Active power distribution network fault location method and system based on double-end voltage waveform comparison

Abstract

The invention relates to the technical field of power distribution network fault distance measurement, in particular to an active power distribution network fault distance measurement method and system based on double-end voltage waveform comparison. The method comprises the following steps: acquiring voltage and current data of a first target point and a second target point of a distribution line; setting an initial fault point on the distribution line by using a dichotomy method, and calculating a first voltage waveform and a second voltage waveform at the initial fault point based on the voltage and current data of the first target point and the second target point; comparing the first voltage waveform with the second voltage waveform by adopting a directed distance algorithm to obtain a waveform difference degree; determining whether the initial fault point is a target fault point position or not according to whether the waveform difference degree meets a preset threshold condition or not; and when the waveform difference degree does not meet a preset threshold condition, based on a comparison result of the first voltage waveform and the second voltage waveform, resetting the position of the fault point by using a bisection method. According to the method, the fault location problem of the power distribution network containing the distributed power supply is solved by combining double-end voltage waveform comparison with dichotomy approximation.

Description

Technical Field

[0001] The invention relates to the technical field of distribution network fault distance measurement, in particular to an active distribution network fault distance measurement method and system based on double-terminal voltage waveform comparison. Background Art

[0002] As a key component of the power system, the safe and stable operation of the distribution network is crucial to ensuring power supply reliability and improving power quality. Faults are the primary factor affecting the reliable operation of the distribution network. More than 90% of power outages are related to faults. Faults not only cause local or large-scale power outages, causing inconvenience to users' lives, but may also cause safety hazards such as fires and traffic accidents. In addition, if the fault is not located and removed in time, it may also cause the non-fault phase voltage to increase, damage the weak insulation in the distribution network, and expand the scope of the accident.

[0003] In the prior art, for a distribution network containing distributed power sources, when a line fails, the distributed power sources will be transformed into weak power sources due to the capacity of the distributed power sources and the way they are connected to the power grid, making ranging more difficult. On the one hand, the distribution network has changed from a traditional single-power radial network to a complex network containing a main power source and multiple weak power sources. The current ranging method based on a single-power radial network is no longer applicable. On the other hand, the access of a large number of controlled distributed power sources has significantly different fault characteristics from those of traditional AC power sources. The accuracy of the phasor-based ranging algorithm is affected by the introduction of complex harmonics and cannot meet the on-site ranging accuracy requirements. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention is proposed.

[0005] Therefore, the problem to be solved by the present invention is how to solve the problem that for a distribution network containing distributed power sources, when a line fails, the distributed power sources will be transformed into weak power sources due to the capacity of the distributed power sources and the way they are connected to the power grid, making ranging more difficult. On the one hand, the distribution network is changed from a traditional single-power radial network to a complex network including a main power source and multiple weak power sources. The current ranging method based on a single-power radial network is no longer applicable. On the other hand, the access of a large number of controlled distributed power sources has fault characteristics that are significantly different from those of traditional AC power supply faults. The accuracy of the ranging algorithm based on phasors is affected by the introduction of complex harmonics, and the requirements for on-site ranging accuracy cannot be met.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides an active distribution network fault location method based on two-terminal voltage waveform comparison, which includes obtaining voltage and current data of a first target point and a second target point of a distribution line;

[0008] Setting an initial fault point on the distribution line by using a binary method, and calculating a first voltage waveform and a second voltage waveform at the initial fault point based on voltage and current data of the first target point and the second target point;

[0009] Using a directed distance algorithm to compare the first voltage waveform and the second voltage waveform to obtain a waveform difference;

[0010] Determining whether the initial fault point is the target fault point location according to whether the waveform difference satisfies a preset threshold condition;

[0011] When the waveform difference does not meet the preset threshold condition, the fault point position is reset by using the binary method based on the comparison result of the first voltage waveform and the second voltage waveform.

[0012] As a preferred solution of the active distribution network fault location method based on two-terminal voltage waveform comparison described in the present invention, wherein: the first target point of the distribution line is the starting end of the distribution line, the second target point of the distribution line is the end of the distribution line, and the distribution line includes a strong power supply end and a weak power supply end.

[0013] As a preferred solution of the active distribution network fault location method based on two-terminal voltage waveform comparison described in the present invention, wherein: the initial fault point is set at the midpoint of the distribution line, and the distance between the first target point and the second target point is the preset total line length.

