A method and system for automatically checking phase sequence of a transformer area based on HPLC synchronous measurement and OFDM group delay multi-source fusion

Abstract

The application relates to a transformer area phase sequence automatic checking method and system based on HPLC synchronous measurement and OFDM group time delay multi-source fusion, and belongs to the field of low-voltage power distribution network intelligent operation and maintenance. The method realizes microsecond-level clock synchronization of transformer area full nodes through HPLC beacon frames and ranging messages; each distributed measurement device synchronously collects power frequency voltage to extract a fundamental wave phase angle, detects a load jump event, and extracts a geometric feature vector of an incremental V-I trajectory through differential operation; an edge fusion terminal calculates OFDM subcarrier group time delay variance by using CSI information in the HPLC communication process, and establishes a mapping relationship between the group time delay variance and cross-phase parasitic capacitance coupling. Two-level judgment is executed through fusion of the power frequency phase angle, the load fingerprint matching degree and the group time delay variance: in the preliminary screening stage, the phase sequence is determined in combination with the phase angle and the fingerprint; in the review stage, a "one-vote veto" mechanism is triggered by using a group time delay variance threshold value, and misjudgment caused by cross-phase crosstalk is effectively identified. The application can realize high-precision, real-time automatic checking of the transformer area phase sequence through only software upgrading.

Description

Technical Field

[0001] This invention belongs to the field of intelligent operation and maintenance of low-voltage distribution networks, and specifically relates to an automatic phase sequence verification method and system for transformer substations based on HPLC synchronous measurement and OFDM group delay multi-source fusion. Background Technology

[0002] Phase sequence management in low-voltage distribution areas is a fundamental aspect of refined operation and maintenance of power distribution networks. The secondary side of the transformer in a distribution area outputs three-phase voltages (A, B, and C), which are then supplied to end users via branch boxes / meter boxes. To achieve optimized three-phase load balance and lean management of line losses, it is necessary to accurately determine the phase connected to each metering terminal. Currently, distribution areas generally deploy communication networks based on HPLC standards (such as the Q / GDW11612 series). Each smart meter (STA node) and concentrator (CCO node) establishes a bidirectional communication link via power lines. The communication physical layer uses OFDM modulation, operating in the 2MHz~12MHz frequency band.

[0003] The existing phase sequence verification technology for low-voltage distribution areas is as follows:

[0004] Option 1: Phase sequence identification method based on zero-crossing detection

[0005] The basic principle of this scheme is as follows: a reference point is set on the transformer side, and a synchronization trigger command is sent to each STA node through the HPLC network. Each node detects the zero-crossing time of the local power frequency voltage waveform and reports the timestamp to the CCO. The CCO determines the phase of each node based on the difference between the zero-crossing time of each node and the zero-crossing time of the reference point—theoretically, the difference in the zero-crossing time of nodes in the same phase is close to 0°, and the difference between adjacent phases is close to ±120°.

[0006] In the specific implementation of this scheme, zero-crossing detection relies on determining the instantaneous moment when the voltage waveform crosses zero potential. In actual transformer substation environments, the voltage waveform is superimposed with a large number of odd harmonics (3rd, 5th, 7th, etc.), causing the waveform to cross zero multiple times (multiple zero-crossing phenomenon). The detection circuit needs to add filtering and hysteresis processing to lock the fundamental zero-crossing point. After the synchronous trigger command is transmitted through the HPLC network, the communication path from each node to the CCO has different propagation delays and processing delays, which require delay compensation.

[0007] Option 2: Phase sequence identification method based on steady-state load curve comparison

[0008] The basic principle of this scheme is to collect active power or current data from each metering terminal over a long period (e.g., at 15-minute intervals), and simultaneously collect phase-specific active power curves on the transformer side as a reference. The correlation coefficient (e.g., Pearson correlation coefficient) is calculated between the load curve of each terminal and the A, B, and C phase load curves on the transformer side. The phase with the largest correlation coefficient is the phase connected to that terminal.

[0009] In the specific implementation of this scheme, it is necessary to accumulate load data for a sufficiently long period of time (usually more than 24 hours) to ensure that the load curves of each phase exhibit distinguishable fluctuation patterns. The calculation of the correlation coefficient depends on the significant differences in the fluctuations of the load curves of each phase—that is, there is a significant asymmetry in the electricity consumption behavior of each phase.

[0010] Option 3: Topology identification technology based on HPLC channel characteristics

[0011] Some existing technologies attempt to utilize HPLC communication physical layer information to assist in network topology identification. For example, they use changes in signal strength (RSSI) or signal-to-noise ratio (SNR) along the signal transmission path to infer network topology hierarchy and branching relationships. Other schemes utilize the frequency response characteristics of the communication channel to distinguish different transmission paths. However, existing technologies for topology identification using channel characteristics mainly focus on topology hierarchy and path differentiation, and do not utilize channel characteristics—especially the group delay characteristics of each OFDM subcarrier—for phase sequence determination and cross-phase interference detection.

