Flexible straight line pilot protection method based on current waveform characteristics and related device

Abstract

The invention provides a flexible direct current line pilot protection method based on current waveform characteristics and a related device, and the method comprises the steps: collecting a fault current signal, judging whether the fault current signal meets a starting criterion standard, and building a mapping interval based on the collected fault current signal if the fault current signal meets the starting criterion standard; on the basis of the relationship between the mapping interval and the fault position, representing the trend characteristics of the transient current during internal and external faults; calculating a coordinate mapping interval psi max and a corresponding identification coefficient Q of currents at two ends of the fault line in each segment of data window by utilizing trend characteristics and combining the segment data windows; and on the basis of the current coordinate mapping interval psi max at the two ends of the fault line and the corresponding Q, internal and external fault identification criteria and fault pole selection criteria are constructed, and a fault area is identified. According to the technical scheme, the coordinate mapping interval is introduced as a key parameter for fault identification, and rapid and reliable identification of internal and external faults in the flexible direct current power transmission system is realized. The technical effect is remarkable, and the method has wide application prospects and popularization value.

Description

Technical Field

[0001] The present invention belongs to the field of flexible direct current transmission line protection, and in particular relates to a flexible direct current line longitudinal protection method and related devices based on current waveform characteristics. Background Art

[0002] As a new type of direct current transmission method, the modular multilevel converter high voltage direct current (MMC-HVDC) system combines the high efficiency of modular multilevel converters with the long-distance transmission characteristics of high voltage direct current transmission. It is favored for its low power loss, significant transmission capability, huge transmission capacity, excellent control flexibility and environmental friendliness. However, the MMC-HVDC system has low impedance characteristics, the current of short-circuit faults rises rapidly and has a large amplitude, the fault characteristics are time-varying and nonlinear, and are easily affected by line impedance, fault location, noise, and distributed capacitance current, resulting in reduced reliability and sensitivity of protection. Summary of the invention

[0003] The purpose of the present invention is to provide a flexible straight line longitudinal protection method and related devices based on current waveform characteristics to solve the problem that the reliability and sensitivity of protection are reduced due to fluctuations caused by line impedance, fault location, noise and distributed capacitance current.

[0004] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a flexible straight line pilot protection method based on current waveform characteristics, comprising: Collect the fault current signal to determine whether the start criterion is met, and if so, construct a mapping interval based on the collected fault current signal; Based on the relationship between the mapping interval and the fault location, the trend characteristics of transient current during internal and external faults are characterized; Using trend characteristics and segmented data windows, calculate the current coordinate mapping interval at both ends of the fault line in each data window. ψ max and the corresponding recognition coefficient Q; Based on the current coordinate mapping interval at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the internal and external fault identification criteria and fault selection criteria to identify the fault area.

[0005] Optionally, collecting the fault current signal and determining whether the start-up criterion is met includes: When a fault occurs in the flexible DC transmission line, the current signal at the line protection installation location is collected to determine whether the startup criteria are met. The startup criteria are: (1) Where: subscript # = p, n represents the positive electrode and negative electrode respectively; Δ i Indicates the change in fault current component; k 1 is the reliability coefficient, k 1 =1.1; continuously evaluate three sampling points, and if all three points satisfy formula (1), the protection is started.