[0014] As a preferred solution of the active distribution network fault location method based on two-terminal voltage waveform comparison described in the present invention, when the waveform difference does not meet the preset threshold condition:

[0015] If the first voltage waveform is greater than the second voltage waveform, resetting the fault point on the line between the initial fault point and the second target point;

[0016] If the first voltage waveform is smaller than the second voltage waveform, a fault point is reset on the line between the first target point and the initial fault point.

[0017] As a preferred solution of the active distribution network fault location method based on two-terminal voltage waveform comparison described in the present invention, the calculation of the waveform difference includes: calculating the voltage difference between the first voltage waveform and the second voltage waveform; integrating the voltage difference within a preset time period; and determining the waveform difference based on the result of the integration operation.

[0018] As a preferred solution of the active distribution network fault location method based on two-terminal voltage waveform comparison described in the present invention, the method of resetting the fault point position using the binary search method includes: selecting the midpoint position as the new fault point within the determined new line section; recalculating the first voltage waveform and the second voltage waveform at the new fault point; and repeating the waveform comparison and fault point update process until the waveform difference meets the preset threshold condition.

[0019] As a preferred solution of the active distribution network fault distance measurement method based on two-terminal voltage waveform comparison described in the present invention, it also includes: establishing a fault distance measurement database to record the waveform difference changes in each distance measurement process; dynamically adjusting the dichotomy split ratio according to the waveform difference change trend; when the waveform difference is less than a preset threshold, outputting the final fault point location information.

[0020] In a second aspect, an embodiment of the present invention provides an active distribution network fault location system based on two-terminal voltage waveform comparison, which includes a data acquisition module to obtain voltage and current data of a first target point and a second target point of a distribution line;

[0021] a voltage waveform calculation module, which sets an initial fault point on the distribution line by using a binary method, and calculates a first voltage waveform and a second voltage waveform at the initial fault point based on voltage and current data of the first target point and the second target point;

[0022] A waveform analysis module, using a directed distance algorithm to compare the first voltage waveform and the second voltage waveform to obtain a waveform difference;

[0023] A fault point determination module determines whether the initial fault point is the target fault point location according to whether the waveform difference satisfies a preset threshold condition;

[0024] The fault point updating module resets the fault point position by using a binary search method based on a comparison result between the first voltage waveform and the second voltage waveform when the waveform difference does not meet a preset threshold condition.

[0025] In a third aspect, an embodiment of the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program instructions are executed by the processor, the steps of the active distribution network fault location method based on two-terminal voltage waveform comparison as described in the first aspect of the present invention are implemented.

[0026] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program instructions are executed by a processor, the steps of the active distribution network fault location method based on two-terminal voltage waveform comparison as described in the first aspect of the present invention are implemented.

[0027] The beneficial effects of the present invention are as follows: the present invention collects the three-phase instantaneous voltage and instantaneous current at both ends of the line after the fault at a preset sampling frequency, uses the binary method to set the initial fault point, calculates the voltage values ​​of the two fault points inferred from the electrical quantities at both ends of the line and obtains the corresponding voltage waveform, compares the sizes of the two voltage waveforms by a directed distance algorithm and calculates their similarity, if the similarity meets the threshold condition, then the fault point position set at this time is the target fault point position, if not, then the binary method is used to set the fault point again according to the waveform size comparison result and iterative calculation is continued, thereby realizing the determination of the fault point position. The present invention determines the fault information by comparing the two-terminal voltage waveforms, effectively reducing the error of fault distance measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 It is a flow chart of the active distribution network fault location method based on two-terminal voltage waveform comparison;

[0030] Figure 2 A computer equipment diagram of an active distribution network fault location method based on two-terminal voltage waveform comparison;

[0031] Figure 3 A schematic diagram of a dual-power distribution network fault of an active distribution network fault location method based on dual-terminal voltage waveform comparison;

[0032] Figure 4 This is a process diagram of the binary method of the active distribution network fault location method based on the comparison of two-terminal voltage waveforms to approximate the true fault distance;

[0033] Figure 5 The voltage waveforms of two fault points of the active distribution network fault location method based on double-terminal voltage waveform comparison are shown;

[0034] Figure 6 The voltage difference waveform of two fault points in the active distribution network fault location method based on two-terminal voltage waveform comparison. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0038] Example 1

[0039] Reference Figure 1-2 , which is the first embodiment of the present invention, provides an active distribution network fault location method based on two-terminal voltage waveform comparison, comprising:

[0040] S100: Acquire voltage and current data of a first target point and a second target point of a distribution line;

[0041] S101: The first target point of the distribution line is the starting end of the distribution line, the second target point of the distribution line is the end of the distribution line, and the distribution line includes a strong power source end and a weak power source end.

