A flexible dc line backup protection method considering fault current limiting control

Abstract

The application discloses a kind of flexible DC line backup protection methods considering fault current limiting control, belong to the field of power system protection and control, this method first defines the positive direction of current at line two ends, reconstructs electrical quantity based on two ends sampling current;Then calculate the Pearson correlation coefficient of reconstructing electrical quantity, with waveform similarity as the basis for fault discrimination;Set action threshold, determine as internal fault;While judging the input state of fault current limiting control through DC voltage and current rate of change, judge the state of main protection action through current zero discrimination, start backup protection when main protection refuses to act.The application is little influenced by fault current limiting control, has strong anti-transition resistance and noise interference ability, does not need strict data synchronization, has high reliability and sensitivity, and can be used as the fast backup protection of flexible DC line.

Description

Technical Field

[0001] This invention belongs to the field of power system protection and control, and specifically relates to a backup protection method for flexible DC lines that considers fault current limiting control. Background Technology

[0002] In flexible DC transmission systems using overhead lines, the DC lines are constantly exposed to complex external environments such as lightning strikes, icing, and pollution, resulting in a high probability of fault occurrence. Fault transient currents rise rapidly and have strong impacts, easily leading to problems such as converter overcurrent, sudden DC voltage drops, and reduced AC side voltage support capacity, posing a severe challenge to the stable operation of power electronic devices and the system. Therefore, fault current limiting control has become a key technical means to solve the problems of fault current impact and stringent protection speed requirements in flexible DC systems. However, the implementation of current limiting control strategies alters the transient characteristics of voltage, current, and other parameters during a fault, thereby reducing the sensitivity of traditional protection methods. Therefore, it is necessary to study protection schemes that can coordinate with current limiting control strategies to quickly and reliably clear faults within the fault zone while ensuring that faults outside the fault zone do not cause false tripping.

[0003] However, existing technologies have the following shortcomings: protection systems that consider the impact of DC current limiting control strategies mainly focus on the main line protection, while lacking sufficient adaptability to backup protection. In extreme cases, the main protection may still fail to operate; at the same time, the implementation of current limiting control slows down the rise of fault current to some extent, reducing the requirements for ultra-high-speed operation of the protection.

[0004] Therefore, there is an urgent need for a new method to address the problem that transient characteristics such as the amplitude of fault electrical quantities change after fault current limiting control is put into operation, and that traditional backup protection is not adaptable enough. Summary of the Invention

[0005] To address the issues of altered transient characteristics such as fault electrical quantity amplitude after fault current limiting control is implemented, and the insufficient adaptability of traditional backup protection, a flexible DC line backup protection method considering fault current limiting control is proposed. This method is less affected by fault current limiting control and can reliably identify faults inside and outside the protection zone under current limiting conditions, ensuring the reliability and sensitivity of backup protection.

[0006] To achieve the above objectives, the present invention provides a flexible DC line backup protection method considering fault current limiting control, comprising the following steps: S1: The protection device collects configuration parameters and installation location information of the protection devices at both ends of the line, defines the unified positive direction of the current on the rectifier side and the inverter side, establishes a fiber optic communication channel to establish a synchronous sampling data interaction mechanism between the sending and receiving ends, and outputs the sampling current sequence of the sending and receiving ends with direction indicators to S2. S2: Receive the current at each sampling time of the sending end and the current at each sampling time of the receiving end output by S1, calculate the reconstructed electrical quantity of the product of the currents at both ends and the reconstructed electrical quantity of the absolute value of the product of the currents at both ends for each sampling time, buffer the continuous sampling points of the preset number of sampling points to form a complete data window sequence, and output the data window sequence corresponding to the product reconstructed electrical quantity and the product absolute value reconstructed electrical quantity to S3. S3: Receive the complete data window sequence of the product reconstructed electrical quantity and the product absolute value reconstructed electrical quantity output from S2, calculate the arithmetic mean of the product reconstructed electrical quantity and the product absolute value reconstructed electrical quantity within a single data window, solve the Pearson correlation coefficient representing the similarity between the two sets of waveforms based on the mean deviation term, and output the Pearson correlation coefficient to S4. S4. Real-time acquisition of DC bus voltage and DC bus current, and calculation of DC current change rate. Combined with voltage fault initiation threshold and current change rate fault initiation threshold, determine whether fault and fault current limiting control are activated. After fault triggering, delay to verify the main protection action status. If the main protection fails to operate, receive the Pearson correlation coefficient output from S3, compare the Pearson correlation coefficient with the correlation coefficient action threshold to complete the fault section identification, and output the fault identification identifier to S5. S5 receives the fault identification flag output by S4. If the fault is determined to be within the DC line zone, a trip isolation command is sent to the DC circuit breaker. If the fault is determined to be outside the zone, the trip circuit is blocked, the data window buffer is cleared, and the timing variable is reset. The protection device automatically resets and then jumps to S1 to start a new round of sampling and identification cycle.

