Wind power low-frequency power transmission line time domain model identification pilot protection method and system

Abstract

The invention discloses a wind power low-frequency power transmission line time domain model identification pilot protection method and system, and the method comprises the steps: collecting the voltage and current of an offshore wind power low-frequency power transmission line, specifically, collecting the A, B and C three-phase voltage and current data of a home terminal and the three-phase current data of an opposite terminal, carrying out the phase-mode conversion of the collected voltage, and carrying out the phase-mode conversion of the collected voltage; the phase-mode transformation matrix can adopt a Clark transformation matrix; when a set condition is met, protection is started; for the collected current data, eliminating the current flowing into the shunt reactor, and subtracting the current of the shunt reactor from the measured current to obtain an actual line differential current; calculating opposite-end voltage current by using the local-end voltage current; determining a first derivative of the differential current variable quantity and a second derivative of the differential voltage variable quantity to obtain a correlation coefficient of the differential current voltage; and comparing the calculated differential current and voltage correlation coefficient with a setting value, and when a fault phase line discrimination condition is satisfied, determining that a corresponding phase has a fault.

Description

Background Art

[0002] Offshore wind resources are abundant, and it is estimated that the global potential for offshore wind power technology development exceeds 71,000GW. Among them, the offshore wind power transmission scheme via low frequency has lower complexity and cost of offshore platform equipment than the flexible direct current transmission scheme; compared with the industrial frequency transmission scheme, it can be transmitted over a longer distance; and has advantages in offshore wind power transmission of 80 to 200 km. As a typical new power system, the offshore wind power low-frequency transmission system has been widely studied and applied. As a two-terminal power electronic power system, its fault response characteristics are very different from those of the traditional synchronous machine system, and the line model is different from the conventional new energy transmission system. Traditional differential protection and model identification protection for onshore wind power lines are not applicable. Therefore, it is of great significance to study new protection principles for offshore wind power low-frequency transmission systems. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method and system for time-domain model identification and longitudinal protection of wind power low-frequency transmission lines in view of the deficiencies in the above-mentioned prior art. The method and system utilize a shunt reactor current compensation algorithm and combine it with the Bergeron model formula to propose a protection principle applicable to offshore wind power low-frequency transmission lines that does not require a terminal voltage, so as to solve the technical problem that the time-domain model identification and longitudinal protection for conventional overhead lines has reduced adaptability to offshore wind power low-frequency transmission systems with low frequencies, unique cable line structures and dominated by power electronic power sources.

[0004] The present invention adopts the following technical solutions:

[0005] A method for time domain model identification and pilot protection of a wind power low-frequency transmission line comprises the following steps:

[0006] Collect the voltage and current of the offshore wind power low-frequency transmission line, specifically collect the three-phase voltage and current data of A, B, and C at the local end and the three-phase current data at the opposite end, and perform phase-mode transformation on the collected voltage. The phase-mode transformation matrix can use the Clark transformation matrix;

[0007] The protection starts when the set conditions are met;

[0008] For the collected current data, the current flowing into the shunt reactor is eliminated, and the actual line differential current is obtained by subtracting the shunt reactor current from the measured current;

[0009] Calculate the voltage and current of the opposite end by using the voltage and current of the local end; determine the first-order derivative of the differential current change and the second-order derivative of the differential voltage change, and obtain the correlation coefficient of the differential current and voltage;

[0010] The calculated differential current-voltage correlation coefficient is compared with the set value, and when the fault phase line discrimination condition is met, it is determined that the corresponding phase has a fault.

[0011] Preferably, the setting conditions are specifically:

[0012]

[0013] Among them, u α 、u β To protect the measured voltage, the 1-mode and 2-mode voltages are transformed by Clark; u set To protect the startup threshold.

[0014] Preferably, the actual line differential current i cdφ The calculation is as follows:

[0015]

[0016] Among them, i cdφt is the measured φ phase differential current, u cdφ is the measured φ phase differential voltage, k l is the compensation coefficient, k l =-3L n / (L+3L n ), L is the inductance of the shunt reactor, L n is the inductance of the small neutral reactor, u cd0 is the zero-sequence differential voltage.