[0042] In the embodiment of the present application, the first target point and the second target point of the distribution line are respectively equipped with high-precision voltage and current acquisition devices, the sampling frequency is set to 4kHz-20kHz adjustable, and the data accuracy is not less than 16 bits. The strong power supply end is usually a 110kV / 10kV substation feeder with a rated capacity of 50MVA and a short-circuit capacity of more than 500MVA; the weak power supply end is a distributed photovoltaic power generation or wind power generation system with an installed capacity of generally 2.5MW-5MW, which is connected to the grid through an intelligent converter.

[0043] Specifically, the voltage and current acquisition device includes a voltage transformer (PT) and a current transformer (CT). The PT uses a 0.2s-class capacitive voltage transformer with a rated voltage of 10kV / 100V, and the CT uses a 0.2s-class current transformer with a rated current ratio of 500 / 5A. The collected data is transmitted to the ranging host in real time via industrial Ethernet, and the transmission delay is controlled within 2ms.

[0044] In an optional embodiment, the system is equipped with an adaptive sampling control module, which can dynamically adjust the sampling parameters according to the fault type. For example, when a metallic single-phase grounding fault is detected, the system automatically increases the sampling frequency to 20kHz and starts the harmonic analysis function; when a phase-to-phase short circuit fault occurs, the system focuses on collecting the transient characteristics of the fault phase, and the sampling frequency can be appropriately reduced to 8kHz to reduce the amount of data.

[0045] In another optional embodiment, the ranging system can also be configured with a real-time data evaluation module to perform quality analysis on the collected voltage and current data. If the signal-to-noise ratio is found to be lower than 40dB or the harmonic distortion rate exceeds 5%, the system automatically switches to the backup sampling channel and issues an alarm message. In addition, the system verifies the validity of the sampled data by calculating parameters such as power factor and phase angle in real time.

[0046] It should be noted that the installation position of the sampling device has an important influence on the ranging accuracy. The voltage transformer should be installed on the power supply side of the circuit breaker and connected to the secondary panel cabinet with a shielded cable; the current transformer should be installed on the line outlet side. All secondary circuits use shielded twisted pair cables with a grounding resistance of no more than 4Ω. The system is equipped with an automatic calibration function, which performs zero drift calibration every 24 hours and automatically adjusts the gain factor according to the ambient temperature to ensure sampling accuracy.

[0047] S200: setting an initial fault point on the distribution line by using a binary method, and calculating a first voltage waveform and a second voltage waveform at the initial fault point based on voltage and current data of a first target point and a second target point;

[0048] S201: The initial fault point is set at the midpoint of the distribution line, and the distance between the first target point and the second target point is the preset total length of the line.

[0049] In the embodiment of the present application, when a fault occurs, the system first obtains line parameters, including line impedance (0.27+j0.347)Ω / km, ground capacitance current 5A / km, etc. At the same time, it reads real-time operating parameters, such as bus voltage 10.5kV, load current 200A, etc. Based on these parameters, the system establishes an accurate line model, laying the foundation for subsequent fault location calculations.

[0050] Distribution lines are usually 10kV overhead lines or cables, and the total length of the lines is generally between 5 and 15km. The maximum distance range supported by this system is 20km, which is suitable for various common wiring methods. The line model uses a distributed parameter equivalent circuit, taking into account the distributed capacitance effect, and can accurately reflect the voltage and current distribution during a fault.

[0051] In an optional embodiment, the setting of the initial fault point can be optimized based on historical fault data. The system establishes a probability distribution model of the fault location by analyzing historical fault records. If the historical fault frequency of a certain line section is high, the system will preferentially select the midpoint of the area as the initial fault point to improve the convergence speed.

[0052] In another optional embodiment, the system can predict the fault area based on the fault characteristics. By analyzing the fault current amplitude, phase relationship and transient characteristics, the electrical distance from the fault point to both ends is preliminarily estimated. This prediction can provide a reference for the setting of the initial fault point and improve the positioning efficiency.

