A power distribution network equivalent wave velocity adaptive calculation method

Abstract

The application discloses a power distribution network equivalent wave velocity adaptive calculation method and belongs to the field of power system relay protection and power distribution network automation. Three-phase voltage and current of a measurement end are acquired, and a specific mode wide-frequency measurement sequence is constructed. Input impedance frequency domain response and time domain impedance impulse response are calculated. A space distance reflection amplitude function under a candidate wave velocity is established in combination with a line impedance discontinuous feature point space distance set. An optimal equivalent wave velocity is obtained through interval optimization of a matching degree function. The method does not need external pulse injection and accurate line parameters, can compensate wave velocity drift caused by environmental factors, and improves ranging reference precision of fault positioning and state perception.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection and distribution network automation technology, and in particular to an adaptive calculation method for equivalent wave velocity in distribution networks. Background Technology

[0002] With the large-scale integration of distributed power sources, the topology, line media, and operating status of medium-voltage distribution networks exhibit greater uncertainty. Traveling wave ranging, high-frequency impedance fault location, and cable condition monitoring all require the propagation speed of electromagnetic waves in the line as a spatial ranging benchmark. Propagation speed errors directly translate into spatial errors in fault location or condition sensing results.

[0003] Traditional methods for obtaining wave velocity typically rely on cable factory parameters, line impedance / admittance models, or specialized active pulse injection equipment. However, in actual distribution networks, factors such as ambient temperature, line sag, aging, and the mixed laying of overhead and cable lines cause dynamic drift in the equivalent wave velocity; relying solely on fixed parameters makes it difficult to reflect the actual operating conditions. Active injection measurements require additional high-frequency signal sources and synchronous measurement equipment, increasing hardware costs and potentially causing additional disturbances to active distribution networks containing power electronic equipment.

[0004] On the other hand, distribution networks naturally possess numerous impedance discontinuity points, such as main feeder branch connection points, lower-level branch connection points of branch lines, and line ends. The geometric spatial distances of these points can typically be obtained from distribution network topology data or geographic information. Direct-connected inverters naturally generate high-frequency harmonic components covering a wide frequency band during pulse width modulation (PWM). These endogenous broadband signals can serve as passive measurement excitation sources, generating reflection responses at impedance discontinuity points. Current technology has not yet fully integrated the inverter's inherent broadband signal, time-domain impedance reflection patterns, and the spatial topology of distribution network points to adaptively solve for the equivalent line wave velocity.

[0005] Therefore, there is a need for a method for calculating the equivalent wave velocity of a power distribution network that does not rely on external active pulse injection, does not rely on precise cable physical parameters, and can self-calibrate according to changes in environment and line conditions. Summary of the Invention

[0006] The purpose of this invention is to provide an adaptive calculation method and system for equivalent wave velocity in power distribution networks, which solves the problems of existing wave velocity acquisition methods that rely on accurate line parameters and external active signal injection equipment, are difficult to adapt to the dynamic drift of wave velocity caused by environmental factors, and thus affect the accuracy of traveling wave ranging and line status sensing.

[0007] To achieve the above objectives, this invention provides an adaptive calculation method for the equivalent wave velocity of a distribution network, comprising: S1, acquiring a three-phase voltage sampling sequence and a three-phase current sampling sequence at the measurement end, and constructing a broadband sampling sequence of a specific mode voltage and a broadband sampling sequence of a specific mode current at the measurement end from the three-phase voltage sampling sequence and the three-phase current sampling sequence at the measurement end; S2, converting the broadband sampling sequence of the specific mode voltage and the broadband sampling sequence of the specific mode current at the measurement end into the frequency domain response of the input impedance at the measurement point, and performing inverse Fourier transform processing on the frequency domain response of the input impedance at the measurement point to obtain the time domain impedance impulse response function of the measurement point; S3, constructing a spatial distance set of line impedance discontinuity feature points based on the topological geometric information of the distribution network line, and mapping the time domain impedance impulse response function of the measurement point to a candidate spatial distance reflection amplitude function according to the candidate equivalent wave velocity adjustment coefficient; S4, constructing a matching degree function based on the spatial distance set of line impedance discontinuity feature points and the candidate spatial distance reflection amplitude function, performing interval optimization processing on the matching degree function to obtain the optimal equivalent wave velocity of the distribution network line.

