Low-voltage power distribution network online ranging method and system based on fusion of hplc synchronous incremental impedance and ofdm attenuation slope

Abstract

The application provides a low-voltage distribution network online ranging method and system based on HPLC synchronous incremental impedance and OFDM attenuation slope fusion, and belongs to the technical field of low-voltage distribution network line parameter online identification. The method obtains the synchronous power frequency electrical quantity data before and after the load disturbance of the to-be-measured line object and the OFDM channel frequency response of the related HPLC communication link under the HPLC synchronous time reference; the power frequency incremental impedance is calculated based on the synchronous power frequency electrical quantity increment, and the power frequency equivalent length is obtained; the attenuation characteristics changing with the frequency are extracted from the OFDM channel frequency response, and the channel physical length is obtained; after the two are corresponded to the same to-be-measured line object according to the transformer area topological relationship, consistency comparison is carried out. If the deviation of the two meets the threshold value, the line length is fused and output; if the power frequency equivalent length is greater than the channel physical length and the attenuation characteristics match the normal cable reference form, it is determined that the contact resistance is abnormal, the corrected line length is output, and the contact resistance value is estimated.

Description

Technical Field

[0001] This invention belongs to the technical fields of online identification of low-voltage distribution network line parameters, intelligent transformer substation status perception, and power line carrier communication channel analysis. Specifically, it relates to an online ranging method and system for low-voltage distribution networks based on the fusion of HPLC synchronous incremental impedance and OFDM attenuation slope. It is particularly suitable for low-voltage transformer substations that have already deployed HPLC communication networks, smart meters, concentrators, edge fusion terminals, or branch box acquisition equipment. It enables line ranging and fault diagnosis of joint contact anomalies without requiring additional dedicated signal injection equipment, power outages, or manual segment-by-segment wiring tests, utilizing naturally occurring load changes during operation and channel estimation results from HPLC communication. Background Technology

[0002] Low-voltage distribution networks typically consist of lines originating from the low-voltage side of distribution transformers, forming a tree-like or near-tree-like network via main lines, branch boxes, meter boxes, and user access points. These networks have numerous branches and joints, and their loads are highly time-varying. Furthermore, field line data is often incomplete, inaccurate, or outdated. Obtaining the physical length, power frequency impedance, and contact resistance anomalies of each line segment is crucial for theoretical calculations of distribution area line losses, segmented loss analysis, low-voltage mitigation, fault location, and investigation of potential joint hazards.

[0003] Existing methods for obtaining low-voltage line parameters mainly include the steady-state voltage drop method, the external signal injection method, and estimation methods based on the characteristics of power line communication channels. The steady-state voltage drop method typically reads voltage, current, active power, and reactive power at the transformer side and the end-user side, respectively, and estimates line parameters using the relationship between line voltage drop and line impedance. Its commonly used approximate formula is:

[0004]

[0005] in, The difference in voltage amplitude between the beginning and end points. and These refer to the active power and reactive power transmitted through the line, respectively. and These are the line resistance and reactance, respectively. This method uses a reference voltage. While simple to implement, it typically relies on frozen data from different meters or non-strictly synchronized sampling data, potentially resulting in second- or even minute-level deviations in sampling timing. In low-voltage areas, load fluctuations are frequent, and asynchronous sampling introduces voltage fluctuations caused by load changes into the voltage difference. Furthermore, traditional voltage drop methods often use voltage amplitude differences, failing to fully utilize the phase angle information at the beginning and end of the voltage line, which can easily lead to significant errors in heavy-load, long-line, or low-power-factor scenarios. Additionally, the resistance obtained through the voltage drop method is usually the sum of the physical resistance of the conductor, the contact resistance of the joint, and other series resistance factors, making it difficult to distinguish between the actual line length and the equivalent resistance increase caused by contact abnormalities.

[0006] The external signal injection method involves injecting a test signal of a specific frequency and amplitude into one end of the line under test, measuring the response signal at the other end, and calculating the line impedance or propagation characteristics through the amplitude and phase relationship. This method can achieve good measurement results under dedicated testing conditions, but it requires additional injection equipment and measuring instruments, and typically necessitates on-site wiring and segment-by-segment operation, resulting in low implementation efficiency. In low-voltage distribution areas with complex loads and numerous branches, this method is not suitable for long-term online and automated operation.

[0007] In recent years, with the widespread application of high-speed power line carrier (HPLC) communication in low-voltage distribution areas, line distance estimation methods based on power line communication channel characteristics have gradually emerged. The HPLC physical layer typically employs OFDM modulation, and the channel frequency response of each subcarrier can be estimated during communication using pilot or preamble signals. Since high-frequency power line signal transmission is affected by factors such as conductor resistance, skin effect, branch reflections, load impedance, and connector conditions, the channel amplitude-frequency response contains certain line length and line condition information. Some existing methods directly estimate the distance using the total attenuation of the communication signal, or use RSSI, SNR, and subcarrier amplitude characteristics for topology-level determination. However, low-voltage power line channels are not simple uniform transmission lines; the actual channel frequency response may be superimposed with multiple branch reflections, load impedance variations, coupler frequency response, and noise interference. Directly mapping the total attenuation to distance easily confuses the physical length of the line, branch reflection losses, load absorption losses, and additional losses caused by contact resistance, resulting in insufficient ranging stability and interpretability.

[0008] On the other hand, many terminals, branch box connectors, and meter box connectors in the distribution area may experience oxidation, loosening, overheating, and poor contact after long-term operation. These contact abnormalities typically manifest as additional series resistance at power frequency, causing the total resistance measured by the voltage drop method or power frequency impedance method to be too high. If this total resistance is directly divided by the resistance per unit length to calculate the line length, an artificially inflated equivalent length will be obtained, thus affecting theoretical calculations of line loss and operational maintenance judgments. Therefore, existing technologies still need improvement to enhance the accuracy of online distance measurement in low-voltage distribution networks and reduce the impact of additional resistance factors such as contact resistance on line length estimation and line condition assessment. Summary of the Invention

[0009] To address the shortcomings and deficiencies of existing technologies, this invention provides an online ranging method and system for low-voltage distribution networks based on the fusion of HPLC synchronous incremental impedance and OFDM attenuation slope. This invention utilizes the existing HPLC communication network deployed in the low-voltage distribution area to simultaneously acquire two types of observation data with different physical sensitivities without adding dedicated signal injection equipment or interrupting power supply: one type is the increment of power frequency voltage and current phasors before and after load disturbance, acquired synchronously by microsecond-level HPLC, from which the power frequency incremental impedance is calculated and converted to obtain the power frequency equivalent length reflecting the total line resistance; the other type is the channel frequency response obtained from OFDM physical layer channel estimation during HPLC communication, from which the attenuation trend characteristics changing with frequency are extracted, and the channel physical length, mainly reflecting the physical length of the line, is estimated through a pre-calibrated correspondence. This invention compares the consistency between the power frequency equivalent length and the channel physical length. When the deviation between the two is within a preset range, the line status is determined to be normal and the fused length is output; when the power frequency equivalent length is significantly greater than the channel physical length and the attenuation characteristic pattern matches that of normal cables, an abnormal contact resistance is determined, the channel physical length is used as the corrected line length, and the contact resistance value is quantitatively estimated. This invention also combines the topological relationship of the transformer substation to convert path-level parameters into segment-level parameters, enabling refined ranging and anomaly diagnosis of each branch line within the substation. Through the above technical solution, this invention effectively solves the problems in existing technologies where the physical resistance of the line and the contact resistance are difficult to separate, and ranging results are easily affected by contact anomalies, thus achieving the integration of online ranging and contact resistance anomaly identification in low-voltage distribution networks.

