A flexible low-frequency power transmission line pilot protection method, device, equipment and medium

Abstract

This application relates to the field of power system relay protection technology. It discloses a method, device, equipment, and medium for longitudinal protection of flexible low-frequency transmission lines. The method includes acquiring the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the M3C low-frequency side and the three-phase voltage and current on the wind power side; based on the three-phase voltage on the M3C low-frequency side, determining whether to initiate fault judgment based on a pre-set start-up criterion model; when fault judgment is determined, determining whether a fault has occurred in that phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line, using a pre-set fault multi-frequency band composite energy model, and triggering protection action upon fault determination. This application uses a fault multi-frequency band composite energy model for fault multi-frequency band composite energy analysis, which can obtain multi-frequency band transient energy information without constructing phasors, and can complete fault judgment during the fault transient stage, improving the speed and reliability of protection.

Description

Technical Field

[0001] This application relates to the field of power system relay protection technology, and more specifically, to a method, device, equipment, and medium for longitudinal protection of flexible low-frequency transmission lines. Background Technology

[0002] In recent years, the installed capacity of new energy sources such as photovoltaics and wind power has grown rapidly. Among them, offshore wind power has become an important direction for future new energy development due to its significant advantages such as stable wind speed and the ability to be built on a large scale. In the transmission methods of offshore wind power, flexible low-frequency AC (LFAC) transmission technology, as a new type of transmission method between DC and power frequency AC, has become one of the important technical solutions for offshore wind power transmission due to its advantages of low line loss and large transmission capacity.

[0003] The offshore wind power flexible low-frequency transmission system consists of a modular multilevel matrix converter (M3C) and a permanent magnet direct-drive wind turbine on each side. Because both ends are highly electronic converters, after a fault, both ends of the line exhibit weak feeder characteristics, with the fault current phase controlled and amplitude limited. This weak feeder characteristic is significantly different from the fault characteristics of traditional power grids dominated by synchronous generators. Existing relay protection algorithms struggle to effectively identify this, posing a risk of false tripping and failure to trip, thus threatening the safe and stable operation of the transmission system.

[0004] Existing methods typically rely on voltage and current phasors for calculations. The specific process involves: measuring electrical quantities in real time using current and voltage transformers installed on both sides of the transmission system; converting the real-time measured values ​​into phasor form using algorithms such as Discrete Fourier Transform; using the phasors to calculate protection action criteria; and if the determination result is a fault, the protection device will issue a trip signal to disconnect the faulty line.

[0005] These schemes are based on phasors for calculation, but these phasors only reach stable values ​​during the steady-state phase of a fault. When a line fault occurs, the operating frequency of the flexible low-frequency transmission system is 20Hz. The reduced operating frequency leads to a longer fault response time, which significantly reduces the operating speed of protection methods based on phasor calculations, making it difficult to achieve rapid isolation and clearance of faults.

[0006] To address the aforementioned technical issues, a novel relay protection method needs to be developed to meet the requirements of flexible low-frequency power transmission systems for high reliability, high selectivity, and high response speed in relay protection. Summary of the Invention

[0007] In view of the above situation, this application provides a method, device, equipment and medium for longitudinal protection of flexible low-frequency transmission lines, which aims to solve the above problems or at least partially solve the above problems.

[0008] In a first aspect, this application provides a longitudinal protection method for flexible low-frequency transmission lines, comprising:

[0009] Acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of the M3C and the three-phase voltage and current on the wind power side;

[0010] Based on the three-phase voltage of the low-frequency side of the M3C, and based on the pre-set start-up criterion model, it is determined whether to start the fault judgment.

[0011] When a fault is detected, the system determines whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model. If a fault is detected, the system will trigger the protection action.

[0012] For example, based on the three-phase voltage on the low-frequency side of the M3C, and based on a pre-set start-up criterion model, it is determined whether to initiate fault detection, including:

[0013] Calculate the d-axis voltage and q-axis voltage of the M3C low-frequency side based on the three-phase voltage of the M3C low-frequency side.

[0014] Based on the d-axis voltage and q-axis voltage of the M3C low-frequency side in two adjacent sampling periods, calculate the difference of the d-axis voltage with respect to time and the difference of the q-axis voltage with respect to time.

[0015] Based on the difference between the d-axis voltage and time and a preset first threshold value, and the difference between the q-axis voltage and time and a preset second threshold value, determine whether to initiate fault detection.

