Fault direction discrimination method based on positive sequence fault component control

Abstract

This invention provides a fault direction determination method based on positive-sequence fault component control. Addressing the issues of decreased sensitivity or misjudgment in traditional protection methods in weakly fed new energy dual-end systems, this method achieves accurate and robust fault location determination through four steps: real-time fault monitoring and rapid identification, positive-sequence polar orientation active reshaping and control, adaptive parameter correction under multi-dimensional constraints, and robust direction determination based on nonlinear mapping. This invention significantly improves the reliability of protection actions in weakly fed scenarios, achieves synergistic optimization of control performance and protection sensitivity, enhances the robustness and accuracy of fault location determination, and exhibits rapid response and good engineering adaptability.

Description

Technical Field

[0001] This invention belongs to the field of control and protection of MMC transmission lines connected to new energy sources, and specifically relates to a fault direction discrimination method based on positive sequence fault component control. Background Technology

[0002] With the accelerated transition to clean energy and the widespread application of power electronic equipment, the integration of large-scale renewable energy sources into the power system has become an inevitable trend. The transient characteristics of these renewable energy sources differ significantly from those of traditional AC power grids, posing an adaptation challenge to protection principles based on power frequency components. Furthermore, conventional protection methods are susceptible to sensitivity degradation or misjudgment due to the influence of the control responses at the power electronic interfaces on both sides of the line. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a fault direction discrimination method based on positive sequence fault component control, which is not affected by the operating conditions and transition resistance of the new energy side and is applicable to the new energy connected MMC access system.

[0004] The fault direction discrimination method based on positive sequence fault component control provided by this invention, after detecting abnormal electrical parameters of the new energy transmission line and determining that a fault has occurred, firstly triggers the start-up protection action program based on the degree of system voltage drop or the negative sequence voltage and current amplitude characteristics. Then, it achieves positive sequence fault component control by actively adjusting the positive sequence current reference value after the converter fault, and forcibly reshapes the controlled positive sequence fault component control phase to the preset discrimination interval. On this basis, the system evaluates the control performance according to the real-time operating conditions and introduces an adaptive correction angle to find the optimal parameter solution that takes into account both converter operating constraints and protection sensitivity. Finally, it extracts the positive equivalent impedance phase after the fault and substitutes it into the adaptive tuning function based on nonlinear mapping. By amplifying the fault polarity characteristics at the judgment boundary, it achieves accurate and robust determination of the fault location of the double-ended weak feeder system.

[0005] The technical solution adopted in this invention is: a fault direction discrimination method based on positive sequence fault component control, comprising the following steps:

[0006] (1) Real-time fault monitoring and rapid identification: Real-time monitoring of the operating parameters of the new energy transmission line; When abnormal fluctuations in system voltage or current are detected, the fault is quickly determined and the protection action program is triggered.

[0007] (2) Positive sequence polarity active reshaping and control: After the fault is confirmed, the positive sequence fault component phase control strategy is activated immediately. By dynamically adjusting the positive sequence current vector distribution at the converter outlet, the controlled positive sequence equivalent impedance phase is forcibly reshaped to the preset protection reliability discrimination range.

[0008] (3) Adaptive parameter correction under multidimensional constraints: Real-time evaluation of the adaptability of the positive sequence fault component phase control strategy under the current operating conditions. Under the premise of meeting the converter current limiting threshold and fault ride-through (FRT) hard constraints, the adaptive adjustment mechanism is activated to dynamically correct the reconfiguration angle in order to seek the optimal coordination balance between system safe operation and protection sensitivity.

[0009] (4) Direction robust discrimination based on nonlinear mapping: extract electrical measurement values ​​within a specific window after the fault and substitute them into an adaptive tuning function with characteristic amplification. By enhancing the polarity of the fault characteristics near the discrimination boundary, the fault location of the double-ended weak feeder system can be discerned.

[0010] Step (1) is as follows:

[0011] By extracting voltage and current parameters from both sides of the line in real time and using multi-dimensional criteria for comprehensive diagnosis, a system fault is determined when the phase voltage amplitude is found to be lower than a preset threshold, or when the amplitude of the negative sequence voltage or negative sequence current components exceeds a set start-up threshold. This judgment process is typically completed within 1 to 2 milliseconds after a fault occurs, aiming to ensure that the converter can quickly switch from steady-state operation to fault response mode and provide accurate triggering timing for subsequent positive sequence fault component phase control strategies and protection criteria.