[0010] The specific technical solution adopted by this invention to solve its technical problem is as follows:

[0011] The basic concept of this invention is to treat the power frequency electrical response of low-voltage lines and the OFDM channel frequency response in HPLC communication links as two types of observation information with different sensitivity characteristics. The power frequency incremental impedance reflects the total impedance of the line under test at power frequency, where the resistance component includes the physical resistance of the conductors and any possible contact resistance. The frequency-dependent attenuation characteristics in the OFDM channel frequency response are related to the line material, line length, distributed parameters, and transmission path. After calibration and channel quality control, they can be used to estimate the physical length of the line under test. Under the condition that contact anomalies can be equivalent to local lumped impedance, such anomalies usually do not exhibit the same distributed frequency-dependent attenuation pattern as the physical length of the line, but rather manifest more as increased power frequency resistance, broadband additional loss, or local reflection characteristics. Therefore, by mapping the equivalent power frequency length and the physical length of the OFDM channel to the same line under test and comparing their consistency, it is possible to distinguish between the contribution of the physical length of the line and the contribution of contact resistance.

[0012] To achieve the above objectives, this invention provides a method for online ranging and contact resistance anomaly identification in low-voltage distribution networks. This method, using an HPLC synchronous time reference, acquires synchronous power frequency electrical quantity data before and after load disturbance for the line object under test in a low-voltage distribution network, as well as the OFDM channel frequency response of the HPLC communication link related to the line object under test. The line object under test can be a power supply path from the distribution transformer side to a certain measurement node, or a line segment determined according to the transformer substation topology. The synchronous power frequency electrical quantity data can include one or more of voltage phasors, current phasors, active power, and reactive power, wherein voltage phasors and current phasors are used to characterize the amplitude and phase angle of the power frequency signal.

[0013] Based on the increments of the synchronous power frequency electrical quantity data, the power frequency incremental impedance of the line under test is calculated, and the power frequency equivalent length is obtained from the resistive component of the power frequency incremental impedance. Specifically, after a load disturbance event is detected, the event timestamp is recorded, and the synchronous voltage phasors and current phasors within the steady-state window before and after the disturbance are extracted. The voltage drop increment is obtained based on the difference in voltage phasor increments of relevant nodes of the line under test, and the current increment is obtained based on the current change before and after the disturbance. The power frequency incremental impedance is then obtained from the relationship between the voltage drop increment and the current increment. The steady-state window is used to avoid switching transients, motor starting transients, or other obvious transient processes, so that the data involved in the calculation reflects the relatively stable state before and after the disturbance. Through the difference before and after the disturbance, the voltage drop component formed by the stable background load within this time scale is weakened, making the impedance estimation more focused on reflecting the voltage drop generated when the disturbance current flows through the line under test.

[0014] The load disturbance events can include natural load jump events or identifiable load disturbance events generated by controllable devices. Natural load jump events can be obtained by distributed measurement devices by monitoring changes in local or downstream load power. When natural load jumps are insufficient to form stable identification conditions, identifiable disturbances can be generated using controllable devices within the distribution area that do not affect normal power supply. The power frequency incremental impedance results calculated from multiple independent effective load disturbance events can be weighted and fused. The weights are positively correlated with at least one of the disturbance amplitude, incremental current amplitude, or signal-to-noise ratio of the corresponding disturbance event to improve the stability of the power frequency incremental impedance results.

[0015] Simultaneously, attenuation characteristics varying with frequency are extracted from the OFDM channel frequency response, and the channel physical length of the line under test is obtained based on a preset correspondence between the attenuation characteristics and the physical length of the line. Unlike directly using the total attenuation of the communication signal, this invention focuses on the trend or pattern of channel attenuation changing with frequency, in order to reduce the confounding effects of factors such as broadband added losses and equipment gain changes on line length estimation. The preset correspondence can be determined based on known length reference segments, cable factory attenuation parameters, verified line data, or historical stable samples, and can be updated during operation based on verified line data or on-site sampling data.

[0016] When extracting the attenuation characteristics, the HPLC operating frequency band can be divided into multiple sub-bands. Within each sub-band, the channel attenuation and frequency are linearly fitted to obtain the attenuation slope of each sub-band. Based on the attenuation slope of each sub-band, the full-band weighted attenuation slope can be calculated, or an attenuation slope vector composed of multiple sub-band attenuation slopes can be formed. The preset correspondence can be a calibration relationship between the full-band weighted attenuation slope and the physical length of the line, or a calibration relationship between the attenuation slope vector and the physical length of the line. The frequency-related attenuation reference shape of a normal cable can be determined based on the attenuation slope vector, slope ratio, or frequency-related attenuation template per unit length of the same type of cable. The slope ratio can be the ratio of the absolute value of the attenuation slope in the high-frequency band to the absolute value of the attenuation slope in the low-frequency band to avoid the attenuation slope sign affecting the shape judgment.

[0017] To improve the reliability of OFDM attenuation features, the OFDM channel frequency response can be preprocessed before extracting the attenuation features. This preprocessing includes removing interfered subcarriers and subcarriers with a signal-to-noise ratio (SNR) lower than a preset requirement, and performing fusion and frequency domain smoothing on the multi-frame channel frequency responses. Furthermore, the channel feature quality can be determined based on at least one of the following: channel fitting residual, attenuation slope variance, goodness of fit, multi-frame stability, and communication SNR. Only when the channel feature quality meets the preset requirements is the corresponding channel physical length used for subsequent consistency comparison; when the channel feature quality does not meet the preset requirements, the corresponding result can be marked as a low-confidence result or not used in this fusion decision. Through the above processing, the impact of narrowband interference, strong noise, multipath ripple, and load impedance variations on attenuation feature extraction can be reduced.

[0018] Since low-voltage distribution areas typically have a tree-like or near-tree-like topology, the directly measured power frequency impedance or channel physical length may correspond to the path parameters from a reference node to a certain measurement node, rather than the segmentation parameters between adjacent nodes. Therefore, this invention maps the power frequency equivalent length and channel physical length to the same line object under test based on the distribution area topology. The low-voltage distribution area topology can be obtained in advance, including retrieving it from the distribution area archive, automatically generating it through the topology recognition function of the HPLC network, entering it in the field archive, or obtaining it through inversion of operational data. The topology at least includes the parent-child node connection relationship between each node. When the HPLC node on the distribution transformer side is used as the reference node, the parent-child node relationship in the low-voltage distribution area topology can be combined, and the segmented impedance and segmented length between adjacent parent-child nodes can be obtained by subtracting the path parameters from the reference node to the child node and the path parameters from the reference node to the parent node of that child node. Thus, the path-level measurement results can be converted into segmented line parameters, meeting the needs of segmented operation and maintenance and segmented line loss analysis of low-voltage distribution areas.

[0019] After obtaining the power frequency equivalent length and channel physical length of the same line under test, this invention compares their consistency. The consistency comparison can use the ratio of the absolute value of the difference between the power frequency equivalent length and the channel physical length to the larger of the two values ​​as a consistency index. When the consistency index is less than or equal to a consistency threshold, the line is considered to be in normal condition, and the fused line length is output. The consistency threshold can be determined based on measured data from the transformer substation, line type, measurement confidence level, or operational experience. The fused line length can be obtained by fusing the power frequency equivalent length and channel physical length according to weights. These weights can be determined based on power frequency impedance identification quality, load disturbance amplitude, communication signal-to-noise ratio, channel fitting quality, or attenuation characteristic stability.