[0006] Optionally, if the condition is satisfied, constructing a mapping interval based on the collected fault current signal includes: The mapping interval is constructed based on the collected current signal, including: In current Ƚ in There is N Sampling points; ( t 0 , i 0 )and( t 1 , i 1 )yes Ƚ in Two points on; any point passing through ( t 0 , i 0 ) l 0 Its normal is expressed as: (2) In the formula, | p 0 |To indicate l 0 The distance to the origin, '|*|' is the absolute value, i 0 ∈(0,п) is l 0 The angle between the normal and the horizontal axis c 0 ; c 0 use i 0 It is expressed as: (3) by t = t 0 ,i = i 0 is a known quantity, i is the independent variable, p As the dependent variable, we get i - p Curves in coordinate systems s 0 for: (4) for( t 1 , i 1 ), any point passing through the sampling point ( t 1 , i 1 ) l 1 Its normal is expressed as: (5) by t = t 1 , i = i 1 is a known quantity, i is the independent variable, p As the dependent variable, we get i - p Curves in coordinate systems s 1 for: (6) For curves s 0 and s 1 The intersection of p 01 , i 01 ), the following relationship exists: (7) The physical meaning of formula (7) is t - i Two sampling points in coordinates ( t 0 , i 0 ),( t 1 , i 1 ) of the straight line; п / 2± i is the angle between this line and the time axis c 01 ;if c 01 ∈(0,п / 2), that is i 01 ∈(п / 2,п), then this line is in an upward trend. c 01 ∈(п / 2,п], that is i 01 ∈(0,п / 2], then this line is in a downward trend; In the fault current waveform ( t - i coordinate system), all sampling points are combined in time order; t - i In the coordinate system, we can get A straight line, that is, θ-p There is a coordinate system The denser the distribution of these intersections, the closer the waveform is to a straight line. i Divide into n The interval with the most intersections is defined as the transient current coordinate mapping interval. ψ max express; The specific calculation method of the coordinate mapping interval is: Any two sampling points in the current component waveform ( t m , i m ), ( t n , i n ) intersects at i - p The horizontal coordinate in the coordinate system i c It is expressed as: (8) Will i ∈(0, п) is divided into i - p The coordinate system is numbered 1, 2, 3... n of n interval, then i c The interval number n θc It is expressed as: (9) Where: " means rounding up; i c The interval ψθc for: (10) The remaining sampling points are calculated by equations (9) and (10) i - p The number of intervals where the horizontal coordinates of the intersection points in the coordinate system are located; calculate the number of intervals containing the most intersection points and find the corresponding intervals ψ max , ψ max That is the coordinate mapping interval of the current.

[0007] Optionally, the characterization of the trend characteristics of transient current during internal and external faults based on the relationship between the mapping interval and the fault location includes: The positive direction of the transient current component of the positive line is from the bus to the line, and the positive direction of the transient current component of the positive line is from the line to the bus; When an in-zone fault occurs, the waveform of the transient current component detected at the protection installations at both ends of the line shows an upward trend; when an out-of-zone fault occurs, the waveform of the transient current component detected at the protection installation at one end of the line shows an upward trend, and the waveform of the transient current component detected at the protection installation at the other end shows a downward trend; For intra-zone faults, the transient current components at both ends of the fault pole line are ψ max ∈(п / 2, п); when there is an out-of-zone fault, the current at one end of the fault line ψ max ∈(п / 2, п), the current at the other end ψ max ∈(0, п / 2]; Defining the recognition coefficient Q Characterization ψ max : (11).

[0008] Optionally, when a high impedance fault occurs at the end of the zone or outside the zone, a minimum range is introduced k , (п / 2-k, п / 2+k] is defined as the fuzzy interval; when a high-resistance fault occurs inside or outside the zone, the coordinate mapping interval of the transient current component waveform far away from the fault point ψ max In the fuzzy interval, the transient current component waveform near the fault point shows an upward or downward trend, and the internal and external faults are identified according to the coordinate mapping interval of the transient current component waveform near the fault point; Combined with the fuzzy interval, Q can be re-expressed as: (12).

[0009] Optionally, using trend features and segmented data windows, calculate the current coordinate mapping intervals at both ends of the fault line in each data window ψ max And the corresponding recognition coefficient Q, including: The segmented data window method is used to divide the data window into 4 segments on average, and the ψ max and the corresponding Q ; If the four-segment data window calculates Q If the results are inconsistent, it indicates that an out-of-zone fault has occurred and the fault direction is calculated by the first small time window. ψ max Decide.

[0010] Optional, based on the current at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the fault identification criteria inside and outside the area and the fault selection criteria to identify the fault area, including: The fault identification criteria are: (13) Where: subscripts B12 and B21 represent the two ends of the line respectively; #=p, n represents the positive and negative poles; The fault selection criteria are: (14).

[0011] Where: subscripts B12 and B21 represent the two ends of the line respectively; p and n represent the positive and negative poles respectively; max and ψ max correspond.