[0012] The above-mentioned Option 1 has the following technical drawbacks:

[0013] (1) The low-voltage distribution area has a high harmonic content and the voltage waveform is severely distorted. The zero-crossing point of the fundamental wave is shifted due to the superposition of harmonic components, which causes the detected zero-crossing time to deviate from the true zero-crossing point of the fundamental wave, thus limiting the accuracy of phase angle measurement. Especially when the content of the third harmonic is high (THD>8%), the zero-crossing offset can reach several electrical degrees, which significantly reduces the discrimination margin of the power frequency phase angle.

[0014] (2) This scheme essentially relies solely on the single power frequency voltage phase angle characteristic for judgment, lacking the ability to identify cross-phase crosstalk. In low-voltage distribution areas, parasitic capacitance exists between transformer windings, and the HPLC high-frequency carrier signal (2~12MHz band) can couple from one phase to another through parasitic capacitance. When a non-phase node establishes a communication link with the CCO through a crosstalk path, although the power frequency phase angle of this node is close to 120° different from that of the other phase, if the signal strength of the crosstalk path is better than that of the normal path in the same phase, the zero-crossing detection may be affected by the superposition of interference signals, resulting in misjudgment. This scheme lacks an identification mechanism for this cross-phase coupling phenomenon.

[0015] The above-mentioned Option 2 has the following technical disadvantages:

[0016] (1) It relies on long-term data accumulation and has poor real-time performance. It requires at least 24 hours or even several days of data accumulation to obtain reliable comparison results, which is not suitable for scenarios that require rapid verification or real-time monitoring after the transformation of the transformer area.

[0017] (2) When the three-phase loads are relatively balanced and the load change patterns of each phase are similar, the difference in correlation coefficients between load curves decreases, the identification accuracy drops significantly, and misjudgment may even occur.

[0018] (3) It also lacks the ability to identify cross-phase interference. When the communication link passes through the cross-phase coupling path, the data acquisition itself may have a bias.

[0019] The disadvantage of the above-mentioned option three is:

[0020] The unique value of OFDM channel group delay characteristics in phase sequence identification was not considered, and the mapping relationship between group delay variance and cross-phase parasitic capacitance coupling was not established. Therefore, the channel physical layer characteristics could not be used to solve the phase sequence misjudgment problem caused by cross-phase crosstalk. Summary of the Invention

[0021] The purpose of this invention is to address the complex operating conditions of high harmonic interference and crosstalk caused by cross-phase parasitic capacitance coupling in low-voltage distribution areas. Existing phase sequence verification methods are prone to misjudgment due to their single feature dimension and lack of cross-phase crosstalk identification mechanism. Therefore, a multi-dimensional collaborative verification scheme that integrates power frequency phase angle, transient load fingerprint, and OFDM physical layer channel characteristics is needed to fundamentally improve the accuracy and robustness of phase sequence verification. Thus, this invention provides an automatic phase sequence verification method and system for distribution areas based on HPLC synchronous measurement and OFDM group delay multi-source fusion.

[0022] To achieve the above objectives, the technical solution of this invention is: an automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group time-delay multi-source fusion, comprising:

[0023] Microsecond-level clock synchronization is performed between the edge fusion terminal and each distributed measurement device;

[0024] Based on clock synchronization, the distributed measurement device synchronously acquires the local power frequency voltage waveform, extracts the fundamental phase angle and reports it to the edge fusion terminal. The edge fusion terminal calculates the difference between the fundamental phase angle and the three-phase reference phase angle of the transformer area to determine the preliminary phase sequence candidate results.

[0025] The distributed measurement device detects load jump events, extracts incremental voltage and incremental current before and after the jump, constructs a VI fingerprint feature vector, and reports it to the edge fusion terminal. The edge fusion terminal determines the load fingerprint phase sequence assignment result based on the matching degree between the VI fingerprint feature vector and the three-phase reference fingerprint.

[0026] When communicating with the distributed measurement device via HPLC, the edge fusion terminal acquires the channel state information of the OFDM subcarrier and calculates the group delay variance.

[0027] The edge fusion terminal fuses the preliminary phase sequence candidate results, the load fingerprint phase sequence assignment results, and the group delay variance to make a phase sequence decision. When the group delay variance exceeds a preset threshold, a veto mechanism is triggered to correct the phase sequence decision result.

[0028] Furthermore, the microsecond-level clock synchronization specifically includes:

[0029] The edge fusion terminal periodically broadcasts beacon frames carrying local absolute timestamps;

[0030] The distributed measurement device receives beacon frames, records the reception time, and calibrates the local clock according to the pre-determined channel propagation delay. The calibration formula is: T_STA_calibrated=T_CCO+τ_prop, where T_CCO is the edge fusion terminal timestamp and τ_prop is the one-way propagation delay.

[0031] Furthermore, the one-way propagation delay τ_prop is obtained through HPLC ranging message interaction, and the calculation formula is: τ_prop=(T2-T1-T_proc) / 2, where T1 is the time when the edge fusion terminal sends the ranging request, T2 is the time when the edge fusion terminal receives the response, and T_proc is the fixed processing delay of the distributed measurement device.