[0053] S300: using a directed distance algorithm to compare the first voltage waveform and the second voltage waveform to obtain a waveform difference;

[0054] S301: When the waveform difference does not meet the preset threshold condition:

[0055] If the first voltage waveform is greater than the second voltage waveform, resetting the fault point on the line between the initial fault point and the second target point;

[0056] If the first voltage waveform is smaller than the second voltage waveform, the fault point is reset on the line between the first target point and the initial fault point.

[0057] In the embodiment of the present application, the system sets the waveform difference threshold to 5%. If the difference calculation result exceeds this threshold, it means that the current assumed fault point location is biased and needs to be corrected. The specific judgment process is as follows: Calculate the waveform difference integral value, a positive value indicates that the first voltage waveform is larger, a negative value indicates that the second voltage waveform is larger, and the absolute size of the integral value reflects the degree of waveform difference.

[0058] In specific implementation, the system adopts a multi-threshold judgment mechanism. In addition to the 5% basic threshold, a 10% warning threshold and a 2% precision threshold are also set. When the difference exceeds the warning threshold, the system will start the fast positioning mode and increase the binary step size; when the difference is close to the precise threshold, it will switch to the fine positioning mode, reduce the step size and improve the accuracy.

[0059] In an optional embodiment, the system can adaptively adjust the threshold according to the fault type. For example, for a metallic single-phase grounding fault, the threshold can be appropriately relaxed to 8% due to the obvious waveform characteristics; while for a high-resistance fault, the threshold needs to be tightened to 3% to ensure positioning accuracy. The system will also dynamically adjust the threshold parameters according to line conditions (such as overhead or cable).

[0060] S400: Determine whether the initial fault point is the target fault point location according to whether the waveform difference satisfies a preset threshold condition;

[0061] S401: Calculation of the waveform difference includes: calculating the voltage difference between the first voltage waveform and the second voltage waveform; integrating the voltage difference within a preset time period; and determining the waveform difference based on the result of the integration operation.

[0062] In the embodiment of the present application, the waveform difference calculation adopts a standardized processing flow. First, the sampled data is normalized to eliminate the influence of the amplitude scale. Then, within the selected time window (usually the first complete cycle after the fault), the instantaneous difference sequence of the two waveforms is calculated. The difference sequence is numerically integrated to obtain the cumulative difference. Finally, the cumulative difference is divided by the reference base value (the arithmetic mean of the integral values ​​of the two waveforms) to obtain the final difference index.

[0063] The specific calculation process has multiple verification mechanisms. The system will simultaneously calculate auxiliary indicators such as power direction and phase advance to verify the rationality of the waveform difference calculation results. If an abnormality is found, the calculation window will be automatically expanded or the integral parameters will be adjusted for recalculation.

[0064] In an optional embodiment, the system adopts an improved adaptive integration algorithm. By analyzing the spectral characteristics of the waveform, the integration step size and weight factor are dynamically adjusted. For waveforms containing high-order harmonics, the sampling point density is increased; for waveforms dominated by fundamental waves, the amount of calculation is appropriately reduced. This adaptive algorithm not only ensures calculation accuracy, but also improves calculation efficiency.

[0065] S500: When the waveform difference does not meet the preset threshold condition, based on the comparison result of the first voltage waveform and the second voltage waveform, the fault point position is reset by using the binary search method.

[0066] S501: Resetting the fault point position using the binary method includes: selecting the midpoint position as the new fault point within the determined new line section; recalculating the first voltage waveform and the second voltage waveform at the new fault point; and repeating the waveform comparison and fault point update process until the waveform difference meets the preset threshold condition.

[0067] In the embodiment of the present application, the binary location process adopts an iterative optimization strategy. Each iteration records the current search interval, fault point location and waveform difference. The system automatically adjusts the binary step size, and the initial step size is set to 1 / 2 of the total line length, which gradually decreases as the number of iterations increases. When the step size is less than the preset minimum value (usually 50m) or the waveform difference meets the requirements, the iteration process ends.

[0068] In actual applications, the system uses an improved binary search algorithm. In addition to the standard bisection point, the system also predicts possible fault areas based on the trend of waveform difference. If the difference changes monotonically for three consecutive iterations, the system will adjust the segmentation ratio accordingly to speed up the convergence.

[0069] In an optional embodiment, the system introduces a parallel computing mechanism. In each iteration, the waveform differences of multiple candidate points are calculated simultaneously, and the optimal result is selected to determine the next search direction. This parallel processing mechanism significantly improves the positioning efficiency, especially in the fault location of long-distance lines.