[0012] The multidimensional criterion is as follows:

[0013]

[0014] In the formula, This indicates the minimum value of the detected phase voltage amplitude; and These represent the amplitudes of the detected negative-sequence voltage and negative-sequence current, respectively. Indicates the phase voltage starting value ( (Take 0.9 times the rated voltage of the converter). and These represent the negative sequence voltage starting value and the negative sequence current starting value, respectively. Take 0.1 times the rated voltage of the converter. Take 0.1 times the rated current of the converter.

[0015] Step (2) specifically involves:

[0016] Different current reconfiguration logics are executed for the sending-end converter and the receiving-end converter respectively:

[0017] For the sending-end converter, the reference value of the q-axis positive sequence current is calculated based on the voltage drop amplitude at its fault point. Then, using a preset fixed impedance angle (-90°) as the control target, combined with the positive sequence voltage before and after the fault... With current Based on the geometric phase relationship, the reference value of the positive sequence current on the d-axis can be calculated by reverse calculation. This ensures reactive power support while forcibly locking the positive sequence impedance phase of the system.

[0018] For the receiving-end converter, based on the preset fixed impedance angle (-90°) and the fault positive-sequence voltage phasor, the d-axis component of the positive-sequence current reference value that satisfies the phase constraint is analytically calculated using trigonometric geometric relationships. and q-axis components ;

[0019] Finally, the reconstructed positive sequence current reference values ​​calculated for the sending and receiving ends are input into their respective current inner loop controllers. Through closed-loop control, the converter ports are forced to exhibit constant phase and predictable impedance characteristics during faults.

[0020] Step (2) specifically includes:

[0021] For the sending-end converter, the reference value for the d-axis positive sequence current is:

[0022] (6)

[0023] In the formula, This indicates the sudden change in the positive sequence voltage of the sending-end converter; This indicates the per-unit value of the positive sequence voltage of the sending-end converter; This indicates the per-unit value of the rated current of the sending-end converter;

[0024] For the receiving-end converter, a voltage reference current limiting control strategy is adopted:

[0025] (8);

[0026] In the formula, This indicates the reference value for the positive sequence voltage of the receiving-end converter; This represents the positive sequence voltage of the receiving-end converter under normal operating conditions. This represents the current limiting coefficient, which is typically set to 1. This indicates the magnitude of the negative sequence voltage at the receiving end of the converter;

[0027] The positive-sequence fault component phase control strategy yields the positive-sequence current reference value:

[0028] (13);

[0029] in:

[0030] (14);

[0031] In the formula, This indicates the sudden change in the positive sequence current of the receiving-end converter; Positive sequence voltage of the receiving-end converter under normal operating conditions.

[0032] Step (3) is as follows:

[0033] The system verifies in real time whether the calculated positive sequence current reference value meets the converter's operating constraints, which include at least converter current limiting and active power limiting. If the calculated current reference value exceeds the operating constraints, the system determines that the current preset constant target reconfiguration angle (e.g., -90 degrees) has failed and immediately initiates adaptive adjustment.

[0034] A set of constraint equations is constructed, including converter current limiting, low voltage ride-through requirements, and line impedance characteristics. The target reconfiguration angle is corrected to a preset angle plus an adaptive correction angle. The allowable range of the correction angle is obtained by solving the constraint equations. An optimal correction value is selected within the allowable range. The positive sequence current reference value of the converter is recalculated using the corrected target reconfiguration angle to ensure that the equivalent impedance phase of the converter remains within a stable range that can be reliably identified by the protection components, provided that all safe operation constraints are met.

[0035] Step (3) specifically includes:

[0036] The fault ride-through requirements for the sending-end converter include current limiting and active power limitation. Additionally, since the reconfiguration angle is -90°, for ease of protection setting, the positive-sequence equivalent impedance amplitude after reconfiguration should be greater than the line impedance, expressed by the formula:

[0037] (15);

[0038] In the formula: and These are the rated voltage and current values ​​of the sending-end converter, respectively. The positive sequence equivalent impedance amplitude per unit length of the AC line; The length of the AC line; and These are the minimum and maximum amplitude limits for the d-axis component of the positive sequence current, respectively.