[0017] Preferably, the shunt reactor current i mAl ,i mBl ,i mCl With phase voltage u mA ,u mB ,u mC The calculation is as follows:

[0018]

[0019] Among them, L n is the inductance of the small neutral point reactor.

[0020] Preferably, the voltage and current of the opposite end are calculated using the voltage and current of the local end; the first-order derivative of the differential current change and the second-order derivative of the differential voltage change are determined, and the correlation coefficient of the differential current and voltage is obtained as follows:

[0021] The calculation of the opposite terminal voltage and current is specifically based on the Berelon model;

[0022] Calculate the first-order derivative of the differential current change and the second-order derivative of the differential voltage change;

[0023] Based on the measured data of the first-order derivative of the φ phase differential current and the second-order derivative of the differential voltage.

[0024] Preferably, the first-order derivative of the differential current variation and the second-order derivative of the differential voltage variation are calculated as follows:

[0025]

[0026] Among them, Δi mφ is the change in current flowing into the line at the φ phase at the m end; Δi nφt Δu is the current change measured by the n-terminal φ phase; mφ is the voltage change of the phase φ at the m end; Δu nφcal , Δu n0cal is the calculated change of the φ-phase voltage and zero-sequence voltage at the n-terminal.

[0027] Preferably, the correlation coefficient of the differential current and voltage is calculated as follows:

[0028]

[0029] ρ φ =ρ(Δi c ' dφ ,Δu c ″ dφ )

[0030] Among them, ρ(x,y) is the correlation coefficient, N E is the end point of the data window, N S is the starting point of the data window, x(k) is the kth value of the discrete data sequence x, y(k) is the kth value of the discrete data sequence y, ρ φ is the phase correlation coefficient, Δi c ' dφ is the first-order derivative of the φ phase differential current change, Δu c ″ dφ is the second-order derivative of the φ phase differential voltage change, and ρ is the function for calculating the correlation coefficient.

[0031] Preferably, the fault phase line determination conditions are as follows:

[0032] ρ φ < set

[0033] Among them, ρ set is the threshold, ρ φ It is the measured data of the second derivative of the differential voltage.

[0034] Preferably, when no fault occurs in the phase, if the timing is less than the upper limit of the cycle calculation time, it is delayed to the next sampling moment and returns to re-acquire the actual line differential current; if the timing is greater than the upper limit of the cycle calculation time, it is judged as an out-of-zone fault and the phase protection is reset; the upper limit of the cycle calculation time is 20ms.

[0035] In a second aspect, an embodiment of the present invention provides a time domain model identification and longitudinal protection system for a wind power low-frequency transmission line, comprising:

[0036] The acquisition module collects the voltage and current of the offshore wind power low-frequency transmission line, specifically, respectively collects the three-phase voltage and current data of the local end A, B, and C and the three-phase current data of the opposite end, and performs phase-mode transformation on the collected voltage. The phase-mode transformation matrix can adopt the Clark transformation matrix;

[0037] Judgment module, protection starts when the set conditions are met;

[0038] The processing module eliminates the current flowing into the shunt reactor from the collected current data, and obtains the actual line differential current by subtracting the shunt reactor current from the measured current;

[0039] The calculation module calculates the voltage and current of the opposite end by using the voltage and current of the local end; determines the first-order derivative of the differential current change and the second-order derivative of the differential voltage change, and obtains the correlation coefficient of the differential current and voltage;

[0040] The output module compares the calculated differential current-voltage correlation coefficient with the set value, and when the fault phase line discrimination condition is met, it is determined that the corresponding phase is faulty.

[0041] In a third aspect, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for identifying longitudinal protection of a wind power low-frequency transmission line using a time domain model when executing the computer program.

[0042] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, including a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for identifying longitudinal protection of a wind power low-frequency transmission line using a time domain model.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects:

[0044] A time domain model identification and longitudinal protection method for wind power low-frequency transmission lines uses a shunt reactor current compensation algorithm and combines the Bergeron model formula to propose a protection principle that does not require the opposite terminal voltage and is applicable to offshore wind power low-frequency transmission lines. The correlation coefficient is calculated to measure the degree to which the differential voltage and differential current conform to the capacitor model to determine whether a fault has occurred and the fault interval. The protection principle uses a time domain model and algorithm, does not require the extraction of phasors, and is not affected by the reduction of system frequency. The protection principle is based on the identification of the line model, avoiding the impact of changes in power supply fault characteristics, and can be applied to different types of power supply systems.

