A flexible direct current power grid line fault resistance estimation method, device and storage medium

Abstract

The application discloses a flexible direct-current power grid line fault resistance estimation method and device and a storage medium, wherein the method comprises the following steps: establishing and utilizing a quantitative relation model of a sudden amplitude ratio of two initial fault traveling waves and a fault resistance, and combining different fault types, fault positions and propagation distance correction factors, so that fault resistance estimation can be completed only by using single-end measurement data at a protection installation position. The application solves the problems that an existing non-unit protection method for the flexible direct-current power grid cannot adapt to different transition resistance fault conditions due to the use of a fixed threshold value, and the sensitivity of the protection is insufficient when a high transition resistance fault occurs, and the reliability is reduced when an out-of-area fault or noise interference occurs.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power system relay protection, and particularly relates to a flexible DC power grid line fault resistance estimation method, device and storage medium. BACKGROUND

[0002] Modular multilevel converter (MMC) based flexible DC transmission technology has been widely recognized as one of the key technologies for building future new power systems due to its outstanding advantages in renewable energy grid connection, asynchronous interconnection of power grids, etc. This technology can realize smooth access and efficient long-distance transmission of large-scale new energy, effectively solving the technical bottlenecks of traditional AC transmission in specific application scenarios. However, the problem of fast and reliable isolation of DC line faults has always been the main challenge restricting the development of this technology. Since the DC system has small natural damping after DC side fault, the fault current has a very high rise rate, which can reach a dangerous level within a few milliseconds. Combined with the weak overcurrent capability of power electronic switching devices, this poses extremely stringent requirements on the action speed of the main protection system, which usually needs to complete fault detection and judgment within 1-2 milliseconds.

[0003] Currently, the non-unit protection scheme based on the protection boundary composed of fault current limiting reactors (CLR) is mainly used in flexible DC power grid engineering practice as the main protection. The theoretical basis of this protection method is to use the blocking or attenuation characteristics of the boundary element to the fault high-frequency transient signal to realize the discrimination of the fault section. Specifically, the existing technology can be mainly divided into the following categories: first, the protection method based on the change rate of fault electrical quantity, such as line side voltage change rate du / dt, reactor voltage change rate, etc.; second, the method based on the characteristics of transient high-frequency components, including the voltage modulus maximum value extracted by wavelet transform, the transient energy function constructed, etc. In addition, in order to accurately identify the fault line and healthy line connected to the same DC bus, the academic circle has also proposed a variety of direction discrimination principles, such as the initial traveling wave polarity comparison of CLR voltage, the forward and reverse traveling wave amplitude ratio, the time difference of line mode and zero mode components, etc.

[0004] However, through in-depth analysis and engineering practice test, the above prior art exposes obvious limitations. First, the existing non-unit protection method generally uses a fixed action threshold. This setting method is difficult to adapt to complex and variable actual operating conditions. When the system operating mode changes or the fault condition changes greatly, the fixed threshold setting faces the contradiction between reliability and sensitivity: when a large transition resistance short circuit occurs, the fault electrical quantity change characteristics are not obvious, and the protection is easy to refuse to act due to the failure to reach the action threshold; and under the condition of external fault or electromagnetic interference, the protection may be misoperated due to the transient quantity exceeding the fixed value. Second, the self-adaptive ability of the existing method is seriously insufficient, and the protection performance depends on the stability of the boundary element parameters to a great extent, and the real state information of the fault point cannot be accurately obtained, especially the effective perception of the fault transition resistance, which makes it difficult for the protection system to dynamically adjust the protection characteristics according to the specific fault condition.

[0005] It is particularly pointed out that the accurate estimation of the fault transition resistance has always been a technical difficulty in the industry. The size of the transition resistance directly determines the strength of the fault transient characteristics and the signal amplitude detected by the protection, and is a key parameter affecting the protection performance. The existing resistance estimation methods have obvious defects: the estimation method based on the parameter model is extremely sensitive to the accuracy of the line parameters, and the line parameters in the actual engineering will change with factors such as environmental temperature and laying method; the method based on double-end electrical quantity depends on reliable communication channels, which not only increases the system complexity and cost, but also the communication delay may affect the speed of the protection; some methods have high computational complexity, which is difficult to meet the real-time requirements of the main protection. These limitations seriously restrict the development of adaptive protection technology. SUMMARY

[0006] The purpose of the present application is to provide a flexible DC power grid line fault resistance estimation method, which can only use single-end electrical quantity to quickly and accurately estimate the transition resistance of the fault line, thereby providing a basis for adaptive protection, and aims to solve the core problem of poor adaptability of the fixed threshold protection scheme under complex fault conditions. Another purpose of the present application is to provide an electronic device and a computer readable storage medium for implementing the above flexible DC power grid line fault resistance estimation method.