[0020] When the consistency index exceeds the consistency threshold, this invention further determines the line status by combining attenuation morphology verification. If the power frequency equivalent length is greater than the channel physical length, and the attenuation characteristics match the frequency-related attenuation reference morphology of a normal cable, then the line under test is determined to have abnormal contact resistance. The matching means that the differences between the attenuation slope vector, slope ratio, unit length frequency-related attenuation template matching result, or other frequency-related morphology indicators of the line under test and the reference morphology of a normal cable of the same type meet preset conditions. The technical meaning of this determination logic is that a larger power frequency equivalent length indicates an additional resistance contribution to the total power frequency resistance, and when the channel physical length and its frequency-related attenuation morphology do not show a corresponding increase in physical length, this additional resistance is more likely to originate from abnormal contact resistance.

[0021] After determining that the contact resistance is abnormal, this invention outputs the physical length of the channel as the corrected line length and estimates the contact resistance value. The contact resistance value can be obtained by subtracting the temperature-compensated conductor resistance corresponding to the physical length of the channel from the resistance component of the power frequency incremental impedance. The temperature-compensated conductor resistance is determined based on the physical length of the channel, the conductor resistance per unit length consistent with the measurement loop, the conductor resistance temperature coefficient, and the conductor operating temperature or estimated temperature. The conductor resistance per unit length consistent with the measurement loop refers to the resistance parameter per unit length that matches the actual current measurement loop; for cases where the phase line and neutral line together form a loop, the resistance parameter per unit length that matches that loop should be used to avoid length or contact resistance estimation deviations due to parameter mixing. The conductor operating temperature can be directly measured or estimated based on ambient temperature, load current, and cable laying method. When the calculated contact resistance value is less than zero, it can be determined that the current data is insufficient to support the conclusion of abnormal contact resistance, or the result can be output as an invalid value.

[0022] To improve applicability under different line conditions, the preset correspondence between the attenuation characteristics and the physical length of the line can be classified and calibrated based on at least one of the following: conductor material, cross-sectional area, insulation type, laying method, and service life. This classification is then updated using verified line data, on-site sampling data, or historical stable samples. This process reduces calibration differences caused by different manufacturers, batches, aging levels, and laying environments, making the channel physical length estimation more suitable for actual low-voltage distribution area environments.

[0023] This invention also provides an online ranging and contact resistance anomaly identification system for low-voltage distribution networks. The system includes an edge fusion terminal and multiple distributed measurement devices connected via an HPLC power line communication network. The distributed measurement devices are used to acquire local power frequency electrical quantity data under HPLC synchronization clock and detect load disturbance events. The edge fusion terminal is used to acquire the OFDM channel frequency response related to the line under test and, in cooperation with the multiple distributed measurement devices, executes the above-mentioned methods to complete power frequency incremental impedance calculation, OFDM attenuation feature extraction, consistency comparison, and contact resistance anomaly determination, and outputs the final ranging result and anomaly information. The edge fusion terminal can be deployed on the low-voltage side of the distribution transformer, and the distributed measurement devices can be deployed on branch boxes, meter boxes, or user access sides, thereby forming an online measurement and diagnostic system using the HPLC communication network on the low-voltage distribution line.

[0024] Compared to existing technologies, this invention and its preferred embodiment utilize HPLC synchronous time reference to obtain synchronous power frequency electrical quantities before and after load disturbance, which can reduce the errors caused by inconsistent sampling times and the use of only voltage amplitude in traditional asynchronous voltage drop methods. By calculating the power frequency incremental impedance by the increment before and after load disturbance, the influence of stable background load on impedance identification can be weakened. Furthermore, this invention does not directly map the total attenuation of the OFDM channel to distance, but extracts the attenuation characteristics that vary with frequency and combines them with calibration relationships to obtain the physical length of the channel, which helps to reduce the confounding effects of branch reflections, load impedance changes, and broadband additional losses on the ranging results. By mapping the power frequency equivalent length and the channel physical length to the same line object under test and comparing their consistency, this invention can fuse the output line length under normal line conditions. When the power frequency equivalent length is abnormally large and the channel attenuation pattern still conforms to the normal cable reference pattern, it can identify abnormal contact resistance, thereby avoiding mistaking the increase in resistance caused by contact resistance as an increase in line length. The preferred scheme further improves its applicability in complex topologies, load fluctuations, and communication noise environments in low-voltage distribution areas by converting path parameters to segmented parameters, temperature compensation, calibration relationship updates, multiple disturbance fusion, and OFDM channel preprocessing and quality control. Attached Figure Description

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0026] Figure 1 This is a flowchart of a method according to an embodiment of the present invention.

[0027] Figure 2 This is a system block diagram of an embodiment of the present invention. Detailed Implementation

[0028] To make the features and advantages of the present invention more apparent and understandable, specific embodiments are described below in detail:

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] This invention provides an online ranging method and system for low-voltage distribution networks based on the fusion of HPLC synchronous incremental impedance and OFDM attenuation slope. The system uses an edge fusion terminal deployed on the low-voltage side of the distribution transformer as the HPLC central node (CCO), and distributed measurement devices deployed in branch boxes, meter boxes, or key user sides as HPLC sub-nodes (STAs). The edge fusion terminal is responsible for HPLC synchronization management, data caching, channel feature reading, fusion calculation, and anomaly alarms; the distributed measurement devices are responsible for local voltage, current, and power acquisition, load jump detection, event timestamp recording, and measurement data reporting.

[0032] The basic idea of ​​this invention is to treat the power frequency electrical response of low-voltage lines and the high-frequency communication channel response of HPLC as two types of observations with different sensitivities. Power frequency incremental impedance is sensitive to conductor physical resistance, line reactance, and contact resistance, thus reflecting the total impedance of the path or segment under test. The frequency-dependent attenuation characteristics in the OFDM high-frequency channel frequency response are mainly related to conductor type, line length, distributed parameters, and transmission path, while local lumped anomalies such as poor contact, under certain conditions, are more often manifested as broadband additional losses or local reflection characteristics. By comparing the consistency between the converted length of power frequency impedance and the converted length of OFDM attenuation characteristics, it can be determined whether the line mainly exhibits normal physical length or whether there is contact resistance that abnormally increases the power frequency resistance.

[0033] It should be noted that in a tree-like low-voltage distribution area, the parameters directly calculated between the edge fusion terminal and a specific STA are typically the power supply path parameters from the transformer side to the node where the STA is located, and are not inherently equivalent to the parameters of a single segmented line. Therefore, in implementation, this invention preferably combines the distribution area topology to further convert the path impedance and path length into segmented impedance and segmented length between the parent node and the child node. For a line segment between a parent node and a child node, the segmented parameters can be directly calculated using the synchronous measurement results of the parent and child nodes; if the parent node does not directly participate in the measurement, the segmented parameters can also be obtained by subtracting the path parameters from the CCO to the child node from the CCO to the parent node.

[0034] The technical solution of this invention does not simply equate the total attenuation of the OFDM channel with the line distance. Instead, it extracts the attenuation trend, segmented slope, template matching results, and fitting reliability as a function of frequency, and combines these with the power frequency impedance results for judgment. As a preferred implementation, after obtaining the OFDM subcarrier channel frequency response, gain normalization, abnormal subcarrier removal, multi-frame averaging, frequency domain smoothing, or multipath ripple suppression are performed first. Then, the attenuation slope characteristics are extracted, and a slope fitting quality or reliability threshold is set. Only when the channel characteristic quality meets the requirements is it used for line length estimation and contact resistance diagnosis. This improves robustness under complex substation, multi-branch, and multi-load variation conditions.