[0045] Furthermore, the instantaneous voltage is used as the protection start criterion, which takes advantage of the fact that offshore wind farms are weak sources and have difficulty supporting voltage in the event of a system short circuit fault, and can quickly start the protection.

[0046] Furthermore, the shunt reactor current is eliminated from the measured current, and the resulting current is the actual differential current flowing through the line, which is close to the true value, and the protection principle is more reliable.

[0047] Furthermore, the calculation method of the correlation coefficient is very simple and fast. It does not need to extract phase quantities, and real-time calculation is realized. The voltage and current at the other end are used to calculate the voltage at the other end. There is no need to communicate to transmit voltage information, which reduces the transmission data of communication. The protection has high sensitivity and speed.

[0048] Furthermore, by comparing whether the correlation coefficient is less than the threshold, it is determined whether an intra-zone fault has occurred. The correlation coefficient reflects the degree to which the differential voltage and differential current conform to the capacitor model. Changes in line parameters will not affect the setting value, which facilitates protection setting.

[0049] Furthermore, the start-up time of the start-up element is about 1 to 2 ms. At this time, the time window contains pre-fault data, and a fault will occur. After a period of time, the correlation coefficient drops below the set value, and the cyclic calculation is performed for a period of time to avoid the false operation of the protection during the start-up process. The upper limit of the cyclic calculation time is set because the protection mainly uses the high-frequency transient component of the initial fault. After a period of time, the high-frequency transient component of the initial fault is completely attenuated, and only the remaining fundamental frequency component can be used. The anti-noise ability at this stage is poor, and there is a risk of false operation of out-of-zone faults. 20ms is set as the upper limit of the time. It can prevent false operation of the protection and ensure the selectivity of the protection principle.

[0050] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0051] In summary, the present invention can realize the protection of offshore wind power low-frequency transmission lines, takes into account the compensation of shunt reactors, and does not require opposite-end voltage information, thereby solving the adaptability problem of traditional protection in offshore low-frequency transmission lines. The protection action is fast, reliable and sensitive.

[0052] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings to be used in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0054] Figure 1 This is the flow chart of time domain model identification and longitudinal protection of offshore wind power low-frequency transmission line;

[0055] Figure 2 This is the topology diagram of the offshore wind power low-frequency transmission system;

[0056] Figure 3 The simulation results of protection criteria are shown in Figure 1, where (a) is the fault criterion within the zone and (b) is the fault criterion outside the zone.

[0057] Figure 4 The correlation coefficient diagrams of different fault moments, where (a) is the fault at the moment of phase A crossing zero, (b) is the fault at the moment of phase B crossing zero, and (c) is the fault at the moment of phase C crossing zero;

[0058] Figure 5 A schematic diagram of a computer device provided by an embodiment of the present invention;

[0059] Figure 6 The present invention is a block diagram of an electronic device provided according to an embodiment. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] In the description of the present invention, it should be understood that the terms “include” and “comprises” indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0062] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0063] It should be further understood that the term "and / or" used in the present specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects are in an "or" relationship.

[0064] It should be understood that, although the terms first, second, third, etc. may be used to describe preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish preset ranges from each other. 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.

[0065] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0066] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0067] The present invention provides a method for identifying longitudinal protection of wind power low-frequency transmission lines by using a time domain model, which measures and calculates instantaneous voltage and current in real time, compares the instantaneous voltage with the starting value, and starts timing when the starting condition is met. The differential current and voltage correlation coefficient is calculated based on the sampling data at this moment; if the correlation coefficient of a phase is less than the threshold, it is judged that a fault occurs in the phase line, and the protection of the phase is activated; if the correlation coefficient of a phase is greater than the threshold, and the timing is less than the upper limit of the cycle calculation time, it is delayed to the next sampling moment, and the correlation coefficient is recalculated to determine the fault situation; if the timing is greater than the upper limit of the cycle calculation time, it is judged to be an out-of-zone fault, and the protection of the phase is reset.