[0007] Technical scheme: The flexible DC power grid line fault resistance estimation method comprises:

[0008] A quantitative relationship model of the sudden amplitude ratio of the initial two fault traveling waves and the fault resistance is established, and the quantitative relationship model includes a propagation distance correction factor for correcting the influence of the fault distance;

[0009] Based on the quantitative relationship model between the abrupt change amplitude ratio of the initial two fault traveling waves and the fault resistance, and combined with different fault types, fault locations, and the propagation distance correction factor, an estimated value of the transition resistance is obtained.

[0010] Optionally, the fault location is determined based on the first and second modulus maxima of the fault traveling wave characteristics. , amplitude ratio The determination is made using the following formula:

[0011]

[0012] in, It is the voltage surge amplitude caused when the initial traveling wave generated by the fault reaches the measurement point at the protection installation location; It is the voltage surge amplitude caused by the second traveling wave, generated after the initial traveling wave is reflected or refracted between the fault point and the protection installation point, when it reaches the measurement point;

[0013] like If so, it is determined to be a near-end fault. If so, it is determined to be a remote fault.

[0014] Optionally, the fault traveling wave features are extracted using a multi-resolution morphological filtering algorithm.

[0015] Preferably, the fault traveling wave characteristics are obtained specifically according to the following steps:

[0016] The positive and negative voltages of the line are measured, and the steady-state component is subtracted to obtain the fault component. Then, pole-mode decoupling is performed to obtain the line-mode and zero-mode fault voltage traveling waves. and ;

[0017] Define the structural elements and their lengths and values, including any line-mode fault voltage signals. Perform fault signal Operation, from Find the maximum point in the filtered signal and set the threshold amplitude of the maximum point to be [value missing]. The first and second modulo maxima are obtained. , and the corresponding time and .

[0018] Furthermore, the aforementioned The operation includes:

[0019] Initialize the parameters of the structuring element SE, including the number of multi-resolution analysis layers. and base length Initial value an effective length of the initial structuring element ;

[0020] according to the number of the multi-resolution analysis layers and a base length , an effective length of the structuring element at a current resolution is calculated ;

[0021] based on the effective length , a stack of complementary flat structuring element sequences is constructed, respectively a forward structuring element and a reverse structuring element , wherein, is a position index within the structuring element; and the initial values are both ;

[0022] traversing each data point of the wired-mode fault voltage signal, for each current point , the following operations are performed:

[0023] using the forward structuring element , mathematical morphological dilation and erosion operations are performed within a neighborhood of the current point , respectively obtaining a forward dilation result and a forward erosion result ;

[0024] using the reverse structuring element , mathematical morphological dilation and erosion operations are performed within a neighborhood of the current point , respectively obtaining a reverse dilation result and a reverse erosion result ;

[0025] according to the forward dilation result, the forward erosion result, the reverse dilation result, and the reverse erosion result, a filtered output value of the current point is calculated .

[0026] Optionally, the fault type includes at least one of the following: single-pole ground fault, double-pole ground fault.

[0027] Optionally, the quantitative relationship model between the mutation amplitude ratio of the initial two fault traveling waves and the fault resistance includes at least one of the following:

[0028] (1) if the fault type is a single-pole ground fault, and the amplitude ratio of the first and second modulus maximum values of the fault traveling wave characteristics ;

[0029] then the fault distance , The total length of the line; For near-end protection, based on the traveling wave propagation network diagram, the second reflected wave... It will be earlier than the first refracted wave. Passed to Therefore, the ratio of the abrupt change amplitudes of the initial two fault traveling waves is:

[0030]

[0031] in, The distance from the fault point to the protection installation location; For line mode wave impedance, Zero-mode impedance; line port reflection coefficient With transition resistance It is irrelevant, and the arrival time of the traveling wave is close to 1, that is... ; and Let these be the initial linear mode fault component and the zero mode fault component at the fault location, respectively. The coefficients for the zero-mode component reflected as the linear mode component at the fault location; and These represent the effects of attenuation, distortion, and delay in traveling wave propagation, respectively. The difference between the two also represents the effect of the time difference between the arrival of the linear mode and zero-mode components, both of which are related to the fault distance. Yes, it's related, using the propagation distance correction factor. To quantify the magnitude of this impact;

[0032] Then the transition resistor Represented as:

[0033]

[0034] Wherein, the fault distance at this time is , The propagation speed of the linear mode fault component is a rough estimate, slightly lower than the speed of light;

[0035] (2) If the fault type is a single-pole ground fault, and the amplitude ratio of the first and second modulus maxima of the fault traveling wave characteristics is... ;