[0016] For example, based on the difference between the d-axis voltage and time and a preset first threshold value, and the difference between the q-axis voltage and time and a preset second threshold value, it is determined whether to initiate fault detection, including:

[0017] When the difference between the d-axis voltage and time is greater than the first threshold value and the difference between the q-axis voltage and time is greater than the second threshold value, a startup fault judgment is determined.

[0018] For example, when determining to initiate fault judgment, based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line, and based on a pre-set fault multi-frequency band composite energy model, it is determined whether a fault has occurred in that phase, including:

[0019] Obtain the voltage and current of the target phases at both ends of the flexible low-frequency transmission line, including the target phase voltage and current on the M3C low-frequency side and the target phase voltage and current on the wind power side;

[0020] The instantaneous power of the target phase on the low-frequency side of M3C is calculated based on the target phase voltage and current on the low-frequency side of M3C, and the instantaneous power of the target phase on the wind power side is calculated based on the target phase voltage and current on the wind power side.

[0021] Based on the pre-set power time window, the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side corresponding to the power time window are obtained;

[0022] Wavelet decomposition is performed on the power signals in the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side to obtain the multi-band transient energy information of the target phase on the low-frequency side of M3C and the multi-band transient energy information of the target phase on the wind power side.

[0023] The energy of each frequency band on the low-frequency side of M3C is calculated based on the multi-frequency band transient energy information of the target phase on the low-frequency side of M3C, and the energy of each frequency band on the wind power side is calculated based on the multi-frequency band transient energy information of the target phase on the wind power side.

[0024] Calculate the total energy of the M3C low-frequency side multi-band based on the energy of each frequency band on the M3C low-frequency side, and calculate the total energy of the wind power side multi-band based on the energy of each frequency band on the wind power side.

[0025] Calculate the differential energy ratio based on the total energy of the M3C low-frequency side multi-band and the total energy of the wind power side multi-band.

[0026] Based on a pre-set action threshold, the differential energy ratio is compared with the action threshold, and the result of the comparison determines whether a fault has occurred in that phase.

[0027] For example, calculating the total energy of the M3C low-frequency side multi-band based on the energy of each frequency band on the M3C low-frequency side, and calculating the total energy of the wind power side multi-band based on the energy of each frequency band on the wind power side, includes:

[0028] The total energy of the M3C low-frequency side multi-band is calculated based on the pre-set weighting coefficients of each frequency band and the energy of each frequency band on the low-frequency side of the M3C.

[0029] The total energy of the wind power side across multiple frequency bands is calculated based on the pre-set weighting coefficients for each frequency band and the energy of each frequency band on the wind power side.

[0030] For example, the method further includes:

[0031] The differential energy ratio is averaged by performing a moving average.

[0032] The average differential energy ratio is compared with the action threshold, and the failure of the phase is determined based on the comparison result.

[0033] For example, the method further includes:

[0034] When the average value of multiple consecutive differential energy ratios is greater than the action threshold, it is determined that a phase has failed.

[0035] Secondly, this application provides a longitudinal protection device for flexible low-frequency transmission lines, comprising:

[0036] The acquisition module is used to acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of the M3C and the three-phase voltage and current on the wind power side.

[0037] The first judgment module is used to determine whether to initiate fault judgment based on the three-phase voltage of the low-frequency side of the M3C and a pre-set start-up criterion model.

[0038] The second judgment module is used to determine whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model when a fault judgment is determined, and to trigger protection action when a fault is determined.

[0039] Thirdly, this application provides a computer device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the flexible low-frequency transmission line longitudinal protection method as described in the first aspect.

[0040] Fourthly, this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the flexible low-frequency transmission line longitudinal protection method as described in the first aspect.

[0041] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects:

[0042] This application processes the voltage and current of each phase at both ends of a flexible low-frequency transmission line separately, and performs multi-frequency band composite energy analysis of the fault through a multi-frequency band composite energy model. This allows for the acquisition of multi-frequency band transient energy information without the need to construct phasors, enabling fault determination to be completed during the transient stage of the fault, thereby improving the speed and reliability of the protection. Attached Figure Description

[0043] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0044] Figure 1 This is a schematic diagram of an application environment for a longitudinal protection method for flexible low-frequency transmission lines according to an embodiment of the present invention;

[0045] Figure 2 This is a schematic flowchart of a longitudinal protection method for flexible low-frequency transmission lines according to an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of the topology of an offshore wind power transmission system via a flexible low-frequency power transmission system in one embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of a specific process of a longitudinal protection method for flexible low-frequency transmission lines in one embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of a specific process of step S30 in one embodiment of the present invention;

[0049] Figure 6 This is a schematic diagram showing the simulation calculation results of phase A of a single-phase ground fault (F1) in an embodiment of the present invention and the protection operation status;

[0050] Figure 7 This is a schematic diagram showing the simulation calculation results of phase B of a single-phase ground fault (F1) in an embodiment of the present invention and the protection operation status.