[0068] See also Figure 2 The present invention provides a method for time domain model identification and longitudinal protection of a wind power low-frequency transmission line, comprising the following steps:

[0069] S1. Collect the voltage and current of the offshore wind power low-frequency transmission line, specifically collect the three-phase voltage and current data of A, B, and C at the local end and the three-phase current data at the opposite end, and perform phase-mode transformation on the collected voltage. The phase-mode transformation matrix can adopt the Clark transformation matrix;

[0070] S2. Determine whether the protection is activated by formula (1). If formula (1) is satisfied, the protection is activated;

[0071]

[0072] Among them, u α 、u β To protect the measured voltage, the 1-mode and 2-mode voltages are transformed by Clark; u set For the protection start threshold, when the instantaneous voltage is less than the threshold, the protection starts, which is generally set to 90% of the rated phase voltage peak.

[0073] S3. Consider the influence of the shunt reactor. Specifically, for the collected current data, eliminate the current flowing into the shunt reactor. The calculation formula of the shunt reactor current and the phase voltage is (2). Subtract the shunt reactor current from the measured current to obtain the actual line differential current calculation formula (3);

[0074]

[0075] S4. Calculate the opposite terminal voltage and current, the first-order derivative of the differential current change, and the second-order derivative of the differential voltage change using the local terminal voltage and current;

[0076] S401, calculating the opposite terminal voltage and current is specifically based on the Berelon model, and the calculation method is as shown in formula (4);

[0077]

[0078] in, is the wave impedance; is the wave speed; r, l, c are the resistance, inductance, and capacitance per unit length of the line; d is the line length; parameter k1 is d / (vT S ) round down, k2=k1+1, k3=d / (vT S )-k1, k4=1-k3; u n is the calculated opposite-end voltage, u m 、i m is the voltage and current at this end.

[0079] S402, calculating the first-order derivative of the differential current change and the second-order derivative of the differential voltage change, specifically for the offshore wind power low-frequency transmission line, the calculation method is as shown in formula (5);

[0080]

[0081] Among them, Δi mφ is the change in current flowing into the line at the φ phase at the m end; Δi nφt Δu is the current change measured by the n-terminal φ phase; mφ is the voltage change of the phase φ at the m end; Δu nφcal , Δu n0cal is the calculated change of the φ-phase voltage and zero-sequence voltage at the n-terminal.

[0082] S403, calculating the correlation coefficient of the differential current and voltage, specifically based on the measurement data of the first-order derivative of the φ-phase differential current and the second-order derivative of the differential voltage, the calculation method is as shown in formula (6) (7);

[0083]

[0084] ρ φ =ρ(Δi′ cdφ ,Δu″ cdφ ) (7)

[0085] S5. Compare the calculated differential current-voltage correlation coefficient with the set value. The specific fault phase line discrimination formula is shown in formula (8). When formula (8) is satisfied, it can be considered that the phase has a fault, otherwise proceed to step S6;

[0086] ρ φ =ρ(Δi′ cdφ ,Δu″ cdφ )<ρ set (8)

[0087] Among them, ρ set is the threshold. When the correlation coefficient is less than the threshold, the protection action is activated. The threshold is generally set to 0.8.

[0088] S6. If the timing is less than the upper limit of the cycle calculation time, delay until the next sampling time and return to step 3. If the timing is greater than the upper limit of the cycle calculation time, it is judged as an out-of-zone fault and the phase protection is reset. The upper limit of the cycle calculation time is 20ms.

[0089] It will be appreciated by those skilled in the art that various aspects of the present invention may be implemented as systems, methods or program products. Therefore, various aspects of the present invention may be specifically implemented in the following forms, namely: complete hardware implementation, complete software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, which may be collectively referred to herein as "circuits", "modules" or "platforms".

[0090] In another embodiment of the present invention, a wind power low-frequency transmission line time domain model identification and longitudinal protection system is provided. The system can be used to implement the above-mentioned wind power low-frequency transmission line time domain model identification and longitudinal protection method. Specifically, the wind power low-frequency transmission line time domain model identification and longitudinal protection system includes an acquisition module, a judgment module, a processing module, a calculation module and an output module.