[0039] If substituting the measured electrical quantities into the above constraint equations results in no feasible solution, indicating a performance degradation issue with the positive-sequence fault component control in this system, then the control objective is adaptively adjusted by widening the impedance reconstruction angle from a fixed value of -90° to -90°+. The feasible region is dynamically determined by resolving the simultaneous constraint set. The value of the current reference command is determined and the current reference command is adjusted accordingly. This method can find a solution that meets the necessary operating requirements while maintaining the protection performance as much as possible.

[0040] (16);

[0041] Substituting the measured electrical quantities after the fault into the above formula, we can obtain... Value, positive sequence current reference value:

[0042] (17).

[0043] Step (4) is as follows:

[0044] After the positive-sequence fault component control strategy takes effect and stabilizes, an adaptive tuning function incorporating a boundary feature enhancement mechanism is constructed. This function consists of the original measured phase angle and a first adaptive deviation term for the zero-degree boundary. And a second adaptive bias term for the positive and negative 180-degree boundaries. Together they form a whole; the first adaptive deviation term and the second adaptive deviation term use an exponential decay function to automatically introduce a compensation component when the phase approaches the discrimination dead zone (0 degrees and 180 degrees) to amplify the fault characteristics;

[0045] The synthesized phase after the above deviation correction is substituted into the hyperbolic tangent function for nonlinear mapping. By setting the amplification factor, the discrimination result is polarized to positive 1 or negative 1. When the function output value is positive 1, it is judged as a forward fault; when the function output value is negative 1, it is judged as a reverse fault, thereby realizing dead-zone-free and highly robust direction discrimination for the entire phase.

[0046] Step (4) specifically includes:

[0047] An adaptive setting function is introduced to reconstruct the protection criteria, thereby enhancing the accuracy of operation when impedance phase angle fluctuates.

[0048] (19);

[0049] in:

[0050] (20);

[0051] In the formula: and These are the adaptive functions for the tuning criteria boundaries of 0° and ±180°, respectively. and They are and The smoothing coefficient is generally taken as 1;

[0052] Substituting the adaptive tuning function into the hyperbolic tangent function:

[0053] (twenty one);

[0054] In the formula: It is the amplification factor of the hyperbolic tangent function, which is usually taken as 3;

[0055] Substituting the negative value of the positive sequence equivalent impedance phase angle measured at the protection installation point into equation (21), and combining it with the traditional positive sequence directional element protection criterion, we can obtain:

[0056] (twenty two);

[0057] In the formula: and These are the negative phase values ​​of the positive sequence equivalent impedance measured at the protection installation points of the sending and receiving ends, respectively.

[0058] Step (4) also includes... A low-pass filter is performed to obtain the low-pass filtered adaptive tuning function, which is then substituted into the hyperbolic tangent function.

[0059] The fault direction discrimination method based on positive-sequence fault component control proposed in this invention overcomes the incompatibility problem of positive-sequence direction components caused by the controlled positive-sequence impedance of the converter, and has a certain degree of adaptability to all fault types, transition resistance, and noise. Compared with the prior art, the beneficial effects of this invention are as follows:

[0060] 1. Significantly improve the reliability of protection actions in weak feeder scenarios: By actively reshaping and forcibly returning the control phase of the positive sequence fault component of the converter, the problem of decreased sensitivity and reliability of traditional fault direction discrimination elements based on the phase angle polarity of positive sequence equivalent impedance caused by the limited amplitude and phase control of short-circuit current in the new energy dual-terminal weak feeder system is effectively overcome, thereby reducing the risk of protection device failure and false operation from the mechanism.

[0061] 2. Achieve synergistic optimization of control performance and protection sensitivity: Introduce an adaptive correction angle and an optimal parameter solution optimization mechanism under converter operation constraints. Under the premise of strictly ensuring the converter current limiting safety and fault ride-through operation hard constraints, maximize the sensitivity margin of fault judgment and resolve the contradiction between protection requirements and equipment operation boundaries.