[0008] Further, step S1 includes: S11, extract the phase B voltage sampling sequence and phase C voltage sampling sequence from the three-phase voltage sampling sequence at the measurement end, and generate a broadband sampling sequence of specific mode voltage at the measurement end by subtracting the phase B voltage sampling sequence and the phase C voltage sampling sequence at the measurement end; S12, extract the phase B current sampling sequence and phase C current sampling sequence from the three-phase current sampling sequence at the measurement end, and generate a broadband sampling sequence of specific mode current at the measurement end by subtracting the phase B current sampling sequence and the phase C current sampling sequence at the measurement end; S13, organize the broadband sampling sequence of specific mode voltage and the broadband sampling sequence of specific mode current at the measurement end into a broadband measurement sequence of specific mode network.

[0009] Further, step S2 includes: S21, Perform Fourier transform processing on the wideband sampling sequence of the specific mode voltage at the measurement end to obtain the frequency domain response of the specific mode voltage at the measurement end; S22, Perform Fourier transform processing on the wideband sampling sequence of the specific mode current at the measurement end to obtain the frequency domain response of the specific mode current at the measurement end; S23 generates the frequency domain response of the input impedance at the measurement point by the ratio of the frequency domain response of the voltage of a specific mode at the measurement end to the frequency domain response of the current of a specific mode at the measurement end; S24. Perform inverse Fourier transform on the frequency domain response of the input impedance at the measurement point to obtain the time domain impedance impulse response function of the measurement point.

[0010] Further, step S3 includes: S31, Select feature points of the distribution network line topology geometry information according to the line branch connection point, line end and lower branch connection point to form a set of line impedance discontinuity feature points; S32, Determine the spatial distance set of line impedance discontinuity feature points based on the geometric path length from the measurement point to each line impedance discontinuity feature point in the set of line impedance discontinuity feature points; S33, determine the candidate equivalent wave velocity based on the initial reference wave velocity and the candidate equivalent wave velocity adjustment coefficient; S34 performs a time-axis to spatial distance-axis transformation on the time-domain impedance impulse response function of the measurement point to obtain the candidate spatial distance reflection amplitude function.

[0011] Further, step S4 includes: S41, extract the reflection amplitude of the candidate spatial distance reflection amplitude function at multiple spatial distance locations corresponding to the spatial distance set of line impedance discontinuity feature points; S42, summates the reflection amplitudes corresponding to multiple spatial distance positions to form the matching degree function value corresponding to the candidate equivalent wave velocity adjustment coefficient; S43, traverse the search interval of candidate equivalent wave velocity adjustment coefficients to obtain the sequence of matching degree function values; S44. Determine the optimal equivalent wave velocity of the distribution network line based on the maximum matching degree function value in the matching degree function value sequence.

[0012] Furthermore, the search interval for candidate equivalent wave velocity adjustment coefficients includes: The search range for the candidate equivalent wave velocity adjustment coefficient is determined based on the line type, the initial reference wave velocity, and the environmental disturbance margin. The search range for the candidate equivalent wave velocity adjustment coefficient is a continuous range that is not greater than the upper reference limit and not less than the preset lower limit. The preset lower limit is determined based on the temperature change, line sag change, and line structure change of the distribution network line.

[0013] Furthermore, the frequency domain response of the input impedance at the measurement point includes: The frequency domain response of the input impedance at the measurement point is obtained by dividing the frequency domain response of the voltage at the measurement point by the frequency domain response of the current at the measurement point. The frequency domain responses of the voltage and current at the measurement point are excited by the broadband harmonic signals generated by the pulse width modulation process of the direct-connected inverter.