[0070] S502: Also includes: establishing a fault distance measurement database to record the waveform difference changes during each distance measurement process; dynamically adjusting the binary division ratio according to the waveform difference change trend; when the waveform difference is less than a preset threshold, outputting the final fault point location information.

[0071] In the embodiment of the present application, the system builds a complete fault ranging database. The database adopts a distributed storage architecture and includes a fault feature table, a positioning process table, and a result statistics table. Each record contains complete information such as the fault time, fault type, ranging process, and final result. The system regularly analyzes historical data, optimizes positioning algorithm parameters, and improves ranging accuracy.

[0072] Specifically, the database records include:

[0073] Basic fault information: occurrence time, fault type, environmental conditions; ranging process data: number of iterations, waveform differences in each round, search interval changes; positioning results: final fault point location, positioning accuracy, time consumption; system parameters: sampling frequency, threshold setting, algorithm parameters.

[0074] In an optional embodiment, the system also implements intelligent analysis functions. Through machine learning algorithms, historical data is analyzed to establish a fault feature-location association model to provide a reference for new fault location. For example, the system can identify the high-incidence characteristics of certain types of faults in specific areas and optimize the initial search strategy accordingly.

[0075] It should be noted that the system's data management adopts a layered architecture: real-time layer: processes the ranging data of the current fault; recent layer: saves detailed records of the past month; historical layer: stores long-term statistical data and analysis results; this layered management ensures real-time performance and facilitates subsequent optimization and analysis.

[0076] Furthermore, this embodiment also provides an active distribution network fault location system based on two-terminal voltage waveform comparison, comprising:

[0077] A data acquisition module, for acquiring voltage and current data of a first target point and a second target point of a distribution line;

[0078] A voltage waveform calculation module is used to set an initial fault point on the distribution line by using a binary method, and calculate a first voltage waveform and a second voltage waveform at the initial fault point based on voltage and current data of a first target point and a second target point;

[0079] A waveform analysis module, using a directed distance algorithm to compare the first voltage waveform and the second voltage waveform to obtain a waveform difference;

[0080] The fault point determination module determines whether the initial fault point is the target fault point location according to whether the waveform difference meets the preset threshold condition;

[0081] The fault point updating module resets the fault point position by using a binary search method based on a comparison result between the first voltage waveform and the second voltage waveform when the waveform difference does not meet a preset threshold condition.

[0082] In summary, by collecting voltage and current data at the beginning and end of the distribution line at the same time, and processing the data in combination with the characteristics of strong and weak power sources, a comprehensive monitoring of the distribution network containing distributed power sources is achieved. This dual-end acquisition solution overcomes the limitations of the traditional single-end measurement method when distributed power sources are connected, effectively solves the measurement accuracy problem caused by weak signals at the weak power source end, and greatly improves the accuracy of fault location.

[0083] By using the midpoint-based binary method to set the initial fault point and dynamically adjusting it in combination with the total line length parameter, a fast and efficient search strategy is achieved. This method avoids the computational burden of traversing the entire line in traditional ranging methods, significantly improving positioning efficiency, especially in long-distance lines.

[0084] By introducing a directed distance algorithm to compare the two-terminal voltage waveforms and obtain the waveform difference, the harmonic interference problem caused by the access of distributed power sources is innovatively solved. The algorithm improves the anti-interference ability and makes the distance measurement results more stable and reliable by comparing and analyzing the overall characteristics of the waveform instead of the traditional single-point phase comparison.

[0085] By establishing an adaptive iteration mechanism based on waveform differences, the search direction is dynamically adjusted according to the size relationship of the voltage waveform, achieving automatic convergence of precise positioning. This method overcomes the limitations of traditional fixed-step search, significantly improves the accuracy of fault location, and avoids the oscillation problem in the ranging process.

[0086] By establishing a complete fault distance measurement database and recording the trend of waveform difference changes, the dynamic optimization of the positioning process is achieved. The system can adaptively adjust the split ratio of the binary method to improve the distance measurement efficiency. At the same time, the accumulated historical data provides a reliable basis for subsequent fault analysis and prediction.