[0032] Furthermore, the extraction of the fundamental phase angle specifically includes:

[0033] The collected voltage sequence v(n) is subjected to discrete Fourier transform, n=0,1,...,N-1, where N is the total number of sampling points. The complex representation of the fundamental component is calculated as follows: V_50Hz=(2 / N)×Σ[n=0toN-1]v(n)×exp(-j×2π×50×n / f_s), where f_s is the sampling frequency and N is the total number of sampling points;

[0034] The formula for calculating the fundamental phase angle φ is: φ = arctan(Im(V_50Hz) / Re(V_50Hz)).

[0035] Furthermore, the construction of the VI fingerprint feature vector specifically includes:

[0036] The incremental components are extracted by differential operation: Δu(t)=u_after(t)-u_before(t), Δi(t)=i_after(t)-i_before(t), where u_before(t) and i_before(t) are the average waveforms of the steady-state window before the jump, and u_after(t) and i_after(t) are the instantaneous waveforms of the transient window after the jump;

[0037] A two-dimensional trajectory graph of VI is constructed with Δu(t) as the horizontal axis and Δi(t) as the vertical axis. The normalized area S_norm, principal axis inclination angle θ_axis, and eccentricity e of the trajectory are extracted to form the feature vector F_vi=[S_norm,θ_axis,e].

[0038] Furthermore, the calculation of group delay variance specifically includes:

[0039] The phase response Φ(f_k) is obtained based on the channel state information H(f_k)=|H(f_k)|×exp(j×Φ(f_k)), where f_k is the center frequency of the k-th subcarrier, and k=1,2,...,K;

[0040] After performing phase expansion on the phase response, the group delay is calculated by differentiation:

[0041] τ_g(fk)≈-[Φ_unwrapped(f_{k+1})-Φ_unwrapped(f_k)] / ( f_{k+1}-f_k )

[0042] Φ_unwrapped(f_k) is the continuous phase function after phase expansion;

[0043] Calculate the variance of the group delay sequence over the entire effective frequency band: σ 2 _gd=(1 / K)×Σ[k=1toK] (τ_g(f_k)- )2, where K is the total number of effective subcarriers, The mean group delay.

[0044] Furthermore, the preset threshold for the group delay variance is obtained in the following way:

[0045] Collect group delay variance samples during the operation of the transformer area, and determine the preset threshold of group delay variance based on statistical analysis methods.

[0046] Furthermore, the fusion-based phase sequence decision specifically includes a first-level initial screening decision and a second-level review decision:

[0047] In the first-level preliminary screening decision, the preliminary screening result is determined based on the matching relationship between the fundamental phase angle determination result and the load fingerprint determination result;

[0048] In the second-level review decision, if the group delay variance is not greater than the preset threshold, the initial screening result is confirmed as the final phase sequence; if the group delay variance is greater than the preset threshold, a veto mechanism is triggered, the phase sequence determination result is corrected, and a cross-phase anomaly prompt is issued.

[0049] Furthermore, it also includes a hierarchical anomaly handling step based on group delay variance:

[0050] Based on the degree of deviation of the group delay variance from the preset threshold, anomaly levels are classified and corresponding early warning or error correction strategies are implemented.

[0051] Furthermore, the preset threshold for the group delay variance is obtained through multi-condition statistical calibration, specifically including:

[0052] Under light load and rated load conditions in the transformer area, the group delay variance samples of the reference node are collected, and the three-phase comprehensive mean μ_all and comprehensive standard deviation s_all are calculated.

[0053] The static threshold is calculated based on the 3σ criterion: σ_th_base = μ_all + 3s_all;

[0054] The final threshold is calculated by introducing a working condition correction factor α: σ_th=α·max(σ_th_light,σ_th_rated), where the value of α ranges from 1.0 to 1.2, and σ_th_light and σ_th_rated are the threshold for light load working condition and the threshold for rated load working condition, respectively.

[0055] The warning threshold is set to σ_th_warn=1.5σ_th.

[0056] Furthermore, the fusion-based phase sequence decision specifically includes a first-level initial screening decision and a second-level review decision:

[0057] In the first-level preliminary screening decision, if the fundamental phase angle determination result is consistent with the load fingerprint determination result, it is confirmed as the preliminary screening result; if they are inconsistent, the one with the larger phase angle difference margin or fingerprint distance margin is selected as the preliminary screening result.

[0058] In the second-level review judgment, if the group delay variance σ 2 If _gd≤σ_th, then the initial screening result is confirmed as the final phase sequence; if σ 2 If _gd>σ_th, then a veto mechanism is triggered, and the phase sequence state is corrected to suspected cross-phase interference.

[0059] Furthermore, the threshold determination rule for the group delay variance also includes tiered early warning:

[0060] When σ_th < σ 2 When _gd≤σ_th_warn, it is judged as mild crosstalk, marked as low risk warning, and an alarm is reported after 3 consecutive abnormalities;

[0061] When σ 2 When _gd>σ_th_warn, it is judged as severe cross-phase interference, and the veto mechanism is immediately triggered.

[0062] This invention also provides an automatic phase sequence verification system for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion, comprising:

[0063] The edge fusion terminal, deployed on the transformer side, includes an HPLC central node communication module, a power frequency voltage sampling module, a beacon frame generation and broadcasting unit, an OFDM channel state information acquisition unit, a group delay calculation unit, and a multi-source fusion decision unit.