[0012] In a second aspect, the present invention provides a flexible straight line longitudinal protection system based on current waveform characteristics, comprising: A data acquisition module is used to collect fault current signals and determine whether the start-up criteria are met. If so, a mapping interval is constructed based on the collected fault current signals. A trend feature acquisition module is used to characterize the trend features of transient currents when faults occur inside and outside the fault area based on the relationship between the mapping interval and the fault location; The segmented calculation module is used to calculate the current coordinate mapping interval at both ends of the fault line in each segment data window by using trend characteristics and combining segmented data windows. ψ max and the corresponding recognition coefficient Q; Identification output module, used to map the interval based on the current coordinates at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the internal and external fault identification criteria and fault selection criteria to identify the fault area.

[0013] In a third aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the flexible straight line longitudinal protection method based on current waveform characteristics when executing the computer program.

[0014] In a fourth aspect, the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the flexible straight line longitudinal protection method based on current waveform characteristics are implemented.

[0015] Compared with the prior art, the present invention has the following technical effects: The present invention utilizes the coordinate mapping principle to convert the transient current component waveform into multiple intersecting curves in the polar coordinate system, determines the angle between the overall current waveform and the time axis according to the intersection area of ​​the curves, and then characterizes the changing trend of the current component waveform. The proposed method quantitatively describes the overall trend change of the current waveform from a macroscopic perspective, and is not affected by current fluctuations and noise. Specifically, the fault current signal is first collected to determine whether the starting criterion standard is met. If it is met, the mapping coordinates and mapping intervals are constructed based on the collected current signal; based on the relationship between the mapping interval and the fault location, the trend characteristics of the transient current during internal and external faults are characterized; a fuzzy interval is set to improve the sensitivity of the protection action during high-resistance faults; a segmented data window is proposed to overcome the problem that the coordinate mapping interval is directly calculated in the near-end and near-opposite end fault duration data window to affect the correct identification of the fault; internal and external fault identification criteria and fault selection criteria are constructed to identify the fault area.

[0016] In summary, this technical solution, by introducing the coordinate mapping interval as the key parameter for fault identification, realizes the rapid and reliable identification of faults inside and outside the zone in the flexible DC transmission system. Its technical effect is remarkable and has broad application prospects and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the logic block diagram.

[0018] Figure 2 This is the topology diagram of the four-terminal flexible DC power grid.

[0019] Figure 3 (a) and (b) are simulation results of various fault conditions.

[0020] Figure 4 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings: Example 1, please refer to Figure 4 The present invention provides a flexible straight line longitudinal protection method based on current waveform characteristics, comprising: Collect the fault current signal to determine whether the start criterion is met, and if so, construct a mapping interval based on the collected fault current signal; Based on the relationship between the mapping interval and the fault location, the trend characteristics of transient current during internal and external faults are characterized; Using trend characteristics and segmented data windows, calculate the current coordinate mapping interval at both ends of the fault line in each data window. ψ max and the corresponding recognition coefficient Q; Based on the current coordinate mapping interval at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the internal and external fault identification criteria and fault selection criteria to identify the fault area.

[0022] The present invention uses transient current coordinate mapping intervals to characterize waveform trend characteristics and constructs internal and external identification criteria. This method is insensitive to abnormal data and fluctuations of distributed capacitance current. It uses the rising and falling trends of the currents at both ends to construct the difference characteristics of internal and external faults. It does not involve the specific calculation of the current amplitude and bending characteristics, and is not affected by transition resistance in principle. It does not need to determine the set value through simulation, and does not require strict synchronization of dual-end data.

[0023] Example 2, please refer to Figure 1 The present invention provides a flexible straight line longitudinal protection method based on current waveform characteristics, which specifically includes: Step 1. Collect the fault current signal and determine whether it meets the start-up criterion. If it does, construct the mapping coordinates and mapping interval based on the collected current signal; Step 2. Based on the relationship between the mapping interval and the fault location, characterize the trend characteristics of transient current during internal and external faults; Step 3. Set the fuzzy interval to improve the sensitivity of the protection action during high resistance faults; Step 4. Propose a segmented data window to overcome the problem that the coordinate mapping interval directly calculated in the near-end and near-opposite end fault duration data windows affects the correct fault identification; Step 5. Construct the in-zone and out-zone fault identification criteria and the fault pole selection criteria to identify the fault area.