[0051] Figure 8 This is a schematic diagram showing the simulation calculation results of phase C of a single-phase ground fault (F1) in an embodiment of the present invention and the protection operation status;

[0052] Figure 9 This is a schematic diagram showing the simulation calculation results of phase A of a two-phase short-circuit fault (F1) in an embodiment of the present invention and the protection operation status;

[0053] Figure 10 This is a schematic diagram of the simulation calculation results and protection operation of phase B of a two-phase short-circuit fault (F1) in an embodiment of the present invention;

[0054] Figure 11 This is a schematic diagram showing the simulation calculation results of phase C of a two-phase short-circuit fault (F1) in an embodiment of the present invention and the protection operation status;

[0055] Figure 12 This is a schematic diagram showing the simulation calculation results of phase A of a two-phase ground fault (F1) in an embodiment of the present invention and the protection operation status;

[0056] Figure 13 This is a schematic diagram showing the simulation calculation results of phase B of a two-phase ground fault (F1) in an embodiment of the present invention and the protection operation status;

[0057] Figure 14 This is a schematic diagram showing the simulation calculation results of phase C of a two-phase ground fault (F1) in an embodiment of the present invention and the protection operation status;

[0058] Figure 15 This is a schematic diagram showing the simulation calculation results and protection operation of phase A of a single-phase ground fault outside the zone (F2) in one embodiment of the present invention;

[0059] Figure 16 This is a schematic diagram showing the simulation calculation results and protection operation of phase B of a single-phase ground fault outside the zone (F2) in one embodiment of the present invention;

[0060] Figure 17 This is a schematic diagram showing the simulation calculation results of phase C of a single-phase ground fault outside the zone (F2) and the protection operation status in one embodiment of the present invention;

[0061] Figure 18 This is a schematic diagram of a flexible low-frequency transmission line longitudinal protection device according to an embodiment of the present invention;

[0062] Figure 19 This is a schematic diagram of the structure of a computer device according to an embodiment of the present invention;

[0063] Figure 20 This is another structural schematic diagram of a computer device according to one embodiment of the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0065] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the term "comprising" and its variations should be interpreted as open-ended terms meaning "including but not limited to."

[0066] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0067] As mentioned earlier, current protection methods based on phasor calculations suffer from significantly reduced operating speeds, hindering rapid fault isolation and clearance. To address this technical problem, this application provides a longitudinal protection method for flexible low-frequency transmission lines.

[0068] The longitudinal protection method for flexible low-frequency transmission lines provided in this invention can be applied to applications such as... Figure 1 In this application environment, the device communicates with the server via a network. The server can obtain the three-phase voltage and current at both ends of the flexible low-frequency transmission line through the device, including the three-phase voltage and current on the M3C low-frequency side and the wind power side. Based on the three-phase voltage on the M3C low-frequency side, and using a pre-set start-up criterion model, it determines whether to initiate fault detection. When fault detection is initiated, based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line, and using a pre-set fault multi-frequency band composite energy model, it determines whether a fault has occurred in that phase, and triggers protection action upon fault detection. This application processes the voltage and current of each phase at both ends of the flexible low-frequency transmission line separately, and performs fault multi-frequency band composite energy analysis through a fault multi-frequency band composite energy model. This allows for the acquisition of multi-frequency band transient energy information without constructing phasors, enabling fault detection to be completed during the fault transient stage, thus improving the speed and reliability of the protection.

[0069] The device side can include, but is not limited to, protective devices, various computers, laptops, smartphones, tablets, and portable wearable devices. The server side can be implemented using a standalone server or a server cluster consisting of multiple servers. The invention will now be described in detail through specific embodiments.

[0070] Please see Figure 2 As shown, Figure 2 A schematic flowchart of a longitudinal protection method for flexible low-frequency transmission lines provided in an embodiment of the present invention includes the following steps:

[0071] S10: Obtain the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of M3C and the three-phase voltage and current on the wind power side.

