Flexible DC line single-ended protection method and system based on voltage first traveling wave characteristics

Abstract

The invention discloses a voltage first traveling wave characteristic-based flexible DC line single-ended protection method and system, and the method comprises the steps: collecting fault voltage and current signals, judging whether the fault voltage and current signals meet a starting criterion standard or not, and building a voltage first traveling wave mathematical model under internal and external faults based on the collected signals if the fault voltage and current signals meet the starting criterion standard; introducing a tangent envelope area ratio k into the voltage first traveling wave mathematical model to represent attenuation characteristics of the voltage first traveling wave; analyzing the relation between the tangent envelope area ratio and the transition resistance and the fault position based on the tangent envelope area ratio; and comparing the tangent envelope area ratio with a setting value, and judging internal and external faults. A voltage first traveling wave tangent envelope area ratio is adopted to represent waveform morphological characteristics, and internal and external identification criteria are constructed. The method is not influenced by transition resistance in principle, can quickly and reliably identify a fault area, has relatively high sensitivity to a high-resistance fault, and has certain noise interference resistance. The method can be used for main protection in a flexible direct-current power transmission system.

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 single-ended quantity protection method and system based on voltage first-travel wave characteristics. Background Art

[0002] High voltage direct current (HVDC) transmission systems based on modular multilevel converters (MMC) have been widely used in fields such as renewable energy integration, long-distance transmission, and cross-border power interconnection due to their advantages such as high power conversion capability, high reliability, and excellent voltage quality. However, in MMC-HVDC systems, overhead lines with a high probability of failure are usually used for power transmission. In addition, when a line fault occurs, the low damping of the DC system and the nonlinear response characteristics of the converter lead to the rapid development of the fault and the complexity of the fault characteristics. Fast and reliable protection response is a prerequisite for ensuring the safe and stable operation of the system, but it also faces huge challenges. Summary of the invention

[0003] The object of the present invention is to provide a flexible DC line single-ended quantity protection method and system based on voltage first traveling wave characteristics, so as to solve the problem that the existing single-ended quantity protection based on traveling waves is insufficiently sensitive to high-resistance faults.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a single-ended protection method for a flexible DC line based on voltage first wave characteristics, comprising:

[0006] Collect fault voltage and current signals to determine whether the start-up criteria are met. If so, a mathematical model of the voltage first wave under fault conditions inside and outside the area is established based on the collected signals;

[0007] The tangent envelope area ratio k is introduced into the mathematical model of the voltage first wave to characterize the attenuation characteristics of the voltage first wave.

[0008] Based on the tangent envelope area ratio, the relationship between the tangent envelope area ratio, transition resistance and fault location is analyzed;

[0009] Compare the tangent envelope area ratio with the set value to determine whether the fault is inside or outside the zone.

[0010] Optionally, the fault voltage and current signals are collected to determine whether the start-up criteria are met, including:

[0011] When a fault occurs in the flexible DC transmission line, the voltage signal at the line protection installation location is collected to determine whether the startup criteria are met. The startup criteria are:

[0012] Δu # =|u # (i+1)-u # (i)|>Δ set (1)

[0013] Wherein: subscript #=p, n represents the positive pole and the negative pole respectively; Δset is the start criterion threshold; the three sampling points are judged continuously, and if all three points meet the start criterion, the protection is started.

[0014] Optionally, a mathematical model of the voltage first wave under the fault inside and outside the zone is established based on the collected signal, including:

[0015] The first traveling wave is defined as the first voltage reverse traveling wave measured at the protection installation;

[0016] When an internal fault occurs, the first voltage wave detected at the protection installation location M is:

[0017] Δu f1 (s)=U f (s)T(s) (2)

[0018] Where U f (s) is the initial voltage wave generated at the fault point; T(s) is the transmission function of the voltage traveling wave on the DC line;

[0019] U f (s) is expressed as:

[0020]

[0021] Where U dc U is the DC voltage when the system is operating normally; fp and U fn are the positive and negative electrode voltages respectively; Z c0 and Z c1 are the zero mode impedance and line mode impedance of the line respectively; R f is the transition resistance; P-PTG is the positive pole grounding fault; PTP is the inter-pole fault.