[0036] Then the fault distance ; For remote protection, the second reflected wave at this time It will be later than the first refracted wave. Passed to Therefore, the ratio of the abrupt change amplitudes of the initial two fault traveling waves is:

[0037]

[0038] wherein, represents the traveling wave transmission attenuation distortion delay impact of the distance from the line mode component, fault distance will affect the ratio , using the propagation distance correction factor to quantify the size of this impact; represents the refractive index of the line mode component at the fault point position;

[0039] then the transition resistance is represented as:

[0040]

[0041] wherein, at this time, the fault distance is ;

[0042] (3) If the fault type is a bipolar short circuit fault, and the amplitude ratio of the first and second modal maxima of the fault traveling wave feature ;

[0043] then the fault distance , is the near-end protection, according to the network diagram of the traveling wave transmission, at this time, the second reflected wave will be earlier than the first refracted wave transmission to , therefore the abrupt amplitude ratio of the initial two fault traveling waves is:

[0044]

[0045] wherein, is the reflection coefficient of the fault point when the fault is a bipolar short circuit fault, the line port reflection coefficient is independent of the transition resistance , and is close to 1, therefore ; attenuation distortion and fault distance have a relationship, using the propagation distance correction factor to quantify the size of this impact;

[0046] then the transition resistance is represented as:

[0047]

[0048] wherein, at this time, the fault distance is ;

[0049] (4) If the fault type is a bipolar ground fault, and the amplitude ratio of the first and second modal maxima of the fault traveling wave feature ;

[0050] then the fault distance ; for remote protection, the second reflected wave will be later than the first refracted wave transmitted to , therefore the amplitude ratio of the initial two fault traveling waves is:

[0051]

[0052] where, the attenuation distortion has a relationship with the fault distance , and a propagation distance correction factor is used to quantify the size of this effect;

[0053] then the transition resistance is expressed as:

[0054]

[0055] where, the fault distance at this time.

[0056] Optionally, the propagation distance correction factor is obtained by:

[0057] In different cases, the fault and the corresponding transition resistance at two different positions are obtained respectively, and the curve of the change of the propagation distance correction factor with the fault distance is linearly fitted. The different cases include different fault types and fault positions.

[0058] The electronic device includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and the processor implements part or all of the steps of the flexible DC power grid line fault resistance estimation method when executing the program.

[0059] The computer readable storage medium has a computer program stored thereon, and the computer program is executed by the processor to implement part or all of the steps of the flexible DC power grid line fault resistance estimation method.

[0060] Advantages: Compared with the prior art, the present application has the following obvious advantages:

[0061] 1. Single-ended estimation, fast and economical: The present application innovatively deduces and utilizes the quantitative relationship between the amplitude ratio of the fault initial traveling wave and the second traveling wave and the fault resistance, and only single-ended measurement data at the protection installation place is needed to complete the calculation. This eliminates the dependence on the communication system, not only reduces the system complexity and cost, but more importantly avoids communication delay, so that the resistance estimation can meet the stringent requirements of the main protection on the action speed (1-2 milliseconds).

[0062] 2. High precision and strong adaptability: The application effectively overcomes the influence of line parameter uncertainty and traveling wave attenuation distortion on estimation precision by introducing a propagation distance correction factor, thereby improving the adaptability and robustness of the method.

[0063] 3. Basis of adaptive protection: The core of the application is to provide accurate resistance information for adaptive protection. The technical solution thereof establishes precise mathematical relationship formulas for calculating transition resistance for four typical cases by first identifying fault types (single pole / double pole) and judging fault intervals (near end / far end). This refined modeling enables the protection system to dynamically adjust its operating characteristics according to the real-time estimated resistance value, thereby balancing sensitivity and reliability under various fault conditions.

[0064] 4. Strong anti-interference capability: The application uses a multi-resolution morphological filtering algorithm to process the fault voltage signal, which has the advantages of high computational efficiency and strong pulse noise suppression capability, and can quickly and accurately extract the amplitude, polarity and arrival time of the initial traveling wave modulus maximum from the noisy signal. This feature extraction method provides a reliable data foundation for subsequent accurate fault interval judgment and resistance calculation, ensuring the practicality and reliability of the entire method in complex electromagnetic environments. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 is a structural schematic diagram of a four-terminal ring-shaped flexible power grid structure;

[0066] Figure 2 is a flexible DC power grid line fault traveling wave transmission network diagram;

[0067] Figure 3 is a flowchart of the method of the application;

[0068] Figure 4 is a correction coefficient fitting situation under different conditions as a function of d;

[0069] Figure 5 is the parameter estimation result after a single-pole ground fault of a DC line, wherein (a)-(d) are the line mode voltage at R12, R21 position and the corresponding mathematical morphological gradient operation, respectively;

[0070] Figure 6 is the parameter estimation result after a double-pole ground fault of a DC line, wherein (a)-(d) are the line mode voltage at R12, R21 position and the corresponding mathematical morphological gradient operation, respectively. DETAILED DESCRIPTION

[0071] The technical solutions of the application will be further described below with reference to the accompanying drawings.