[0062] 3. Enhance the robustness and accuracy of fault location determination: The measured phase is processed by an adaptive tuning function based on nonlinear mapping. By amplifying the fault polarity characteristics in the determination boundary region, it can effectively cope with the interference caused by the fluctuation of new energy output and the complex power grid impedance changes, and realize accurate and robust identification of fault location.

[0063] 4. Rapid response and good engineering adaptability: The protection action program is triggered by voltage drop and negative sequence characteristics. Combined with the extraction and calculation of specific short window data after the fault, the rapid action capability of the protection algorithm is guaranteed. At the same time, the control strategy directly acts on the converter reference value without the need for additional hardware equipment, which facilitates engineering transformation and application in existing new energy grid-connected systems. Attached Figure Description

[0064] Figure 1 This is a flowchart of the present invention.

[0065] Figure 2 This is the topology of a large-scale photovoltaic system connected directly to the power system via a flexible grid in an embodiment of the present invention.

[0066] Figure 3 These are the positive sequence impedance measurements of the photovoltaic side and the flexible DC side when a fault occurs at point f1 on the AC line.

[0067] Figure 4 These are the positive sequence impedance measurements of the photovoltaic side and the flexible DC side when a fault occurs at point f2 on the AC line.

[0068] Figure 5 These are the positive sequence impedance measurements of the photovoltaic side and the flexible DC side when a fault occurs at point f3 on the AC line.

[0069] Figure 6 These are the positive sequence impedance measurements on the photovoltaic side when faults occur at points f1, f2, and f3 on the AC line.

[0070] Figure 7 These are the positive sequence impedance measurements on the flexible DC side when faults occur at points f1, f2, and f3 on the AC line. Detailed Implementation

[0071] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0072] This invention provides a fault direction discrimination method applicable to dual-ended weakly fed systems. After a fault occurs on a new energy transmission line, a positive-sequence fault component control strategy is activated to change the phase of the positive-sequence fault component in the converter. The performance of the positive-sequence fault component control is evaluated based on system parameters, and an adaptive adjustment mechanism is initiated to find the optimal solution that balances system operation and protection performance. The negative phase angle of the positive-sequence equivalent impedance measured at the protection installation point is substituted into an adaptive tuning function that includes boundary feature enhancement and low-pass filtering to amplify the phase polarity characteristics near the 0° and ±180° discrimination boundaries, thereby improving the reliability of fault direction discrimination. Figure 1 As shown, the process includes detecting a fault, activating a forward fault component phase control strategy, and determining the fault direction using protection criteria; the specific steps are as follows:

[0073] Step 1. Real-time acquisition of three-phase voltage and current at the protection installation location and converter port; amplitude calculation and sequence component decomposition of the acquired quantities to obtain the minimum phase voltage amplitude, negative sequence voltage amplitude, and negative sequence current amplitude; when the phase voltage drops beyond the limit or the negative sequence component exceeds the limit, quickly determine the occurrence of the fault and trigger the subsequent protection action program.

[0074] Step 2. Positive Sequence Pole Active Reshaping and Control: Immediately after confirming the fault, the positive sequence fault component phase control strategy is activated. By dynamically adjusting the positive sequence current vector distribution at the converter outlet, the controlled positive sequence equivalent impedance phase is forcibly reshaped to the preset protection reliability discrimination range.

[0075] Step 3. Adaptive parameter correction under multidimensional constraints: Real-time evaluation of the adaptability of the positive sequence fault component phase control strategy under the current operating conditions. Under the premise of meeting the converter current limiting threshold and fault ride-through (FRT) hard constraints, the adaptive adjustment mechanism is activated to dynamically correct the reconfiguration angle in order to seek the optimal coordination balance between system safe operation and protection sensitivity.

[0076] Step 4. Direction Robust Discrimination Based on Nonlinear Mapping: Extract electrical measurement values ​​within a specific window after a fault and substitute them into an adaptive tuning function with characteristic amplification. By enhancing the polarity of fault characteristics near the discrimination boundary, accurate and robust discrimination of fault location in a two-terminal weak feeder system can be achieved.