[0035] The implementation of the solution will be further described below with reference to the accompanying drawings and through more specific embodiments:

[0036] like Figure 1 As shown, the low-voltage distribution network online ranging method of this invention is based on the online operation data of transformer substations using HPLC, and forms a power frequency electrical quantity processing branch and an OFDM communication channel processing branch. In the power frequency electrical quantity processing branch, the system uses the HPLC synchronization mechanism to acquire synchronous voltage and current data of different measurement nodes, and uses natural load jumps as excitation events under operating conditions. The power frequency incremental impedance identification result is obtained by the difference in synchronous electrical quantities before and after the jump. This result reflects the total power frequency impedance of the path or segment of the line under test.

[0037] In the OFDM communication channel processing branch, the system acquires OFDM channel response data from the HPLC communication process, preprocesses the channel response, and extracts attenuation features to obtain high-frequency attenuation features related to the physical length of the line and the corresponding physical length estimation results. This branch does not directly rely on power frequency resistance to convert the length, but instead uses the attenuation trend of the communication channel at different frequencies to assist in estimating the line length.

[0038] Subsequently, the system combines the transformer area topology and calibration information to perform path / segment conversion and calibration alignment on the power frequency incremental impedance identification results and OFDM physical length estimation results, ensuring that the two types of results correspond to the same path under test or the same line segment. Based on this, the system performs multi-source consistency fusion decision. When the two types of ranging results are consistent, the line status is determined to be normal, and the line length is fused and output; when the equivalent length corresponding to the power frequency impedance is significantly inconsistent with the physical length corresponding to the OFDM attenuation characteristics, and meets the contact resistance anomaly characteristics, the system determines that there is an abnormal contact resistance, corrects the physical length, and generates an anomaly alarm message. This process achieves integrated processing of online line ranging and contact resistance anomaly identification.

[0039] like Figure 2 As shown, the low-voltage distribution network online ranging system of this invention includes an edge fusion terminal, distributed measurement devices, low-voltage distribution lines, and an HPLC communication network, as well as a distribution master station or maintenance platform communicatively connected to the edge fusion terminal. The edge fusion terminal is deployed on the low-voltage side of the distribution transformer, serving as the HPLC central node (CCO); the distributed measurement devices are deployed on the branch boxes, meter boxes, or user access sides, serving as HPLC sub-nodes (STAs). The edge fusion terminal and each distributed measurement device are connected through an HPLC communication network formed by the low-voltage distribution lines. This network simultaneously carries synchronization beacon data, load jump event data, power frequency measurement data, and OFDM channel response data.

[0040] The edge fusion terminal includes an HPLC central node communication and synchronization unit, a power frequency sampling and data caching unit, an OFDM channel response acquisition unit, a topology and calibration information management unit, and a fusion ranging and anomaly identification unit. The HPLC central node communication and synchronization unit sends synchronization beacons to each distributed measurement device and maintains a unified time reference for all measurement nodes within the distribution area. The power frequency sampling and data caching unit collects and caches power frequency electrical quantities such as voltage and current on the transformer side. The OFDM channel response acquisition unit reads the channel frequency response or equivalent channel characteristics formed during communication with each STA from the HPLC communication module. The topology and calibration information management unit stores the parent-child relationship of distribution area nodes, line type, resistance per unit length, temperature compensation parameters, and OFDM attenuation calibration model. The fusion ranging and anomaly identification unit performs power frequency incremental impedance calculation, OFDM attenuation characteristic ranging, path and segment conversion, multi-source consistency judgment, and contact resistance anomaly identification.

[0041] The distributed measurement equipment includes an HPLC sub-node communication unit, a clock synchronization calibration unit, a power frequency voltage and current sampling unit, a local phasor calculation unit, a load jump detection unit, and an event notification and data reporting unit. The HPLC sub-node communication unit is used for power line carrier communication with the edge fusion terminal; the clock synchronization calibration unit is used to calibrate the local clock according to the synchronization beacon issued by the edge fusion terminal; the power frequency voltage and current sampling unit and the local phasor calculation unit are used to collect local electrical quantities and extract the power frequency fundamental phasor; the load jump detection unit is used to identify natural load change events; and the event notification and data reporting unit is used to send the jump event timestamp, electrical quantities before and after the jump, phasor data, and node number to the edge fusion terminal.

[0042] During system operation, the edge fusion terminal uses the HPLC communication network to synchronize with each distributed measurement device and receives load jump events and local measurement data reported by each STA. Simultaneously, the edge fusion terminal obtains OFDM channel response data with each STA from the HPLC communication module. Combining the transformer area topology and calibration information, the edge fusion terminal maps the power frequency incremental impedance identification results and OFDM attenuation characteristic ranging results to the same test path or segment, and then performs fused ranging and contact resistance anomaly identification. The identification results include line length, corrected physical length, contact resistance anomaly alarm, and related confidence information, and can be further reported to the distribution master station or maintenance platform.

[0043] In this embodiment, the system preferably obtains the low-voltage distribution area topology in advance, including at least the parent-child relationships between the low-voltage side of the transformer, main line nodes, branch box nodes, meter box nodes, and user access points. The topology relationships can be derived from distribution area archives, HPLC topology identification results, on-site documentation results, or operational data inversion results. For nodes... Let its parent node be . Record CCO to node The path is When performing segmented calculations, the system converts the path parameters from CCO to each node into segmented parameters between adjacent parent and child nodes. For three-phase four-wire low-voltage distribution areas, this invention can perform measurements and calculations separately for each phase. If the load jump occurs in phase A, it is preferable to use the voltage, current, and power data of phase A to calculate the corresponding phase line and loop impedance. The resistance parameter per unit length should be consistent with the actual measured loop, such as the single-line resistance of the phase line, the loop resistance of the phase line plus the neutral line, or the three-phase equivalent loop resistance; these should not be mixed. For ease of explanation, the following description uses a single-phase equivalent loop as an example.

[0044] The edge fusion terminal periodically sends beacon frames with high-precision timestamps via the HPLC network. Distributed measurement devices receive these beacon frames and, through communication propagation delay compensation, local clock calibration, and the HPLC protocol time synchronization mechanism, achieve microsecond-level time synchronization with the edge fusion terminal. For a 50Hz power frequency signal, a 1-microsecond time error corresponds to a phase angle error of approximately 0.018°, which meets the basic synchronization requirements for phasor differential calculation of low-voltage lines. Each measurement node continuously acquires local voltage and current waveforms under a unified time reference and extracts the 50Hz fundamental phasor within a sliding window. The voltage phasor can be expressed as:

[0045]

[0046] The current phasor can be expressed as:

[0047]

[0048] in, and These are the fundamental effective values, and These are the fundamental phase angles referenced to the HPLC synchronous clock. The unit is the imaginary number. Phasor extraction can be performed using integer-cycle DFT, synchronous sampling DFT, PLL combined with filtering algorithms, or other methods capable of extracting the fundamental frequency phasor. As a preferred implementation, the system performs harmonic suppression, outlier removal, and phase angle continuity verification on the phasor results to avoid significant impacts from voltage distortion, transient impacts, and sampling jitter on incremental impedance calculations.