[0014] Furthermore, the set of characteristic points of line impedance discontinuity includes: The set of line impedance discontinuity feature points includes main feeder branch connection points, branch line lower-level branch connection points, and line ends. Each line impedance discontinuity feature point in the set of line impedance discontinuity feature points is configured with a geometric path length relative to the measurement point.

[0015] Furthermore, the optimal equivalent wave velocity of the distribution network line includes: The optimal equivalent wave velocity of a distribution network line is obtained by multiplying the initial reference wave velocity by the optimal equivalent wave velocity adjustment coefficient. The optimal equivalent wave velocity adjustment coefficient is the candidate equivalent wave velocity adjustment coefficient that maximizes the matching degree function.

[0016] This invention also provides an adaptive calculation system for the equivalent wave velocity of a distribution network for online adaptive calculation of distribution network line wave velocity, comprising: a single-ended acquisition unit, a mode transformation unit, an impedance response calculation unit, a topology feature point storage unit, a spatial matching optimization unit, and a result output unit; the single-ended acquisition unit is connected to the distribution network measurement end and acquires the three-phase voltage sampling sequence and the three-phase current sampling sequence of the measurement end; the mode transformation unit is connected to the single-ended acquisition unit and generates a broadband sampling sequence of specific mode voltage and a broadband sampling sequence of specific mode current of the measurement end; the impedance response calculation unit is connected to the mode transformation unit and generates the time-domain impedance impulse response function of the measurement point; the topology feature point storage unit stores the topological geometric information of the distribution network line and the spatial distance set of line impedance discontinuity feature points; the spatial matching optimization unit is connected to the impedance response calculation unit and the topology feature point storage unit respectively, and executes the above-mentioned adaptive calculation method for the equivalent wave velocity of the distribution network; the result output unit is connected to the spatial matching optimization unit and outputs the optimal equivalent wave velocity of the distribution network line.

[0017] Compared with existing technologies, the present invention has at least the following advantages: First, it utilizes the endogenous broadband harmonics generated by the pulse width modulation process of the direct-connected inverter as a passive measurement excitation, avoiding the addition of external active pulse injection equipment and its additional disturbance to the distribution network operation status; Second, it matches and optimizes the time-domain impedance impulse response of the measurement point with the spatial distance set of line impedance discontinuity characteristic points, and the wave velocity acquisition process does not depend on conductor type, conductor material, and accurate high-frequency impedance model; Third, it adaptively compensates for wave velocity drift caused by changes in ambient temperature, line sag, and line structure through the candidate equivalent wave velocity adjustment coefficient search interval and the matching degree function maximization process; Fourth, the output optimal equivalent wave velocity of the distribution network line can be used as a ranging benchmark for traveling wave ranging, fault location, and line status perception, improving the online self-sensing capability of complex multi-branch topology distribution networks. Attached Figure Description

[0018] Figure 1 is a flowchart of the adaptive calculation method for equivalent wave velocity in power distribution networks according to the present invention.

[0019] Figure 2 is a structural diagram of the 10kV distribution network model in the embodiment.

[0020] Figure 3 shows the waveforms of the broadband sampling sequences of the voltage and current of the specific mode at the measurement end in the embodiment.

[0021] Figure 4 shows the calculation results of the time-domain impedance impulse response function at the measurement point in the embodiment.

[0022] Figure 5 shows the matching function in the embodiment. The calculation results are shown in the figure.

[0023] Figure 6 shows the calculation results of the optimal equivalent wave velocity of the distribution network line in the embodiment. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These specific embodiments are used to explain the present invention and do not limit the scope of protection of the present invention.

[0025] As shown in Figure 1, the calculation process of this invention includes constructing a specific mode broadband measurement sequence, calculating the input impedance response, constructing a set of spatial distances for topological feature points, mapping the spatial distance reflection amplitude function, and optimizing the matching degree function. This process can be deployed in distribution network automation terminals, fault location devices, edge computing units, or monitoring platforms containing processors and memory.