[0064] Multiple distributed measurement devices are deployed in various branch boxes or meter boxes in the transformer area, including an HPLC sub-node communication module, a high-frequency voltage and current synchronous sampling module, a clock synchronization calibration unit, a load jump detection unit, and a VI incremental fingerprint extraction unit;

[0065] The edge fusion terminal is connected to the distributed measurement device via an HPLC power line communication network, and the edge fusion terminal is configured to perform the automatic phase sequence verification method for the station area as described above.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] 1. This application solves the problem of false in-phase misjudgment caused by cross-phase crosstalk. Existing zero-crossing detection methods and load curve comparison methods operate at the power frequency or low-frequency information dimension, and cannot detect the physical phenomenon of cross-phase coupling of HPLC high-frequency carrier signals through the parasitic capacitance of transformer windings. This application creatively introduces OFDM group delay variance as a detection index for cross-phase crosstalk. The group delay variance is highly sensitive to multipath propagation (i.e., the multipath effect caused by cross-phase coupling), and can directly reflect whether the propagation path has undergone inter-phase coupling from the physical layer characteristics of the channel, thus providing a "physical layer evidence" of cross-phase crosstalk for phase sequence determination. Through a "one-vote veto" mechanism, even if the initial screening results of power frequency phase angle and load fingerprint are misled by crosstalk signals, the anomaly of group delay variance can still effectively intercept false judgments.

[0068] 2. Improved robustness of verification in complex transformer substation environments. This application integrates three feature dimensions with different physical mechanisms and time scales: the power frequency phase angle reflects the fundamental steady-state characteristics, the VI increment fingerprint reflects the transient load event characteristics, and the group delay variance reflects the high-frequency channel propagation characteristics. These three dimensions are complementary—when harmonic interference reduces the power frequency phase angle margin, the load fingerprint can provide an independent criterion; when three-phase load balancing leads to insufficient fingerprint differentiation, the power frequency phase angle can still provide an effective determination; and when both of the above features are misled by crosstalk, the group delay variance can provide a fallback correction.

[0069] 3. Significantly improved verification timeliness. Unlike the steady-state load curve comparison method, which requires accumulating more than 24 hours of data, the power frequency phase angle measurement in this application can be completed in seconds, the load fingerprint extraction only needs to capture one natural load jump event, and the group delay variance can be obtained in real time during each HPLC communication interaction. The entire verification process does not require additional test signal injection and can be completed using information from the natural operating state of the transformer area, possessing online real-time verification capabilities.

[0070] 4. It fully utilizes the existing capabilities of the HPLC communication network without requiring additional hardware investment. Clock synchronization utilizes the beacon frame mechanism in the HPLC standard protocol, and group delay extraction utilizes the existing channel estimation function of the HPLC physical layer. The overall solution can be implemented through software upgrades based on the existing HPLC smart meter communication architecture. Attached Figure Description

[0071] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0072] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0073] This invention provides an automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group time delay multi-source fusion, comprising:

[0074] Microsecond-level clock synchronization is performed between the edge fusion terminal and each distributed measurement device;

[0075] Based on clock synchronization, the distributed measurement device synchronously acquires the local power frequency voltage waveform, extracts the fundamental phase angle and reports it to the edge fusion terminal. The edge fusion terminal calculates the difference between the fundamental phase angle and the three-phase reference phase angle of the transformer area to determine the preliminary phase sequence candidate results.

[0076] The distributed measurement device detects load jump events, extracts incremental voltage and incremental current before and after the jump, constructs a VI fingerprint feature vector, and reports it to the edge fusion terminal. The edge fusion terminal determines the load fingerprint phase sequence assignment result based on the matching degree between the VI fingerprint feature vector and the three-phase reference fingerprint.

[0077] When communicating with the distributed measurement device via HPLC, the edge fusion terminal acquires the channel state information of the OFDM subcarrier and calculates the group delay variance.

[0078] The edge fusion terminal fuses the preliminary phase sequence candidate results, the load fingerprint phase sequence assignment results, and the group delay variance to make a phase sequence decision. When the group delay variance exceeds a preset threshold, a veto mechanism is triggered to correct the phase sequence decision result.

[0079] This invention also provides an automatic phase sequence verification system for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion, comprising:

[0080] The edge fusion terminal, deployed on the transformer side, includes an HPLC central node communication module, a power frequency voltage sampling module, a beacon frame generation and broadcasting unit, an OFDM channel state information acquisition unit, a group delay calculation unit, and a multi-source fusion decision unit.

[0081] Multiple distributed measurement devices are deployed in various branch boxes or meter boxes in the transformer area, including an HPLC sub-node communication module, a high-frequency voltage and current synchronous sampling module, a clock synchronization calibration unit, a load jump detection unit, and a VI incremental fingerprint extraction unit;

[0082] The edge fusion terminal is connected to the distributed measurement device via an HPLC power line communication network, and the edge fusion terminal is configured to perform the automatic phase sequence verification method for the station area as described above.

[0083] The following is a detailed implementation process of the present invention.