[0072] The flexible DC power grid line fault resistance estimation method can be applied to a flexible DC power grid based on a modular multilevel converter or a two-level voltage source converter.

[0073] First, according to a typical four-terminal ring-shaped flexible power grid structure and multiple refraction and reflection conditions of a fault traveling wave, an equivalent circuit model of traveling wave transmission is established, and quantitative relationships between a ratio of a first fault traveling wave mutation amplitude and a second fault traveling wave mutation amplitude and a fault resistance under different fault types and fault positions are derived. The four-terminal ring-shaped flexible power grid structure adopts a true bipolar connection form, and four converter stations are converter stations 1-4, each of which is composed of two modular multilevel converters (MMC). The neutral points between the converter stations are connected to the ground equipotential surface (in an actual power grid, the neutral points are connected by a metal return line, which is more complex in modulus decoupling analysis). Figure 1 In the four-terminal ring-shaped flexible power grid structure, transmission lines are composed of overhead transmission lines, and the lengths of the lines are l 12 , l 14 , l 23 and l 43 . DC circuit breakers (DCCB) and current limiting reactors (CLR) are arranged at both ends of each line, the DCCB is used to quickly isolate the fault area, and the CLR suppresses the rising speed of the fault current and provides a protection boundary for protection. In addition, the fault current is measured at the line side of each line, so the signal measurement points R12, R21… are the installation positions of each line relay protection.

[0074] The bipolar transmission line on the same pole is coupled and needs to be decoupled into modulus for modulus analysis. After ignoring the influence of the metal return line, the line modulus component and the ground modulus component can be obtained by using a decoupling matrix . The transmission line can be described by a classic telegraph equation and can be equivalent to a Thevenin equivalent model.

[0075] The multiple refraction and reflection conditions of the fault traveling wave are shown in Figure 2 , taking the line modulus fault component as an example. When a single-pole grounding fault occurs, the initial fault equivalent circuit is solved, and the initial fault traveling wave , the second reflected fault traveling wave and the first refracted fault traveling wave are respectively:

[0076]

[0077] wherein, and are the initial line modulus and zero modulus fault voltages at the fault point. is the initial fault traveling wave transmitted to the DC fault line port; is the transmission function of the line mode component and the zero mode component respectively is the delay and attenuation distortion function of the line length, is the full length of the line, is the distance from the fault point to the installation of the protection, is twice the distance of the far end; is the reflection coefficient of the line mode fault traveling wave at the line port, is the reflection coefficient of the zero mode fault traveling wave at the line port, are the line mode traveling wave reflection coefficient, the refraction coefficient, the zero mode reflection coefficient, the line mode coefficient, the zero mode component refraction coefficient at the fault point position respectively, is the DC line wave impedance, is the DC current limiting reactor, is the MMC equivalent reactance, is the MMC equivalent capacitance, is the complex frequency domain variable in Laplace transform.

[0078] For a bipolar fault, the initial fault traveling wave are also obtained as follows:

[0079]

[0080] Based on the above formulas, the quantitative relationship between the amplitude ratio of the initial fault traveling wave and the second traveling wave and the fault resistance is derived as follows.

[0081] First, the amplitude ratio of the initial fault traveling wave and the second traveling wave is calculated: the amplitude ratio of the initial two fault traveling waves is the amplitude ratio of the first and second mode maxima of the fault traveling wave characteristics , as shown in the following formula:

[0082]

[0083] wherein, is the voltage surge amplitude caused by the initial traveling wave generated by the fault when it reaches the measurement point at the installation of the protection; is the voltage surge amplitude caused by the second traveling wave generated by the reflection or refraction of the initial traveling wave between the fault point and the installation of the protection when it reaches the measurement point; ​​​​​​​​

[0084] If , it is determined as a near-end fault, if , it is determined as a far-end fault.

[0085] The quantitative relationship model between the amplitude ratio of the initial two fault traveling waves and the fault resistance is: the alternative fault resistance calculation model provided by the judgment result of different fault types and positions.

