Response manifold-based low-frequency power transmission active detection type pilot protection method and system

Abstract

The application discloses a low-frequency power transmission active detection type pilot protection method and system based on a response manifold, belongs to the technical field of new energy power generation grid connection and alternating current line relay protection, and comprises the following steps: collecting electrical quantities at both ends of a protected line and forming injected start state quantities, and superimposing a characteristic frequency voltage signal on a low-frequency side by using a modular multi-level matrix converter; extracting voltage and current complex phasors under an injection frequency, constructing virtual opposite end quantities based on a complete line propagation matrix, and forming a joint characteristic vector by combining the real measured quantities at the local end with the virtual opposite end quantities; calculating a normal consistency residual of the joint characteristic relative to the complete line response manifold and a normalized protection index, and forming a pilot tripping logic according to the local protection logic at both ends. The application can realize in-zone and out-zone fault identification of a low-frequency power transmission line, and reduces double-end electrical quantity communication.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation grid connection and AC line relay protection technology, specifically involving a low-frequency transmission active detection longitudinal protection method and system based on response manifold. Background Technology

[0002] As offshore wind power develops towards deeper waters and larger capacities, long-distance transmission of new energy places higher demands on the economy, capacity, and reliability of power transmission systems. Low-frequency transmission systems can reduce the charging current of submarine cables, improve long-distance AC transmission capacity, and also have certain engineering economic advantages, thus gradually becoming an important technical solution for centralized transmission of offshore wind power.

[0003] However, the operating characteristics of low-frequency transmission systems differ significantly from those of traditional power frequency AC systems. After a fault occurs, the electrical response of the line is no longer primarily determined by the electromagnetic transient characteristics of the synchronous power source, but is instead influenced by the combined effects of low-voltage ride-through control on the wind power side, voltage / frequency support control on the M3C low-frequency side, current limiting mechanisms, and imbalance suppression control. The fault current exhibits weak feedback, strong controllability, and non-power frequency characteristics; its amplitude is limited, and the phase angle relationship changes with the control strategy. The fault characteristics relied upon by traditional protection systems may be weakened or even shifted.

[0004] Traditional AC line protection typically relies on characteristics such as fault current amplitude, phase relationship, measured impedance trajectory, or differential current. For differential protection, the basic premise is that during an intra-zone fault, both power supplies provide significant natural short-circuit currents to the fault point, causing a significant increase in differential current. However, in low-frequency double-ended weak-feed systems, both converters act as controlled current sources or controlled voltage ports. The amplitude, phase angle, and sequence component distribution of the fault current are reshaped by the control loop, causing the differential quantity to no longer stably reflect the intra-zone / extra-zone fault differences.

[0005] Existing research on the protection of new energy lines mainly includes adaptive improvements to traditional protection, transient quantity protection, model identification protection, and active detection protection. Transient quantity and traveling wave protection can improve the speed of action by utilizing high-frequency information in the initial stage of a fault, but they often rely on clear line boundaries, high sampling rates, or accurate wavefront identification. Longitudinal protection can achieve fault identification across the entire line, but many methods require exchanging sampled quantities, phasors, or complex characteristic quantities at both ends, which places high demands on communication bandwidth, synchronization accuracy, and data continuity.

[0006] Active detection-based protection proactively constructs fault responses by injecting controllable characteristic signals, providing a new approach for the protection of renewable energy systems. However, existing research is mostly geared towards power frequency transmission systems, and the injection point is usually located on the renewable energy side. For offshore wind farms containing a large number of wind turbines, this implementation method is complex and may have additional impacts on system control and operational stability. Therefore, there is an urgent need for a longitudinal protection method that can utilize the control capabilities of onshore M3C, proactively enhance fault identifiable characteristics, avoid extensive two-way electrical communication, and is applicable to low-frequency transmission systems.

[0007] Furthermore, in converter-controlled low-frequency transmission systems, fault current is not solely determined by line parameters, fault location, and transition resistance; it is also influenced by converter control modes, current limiting thresholds, and the dynamic processes of the control loop. The same fault location may exhibit different voltage and current characteristics under different control states, while different fault locations may produce similar controlled fault responses. Therefore, using fixed current thresholds, fixed impedance boundaries, or single sequence component characteristics makes it difficult to maintain a consistently stable ability to distinguish between intra- and extra-zone faults under different operating modes and control states.

[0008] For longitudinal protection systems that rely on dual-terminal electrical quantities, directly transmitting the original sampled values ​​or complex phase quantities from both ends requires addressing issues such as sampling timing alignment, communication delays, data loss, and channel anomalies. Especially when the protection action time is short, asynchronous or discontinuous data communication between the two ends can directly affect the calculation results of differential quantities, phase relationships, or joint characteristic quantities. Therefore, how to reduce the amount of data to be transmitted and decrease the reliance on high-precision synchronization at both ends while retaining the selectivity of dual-terminal longitudinal protection is a problem that needs to be solved in low-frequency transmission line protection engineering applications.

[0009] Furthermore, existing active detection protection systems typically establish action criteria directly based on changes in the amplitude, phase, or equivalent impedance of the injected signal. This type of single response characteristic can still be affected by operating conditions, line parameter errors, and changes in control status. For the protected line, when the fault is located outside the line, although the external network state changes, the complete topology of the protected line itself remains unchanged. When the fault is located inside the protected line, the fault branch will alter the propagation path of the injected signal in the line and the port response relationship. Therefore, if a reference response can be constructed using the propagation relationship under the complete line state, and based on this, it can be determined whether the online response still conforms to the complete line response pattern, thus distinguishing between in-zone and out-of-zone faults from the perspective of line topology integrity, reducing the dependence on the amplitude of the natural short-circuit current and fixed phase angle relationships.

[0010] In summary, existing line protection systems for low-frequency transmission systems have at least the following shortcomings: First, the characteristics of natural fault currents are limited and reshaped by double-ended weak feeders and converter control, making traditional current, impedance, and differential criteria insufficiently adaptable. Second, transient quantity and traveling wave protection have high requirements for sampling rate, line boundary, and wavefront identification. Third, existing longitudinal protection systems typically require the exchange of a large number of double-ended electrical quantities, making them highly dependent on communication bandwidth, synchronization accuracy, and data continuity. Fourth, existing active detection methods are mostly implemented on the renewable energy side, which is not conducive to unified control and engineering deployment in offshore wind farms containing a large number of wind turbines. Fifth, existing active detection criteria have not fully utilized the signal propagation consistency under the complete topology of the protected line, making it difficult to stably characterize the damage caused by faults within the area to the line propagation relationship.