[0077] Furthermore, in step 1, when a system fault occurs, the positive-sequence fault component phase control strategy and fault direction discrimination start criteria are constructed using the characteristics of voltage drop and sudden increase in negative-sequence component after the fault, as shown in the following equation:

[0078]

[0079] In the formula, This indicates the minimum value of the detected phase voltage amplitude; and These represent the amplitudes of the detected negative-sequence voltage and negative-sequence current, respectively. This represents the phase voltage starting value, which is taken as 0.9 times the corresponding converter rated voltage in this article; and These represent the starting values ​​of negative sequence voltage and negative sequence current, respectively. In this paper, we consider taking 0.1 times the corresponding rated voltage and rated current of the converter.

[0080] The above formulas are the starting criteria for the positive-sequence fault component phase control strategy and the positive-sequence directional element protection in the AC system of new energy transmission via flexible direct transmission. The electrical quantities required for their application vary depending on the location. The positive-sequence fault component phase control strategy requires electrical quantities measured at the converter port, while the fault direction discrimination element requires electrical quantities measured at the protection device.

[0081] Furthermore, in step 2, by modifying the positive-sequence current reference value after the fault and changing the phase angle of the positive-sequence equivalent impedance on the photovoltaic side, the d-axis component of the positive-sequence current reference value on the photovoltaic side can be obtained as follows:

[0082]

[0083] To avoid affecting the system's reactive power support capability, its positive sequence reactive current must satisfy the following formula:

[0084] (5)

[0085] The positive sequence current reference value is:

[0086] (6)

[0087] The flexible DC-side converter employs a voltage reference current limiting control strategy:

[0088] (8)

[0089] The positive-sequence fault component phase control strategy yields the positive-sequence current reference value:

[0090] (13)

[0091] in:

[0092] (14)

[0093] Furthermore, in step 3, the fault ride-through requirements for the photovoltaic-side converter generally include current limiting and active power limiting. Also, since the reconfiguration angle is -90°, to facilitate protection settings, the positive-sequence equivalent impedance amplitude after reconfiguration should be greater than the line impedance, expressed by the formula:

[0094] (15)

[0095] In the formula: and These are the rated voltage and current values ​​of the photovoltaic-side converter, respectively. The positive sequence equivalent impedance amplitude per unit length of the AC line; The length of the AC line; and These are the minimum and maximum amplitude limits for the d-axis component of the positive sequence current, respectively.

[0096] If substituting the measured electrical quantities into the above constraint equations results in no feasible solution, it indicates a performance degradation issue with the positive-sequence fault component control in this system. Therefore, the control objective is adaptively adjusted, relaxing the impedance reconstruction angle from a fixed value of -90° to +90°. The feasible region is dynamically determined by resolving the simultaneous constraint set. The value of is determined, and the current reference command is adjusted accordingly. This method can find a solution that meets the necessary operating requirements while maintaining protection performance as much as possible.

[0097] (16)

[0098] Substituting the measured electrical quantities after the fault into the above formula, we can obtain... Value, positive sequence current reference value:

[0099] (17)

[0100] Furthermore, in step 4, the electrical measurement values ​​within a specific window after the fault are extracted and substituted into an adaptive tuning function with characteristic amplification. By enhancing the polarity of the fault characteristics near the discrimination boundary, accurate and robust discrimination of the fault location of the dual-end weak feeder system is achieved.

[0101] An adaptive function is introduced into the traditional fault direction discrimination principle based on the polarity of the positive-sequence equivalent impedance phase angle. The traditional fault direction discrimination principle involves calculating the positive-sequence equivalent impedance phase angle from the positive-sequence fault component voltage and current measured at the protection installation point, and distinguishing between forward and reverse faults based on the polarity of this phase angle. The protection criterion is reconstructed after introducing an adaptive setting function to enhance the accuracy of operation when the impedance phase angle fluctuates.

[0102] (19)

[0103] in:

[0104] (20)

[0105] In the formula: and These are the adaptive functions for the tuning criteria boundaries of 0° and ±180°, respectively. and They are and The smoothing coefficient is typically set to 1.

[0106] The synthesized phase function f(θ) obtained by formula (19) is used as the input α(t) to be filtered and input to the low-pass filter for smoothing. The typical shape of the frequency response H(f) of the low-pass filter is as follows:

[0107] (twenty three)

[0108] In the formula: f represents the signal frequency variable in the frequency response of the low-pass filter; fc is the cutoff frequency; j is the imaginary unit.