[0007] Preferably, in S1, the rule for defining the positive direction of the currents on the rectifier side and the inverter side satisfies the following: When the current flows from the local converter to the DC line, the corresponding sampling current value is positive; when the current flows back from the DC line to the local converter, the corresponding sampling current value is negative. When a DC line fault occurs within the zone, the positive and negative signs of the sampling current at the sending and receiving ends are the same; when a fault occurs outside the zone, the positive and negative signs of the sampling current at the sending and receiving ends are opposite.

[0008] Preferably, in S2, the product-reconstructed electrical quantity and the product-absolute-value-reconstructed electrical quantity satisfy the following calculation formula: ; In the formula, For the first The sum of the modulus reconstructed electrical quantities at each sampling moment; For the first Differential-mode reconstructed electrical quantities at each sampling time; For the rectifier side Current sample values ​​at each sampling time; For the inverter side Current sample values ​​at each sampling time; This is the sampling time sequence number.

[0009] Preferably, in S3, the arithmetic mean of the two sets of reconstructed electrical quantities within a single data window satisfies the following calculation formula: ; In the formula, Within a single complete data window The arithmetic mean of the sequence; Within a single complete data window The arithmetic mean of the sequence; The number of sampling points within a data window; This is the sampling time sequence number.

[0010] Preferably, the Pearson correlation coefficient in S3 satisfies the following calculation formula: ; In the formula, The Pearson correlation coefficient; For the first time The deviation from the window mean; For the first time The deviation from the window mean.

[0011] Preferably, the fault and fault current limiting control activation criteria in S4 satisfy the following set of inequalities: ; In the formula, This represents the real-time DC voltage amplitude of the DC bus. The threshold for triggering a DC voltage sag fault; This represents the real-time DC current of the DC bus. The rate of change of DC current over time; The threshold for the rate of change of current.

[0012] Preferably, in S4, the conditions for determining a successful main protection action are met: ; In the formula, This is the absolute value of the DC current; The fault current zeroing judgment setting value; The absolute value of the DC current is consistently less than The cumulative timeout duration; The threshold for determining when the fault current returns to zero is set; when the condition is met, it is determined that the main protection has successfully isolated the fault.

[0013] Preferably, the fault segment identification criterion in S4 satisfies: ; In the formula, The threshold value for the Pearson correlation coefficient is used; when the inequality holds, the fault is determined to be within the DC line zone, otherwise it is determined to be outside the zone.