[0011] Therefore, there is a need to provide a longitudinal protection method suitable for offshore wind power low-frequency transmission systems. This method utilizes the modulation capability of onshore modular multilevel matrix converters to actively inject characteristic frequency signals. Based on local measurements and the propagation relationship of the complete line, a joint feature including virtual peer response is constructed. By identifying intra-zone and extra-zone faults through the consistency of the online response and the complete line response manifold, the method ensures that only local logic quantities are exchanged at both ends of the line, thereby reducing the dependence of longitudinal protection on communication bandwidth and dual-end synchronization accuracy. Summary of the Invention

[0012] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a low-frequency transmission active detection longitudinal protection method and system based on response manifold. By actively injecting characteristic frequency signals after a fault and combining the consistency identification of the response manifold of the complete line, it can achieve rapid and reliable identification of faults within and outside the low-frequency transmission line. This invention is used to solve the technical problems of fault current being reshaped by the converter control link and natural fault characteristics being weakened in low-frequency double-ended weak feeder systems, making it difficult for traditional current protection, impedance protection and differential protection to stably distinguish between faults within and outside the area. It also addresses the technical problems of existing longitudinal protection relying heavily on the double-ended electrical quantity communication bandwidth, synchronization accuracy and data continuity, and the complex engineering implementation of existing active injection methods on the new energy side. This invention is applicable to new energy transmission scenarios where wind farms transmit power through low-frequency AC lines and the onshore side uses a modular multilevel matrix converter (M3C) to realize the conversion between low-frequency AC and power frequency AC.

[0013] The present invention adopts the following technical solution: The low-frequency transmission active detection longitudinal protection method based on response manifold includes the following steps: S1. Collect the three-phase voltage and current signals at the m and n ends of the protected line respectively. Decompose the three-phase voltage into positive and negative sequence values ​​to obtain the positive sequence voltage amplitude and the negative sequence voltage amplitude. Construct a low-through voltage term and a voltage change rate term based on the positive sequence voltage amplitude. Construct a negative sequence imbalance term based on the positive sequence voltage amplitude and the negative sequence voltage amplitude. Perform a weighted summation of the low-through voltage term, the voltage change rate term, and the negative sequence imbalance term to obtain a comprehensive fault characteristic factor. Compare the comprehensive fault characteristic factor with the start-up threshold and the exit threshold to obtain the injected start-up state quantity. S2. Based on the injected start-up state quantity, a characteristic frequency voltage signal is superimposed on the low-frequency side using the modulation capability of the modular multilevel matrix converter. S3. During the active injection of the characteristic frequency voltage signal, the voltage and current complex phase quantities at the injection frequency at the m-end and n-end are extracted respectively; the virtual n-end quantity is calculated at the m-end based on the voltage and current complex phase quantities at the injection frequency measured at this end and the inverse matrix of the complete line propagation matrix; the virtual m-end quantity is calculated at the n-end based on the voltage and current complex phase quantities at the injection frequency measured at this end and the complete line propagation matrix. S4. The m-end constructs a joint feature vector based on the actual measurement of this end and the virtual n-end quantity, and the n-end constructs a joint feature vector based on the actual measurement of this end and the virtual m-end quantity; the m-end joint feature vector and the n-end joint feature vector are standardized using the mean vector and standard deviation vector of the complete line response characteristics of the corresponding ends, respectively, to obtain the standardized joint features of the corresponding ends; S5. Each end calculates the normal consistency residual based on the joint characteristics after standardization of its own end and the local tangential principal subspace of the complete line response manifold of the corresponding end; calculates the consistency statistic based on the normal consistency residual, the covariance matrix of the complete line response residual of the corresponding end, and the regularization term; normalizes the consistency statistic based on the threshold of the corresponding end statistic to obtain the normalized protection index. S6. Each end compares its own normalized protection index with the unified discrimination boundary to obtain local protection logic, and sends the logic quantity corresponding to the local protection logic to the other end. S7. Perform an AND operation on the logic quantities corresponding to the local protection logic of the m and n terminals to obtain the longitudinal trip logic.

[0014] Further, in step S1, the low-suspension associated voltage term is calculated based on the positive-sequence voltage reference value before the fault, the low-suspension associated reference threshold, and the positive-sequence voltage amplitude; the voltage change rate term is calculated based on the corresponding positive-sequence voltage amplitude and time interval between two adjacent start-up criteria; and the negative-sequence imbalance term is calculated based on the positive-sequence voltage amplitude, the negative-sequence voltage amplitude, and the negative-sequence imbalance normalization threshold.

[0015] Further, in step S1, when the comprehensive fault characteristic factor reaches the start-up threshold, the injected start-up state quantity is set to start-up state; when the comprehensive fault characteristic factor is lower than the exit threshold, the injected start-up state quantity is set to exit state, wherein the start-up threshold is greater than the exit threshold.

[0016] Further, in step S2, the injection frequency is determined based on the fundamental frequency of the low-frequency system, and the characteristic frequency voltage signal is generated based on the injection frequency, the injection voltage amplitude, the injection duration, and the initial phase of the injection signal.

[0017] Furthermore, the injection frequency is 8 times the fundamental frequency of the low-frequency system, the injection voltage amplitude is 0.1 per unit, and the injection duration is 100 milliseconds.

[0018] Further, in step S3, the m-end calculates the voltage and current complex phase quantities at the injection frequency measured at the m-end based on the inverse matrix of the complete line propagation matrix to obtain the virtual n-end quantity; the n-end calculates the voltage and current complex phase quantities at the injection frequency measured at the n-end based on the complete line propagation matrix to obtain the virtual m-end quantity.

[0019] Further, in step S4, the m-end uses the m-end feature mapping function to perform feature mapping on the actual measurement of the m-end and the virtual n-end quantity to obtain the joint feature vector of the m-end; the n-end uses the n-end feature mapping function to perform feature mapping on the actual measurement of the n-end and the virtual m-end quantity to obtain the joint feature vector of the n-end; each end performs standardization processing on its own joint feature vector according to the mean vector and standard deviation vector of the complete line response characteristics of the corresponding end to obtain the standardized joint feature of the end.