[0049] Distributed measurement devices continuously monitor changes in active power, reactive power, and current of local or downstream loads. A natural load transition event can be preliminarily determined when the active power meets the following conditions:

[0050]

[0051] in, The active power at the current moment or within the current sliding window. The width of the sliding window is preferably between 100ms and 200ms. This is the threshold for transition detection. As a preferred implementation... The threshold can be determined based on the transformer area capacity, node load level, and recent power fluctuations. For example, a certain percentage of the transformer area's rated capacity can be used as the initial threshold, which is then adjusted according to power fluctuation levels during operation. As a preferred implementation, the threshold can also be adaptively determined based on the node's recent power noise level and load fluctuations, for example, by taking:

[0052]

[0053] in, To minimize effective switching power, This represents the standard deviation of active power fluctuation over a recent period. A value of 3 to 5 is recommended. This can reduce the probability of missed detections during periods of light load and decrease false triggers during periods of strong fluctuations.

[0054] After detecting a transition event, the STA records the event timestamp. The system sends an event notification frame to the edge fusion terminal. Upon receiving the notification, the edge fusion terminal retrieves the transformer-side voltage and current data from its local cache for the same time period based on the timestamp, and simultaneously requests the relevant STAs to report local measurement data before and after the jump. To ensure the effectiveness of incremental impedance calculation, the system preferentially filters events. First, the jump events involved in the calculation should be reported by the target node or the downstream node of the target line segment, ensuring that the jump current actually flows through the path or line segment under test. Load disturbance events that do not flow through the line object under test are not used for the power frequency incremental impedance calculation of that line object. Second, multiple unrelated load jumps with similar amplitudes should not exist within the same time window; otherwise, the incremental voltage and current will be difficult to correspond to the same excitation source. Third, the jump should avoid switching transients and motor starting transients, and a relatively stable post-steady-state window should be selected. As a preferred implementation, the window before the jump can be [missing information]. The first 200ms to The window can be retrieved after the jump. The steady-state window is automatically shifted back for 300ms to 500ms if a prolonged transient is detected, until voltage, current, and power fluctuations fall below set thresholds. When there is no sufficiently large natural load change over a long period, the system can continue to accumulate small load changes and obtain impedance estimates through recursive least squares or multi-event joint estimation, but the confidence level of the results should be reduced. As a preferred implementation, when there are remotely controllable devices in the distribution area that do not affect user power consumption, such as reactive power compensation devices, street light circuits, or controllable power regulation of energy storage or charging facilities, these can also be used to form identifiable, known small disturbances as supplementary excitation sources when natural load changes are insufficient.

[0055] For a certain node The system extracts the CCO side and nodes before and after the transition. Voltage phasors on the side:

[0056]

[0057]

[0058] Wherein, the subscript 0 indicates the CCO or transformer-side node, and the subscript... Indicates the target STA node. CCO to node The path pressure drop increment is:

[0059]

[0060] The physical meaning of this formula is that, before and after the same load switching event, the change in the voltage phasor difference between CCO and STA is the voltage drop increment caused by the switching current on the common power supply path between them. By differentiating before and after the switching, the voltage drop component generated by the stable background load within this time scale is weakened or canceled.

[0061] The incremental current is preferably obtained by directly acquiring the current phasor from the target STA or downstream measurement node and then differentially analyzing it.

[0062]

[0063] When current phasors cannot be directly obtained, or when power data is needed to assist in calculations, the incremental current can be estimated based on complex power relationships. When the convention is met, the incremental current can be approximated as:

[0064]

[0065] in:

[0066]

[0067]

[0068] The average value of the voltage phasors before and after the transition can be taken, with the superscript indicating the value. This represents the complex conjugate. The above expression determines the incremental current phasor based on the complex power relationship and can be used to estimate the incremental current when the difference result of the current phasor is not directly obtained. In practice, it is obtained by direct difference of the current waveform. A more preferred option.

[0069] Therefore, CCO to node The path power frequency complex impedance is:

[0070]

[0071] in, The total resistance of the path. This is the total reactance of the path. The total resistance of the path includes the physical resistance of the wires and any contact resistance that may exist.

[0072] If what we need to find is the parent node To child nodes Given the segmented impedance and the fact that both the parent and child nodes have synchronous voltage sampling capability, the segmented voltage increment can be directly calculated:

[0073]

[0074] And obtained:

[0075]

[0076] If the parent node has no direct measurement data, the segmented impedance can also be obtained using the path impedance difference:

[0077]

[0078] in, This is the path impedance from CCO to the parent node. This path impedance can be estimated from the parent node or its downstream effective switching events. Therefore, this invention can further obtain the power frequency impedance of the segmented line from the path measurement results.

[0079] To improve the stability of impedance estimation, the system performs weighted fusion of impedance results calculated from multiple effective transition events:

[0080]

[0081] Weight It can be positively correlated with the signal-to-noise ratio of that transition. As one implementation method, weights... It can be determined based on the active power increment of the i-th load disturbance event, for example, taking... As a preferred implementation, the following approach can also be taken:

[0082]

[0083] Alternatively, the weight of the event can be determined by considering factors such as voltage phasor residuals, current measurement noise, and the degree of steady-state condition after the transition. A higher weight is awarded for events with larger transition amplitudes, more stable windows, and smaller phasor fitting residuals.

[0084] As a further preferred implementation, whether the power frequency incremental impedance estimation result meets the reliability requirements can be determined based on at least one of the following: load disturbance amplitude, incremental current amplitude, voltage and current fluctuations within the steady-state window before and after the disturbance, phasor extraction residuals, and the dispersion of impedance results obtained from multiple disturbance events. When the load disturbance amplitude or incremental current amplitude is lower than the minimum effective disturbance requirement, or the voltage and current fluctuations within the steady-state window exceed a preset stability threshold, or the dispersion of impedance results obtained from multiple disturbance events exceeds a preset range, the corresponding power frequency incremental impedance result can be marked as a low-reliability result, or it can be excluded from this fusion decision.

[0085] For a certain segment of the line, let its power frequency impedance after merging be:

[0086]

[0087] in This represents the total resistance at the operating temperature of this section. If the line type, material, and cross-sectional area of ​​this section are known, the equivalent length at power frequency can be calculated based on the resistance per unit length:

[0088]

[0089] in, The resistance per unit length, consistent with the measurement circuit at 20℃, can be expressed in units of... or ; The temperature coefficient of resistance of the conductor; This refers to the conductor's operating temperature or estimated temperature. If the conductor temperature cannot be directly measured, it can be estimated based on the ambient temperature, load current, and cable laying method. Alternatively, a temperature range can be used to correct for uncertainty. It is important to emphasize that... It should be called resistance per unit length, not material resistivity. If the actual calculation is of the phase-to-neutral loop impedance, then... The calculation should include the resistance for the corresponding lengths of the phase and neutral lines; if the calculation is for the equivalent impedance of a single phase line, then the resistance per unit length of the phase line should be used. Inconsistent definitions of this parameter will cause significant length deviations.

[0090] During communication between the CCO and each STA, the HPLC communication module can obtain the channel frequency response of each subcarrier through the OFDM preamble signal, pilot signal, or physical layer channel estimation function.

[0091]

[0092] in, For the first The center frequency of each subcarrier. Convert the channel response amplitude to a dB scale:

[0093]

[0094] like This represents the amplitude ratio of the received signal to the transmitted signal. Typically, these are negative values ​​or relative attenuation values. For easier subsequent processing, a positive attenuation amount can be defined:

[0095]

[0096] in, This represents the normalized channel amplitude. The purpose of normalization is to reduce the impact of transmit power differences, receiver AGC gain variations, coupler frequency response, analog front-end frequency response, and long-term equipment differences on slope extraction.