[0087] Example 2

[0088] Reference Figure 2 - Figure 6 , which is the second embodiment of the present invention, provides an active distribution network fault location method based on double-terminal voltage waveform comparison. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0089] The three-phase instantaneous voltage and the three-phase instantaneous current at both ends of the line after the fault occurs are collected within the preset sampling frequency;

[0090] In this embodiment, the three-phase instantaneous voltage is the actual voltage value of each phase of the three-phase electricity at a certain moment, and the three-phase instantaneous current is the actual current value of each phase of the three-phase electricity at a certain moment. When a fault occurs, the voltage and current of the three-phase electricity will change. By collecting these changes, the subsequent algorithm can be used to determine the fault location. The preset sampling frequency here can be set to 4kHz. This acquisition method can comprehensively obtain the electrical status information of the line after the fault, providing an accurate data basis for fault distance measurement.

[0091] The three-phase instantaneous voltage and three-phase instantaneous current at both ends of the line are converted into modal components respectively through Karenbauer phase-mode transformation;

[0092] In this embodiment, when an asymmetric fault occurs in the power system, the three phases need to be decoupled in consideration of the electromagnetic coupling effect between the three phases. Here, the Karenbauer phase-mode transformation is used to transform the current sampling value, and the 0 modulus, 1 modulus and 2 modulus are obtained based on the three-phase electrical quantity transformation. The transformation process is as follows:

[0093]

[0094] Where: i0(t), i1(t) and i2(t) are the 0 modulus, 1 modulus and 2 modulus of the three-phase current after phase transformation, i a (t), i b (t) and i c (t) are the instantaneous current values ​​of the three phases respectively.

[0095] In the case of an asymmetric fault, there is electromagnetic coupling between the three phases. The Karenbauer phase mode transformation decouples the three-phase coupled system into three independent modal components. Each modal component has its own independent characteristics and laws, which facilitates the analysis of the impact of the fault on different modes.

[0096] An initial fault point is set by using a binary method, a first voltage value and a second voltage value of the initial fault point are respectively calculated from electrical quantities at both ends of the line, and a corresponding first voltage waveform and a second voltage waveform are determined based on the first voltage value and the second voltage value;

[0097] like Figure 3 As shown in the figure, it is a 10kV AC distribution network with distributed power sources. The power source on the left is an infinite power source, and the power source on the right is an inverter-type distributed power source. After the fault occurs, the voltage on both sides of the power source drops and the current rises, but the voltage and current on the right side are significantly smaller than those on the left, showing a strong power source and a weak power source. Here, the bus voltage sampling value on the M side of the figure is set to u m , the voltage sampling value on the N side is u n , the line current sampling value on the M side is i m , the N-side line current sampling value is i n ; The resistance per unit length of the line is r, the inductance is l, and the fault distance is L1. Based on u m 、i m , r and l, using the differential equation, the voltage at L1 can be calculated Similarly, using the N side u n 、i n , r and l can be used to calculate the voltage at (L-L1) If L1 is the fault distance, then and Indicates the voltage at the same position. The two are theoretically overlapped in terms of waveform. If L1 is not the fault distance, then and It represents the voltage at two different points. The two have different waveforms and the waveforms will not overlap.

[0098] Based on the above theoretical analysis, please refer to Figure 4 , the binary method is used to determine the true fault distance. First, the initial fault point is set, for example, the initial fault point is set to the midpoint of the line, and the voltage values ​​of the two fault points are calculated based on the voltage and current on the M side and the voltage and current on the N side, that is, the M side corresponds to the first voltage value and the N side corresponds to the second voltage value. Substitute the instantaneous electrical quantities collected on the M side and the N side into the following formulas to obtain the first voltage waveform of the fault point on the M side and the second voltage waveform of the fault point on the N side:

[0099]

[0100] Where: i m0 、i m1 and i m2 are the 0 modulus, 1 modulus and 2 modulus of the three-phase current at the line end corresponding to the first voltage value after phase modulus transformation, i n0 、i n1 and i n2They are respectively the 0 modulus, 1 modulus and 2 modulus of the three-phase current at the line end corresponding to the second voltage value after phase modulus transformation, r0 and l0 are respectively the 0 modulus resistance and inductance per unit length of the line, r1 and l1 are respectively the 1 modulus resistance and inductance per unit length of the line, r2 and l2 are respectively the 2 modulus resistance and inductance per unit length of the line.