[0020] Further, in step S5, the projection matrix to the local tangential principal subspace is determined based on the basis matrix of the local tangential principal subspace of the complete line response manifold of the corresponding end; the standardized joint features of the local end are projected based on the projection matrix, and the normal consistency residual is obtained based on the components of the standardized joint features of the local end outside the local tangential principal subspace; the consistency statistic is calculated based on the normal consistency residual, the covariance matrix of the complete line response residual, the regularization coefficient, and the regularization term.

[0021] Further, in step S5, the ratio of the consistency statistic to the corresponding end statistic threshold is calculated to obtain the normalized protection index, and the unified discrimination boundary is 1; when the normalized protection index of this end is greater than the unified discrimination boundary for a consecutive preset number of calculation points, the local protection logic of this end is generated.

[0022] Secondly, embodiments of the present invention provide a low-frequency transmission active detection longitudinal protection system based on response manifold, including a modular multilevel matrix converter, an m-end protection device disposed at the m end of the protected line, and an n-end protection device disposed at the n end of the protected line. The m-terminal protection device and the n-terminal protection device are respectively used to collect the three-phase voltage and current signals of this terminal, and form an injection start-up state quantity based on the three-phase voltage of this terminal. The modular multilevel matrix converter is used to superimpose a characteristic frequency voltage signal on the low-frequency side according to the injected startup state quantity; The m-terminal protection device and the n-terminal protection device are also used to extract the voltage and current complex quantities at the injection frequency at their respective terminals, calculate the virtual peer quantity based on the voltage and current complex quantities at the injection frequency measured at their respective terminals and the complete line propagation matrix, construct a joint feature vector based on the actual measurements at their respective terminals and the virtual peer quantity, obtain a normalized protection index based on the degree of deviation of the joint feature vector from the complete line response manifold, generate local protection logic based on the normalized protection index, and send the logic quantity corresponding to the local protection logic to the peer terminal. The m-terminal protection device and the n-terminal protection device are also used to perform AND logic operations on the logic quantities corresponding to the local protection logic of the m-terminal and n-terminal to obtain the longitudinal tripping logic.

[0023] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described low-frequency transmission active detection longitudinal protection method based on response manifold.

[0024] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described low-frequency transmission active detection longitudinal protection method based on response manifold.

[0025] Fifthly, a chip includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described low-frequency transmission active detection longitudinal protection method based on response manifold.

[0026] In a sixth aspect, embodiments of the present invention provide an electronic device, including a computer program, which, when executed by the electronic device, implements the steps of the above-described low-frequency transmission active detection longitudinal protection method based on response manifold.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects: A low-frequency transmission active detection longitudinal protection method based on response manifold actively injects characteristic frequency signals through a modular multilevel matrix converter, so that the protection criteria no longer rely on the natural fault current affected by current-limited control and low-voltage ride-through control. A virtual peer quantity is constructed based on the complete line propagation matrix, and the measured response at the local end and the virtual peer response are combined to form a joint feature. The degree of normal deviation of the complete line response manifold is used to identify whether the line topology has been disrupted by a faulty branch. This method can transform fault identification within and outside the protection zone into a complete line propagation consistency judgment. Only local protection logic quantities are exchanged between the two ends, preserving the full-line selectivity of longitudinal protection while reducing the dependence on original sampled values, synchronous phasor communication, and high-precision synchronization at both ends.

[0028] Furthermore, the low-downtime associated voltage term, positive-sequence voltage change rate term, and negative-sequence imbalance term are weighted and fused to characterize the voltage drop, initial voltage surge during fault occurrence, and negative-sequence enhancement characteristics of asymmetrical faults. Compared to starting solely based on positive-sequence voltage amplitude, this method improves the adaptability of active injection starting under minor faults, high-resistance faults, and asymmetrical faults, while reducing the risk of starting hysteresis or failure to start.

[0029] Furthermore, by setting a start threshold and an exit threshold below the start threshold, a start logic with hysteresis characteristics is formed. This can prevent the comprehensive fault characteristic factor from repeatedly flipping around the threshold due to measurement noise or short-term fluctuations, reduce the frequent input and output of characteristic frequency signals, and improve the stability of the active detection process.

[0030] Furthermore, a characteristic frequency is determined based on the fundamental frequency of the low-frequency transmission line, and the injection amplitude and duration are limited. This distinguishes the injected signal from the system's fundamental frequency component, while restricting the injection process within a predetermined amplitude and protection time scale. This results in a clearly defined and extractable line response, providing a data foundation for subsequent complex phase extraction and propagation consistency identification.

[0031] Furthermore, the characteristic frequency is set to 8 times the fundamental frequency, and an injection amplitude of 0.1 per unit and an injection duration of 100 milliseconds are used. According to the simulation conditions described in the disclosure document, an observable 133.33Hz response can be formed in the two-terminal voltage and current, while the background component of the corresponding frequency is close to zero when no injection is performed. This facilitates the separation of the active detection response from the fundamental frequency operating quantity and meets the short-time protection discrimination requirements.

[0032] Furthermore, the voltage and current phasors at the local characteristic frequency are combined to form a port state vector, and the virtual peer state vector is calculated using the complete line propagation matrix or its inverse matrix. This allows each end to reconstruct the peer response under the complete line assumption based solely on its own measurements, introducing the propagation relationship between the two ends of the line into the local criterion and reducing the need for real-time transmission of electrical quantities between both ends.

[0033] Furthermore, a joint feature vector is constructed by using feature mapping to combine the local and virtual parallel phase quantities, and then standardized using the mean and standard deviation vectors of the complete line response characteristics. This eliminates the differences in dimensions and amplitude scales between different electrical quantities, enabling each dimension of the feature to participate in manifold deviation calculations on a unified scale, thereby improving the comparability of protection indicators under different operating conditions.