[0014] Therefore, the present invention employs the above-mentioned flexible DC line backup protection method considering fault current limiting control. Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The electrical quantity reconstruction method based on the sampling current at both ends of the line is adopted. By constructing the reconstructed electrical quantity, the problem that the transient characteristics such as the amplitude of the fault electrical quantity are changed after the fault current limiting control is put into operation and the traditional protection criteria are not adaptable enough is overcome. The effect of enhancing the difference of fault protection characteristics inside and outside the area and improving the reliability of protection discrimination is achieved. (2) The fault discrimination method based on Pearson correlation coefficient is adopted. By utilizing the characteristic that the waveform of the reconstructed electrical quantity is highly consistent when the fault occurs within the zone and significantly opposite when the fault occurs outside the zone, the problem of the traditional protection criterion based on amplitude being greatly affected by current limiting control is overcome. This achieves the effect of small impact of protection current limiting control strategy, strong resistance to transition resistance and noise interference, and high reliability and sensitivity. (3) The backup protection startup and operation process design method considering fault current limiting control is adopted. Through the complete process of fault detection, current limiting control input judgment, main protection operation status judgment and backup protection operation, the problem of insufficient research on backup protection and poor coordination with current limiting control is overcome. It achieves the effect of clear principle, simple calculation, good speed, no need for strict data synchronization, and strong engineering applicability. It can be used as a fast backup protection for flexible DC lines and has good engineering application value.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a system architecture diagram of a dual-ended bipolar modular multilevel converter (MMC) high-voltage direct current (HVDC) transmission system, representing an embodiment of a flexible DC line backup protection method considering fault current limiting control according to the present invention. Figure 2 This is a flowchart illustrating the logic of a bipolar MMC-HVDC DC line correlation differential backup protection method based on an embodiment of the present invention, which considers fault current limiting control for flexible DC line backup protection. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used in the present invention should have the ordinary meaning understood by those skilled in the art.

[0018] Example 1 like Figures 1-2 As shown, this embodiment provides a flexible DC line backup protection method considering fault current limiting control. It should be understood that the specific parameters, models and protocols mentioned in this embodiment are only examples to help those skilled in the art understand the present invention, and are not intended to limit the present invention.

[0019] The present invention provides a flexible DC line backup protection method considering fault current limiting control, comprising the following steps: S1. Receive system configuration parameters and protection device installation location information, define the positive and negative dual-branch current positive directions and establish a synchronous data interaction mechanism between the sending end and the receiving end; the determined positive direction of the full branch current is passed to step S2 for reconstructing electrical quantity calculation.

[0020] In this step, a three-in-one directional reference system is constructed, which includes the bipolar direction definition on the rectifier side, the bipolar direction definition on the inverter side, and the dual-end synchronous communication interaction mechanism. Unlike the traditional single-end protection method that does not require a unified direction, this step introduces a globally consistent convention for the current direction of the four measurement points at both the sending and receiving ends, which is suitable for the application scenario of bipolar DC line differential protection.

[0021] The positive current is determined based on the installation positions of the positive and negative protection on the rectifier side of the sending end. Negative current Positive direction; the positive current is determined based on the installation positions of the positive and negative protection on the inverter side at the receiving end. Negative current Positive direction; based on the optical fiber communication channel, the four measurement points at both ends of the sending and receiving ends are synchronously sampled and interacted to jointly form a unified current direction reference for the entire bipolar DC line.

[0022] The positive direction definition function for the total branch current is expressed as: Positive direction: Sending end positive converter MMC1 → DC positive line; Positive direction: Sending end negative converter MMC2 → DC negative line; Positive direction: Receiving end positive converter MMC3 → DC positive line; Positive direction: Receiving end positive converter MMC4 → DC negative line; in, , The sampling current is used at the positive and negative protection installation points on the rectifier side of the sending end. , The sampling current is used at the positive and negative protection installation points on the inverter side of the receiving end. A unified positive direction reference is established: current flows from the DC port of the converter to the DC transmission line.

[0023] The direction of the rectifier-side current is defined as follows: Positive branch Current flows from MMC1 to the DC positive circuit. It is a positive value; the current flows back from the DC positive line to MMC1. It is a negative value; Negative branch Current flows from MMC2 to the DC negative terminal circuit. It is a positive value; the current flows back from the DC negative line to MMC2. It is a negative value; , For bipolar sampling current at the sending end, the "converter-to-line flow" is uniformly used as the positive direction to provide a unified symbol reference for subsequent electrical quantity calculations; the direction definition provides a symbol reference for subsequent electrical quantity calculations.