[0022] The transfer function T(s) is:

[0023]

[0024] Where: e -sx / v is the transmission delay; k a is the attenuation coefficient per unit length of the line, reflecting the attenuation of the voltage traveling wave after unit transmission distance; τ a is the dispersion time constant per unit length of the line; x is the distance from the fault point to M;

[0025] Ignoring the propagation delay of the traveling wave, the time domain form of formula (2) is as follows:

[0026]

[0027] When a fault occurs outside the forward zone, the time domain expression of the first traveling wave of the voltage at point M is:

[0028] Δu f2 (t) = F -1 (u B21 (s)T(s)) (7)

[0029] in:

[0030]

[0031] Right now:

[0032]

[0033] Where l is the line length; before M detects the reflected traveling wave at the other end, the amplitude of the first traveling wave at point M is 0.

[0034] Optionally, the tangent envelope area ratio k is introduced into the voltage first wave mathematical model, including:

[0035] Construct tangents at the falling edge and the tail of the first wave, connect the intersection points O and Q of the tangents and the waveform and the intersection point Y of the two tangents, and form an envelope triangle area, which contains the steepness information of the waveform; let the area formed by the line connecting the two tangent points and the waveform be the curve enclosed area, and the curve enclosed area is contained in the envelope triangle area;

[0036] Let the area of ​​the curve enclosed region be S', and the area of ​​the enveloping triangle region be S; define the ratio of the area of ​​the curve enclosed region to the area of ​​the enveloping triangle region as the tangent envelope area ratio, denoted by k, k<1;

[0037]

[0038] Optionally, the relationship between the tangent envelope area ratio, the transition resistance and the fault location is analyzed based on the tangent envelope area ratio, including:

[0039] When there is a fault in the area, the waveform is at O(t O 、u(t O )) and Q(t Q 、u(t Q The tangent line at )) is:

[0040]

[0041] Where: k O and k Qis the slope of the two tangent lines, which can be expressed as follows:

[0042]

[0043] Where: Ts is the time interval between two adjacent sampling points;

[0044] make:

[0045]

[0046] Combining equations (8) and (9), we can obtain the intersection point Y(t k ,u k ):

[0047]

[0048] Therefore, the area S of triangle ΔOYQ is:

[0049]

[0050] Combining equation (5), we get:

[0051]

[0052] The traveling wave curve between O and Q forms an irregular polygon; suppose each vertex of this polygon has coordinates (t1, u1), (t2, u2), (t i 、u i )…(t ns 、u ns ), ns is the number of vertices. Among them, (t1, u1) corresponds to (t O 、u O ), (t ns 、u ns ) corresponds to (t Q 、u Q ); the curve trapezoid area S' is expressed as:

[0053]

[0054] Where: t ns+1 =t1,u ns+1 =u1;

[0055] Therefore, when there is a fault in the area, the expression of k is:

[0056]

[0057] At this time, the intersection point of the tangents on both sides of the voltage first wave is Y(t k ,u k )for:

[0058]

[0059] The area S of triangle ΔOYQ is:

[0060]

[0061] In summary, when a fault outside the forward zone occurs, the expression of k is:

[0062]

[0063] When a fault occurs outside the reverse zone, the first voltage wave measured by M is 0. At this time, the vertices of the polygon inside ΔOYQ are (t1, 0), (t2, 0), (t i ,0)...(t ns , 0); Substituting the coordinates of these vertices into equation (13), we get S'=0; Therefore, when a reverse zone fault occurs, it is considered that k=0;

[0064] When the traveling wave propagation distance is very short, k is close to 1; as the fault distance increases, the waveform attenuation increases and the k value decreases.