[0034] Furthermore, the standardized joint features are projected onto the local tangential principal subspace of the complete line response manifold, and the normal consistency residuals are constructed using the projected out-of-projection components. This preserves the normal response variations along the manifold direction under the complete line topology and highlights the out-of-manifold deviations caused by the propagation of faults within the region. By combining the residual covariance matrix and regularization terms to calculate the consistency statistics, the statistical correlation between the residual components can be considered, and the stability of matrix calculation can be improved.

[0035] Furthermore, by normalizing the consistency statistics through statistical thresholds, the protection indicators at both ends of the line adopt a unified judgment boundary, which facilitates the formation of consistent dual-end logic criteria. By confirming the protection indicators exceeding the limit through multiple consecutive calculation cycles, it is possible to suppress misjudgments caused by a single abnormal calculation point, transient disturbance, or measurement noise, thereby improving the stability of local protection logic and longitudinal tripping logic.

[0036] It is understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0037] In summary, this invention actively injects characteristic frequency signals through M3C, constructs virtual peer quantities by combining the line propagation model, and identifies faults within the region by the response manifold consistency residual. It only exchanges logic quantities to form longitudinal tripping, which is suitable for low-frequency double-ended weak feeder and converter operating conditions, and takes into account identification reliability, communication simplification and engineering implementation.

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0039] Figure 1 This is a typical topology diagram of a low-frequency power transmission system for new energy sources. Figure 2 This is a flowchart of the method of the present invention; Figure 3 This is a schematic diagram of the time-domain response of the net 133Hz component after fundamental frequency suppression at both ends. Figure 4The diagram shows the normalized protection indicators and longitudinal tripping logic at both ends of the fault point. Specifically, (f1) is the normalized protection indicators and longitudinal tripping logic at both ends under fault f1, (f2) is the normalized protection indicators and longitudinal tripping logic at both ends under fault f2, (f3) is the normalized protection indicators and longitudinal tripping logic at both ends under fault f3, (f4) is the normalized protection indicators and longitudinal tripping logic at both ends under fault f4, and (f5) is the normalized protection indicators and longitudinal tripping logic at both ends under fault f5. Figure 5 The following are comparison charts of consistency deviation indicators and protection logic at both ends under different fault locations: (a) is a comparison chart of consistency deviation indicators at end m, (b) is a comparison chart of consistency deviation indicators at end n, (c) is a comparison chart of local protection logic and longitudinal tripping logic at end m, and (d) is a comparison chart of local protection logic and longitudinal tripping logic at end n. Figure 6 A schematic diagram of a computer device provided in an embodiment of the present invention; Figure 7 This is a block diagram of a chip provided according to an embodiment of the present invention.

[0040] Among them, 60. Computer equipment; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic device; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0043] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0044] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0045] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0046] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0047] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0048] This invention provides a response manifold-based active detection longitudinal protection method for low-frequency power transmission. Addressing the problem in low-frequency power transmission systems where fault current is affected by wind power-side low-voltage ride-through control, M3C control, and current-limiting mechanisms, leading to weakened natural fault characteristics and difficulty in identifying faults inside and outside the transmission zone, this invention improves upon traditional protection methods that rely on fault current amplitude, phase angle, or differential quantity. First, utilizing the rapid modulation capability of a modular multilevel matrix converter (M3C) after a fault, a characteristic frequency signal with limited amplitude, defined frequency, and fixed duration is superimposed onto the low-frequency side within the protection timescale, actively constructing a stable and observable line response and reducing the dependence of protection criteria on natural short-circuit current characteristics. Second, based on the assumption of a complete line, the protection device constructs virtual peer quantities using the injected frequency voltage, current complex phasors, and the complete line propagation matrix measured at the local end. The measured values ​​at the local end and the virtual peer quantities form a joint feature vector, enabling the single-end protection device to obtain response information containing the propagation relationship between the two ends of the complete line. Furthermore, by constructing a consistency statistic based on the deviation of online joint characteristics from the complete line response manifold, the identification of faults inside and outside the protection zone is transformed into a complete line topology consistency judgment, thereby improving the selectivity and adaptability of the protection. Finally, by exchanging only local logic quantities at both ends to form the longitudinal tripping criterion, the amount of original sampling or phasor communication at both ends can be reduced, thus lowering the dependence on communication bandwidth, synchronization accuracy, and data continuity.

[0049] Please see Figure 1 Offshore wind farms collect power through their on-site collection system and connect to low-frequency AC lines via step-up transformers. Onshore, an M3C (Mechanical and Controlled Transmission) system is used to convert energy between low-frequency AC and power-frequency AC. The wind turbine side line end is designated as end m, and the M3C side line end as end n. Current flows from the busbar to the line in the positive direction. The protected line mn has a total length L. Fault points f1–f3 are set within the line, and external fault points f4 and f5 are set at both ends of the line.

[0050] The core idea of ​​this method is as follows: When no in-zone fault occurs on the protected line, the line topology remains intact, and the propagation relationship of the injected signal in the line should be consistent with the distributed parameter model of the complete line. The joint characteristics formed by the measured response at the local end and the virtual response at the remote end are located near the response manifold of the complete line. When an in-zone fault occurs, the faulty branch disrupts the complete line topology, the propagation path and response relationship of the injected signal change, and the online joint characteristics deviate from the response manifold of the complete line. Therefore, in-zone / out-of-zone fault identification can be transformed into a complete line consistency discrimination problem under active injection conditions.

[0051] Please see Figure 2 The present invention discloses a low-frequency transmission active detection longitudinal protection method based on response manifold, comprising the following steps: Step 1: Collect electrical quantities at both ends and form an active injection start criterion. During the operation of the low-frequency transmission system, the three-phase voltage and current signals at the protection installation points at both the m and n ends are collected in real time. For the m end, the collected signal is denoted as: (1) For the n-end, the acquired signal is denoted as: (2) The collected three-phase voltages are subjected to short-window filtering and positive / negative sequence decomposition to obtain the positive-sequence voltage amplitude and negative-sequence voltage amplitude within the k-th detection window. , .

[0052] To characterize the voltage drop, imbalance enhancement, and low-suspension correlation after a fault occurs, low-suspension correlation voltage terms are constructed respectively. Voltage rate of change term and negative order imbalance terms .

[0053] (3) The low-drive-related voltage term is further defined as follows: (4) The truncation operator is defined as follows: (5) in, The reference value of the positive sequence voltage before the fault can be the value held before the fault or the rated value. This is the reference threshold for low-penetration correlation.

