave indicates that the fault point is located between the positive and negative poles of the line.

[0077] Further, refer to Figure 3 The hierarchical response strategy includes a Level I response strategy, a Level II response strategy, and a Level III response strategy;

[0078] Among them, the Level I response strategy is local isolation, that is, SVF branch isolation or bypass operation is performed, and the LCC converter continues to operate; the Level II response strategy is derating ride-through, that is, the SLCC DC transmission system enters derating operation; the Level III response strategy is pole blocking, that is, pole blocking operation or pole isolation operation is performed.

[0079] Specifically, when the fault is located in the SVF region and the fault can be locally handled (such as a short circuit or overload in the SVF branch), a Level I response strategy is used for fault recovery. After the Level I response strategy is completed, it is determined whether the reactive power support margin is not less than the minimum allowable threshold for reactive power support margin. If the commutation margin is not less than the preset threshold, then execute the Level II response strategy; otherwise, execute the Level III response strategy.

[0080] Furthermore, during the execution of the Level II response strategy, if the reactive power support margin is less than the minimum allowable reactive power support margin threshold for a period exceeding the preset protection duration ( ) or the commutation margin is less than the preset dead time for a period exceeding the preset protection duration ( When the converter differential protection is activated, the Level III response strategy shall be executed immediately.

[0081] During the execution of the Level III response strategy, it is determined whether the differential protection has been contacted, whether the blocking has been released, and whether the fault has been isolated. If so, the Level I or Level II response strategy is rolled back; otherwise, the Level III response strategy is maintained.

[0082] When the fault is located in the converter area, the Level III response strategy is executed directly.

[0083] Further, refer to Figure 4 When a fault occurs in the DC line area, the SLCC DC transmission system directly utilizes a restart coordination strategy for fault recovery. This restart coordination strategy is divided into a regular restart operation and a reduced-voltage restart operation. First, a regular restart operation is used for fault recovery. If the regular restart operation fails (i.e., the voltage does not establish after restart or the fault recurs), a reduced-voltage restart operation is used again for fault recovery. If the reduced-voltage restart operation also fails, the pole blocking is maintained. Furthermore, the Level III response (pole blocking) is only executed as a last resort after restart failure.

[0084] Specifically, when performing fault recovery using a conventional restart operation, it is determined whether the SVF health status is normal and whether the reactive power support margin is not less than a preset threshold. If so, the rated transmission power of the DC system is used as the restart power. ,in The rated transmission power of the DC system. To restart power; simultaneously, the SVF enters grid-connected or Static Synchronous Compensator (STATCOM) mode to provide dynamic reactive power support to the AC bus, otherwise ;

[0085] Furthermore, when the SVF enters grid-connected or Static Synchronous Compensator (STATCOM) mode, the reactive power output is dynamically adjusted according to the following formula: ;

[0086] in, This is the AC voltage reference value. This is the actual voltage measurement value. This is a proportionality coefficient used to determine the speed of response; These are the integral coefficients used to eliminate steady-state errors; The reactive current / power command of the SVF is used to support AC voltage and suppress overvoltage or voltage drop caused by LCC phase shift or load change.

[0087] When using a reduced-voltage restart operation for fault recovery , ,in This is the voltage reference value.

[0088] The following section will further explain the technical effects of this embodiment by combining comparative experiments with a symmetrical unipolar SLCC DC system modified based on the first standard model of CIGRE HVDC Benchmark. Specifically, the symmetrical unipolar SLCC DC system has a ±150 Mvar SVF connected in parallel on the rectifier side, a rated voltage of ±500 kV, a rated power of 1000 MW, and a short-circuit ratio (SCR) of 2.5 for the receiving-end AC system.

[0089] In this embodiment, the comparative experiment was implemented based on MATLAB / Simulink R2025a, and the specific key parameters were set as follows:

[0090] LCC converter: The converter transformer capacity is 2×600MVA, the leakage reactance is 0.18pu, the smoothing reactor is 0.5H, the firing angle α=15° (rectifier side), β=140° (inverter side).

[0091] SVF parameters: capacity is 150Mvar, control mode is switchable, and health status can be set;

[0092] Protection setting: Commutation failure protection =12, time window =100ms; Dead zone =0.1, verification time =200ms.

[0093] Figure 5 This is a comparison curve of the misjudgment rate under the SVF state change condition of this invention. From Figure 5 It can be observed that when the SVF is in an output-limited state, the misclassification rate of the traditional method is 8.5%, while that of the method of the present invention is only 0.4%, a reduction of about 95%; under all SVF operating states, the average misclassification rate of the method of the present invention is less than 1.0%, which is significantly better than the traditional method (up to 14.8%), fully demonstrating the effectiveness of adaptive protection.

[0094] Figure 6 This is a comparison chart of the success rate of DC line fault restart in this invention. From... Figure 6 It can be observed that under a weak AC system (SCR=2.5), the first success rate of the traditional LCC passive restart is 68%. The method of this invention uses SVF active support and a phased pressure reduction restart strategy to increase the success rate to 94%, a relative improvement of 38%, which significantly improves the system recovery capability.

[0095] Figure 7 This is a comparison chart showing the probability of a local fault being misjudged as a system fault in this invention. From... Figure 7 It can be observed that for non-fatal faults occurring in SVF branches, traditional methods, due to their lack of partitioning capabilities, result in a fault escalating into a full-pole outage in up to 34% of cases. However, the method of this invention, through Level I local isolation and Level II derating traversal, reduces this proportion to 2%, improving the situation by 94% and significantly narrowing the scope of the fault's impact.