[0072] In one embodiment, a topology diagram of offshore wind power via a flexible low-frequency transmission system is shown below. Figure 3 As shown, the low-frequency transmission line has an M3C side and a wind turbine side on both sides, respectively. Protection devices are installed on both the M3C side and the wind turbine side. These protection devices collect the three-phase voltage and current through voltage and current transformers, respectively. For example, the voltage of phase A on the low-frequency side of M3C... and current Phase A voltage on the wind power side and current .

[0073] S20: Based on the three-phase voltage of the low-frequency side of the M3C, and based on the pre-set start-up criterion model, determine whether to start the fault judgment.

[0074] In one embodiment, such as Figure 4 The process first analyzes whether to initiate a fault judgment. Only when it is determined that fault judgment needs to be initiated will the subsequent process be entered. If fault judgment does not need to be initiated, the subsequent process will not be entered, which reduces the risk of erroneous operation and improves the safety and stability of the power transmission system.

[0075] In one embodiment, such as Figure 5 Step S20, as shown, determines whether to initiate fault detection based on the three-phase voltage on the low-frequency side of the M3C and a pre-set start-up criterion model, including:

[0076] S21: Calculate the d-axis voltage and q-axis voltage of the low-frequency side of M3C based on the three-phase voltage of the low-frequency side of M3C.

[0077] In one embodiment, the d-axis voltage and q-axis voltage of the M3C low-frequency side are the per-unit values ​​of the d-axis and q-axis components of the M3C low-frequency side voltage. The per-unit value is obtained by calculating the ratio of the actual values ​​to a preset reference value based on the actual values ​​of the d-axis and q-axis components of the three-phase voltage on the M3C low-frequency side after coordinate transformation.

[0078] S22: Based on the d-axis voltage and q-axis voltage of the M3C low-frequency side in two adjacent sampling periods, calculate the difference of the d-axis voltage with respect to time and the difference of the q-axis voltage with respect to time.

[0079] In one embodiment, via Calculate the d-axis voltage difference on the low-frequency side of the M3C between two adjacent sampling periods. Calculate the q-axis voltage difference on the low-frequency side of the M3C between two adjacent sampling periods. Calculate the difference between the d-axis voltage and time, where The sampling period. (Through...) Calculate the difference of the q-axis voltage with respect to time, where The sampling period.

[0080] S23: Based on the difference between the d-axis voltage and time and the preset first threshold value, and the difference between the q-axis voltage and time and the preset second threshold value, determine whether to initiate fault judgment.

[0081] In one embodiment, a startup fault is determined when the difference between the d-axis voltage and time is greater than the first threshold value and the difference between the q-axis voltage and time is greater than the second threshold value. This can be expressed by the following formula:

[0082]

[0083] In the formula, This is the first threshold value; This is the second threshold value.

[0084] S30: When a fault judgment is initiated, based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and the pre-set fault multi-frequency band composite energy model, it is determined whether a fault has occurred in that phase, and the protection action is triggered when a fault is determined.

[0085] In one embodiment, when step S30 determines to initiate fault judgment, based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model, it determines whether a fault has occurred in that phase, including:

[0086] S31: Obtain the voltage and current of the target phases at both ends of the flexible low-frequency transmission line, including the voltage and current of the target phases on the low-frequency side of M3C and the voltage and current of the target phases on the wind power side.

[0087] In one embodiment, the target phase is phase A, phase B, or phase C.

[0088] In one embodiment, the target phase voltage and current on the low-frequency side of the M3C and the target phase voltage and current on the wind power side are acquired synchronously.

[0089] S32: Calculate the instantaneous power of the target phase on the low-frequency side of M3C based on the target phase voltage and current on the low-frequency side of M3C, and calculate the instantaneous power of the target phase on the wind power side based on the target phase voltage and current on the wind power side.

[0090] In one embodiment, taking phase A as the target phase as an example, the instantaneous power of phase A on the low-frequency side of M3C is... p 1( t ) and instantaneous power of phase A on the wind power side p 2( t The result is obtained by calculation using the following formula:

[0091]

[0092] S33: Based on the preset power time window, obtain the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side corresponding to the power time window.

[0093] In one embodiment, the power time window includes N sampling periods. The window length of the power time window is .

[0094] Taking phase A as the target phase as an example, the instantaneous power set of phase A on the low-frequency side of M3C corresponding to the power time window. Instantaneous power collection of phase A on the wind power side As shown in the following formula:

[0095]

[0096] S34: Perform wavelet decomposition on the power signals in the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side, respectively, to obtain the multi-band transient energy information of the target phase on the low-frequency side of M3C and the multi-band transient energy information of the target phase on the wind power side.