[0054] Considering that the positive-sequence voltage drop may not be significant under minor faults and high-impedance faults, relying solely on the voltage drop amplitude could easily lead to startup lag or even failure to operate. Therefore, a voltage change rate term and a negative-sequence imbalance term are further introduced. The voltage change rate term is defined as: (6) The negative order imbalance term is defined as: (7) in, The time interval between two consecutive calculations of the activation criterion; This is the normalized threshold for voltage sag rate; A small positive number is introduced to prevent the denominator from being too small; This is the negative order imbalance normalization threshold.

[0055] Based on this, the comprehensive fault characteristic factor is defined as: (8) Among them, the first item This reflects the degree to which the positive sequence voltage approaches or enters the low-pass boundary after a fault; the second item. The third item reflects the degree of voltage fluctuation in the early stages of a fault; Reflecting the negative-order enhancement characteristics under asymmetric faults, , and For the weighting coefficients, satisfying (9) To suppress the impact of short-term fluctuations and measurement noise on the startup logic during the initial stage of a fault, a comparison method with hysteresis is used to generate the injected startup state variables: (10) in, and These are the start threshold and the exit threshold, respectively, and they satisfy... .

[0056] S2, Initiate characteristic frequency signal injection Once the active injection startup logic is established, the modulation capability of the modular multilevel matrix converter is used to superimpose a characteristic frequency voltage signal on the low-frequency side. Let the fundamental frequency of the low-frequency system be: (11) The injection frequency is 8 times the base frequency. (12) Injection voltage amplitude is taken as: (13) Injection duration is: (14) The injected characteristic frequency voltage can be expressed as: (15) in, The initial phase of the injected signal.

[0057] This characteristic frequency signal is used to actively enhance the observability of low-frequency line response after a fault.

[0058] S3. Extract the injection frequency complex phase and construct the virtual counterpart.

[0059] During active injection, the protection devices at both ends extract the voltage and current complex quantities at 133.33Hz.

[0060] (16) Based on the complete line propagation matrix Under the assumption of a complete line, the virtual n-terminal quantity can be calculated from the m-terminal quantity: (17) in, This is the inverse of the complete path propagation matrix; subscripts This means that the n-end is estimated from the m-end.

[0061] Similarly, virtual m-terminal quantities can be calculated from n-terminal quantities: (18) The n-terminal calculates the virtual m-terminal quantity based on the injection frequency complexity measured at this terminal.

[0062] This step enables the protection device to generate information locally that includes the propagation relationship between the two ends, avoiding the real-time transmission of raw sampled values ​​or complex electrical quantities from both ends.

[0063] S4. Construct the joint feature vector and perform standardization. Based on the actual measurements at this end and the virtual measurements at the other end, a joint feature vector is constructed for both ends. For the m-end, we have: (19) in, The joint feature vector at the m-end; This is the feature mapping function for the m-end.

[0064] (20) in, The joint eigenvectors of the n-end; It is the feature mapping function for the n-end.

[0065] To eliminate differences in the dimensions and amplitudes of different electrical quantities, the joint eigenvector of any terminal i is standardized: (twenty one) in, for Joint features after end-to-end standardization; for End-original joint features; for The mean vector of the complete line response characteristics; for The standard deviation vector of the complete line response characteristics.

[0066] S5. Calculate manifold consistency residuals and normalization protection indices. Based on the local tangential principal subspace of the complete line response manifold, calculate the normal residuals of the online joint features deviating from the complete line response manifold. Let... The tangential principal subspace basis matrix of the end-complete line response manifold under the local linear approximation is: Then the normal residual of the online sample outside the tangential principal subspace is (twenty two) in, for End-normal consistency residual; It is the identity matrix; Let be the projection matrix to the tangential principal subspace.

[0067] Equation (22) shows that if the online response still satisfies the consistency of the complete line propagation, its main changes should be located in the tangential principal subspace and the normal residual is small; if the fault in the area destroys the propagation relationship of the complete line, the online response will deviate from the principal subspace and the normal residual will increase.

[0068] Further construct consistency statistics (twenty three) in, for Complete line response residual covariance matrix; For regularization terms; is the regularization coefficient.

[0069] Since the measurement scales, feature composition, and statistical amplitudes at both ends may differ, this invention employs a normalized protection index: (twenty four) in, for End-to-end normalized protection indicators; This is the original consistency statistic; for Thresholds for end statistics. After normalization, the protection indicators at both ends are based on... As a unified discrimination boundary.

[0070] therefore, The end-point criterion is written as: (25) in, Indicates the first The deviation of the end-to-end online joint characteristics from the complete line response manifold exceeds the allowable range; if If the response at that end is consistent with the propagation of the complete line, then it is considered that the response at that end is still consistent with the propagation of the complete line.

[0071] S6. Form local protection logic at both ends and perform logical quantity communication.

[0072] According to normalized protection indicators Definition end The local protection logic is as follows: (26) For the m-end and n-end respectively, we have: (27) (28) In engineering implementation, to avoid misjudgments caused by abnormal fluctuations at a single calculation point, it is possible to... A necessary continuous confirmation step is set up. This step is only used to improve immunity and does not change the protection criterion itself. In other words, the protection criterion remains the same. Continuous confirmation is only used as a way to implement engineering logic.

[0073] S7. Form a longitudinal tripping criterion based on the two-terminal logic values. The protection devices at both ends only exchange local logic values. and The final longitudinal trip logic is defined as follows: (29) When both ends output internal fault confirmation logic If the protection determines it to be a fault within the zone, otherwise... Protect and maintain the lock.

[0074] Through the above steps, this invention transforms the problem of identifying faults within and outside a low-frequency transmission system into a problem of determining the consistency of the complete line response under active injection conditions. When the fault is located outside the protected line, the topology of the protected line remains intact, and the online joint characteristics are still near the complete line response manifold. The protection indicators at both ends will not simultaneously and stably exceed the action threshold. When the fault is located inside the protected line, the fault branch disrupts the propagation relationship of the complete line, the online joint characteristics deviate from the complete line response manifold, and the protection indicators at both ends exceed the threshold and form a double-ended logical confirmation, thereby achieving reliable tripping for faults within the protected area.