[0109] Low-pass filtering is implemented using a discretized filter, and the output of the low-pass filter is denoted as . The processing can be described by the following formula:

[0110] (twenty four)

[0111] Where h(t) is the impulse response function of the low-pass filter, and α(t) is the time-domain input corresponding to f(θ) obtained by formula (19); The synthesized phase function after low-pass filtering is used as the input to the hyperbolic tangent function in formula (21):

[0112] (25)

[0113] The synthesized phase function after low-pass filtering Substitute the values ​​into the hyperbolic tangent function and set an appropriate amplification factor:

[0114] (twenty one)

[0115] In the formula: k3 is the amplification factor of the hyperbolic tangent function, which is generally taken as 3; f(θ) in formula (21) is the value after low-pass filtering. .

[0116] Substituting the negative value of the positive-sequence equivalent impedance phase angle measured at the protection installation point into equation (21), and combining it with the traditional fault direction discrimination criterion based on the polarity of the positive-sequence equivalent impedance phase angle to distinguish between positive and reverse faults:

[0117] (twenty two)

[0118] In the formula: and These are the negative phase values ​​of the positive sequence equivalent impedance measured at the photovoltaic side and the flexible DC side protection installation location, respectively.

[0119] Example 1: Create as shown in the attached document Figure 2 The large-scale double-ended weak-feed system shown is used as a simulation model. The system output lines are configured as attached. Figure 2 The fault points shown in the topology exhibit asymmetrical faults.

[0120] like Figure 2 As shown, the fault direction discrimination method based on positive sequence fault component control is applied in the AC current limiting scenario, with the sending-end system being a photovoltaic inverter and the receiving-end system being a flexible DC converter.

[0121] like Figure 3 As shown, there is a fault at point f1 on the AC line (see details). Figure 2The fault direction discrimination method based on positive sequence fault component control can correctly identify faults such as A-phase ground fault, AB-phase ground fault, AB-phase inter-fault, and three-phase ground fault.

[0122] like Figure 4 As shown, there is a fault at point f2 on the AC line (see details). Figure 2 The fault direction discrimination method based on positive sequence fault component control can correctly identify faults such as A-phase ground fault, AB-phase ground fault, AB-phase inter-fault, and three-phase ground fault.

[0123] like Figure 5 As shown, there is a fault at point f3 on the AC line (see details). Figure 2 The fault direction discrimination method based on positive sequence fault component control can correctly identify faults such as A-phase ground fault, AB-phase ground fault, AB-phase inter-fault, and three-phase ground fault.

[0124] like Figure 6 As shown, there are faults at points f1, f2, and f3 on the AC line (see details). Figure 2 A phase-A ground fault occurred, with grounding resistances of 0.01Ω, 50Ω, 100Ω and 300Ω respectively. The fault direction discrimination method based on the sending end positive sequence fault component control can correctly identify the fault.

[0125] like Figure 7 As shown, there are faults at points f1, f2, and f3 on the AC line (see details). Figure 2 A phase-A ground fault occurs, with grounding resistances of 0.01Ω, 50Ω, 100Ω and 300Ω respectively. The fault direction discrimination method based on the positive sequence fault component control at the receiving end can correctly identify the fault.

[0126] When AG, ABG, and AB faults occur, the positive-sequence fault component phase control strategy is activated. The collected positive-sequence voltage and current signal data from the photovoltaic and MMC side transmission lines are preprocessed, the positive-sequence impedance angle is calculated, and the measured angle is substituted into an adaptive function to determine the fault direction. The simulation results are shown in the table below.

[0127] Table 1. Judgment results when different types of faults occur at different locations on the outgoing line of a double-ended weak feeder system.

[0128]

[0129] Example 2: Create as shown in the attached document Figure 2 The large-scale double-ended weak-feed system shown is used as a simulation model. The system output lines are configured as attached. Figure 2 The topology shows that each fault point experiences a ground fault via different transition resistors for the AG.

[0130] When an AG experiences a grounding fault via different transition resistors, the collected positive sequence voltage and current signals from the photovoltaic and MMC side transmission lines are preprocessed to calculate the positive sequence impedance angle. The measured angle is then substituted into an adaptive function to determine the fault direction and distinguish between faults inside and outside the fault zone. The simulation results are shown in the table below.