[0084] like Figure 1 As shown, this invention provides an automatic phase sequence verification method for transformer substations based on simultaneous HPLC measurement and OFDM group delay multi-source fusion, applied to a transformer substation communication system including an edge fusion terminal and distributed measurement devices. The edge fusion terminal is deployed on the transformer side, acting as the HPLC central node (CCO), responsible for synchronization and fusion algorithm execution; the distributed measurement devices are deployed in each branch box / meter box, acting as HPLC sub-nodes (STA), possessing high-frequency sampling capabilities, responsible for local electrical quantity acquisition and feature extraction. The method includes the following steps:

[0085] Step S1: Microsecond-level clock synchronization based on HPLC beacon frames

[0086] The edge fusion terminal periodically broadcasts beacon frames with high-precision timestamps via the HPLC network. The beacon frame encapsulates the absolute timestamp T_CCO of the fusion terminal's local clock.

[0087] After receiving the beacon frame, each distributed measurement device records its local reception time T_STA_rx. Based on the channel propagation delay τ_prop already measured in the HPLC network (this delay can be obtained through preceding ranging message interactions; the specific process is as follows: the CCO sends a ranging request frame and records the sending time T1; the STA immediately replies with a response frame after receiving it; the CCO records the reception time T2; after deducting the known fixed processing delay T_proc at the STA, the one-way propagation delay τ_prop = (T2 - T1 - T_proc) / 2), the local clock is calibrated to:

[0088] T_STA_calibrated=T_CCO+τ_prop

[0089] After each STA node completes clock calibration, it synchronously acquires the local power frequency voltage instantaneous waveform at the full-second synchronization trigger time specified by the fusion terminal. The sampling rate is not less than 6.4kHz (i.e., not less than 128 sampling points per power frequency cycle), and the acquisition window covers 10 consecutive power frequency cycles.

[0090] Within their local acquisition window, each STA node extracts the amplitude and phase angle of the fundamental (50Hz) component using Discrete Fourier Transform (DFT):

[0091] Let the acquired voltage sequence be v(n), n=0,1,...,N-1, where N is the total number of sampling points. Then the complex representation of the fundamental component is:

[0092] V_50Hz=(2 / N)×Σ[n=0toN-1]v(n)×exp(-j×2π×50×n / f_s)

[0093] Where f_s is the sampling frequency. The fundamental phase angle is:

[0094] φ=arctan(Im(V_50Hz) / Re(V_50Hz))

[0095] Each STA node reports its extracted fundamental phase angle φ_STA to the fusion terminal. The fusion terminal uses its own collected fundamental phase angles φ_A, φ_B, and φ_C from the transformer side (A, B, and C phases) as a reference to calculate the phase angle difference between each STA node and the three-phase reference.

[0096] Δφ_X=φ_STA-φ_X,X∈{A,B,C}

[0097] After normalizing Δφ_X to the range of [-180°, 180°], the phase with the smallest |Δφ_X| is selected as the preliminary phase sequence candidate result.

[0098] Step S2: Incremental fingerprint feature extraction based on load jump events

[0099] During the continuous monitoring of local active power P(t), each distributed measurement device detects load transition events using the sliding window differential method:

[0100] When |P(t)-P(t-Δt)|>P_threshold (the threshold P_threshold is set according to the capacity of the transformer area, and is generally taken as 2%~5% of the rated capacity of the transformer area), a load jump event is determined to have occurred.

[0101] Upon detecting a jump event, the measuring device activates a high-speed acquisition mode, simultaneously acquiring the instantaneous voltage and current waveforms of the steady-state window before the jump (e.g., 200ms before the jump) and the transient window after the jump (e.g., 500ms after the jump) at a sampling rate of no less than 12.8kHz.

[0102] Extracting the incremental component through difference operations:

[0103] Δu(t) = u_after(t) - u_before(t)

[0104] Δi(t) = i_after(t) - i_before(t)

[0105] Where u_before(t) and i_before(t) are the average waveforms of the steady-state window before the jump, and u_after(t) and i_after(t) are the instantaneous waveforms of the transient window after the jump.

[0106] A "VI two-dimensional trajectory diagram" is constructed with Δu(t) as the horizontal axis and Δi(t) as the vertical axis. The sampling points (Δu, Δi) within one power frequency cycle are connected to form a closed trajectory. The shape, area, and principal axis direction of this trajectory reflect the load type and power characteristics that caused the jump, constituting the "VI fingerprint" of the jump event.

[0107] Trajectory feature compression: Calculate the normalized area S_norm, principal axis tilt angle θ_axis, eccentricity e and other geometric parameters of the trajectory, form a feature vector F_vi=[S_norm,θ_axis,e], and report it to the fusion terminal.

[0108] After detecting a power jump in the transformer substation, the fusion terminal synchronously acquires the incremental waveforms of phases A, B, and C on the transformer side, and extracts the VI fingerprint feature vectors F_A, F_B, and F_C for each phase. The Euclidean distance between the F_vi reported by the STA node and the three-phase reference fingerprint is calculated.

[0109] d_X=||F_vi-F_X||2,X∈{A,B,C}

[0110] The phase with the smallest d_X is selected as the phase sequence assignment result of the load fingerprint.