[0024] In step 1, when a fault occurs in the flexible DC transmission line, the current signal at the line protection installation location is collected to determine whether the startup criterion is met. The startup criterion is: (1) Where: subscript # = p, n represents the positive electrode and negative electrode respectively; Δ i Indicates the change in fault current component;k 1 is the reliability coefficient, k 1 =1.1; In order to ensure the anti-interference ability of the start criterion, three sampling points are evaluated continuously. If all three points satisfy formula (1), the protection is started.

[0025] In step 2, mapping coordinates and mapping intervals are constructed based on the collected current signals. By current Ƚ in For example, in Ƚ in There is N sampling points. t 0 , i 0 )and( t 1 , i 1 )yes Ƚ in Any two points on . t 0 , i 0 ) l 0 It can be expressed by its normal as: (2) In the formula, | p 0 |To indicate l 0 The distance to the origin, '|*|' is the absolute value, i 0 ∈(0,п) is l 0 The angle between the normal and the horizontal axis c 0 . at this time, c 0 Can be used i 0 It is expressed as: (3) by t = t 0 , i = i 0 is a known quantity, i is the independent variable, p As the dependent variable, we can get i - p Curves in coordinate systems s0 for: (4) for( t 1 , i 1 ), any point passing through the sampling point ( t 1 , i 1 ) l 1 can be expressed by their normals as: (5) by t = t 1 , i = i 1 is a known quantity, i is the independent variable, p As the dependent variable, we can get i - p Curves in coordinate systems s 1 for: (6) For curves s 0 and s 1 The intersection of p 01 , i 01 ), the following relationship exists: (7) The physical meaning of formula (7) is t - i Two sampling points in coordinates ( t 0 , i 0 ),( t 1 , i 1 ) line. п / 2± i is the angle between this line and the time axis c 01 .if c 01 ∈(0,п / 2), that is i 01 ∈(п / 2,п), then this line is in an upward trend. c 01 ∈(п / 2,п], that is i 01 ∈(0,п / 2], then the straight line is in a downward trend.

[0026] Through the above coordinate mapping method, in the fault current waveform ( t - i In the ti coordinate system, all sampling points are combined in time order. In the ti coordinate system, we can get A straight line, that is, θ-p There is a coordinate system The denser the distribution of these intersections, the closer the waveform is to a straight line. i Divide into n The interval with the most intersections is defined as the transient current coordinate mapping interval. ψ max express.

[0027] The specific calculation method of the coordinate mapping interval is: Any two sampling points in the current component waveform ( t m , i m ), ( t n , i n ) intersects at i - p The horizontal coordinate in the coordinate system i c It is expressed as: (8) Will i ∈(0, п) is divided into i - p The coordinate system is numbered 1, 2, 3... n of n interval, then i c The interval number n θc It can be expressed as: (9) Where: " indicates rounding up.

[0028] i c The interval ψ θc for: (10) The remaining sampling points can be calculated by equations (9) and (10). i -p The number of intervals in which the horizontal coordinates of the intersection points in the coordinate system are located. Calculate the number of intervals containing the most intersection points and find the corresponding intervals ψ max , ψ max That is the coordinate mapping interval of the current.

[0029] In step 3, based on the relationship between the mapping interval and the fault location, the trend characteristics of the transient current during the internal and external faults are characterized. Taking the occurrence of a positive grounding fault as an example, it is assumed that the positive direction of the transient current component of the positive line is from the busbar to the line. The positive direction of the transient current component of the positive line is from the line to the busbar.

[0030] When an in-zone fault occurs, the waveform of the transient current component detected at the protection installations at both ends of the line shows an upward trend. When an out-of-zone fault occurs, the waveform of the transient current component detected at the protection installation at one end of the line shows an upward trend, while the waveform of the transient current component detected at the protection installation at the other end shows a downward trend.

[0031] Therefore, for an intra-zone fault, the transient current components at both ends of the fault line are ψ max ∈(п / 2, п); when there is an out-of-zone fault, the current at one end of the fault line ψ max ∈(п / 2, п), the current at the other end ψ max ∈(0, п / 2].