[0065] Optionally, the tangent envelope area ratio is compared with the set value to determine the fault inside or outside the zone, including:

[0066] Use the sliding data window to calculate the k value. The maximum value of k is the most curved part of the traveling wave in the data window. max To construct the fault identification criterion:

[0067]

[0068] Where: k max is the maximum value of the tangent envelope area ratio in the data window, k set is the setting threshold. O_max is the maximum value of k under metallic fault outside the positive zone, K1=1.2 is the reliability coefficient;

[0069] If the maximum value k of the tangent envelope area ratio calculated in the data window max If equation (18) is satisfied, it is identified as an internal fault; if the maximum value k of the tangent envelope area ratio calculated in the data window is max ≤k set , it is identified as an out-of-zone fault.

[0070] Optionally, use the fault pole voltage to determine the fault pole:

[0071]

[0072] The expression of W is:

[0073]

[0074] Where: Δu p，n are the positive and negative voltage components, n is the number of sampling points in the data window, W set is the threshold, which is 1.2.

[0075] In a second aspect, the present invention provides a flexible DC line single-ended quantity protection system based on voltage first wave characteristics, comprising:

[0076] The data acquisition module is used to collect fault voltage and current signals to determine whether the start-up criteria are met. If so, a mathematical model of the voltage first wave under the fault inside and outside the zone is established based on the collected signals;

[0077] A characteristic characterization module is used to introduce the tangent envelope area ratio k into the mathematical model of the voltage first wave to characterize the attenuation characteristics of the voltage first wave;

[0078] A position relationship determination module, used for analyzing the relationship between the tangent envelope area ratio, the transition resistance and the fault position based on the tangent envelope area ratio;

[0079] The comparison output module is used to compare the tangent envelope area ratio with the set value to determine the fault inside or outside the zone.

[0080] 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 when the processor executes the computer program, the processor implements the steps of a single-ended protection method for a flexible DC line based on the characteristics of a first-wave voltage wave.

[0081] In a fourth aspect, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of a single-ended protection method for a flexible DC line based on voltage first wave characteristics.

[0082] Compared with the prior art, the present invention has the following technical effects:

[0083] The present invention uses the voltage first wave tangent envelope area ratio to characterize the waveform morphology characteristics and constructs the identification criteria for inside and outside the zone. In principle, this method is not affected by the transition resistance, can quickly and reliably identify the fault area, has a strong sensitivity to high-resistance faults, and has a certain ability to resist noise interference. It can be used for main protection in flexible direct current transmission systems. Specifically, the fault voltage and current signals are first collected to determine whether the start-up criterion standard is met. If it is met, proceed to the next step; establish a mathematical model of the voltage first wave under inside and outside faults, introduce the tangent envelope area ratio k to characterize the attenuation characteristics of the voltage first wave, derive the expression of the tangent envelope area ratio, and analyze the relationship between the tangent envelope area ratio and the transition resistance and fault location; finally, compare the tangent envelope area ratio with the set value to determine the inside and outside faults.

[0084] The system first collects the voltage and current signals in real time when the fault occurs.

[0085] Through the preset startup criteria, it is possible to quickly determine whether further fault analysis is necessary. This can effectively reduce unnecessary calculation and analysis time and improve system response speed.

[0086] According to the characteristics of the faults inside and outside the area, a mathematical model of the voltage first wave is established. This model can accurately reflect the changing law of the voltage first wave when a fault occurs.

[0087] The tangent envelope area ratio k is introduced as a characteristic parameter to quantitatively describe the attenuation characteristics of the first voltage wave. This parameter is selected based on its sensitivity and effectiveness in fault area identification.

[0088] The expression of tangent envelope area ratio is derived, and its relationship with transition resistance and fault location is deeply analyzed. This step is the key to determine whether tangent envelope area ratio can be used as an effective criterion.

[0089] Through theoretical analysis and simulation experiments, the stability and reliability of the tangent envelope area ratio under different fault conditions are verified.

[0090] Compare the calculated tangent envelope area ratio with the preset setting value. Based on the comparison result, determine whether the fault occurs inside or outside the protection zone.

[0091] This method is not affected by transition resistance, can quickly and reliably identify the fault area, and has a strong sensitivity to high-resistance faults.