[0026] In one implementation, the single-ended acquisition unit is located at the connection point of the direct-connected inverter or the measurable end of the line under test. The single-ended acquisition unit acquires the three-phase voltage sampling sequence and the three-phase current sampling sequence at the measurement end. To reduce the electromagnetic coupling effect between the three-phase lines, phases B and C are selected to construct a specific mode network broadband measurement sequence, wherein the specific mode voltage broadband sampling sequence and the specific mode current broadband sampling sequence at the measurement end can be expressed as follows: ; ; In the formula, This is the sampling sequence of phase B voltage at the measurement terminal. This is the sampling sequence of phase C voltage at the measurement terminal. This is the sampling sequence of phase B current at the measurement terminal. This is the sampling sequence of the C-phase current at the measurement terminal. This is a wideband sampling sequence of specific mode voltages at the measurement end. This is a broadband sampling sequence for specific mode current at the measurement end. In addition to the combination of phase B and phase C, in another embodiment, the combination of phase A and phase B or phase A and phase C can also be used to construct a broadband measurement sequence for a specific mode network, as long as the selected phase combination can form a stable broadband measurement response within the measurement frequency band.

[0027] The high-frequency switching harmonics generated during multi-level pulse width modulation (PWM) in a direct-connected inverter serve as passive broadband excitation. Fourier transforms are performed on the broadband sampling sequences of the voltage and current at the measurement terminals for specific modes to obtain the frequency domain response of the voltage at the measurement terminals. Frequency domain response of specific mode current at the measurement end Frequency domain response of input impedance at the measurement point Calculate using the following formula: ; Frequency domain response of input impedance at the measurement point Perform inverse Fourier transform processing to obtain the time-domain impedance impulse response function at the measurement point. : ; Time-domain impedance impulse response function at the measurement point The pulse peak time corresponds to the round-trip propagation time of a broadband signal at impedance discontinuity points. This correspondence is used to convert the time-reflection response into a spatial distance-reflection response.

[0028] The topological geometry information of the distribution network lines can be obtained from line design data, operation and maintenance records, or geographic information data. Line impedance discontinuity feature points are selected according to line branch connection points, line ends, and lower-level branch connection points to form a set of line impedance discontinuity feature points. Using the measurement point as a distance reference point, the geometric path length of each line impedance discontinuity feature point relative to the measurement point is recorded, resulting in a set of spatial distances for the line impedance discontinuity feature points. ; In the formula, For the first The geometric path length from each line impedance discontinuity characteristic point to the measurement point. This represents the number of line impedance discontinuity feature points. Line impedance discontinuity feature points can include main feeder branch connection points, lower-level branch connection points of branch lines, and line ends. This set uses only spatial geometric distances and does not use line material parameters, impedance parameters, or admittance parameters as necessary inputs for wave velocity calculations.

[0029] The candidate equivalent wave velocity adjustment coefficient is The initial reference wave velocity is Under the condition of, candidate equivalent wave velocity Represented as: ; Based on the round-trip propagation relationship of broadband signal reflection, the time-domain impedance impulse response function at the measurement point is... Mapped to candidate spatial distance reflection amplitude function : ; In the formula, This represents the distance variable on the spatial distance axis. If the single-way propagation time definition is used on-site, the coefficients in the mapping relationship can be adjusted according to the time calibration method of the measurement system; in the same project implementation, the time calibration method, spatial distance set, and candidate equivalent wave velocity adjustment coefficient search process remain consistent.