[0032] Defining the recognition coefficient Q Characterization ψ max : (11) In step 4, the fuzzy interval is set to improve the sensitivity of the protection action during high-resistance faults.

[0033] When a high-resistance fault occurs at the end of the zone or outside the zone, the transient current component on the line far from the fault point changes slowly, and the overall waveform is almost parallel to the time axis. ψ max It may be near п / 2 or even in the range containing п / 2, and it is difficult to accurately distinguish the overall upward / downward trend of the current component waveform. In order to improve the accuracy of judging the current waveform trend under high-resistance faults and ensure the sensitivity of protection, the minimum range is introduced. k , providing a certain margin for protection, and defining (п / 2-k, п / 2+k] as a fuzzy interval. When a high-resistance fault occurs inside or outside the zone, the coordinate mapping interval of the transient current component waveform far from the fault point ψ maxIt may be in a fuzzy interval, but the transient current component waveform near the fault point still has an obvious upward or downward trend. Therefore, internal and external faults can be identified based on the coordinate mapping interval of the transient current component waveform near the fault point.

[0034] Combined with the fuzzy interval, Q can be re-expressed as: (12) In step 5, a segmented data window is proposed to overcome the problem that the coordinate mapping interval directly calculated in the near-end and near-opposite-end fault duration data windows affects the correct fault identification.

[0035] The proposed method uses the first trend feature of the transient current at the initial moment of the fault. When an out-of-zone fault occurs, the current rising trend measured at the remote protection installation lasts for a short time interval, and as the fault resistance increases, the time interval shortens. In order to prevent misjudgment of protection during out-of-zone high-resistance faults, the segmented data window method is used to divide the data window into 4 segments on average, and the data in each small data window is calculated separately. ψ max and the corresponding Q If the four-segment data window is calculated Q If the results are inconsistent, it indicates that an out-of-zone fault has occurred and the fault direction is calculated by the first small time window. ψ max It should be noted that after a fault occurs in the area, the current trend measured at the protection installation will remain for a period of time. t c , and the long data window protected by t c Therefore, when a fault occurs within the zone, the four time windows are calculated Q Therefore, the segmented data window does not affect the identification of faults within the area.

[0036] In step 6, the in-zone and out-zone fault identification criteria and the fault pole selection criteria are constructed to identify the fault area.

[0037] The fault identification criteria are: (13) Where: subscripts B12 and B21 represent the two ends of the line respectively; #= p , n Represents positive and negative poles.

[0038] The fault selection criteria are: (14) Where: subscripts B12 and B21 represent the two ends of the line respectively; p and n represent the positive and negative poles respectively; max and ψ max correspond.

[0039] Example 3: Create the following Figure 2 The four-terminal flexible DC grid model is shown in FIG. Among them, MMC1-MMC3 adopt fixed active power and reactive power control, and MMC4 adopts fixed DC voltage and reactive power control. Q B12p and Q B21p Calculated for line B12 and B21 Q , f 0 is a fault outside the reverse zone, f 1 is the fault in the area (line midpoint), f 2 is a fault outside the forward zone; 1), 2), 3), and 4) represent the 1st, 2nd, 3rd, and 4th data windows respectively. The fault identification results are as follows: Figure 3 And as shown in Table 1.

[0040] Table 1. Protection action performance at different fault locations

[0041] It can be seen from the simulation results that the proposed fault identification method can reliably identify faults inside and outside the zone.

[0042] Example 4: A positive ground fault is set at the midpoint of the line, and the transition resistance is 0.1Ω and 500Ω. The fault identification results are shown in Table 2.

[0043] Table 2. Fault identification results under different transition resistances

[0044] It can be seen from the simulation results that the proposed fault identification method can reliably identify the fault under 500Ω transition resistance.

[0045] In yet another embodiment of the present invention, a flexible straight line pilot protection system based on current waveform characteristics is provided, which can be used to implement the flexible straight line pilot protection method based on current waveform characteristics. Specifically, the system includes: A data acquisition module is used to collect fault current signals and determine whether the start-up criteria are met. If so, a mapping interval is constructed based on the collected fault current signals. A trend feature acquisition module is used to characterize the trend features of transient currents when faults occur inside and outside the fault area based on the relationship between the mapping interval and the fault location; The segmented calculation module is used to calculate the fault line end current ψmax and the corresponding Q in each data window by using the trend characteristics and combining the segmented data window; The identification output module is used to construct the internal and external fault identification criteria and the fault pole selection criteria based on the fault line end current ψmax and the corresponding Q to identify the fault area.