[0131] Table 2. Judgment results when an AG grounding fault occurs at different locations on the outgoing line of a dual-ended weak feeder system.

[0132]

Claims

1. A fault direction discrimination method based on positive sequence fault component control, characterized in that, Includes the following steps: (1) Real-time fault monitoring and rapid identification: Real-time monitoring of the operating parameters of the new energy transmission line; When abnormal fluctuations in system voltage or current are detected, the fault is quickly determined and the protection action program is triggered. (2) Positive sequence polarity active reshaping and control: After the fault is confirmed, the positive sequence fault component phase control strategy is activated immediately. By dynamically adjusting the positive sequence current vector distribution at the converter outlet, the controlled positive sequence equivalent impedance phase is forcibly reshaped to the preset protection reliability discrimination range. (3) Adaptive parameter correction under multidimensional constraints: Real-time evaluation of the adaptability of the positive sequence fault component phase control strategy under the current operating conditions, and under the premise of meeting the converter current limiting threshold and fault ride hard constraints, the adaptive adjustment mechanism is activated to dynamically correct the reconfiguration angle. (4) Direction robust discrimination based on nonlinear mapping: extract electrical measurement values ​​within a specific window after the fault and substitute them into an adaptive tuning function with characteristic amplification. By enhancing the polarity of the fault characteristics near the discrimination boundary, the fault location of the double-ended weak feeder system can be discerned.

2. The method according to claim 1, characterized in that, Step (1) is as follows: By extracting voltage and current parameters on both sides of the line in real time and using multi-dimensional criteria for comprehensive diagnosis: when the phase voltage amplitude is detected to be lower than the preset threshold, or when the amplitude of the negative sequence voltage or negative sequence current exceeds the set start threshold, the system is judged to have a fault.

3. The method according to claim 2, characterized in that, The multidimensional criterion is as follows: ； In the formula, This indicates the minimum value of the detected phase voltage amplitude; and These represent the amplitudes of the detected negative-sequence voltage and negative-sequence current, respectively. Indicates the phase voltage starting value; and These represent the negative sequence voltage initiation value and the negative sequence current initiation value, respectively.

4. The method according to claim 1, characterized in that, Step (2) specifically involves: Different current reconfiguration logics are executed for the sending-end converter and the receiving-end converter respectively: For the sending-end converter, the reference value of the q-axis positive sequence current is calculated based on the voltage drop amplitude at its fault point. Then, the target is controlled by a preset fixed impedance angle, combined with the positive sequence voltage before and after the fault. With current Based on the geometric phase relationship, the reference value of the positive sequence current on the d-axis can be calculated by reverse calculation. This ensures reactive power support while forcibly locking the positive sequence impedance phase of the system. For the receiving-end converter, based on the preset fixed impedance angle and the fault positive-sequence voltage phasor, the d-axis component of the positive-sequence current reference value that satisfies the phase constraint is analytically calculated using trigonometric geometric relationships. and q-axis components ; Finally, the reconstructed positive sequence current reference values ​​calculated for the sending and receiving ends are input into their respective current inner loop controllers. Through closed-loop control, the converter ports are forced to exhibit constant phase and predictable impedance characteristics during faults.

5. The method according to claim 1 or 4, characterized in that, Step (2) specifically includes: For the sending-end converter, the reference value for the d-axis positive sequence current is: （6） In the formula, This indicates the sudden change in the positive sequence voltage of the sending-end converter; This indicates the per-unit value of the positive sequence voltage of the sending-end converter; This indicates the per-unit value of the rated current of the sending-end converter; For the receiving-end converter, a voltage reference current limiting control strategy is adopted: （8）； In the formula, This indicates the reference value for the positive sequence voltage of the receiving-end converter; This represents the positive sequence voltage of the receiving-end converter under normal operating conditions. This represents the current limiting coefficient, which is typically set to 1. This indicates the magnitude of the negative sequence voltage at the receiving end of the converter; The positive-sequence fault component phase control strategy yields the positive-sequence current reference value: (13)； in: (14)； In the formula, This indicates the sudden change in the positive sequence current of the receiving-end converter; Positive sequence voltage of the receiving-end converter under normal operating conditions.