[0075] In another embodiment of the present invention, a low-frequency transmission active detection longitudinal protection system based on response manifold is provided. This system can be used to implement the above-mentioned low-frequency transmission active detection longitudinal protection method based on response manifold. Specifically, the low-frequency transmission active detection longitudinal protection system based on response manifold includes a modular multilevel matrix converter, an m-end protection device disposed at the m end of the protected line, and an n-end protection device disposed at the n end of the protected line. The m-terminal protection device and the n-terminal protection device are respectively used to collect the three-phase voltage and current signals of this terminal, and form an injection start-up state quantity based on the three-phase voltage of this terminal; The modular multilevel matrix converter is used to superimpose a characteristic frequency voltage signal on the low-frequency side according to the injected startup state quantity; The m-terminal protection device and the n-terminal protection device are also used to extract the voltage and current complex quantities at the injection frequency at their respective terminals, calculate the virtual peer quantity based on the voltage and current complex quantities at the injection frequency measured at their respective terminals and the complete line propagation matrix, construct a joint feature vector based on the actual measurements at their respective terminals and the virtual peer quantity, obtain a normalized protection index based on the degree of deviation of the joint feature vector from the complete line response manifold, generate local protection logic based on the normalized protection index, and send the logic quantity corresponding to the local protection logic to the peer terminal. The m-terminal protection device and the n-terminal protection device are also used to perform AND logic operations on the logic quantities corresponding to the local protection logic of the m-terminal and n-terminal to obtain the longitudinal tripping logic.

[0076] This invention provides a terminal device comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment can be used in the operation of a low-frequency power transmission active detection longitudinal protection method based on response manifold, including: Three-phase voltage and current signals are collected at both the m and n ends of the protected line. The three-phase voltages are decomposed into positive and negative sequence values ​​to obtain positive-sequence and negative-sequence voltage amplitudes. Based on the positive-sequence voltage amplitude, a low-throughput correlation voltage term and a voltage change rate term are constructed. Based on the positive-sequence and negative-sequence voltage amplitudes, a negative-sequence imbalance term is constructed. The low-throughput correlation voltage term, the voltage change rate term, and the negative-sequence imbalance term are then weighted and summed to obtain a comprehensive fault characteristic factor. This comprehensive fault characteristic factor is then compared with a start-up threshold and a stop-loss threshold. Threshold comparisons are performed to obtain the injection initiation state quantity. Based on the injection initiation state quantity, a characteristic frequency voltage signal is superimposed on the low-frequency side using the modulation capability of the modular multilevel matrix converter. During the active injection of the characteristic frequency voltage signal, the voltage and current complex quantities at the injection frequency are extracted from the m-terminal and n-terminal respectively. The m-terminal calculates the virtual n-terminal quantity based on the voltage and current complex quantities measured at the injection frequency and the inverse matrix of the complete line propagation matrix. The n-terminal calculates the virtual n-terminal quantity based on the voltage and current complex quantities measured at the injection frequency and the inverse matrix of the complete line propagation matrix. The propagation matrix is ​​used to calculate the virtual m-terminal quantity. The m-terminal constructs a joint feature vector based on its actual measurements and the virtual n-terminal quantity, and the n-terminal constructs a joint feature vector based on its actual measurements and the virtual m-terminal quantity. The m-terminal joint feature vector and the n-terminal joint feature vector are standardized using the mean vector and standard deviation vector of the corresponding end's complete line response characteristics, respectively, to obtain the standardized joint features of the corresponding end. Each end calculates the normal consistency residual based on its standardized joint features and the local tangential principal subspace of the corresponding end's complete line response manifold. A consistency statistic is calculated based on the normal consistency residual, the covariance matrix of the corresponding end's complete line response residual, and the regularization term. The consistency statistic is normalized based on the corresponding end's statistic threshold to obtain a normalized protection index. Each end compares its normalized protection index with the unified discrimination boundary to obtain local protection logic, and sends the logic quantity corresponding to the local protection logic to the other end. An AND operation is performed on the logic quantities corresponding to the local protection logic of the m-terminal and the n-terminal to obtain the longitudinal tripping logic.

[0077] Please see Figure 6 The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the response manifold-based active detection longitudinal protection method for low-frequency transmission in this embodiment. To avoid repetition, details are omitted here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the response manifold-based active detection longitudinal protection system for low-frequency transmission in this embodiment. To avoid repetition, details are omitted here.

[0078] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 6 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0079] The processor 61 may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0080] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on the computer device 60.

[0081] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0082] Please see Figure 7 The terminal device is an electronic device 600, which is manifested in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0083] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 2 The steps are shown in the figure.

[0084] Storage unit 620 may include readable media in the form of volatile storage units, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include read-only memory (ROM) 6203.

[0085] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0086] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0087] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem). This communication can be performed via input / output interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network, wide area network, and / or public network, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0088] This invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). More specific examples of the computer-readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, random access memory, read-only memory, erasable programmable read-only memory, optical fiber, portable compact disk read-only memory, optical storage device, magnetic storage device, or any suitable combination thereof.

[0089] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, radio frequency, etc., or any suitable combination thereof.