[0097] Low-voltage power line HPLC channels often exhibit strong multipath reflections and frequency-selective ripple. If directly applied to the original... Linear fitting can result in slopes that are significantly affected by branch reflections and load impedance variations. As a preferred implementation, the system performs the following preprocessing steps before extracting the attenuation slope: removing subcarriers that are shielded or subject to narrowband interference in the communication protocol; removing subcarriers with an SNR below a threshold; averaging or median fusion of the CFR obtained from multiple communication frames; removing local spikes along the frequency dimension using median filtering, LOESS smoothing, Savitzky-Golay smoothing, or low-order trend fitting; and suppressing high-frequency ripple components by using cepstral gating or frequency domain smoothing when multipath ripple is severe, retaining only low-frequency trend components related to line length. Simultaneously, the system preferably calculates channel characteristic quality indicators, such as fitting residuals for each frequency band, slope variance, and goodness of fit. Multi-frame slope stability and communication SNR. If the channel quality is lower than the set threshold, the OFDM attenuation slope result for that instance will not be used for length fusion and contact resistance determination, or it will only be used as a low-confidence reference value to be supplemented by subsequent communication frames.

[0098] As a further preferred implementation, whether the OFDM attenuation characteristics meet the reliability requirements can be determined based on at least one of the following: channel signal-to-noise ratio, effective subcarrier ratio, attenuation characteristic fitting residual, goodness of fit, multi-frame attenuation slope stability, and template matching error. When the above indicators meet the preset quality conditions, the corresponding channel physical length is used for consistency comparison; when the above indicators do not meet the preset quality conditions, the corresponding channel physical length is marked as a low-reliability result, or it is allowed to participate in the fusion decision after subsequent communication frames are added.

[0099] After channel preprocessing, the system divides the HPLC operating frequency band into multiple sub-bands. For example, the 2MHz to 12MHz band can be divided into a low-frequency band of 2MHz to 5MHz, a mid-frequency band of 5MHz to 8MHz, and a high-frequency band of 8MHz to 12MHz. Within each sub-band, the positive attenuation is... With frequency Linear fitting of the relationship:

[0100]

[0101] in, For the first Attenuation slope of each sub-band The intercept is used. From this, the attenuation slope vector is obtained:

[0102]

[0103] It can also calculate the weighted attenuation slope across the entire frequency band:

[0104]

[0105] in, It can be determined by sub-band bandwidth, fitting reliability, or communication SNR.

[0106] When a wire transmits high-frequency signals in the MHz band, the skin effect and dielectric loss cause the attenuation per unit length to vary with frequency. For an idealized uniform cable, the attenuation constant can be approximated as independent of frequency. Relationships in the form of:

[0107]

[0108] That is, the high-frequency attenuation constant is correlated with the frequency, and under the condition that the skin effect dominates, it can be approximately correlated with the square root of the frequency.

[0109] However, in real low-voltage distribution areas, branch reflections, load impedance, and coupling devices will superimpose this pattern. Therefore, this invention does not require the actual channel slope to strictly satisfy a single theoretical function, but rather obtains a frequency-dependent attenuation template adapted to the line type, laying method, and distribution area environment through calibration. As a preferred implementation, the following empirical model can be established:

[0110]

[0111] in, The physical length to be estimated is... This is a calibrated frequency-dependent attenuation template per unit length. This includes the approximate broadband additional loss term that may be caused by contact resistance, local joints, coupling conditions, etc. For system constants or normalized residuals, To account for noise and multipath residuals, the physical length estimate based on OFDM attenuation characteristics can be obtained through multi-frequency least squares fitting, template matching, or piecewise slope regression. .

[0112] In a simplified implementation, a calibration function relating segmented slope or full-band slope to length can also be used:

[0113]

[0114] in, and This is the calibration coefficient. If there is only one known reference line segment, it is preferable to fix it. Alternatively, the system bias can be determined by the equipment's factory calibration, and then the scaling factor can be determined based on this reference line segment; if there are two or more known reference line segments, it can be determined through linear regression. and More preferably, the system uses multiple lines of known length for least-squares calibration and records the fitting residuals and confidence intervals. For cables from different manufacturers, batches, with different aging levels, and laid in different environments, the high-frequency attenuation characteristics per unit length may differ. As a preferred implementation, the system establishes a parameter library based on conductor material, cross-sectional area, insulation type, laying method, and service life, and allows online correction of calibration parameters during operation using verified lines, on-site sampling data, or historical stable samples. This improves calibration consistency across distribution areas, equipment, and under long-term operating conditions.

[0115] In HPLC communication, the channel response between the CCO and a specific STA is obtained. This typically corresponds to the communication path length or equivalent propagation path length from the CCO to the STA. If the station topology is tree-like and the path relationships from the CCO to each node are known, the path length can be converted into segment lengths. For child nodes... and its parent node It can be calculated:

[0116]

[0117] in, CCO to node OFDM estimation of path length, Estimate the OFDM path length from CCO to the parent node. If the system supports HPLC channel measurements between adjacent nodes directly or via relay, the channel characteristics between parent and child nodes can also be directly obtained, and the segment length estimated. The same path-to-segment conversion can be performed for power frequency impedance. If already obtained... and ,but:

[0118]

[0119] This yields the corresponding segmentation. and To avoid errors caused by different events in estimating path impedance, the system preferably accumulates multiple events for the same path and the same segment, and performs weighted fusion under the same operating conditions. If a segment lacks valid events for an extended period, the system can output path-level ranging results and mark the results for that segment as data to be supplemented.

[0120] For a given segment, the system obtains the converted length of the power frequency resistance. and OFDM attenuation characteristic estimation length Construct a consistency index:

[0121]

[0122] in, The smaller the value, the more consistent the two ranging results are. Consistency threshold. The initial range for the project can be determined based on the measured data of the transformer area, the line type, and the measurement confidence level, and can be selected as 0.15 to 0.25. As a preferred implementation, when the variance of the power frequency impedance estimation is large or the OFDM channel fitting quality is poor, the system should appropriately increase the uncertainty or postpone anomaly detection, rather than relying solely on a single measurement. Output alarm value.

[0123] When the following conditions are met:

[0124]

[0125] Furthermore, when both the power frequency impedance estimation and OFDM attenuation characteristics meet the reliability requirements, the system determines that the converted length of the power frequency resistance of the line segment is basically consistent with the estimated length of the high-frequency attenuation, and the line does not exhibit obvious contact resistance anomalies. At this point, the two length estimates can be weighted and fused to obtain the final physical length.

[0126]

[0127] in, For weighting. When the load jump amplitude is large, the phasor measurement is stable, and the power frequency impedance residual is small, It can be appropriately increased; when the communication SNR is high, the CFR is stable across multiple frames, and the attenuation slope fitting residual is small, It can be appropriately reduced, thereby increasing The weight.

[0128] When the following conditions are met:

[0129]

[0130] and:

[0131]

[0132] Meanwhile, if the frequency-dependent shape of the OFDM attenuation characteristic is basically consistent with that of a normal cable template of the same type, or if the similarity of the segmented slope vector to the normal reference slope vector meets the requirements, but there is a wide bandwidth deviation, a large power frequency resistance, or an abnormally obvious historical trend, the system determines that the segment may have abnormal contact resistance. As an attenuation shape verification method, the ratio between the high-frequency band attenuation slope and the low-frequency band attenuation slope can be used to determine whether the current attenuation characteristic conforms to the frequency-dependent attenuation reference shape of a normal cable. To improve robustness, it is preferable to use absolute slope or normalized slope vectors for comparison, for example, comparing:

[0133]

[0134] in, This is a reference slope ratio for normal cables within the same frequency band. Tolerance. Alternatively, the similarity between the slope vector and the reference template, the fitting residual, or the template matching error can be used as alternative criteria. Since real low-voltage channels may not strictly satisfy a single... In practice, the actual measurement and calibration template should be preferred.