[0097] In one embodiment, the power signals in the set are subjected to four-level wavelet decomposition. Wavelet decomposition is used to extract multi-frequency band components, accurately capture the transient features of the signal, and improve the accuracy and robustness of feature extraction. Secondly, through the multi-resolution analysis characteristics of wavelet decomposition, different sampling rates and processing strategies can be adopted for different frequency bands. High-frequency components adopt higher time resolution, and low-frequency components adopt lower time resolution, which reduces redundant calculations and lowers computational complexity.

[0098] In one embodiment, taking phase A as an example, the multi-band transient energy information of phase A on the low-frequency side of M3C is obtained by wavelet decomposition of the instantaneous power set of phase A on the low-frequency side of M3C. The multi-band transient energy information of phase A of the wind power side is obtained by wavelet decomposition of the power signal in the instantaneous power set of phase A on the wind power side. As shown in the following formula:

[0099]

[0100] In the formula, j This represents the number of wavelet decomposition layers.

[0101] S35: Calculate the energy of each frequency band on the low-frequency side of M3C based on the multi-band transient energy information of the target phase on the low-frequency side of M3C, and calculate the energy of each frequency band on the wind power side based on the multi-band transient energy information of the target phase on the wind power side.

[0102] In one embodiment, taking phase A as an example, the energy of each frequency band on the low-frequency side of the M3C... Energy in various frequency bands on the wind power side The calculation is as follows:

[0103]

[0104] S36: Calculate the total energy of the M3C low-frequency side multi-band based on the energy of each frequency band on the M3C low-frequency side, and calculate the total energy of the wind power side multi-band based on the energy of each frequency band on the wind power side.

[0105] In one embodiment, the total energy of the M3C low-frequency side multi-band is calculated based on pre-set weighting coefficients for each frequency band and the energy of each frequency band on the M3C low-frequency side; the total energy of the wind power side multi-band is calculated based on pre-set weighting coefficients for each frequency band and the energy of each frequency band on the wind power side. Calculating the composite energy at both ends using pre-set weighting coefficients amplifies weak transient high-frequency fault characteristics, more accurately captures fault information, and improves the distinction between faults and non-faults, thereby enhancing the sensitivity and reliability of this protection algorithm.

[0106] Taking phase A as the target phase as an example, the total energy of the M3C low-frequency side multi-band... and the total energy of multi-frequency bands on the wind power side The following formula is used to calculate:

[0107]

[0108] In the formula, w j For the first j The weighting coefficients for each layer frequency band are preset.

[0109] S37: Calculate the differential energy ratio based on the total energy of the M3C low-frequency side multi-band and the total energy of the wind power side multi-band;

[0110] In one embodiment, by employing a ratio-based criterion, the protection action criterion is normalized to the wind farm's handling level. When the wind farm's output changes, the absolute value of the energy difference between the two sides after the fault also changes. In contrast, the ratio-based protection action criterion can adapt to fluctuations in wind farm output, reducing the difficulty of setting the protection device. It can adapt to changes in wind farm output, and there is no need to reset the action threshold after changes in wind farm output.

[0111] In one embodiment, taking phase A as an example, the differential energy ratio The following formula is used to calculate:

[0112]

[0113] S38: Based on the preset action threshold, the differential energy ratio is compared with the action threshold, and the phase is determined to be faulty based on the comparison result.

[0114] In one embodiment, when the differential energy ratio is greater than or equal to the action threshold, it is determined that the fault occurs in the phase within the zone, and the phase protection is activated; when the differential energy ratio is less than the action threshold, it is determined that the fault occurs outside the zone or that the phase is a non-faulty phase, and the phase protection is not activated.

[0115] In one embodiment, to eliminate the effects of high-frequency noise, the differential energy ratio is... As the value at the end of the power time window, the method further includes: using a length of The differential energy ratio is averaged over a time window to obtain the mean differential energy ratio. The average of the differential energy ratio With the action threshold The comparison is performed, and the result is used to determine whether the phase has failed.

[0116] In one embodiment, the differential energy ratio is average. The value is obtained by calculation using the following formula:

[0117]

[0118] In one embodiment, the method further includes: when the average of multiple consecutive differential energy ratios Greater than the action threshold At that time, it was determined that a fault had occurred in the designated area or phase.