[0101] Comparing the magnitudes of the first voltage waveform and the second voltage waveform by a directed distance algorithm, and calculating the similarity between the first voltage waveform and the second voltage waveform;

[0102] In the process of extrapolation, the waveform may be negative. Here, a directed distance algorithm is used to compare the first voltage waveform and the second voltage waveform to determine the direction of the next step, and calculate the waveform similarity to determine whether it has converged. Figure 5 , the voltage waveform of the fault point calculated from both sides, let and is the instantaneous voltage series, and we get Figure 6 The waveform of the voltage difference at the fault point is shown in Figure 2. n-1 ,t0=T,t n-1 ≤T) is integrated using the trapezoidal method, and we get:

[0103]

[0104] Where: Δu is and The instantaneous voltage difference, T1 and T2 are the two adjacent zero-crossing points of the Δu waveform, A1 is the result of integrating Δu in the time interval [T1, T2], and A2 is The result obtained by integrating in the time interval [T1, T2], A3 is The result obtained by integrating in the time interval [T1, T2], t i is the time corresponding to the ith data point, t i+1 is the time corresponding to the i+1th data point, Δu(t i ) is t i The voltage change corresponding to time, Δu(t i+1 ) is t i+1 The voltage change corresponding to time, |u L1 (t i )|for In t i The voltage value corresponding to the time, |u L1 (t i+1 )|for u L1 In t i+1 The voltage value corresponding to the time, |u (L-L1) (t i )|for In ti The voltage value corresponding to the time, |u (L-L1) (t i+1 )|for In t i+1 The voltage value corresponding to the time.

[0105] Assuming that the initial fault point is at the midpoint of the line, when A1>0, the first voltage waveform is greater than the second voltage waveform, which means that the voltage waveform obtained on the M side is greater than the voltage waveform obtained on the N side; when A1<0, the first voltage waveform is less than the second voltage waveform, which means that the voltage waveform obtained on the M side is less than the voltage waveform obtained on the N side. When the first voltage waveform is greater than the second voltage waveform, the binary method is used again to select the point on the right half as the new fault point; when the first voltage waveform is less than the second voltage waveform, the binary method is used again to select the point on the left half as the new fault point.

[0106] The steps of comparing the size of two waveforms and calculating the similarity are not repeated and cannot replace each other. The purpose of comparing the size of two waveforms is to determine the location of the next hypothetical fault point, and the comparison has positive and negative properties (such as Figure 3 middle and Although at this time but Located on the negative half of the vertical axis, Located on the positive semi-axis, ), so the similarity alone cannot be used to determine the fault point and find the direction; the similarity is calculated to stop the calculation when the ranging accuracy is met, otherwise the assumed fault point will oscillate back and forth near the real fault point and fail to converge.

[0107] When the similarity between the first voltage waveform and the second voltage waveform meets the threshold condition, the initial fault point is determined to be the target fault point location;

[0108] When the similarity between the first voltage waveform and the second voltage waveform does not meet the threshold condition, the fault point is reset by using the binary method according to the result of comparing the magnitudes of the first voltage waveform and the second voltage waveform.

[0109] The similarity calculation formula is as follows:

[0110]

[0111] Wherein: η is the similarity between the first voltage waveform and the second voltage waveform.

[0112] After the fault point is re-determined, the two voltage waveforms of the new fault point are calculated again from both ends, the two waveforms are compared, and the waveform similarity is calculated. When the similarity meets the threshold condition, the fault point position set at this time is the target fault point position, and the distance measurement ends; if it does not meet the threshold condition, the next fault point position is re-determined based on the waveform size comparison result, using the binary search method, and so on.

[0113] The following experiments are combined to verify:

[0114] In PSCAD / EMTDC simulation software, Figure 2 The 10kV AC distribution network model with DG is shown. The rated capacity of the system is 50MVA, the rated voltage is 10.5kV; the distributed power source is a 2.5MW photovoltaic power source, and the grid-connected inverter adopts a constant power control strategy; the total length of the line is 10km, the line impedance parameter is (0.27+j0.347)Ω / km, and the fault point is set at 2km from the M-side bus; the sampling frequency is 4kHz, and the sampling window length is 2.5ms. The ranging process data is shown in Table 1 below:

[0115] Table 1 2km fault distance measurement process

[0116]

[0117] Using the above model, different fault locations are set, and the distance measurement results are shown in Table 2 below:

[0118] Table 2 Ranging results

[0119]

[0120] According to the data in the table, it can be concluded that the present invention, on the basis of considering the influence of distributed power supply on the ranging result, obtains rich fault information by comparing the double-terminal voltage waveform, reduces the ranging error, and effectively improves the accuracy of fault ranging.

[0121] Example 3

[0122] This embodiment also provides a computer device, which is applicable to a method for fault location in an active distribution network based on comparison of two-terminal voltage waveforms, and includes a memory and a processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement a forced oscillation detection and positioning method for a distribution network as proposed in the above embodiment.