[0046] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0047] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in a computer storage medium to implement a corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a flexible straight line longitudinal protection method based on current waveform characteristics.

[0048] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the flexible straight line longitudinal protection method based on current waveform characteristics in the above embodiment.

[0049] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0050] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure one A process or multiple processes and / or boxes Figure one A device that provides the functions specified in a block or multiple blocks.

[0051] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure one A process or multiple processes and / or boxes Figure one A function specified in one or more boxes.

[0052] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure one A process or multiple processes and / or boxes Figure one The steps for the functions specified in one or more boxes.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A flexible straight line longitudinal protection method based on current waveform characteristics, characterized in that: include: Collect the fault current signal to determine whether the start criterion is met, and if so, construct a mapping interval based on the collected fault current signal; Based on the relationship between the mapping interval and the fault location, the trend characteristics of transient current during internal and external faults are characterized; Using trend characteristics and segmented data windows, calculate the current coordinate mapping interval at both ends of the fault line in each data window. ψ max and the corresponding recognition coefficient Q; Based on the current at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the internal and external fault identification criteria and fault selection criteria to identify the fault area.

2. The flexible straight line pilot protection method based on current waveform characteristics according to claim 1 is characterized in that: The collecting of the fault current signal and judging whether the starting criterion is met include: When a fault occurs in the flexible DC transmission line, the current signal at the line protection installation location is collected to determine whether the startup criteria are met. The startup criteria are: (1) Where: subscript # = p, n represents the positive electrode and negative electrode respectively; Δ i Indicates the change in fault current component; k 1 is the reliability coefficient, k 1=1.1; Continuously evaluate three sampling points. If all three points satisfy formula (1), the protection is activated.

3. The flexible straight line pilot protection method based on current waveform characteristics according to claim 2 is characterized in that: If the above conditions are met, a mapping interval is constructed based on the acquired fault current signal, including: The mapping interval is constructed based on the collected current signal, including: In current Ƚ in There is N Sampling points; ( t 0, i 0) and ( t 1, i 1) Yes Ƚ in Two points on; any point passing through ( t 0, i 0) l 0 is represented by its normal as: (2) In the formula, | p 0| indicates l The distance from 0 to the origin, '|*|' is the absolute value, θ 0∈(0,п) is l The angle between the 0 normal and the horizontal axis γ 0; γ 0 Use θ 0 is represented by: (3) by t = t 0, i = i 0 is a known quantity, θ is the independent variable, p As the dependent variable, we get θ - p Curves in coordinate systems s 0 is: (4) for( t 1, i 1), any passing through the sampling point ( t 1, i 1) Straight line l 1 is expressed using its normal as: (5) by t = t 1, i = i 1 is a known quantity, θ is the independent variable, p As the dependent variable, we get θ - p Curves in coordinate systems s 1 is: (6) For curves s 0 and s 1 intersection ( p 01 , θ 01 ), the following relationship exists: (7) The physical meaning of formula (7) is t - i Two sampling points in coordinates ( t 0, i 0),( t 1, i 1) Straight line; п / 2± θ is the angle between this line and the time axis γ 01 ;if γ 01 ∈(0,п / 2), that is θ 01 ∈(п / 2,п), then this line is in an upward trend. γ 01 ∈(п / 2,п], that is θ 01 ∈(0,п / 2], then this line is in a downward trend; In the fault current waveform ( t - i coordinate system), all sampling points are combined in time order; t - i In the coordinate system, we can get A straight line, that is, θ-p There is a coordinate system The denser the distribution of these intersections, the closer the waveform is to a straight line. θ Divide into n The interval with the most intersections is defined as the transient current coordinate mapping interval. ψ max express; The specific calculation method of the coordinate mapping interval is: Any two sampling points in the current component waveform ( t m , i m ), ( t n , i n ) intersects at θ - p The horizontal coordinate in the coordinate system θ c It is expressed as: (8) Will θ ∈(0, п) is divided into θ - p The coordinate system is numbered 1, 2, 3... n of n interval, then θ c The interval number n θc It is expressed as: (9) Where: " means rounding up; θ c The interval ψ θc for: (10) The remaining sampling points are calculated by equations (9) and (10) θ - p The number of intervals where the horizontal coordinates of the intersection points in the coordinate system are located; calculate the number of intervals containing the most intersection points and find the corresponding intervals ψ max , ψ max That is the coordinate mapping interval of the current.