[0111] Step S3: Extraction of OFDM underlying physical channel group delay features

[0112] During HPLC communication, OFDM data frames are transmitted between the fusion terminal and each distributed measurement device. After each communication interaction, the HPLC module at the receiving end can obtain the channel state information (CSI) of the current frame, that is, the channel frequency response H(f_k) of each OFDM subcarrier, where f_k is the center frequency of the k-th subcarrier, k=1,2,...,K (K is the total number of effective subcarriers).

[0113] H(f_k) is a complex number, which can be represented as:

[0114] H(f_k)=|H(f_k)|×exp(j×Φ(f_k))

[0115] Where |H(f_k)| is the amplitude response and Φ(f_k) is the phase response.

[0116] After performing phase expansion on the phase response Φ(f_k) to obtain the continuous phase-frequency function Φ_unwrapped(f), the group delay is calculated:

[0117] τ_g(f_k)=-dΦ_unwrapped(f) / df|_{f=f_k}

[0118] In the discrete implementation, the derivative is approximated by the phase difference between adjacent subcarriers:

[0119] τ_g(f_k)≈-(Φ_unwrapped(f_{k+1})-Φ_unwrapped(f_k)) / (f_{k+1}-f_k)

[0120] After obtaining the group delay sequence {τ_g(f_k)}, calculate its variance over the entire effective frequency band:

[0121] σ²_gd=(1 / K)×Σ[k=1toK](τ_g(f_k)- )²

[0122] in The mean group delay.

[0123] The physical meaning of the group delay variance σ²_gd is as follows: When the signal propagates along the same phase line, the channel is a relatively simple single-path propagation, and the group delay changes gently among the subcarriers with a small variance. When the signal undergoes cross-phase coupling through the parasitic capacitance of the transformer winding, a multipath propagation environment is formed through different phase lines. The length and impedance characteristics of each path are different, resulting in different subcarriers experiencing different group delays. The group delay exhibits violent fluctuations in the frequency domain, and the variance increases significantly.

[0124] The latency variance threshold σ_th and the warning threshold σ_th_warn of the integrated terminal maintenance group are obtained by statistical calibration of multiple working conditions in the transformer area. The specific calibration rules, value descriptions and judgment logic are as follows:

[0125] 1. Prerequisites for threshold calibration

[0126] The calibration work is performed after the construction and maintenance of the transformer substation is completed and before the phase sequence verification function is officially launched. Reference nodes within the transformer substation with correct physical wiring, no line faults, and coverage of different transmission distances are manually selected. No less than 5 samples are selected for each phase, and the total number of samples for the three phases is no less than 15. During the calibration period, the transformer substation is operated under normal load, distinguishing between two operating conditions: light load (30% and below of rated load) and rated load (70%~100%). Abnormal operations such as temporary construction and line splicing are prohibited. All nodes have completed HPLC microsecond-level clock synchronization, and the channel status information and group delay calculation functions are operating normally.

[0127] 2. Complete calibration process

[0128] (1) Single node sampling: The CCO continuously communicates with a single reference STA node, and the single node continuously collects no less than 50 sets of independent communication frame data. The group delay variance is calculated frame by frame to form a single node sample set;

[0129] (2) Phase-by-phase statistics: The mean values ​​μA, μB, μC and the standard deviations sA, sB, sC of the time delay variances of all reference node groups in phases A, B, and C are respectively calculated. The comprehensive mean value of the three phases is μ_all = (μA + μB + μC) / 3 and the comprehensive standard deviation is s_all = (sA + sB + sC) / 3.

[0130] (3) Static threshold calculation: Based on the 3σ criterion, the single-condition static threshold σ_th_base=μ_all+3s_all is calculated, and the light-load condition threshold σ_th_light and the rated load condition threshold σ_th_rated are obtained respectively.

[0131] (4) Operating condition correction: Introduce operating condition correction coefficient α (value range 1.0~1.2, take 1.0 for short line and little interference, take 1.1~1.2 for long line, many branches and old cables), the final operating threshold of the transformer area: σ_th=α·max(σ_th_light,σ_th_rated);

[0132] (5) Warning threshold setting: The secondary warning threshold is fixed at σ_th_warn=1.5·σ_th;

[0133] (6) Validity verification: The measured variance of normal in-phase reference nodes is less than the main threshold. After artificially simulating cross-phase interference, the variance is greater than the main threshold. Only after the verification is passed can the threshold be enabled.

[0134] 3. Threshold dynamic update mechanism

[0135] (1) Regular automatic update: The system performs a lightweight recalibration every 6 months, selects trusted nodes in the transformer area that have been judged to be normal in phase for a long time, re-statistically re-adjusts the threshold;

[0136] (2) Trigger-driven recalibration: After the completion of major projects such as line renovation, transformer replacement, and large-scale addition of meters in the distribution area, the full sample recalibration is initiated immediately;

[0137] (3) Anti-jump protection: The single threshold adjustment range shall not exceed 15% of the original threshold to avoid threshold mutation caused by abnormal sampling.