[0119] As a specific example:

[0120] A simulation model based on the PSCAD / EMTDC platform is shown in the schematic diagram of the topology of offshore wind power via a flexible low-frequency transmission system, as illustrated below. Figure 3 As shown, the offshore wind farm is connected to the wind farm-side transformer via a 35kV collection line. The wind farm capacity is 600MW, and the fault time is 1.5s. The signal sampling rate is 10kHz, the number of sampling periods N=100 within the power time window, the number of sampling periods M=5 within the differential energy ratio sliding time window, and the four frequency bands of wavelet decomposition include 2500-5000Hz, 1250-2500Hz, 625-1250Hz, and 312-625Hz, with weighting coefficients of 0.15, 0.35, 0.35, and 0.15 respectively. The action threshold... This application provides the simulation calculation results and protection operation status of a) zone (F1) single-phase ground fault. Figure 6 , Figure 7 , Figure 8 As shown, the simulation calculation results and protection operation status for the two-phase short-circuit fault (F1) in zone b) are as follows. Figure 9 , Figure 10 , Figure 11 As shown, the simulation calculation results and protection operation status for the two-phase ground fault (F1) in zone c) are as follows. Figure 12 , Figure 13 , Figure 14 As shown, the simulation calculation results and protection operation status for a single-phase ground fault outside zone d (F2) are as follows. Figure 15 , Figure 16 , Figure 17As shown, the simulation results and protection operation status show that when there is a fault within the zone, the differential energy ratio of the faulty phase is greater than the threshold, and the protection can operate normally. When the differential energy ratio of the non-faulty phase is less than the threshold, the protection reliably does not operate. When there is a fault outside the zone, the differential energy ratio of all three phases is less than the threshold, and the protection reliably does not operate. This solves the problems of false operation, failure to operate, and slow operation speed.

[0121] As can be seen, in the above scheme, this application utilizes wavelet transform technology to extract multi-band transient energy information of the power signals at both ends of the line, calculates the composite energy at both ends using preset frequency band weighting coefficients, and then constructs a protection action criterion based on the ratio of differential energy to braking energy. By comprehensively utilizing the transient energy information of each frequency band, fast and reliable protection action is achieved. Since there is no need to construct phasors, fault determination can be completed during the fault transient stage, improving the speed and reliability of the protection.

[0122] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0123] In one embodiment, a longitudinal protection device for flexible low-frequency transmission lines is provided, which corresponds one-to-one with the longitudinal protection method for flexible low-frequency transmission lines described in the above embodiments. For example... Figure 18 As shown, the flexible low-frequency transmission line longitudinal protection device includes an acquisition module 101, a first judgment module 102, and a second judgment module 103. Detailed descriptions of each functional module are as follows:

[0124] The acquisition module 101 is used to acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the M3C low-frequency side and the three-phase voltage and current on the wind power side.

[0125] The first judgment module 102 is used to determine whether to initiate fault judgment based on the three-phase voltage of the low-frequency side of the M3C and a pre-set start-up criterion model.

[0126] The second judgment module 103 is used to determine whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model when a fault judgment is determined, and to trigger a protection action when a fault is determined.

[0127] Specifically, the first judgment module 102 is also used to calculate the d-axis voltage and q-axis voltage of the low-frequency side of the M3C based on the three-phase voltage of the low-frequency side of the M3C.

[0128] Based on the d-axis voltage and q-axis voltage of the M3C low-frequency side in two adjacent sampling periods, calculate the difference of the d-axis voltage with respect to time and the difference of the q-axis voltage with respect to time.

[0129] Based on the difference between the d-axis voltage and time and a preset first threshold value, and the difference between the q-axis voltage and time and a preset second threshold value, determine whether to initiate fault detection.

[0130] Specifically, the first judgment module 102 is also used to determine to start fault judgment when the difference between the d-axis voltage and time is greater than the first threshold value and the difference between the q-axis voltage and time is greater than the second threshold value.

[0131] Specifically, the second judgment module 103 is also used to obtain the voltage and current of the target phases at both ends of the flexible low-frequency transmission line, including the voltage and current of the target phase on the M3C low-frequency side and the voltage and current of the target phase on the wind power side.

[0132] The instantaneous power of the target phase on the low-frequency side of M3C is calculated based on the target phase voltage and current on the low-frequency side of M3C, and the instantaneous power of the target phase on the wind power side is calculated based on the target phase voltage and current on the wind power side.

[0133] Based on the pre-set power time window, the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side corresponding to the power time window are obtained;

[0134] Wavelet decomposition is performed on the power signals in the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side to obtain the multi-band transient energy information of the target phase on the low-frequency side of M3C and the multi-band transient energy information of the target phase on the wind power side.