[0123] This embodiment further provides a storage medium on which a computer program is stored. When the program is executed by a processor, a forced oscillation detection and positioning method for a distribution network is implemented as proposed in the above embodiment.

[0124] The computer device may be a terminal, and the computer device includes a processor, a memory, a communication interface, a display screen and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. The display screen of the computer device may be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device may be a touch layer covering the display screen, or a key, trackball or touchpad provided on the housing of the computer device, or an external keyboard, touchpad or mouse, etc.

[0125] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0126] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0127] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0128] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used to implement: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0129] 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 preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for fault location in an active distribution network based on comparison of two-terminal voltage waveforms, characterized in that: It includes obtaining voltage and current data of a first target point and a second target point of a distribution line; Setting an initial fault point on the distribution line by using a binary method, and calculating a first voltage waveform and a second voltage waveform at the initial fault point based on voltage and current data of the first target point and the second target point; Using a directed distance algorithm to compare the first voltage waveform and the second voltage waveform to obtain a waveform difference; Determining whether the initial fault point is the target fault point location according to whether the waveform difference satisfies a preset threshold condition; When the waveform difference does not meet the preset threshold condition, the fault point position is reset by using the binary method based on the comparison result of the first voltage waveform and the second voltage waveform.

2. The active distribution network fault location method based on two-terminal voltage waveform comparison according to claim 1, characterized in that: The first target point of the distribution line is the starting end of the distribution line, the second target point of the distribution line is the end of the distribution line, and the distribution line includes a strong power supply end and a weak power supply end.

3. The active distribution network fault location method based on two-terminal voltage waveform comparison as claimed in claim 2, characterized in that: The initial fault point is set at the midpoint of the distribution line, and the distance between the first target point and the second target point is a preset total line length.

4. The active distribution network fault location method based on two-terminal voltage waveform comparison as claimed in claim 3, characterized in that: When the waveform difference does not meet the preset threshold condition: If the first voltage waveform is greater than the second voltage waveform, resetting the fault point on the line between the initial fault point and the second target point; If the first voltage waveform is smaller than the second voltage waveform, a fault point is reset on the line between the first target point and the initial fault point.

5. The method for fault location in active distribution network based on comparison of two-terminal voltage waveforms according to claim 4, characterized in that: The calculation of the waveform difference includes: calculating the voltage difference between the first voltage waveform and the second voltage waveform; performing an integration operation on the voltage difference within a preset time period; and determining the waveform difference based on a result of the integration operation.

6. The active distribution network fault location method based on two-terminal voltage waveform comparison as claimed in claim 5, characterized in that: The method of resetting the fault point position by using the binary search method includes: selecting the midpoint position as the new fault point within the determined new line section; recalculating the first voltage waveform and the second voltage waveform at the new fault point; and repeating the waveform comparison and fault point update process until the waveform difference meets the preset threshold condition.

7. The method for fault location in an active distribution network based on comparison of two-terminal voltage waveforms according to claim 6, characterized in that: Also includes: Establish a fault distance measurement database to record the waveform difference changes during each distance measurement process; Dynamically adjusting the dichotomy split ratio according to the waveform difference change trend; When the waveform difference is less than a preset threshold, the final fault point location information is output.

8. An active distribution network fault location system based on two-terminal voltage waveform comparison, based on the active distribution network fault location method based on two-terminal voltage waveform comparison according to any one of claims 1 to 7, characterized in that: It also includes a data acquisition module to obtain voltage and current data of a first target point and a second target point of the distribution line; a voltage waveform calculation module, which sets an initial fault point on the distribution line by using a binary method, and calculates a first voltage waveform and a second voltage waveform at the initial fault point based on voltage and current data of the first target point and the second target point; A waveform analysis module, using a directed distance algorithm to compare the first voltage waveform and the second voltage waveform to obtain a waveform difference; A fault point determination module determines whether the initial fault point is the target fault point location according to whether the waveform difference satisfies a preset threshold condition; The fault point updating module resets the fault point position by using a binary search method based on a comparison result between the first voltage waveform and the second voltage waveform when the waveform difference does not meet a preset threshold condition.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the active distribution network fault location method based on two-terminal voltage waveform comparison according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the active distribution network fault location method based on two-terminal voltage waveform comparison according to any one of claims 1 to 7 are implemented.

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