[0092] In summary, this technical solution, by introducing the tangent envelope area ratio as a key parameter for fault identification, achieves 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

[0093] Figure 1 This is the logic block diagram.

[0094] Figure 2 This is the topology diagram of the four-terminal flexible DC power grid.

[0095] Figure 3 Simulation results for various fault conditions.

[0096] Figure 4 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0097] The present invention is further described below in conjunction with the accompanying drawings:

[0098] Example 1, please refer to Figure 4 , a single-ended protection method for flexible DC transmission lines based on the characteristics of the voltage first wave includes:

[0099] Collect fault voltage and current signals to determine whether the start-up criteria are met. If so, a mathematical model of the voltage first wave under fault conditions inside and outside the area is established based on the collected signals;

[0100] The tangent envelope area ratio k is introduced into the mathematical model of the voltage first wave to characterize the attenuation characteristics of the voltage first wave.

[0101] Based on the tangent envelope area ratio, the relationship between the tangent envelope area ratio, transition resistance and fault location is analyzed;

[0102] Compare the tangent envelope area ratio with the set value to determine whether the fault is inside or outside the zone.

[0103] The present invention uses the envelope area ratio of the tangent line of the first wave of voltage to characterize the waveform morphology characteristics and construct the identification criteria for the inside and outside of the area. In principle, this method is not affected by the transition resistance, can quickly and reliably identify the fault area, has a strong sensitivity to high-resistance faults, and has a certain ability to resist noise interference. It can be used for main protection in the flexible DC transmission system.

[0104] Example 2, please refer to Figure 1 First, the fault voltage and current signals are collected to determine whether they meet the start-up criteria. If they do, proceed to the next step. A mathematical model of the first wave of voltage under internal and external faults is established. The tangent envelope area ratio k is introduced to characterize the attenuation characteristics of the first wave of voltage. The expression of the tangent envelope area ratio is derived, and the relationship between the tangent envelope area ratio, the transition resistance and the fault position is analyzed. Finally, the tangent envelope area ratio is compared with the setting value to determine the internal and external faults.

[0105] A single-ended protection method for a flexible DC line based on the first-travel wave characteristics of a fault voltage, the specific steps are as follows:

[0106] Step 1. Collect fault voltage and current signals to determine whether the start-up criteria are met. If so, proceed to the next step;

[0107] Step 2. Establish a mathematical model of the voltage first wave under internal and external faults;

[0108] Step 3. Introduce the tangent envelope area ratio k to characterize the attenuation characteristics of the first voltage wave;

[0109] Step 4. Derive the expression of tangent envelope area ratio and analyze the relationship between tangent envelope area ratio, transition resistance and fault location;

[0110] Step 5. Compare the tangent envelope area ratio with the set value to determine whether the fault is inside or outside the zone.

[0111] In step 1, when a fault occurs in the flexible DC transmission line, the voltage signal at the line protection installation is collected to determine whether the startup criteria are met. The startup criteria are:

[0112] Δu # =|u # (i+1)-u # (i)|>Δ se t (1)

[0113] Where: subscript # = p, n represents the positive electrode and negative electrode respectively; Δ set is the start criterion threshold.

[0114] In order to ensure the anti-interference ability of the start-up criterion, the three sampling points are judged continuously. If all three points meet (1), the protection is started.

[0115] In step 2, a mathematical model of the first voltage wave under faults inside and outside the zone is established, where the first voltage wave is defined as the first voltage reverse wave measured at the protection installation.

[0116] When an internal fault occurs, the first voltage wave detected at the protection installation location M is:

[0117] Δu f1 (s)=U f (s)T(s) (2)

[0118] Where U f (s) is the initial voltage wave generated at the fault point; T(s) is the transmission function of the voltage traveling wave on the DC line.

[0119] U f (s) can be expressed as:

[0120]

[0121]

[0122] Where U dc Uf is the DC voltage when the system is operating normally; p and U fn are the positive and negative electrode voltages respectively; Z c0 and Z c1 are the zero mode impedance and line mode impedance of the line respectively; R f is the transition resistance; P-PTG is the positive pole grounding fault; PTP is the inter-pole fault.