[0091] Among them, the acquisition module collects the voltage and current of the offshore wind power low-frequency transmission line, specifically, respectively collects the three-phase voltage and current data of A, B, and C at the local end and the three-phase current data at the opposite end, and performs phase-mode transformation on the collected voltage. The phase-mode transformation matrix can adopt the Clark transformation matrix;

[0092] Judgment module, protection starts when the set conditions are met;

[0093] The processing module eliminates the current flowing into the shunt reactor from the collected current data, and obtains the actual line differential current by subtracting the shunt reactor current from the measured current;

[0094] The calculation module calculates the voltage and current of the opposite end by using the voltage and current of the local end; determines the first-order derivative of the differential current change and the second-order derivative of the differential voltage change, and obtains the correlation coefficient of the differential current and voltage;

[0095] The output module compares the calculated differential current-voltage correlation coefficient with the set value, and when the fault phase line discrimination condition is met, it is determined that the corresponding phase is faulty.

[0096] In another embodiment of the present invention, a terminal device is provided, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the time domain model identification and longitudinal protection method of wind power low-frequency transmission lines, including:

[0097] The voltage and current of the offshore wind power low-frequency transmission line are collected, specifically, the three-phase voltage and current data of A, B, and C at the local end and the three-phase current data at the opposite end are collected respectively, and the collected voltage is subjected to phase-mode transformation. The phase-mode transformation matrix can adopt the Clark transformation matrix; the protection is started when the set conditions are met; for the collected current data, the current flowing into the shunt reactor is eliminated, and the actual line differential current is obtained by subtracting the measured current from the shunt reactor current; the voltage and current of the opposite end are calculated using the voltage and current at the local end; the first-order derivative of the differential current change and the second-order derivative of the differential voltage change are determined to obtain the correlation coefficient of the differential current and voltage; the calculated differential current and voltage correlation coefficient is compared with the set value, and when the fault phase line discrimination conditions are met, it is determined that the corresponding phase has a fault.

[0098] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and the extended storage medium supported by the terminal device, and can be any tangible medium containing or storing a program, which can be used by an instruction execution system, device or device or used in combination with it. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that more specific examples (non-exhaustive list) of the computer-readable storage medium here include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0099] Computer readable storage media also include data signals propagated in baseband or as part of a carrier wave, which carry readable program codes. Such propagated data signals can take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. The readable storage medium can also be any readable medium other than a readable storage medium, which can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, device, or device. The program code contained on the readable storage medium can be transmitted using any appropriate medium, including but not limited to wireless, wired, optical cable, RF, etc., or any suitable combination of the above.

[0100] Program code for performing the operations of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, etc., and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user device, as a separate software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server. In the case of a remote computing device, the remote computing device may be connected to the user computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., through the Internet using an Internet service provider).

[0101] One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the corresponding steps of the method for identifying a time domain model of a wind power low-frequency transmission line with longitudinal protection in the above embodiment; one or more instructions in the computer-readable storage medium may be loaded and executed by a processor as follows:

[0102] The voltage and current of the offshore wind power low-frequency transmission line are collected, specifically, the three-phase voltage and current data of A, B, and C at the local end and the three-phase current data at the opposite end are collected respectively, and the collected voltage is subjected to phase-mode transformation. The phase-mode transformation matrix can adopt the Clark transformation matrix; the protection is started when the set conditions are met; for the collected current data, the current flowing into the shunt reactor is eliminated, and the actual line differential current is obtained by subtracting the measured current from the shunt reactor current; the voltage and current of the opposite end are calculated using the voltage and current at the local end; the first-order derivative of the differential current change and the second-order derivative of the differential voltage change are determined to obtain the correlation coefficient of the differential current and voltage; the calculated differential current and voltage correlation coefficient is compared with the set value, and when the fault phase line discrimination conditions are met, it is determined that the corresponding phase has a fault.

[0103] See also Figure 5 , the terminal device is a computer device, and the computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When the computer program 63 is executed by the processor 61, the method for identifying the longitudinal protection of the wind power low-frequency transmission line in the time domain model in the embodiment is implemented. To avoid repetition, it is not described one by one here. Alternatively, when the computer program 63 is executed by the processor 61, the functions of each model / unit in the longitudinal protection system for identifying the time domain model of the wind power low-frequency transmission line in the embodiment are implemented. To avoid repetition, it is not described one by one here.