6. The method according to claim 1, characterized in that, Step (3) is as follows: The system verifies in real time whether the calculated positive sequence current reference value meets the converter's operating constraints, which include at least converter current limiting and active power limiting. If the calculated current reference value exceeds the operating constraints, the system determines that the current preset constant target reconfiguration angle has failed and immediately initiates adaptive adjustment. A set of constraint equations is constructed, including converter current limiting, low voltage ride-through requirements, and line impedance characteristics. The target reconfiguration angle is corrected to a preset angle plus an adaptive correction angle. The allowable range of the correction angle is obtained by solving the constraint equations. An optimal correction value is selected within the allowable range. The positive sequence current reference value of the converter is recalculated using the corrected target reconfiguration angle to ensure that the equivalent impedance phase of the converter remains within a reliably identifiable stable range while meeting all safe operation constraints.

7. The method according to claim 1 or 6, characterized in that, Step (3) specifically includes: The fault ride-through requirements for the sending-end converter include current limiting and active power limitation. Additionally, since the reconfiguration angle is -90°, for ease of protection setting, the positive-sequence equivalent impedance amplitude after reconfiguration should be greater than the line impedance, expressed by the formula: （15）； In the formula: and These are the rated voltage and current values ​​of the sending-end converter, respectively. The positive sequence equivalent impedance amplitude per unit length of the AC line; The length of the AC line; and These are the minimum and maximum amplitude limits for the d-axis component of the positive sequence current, respectively. If substituting the measured electrical quantities into the above constraint equations results in no feasible solution, indicating a performance degradation issue with the positive-sequence fault component control in this system, then the control objective is adaptively adjusted by widening the impedance reconstruction angle from a fixed value of -90° to -90°+. The feasible region is dynamically determined by resolving the simultaneous constraint set. The value of the current reference command is determined and the current reference command is adjusted accordingly. This method can find a solution that meets the necessary operating requirements while maintaining the protection performance as much as possible. （16）； Substituting the measured electrical quantities after the fault into the above formula, we can obtain... Value, positive sequence current reference value: （17）。 8. The method according to claim 1, characterized in that, Step (4) is as follows: After the positive-sequence fault component control strategy takes effect and stabilizes, an adaptive tuning function incorporating a boundary feature enhancement mechanism is constructed. This function consists of the original measured phase angle and a first adaptive deviation term for the zero-degree boundary. And a second adaptive bias term for the positive and negative 180-degree boundaries. Together they form a whole; the first adaptive deviation term and the second adaptive deviation term use an exponential decay function to automatically introduce a compensation component when the phase approaches the discrimination dead zone, so as to amplify the fault characteristics; The synthesized phase after the above deviation correction is substituted into the hyperbolic tangent function for nonlinear mapping. By setting the amplification factor, the discrimination result is polarized to positive 1 or negative 1. When the function output value is positive 1, it is judged as a forward fault; when the function output value is negative 1, it is judged as a reverse fault, thereby realizing dead-zone-free and highly robust direction discrimination for the entire phase.

9. The method according to claim 1 or 8, characterized in that, Step (4) specifically includes: An adaptive setting function is introduced to reconstruct the protection criteria, thereby enhancing the accuracy of operation when impedance phase angle fluctuates. （19）； in: （20）； In the formula: and These are the adaptive functions for the tuning criteria boundaries of 0° and ±180°, respectively. and They are and The smoothing coefficient is generally taken as 1; Substituting the adaptive tuning function into the hyperbolic tangent function: （21）； In the formula: It is the amplification factor of the hyperbolic tangent function, which is usually taken as 3; Substituting the negative value of the positive sequence equivalent impedance phase angle measured at the protection installation point into equation (21), and combining it with the traditional positive sequence directional element protection criterion, we can obtain: （22）； In the formula: and These are the negative phase values ​​of the positive sequence equivalent impedance measured at the protection installation points of the sending and receiving ends, respectively.

10. The method according to claim 9, characterized in that, Step (4) also includes... A low-pass filter is performed to obtain the low-pass filtered adaptive tuning function, which is then substituted into the hyperbolic tangent function.

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