[0024] The inverter-side current direction is defined as follows: Positive branch Current flows from MMC3 to the DC positive circuit. It is a positive value; the current flows back from the DC positive line to MMC3. It is a negative value; Negative branch Current flows from MMC4 to the DC negative terminal circuit. It is a positive value; the current flows back from the DC negative line to MMC4. It is a negative value; the receiving end and the sending end adopt the same positive definition rules to achieve global unification of the direction reference at both the sending and receiving ends.

[0025] When a fault occurs within the zone, it is determined independently for each individual pole (positive / negative branch): Faults within the polar region: The current directions at both the sending and receiving ends of the faulty pole are the same, and the sampling currents at both ends are positive; Example: Positive line short circuit fault, sending end positive outflow ( The fault current at the receiving end flows into the line from MMC3 ( ); Outside the polarity: The current directions at the sending and receiving ends of the faulty pole are opposite, the sampling current at one end is positive, and the sampling current at the other end is negative; Example: MMC3 valve arm short circuit fault, power continues to be delivered in the positive direction. The signs at both ends are opposite.

[0026] A data interaction mechanism is established so that the protection devices at both ends can exchange sampling data through an optical fiber communication channel, ensuring that the data at both ends can be used synchronously for subsequent calculations.

[0027] The sending-end rectifier-side protection device and the receiving-end inverter-side protection device exchange synchronous sampling data at four measurement points in real time through a point-to-point fiber optic communication channel, and are configured with a unified sampling clock synchronization mechanism to ensure the sending end , With the receiving end , Timing alignment ensures that sampled data can be synchronously incorporated into subsequent calculations of differential electrical quantities. The protection devices at both the sending and receiving ends complete the calculations according to the system's fixed sampling frequency. The system simultaneously acquires and calibrates four-channel currents; it outputs four-channel sampled current sequences carrying branch identifiers and positive / negative direction identifiers, providing a globally unified direction reference for subsequent reconstruction of polarity electrical quantities and fault segment identification.

[0028] The protection device completes current acquisition and direction calibration at a fixed sampling frequency; it outputs a sampled current sequence with direction markings to provide a directional reference for subsequent reconstructed electrical quantity calculation and fault diagnosis.

[0029] S2. Receive the sampled current data with direction indicators from both ends output by S1, construct the reconstructed electrical quantities and calculate the reconstructed current sequence; the calculated reconstructed electrical quantity sequence is passed to step S3 for average value calculation.

[0030] In this step, a two-dimensional reconstructed electrical quantity containing sum-mode and differential-mode components is constructed. Unlike the traditional method of directly using the original single-ended current for discrimination, this step introduces a feature enhancement method for reconstructing the combined current at both ends, which is suitable for the backup protection scenario of flexible DC lines under fault current limiting control.

[0031] The reconstructed electrical quantities are calculated by summing the rectifier-side sampled current and the inverter-side sampled current, and the differential-mode reconstructed electrical quantities are calculated by difference between the rectifier-side sampled current and the inverter-side sampled current. These are then combined to form a reconstructed electrical quantity matrix.

[0032] The reconstructed electrical quantity function is expressed as: ; In the formula, For the first The sum of the modulus reconstructed electrical quantities at each sampling moment; For the first Differential-mode reconstructed electrical quantities at each sampling time; For the rectifier side Current sample values ​​at each sampling time; For the inverter side Current sample values ​​at each sampling time; This is the sampling time sequence number.

[0033] Constructing product-reconstructed electrical quantities The decision logic is expressed as follows: When there is a fault in the area Same symbols Always positive; when there is a fault outside the zone opposite signs It is always a negative number; in, The directional coupling characteristic of the current at both ends is the core characteristic quantity for distinguishing faults inside and outside the zone.