[0104] The computer device 60 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will appreciate that Figure 5 This is only an example of the computer device 60 and does not constitute a limitation of the computer device 60. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0105] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, central processing units, graphics processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, data processing logic based on quantum computing, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may be any conventional processor, etc.

[0106] The memory 62 may 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 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc., equipped on the computer device 60.

[0107] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.

[0108] Any reference to memory, database or other media used in the embodiments provided in the present application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0109] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0110] See also Figure 6 The terminal device 600 is an electronic device, and the electronic device is in the form of a general 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 the storage unit 620 and the processing unit 610), a display unit 640, etc.

[0111] The storage unit stores program codes, which can be executed by the processing unit 610, so that the processing unit 610 performs the steps according to various exemplary embodiments of the present invention described in the above method section of this specification. For example, the processing unit 610 can perform the following steps: Figure 1 Follow the steps shown in .

[0112] The storage unit 620 may include a readable medium in the form of a volatile storage unit, such as a random access memory unit (RAM) 6201 and / or a cache memory unit 6202 , and may further include a read-only memory unit (ROM) 6203 .

[0113] The storage unit 620 may also include a program / utility 6204 having a set (at least one) of program modules 6205, such program modules 6205 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0114] Bus 630 may represent one or more of several types of bus structures, including a memory unit bus or memory unit controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.

[0115] The electronic device 600 may also communicate with one or more external devices 700 (e.g., keyboards, pointing devices, Bluetooth devices, etc.), may also communicate with one or more devices that enable a user to interact with the electronic device 600, and / or communicate with any device that enables the electronic device 600 to communicate with one or more other computing devices (e.g., routers, modems, etc.). Such communication may be performed via an input / output (I / O) interface 650. Furthermore, the electronic device 600 may also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter 660. The network adapter 660 may communicate with other modules of the electronic device 600 via a bus 630. It should be understood that, although not shown in the figure, other hardware and / or software modules may be used in conjunction with the 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, etc.

[0116] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0117] Experimental verification:

[0118] In order to verify the correctness of the proposed protection scheme, a simulation model of the offshore wind power low-frequency transmission system is built in PSCAD. Figure 2 , the line model adopts the PSCAD frequency-variable parameter model, and the total length of the line is 100km. In particular, the parameters of the model at 50 / 3Hz are approximately: positive sequence resistance 0.029Ω / km, zero sequence resistance 0.1536Ω / km, positive sequence inductance 0.451mH / km, zero sequence inductance 0.689mH / km, positive sequence and zero sequence capacitance are both 0.125μF / km, and the interpolation method Bergeron model voltage and current calculation formula uses the above parameters. The size of the parallel reactor is 15H. Since the positive sequence and zero sequence capacitance are equal, a small neutral point reactor can be configured. The protection sampling frequency is 4kHz, the time window length used for correlation coefficient calculation is 10ms, the integral time window length is 5ms, the data window length can be obtained by dividing the time window length by the sampling interval, and the upper limit of the cycle calculation time is 20ms. The wind farm adopts conventional dynamic reactive support strategy and negative sequence current suppression strategy.

[0119] In order to verify the correctness of the shunt reactor compensation algorithm and the scheme of replacing the measured value with the calculated value of the opposite terminal voltage, the sliding window calculation protection criterion is used. The results are as follows: Figure 3 Considering the extreme cases of faults within the area and faults outside the area, a BC phase-to-phase fault with a transition resistance of 300Ω is set at the midpoint of the line, and a three-phase metallic fault is set on the back side of the protection at the wind farm side (end m), and the fault occurs at 1s.

[0120] In order to verify the ability of the protection criterion to withstand transition resistance, and the accuracy and speed of distinguishing the fault phase and fault interval, two groups of simulation experiments were carried out to test the protection performance.

[0121] The first group of simulation experiments set different types of metallic faults on the back side of the m-terminal, the front side of the m-terminal, the midpoint of the line, the front side of the n-terminal, and the back side of the n-terminal to test the ability of the protection to judge the faults inside and outside the zone and the fault phase. Table 1 shows the calculation results of the criterion correlation coefficient of the protection start-up time under this group of experimental conditions, as well as the protection start-up time and protection action time (i.e., the time when the correlation coefficient drops below 0.8).