[0123] The transfer function T(s) is:

[0124]

[0125] Where: e -sx / v is the transmission delay; k a is the attenuation coefficient per unit length of the line, reflecting the attenuation of the voltage traveling wave after unit transmission distance; τ a is the dispersion time constant per unit length of the line; x is the distance from the fault point to M.

[0126] Ignoring the propagation delay of the traveling wave, the time domain form of (2) can be expressed as follows:

[0127]

[0128] When a fault occurs outside the forward zone, the time domain expression of the first traveling wave of the voltage at point M is:

[0129] Δu f2 (t) = F -1 (u B21 (s) T(s)) (7)

[0130] in:

[0131]

[0132] Right now:

[0133]

[0134] Where l is the line length.

[0135] When a fault occurs outside the reverse zone, the voltage reverse wave (first wave) detected at point M for the first time is generated by the impedance discontinuity point at the end of the line. Therefore, before M detects the reflected wave at the opposite end, the amplitude of the first wave at point M is 0.

[0136] In step 3, the tangent envelope area ratio k is introduced to characterize the attenuation characteristics of the first voltage wave. The specific steps are:

[0137] Tangents are constructed at the falling edge and the tail of the first wave, and the intersection points O and Q of the tangents and the waveform are connected, as well as the intersection point Y of the two tangents to form an envelope triangle area, which contains the steepness information of the waveform. Let the area formed by the line connecting the two tangent points and the waveform be the curve enclosed area, and the curve enclosed area is contained in the envelope triangle area.

[0138] Let the area of ​​the region enclosed by the curve be S', and the area of ​​the enveloping triangle be S. Define the ratio of the area of ​​the region enclosed by the curve to the area of ​​the enveloping triangle to be the tangent envelope area ratio, denoted by k, where k<1.

[0139]

[0140] In step 4, the expression of the tangent envelope area ratio is derived, and the relationship between the tangent envelope area ratio, the transition resistance and the fault location is analyzed. The specific steps are:

[0141] When there is a fault in the area, the waveform is at O(t O 、u(t O )) and Q(t Q 、u(t Q The tangent line at )) is:

[0142]

[0143] Where: k O and k Q is the slope of the two tangent lines, which can be expressed as follows:

[0144]

[0145] Where: T s is the time interval between two adjacent sampling points.

[0146] make:

[0147]

[0148] Combining equations (8) and (9), we can get the intersection point Y(t k ,u k ):

[0149]

[0150] Therefore, the area S of triangle ΔOYQ is:

[0151]

[0152] Combining equation (5), we get:

[0153]

[0154] The traveling wave curve between O and Q forms an irregular polygon. Assume that each vertex of this polygon has coordinates (t1, u1), (t2, u2), (t i 、u i )…(t ns 、u ns ), ns is the number of vertices. Among them, (t1, u1) corresponds to (t O 、u O ), (t ns 、u ns ) corresponds to (t Q 、u Q ). The curve trapezoid area S' can be expressed as:

[0155]

[0156] Where: t ns+1 =t1,u ns+1 =u1.

[0157] Therefore, when there is a fault in the area, the expression of k is:

[0158]

[0159] When a fault occurs in the forward zone, the structure of the time domain expression of the voltage first wave is similar. Therefore, the derivation process of k is also similar. At this time, the intersection point Y(t k ,u k )for:

[0160]

[0161] The area S of triangle ΔOYQ is:

[0162]

[0163] In summary, when a fault outside the forward zone occurs, the expression of k is:

[0164]

[0165] When a fault occurs outside the reverse zone, the first voltage wave measured by M is 0. At this time, the vertices of the polygon inside ΔOYQ are (t1, 0), (t2, 0), (t i ,0)...(t ns , 0). Substituting the coordinates of these vertices into equation (13), we get S' = 0. Therefore, when a reverse out-of-zone fault occurs, it is considered that k = 0.