[0096] Example 2:

[0097] This embodiment provides an SLCC fault identification and recovery system based on SVF state awareness, including:

[0098] The status monitoring module is used to acquire the operating status of the static var generator in real time and calculate the reactive power support margin; at the same time, it monitors the converter turn-off angle and calculates the commutation margin.

[0099] The protection threshold adaptive module, connected to the condition monitoring module, is used to generate protection threshold correction coefficients and time window correction coefficients based on reactive power support margin and commutation margin.

[0100] The fault zone identification module is used to integrate protection action signals, electrical quantity spatial distribution and SVF state change timing to determine whether a fault has occurred and to identify the functional area to which the fault belongs.

[0101] The graded response module is used to generate fault recovery instructions according to the graded response strategy, wherein the fault recovery instructions include partial isolation, derating pass-through or extreme blocking.

[0102] The extreme restart coordination module is used to select between regular restart operations or buck restart operations for fault recovery based on SVF availability, and to generate restart power commands.

[0103] 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 identification and recovery based on SVF state awareness, characterized in that, Within each control cycle, the SLCC DC transmission system is subjected to fault diagnosis and recovery according to the following steps S1 to S3: Step S1: Obtain the operating status of the static var generator in real time and calculate the reactive power support margin; Simultaneously, the converter turn-off angle is collected, and the commutation margin is calculated; Step S2: Based on the operating status and reactive power support margin of the static var generator, and according to the preset adaptive correction rule and combined with the commutation margin, determine the protection threshold correction coefficient and the time window correction coefficient, and use the protection threshold correction coefficient and the time window correction coefficient to correct the protection threshold and time window of the polarity protection device setpoint area. Step S3: Based on the corrected protection threshold and time window, determine whether there is a fault in the SLCC DC transmission system according to the instantaneous values ​​of AC and DC side voltage and current. If so, determine the functional area to which the fault belongs according to the spatial distribution of electrical quantities and the timing of SVF state changes, and use a graded response strategy or restart coordination strategy to restore the fault; otherwise, proceed to step S1.

2. The SLCC fault identification and recovery method based on SVF state awareness according to claim 1, characterized in that, The operating status includes control mode, health status, and reactive power command value; wherein the control status includes voltage support mode, filter-dominated mode, and hybrid mode, and the health status includes normal, current limiting, loop exit, and bypass.

3. The SLCC fault identification and recovery method based on SVF state awareness according to claim 2, characterized in that, Step S1 calculates the reactive power support margin according to the following formula: ； in, Indicates reactive power support margin. This refers to the rated reactive power capacity of the static var generator. This is the reactive power command value.

4. The SLCC fault identification and recovery method based on SVF state awareness according to claim 1, characterized in that, Step S1 calculates the commutation margin using the following formula: ； in, For commutation margin, and This indicates that the commutation margin is sufficient; The converter turn-off angle. For reference shut-off angle.

5. The SLCC fault identification and recovery method based on SVF state awareness according to claim 1, characterized in that, The functional areas to which the fault belongs in step S3 include the SVF area, the converter area, and the DC line area. When the fault occurs in the SVF area or the converter area, a hierarchical response strategy is used for fault recovery. When the fault occurs in the DC line area, a restart coordination strategy is used for fault recovery.

6. The SLCC fault identification and recovery method based on SVF state awareness according to claim 5, characterized in that, The graded response strategy includes a Level I response strategy, a Level II response strategy, and a Level III response strategy; Among them, the Level I response strategy is local isolation, that is, SVF branch isolation or bypass operation is performed, and the LCC converter continues to operate; the Level II response strategy is derating ride-through, that is, the SLCC DC transmission system enters derating operation; the Level III response strategy is pole blocking, that is, pole blocking operation or pole isolation operation is performed. Specifically, when the fault is located in the SVF region and the fault can be locally handled, the Level I response strategy is used for fault recovery. After the Level I response strategy is completed, it is determined whether the reactive power support margin is not less than the minimum reactive power support margin allowable threshold and whether the commutation margin is not less than the preset threshold. If so, the Level II response strategy is executed; otherwise, the Level III response strategy is executed. When the fault is located in the converter area, the Level III response strategy is executed directly.

7. The SLCC fault identification and recovery method based on SVF state awareness according to claim 5, characterized in that, The restart coordination strategy is divided into regular restart operations and reduced-voltage restart operations; When a fault occurs in the DC line area, the fault is first restored by the conventional restart operation. If the conventional restart operation fails, the fault is restored by the reduced voltage restart operation. If the reduced voltage restart operation still fails, the pole is locked. Specifically, when performing fault recovery using a conventional restart operation, it is determined whether the SVF health status is normal and whether the reactive power support margin is not less than a preset threshold. If so, the rated transmission power of the DC system is used as the restart power. ,in The rated transmission power of the DC system. To restart power; simultaneously, SVF enters grid-connected or static synchronous compensator mode, providing dynamic reactive power support to the AC bus; otherwise ; When using a reduced-voltage restart operation for fault recovery , .

8. A SLCC fault identification and recovery system based on SVF state awareness, characterized in that, include: The status monitoring module is used to acquire the operating status of the static var generator in real time and calculate the reactive power support margin. Simultaneously monitor the converter turn-off angle and calculate the commutation margin; The protection threshold adaptive module is used to generate protection threshold correction coefficients and time window correction coefficients based on reactive power support margin and commutation margin. The fault zone identification module is used to integrate protection action signals, electrical quantity spatial distribution and SVF state change timing to determine whether a fault has occurred and to identify the functional area to which the fault belongs. The graded response module is used to generate fault recovery instructions according to the graded response strategy, wherein the fault recovery instructions include partial isolation, derating pass-through or extreme blocking. The extreme restart coordination module is used to select between regular restart operations or buck restart operations for fault recovery based on SVF availability, and to generate restart power commands.

Images