[0090] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0091] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the low-frequency transmission active detection longitudinal protection method based on response manifold in the above embodiments; one or more instructions in the computer-readable storage medium are loaded by the processor and executed as follows: Three-phase voltage and current signals are collected at both the m and n ends of the protected line. The three-phase voltages are decomposed into positive and negative sequence values ​​to obtain positive-sequence and negative-sequence voltage amplitudes. Based on the positive-sequence voltage amplitude, a low-throughput correlation voltage term and a voltage change rate term are constructed. Based on the positive-sequence and negative-sequence voltage amplitudes, a negative-sequence imbalance term is constructed. The low-throughput correlation voltage term, the voltage change rate term, and the negative-sequence imbalance term are then weighted and summed to obtain a comprehensive fault characteristic factor. This comprehensive fault characteristic factor is then compared with a start-up threshold and a stop-loss threshold. Threshold comparisons are performed to obtain the injection initiation state quantity. Based on the injection initiation state quantity, a characteristic frequency voltage signal is superimposed on the low-frequency side using the modulation capability of the modular multilevel matrix converter. During the active injection of the characteristic frequency voltage signal, the voltage and current complex quantities at the injection frequency are extracted from the m-terminal and n-terminal respectively. The m-terminal calculates the virtual n-terminal quantity based on the voltage and current complex quantities measured at the injection frequency and the inverse matrix of the complete line propagation matrix. The n-terminal calculates the virtual n-terminal quantity based on the voltage and current complex quantities measured at the injection frequency and the inverse matrix of the complete line propagation matrix. The propagation matrix is ​​used to calculate the virtual m-terminal quantity. The m-terminal constructs a joint feature vector based on its actual measurements and the virtual n-terminal quantity, and the n-terminal constructs a joint feature vector based on its actual measurements and the virtual m-terminal quantity. The m-terminal joint feature vector and the n-terminal joint feature vector are standardized using the mean vector and standard deviation vector of the corresponding end's complete line response characteristics, respectively, to obtain the standardized joint features of the corresponding end. Each end calculates the normal consistency residual based on its standardized joint features and the local tangential principal subspace of the corresponding end's complete line response manifold. A consistency statistic is calculated based on the normal consistency residual, the covariance matrix of the corresponding end's complete line response residual, and the regularization term. The consistency statistic is normalized based on the corresponding end's statistic threshold to obtain a normalized protection index. Each end compares its normalized protection index with the unified discrimination boundary to obtain local protection logic, and sends the logic quantity corresponding to the local protection logic to the other end. An AND operation is performed on the logic quantities corresponding to the local protection logic of the m-terminal and the n-terminal to obtain the longitudinal tripping logic.

[0092] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0093] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0094] To verify the correctness, reliability, and engineering feasibility of the proposed method in offshore wind power low-frequency transmission systems, an electromagnetic transient simulation platform was used to build a system model of wind farm—low-frequency AC line—M3C frequency converter station. The simulation focused on examining the effectiveness of active injection, in-zone / out-zone fault selectivity, and adaptability to different fault locations and transition resistances.

[0095] The simulation system parameters are shown in Table 1. Table 1. Main parameters of low-frequency transmission system and protection algorithm

[0096] Please see Figure 3 To verify whether the actively injected signals of 0.1 pu, 133.33 Hz, and 100 ms can form an observable response at the protection mounting end, the fundamental frequency component of the voltage and current signals at the m and n terminals was suppressed, and the net 133 Hz component was extracted. Figure 3 The time-domain variations of the net 133Hz component in the voltage and current after fundamental frequency suppression are presented. It can be seen that under fault-free and non-injection conditions, the net 133Hz component at each measuring point is basically close to zero, indicating that there is no obvious 133Hz characteristic component in the normal operating background.

[0097] Please see Figure 4 and Figure 5An internal line fault (f2) and external faults on both sides (f4 and f5) are set. Simulation results show that for internal faults, the normalized protection indices H_m and H_n at the m and n ends significantly exceed the unified threshold 1, and form stable local confirmation logic and longitudinal tripping logic in a short time. This indicates that internal faults disrupt the propagation relationship of the complete line, causing the online response to deviate from the complete line response manifold.

[0098] For faults outside the protected area on both sides of f4 and f5, the external network boundary changes, but the internal topology of the protected line remains intact. Therefore, the responses at both ends still satisfy the propagation constraints of the complete line. Even if the single-end indicators fluctuate, the logic at both ends will not simultaneously meet the longitudinal linkage action condition, and the tripping logic remains blocked. This result verifies the intra-zone / outside-zone selectivity based on the virtual peer quantity and response manifold consistency criterion.

[0099] Simulation results show that the active detection-based response manifold consistency identification longitudinal protection method proposed in this invention can actively construct stable and observable characteristic frequency responses during low-frequency double-ended weak feed and converter control-dominated fault processes; it can reliably identify in-zone / out-zone faults by utilizing the deviation of the complete line response manifold; it can maintain good adaptability under different fault locations, fault types, transition resistances, and control states; and it only requires the exchange of logic quantities at both ends, reducing the dependence of longitudinal protection on communication bandwidth and synchronization accuracy, thus possessing good engineering application value.

[0100] In summary, this invention provides a low-frequency transmission active detection longitudinal protection method and system based on response manifold, which can form a stable and observable characteristic frequency response under low-frequency double-ended weak feeder and converter control-dominated conditions. After actively injecting a 133.33Hz signal with a per-unit value of 0.1 and a duration of 100ms, a significant net 133Hz component can be extracted from the voltage and current at both the m-end and n-end, while the corresponding frequency component is close to zero when there is no fault and no injection. For faults within the line zone, the normalized protection indicators at both ends exceed the unified discrimination boundary and form longitudinal tripping logic; for faults outside the zone on both sides, although the single-end indicators may fluctuate, the double-end logic will not simultaneously meet the operating conditions, and the protection remains blocked. This invention can reliably distinguish between faults within and outside the zone by utilizing the deviation of the complete line response manifold, and remains adaptable to different fault locations, fault types, transition resistances, and control states; the two ends only exchange local logic quantities, which can reduce the dependence on communication bandwidth, synchronization accuracy, and data continuity.