[0030] Spatial distance set of characteristic points of line impedance discontinuity Extract candidate spatial distance reflection amplitude functions at multiple spatial distance locations. The reflection amplitudes are calculated and summed to form candidate equivalent wave velocity adjustment coefficients. Corresponding matching degree function value: ; Traversing the search interval of candidate equivalent wave velocity adjustment coefficients This yields a sequence of matching degree function values. The matching degree function is then... The candidate equivalent wave velocity adjustment coefficient that achieves the maximum value is the optimal equivalent wave velocity adjustment coefficient. : ; Optimal equivalent wave velocity of distribution network lines We obtain the following formula: ; The search range for the candidate equivalent wave velocity adjustment coefficient can be set according to the line type, initial reference wave velocity, and environmental disturbance margin. For overhead lines, the initial reference wave velocity can be a reference value close to the speed of light; for cables, the initial reference wave velocity can be a reference value of the typical propagation speed of the cable. The search range can be set as a continuous interval not greater than the upper limit of the reference range and not less than the preset lower limit to cover wave velocity drift caused by temperature changes, line sag changes, and line structure changes. The search method can adopt uniform traversal, coarse and fine two-level search, golden section search, or other one-dimensional extreme value search methods; once the adjustment coefficient corresponding to the maximum value of the matching degree function is determined, the equivalent wave velocity of the current line is locked.

[0031] In one specific embodiment, as shown in Figure 2, a 10kV medium-voltage distribution network model is constructed. This model includes a 110kV system power supply, a system main transformer with a transformation ratio of 110 / 10.5, one main line, and four branch lines, some of which include lower-level branch lines. Overhead lines include three types with wire diameters of 240mm, 150mm, and 95mm. Cable lines are 95mm copper-core cross-linked polyethylene insulated power cables. The line model adopts a distributed parameter model. The calculation process is illustrated below using the case where the inverter is connected to the end of the main line and the fault location is near a branch line.

[0032] In this embodiment, the three-phase voltage and three-phase current at the inverter-line connection during normal operation are sampled at a high frequency of 2MHz, retaining 40ms of sampled data within the range of 10ms to 50ms. A broadband sampling sequence for specific mode voltage and current at the measurement terminal is constructed using the voltage and current differences between phases B and C. Figure 3 shows the specific mode voltage and current waveforms under this operating condition.

[0033] Based on the broadband sampling sequences of specific mode voltage and specific mode current at the measurement end, the frequency domain response of the input impedance at the measurement point is calculated, and then the time domain impedance impulse response function at the measurement point is obtained by inverse Fourier transform. Figure 4 shows the time domain function. The calculation results show that multiple peak values ​​in the results correspond to the reflection responses of broadband signals at the main feeder branch connection points, lower-level branch connection points, and line ends.

[0034] An initial reference wave velocity is set using the spatial distance set of recorded line impedance discontinuity feature points. Considering common overhead line parameters, line sag, and the engineering margins brought about by ambient temperature, the search range for candidate equivalent wave velocity adjustment coefficients is set to... .according to The time-domain impedance impulse response function at the measurement point is mapped to the spatial distance reflection amplitude function, and the matching function is calculated. Figure 5 shows the matching function. The calculation results.

[0035] Within the search interval of the candidate equivalent wave velocity adjustment coefficient, After optimization, the optimal equivalent wave velocity adjustment coefficient is found. The corresponding optimal equivalent wave velocity of the distribution network line Figure 6 shows the optimized feature point matching results and the equivalent wave velocity calculation results. The results indicate that the time-domain reflection peak achieves a high degree of matching with known spatial feature points under the optimal equivalent wave velocity, thus enabling online adaptive calculation of the line's equivalent wave velocity.

[0036] In another embodiment, the measuring end can be located at the beginning or end of the main feeder, or at the measurable end of a branch line; the spatial distance set of discontinuous characteristic points of line impedance is correspondingly replaced by the set of geometric path lengths from the corresponding measuring end to each branch connection point, the end of the line, or the lower-level branch connection point. In another embodiment, the search interval for the candidate equivalent wave velocity adjustment coefficient can be set according to the typical propagation speed of cable lines, the typical propagation speed of overhead lines, or the segmented reference speed of mixed overhead and cable lines; as long as the optimal equivalent wave velocity adjustment coefficient is determined by maximizing the matching degree function, the overall inventive concept of this invention—using broadband impedance reflection and spatial matching of characteristic points to calculate the equivalent wave velocity—remains unchanged.