[0086] Case 1: If the fault type is single-pole grounding fault, and the amplitude ratio of the first and second modulus maximum values of the fault traveling wave characteristics is ;

[0087] The fault distance , is the full length of the line; is the near-end protection, and the second reflected wave will be earlier than the first refracted wave to , so the amplitude ratio of the initial two fault traveling waves is:

[0088]

[0089] Wherein, is the distance from the fault point to the protection installation; is the line mode wave impedance, is the zero mode wave impedance; the line port reflection coefficient is independent of the transition resistance , and the traveling wave arrival time is close to 1, i.e. ; and are the initial line mode fault component and zero mode fault component at the fault point position respectively, is the coefficient of the zero mode component reflected as the line mode component at the fault point position; and respectively represent the attenuation distortion delay influence of the traveling wave transmission, and the difference between the two also represents the time difference influence of the arrival of the line mode and zero mode components, both of which are related to the fault distance , and the propagation distance correction factor is used to quantify the size of this influence;

[0090] The transition resistance is represented as:

[0091]

[0092] Wherein, the fault distance at this time is , is the transmission speed of the line mode fault component, which is slightly lower than the speed of light.

[0093] Case 2: If the fault type is single-pole-to-ground fault, and the amplitude ratio of the first and second modal maxima of the fault traveling wave feature is ;

[0094] then the fault distance ; is far-end protection, in which case the second reflected wave will arrive at later than the first reflected wave , so the abrupt amplitude ratio of the initial two fault traveling waves is:

[0095]

[0096] wherein represents the attenuation distortion delay effect of the line modal component after the traveling wave propagation distance, and the fault distance will affect the ratio , and the propagation distance correction factor is used to quantify the size of this effect; represents the refraction coefficient of the line modal component at the fault point location;

[0097] then the transition resistance is represented as:

[0098]

[0099] wherein the fault distance at this time is .

[0100] Case 3: If the fault type is double-pole-to-short-circuit fault, and the amplitude ratio of the first and second modal maxima of the fault traveling wave feature is ;

[0101] then the fault distance , is near-end protection, according to the network diagram of the traveling wave propagation, in which case the second reflected wave will arrive at earlier than the first reflected wave , so the abrupt amplitude ratio of the initial two fault traveling waves is:

[0102]

[0103] wherein is the reflection coefficient of the fault point when the double-pole-to-short-circuit fault occurs, and the line port reflection coefficient is independent of the transition resistance and is close to 1, so ; attenuation distortion and the fault distance has a relationship with the propagation distance correction factor to quantify the size of this effect;

[0104] The transition resistance is expressed as:

[0105]

[0106] where the fault distance at this time is ;

[0107] Case 4: If the fault type is a bipolar ground fault, and the amplitude ratio of the first and second modal maxima of the fault traveling wave characteristic is ;

[0108] The fault distance ; For far-end protection, the second reflected wave will be later than the first refracted wave to arrive at , so the abrupt amplitude ratio of the initial two fault traveling waves is:

[0109]

[0110] where, The attenuation distortion has a relationship with the fault distance , and the propagation distance correction factor is used to quantify the size of this effect;

[0111] The transition resistance is expressed as:

[0112]

[0113] where the fault distance at this time is .

[0114] In an embodiment, the , , , is a propagation distance correction factor establishment method related to the fault distance , two different positions of faults and corresponding transition resistances are obtained respectively in different cases, and the , , , corresponding curves are obtained by linear fitting, and the fitting results are shown in Figure 4 .

[0115] Using the quantitative relationship model described above, calculations can be completed with only single-end measurement data from the protection installation location. This eliminates the dependence on communication systems, reducing system complexity and cost, and more importantly, avoiding communication delays, enabling the resistance estimation to meet the stringent requirements of the main protection system for operating speed (1-2 milliseconds).

[0116] Therefore, the flexible DC power grid line fault resistance estimation method of the present invention includes:

[0117] A quantitative relationship model is established between the abrupt change amplitude ratio of the initial two fault traveling waves and the fault resistance. This quantitative relationship model includes a propagation distance correction factor to correct for the influence of fault distance.

[0118] Based on the quantitative relationship model between the abrupt change amplitude ratio of the initial two fault traveling waves and the fault resistance, and combined with different fault types, fault locations, and the propagation distance correction factor, an estimated value of the transition resistance is obtained.

[0119] The amplitude, direction, and corresponding time of the sudden change in the fault traveling wave can be extracted using a multi-resolution morphological filtering algorithm.