[0101] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0102] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0103] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0104] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0105] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0106] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0107] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random-access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0108] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus, and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0109] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0110] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0111] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A low-frequency transmission active detection longitudinal protection method based on response manifold, characterized in that, Includes the following steps: S1. Collect the three-phase voltage and current signals at the m and n ends of the protected line respectively, and decompose the three-phase voltage into positive and negative sequence values ​​to obtain the positive sequence voltage amplitude and the negative sequence voltage amplitude. Construct a low-throughput correlation voltage term and a voltage change rate term based on the positive sequence voltage amplitude, and construct a negative sequence imbalance term based on the positive sequence voltage amplitude and the negative sequence voltage amplitude. Perform a weighted summation of the low-throughput correlation voltage term, the voltage change rate term, and the negative sequence imbalance term to obtain a comprehensive fault characteristic factor. The comprehensive fault characteristic factor is compared with the start threshold and the exit threshold to obtain the injected start state quantity; S2. Based on the injected start-up state quantity, a characteristic frequency voltage signal is superimposed on the low-frequency side using the modulation capability of the modular multilevel matrix converter. S3. During the active injection of the characteristic frequency voltage signal, extract the voltage and current complex quantities of the m-end and n-end at the injection frequency, respectively. The virtual n-terminal quantity is calculated from the voltage and current phasors at the injection frequency measured at this terminal and the inverse matrix of the complete line propagation matrix. Based on the voltage and current phasors measured at the injection frequency at this terminal and the complete line propagation matrix, the n-terminal calculates the virtual m-terminal quantity. S4. The m-end constructs a joint feature vector based on the actual measurement of this end and the virtual n-end quantity, and the n-end constructs a joint feature vector based on the actual measurement of this end and the virtual m-end quantity; the m-end joint feature vector and the n-end joint feature vector are standardized using the mean vector and standard deviation vector of the complete line response characteristics of the corresponding ends, respectively, to obtain the standardized joint features of the corresponding ends; S5. Each end calculates the normal consistency residual based on the joint characteristics after standardization of its own end and the local tangential principal subspace of the complete line response manifold of the corresponding end; calculates the consistency statistic based on the normal consistency residual, the covariance matrix of the complete line response residual of the corresponding end, and the regularization term; normalizes the consistency statistic based on the threshold of the corresponding end statistic to obtain the normalized protection index. S6. Each end compares its own normalized protection index with the unified discrimination boundary to obtain local protection logic, and sends the logic quantity corresponding to the local protection logic to the other end. S7. Perform an AND operation on the logic quantities corresponding to the local protection logic of the m and n terminals to obtain the longitudinal trip logic.

2. The low-frequency transmission active detection longitudinal protection method based on response manifold as described in claim 1, characterized in that, In step S1, the low-suspension associated voltage term is calculated based on the pre-fault positive sequence voltage reference value, the low-suspension associated reference threshold, and the positive sequence voltage amplitude; the voltage change rate term is calculated based on the corresponding positive sequence voltage amplitude and time interval between two adjacent start-up criteria. The negative sequence imbalance term is calculated based on the positive sequence voltage amplitude, the negative sequence voltage amplitude, and the negative sequence imbalance normalization threshold.

3. The low-frequency transmission active detection longitudinal protection method based on response manifold as described in claim 1, characterized in that, In step S1, when the comprehensive fault characteristic factor reaches the start-up threshold, the injected start-up state quantity is set to the start-up state. When the comprehensive fault characteristic factor is lower than the exit threshold, the injection start-up state quantity is set to the exit state, and the start-up threshold is greater than the exit threshold.

4. The low-frequency transmission active detection longitudinal protection method based on response manifold as described in claim 1, characterized in that, In step S2, the injection frequency is determined based on the fundamental frequency of the low-frequency system, and the characteristic frequency voltage signal is generated based on the injection frequency, the injection voltage amplitude, the injection duration, and the initial phase of the injection signal.

5. The low-frequency transmission active detection longitudinal protection method based on response manifold according to claim 4, characterized in that, The injection frequency is 8 times the fundamental frequency of the low-frequency system, the injection voltage amplitude is 0.1 per unit, and the injection duration is 100 milliseconds.

6. The low-frequency transmission active detection longitudinal protection method based on response manifold according to claim 1, characterized in that, In step S3, the m-terminal calculates the voltage and current complex phase quantities measured at the injection frequency based on the inverse matrix of the complete line propagation matrix to obtain the virtual n-terminal quantity. Based on the complete line propagation matrix, the n-terminal calculates the voltage and current complex phase quantities at the injection frequency measured at the n-terminal to obtain the virtual m-terminal quantity.

7. The low-frequency transmission active detection longitudinal protection method based on response manifold as described in claim 1, characterized in that, In step S4, the m-end uses the m-end feature mapping function to perform feature mapping on the actual measurement of the m-end and the virtual n-end quantity to obtain the joint feature vector of the m-end; the n-end uses the n-end feature mapping function to perform feature mapping on the actual measurement of the n-end and the virtual m-end quantity to obtain the joint feature vector of the n-end; each end performs standardization processing on its own joint feature vector according to the mean vector and standard deviation vector of the complete line response characteristics of the corresponding end to obtain the standardized joint feature of the end.

8. The low-frequency transmission active detection longitudinal protection method based on response manifold according to claim 1, characterized in that, In step S5, the projection matrix to the local tangential principal subspace is determined based on the basis matrix of the local tangential principal subspace of the complete line response manifold of the corresponding end; the standardized joint features of the local end are projected based on the projection matrix, and the normal consistency residual is obtained based on the components of the standardized joint features of the local end outside the local tangential principal subspace; the consistency statistic is calculated based on the normal consistency residual, the covariance matrix of the complete line response residual, the regularization coefficient, and the regularization term.

9. The low-frequency transmission active detection longitudinal protection method based on response manifold according to claim 1, characterized in that, In step S5, the ratio of the consistency statistic to the corresponding end statistic threshold is calculated to obtain the normalized protection index, and the unified discrimination boundary is 1; when the normalized protection index of this end is greater than the unified discrimination boundary for a consecutive preset number of calculation points, the local protection logic of this end is generated.

10. A low-frequency transmission active detection longitudinal protection system based on response manifold, characterized in that, It includes a modular multilevel matrix converter, an m-terminal protection device installed at the m-end of the protected line, and an n-terminal protection device installed at the n-end of the protected line. The m-terminal protection device and the n-terminal protection device are respectively used to collect the three-phase voltage and current signals of this terminal, and form an injection start-up state quantity based on the three-phase voltage of this terminal. The modular multilevel matrix converter is used to superimpose a characteristic frequency voltage signal on the low-frequency side according to the injected startup state quantity; The m-terminal protection device and the n-terminal protection device are also used to extract the voltage and current complex quantities at the injection frequency at their respective terminals, calculate the virtual peer quantity based on the voltage and current complex quantities at the injection frequency measured at their respective terminals and the complete line propagation matrix, construct a joint feature vector based on the actual measurements at their respective terminals and the virtual peer quantity, obtain a normalized protection index based on the degree of deviation of the joint feature vector from the complete line response manifold, generate local protection logic based on the normalized protection index, and send the logic quantity corresponding to the local protection logic to the peer terminal. The m-terminal protection device and the n-terminal protection device are also used to perform AND logic operations on the logic quantities corresponding to the local protection logic of the m-terminal and n-terminal to obtain the longitudinal tripping logic.

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