4. The flexible straight line pilot protection method based on current waveform characteristics according to claim 1 is characterized in that: The trend characteristics of transient currents during internal and external faults based on the relationship between the mapping interval and the fault location are characterized, including: The positive direction of the transient current component of the positive line is from the bus to the line, and the positive direction of the transient current component of the positive line is from the line to the bus; When an in-zone fault occurs, the waveform of the transient current component detected at the protection installations at both ends of the line shows an upward trend; when an out-of-zone fault occurs, the waveform of the transient current component detected at the protection installation at one end of the line shows an upward trend, and the waveform of the transient current component detected at the protection installation at the other end shows a downward trend; For an intra-zone fault, the transient current components at both ends of the fault pole line are ψ max ∈(п / 2, п); when there is an out-of-zone fault, the current at one end of the fault line ψ max ∈(п / 2, п), the current at the other end ψ max ∈(0, п / 2]; Defining the recognition coefficient Q Characterization ψ max : (11)。 5. The flexible straight line pilot protection method based on current waveform characteristics according to claim 4 is characterized in that: When a high resistance fault occurs at the end of the zone or outside the zone, the minimum range is introduced k , (п / 2-k, п / 2+k] is defined as the fuzzy interval; when a high-resistance fault occurs inside or outside the zone, the coordinate mapping interval of the transient current component waveform far away from the fault point ψ max In the fuzzy interval, the transient current component waveform near the fault point shows an upward or downward trend, and the internal and external faults are identified according to the coordinate mapping interval of the transient current component waveform near the fault point; Combined with the fuzzy interval, Q can be re-expressed as: (12)。 6. The flexible straight line pilot protection method based on current waveform characteristics according to claim 1 is characterized in that: Using trend characteristics and segmented data windows, calculate the current coordinate mapping interval at both ends of the fault line in each data window. ψ max And the corresponding recognition coefficient Q, including: The segmented data window method is used to divide the data window into 4 segments on average, and the ψ max and the corresponding Q ; If the four-segment data window calculates Q If the results are inconsistent, it indicates that an out-of-zone fault has occurred and the fault direction is calculated by the first small time window. ψ max Decide.

7. The flexible straight line pilot protection method based on current waveform characteristics according to claim 1 is characterized in that: Based on the current coordinate mapping interval at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the fault identification criteria inside and outside the area and the fault selection criteria to identify the fault area, including: The fault identification criteria are: (13) Where: subscripts B12 and B21 represent the two ends of the line respectively; #=p, n represents the positive and negative poles; The fault selection criteria are: (14) Where: subscripts B12 and B21 represent the two ends of the line respectively; p and n represent the positive and negative poles respectively; max and ψ max correspond.

8. A flexible straight line longitudinal protection system based on current waveform characteristics, characterized in that: include: A data acquisition module is used to collect fault current signals and determine whether the start criterion is met. If so, a mapping interval is constructed based on the collected fault current signals. A trend feature acquisition module is used to characterize the trend features of transient currents during internal and external faults based on the relationship between the mapping interval and the fault location; The segmented calculation module is used to calculate the current coordinate mapping interval at both ends of the fault line in each segment data window by using trend characteristics and combining segmented data windows. ψ max and the corresponding recognition coefficient Q; Identification output module, used to map the interval based on the current coordinates at both ends of the fault line ψ max And the corresponding identification coefficient Q, construct the internal and external fault identification criteria and fault selection criteria to identify the fault area.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the flexible straight line longitudinal protection method based on current waveform characteristics as described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the flexible straight line longitudinal protection method based on current waveform characteristics as described in any one of claims 1 to 7 are implemented.

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