[0166] In summary, the distortion degree of the first traveling wave of the voltage is closely related to the fault location. When the traveling wave propagation distance is very short, the area enclosed by the curve is relatively large, and k is close to 1. As the fault distance increases, the waveform attenuation increases and the k value decreases. And from equations (18) and (21), it can be seen that the expression of k does not contain the transition resistance term and is only related to the fault location. In theory, the use of the tangent envelope area ratio k to identify the internal and external faults has a strong robustness to the transition resistance.

[0167] In step 5, the tangent envelope area ratio is compared with the set value to determine whether the fault is inside or outside the zone.

[0168] The specific steps are:

[0169] The k value is calculated using a sliding data window. The maximum value of k is the most curved part of the traveling wave in the data window. max To construct the fault identification criterion:

[0170]

[0171] Where: k max is the maximum value of the tangent envelope area ratio in the data window, k set is the setting threshold. kO_max is the maximum value of k under metallic fault outside the positive zone. K1=1.2 is the reliability coefficient.

[0172] If the maximum value k of the tangent envelope area ratio calculated in the data window max If equation (18) is satisfied, it is identified as an internal fault; if the maximum value k of the tangent envelope area ratio calculated in the data window is max ≤k set , it is identified as an out-of-zone fault.

[0173] In step 6, the fault pole is determined using the fault pole voltage.

[0174] Use the fault pole voltage to determine the fault pole:

[0175]

[0176] The expression of W is:

[0177]

[0178] Where: Δup, n is the positive and negative voltage components, n is the number of sampling points in the data window, W set is the threshold, which is 1.2.

[0179] Example 3: Create the following Figure 2The ±520kV four-terminal flexible DC grid model is shown in Figure 1. Among them, MMC1-MMC3 adopts fixed active power and reactive power control, and MMC4 adopts fixed DC voltage and reactive power control. f0, f1 and f2 represent reverse out-of-zone fault, in-zone fault and forward out-of-zone fault respectively. The specific parameters of the system are shown in Table 1. The DC line adopts a frequency-variable parameter model, the line length is 400km, and Ldc is 150mH. The protection sampling frequency is 50kHz.

[0180] Positive grounding faults are set at different positions of f0, f1 and f2 respectively, and the transition resistance is 0.1Ω, 200Ω, 400Ω and 600Ω to verify the proposed protection performance. The simulation results of various fault conditions are shown in the attached figure. Figure 3 The protection action is shown in Table 1. In the table, f1_200km and f1_400km represent faults at the midpoint and end of Line 1, respectively.

[0181]

[0182] It can be seen from Table 1 that the proposed protection method can correctly distinguish between internal and external faults and has good performance in resisting transition resistance.

[0183] Example 4: Create the following Figure 2 The ±520kV four-terminal flexible HVDC transmission system model is shown in Figure 2. 30dB Gaussian white noise is added to the sampled signal to verify the impact of noise interference on the proposed protection scheme. The simulation results are shown in Table 2.

[0184] Table 2. Protection action results under 30dB noise interference

[0185]

[0186] The simulation results show that the addition of noise does have an impact on the waveform and the tangent envelope area ratio. The envelope triangle is determined by 5 sampling points, and the sliding window algorithm is used to calculate kmax, which reduces the interference of noise to a certain extent. In summary, the proposed protection can reliably identify faults inside and outside the zone under 30dB noise interference.

[0187] In another embodiment of the present invention, a flexible DC line single-ended quantity protection system based on voltage first wave characteristics is provided, which can be used to implement the above-mentioned flexible DC line single-ended quantity protection method based on voltage first wave characteristics. Specifically, the system includes:

[0188] The data acquisition module is used to collect fault voltage and current signals to determine whether the start-up criteria are met. If so, a mathematical model of the voltage first wave under the fault inside and outside the zone is established based on the collected signals;

[0189] A characteristic characterization module is used to introduce the tangent envelope area ratio k into the mathematical model of the voltage first wave to characterize the attenuation characteristics of the voltage first wave;

[0190] A position relationship determination module, used for analyzing the relationship between the tangent envelope area ratio, the transition resistance and the fault position based on the tangent envelope area ratio;

[0191] The comparison output module is used to compare the tangent envelope area ratio with the set value to determine the fault inside or outside the zone.