[0120] Example 1

[0121] like Figure 3 As shown, before calculating the abrupt change amplitude ratio of the initial two fault traveling waves, the fault traveling wave characteristics are first obtained. The specific steps are as follows:

[0122] The positive and negative voltages of the line are measured, and the steady-state component is subtracted to obtain the fault component. Pole-mode decoupling is then performed, including mode decomposition. The positive and negative voltages are then converted into line-mode and zero-mode components to obtain the line-mode and zero-mode fault voltage traveling waves. and ;

[0123] Define the structural elements and their lengths and values, including any line-mode fault voltage signals. Perform fault signal Operation, from Find the maximum point in the filtered signal and set the threshold amplitude of the maximum point to be [value missing]. The first and second modulo maxima are obtained. , and the corresponding time and .

[0124] The mathematical morphological gradient operation include:

[0125] Initialize the parameters of the structuring element SE, including the number of multi-resolution analysis layers. and base length Initial value , the effective length of the initial structuring element ;

[0126] According to the number of the multi-resolution analysis layers and the base length , the effective length of the structuring element at the current resolution is calculated ;

[0127] Based on the effective length , a stack of complementary flat structuring element sequences is constructed, respectively, the forward structuring element and the reverse structuring element , wherein, is the position index within the structuring element; and The initial values are both ;

[0128] Traverse each data point of the line-mode fault voltage signal, and for each current point , perform the following operations:

[0129] Using the forward structuring element , perform mathematical morphological dilation and erosion operations within the neighborhood of the current point t, respectively, to obtain the forward dilation result and the forward erosion result ;

[0130] Using the reverse structuring element , perform mathematical morphological dilation and erosion operations within the neighborhood of the current point , respectively, to obtain the reverse dilation result and the reverse erosion result ;

[0131] According to the forward dilation result, the forward erosion result, the reverse dilation result, and the reverse erosion result, calculate the filter output value of the current point t .

[0132] Before fault resistance estimation, use existing mature methods to identify the fault type, and determine whether it is a two-pole short-circuit fault or a single-pole ground fault.

[0133] Then, according to the quantitative relationship model between the sudden amplitude ratio of the initial two fault traveling waves and the fault resistance established above, combined with the fault type, fault location, and propagation distance correction factor, the estimated value of the transition resistance is obtained.

[0134] Embodiment 2

[0135] In PSCAD / EMTDC, a model as shown in Figure 1The ±500kV flexible DC power grid shown in the simulation has a common neutral point for all converters. Converter 1 controls the DC side voltage to ±500kV, while the other converters use active power sampling control. The transmission line is an overhead transmission line, and the simulation uses a phase-domain frequency-dependent model. The simulation demonstrates the performance of the proposed protection scheme by simulating different types (single-pole and double-pole) and different transition resistances (0 ohms to 600 ohms) in region 12, using in-region protection positions R12 and R21 and out-of-region protection positions R14 and R41 as examples.

[0136] During a single-pole ground fault, simulations were performed at l. 12 A single-pole ground fault with transition resistances of 0.01 ohms, 100 ohms, and 400 ohms occurred 30 km away from protection R12. The changes in the line-mode fault voltage measured by protections R12 and R21 are as follows: Figure 5 As shown in (a) and (b) in the figure, a mathematical morphological gradient operation is performed on the line-mode fault voltage to obtain the corresponding... Figure 5 In (c) and (d), the abrupt change amplitude, abrupt change direction, and corresponding time of the initial two fault traveling waves are obtained, respectively. After performing mathematical morphological gradient operations in R12, as shown... Figure 5 As shown in (c) of the figure, the amplitude, direction, and corresponding time of the first traveling wave mutation are: 0.1 ms, negative direction, -559.336 kV; the amplitude, direction, and corresponding time of the second traveling wave mutation are: 0.31 ms, positive direction, 438.303 kV. After performing the mathematical morphological gradient operation in R21, as shown... Figure 5 As shown in (d) of the figure, the amplitude, direction, and corresponding time of the first traveling wave mutation are 0.59 ms, negative direction, -535.909 kV, and the amplitude, direction, and corresponding time of the second traveling wave mutation are 0.79 ms, negative direction, -222.485 kV, respectively. The estimated absolute errors at these times are |ΔR|. f | The ohms were 2.74, 4.21, and 8.59 ohms, respectively, demonstrating the excellent performance of the method of the present invention.