[0037] The system implementation of this invention can be achieved using a processor, a memory, a sampling interface, and a communication interface. The memory stores the topological geometry information of the distribution network lines, the spatial distance set of line impedance discontinuity characteristic points, the initial reference wave velocity, and the search interval for candidate equivalent wave velocity adjustment coefficients. When the processor executes program instructions, it completes the construction of a specific mode broadband measurement sequence, the calculation of the input impedance frequency domain response, the calculation of the time domain impedance impulse response function of the measurement point, the mapping of the candidate spatial distance reflection amplitude function, the construction of the matching degree function, and the interval optimization processing, and outputs the optimal equivalent wave velocity of the distribution network lines to the fault location device, the condition monitoring system, or the distribution network automation platform.

Claims

1. An adaptive calculation method for equivalent wave velocity in a distribution network, characterized in that, include: S1, acquire the three-phase voltage sampling sequence and the three-phase current sampling sequence at the measurement terminal, and construct the broadband sampling sequence of the specific mode voltage and the broadband sampling sequence of the specific mode current at the measurement terminal from the three-phase voltage sampling sequence and the three-phase current sampling sequence at the measurement terminal; S2, convert the broadband sampling sequence of the voltage and current of the specific mode at the measurement end into the frequency domain response of the input impedance at the measurement point, and perform inverse Fourier transform on the frequency domain response of the input impedance at the measurement point to obtain the time domain impedance impulse response function of the measurement point; S3, based on the topological geometric information of the distribution network line, construct the spatial distance set of line impedance discontinuity feature points, and map the time-domain impedance impulse response function of the measurement point to the candidate spatial distance reflection amplitude function according to the candidate equivalent wave velocity adjustment coefficient; S4. Based on the set of spatial distances of discontinuous characteristic points of line impedance and the candidate spatial distance reflection amplitude function, a matching degree function is constructed. The matching degree function is then subjected to interval optimization to obtain the optimal equivalent wave velocity of the distribution network line.

2. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 1, characterized in that, Step S1 includes: S11, extract the phase B voltage sampling sequence and phase C voltage sampling sequence from the three-phase voltage sampling sequence at the measurement end, and generate a broadband sampling sequence of specific mode voltage at the measurement end by subtracting the phase B voltage sampling sequence and the phase C voltage sampling sequence at the measurement end; S12, extract the phase B current sampling sequence and phase C current sampling sequence from the three-phase current sampling sequence of the measurement terminal, and generate a broadband sampling sequence of specific mode current of the measurement terminal by subtracting the phase B current sampling sequence and the phase C current sampling sequence of the measurement terminal; S13, organize the broadband sampling sequence of specific mode voltage and the broadband sampling sequence of specific mode current at the measurement end into a broadband measurement sequence of specific mode network.

3. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 1, characterized in that, Step S2 includes: S21, Perform Fourier transform processing on the wideband sampling sequence of the specific mode voltage at the measurement end to obtain the frequency domain response of the specific mode voltage at the measurement end; S22, Perform Fourier transform processing on the wideband sampling sequence of the specific mode current at the measurement end to obtain the frequency domain response of the specific mode current at the measurement end; S23 generates the frequency domain response of the input impedance at the measurement point by the ratio of the frequency domain response of the voltage of a specific mode at the measurement end to the frequency domain response of the current of a specific mode at the measurement end; S24. Perform inverse Fourier transform on the frequency domain response of the input impedance at the measurement point to obtain the time domain impedance impulse response function of the measurement point.

4. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 1, characterized in that, Step S3 includes: S31, Select feature points of the distribution network line topology geometry information according to the line branch connection point, line end and lower branch connection point to form a set of line impedance discontinuity feature points; S32, Determine the spatial distance set of line impedance discontinuity feature points based on the geometric path length from the measurement point to each line impedance discontinuity feature point in the set of line impedance discontinuity feature points; S33, determine the candidate equivalent wave velocity based on the initial reference wave velocity and the candidate equivalent wave velocity adjustment coefficient; S34 performs a time-axis to spatial distance-axis transformation on the time-domain impedance impulse response function of the measurement point to obtain the candidate spatial distance reflection amplitude function.

5. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 1, characterized in that, Step S4 includes: S41, extract the reflection amplitude of the candidate spatial distance reflection amplitude function at multiple spatial distance locations corresponding to the spatial distance set of line impedance discontinuity feature points; S42, summates the reflection amplitudes corresponding to multiple spatial distance positions to form the matching degree function value corresponding to the candidate equivalent wave velocity adjustment coefficient; S43, traverse the search interval of candidate equivalent wave velocity adjustment coefficients to obtain the sequence of matching degree function values; S44. Determine the optimal equivalent wave velocity of the distribution network line based on the maximum matching degree function value in the matching degree function value sequence.

6. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 5, characterized in that, The search range for candidate equivalent wave velocity adjustment coefficients includes: The search range for the candidate equivalent wave velocity adjustment coefficient is determined based on the line type, the initial reference wave velocity, and the environmental disturbance margin. The search range for the candidate equivalent wave velocity adjustment coefficient is a continuous range that is not greater than the upper reference limit and not less than the preset lower limit. The preset lower limit is determined based on the temperature change, line sag change, and line structure change of the distribution network line.

7. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 1, characterized in that, The frequency domain response of the input impedance at the measurement point includes: The frequency domain response of the input impedance at the measurement point is obtained by dividing the frequency domain response of the voltage at the measurement point by the frequency domain response of the current at the measurement point. The frequency domain responses of the voltage and current at the measurement point are excited by the broadband harmonic signals generated by the pulse width modulation process of the direct-connected inverter.

8. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 4, characterized in that, The set of characteristic points of line impedance discontinuity includes: The set of line impedance discontinuity feature points includes main feeder branch connection points, branch line lower-level branch connection points, and line ends. Each line impedance discontinuity feature point in the set of line impedance discontinuity feature points is configured with a geometric path length relative to the measurement point.

9. The adaptive calculation method for equivalent wave velocity in a distribution network according to claim 1, characterized in that, The optimal equivalent wave velocity of a distribution network line includes: The optimal equivalent wave velocity of a distribution network line is obtained by multiplying the initial reference wave velocity by the optimal equivalent wave velocity adjustment coefficient. The optimal equivalent wave velocity adjustment coefficient is the candidate equivalent wave velocity adjustment coefficient that maximizes the matching degree function.

10. A distribution network equivalent wave velocity adaptive calculation system for online adaptive calculation of distribution network line wave velocity, characterized in that, include: The system comprises a single-ended acquisition unit, a mode transformation unit, an impedance response calculation unit, a topology feature point storage unit, a spatial matching optimization unit, and a result output unit. The single-ended acquisition unit connects to the distribution network measurement terminal and acquires the three-phase voltage and current sampling sequences. The mode transformation unit connects to the single-ended acquisition unit and generates broadband sampling sequences of specific mode voltage and current at the measurement terminal. The impedance response calculation unit connects to the mode transformation unit and generates the time-domain impedance impulse response function of the measurement point. The topology feature point storage unit stores the topological geometric information of the distribution network lines and the spatial distance set of line impedance discontinuity feature points; the spatial matching optimization unit is connected to the impedance response calculation unit and the topology feature point storage unit respectively, and executes the distribution network equivalent wave velocity adaptive calculation method according to any one of claims 1 to 9; the result output unit is connected to the spatial matching optimization unit and outputs the optimal equivalent wave velocity of the distribution network lines.

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