[0192] 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.

[0193] 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., which are the computing core and control core of the terminal, and are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in a computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a single-ended quantity protection method for a flexible DC line based on the voltage first wave characteristic.

[0194] 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 the built-in storage medium in the computer device and the extended storage medium 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 single-ended quantity protection method for flexible DC lines based on the voltage first wave characteristics in the above embodiment.

[0195] Those skilled in the art will appreciate 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. Moreover, 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.

[0196] 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 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0197] 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 1A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0198] 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. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0199] 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 single-ended protection method for flexible DC lines based on the characteristics of the voltage first wave, characterized in that: include: Collect fault voltage and current signals to determine whether the start-up criteria are met. If so, a mathematical model of the voltage first wave under fault conditions inside and outside the area is established based on the collected signals; The tangent envelope area ratio k is introduced into the mathematical model of the voltage first wave to characterize the attenuation characteristics of the voltage first wave. Based on the tangent envelope area ratio, the relationship between the tangent envelope area ratio, transition resistance and fault location is analyzed; Compare the tangent envelope area ratio with the set value to determine whether the fault is inside or outside the zone.

2. The single-ended protection method for flexible DC line based on voltage first wave characteristics according to claim 1 is characterized in that: Collect fault voltage and current signals to determine whether the start criteria are met, including: When a fault occurs in the flexible DC transmission line, the voltage signal at the line protection installation location is collected to determine whether the startup criteria are met. The startup criteria are: Δu # =|u # (i+1)-u # (i)|>Δ set (1) Wherein: subscript #=p, n represents the positive pole and the negative pole respectively; Δset is the start criterion threshold; the three sampling points are judged continuously, and if all three points meet the start criterion, the protection is started.

3. The single-ended protection method for flexible DC line based on voltage first wave characteristics according to claim 1 is characterized in that: Based on the collected signals, a mathematical model of the voltage first wave under fault conditions inside and outside the area is established, including: The first traveling wave is defined as the first voltage reverse traveling wave measured at the protection installation; When an internal fault occurs, the first voltage wave detected at the protection installation location M is: Δu f1 (s)=U f (s)T(s) (2) Where U f (s) is the initial voltage wave generated at the fault point; T(s) is the transmission function of the voltage traveling wave on the DC line; U f (s) is expressed as: Where U dc U is the DC voltage when the system is operating normally; fp and U fn are the positive and negative electrode voltages respectively; Z c0 and Z c1 are the zero mode impedance and line mode impedance of the line respectively; R f is the transition resistance; P-PTG is the positive grounding fault; PTP is the inter-pole fault; The transfer function T(s) is: Where: e -sx / v is the transmission delay; k a is the attenuation coefficient per unit length of the line, reflecting the attenuation of the voltage traveling wave after unit transmission distance; τ a is the dispersion time constant per unit length of the line; x is the distance from the fault point to M; Ignoring the propagation delay of the traveling wave, the time domain form of formula (2) is as follows: When a fault occurs outside the forward zone, the time domain expression of the first traveling wave of the voltage at point M is: Δu f2 (t)=F -1 (u B21 (s)T(s)) (7) in: Right now: Where l is the line length; before M detects the reflected traveling wave at the other end, the amplitude of the first traveling wave at point M is 0.