[0135] The energy of each frequency band on the low-frequency side of M3C is calculated based on the multi-frequency band transient energy information of the target phase on the low-frequency side of M3C, and the energy of each frequency band on the wind power side is calculated based on the multi-frequency band transient energy information of the target phase on the wind power side.

[0136] Calculate the total energy of the M3C low-frequency side multi-band based on the energy of each frequency band on the M3C low-frequency side, and calculate the total energy of the wind power side multi-band based on the energy of each frequency band on the wind power side.

[0137] Calculate the differential energy ratio based on the total energy of the M3C low-frequency side multi-band and the total energy of the wind power side multi-band.

[0138] Based on a pre-set action threshold, the differential energy ratio is compared with the action threshold, and the result of the comparison determines whether a fault has occurred in that phase.

[0139] Specifically, the second judgment module 103 is also used to calculate the total energy of the M3C low-frequency side multi-band based on the preset weighting coefficients of each frequency band and the energy of each frequency band on the low-frequency side of the M3C.

[0140] The total energy of the wind power side across multiple frequency bands is calculated based on the pre-set weighting coefficients for each frequency band and the energy of each frequency band on the wind power side.

[0141] Specifically, the second judgment module 103 is also used to perform a moving average on the differential energy ratio to obtain the average value of the differential energy ratio;

[0142] The average differential energy ratio is compared with the action threshold, and the failure of the phase is determined based on the comparison result.

[0143] Specifically, the second judgment module 103 is also used to determine that a phase has failed when the average value of multiple consecutive differential energy ratios is greater than the action threshold.

[0144] This invention provides a flexible low-frequency transmission line longitudinal protection device. First, a preliminary ranking result of candidate questions is obtained through semantic matching. Then, a scheme based on entity alignment to optimize the question answering engine is proposed. Through entity alignment, the ranking result of candidate questions is ranked again, so that more matching candidate questions are selected. This can effectively avoid the generalization ability defects of the model, greatly improve the effect of entity matching, and improve the effect of the question answering engine.

[0145] Specific limitations regarding the longitudinal protection device for flexible low-frequency transmission lines can be found in the above description of the longitudinal protection method for flexible low-frequency transmission lines, and will not be repeated here. Each module in the aforementioned longitudinal protection device for flexible low-frequency transmission lines can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the corresponding operations of each module.

[0146] In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 19 As shown, the computer device includes a processor, memory, network interface, and database connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile and / or volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The network interface is used for communication with external devices via a network connection. When the computer program is executed by the processor, it implements the functions or steps of a flexible low-frequency transmission line longitudinal protection method on the server side.

[0147] In one embodiment, a computer device is provided, which may be a device terminal, and its internal structure diagram may be as follows: Figure 20 As shown, the computer device includes a processor, memory, network interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The network interface is used to communicate with an external server via a network connection. When the computer program is executed by the processor, it implements the functions or steps of a flexible low-frequency transmission line longitudinal protection method at the device end.

[0148] In one embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to perform the following steps:

[0149] Acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of the M3C and the three-phase voltage and current on the wind power side;

[0150] Based on the three-phase voltage of the low-frequency side of the M3C, and based on the pre-set start-up criterion model, it is determined whether to start the fault judgment.

[0151] When a fault is detected, the system determines whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model. If a fault is detected, the system will trigger the protection action.

[0152] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0153] Acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of the M3C and the three-phase voltage and current on the wind power side;

[0154] Based on the three-phase voltage of the low-frequency side of the M3C, and based on the pre-set start-up criterion model, it is determined whether to start the fault judgment.

[0155] When a fault is detected, the system determines whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model. If a fault is detected, the system will trigger the protection action.

[0156] It should be noted that the functions or steps that can be implemented by the computer-readable storage medium or computer device described above can be referred to the relevant descriptions on the server side and device side in the foregoing method embodiments. To avoid repetition, they will not be described one by one here.

[0157] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0158] 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 used as 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.