[0137] In the case of a bipolar fault, simulations are performed at l. 12 A bipolar fault with transition resistances of 0.01 ohms, 100 ohms, and 400 ohms occurred at a location 60 km away from protection R12. The changes in the line-mode fault voltage measured by protections R12 and R21 are as follows: Figure 6 As shown in (a) and (b) in the figure, a mathematical morphological gradient operation is performed on the line-mode fault voltage to obtain the corresponding... Figure 6 In (c) and (d), the abrupt change amplitude, abrupt change direction, and corresponding time of the initial two fault traveling waves are obtained, respectively. After performing mathematical morphological gradient operations in R12, as shown... Figure 6The first traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.2ms, negative direction, -1372.78kV, and the second traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.60ms, positive direction, 1325.34kV. In R21, after the mathematical morphology gradient operation, as shown in (c) of FIG. 6, the first traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.2ms, negative direction, -1372.78kV, and the second traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.60ms, positive direction, 1325.34kV. In R21, after the mathematical morphology gradient operation, as shown in (c) of FIG. 6, the first traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.2ms, negative direction, -1372.78kV, and the second traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.60ms, positive direction, 1325.34kV. Figure 6 The first traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.2ms, negative direction, -1372.78kV, and the second traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.60ms, positive direction, 1325.34kV. In R21, after the mathematical morphology gradient operation, as shown in (c) of FIG. 6, the first traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.2ms, negative direction, -1372.78kV, and the second traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.60ms, positive direction, 1325.34kV. In R21, after the mathematical morphology gradient operation, as shown in (c) of FIG. 6, the first traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.2ms, negative direction, -1372.78kV, and the second traveling wave mutation amplitude, mutation direction and corresponding time in the figure are 0.60ms, positive direction, 1325.34kV. f | respectively, which shows excellent performance of the method.

[0138] In the flexible DC power grid with voltage level of 110-500kV, the method can accurately estimate the transition resistance of the fault line, and can provide a basis for adaptive protection, and aims to solve the core problem that the fixed threshold protection scheme has poor adaptability under complex fault conditions.

[0139] To realize the above-mentioned flexible DC power grid line fault resistance estimation method, the application further provides an electronic device and a computer readable storage medium.

[0140] The electronic device comprises a memory, a processor and a computer program stored on the memory and executable on the processor, and the processor implements part or all of the steps of the above-mentioned flexible DC power grid line fault resistance estimation method when executing the program.

[0141] The computer readable storage medium has a computer program stored thereon, and the computer program is executed by the processor to implement part or all of the steps of the above-mentioned flexible DC power grid line fault resistance estimation method.

[0142] The above examples are only for the purpose of describing the application, and are not intended to limit the scope of the application. The scope of the application is defined by the appended claims. Various equivalent replacements and modifications made without departing from the spirit and principles of the application shall be encompassed within the scope of the application.

Claims

1. A method for estimating the fault resistance of a flexible DC power grid line, characterized in that, The method includes: A quantitative relationship model is established between the abrupt change amplitude ratio of the initial two fault traveling waves and the fault resistance. This quantitative relationship model includes a propagation distance correction factor to correct for the influence of fault distance. Based on the quantitative relationship model between the abrupt change amplitude ratio of the initial two fault traveling waves and the fault resistance, and combined with different fault types, fault locations, and the propagation distance correction factor, an estimated value of the transition resistance is obtained; the quantitative relationship model between the abrupt change amplitude ratio of the initial two fault traveling waves and the fault resistance includes at least one of the following: (1) If the fault type is a single-pole ground fault, and the amplitude ratio of the first and second modulus maxima of the fault traveling wave characteristics is... ; Then the fault distance , The total length of the line; For near-end protection, based on the traveling wave propagation network diagram, the second reflected wave... It will be earlier than the first refracted wave. Passed to Therefore, the ratio of the abrupt change amplitudes of the initial two fault traveling waves is: in, The distance from the fault point to the protection installation location; For line mode wave impedance, Zero-mode impedance; line port reflection coefficient With transition resistance It is irrelevant, and the arrival time of the traveling wave is close to 1, that is... ; and Let these be the initial linear mode fault component and the zero mode fault component at the fault location, respectively. The coefficients for the zero-mode component reflected as the linear mode component at the fault location; and These represent the effects of attenuation, distortion, and delay in traveling wave propagation, respectively. The difference between the two also represents the effect of the time difference between the arrival of the linear mode and zero-mode components, both of which are related to the fault distance. Yes, it's related, using the propagation distance correction factor. To quantify the magnitude of this impact; Then the transition resistor Represented as: Wherein, the fault distance at this time is , The propagation speed of the linear mode fault component is a rough estimate, slightly lower than the speed of light; (2) If the fault type is a single-pole ground fault, and the amplitude ratio of the first and second modulus maxima of the fault traveling wave characteristics is... ; Then the fault distance ; For remote protection, the second reflected wave at this time It will be later than the first refracted wave. Passed to Therefore, the ratio of the abrupt change amplitudes of the initial two fault traveling waves is: in, Indicates the propagation of traveling waves The effects of attenuation, distortion, and delay on the post-distance linear mode components, and the propagation distance correction factor. Used to quantify fault distance Comparison value The magnitude of the impact; The refractive index of the linear mode component indicating the location of the fault point; Then the transition resistor Represented as: Wherein, the fault distance at this time is ; (3) If the fault type is a bipolar short-circuit fault, and the amplitude ratio of the first and second modulus maxima of the fault traveling wave characteristics is greater than that of the fault traveling wave characteristics, then the fault type is a bipolar short-circuit fault. ; Then the fault distance , For near-end protection, according to the traveling wave propagation network diagram, the second reflected wave at this time... It will be earlier than the first refracted wave. Passed to Therefore, the ratio of the abrupt change amplitudes of the initial two fault traveling waves is: in, The reflection coefficient at the fault point during a bipolar short-circuit fault, and the reflection coefficient at the line port relative to the transition resistance. It is irrelevant and close to 1, therefore Propagation distance correction factor Used to quantify fault distance right The magnitude of the effect of attenuation distortion; Then the transition resistor Represented as: Wherein, the fault distance at this time is ; (4) If the fault type is a bipolar ground fault, and the amplitude ratio of the first and second modulus maxima of the fault traveling wave characteristics is greater than that of the fault traveling wave characteristics, then the fault type is a bipolar ground fault. ; Then the fault distance ; For remote protection, the second reflected wave at this time It will be later than the first refracted wave. Passed to Therefore, the ratio of the abrupt change amplitudes of the initial two fault traveling waves is: Among them, the propagation distance correction factor Used to quantify fault distance right The magnitude of the effect of attenuation distortion; Then the transition resistor Represented as: Wherein, the fault distance at this time .