[0138] 4. Threshold grading determination rules

[0139] (1) Normal range: σ 2 If _gd≤σ_th, it is determined to be a direct transmission channel in phase, with no cross-phase interference;

[0140] (2) Warning interval: σ_th < σ 2 If _gd≤σ_th_warn, it indicates abnormal channel fluctuations, mild crosstalk, or line contact problems. A low-risk warning is issued, and an alarm is reported only after three consecutive abnormalities.

[0141] (3) Crosstalk interval: σ 2 If _gd>σ_th_warn, it is determined that there is serious cross-phase parasitic capacitance coupling and multipath crosstalk, and the veto mechanism is activated.

[0142] 5. Special Scenario Adaptation Instructions

[0143] For remote end nodes and small-capacity distribution areas (number of users < 30 households), the number of baseline samples can be appropriately reduced according to the actual situation (no less than 3 per phase); for short-term pulse interference caused by lightning strikes and the start-up and shutdown of high-power equipment, the system adopts a joint judgment of 3 consecutive frames, and the single variance exceeding the limit will not trigger alarm and rejection logic.

[0144] Step S4: Multi-source fusion phase sequence decision

[0145] The fusion terminal aggregates the above three types of feature data and executes a two-level fusion decision logic:

[0146] Level 1 – Initial Screening Decision (Combined Decision Based on Power Frequency Phase Angle and Load Fingerprint):

[0147] (a) If the phase angle determination result of step S1 is consistent with the fingerprint determination result of step S2 (both point to the same phase, such as both being determined as phase A), then the initial screening result is that phase, and the confidence level is marked as "high".

[0148] (b) If the two are inconsistent, compare the phase angle difference margin |Δφ_A| with the fingerprint distance margin d_A, and select the one with the larger margin as the initial screening result, and mark the confidence level as "medium".

[0149] (c) If both are close to the decision boundary (phase angle difference close to 60°, fingerprint distance difference not significant), the initial screening result is marked as "pending" with a confidence level of "low".

[0150] Level 2 – Group Delay Review Decision (Cross-Phase Interference Detection):

[0151] For nodes initially identified as being in phase, check their OFDM group delay variance σ²_gd:

[0152] (a) If σ²_gd≤σ_th, it indicates that the communication channel has the characteristics of a direct transmission path with in-phase, and the group delay is stable. The verification is passed, and the initial screening result is confirmed as the final phase sequence.

[0153] (b) If σ²_gd>σ_th, it indicates that the communication channel exhibits multipath propagation characteristics and there are signs of cross-phase parasitic capacitance coupling, triggering the "one-vote veto" mechanism—overturning the initial in-phase judgment, correcting the phase sequence status of the node to "suspected cross-phase interference", generating alarm information to report to the main station, and waiting for manual review or re-judgment based on subsequent multiple measurement data.

[0154] For nodes with an initial confidence level of "low" or "pending", the fusion terminal will accumulate multiple measurement results when load changes occur in the future, use a voting method to count the cumulative number of votes for each phase, and give a final judgment after the cumulative number reaches a preset value (such as 5 times).

[0155] This invention also provides an automatic phase sequence verification system for transformer substations, comprising:

[0156] The edge fusion terminal, deployed on the transformer side, includes an HPLC central node communication module, a power frequency voltage sampling module, a beacon frame generation and broadcasting unit, an OFDM channel state information acquisition unit, a group delay calculation unit, and a multi-source fusion decision unit;

[0157] The distributed measurement equipment is deployed in each branch box / meter box and includes an HPLC sub-node communication module, a high-frequency voltage and current synchronous sampling module, a clock synchronization calibration unit, a load jump detection unit, a VI incremental fingerprint extraction unit, and a feature data reporting unit.

[0158] The edge fusion terminal and the distributed measurement devices are connected via an HPLC power line communication network. The distributed measurement devices report the locally acquired and extracted power frequency phase angle and VI fingerprint feature vector to the edge fusion terminal in the form of HPLC data frames. At the same time, the edge fusion terminal obtains the channel state information when communicating with each distributed measurement device from the HPLC module and calculates the group delay variance, and executes the above-mentioned multi-source fusion phase sequence decision logic.

[0159] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. An automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group time-delay multi-source fusion, characterized in that, include: Microsecond-level clock synchronization is performed between the edge fusion terminal and each distributed measurement device; Based on clock synchronization, the distributed measurement device synchronously acquires the local power frequency voltage waveform, extracts the fundamental phase angle and reports it to the edge fusion terminal. The edge fusion terminal calculates the difference between the fundamental phase angle and the three-phase reference phase angle of the transformer area to determine the preliminary phase sequence candidate results. The distributed measurement device detects load jump events, extracts incremental voltage and incremental current before and after the jump, constructs a VI fingerprint feature vector, and reports it to the edge fusion terminal. The edge fusion terminal determines the load fingerprint phase sequence assignment result based on the matching degree between the VI fingerprint feature vector and the three-phase reference fingerprint. When communicating with the distributed measurement device via HPLC, the edge fusion terminal acquires the channel state information of the OFDM subcarrier and calculates the group delay variance. The edge fusion terminal fuses the preliminary phase sequence candidate results, the load fingerprint phase sequence assignment results, and the group delay variance to make a phase sequence decision. When the group delay variance exceeds a preset threshold, a veto mechanism is triggered to correct the phase sequence decision result.

2. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion as described in claim 1, characterized in that, The microsecond-level clock synchronization specifically includes: The edge fusion terminal periodically broadcasts beacon frames carrying local absolute timestamps; The distributed measurement device receives beacon frames, records the reception time, and calibrates the local clock according to the pre-determined channel propagation delay. The calibration formula is: T_STA_calibrated=T_CCO+τ_prop, where T_CCO is the edge fusion terminal timestamp and τ_prop is the one-way propagation delay.

3. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion as described in claim 2, is characterized in that, The one-way propagation delay τ_prop is obtained through HPLC ranging message interaction and is calculated as follows: τ_prop=(T2-T1-T_proc) / 2, where T1 is the time when the edge fusion terminal sends the ranging request, T2 is the time when the edge fusion terminal receives the response, and T_proc is the fixed processing delay of the distributed measurement device.

4. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion as described in claim 1, characterized in that, The extraction of the fundamental phase angle specifically includes: The collected voltage sequence v(n) is subjected to discrete Fourier transform, n=0,1,...,N-1, where N is the total number of sampling points. The complex representation of the fundamental component is calculated as follows: V_50Hz=(2 / N)×Σ[n=0toN-1]v(n)×exp(-j×2π×50×n / f_s), where f_s is the sampling frequency and N is the total number of sampling points; The formula for calculating the fundamental phase angle φ is: φ = arctan(Im(V_50Hz) / Re(V_50Hz)).

5. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion as described in claim 1, characterized in that, The construction of the VI fingerprint feature vector specifically includes: The incremental components are extracted by differential operation: Δu(t)=u_after(t)-u_before(t), Δi(t)=i_after(t)-i_before(t), where u_before(t) and i_before(t) are the average waveforms of the steady-state window before the jump, and u_after(t) and i_after(t) are the instantaneous waveforms of the transient window after the jump; A two-dimensional trajectory graph of VI is constructed with Δu(t) as the horizontal axis and Δi(t) as the vertical axis. The normalized area S_norm, principal axis inclination angle θ_axis, and eccentricity e of the trajectory are extracted to form the feature vector F_vi=[S_norm,θ_axis,e].

6. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion according to claim 1, characterized in that, The calculation of the group delay variance specifically includes: The phase response Φ(f_k) is obtained based on the channel state information H(f_k)=|H(f_k)|×exp(j×Φ(f_k)), where f_k is the center frequency of the k-th subcarrier, and k=1,2,...,K; After performing phase expansion on the phase response, the group delay is calculated by differentiation: τ_g(fk)≈-[Φ_unwrapped(f_{k+1})-Φ_unwrapped(f_k)] / ( f_{k+1}-f_k ) Φ_unwrapped(f_k) is the continuous phase function after phase expansion; Calculate the variance of the group delay sequence over the entire effective frequency band: σ 2 _gd=(1 / K)×Σ[k=1toK] (τ_g(f_k)- )2, where K is the total number of effective subcarriers, The group delay is the average.

7. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion as described in claim 1, characterized in that, The preset threshold for the group delay variance is obtained in the following way: Collect group delay variance samples during the operation of the transformer area, and determine the preset threshold of group delay variance based on statistical analysis methods.

8. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion according to claim 7, characterized in that, The fusion-based phase sequence decision specifically includes a first-level initial screening decision and a second-level review decision: In the first-level preliminary screening decision, the preliminary screening result is determined based on the matching relationship between the fundamental phase angle determination result and the load fingerprint determination result; In the second-level review decision, if the group delay variance is not greater than the preset threshold, the initial screening result is confirmed as the final phase sequence. If the group delay variance is greater than the preset threshold, a veto mechanism is triggered to correct the phase sequence determination result and issue a cross-phase anomaly warning.

9. The automatic phase sequence verification method for a station area based on simultaneous HPLC measurement and OFDM group delay multi-source fusion according to claim 8, characterized in that, It also includes a hierarchical anomaly handling step based on group delay variance: Based on the degree of deviation of the group delay variance from the preset threshold, anomaly levels are classified and corresponding early warning or error correction strategies are implemented.

10. An automatic phase sequence verification system for a station area based on simultaneous HPLC measurement and OFDM group time delay multi-source fusion, characterized in that, include: The edge fusion terminal, deployed on the transformer side, includes an HPLC central node communication module, a power frequency voltage sampling module, a beacon frame generation and broadcasting unit, an OFDM channel state information acquisition unit, a group delay calculation unit, and a multi-source fusion decision unit; Multiple distributed measurement devices are deployed in various branch boxes or meter boxes in the transformer area, including HPLC sub-node communication module, high-frequency voltage and current synchronous sampling module, clock synchronization calibration unit, load jump detection unit and VI incremental fingerprint extraction unit; The edge fusion terminal is connected to the distributed measurement device via an HPLC power line communication network, and the edge fusion terminal is configured to perform the automatic phase sequence verification method for the station area as described in any one of claims 1 to 9.

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