[0135] As a further preferred embodiment, the attenuation characteristic matches the frequency-related attenuation reference pattern of a normal cable, which can be determined by at least one of the following: slope ratio, normalized slope vector similarity, or template matching error. The normalized slope vector similarity can be determined using cosine similarity, correlation coefficient, or normalized Euclidean distance. For example, after normalizing the current attenuation slope vector and the reference attenuation slope vector of the normal cable, their cosine similarity is calculated; when the cosine similarity is greater than a preset similarity threshold, their frequency-related attenuation patterns are determined to match. Alternatively, the normalized distance between the current attenuation slope vector and the reference attenuation slope vector is calculated; when the normalized distance is less than a preset distance threshold, their frequency-related attenuation patterns are determined to match.

[0136] After determining that the contact resistance is abnormal, the system estimates the contact resistance:

[0137]

[0138] in, The total resistance is the value measured at the operating temperature of this segment at the power frequency. This represents the physical length estimated from the OFDM frequency-dependent attenuation characteristics. The second item on the right is the temperature-compensated wire resistance corresponding to this physical length. If the calculated result is less than zero, it indicates that the current data is insufficient to support the conclusion of abnormal contact resistance, and the wire resistance can be adjusted accordingly. Set to zero or output an invalid value. In cases of abnormal contact resistance, the corrected physical length can be:

[0139]

[0140] The system simultaneously generates abnormal alarm information, including the abnormal transformer area, node number, line segment identifier, estimated contact resistance, ranging result, judgment basis, credibility, and recommended review level, and reports it to the distribution master station or operation and maintenance system. It should be noted that contact resistance at high frequencies may not be a completely ideal frequency-independent pure resistance. Oxide layers, loose joints, and localized hot spots may introduce nonlinear, capacitive, or reflective characteristics. Therefore, this invention describes the impact of contact resistance on the OFDM channel as, under certain conditions, attenuation relative to line distributed parameters being closer to broadband additional loss or local reflection, rather than having absolutely no effect on the slope. The system uses multiple conditions, such as excessively high power frequency resistance, asynchronous increase in OFDM physical length, and frequency-related morphology still close to the normal template, to jointly determine the risk of misjudgment.

[0141] As a further preferred embodiment, the credibility or confidence level is used to characterize the reliability of the current ranging result or contact resistance anomaly judgment result. It can be comprehensively determined based on at least one of the following: power frequency incremental impedance estimation quality, OFDM attenuation characteristic quality, number of effective load disturbance events, historical result stability, and topology matching integrity. Specifically, each quality indicator can be normalized into a quality score with a consistent value range, and then weighted according to a preset weight to obtain the result confidence level; the preset weight can be determined based on equipment accuracy, actual measurement data of the transformer area, or operating experience. When the result confidence level is lower than the preset confidence level threshold, the system can output a low confidence level prompt, temporarily suspend the anomaly alarm, or wait for subsequent valid data for verification.

[0142] For scenarios with strong noise, complex loads, and anomalous data, the system shields interfered subcarriers during OFDM feature extraction, uses robust statistics such as the median or truncated mean for multi-frame CFRs, and employs robust regression to reduce the impact of outlier frequencies during the fitting process. If a frequency band is subject to long-term interference, its weight can be reduced, or a combination of other frequency bands can be used for length estimation. In power frequency incremental impedance calculation, the system preferentially performs steady-state detection on event windows. When there are significant transients in voltage and current after a transition, a sudden increase in harmonics, frequency shift, or simultaneous changes in multiple loads, the event is not included in impedance fusion. For scenarios with small but numerous load changes, the system can use multi-event joint estimation, assembling overdetermined equations from the voltage and current increments of multiple small disturbances, and obtaining the impedance result through least squares or recursive estimation. This can alleviate the problem of insufficient available events caused by insufficient natural load transitions.

[0143] In a preferred embodiment, an edge fusion terminal and several distributed measurement devices have been deployed in a low-voltage distribution area, with the HPLC operating frequency band ranging from 2MHz to 12MHz. The system pre-determines the parent-child relationships between the low-voltage side of the transformer, branch boxes, and meter boxes based on the distribution area archive and HPLC topology identification results. The edge fusion terminal periodically broadcasts a synchronization beacon, and each STA samples the local voltage and current waveforms at a unified clock, extracting the 50Hz fundamental phasor through DFT.

[0144] A certain meter box node A load input event was detected. The system extracted data from the steady-state window 200ms before the transition and the steady-state window 300ms to 500ms after the transition, based on the timestamp. Node The current phasor difference is obtained Edge fusion terminals and nodes The voltage phasor difference is obtained Calculate the CCO to the node Path impedance Since the system has known nodes The parent node is Furthermore, the CCO had already been obtained from the parent node. Path impedance Therefore, through The segmented impedance between the parent and child nodes is obtained.

[0145] Simultaneously, the HPLC module reads CCO and node. In the multi-frame CFR data during communication, after removing low-SNR subcarriers and subcarriers affected by narrowband interference, the amplitudes of the remaining subcarriers are normalized and smoothed. The system divides the 2MHz to 12MHz frequency range into three sub-bands: low, medium, and high. Attenuation slopes are fitted to each sub-band to obtain the slope vector. Based on the reference calibration model of the same type of cable, the system obtains the CCO to node. The OFDM path length estimate is then compared with the CCO to the parent node. The path length estimates are subtracted to obtain the segmented OFDM physical length. .

[0146] This section uses aluminum core low-voltage cable, and its equivalent circuit resistance per unit length at 20℃ is: The conductor temperature is estimated to be 30℃, and the temperature coefficient is taken as... The total resistance of this segment is obtained by calculating the incremental impedance at power frequency. The resistance of the temperature-compensated wire corresponding to this physical length is approximately:

[0147]

[0148] Therefore, the contact resistance is estimated to be:

[0149]

[0150] If the slope shape is normal, the channel fitting quality is acceptable, and the results of multiple events are stable, the system will output an alarm indicating abnormal contact resistance in that segment and set the corrected physical length to 120m. The above values ​​are merely examples to illustrate the calculation process; in actual engineering, specific parameters should be determined based on the cable type, measurement circuit, temperature, and calibration data.

[0151] Compared to the traditional steady-state voltage drop method, this invention utilizes an HPLC synchronous clock to obtain synchronous phasors at both ends, and uses complex voltage differences instead of simple voltage amplitude differences for impedance calculation, which can reduce errors caused by neglecting phase angle and asynchronous sampling. Simultaneously, this invention uses incremental data before and after natural load jumps for differential calculation, weakening the influence of stable background load on voltage drop, making the impedance estimation more focused on reflecting the voltage drop generated when the changing load current flows through the test path or segments.

[0152] Compared to external signal injection methods, this invention does not require dedicated injection equipment, manual wiring, power outages, or dedicated testing periods. The system can operate online using existing HPLC communication networks, edge fusion terminals, and distributed measurement devices in the low-voltage testing area, resulting in lower engineering deployment costs and suitability for long-term monitoring and automated diagnostics.

[0153] Compared to ranging methods based solely on the total attenuation of the communication channel, this invention does not simply map the total attenuation to distance. Instead, it extracts the frequency-varying attenuation trend, segmented slope, and template matching characteristics of the OFDM channel. Furthermore, it reduces the impact of multi-branch reflections, load impedance variations, and narrowband interference through preprocessing and reliability assessment. The resulting OFDM physical length estimate complements the power frequency impedance length, significantly improving the stability and reliability of ranging.