2. The method for estimating the fault resistance of a flexible DC power grid line according to claim 1, characterized in that, The fault location is determined based on the first and second modulus maxima of the fault traveling wave characteristics. , amplitude ratio The determination is made using the following formula: in, It is the voltage surge amplitude caused when the initial traveling wave generated by the fault reaches the measurement point at the protection installation location; It is the voltage surge amplitude caused by the second traveling wave, generated after the initial traveling wave is reflected or refracted between the fault point and the protection installation point, when it reaches the measurement point; like If so, it is determined to be a near-end fault. If so, it is determined to be a remote fault.

3. The method for estimating the fault resistance of a flexible DC power grid line according to claim 2, characterized in that, The fault traveling wave features were extracted using a multi-resolution morphological filtering algorithm.

4. The method for estimating the fault resistance of a flexible DC power grid line according to claim 3, characterized in that, The fault traveling wave characteristics are obtained specifically through the following steps: The positive and negative voltages of the line are measured, and the steady-state component is subtracted to obtain the fault component. Then, pole-mode decoupling is performed to obtain the line-mode and zero-mode fault voltage traveling waves. and ; Define the structural elements and their lengths and values, including any line-mode fault voltage signals. Perform fault signal Operation, from Find the maximum point in the filtered signal and set the threshold amplitude of the maximum point to be [value missing]. The first and second modulo maxima are obtained. , and the corresponding time and .

5. The method for estimating the fault resistance of a flexible DC power grid line according to claim 4, characterized in that, The The operation includes: Initialize the parameters of the structuring element SE, including the number of multi-resolution analysis layers. and base length Initial value The effective length of the initial structuring element ; Based on the number of multi-resolution analysis layers and base length Calculate the effective length of the structuring element at the current resolution. ; Based on the effective length Construct a sequence of complementary flat structural elements, which are positive structural elements. and reverse structural elements ,in, For the position index within the structure element; and The initial values ​​are all ; Iterate through each data point of the wired mode fault voltage signal, and for each current point... Perform the following operations: Using the aforementioned positive structural element At the current point Mathematical morphological dilation and erosion operations are performed within the neighborhood of the target area to obtain the positive dilation result. and positive corrosion results ; Using the reverse structural element At the current point Mathematical morphological dilation and erosion operations are performed within the neighborhood of the target area to obtain the reverse dilation results. and reverse corrosion results ; Based on the results of forward expansion, forward corrosion, reverse expansion, and reverse corrosion, calculate the current point. Filtered output value .

6. The method for estimating the fault resistance of a flexible DC power grid line according to claim 1, characterized in that, The fault types include at least one of the following: single-pole grounding fault and double-pole grounding fault.

7. The method for estimating the fault resistance of a flexible DC power grid line according to claim 1, characterized in that, The propagation distance correction factor is obtained in the following manner: Under different conditions, faults and corresponding transition resistances at two different locations were obtained, and the curve of the propagation distance correction factor as a function of fault distance was linearly fitted.

8. An electronic 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 program, it implements the steps of the flexible DC power grid line fault resistance estimation method as described in any one of claims 1-7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the flexible DC power grid line fault resistance estimation method as described in any one of claims 1-7.

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