4. The single-ended protection method for flexible DC line based on voltage first wave characteristics according to claim 1 is characterized in that: The tangent envelope area ratio k is introduced into the mathematical model of the voltage first wave, including: Construct tangents at the falling edge and the tail of the first wave, connect the intersection points O and Q of the tangents and the waveform and the intersection point Y of the two tangents, and form an envelope triangle area, which contains the steepness information of the waveform; let the area formed by the line connecting the two tangent points and the waveform be the curve enclosed area, and the curve enclosed area is contained in the envelope triangle area; Let the area of ​​the curve enclosed region be S', and the area of ​​the enveloping triangle region be S; define the ratio of the area of ​​the curve enclosed region to the area of ​​the enveloping triangle region as the tangent envelope area ratio, denoted by k, k<1; 5. The single-ended protection method for flexible DC line based on voltage first wave characteristics according to claim 1 is characterized in that: The relationship between the tangent envelope area ratio, transition resistance and fault location is analyzed based on the tangent envelope area ratio, including: When there is a fault in the area, the waveform is at O(t O 、u(t O )) and Q(t Q 、u(t Q The tangent line at )) is: Where: k O and k Q is the slope of the two tangent lines, which can be expressed as: Where: Ts is the time interval between two adjacent sampling points; make: Combining equations (8) and (9), we can obtain the intersection point Y(t k ,u k ): Therefore, the area S of triangle ΔOYQ is: Combining equation (5), we get: The traveling wave curve between O and Q forms an irregular polygon; suppose each vertex of this polygon has coordinates (t1, u1), (t2, u2), (t i 、u i )…(t ns 、u ns ), ns is the number of vertices; where (t1, u1) corresponds to (t O 、u O ), (t ns 、u ns ) corresponds to (t Q 、u Q ); the curve trapezoid area S' is expressed as: Where: t ns+1 =t1,u ns+1 =u1; Therefore, when there is an internal fault, the expression of the tangent envelope area ratio k is: At this time, the intersection point of the tangents on both sides of the voltage first wave is Y(t k ,u k )for: The area S of triangle ΔOYQ is: In summary, when a fault outside the forward zone occurs, the expression of k is: When a fault occurs outside the reverse zone, the first voltage wave measured by M is 0. At this time, the vertices of the polygon inside ΔOYQ are (t1, 0), (t2, 0), (t i ,0)...(t ns , 0); Substituting the coordinates of these vertices into equation (13), we get S'=0; Therefore, when a reverse zone fault occurs, it is considered that k=0; When the traveling wave propagation distance is very short, k is close to 1; as the fault distance increases, the waveform attenuation increases and the k value decreases.

6. The single-ended protection method for flexible DC line based on voltage first wave characteristics according to claim 1 is characterized in that: Compare the tangent envelope area ratio with the setting value to determine the fault inside and outside the zone, including: Use the sliding data window to calculate the k value. The maximum value of k is the most curved part of the traveling wave in the data window. max To construct the fault identification criterion: Where: k max is the maximum value of the tangent envelope area ratio in the data window, k set is the setting threshold; k O_max is the maximum value of k under metallic fault outside the positive zone, K1=1.2 is the reliability coefficient; If the maximum value k of the tangent envelope area ratio calculated in the data window max If equation (18) is satisfied, it is identified as an internal fault; if the maximum value k of the tangent envelope area ratio calculated in the data window is max ≤k set , it is identified as an out-of-zone fault.

7. The single-ended protection method for flexible DC line based on voltage first wave characteristics according to claim 6 is characterized in that: Use the fault pole voltage to determine the fault pole: The expression of W is: Where: Δu p，n are the positive and negative voltage components, n is the number of sampling points in the data window, W set is the threshold, which is 1.

2.

8. A single-ended protection system for flexible DC lines based on the characteristics of the voltage first wave, characterized in that: include: The data acquisition module is used to collect fault voltage and current signals to determine whether the start-up criteria are met. If so, a mathematical model of the voltage first wave under the fault inside and outside the zone is established based on the collected signals; A characteristic characterization module is used to introduce the tangent envelope area ratio k into the mathematical model of the voltage first wave to characterize the attenuation characteristics of the voltage first wave; A position relationship determination module, used for analyzing the relationship between the tangent envelope area ratio, the transition resistance and the fault position based on the tangent envelope area ratio; The comparison output module is used to compare the tangent envelope area ratio with the set value to determine the fault inside or outside the zone.

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 DC line single-ended protection method based on the voltage first wave characteristic as claimed 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 DC line single-ended protection method based on the voltage first wave characteristic as claimed in any one of claims 1 to 7 are implemented.

Images