[0159] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A longitudinal protection method for flexible low-frequency transmission lines, characterized in that, include: Acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of the M3C and the three-phase voltage and current on the wind power side; Based on the three-phase voltage of the low-frequency side of the M3C, and based on the pre-set start-up criterion model, it is determined whether to start the fault judgment. When a fault is detected, the system determines whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model. The system then triggers protection actions when a fault is detected. Based on the three-phase voltage on the low-frequency side of the M3C, and using a pre-set start-up criterion model, a fault judgment is determined to initiate, including: Calculate the d-axis voltage and q-axis voltage of the M3C low-frequency side based on the three-phase voltage of the M3C low-frequency side. Based on the d-axis voltage and q-axis voltage of the M3C low-frequency side in two adjacent sampling periods, calculate the difference of the d-axis voltage with respect to time and the difference of the q-axis voltage with respect to time. Based on the difference between the d-axis voltage and time and the preset first threshold value, and the difference between the q-axis voltage and time and the preset second threshold value, determine whether to initiate fault detection; When determining whether a fault has occurred, based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set multi-frequency band composite energy model for faults, it is determined whether a fault has occurred in that phase, including: Obtain the voltage and current of the target phases at both ends of the flexible low-frequency transmission line, including the target phase voltage and current on the M3C low-frequency side and the target phase voltage and current on the wind power side; The instantaneous power of the target phase on the low-frequency side of M3C is calculated based on the target phase voltage and current on the low-frequency side of M3C, and the instantaneous power of the target phase on the wind power side is calculated based on the target phase voltage and current on the wind power side. Based on the pre-set power time window, the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side corresponding to the power time window are obtained; Wavelet decomposition is performed on the power signals in the instantaneous power set of the target phase on the low-frequency side of M3C and the instantaneous power set of the target phase on the wind power side to obtain the multi-band transient energy information of the target phase on the low-frequency side of M3C and the multi-band transient energy information of the target phase on the wind power side. The energy of each frequency band on the low-frequency side of M3C is calculated based on the multi-frequency band transient energy information of the target phase on the low-frequency side of M3C, and the energy of each frequency band on the wind power side is calculated based on the multi-frequency band transient energy information of the target phase on the wind power side. Calculate the total energy of the M3C low-frequency side multi-band based on the energy of each frequency band on the M3C low-frequency side, and calculate the total energy of the wind power side multi-band based on the energy of each frequency band on the wind power side. Calculate the differential energy ratio based on the total energy of the M3C low-frequency side multi-band and the total energy of the wind power side multi-band. Based on a pre-set action threshold, the differential energy ratio is compared with the action threshold, and the result of the comparison determines whether a fault has occurred in that phase.

2. The method according to claim 1, characterized in that, Based on the difference between the d-axis voltage and time and a preset first threshold value, and the difference between the q-axis voltage and time and a preset second threshold value, determine whether to initiate fault detection, including: When the difference between the d-axis voltage and time is greater than the first threshold value and the difference between the q-axis voltage and time is greater than the second threshold value, a startup fault judgment is determined.

3. The method according to claim 1, characterized in that, The total energy of the M3C low-frequency side multi-band is calculated based on the energy of each frequency band on the M3C low-frequency side, and the total energy of the wind power side multi-band is calculated based on the energy of each frequency band on the wind power side, including: The total energy of the M3C low-frequency side multi-band is calculated based on the pre-set weighting coefficients of each frequency band and the energy of each frequency band on the low-frequency side of the M3C. The total energy of the wind power side across multiple frequency bands is calculated based on the pre-set weighting coefficients for each frequency band and the energy of each frequency band on the wind power side.

4. The method according to claim 1, characterized in that, The method further includes: The differential energy ratio is averaged by performing a moving average. The average differential energy ratio is compared with the action threshold, and the failure of the phase is determined based on the comparison result.

5. The method according to claim 1, characterized in that, The method further includes: When the average value of multiple consecutive differential energy ratios is greater than the action threshold, it is determined that a phase has failed.

6. A flexible low-frequency transmission line longitudinal protection device, characterized in that, The apparatus comprising, using the method as described in any one of claims 1 to 5, includes: The acquisition module is used to acquire the three-phase voltage and current at both ends of the flexible low-frequency transmission line, including the three-phase voltage and current on the low-frequency side of the M3C and the three-phase voltage and current on the wind power side. The first judgment module is used to determine whether to initiate fault judgment based on the three-phase voltage of the low-frequency side of the M3C and a pre-set start-up criterion model. The second judgment module is used to determine whether a fault has occurred in a phase based on the voltage and current of each phase at both ends of the flexible low-frequency transmission line and a pre-set fault multi-frequency band composite energy model when a fault judgment is determined, and to trigger protection action when a fault is determined.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the longitudinal protection method for flexible low-frequency transmission lines as described in any one of claims 1 to 5.

8. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the longitudinal protection method for flexible low-frequency transmission lines as described in any one of claims 1 to 5.

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