[0034] Constructing absolute value reconstructed electrical quantities The decision logic is expressed as follows: Regardless of whether the fault is inside or outside the zone, It is always greater than or equal to 0, and only represents the magnitude of the fault current. The waveform reference value; in, The influence of directional sign is eliminated, and only the current amplitude waveform trend is retained for matching the similarity calculation of Pearson correlation coefficient.

[0035] The protection device completes the current acquisition and reconstructed electrical quantity calculation at both ends according to a fixed sampling frequency; it outputs the reconstructed electrical quantity sequence to provide characteristic basis for subsequent correlation analysis and fault diagnosis.

[0036] S3. Receive the reconstructed electrical quantity sequence and data window length parameter output by S2, calculate the mean of the two sets of characteristic quantities within a single window and solve for the Pearson correlation coefficient; pass the Pearson correlation coefficient to step S4 for fault section identification.

[0037] In this step, a waveform similarity quantification system is constructed, which includes mean preprocessing and covariance normalization. Unlike the traditional single time-domain amplitude comparison criterion, this step utilizes the Pearson correlation coefficient for quantification. and The degree of waveform fit reduces the interference of fault current limiting, transition resistance, and measurement noise on protection criteria.

[0038] Based on data window Calculate each sampling point separately. The mean value is used, and then the covariance and standard deviation are calculated by combining the mean deviation term. After normalization, the Pearson correlation coefficient, which characterizes the waveform similarity, is obtained. .

[0039] The mean function for a single data window is expressed as: ; In the formula, Within a single complete data window The arithmetic mean of the sequence; Within a single complete data window The arithmetic mean of the sequence; The number of sampling points within a data window; This is the sampling time sequence number.

[0040] The Pearson correlation coefficient calculation function is constructed as follows: ; In the formula, for Pearson correlation coefficient between the two sets of waveforms; For the first time The deviation from the window mean; For the first time The deviation from the window mean.

[0041] The protection device completes the data window sliding and average value update calculation at a fixed sampling frequency; it outputs the reconstructed electrical quantity average value to provide an average benchmark for subsequent Pearson correlation coefficient calculation and waveform similarity assessment.

[0042] S4 receives the Pearson correlation coefficient and real-time sampled values ​​of DC side voltage and current output from S3, and sequentially completes fault initiation judgment, main protection operation status judgment, and finally performs backup protection fault section judgment. The judgment result is transmitted to step S5 for outputting trip command or device reset.

[0043] In this step, a three-layer criterion system is constructed, which includes action threshold setting, discrimination logic design, and reliability margin setting. Unlike the traditional fixed threshold protection criterion method, this step introduces a threshold setting method based on the physical meaning of waveform similarity, which is suitable for flexible DC protection scenarios where the fault characteristics inside and outside the protection zone are significantly different.

[0044] The fault and current limiting control activation status are determined based on DC voltage drop threshold and current change rate threshold; the success of main protection in isolating the fault is verified based on the fault current zero-reset time criterion; based on... With threshold The size of the fault determines whether it is located within or outside the line area.

[0045] The fault current limiting start-up discrimination function is expressed as follows: ; In the formula, This represents the real-time DC voltage amplitude of the DC bus. The threshold for triggering a DC voltage sag fault; This represents the real-time DC current of the DC bus. The rate of change of DC current over time; The threshold for the rate of change of current.

[0046] The rules for determining successful actions of the main protection are as follows: when The fault current is determined to remain at zero, indicating that the main protection has successfully isolated the fault.

[0047] in, This is the absolute value of the DC current; The fault current zeroing judgment setting value; The absolute value of the DC current is consistently less than The cumulative timeout duration; The threshold for determining when the fault current returns to zero.

[0048] Construct a backup protection fault discrimination criterion, expressed as: like Determine the fault within the DC line area; if The fault was determined to be outside the designated area.

[0049] in, The action threshold for the Pearson correlation coefficient is set to 0; the threshold for the fault boundary between the area and the outside area can be adjusted within the range of -0.5 to 0.5 according to actual engineering needs.