[0154] The advantage of this invention lies in its ability to distinguish between conductor resistance caused by the physical length of the line and additional contact resistance caused by poor contact. The power frequency incremental impedance reflects the total resistance, while the frequency-dependent attenuation characteristics of OFDM are primarily used to estimate the physical length of the line. When the converted length based on the power frequency resistance is significantly greater than the OFDM physical length, and the high-frequency attenuation pattern still conforms to a normal cable template, the system can determine that there is an abnormal contact resistance and further estimate its magnitude. This not only improves the accuracy of line ranging results but also provides online early warning for potential oxidation, loosening, and overheating of terminal blocks, achieving a dual function of ranging and hazard diagnosis.

[0155] Furthermore, this invention transforms path parameters into segmented parameters by incorporating the topology of distribution areas, thus meeting the practical needs of segmented operation and maintenance in low-voltage distribution areas. Through adaptive thresholding, multi-event joint estimation, robust statistics, and online calibration, the system's adaptability and long-term operational stability under complex loads, strong noise, and cross-distribution area environments are significantly improved. This invention provides more accurate line parameters for lean management of distribution area line losses. By eliminating the influence of contact resistance on equivalent length, it avoids misinterpreting contact anomalies as excessive line length, reducing deviations in theoretical line loss calculations. Simultaneously, the location of contact resistance anomalies helps maintenance personnel to specifically inspect branch boxes, meter boxes, and terminal blocks, reducing the risk of overheating, losses, and failures caused by poor contact.

[0156] This invention is not limited to the specific embodiments described above. Anyone inspired by this invention can derive various other forms of online ranging methods and systems for low-voltage power distribution networks based on the fusion of HPLC synchronous incremental impedance and OFDM attenuation slope. All equivalent changes and modifications made within the scope of the claims of this invention should be included in the scope of this invention.

Claims

1. A method for online ranging of low-voltage distribution networks based on the fusion of HPLC synchronous incremental impedance and OFDM attenuation slope, characterized in that, Includes the following steps: Under HPLC synchronous time reference, acquire synchronous power frequency electrical quantity data before and after load disturbance of the line object under test in the low voltage distribution network, as well as the orthogonal frequency division multiplexing (OFDM) channel frequency response of the high-speed power line carrier HPLC communication link related to the line object under test, wherein the line object under test is a power supply path or line segment. Based on the increment of the synchronous power frequency electrical quantity data, the power frequency incremental impedance of the line object under test is calculated, and the power frequency equivalent length is obtained from the resistive component of the power frequency incremental impedance. The attenuation characteristics that vary with frequency are extracted from the OFDM channel frequency response, and the channel physical length of the line under test is obtained according to the preset correspondence between the attenuation characteristics and the physical length of the line. Based on the transformer substation topology, the power frequency equivalent length and the channel physical length are mapped to the same line under test. The equivalent length of the power frequency is compared with the physical length of the channel for consistency. When the relative deviation between the two is not greater than the preset consistency threshold, the line status is determined to be normal, and the fused line length is output. When the relative deviation is greater than the preset consistency threshold and the power frequency equivalent length is greater than the channel physical length, and the attenuation characteristic matches the frequency-related attenuation reference shape of a normal cable, it is determined that the line object under test has abnormal contact resistance, the channel physical length is output as the corrected line length, and the contact resistance value is estimated.

2. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: The steps for calculating the power frequency incremental impedance include: Detect load disturbance events and record event timestamps; Extract the synchronous voltage phasor and current phasor within the steady-state window before and after the disturbance; The voltage drop increment is obtained by calculating the difference in voltage phasor increments of relevant nodes of the line under test. Calculate the current increment before and after the disturbance; The power frequency incremental impedance is the ratio of the voltage drop increment to the current increment.

3. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: The step of extracting the attenuation features that vary with frequency includes: The HPLC operating frequency band is divided into multiple sub-bands; In each sub-band, the channel attenuation is linearly fitted to the frequency to obtain the attenuation slope of each sub-band. Calculate the weighted attenuation slope of the entire frequency band based on the attenuation slope of each sub-band, or form an attenuation slope vector composed of the attenuation slopes of each sub-band; The preset correspondence is the calibration relationship between the full-band weighted attenuation slope or the attenuation slope vector and the physical length of the line. The frequency-dependent attenuation reference shape of the normal cable is determined based on the attenuation slope vector, slope ratio, or frequency-dependent attenuation template per unit length of the same type of cable. The slope ratio includes the ratio of the absolute value of the attenuation slope in the high-frequency band to the absolute value of the attenuation slope in the low-frequency band.

4. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: The consistency comparison steps include: The ratio of the absolute value of the difference between the power frequency equivalent length and the channel physical length to the larger of the two values ​​is used as a consistency index. When the consistency index is less than or equal to the consistency threshold, the line status is determined to be normal. When the consistency index is greater than the consistency threshold, the line status is determined by combining the attenuation pattern verification.

5. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: The step of estimating the contact resistance value includes: The contact resistance value is obtained by subtracting the temperature-compensated wire resistance corresponding to the physical length of the channel from the resistance component of the power frequency incremental impedance. The temperature-compensated conductor resistance is determined based on the physical length of the channel, the resistance per unit length of the conductor consistent with the measurement loop, the temperature coefficient of the conductor resistance, and the conductor operating temperature or estimated temperature.

6. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: It also includes the conversion of path parameters to segmentation parameters: When the HPLC node on the distribution transformer side is used as the reference node, the parent-child node relationship in the low-voltage distribution area topology is combined with the difference between the path parameters from the reference node to the child node and the path parameters from the reference node to the parent node of the child node to obtain the segmented impedance and segmented length between adjacent parent-child nodes.

7. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 2, characterized in that: The load disturbance events include natural load jump events and identifiable load disturbance events generated by controllable equipment; The power frequency incremental impedance results calculated from multiple independent effective load disturbance events are weighted and fused, with the weights being positively correlated with at least one of the disturbance amplitude, incremental current amplitude, or signal-to-noise ratio of the corresponding disturbance event.

8. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: In the process of calculating the power frequency equivalent length, temperature compensation is performed on the resistance per unit length of the conductor that is consistent with the measurement circuit, based on the temperature coefficient of conductor resistance and the conductor operating temperature or estimated temperature. The preset correspondence is determined based on known length reference segments, cable factory attenuation parameters, verified line data, or historical stable samples, and is updated during operation based on verified line data or on-site sampling data.

9. The method for online ranging and contact resistance anomaly identification in low-voltage distribution networks according to claim 1, characterized in that: Before extracting the attenuation features, the OFDM channel frequency response is preprocessed, the preprocessing including: Discard interfering subcarriers and subcarriers with a signal-to-noise ratio lower than the preset requirement; Multi-frame channel frequency response is fused and frequency domain smoothed. The channel feature quality is determined based on at least one of the following: channel fitting residual, attenuation slope variance, goodness of fit, multi-frame stability, and communication signal-to-noise ratio. The corresponding channel physical length is used for the consistency comparison only when the channel characteristic quality meets the preset requirements.

10. A low-voltage distribution network online ranging and contact resistance anomaly identification system, characterized in that, This includes an edge fusion terminal and multiple distributed measurement devices connected via an HPLC power line communication network; The distributed measurement device is used to acquire local power frequency electrical quantity data under HPLC synchronous clock and detect load disturbance events; The edge fusion terminal is used to acquire the OFDM channel frequency response related to the line object under test, and is used to cooperate with the multiple distributed measurement devices to execute the method as described in any one of claims 1 to 9, to complete the power frequency incremental impedance calculation, OFDM attenuation feature extraction, consistency comparison and contact resistance anomaly determination, and output the final ranging result and anomaly information.

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