[0050] The protection device continuously monitors the fault status by collecting DC electrical quantities in real time. After the fault is triggered, the main protection action result is verified after a delay. When the main protection fails to operate, the correlation criteria are activated to complete the fault location. The fault identification identifier (in-zone fault / out-of-zone fault) is output to the downstream execution logic.

[0051] S5 receives the fault identification flag output by S4, executes the backup protection output action logic, and outputs a trip command or triggers the device to automatically reset. The action execution result is synchronously fed back to the front-end sampling and acquisition module, and the next round of sampling and identification loop begins.

[0052] In this step, a closed-loop execution system is constructed, which includes trip output, device reset, and cyclic sampling. Unlike the open-loop trip logic without feedback of the main protection, this step adds a reset loop mechanism to adapt to the differentiated handling requirements of permanent faults and transient faults.

[0053] Based on the fault identification within the zone, a trip isolation command is issued to the DC circuit breaker; based on the fault identification outside the zone, the trip circuit is blocked and the protection device is automatically reset; after completing one round of judgment, the timing and buffer data window are reset, and the synchronous sampling process is restarted.

[0054] The fault exit action rules within the zone are expressed as follows: If the fault identification is a fault within the line area, the protection device will immediately output a trip hard contact command to trip the DC circuit breakers at both ends of the fault pole and isolate the faulty line. Among them, the trip command with the pole identifier only disconnects the faulty pole, while the healthy pole continues to operate.

[0055] The fault return rule outside the zone is expressed as follows: If the fault identification is an external fault, all trip outputs are blocked, the current data window cache is cleared, the fault timer is reset to zero, and the protection device automatically returns to normal monitoring status. Among them, the recovery is instantaneous and can immediately proceed to the next round of sampling and discrimination process.

[0056] The closed-loop logic is as follows: After completing the trip / reset operation, the protection device resets all timing variables, clears the reconstructed electrical quantity buffer, maintains a fixed sampling frequency to continuously collect the current at both ends, and re-executes the complete process of S1~S5 in sequence.

[0057] The protection device continuously outputs hard contact trip signals or reset status signals to realize closed-loop fault identification and fault isolation of DC line backup protection under current limiting conditions.

[0058] Therefore, the present invention adopts the above-mentioned flexible DC line backup protection method considering fault current limiting control. This method is less affected by fault current limiting control and can reliably identify faults inside and outside the area under current limiting conditions, thus ensuring the reliability and sensitivity of backup protection.

[0059] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for backup protection of flexible DC lines considering fault current limiting control, characterized in that, Includes the following steps: S1: The protection device collects configuration parameters and installation location information of the protection devices at both ends of the line, defines the unified positive direction of the current on the rectifier side and the inverter side, establishes a fiber optic communication channel to establish a synchronous sampling data interaction mechanism between the sending and receiving ends, and outputs the sampling current sequence of the sending and receiving ends with direction indicators to S2. S2: Receive the current at each sampling time of the sending end and the current at each sampling time of the receiving end output by S1, calculate the reconstructed electrical quantity of the product of the currents at both ends and the reconstructed electrical quantity of the absolute value of the product of the currents at both ends for each sampling time, buffer the continuous sampling points of the preset number of sampling points to form a complete data window sequence, and output the data window sequence corresponding to the product reconstructed electrical quantity and the product absolute value reconstructed electrical quantity to S3. S3: Receive the complete data window sequence of the product reconstructed electrical quantity and the product absolute value reconstructed electrical quantity output from S2, calculate the arithmetic mean of the product reconstructed electrical quantity and the product absolute value reconstructed electrical quantity within a single data window, solve the Pearson correlation coefficient representing the similarity between the two sets of waveforms based on the mean deviation term, and output the Pearson correlation coefficient to S4. S4. Real-time acquisition of DC bus voltage and DC bus current, and calculation of DC current change rate. Combined with voltage fault initiation threshold and current change rate fault initiation threshold, determine whether fault and fault current limiting control are activated. After fault triggering, delay to verify the main protection action status. If the main protection fails to operate, receive the Pearson correlation coefficient output from S3, compare the Pearson correlation coefficient with the correlation coefficient action threshold to complete the fault section identification, and output the fault identification mark to S5. S5 receives the fault identification flag output by S4. If the fault is determined to be within the DC line zone, a trip isolation command is sent to the DC circuit breaker. If the fault is determined to be outside the zone, the trip circuit is blocked, the data window buffer is cleared, and the timing variable is reset. The protection device automatically resets and then jumps to S1 to start a new round of sampling and identification cycle.

2. The method for backup protection of flexible DC lines considering fault current limiting control according to claim 1, characterized in that, In S1, the rule for defining the positive direction of the currents on the rectifier side and inverter side is satisfied as follows: When the current flows from the local converter to the DC line, the corresponding sampling current value is positive; when the current flows back from the DC line to the local converter, the corresponding sampling current value is negative. When a DC line fault occurs within the zone, the positive and negative signs of the sampling current at the sending and receiving ends are the same; when a fault occurs outside the zone, the positive and negative signs of the sampling current at the sending and receiving ends are opposite.

3. A flexible DC line backup protection method considering fault current limiting control according to claim 2, characterized in that, In S2, the product-reconstructed electrical quantity and the product-absolute-value-reconstructed electrical quantity satisfy the following calculation formula: ； In the formula, For the first The sum of the modulus reconstructed electrical quantities at each sampling moment; For the first Differential-mode reconstructed electrical quantities at each sampling time; For the rectifier side Current sample values ​​at each sampling time; For the inverter side Current sample values ​​at each sampling time; This is the sampling time sequence number.

4. A flexible DC line backup protection method considering fault current limiting control according to claim 3, characterized in that, In S3, the arithmetic mean of two sets of reconstructed electrical quantities within a single data window satisfies the following calculation formula: ； In the formula, Within a single complete data window The arithmetic mean of the sequence; Within a single complete data window The arithmetic mean of the sequence; The number of sampling points within a data window; This is the sampling time sequence number.

5. A flexible DC line backup protection method considering fault current limiting control according to claim 4, characterized in that, The Pearson correlation coefficient in S3 satisfies the following calculation formula: ； In the formula, Pearson correlation coefficient; For the first time The deviation from the window mean; For the first time The deviation from the window mean.

6. A flexible DC line backup protection method considering fault current limiting control according to claim 5, characterized in that, The fault and fault current limiting control activation conditions in S4 satisfy the following set of inequalities: ； In the formula, This represents the real-time DC voltage amplitude of the DC bus. The threshold for triggering a DC voltage sag fault; This represents the real-time DC current of the DC bus. The rate of change of DC current over time; The threshold for the rate of change of current.

7. A flexible DC line backup protection method considering fault current limiting control according to claim 6, characterized in that, In S4, the conditions for determining a successful main protection action are met: ； In the formula, This is the absolute value of the DC current; The fault current zeroing judgment setting value; The absolute value of the DC current is consistently less than The cumulative timeout duration; The threshold for determining when the fault current returns to zero is set; when the condition is met, it is determined that the main protection has successfully isolated the fault.

8. A flexible DC line backup protection method considering fault current limiting control according to claim 7, characterized in that, The fault section identification criterion in S4 is satisfied as follows: ； In the formula, The threshold value for the Pearson correlation coefficient is used; when the inequality holds, the fault is determined to be within the DC line zone, otherwise it is determined to be outside the zone.

9. A computer device, characterized in that, include: A processor configured to be coupled to a memory, read and execute instructions and / or program code in the memory to perform the method as described in any one of claims 1-8.

10. A computer-readable medium, characterized in that, The computer-readable medium stores computer program code that, when executed on a computer, causes the computer to perform the method as described in any one of claims 1-8.

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