[0122] Table 1 Experimental results of simulation experiment group 1

[0123]

[0124]

[0125] Note: ×: protection does not work

[0126] From the experimental results, it can be seen that when a fault occurs outside the zone, the protection will reliably not operate. When a fault occurs within the zone, the fault phase protection will reliably operate and the non-fault phase protection will reliably not operate. The protection operation time is within 10ms.

[0127] The second group of simulation experiments set up faults of different types and transition resistances at the midpoint of the line to test the protection's ability to withstand transition resistance. The calculation results are shown in Table 2.

[0128] Table 2 Experimental results of simulation experiment group 2

[0129]

[0130]

[0131] Note: ×: protection does not work

[0132] The experimental results show that the protection can still work correctly under 300Ω transition resistance, but the action time may be slower. Even so, the protection action time is within 20ms. Therefore, the protection has high sensitivity and speed.

[0133] In particular, it is found that in some cases, the correlation coefficient calculated at the time of fault phase protection startup is greater than the threshold, and the protection action is judged to be a certain period after the protection is started. This is because, in the case of high-resistance faults or voltage zero-crossing faults, the voltage mutation is very small, the high-frequency transient component is very small, the electrical quantity is mainly based on the fundamental frequency, the fundamental frequency waveform change trend changes very slowly, and the correlation coefficient decreases very slowly. The correlation coefficient calculated at the time of protection startup may be greater than the threshold. Therefore, when designing the protection program, it will be calculated for a certain period of time after startup.

[0134] To demonstrate the impact of the fault timing, a three-phase fault with a 100Ω transition resistor at the midpoint of the line is set at the zero-crossing moment of the A, B, and C phase voltages. Figure 4 shown.

[0135] It can be seen that the correlation coefficient of the phase with zero voltage at the time of fault decreases the slowest, and the protection action is the latest. This also shows that the fast protection action depends on the high-frequency transient component generated by the voltage mutation. When the voltage is zero, the fault will hardly generate high-frequency transient components, and can only rely on the slowly changing fundamental frequency component, so the protection action speed is naturally reduced.

[0136] In summary, the present invention provides a method and system for identifying longitudinal protection of wind power low-frequency transmission lines by using a time domain model, and uses a shunt reactor current compensation algorithm, combined with the Bergeron model formula, to propose a protection principle applicable to offshore wind power low-frequency transmission lines that does not require a terminal voltage. By calculating the correlation coefficient of the differential current and voltage, the line is protected, which solves the adaptability problem of the traditional differential protection principle brought about by the offshore low-frequency transmission line model, and the protection action is fast, reliable and sensitive.

[0137] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by 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 embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0138] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0139] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the present invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0140] In the embodiments provided by the present 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 only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0141] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0142] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0143] If the integrated module / unit is implemented in the form of 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, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0144] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0145] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0146] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0147] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for time domain model identification and pilot protection of wind power low-frequency transmission lines, characterized in that: The following steps are involved: Collect the voltage and current of the offshore wind power low-frequency transmission line, specifically collect the three-phase voltage and current data of A, B, and C at the local end and the three-phase current data at the opposite end, and perform phase-mode transformation on the collected voltage. The phase-mode transformation matrix can use the Clark transformation matrix; The protection starts when the set conditions are met; For the collected current data, the current flowing into the shunt reactor is eliminated, and the actual line differential current is obtained by subtracting the shunt reactor current from the measured current; Calculate the opposite terminal voltage and current using the local terminal voltage and current; Determine the first-order derivative of the differential current change and the second-order derivative of the differential voltage change, and obtain the correlation coefficient of the differential current and voltage; The calculated differential current-voltage correlation coefficient is compared with the set value, and when the fault phase line discrimination condition is met, it is determined that the corresponding phase has a fault.

2. The method for time domain model identification and pilot protection of wind power low-frequency transmission line according to claim 1 is characterized in that: The specific setting conditions are: Among them, u α 、u β To protect the measured voltage, the 1-mode and 2-mode voltages are transformed by Clark; u set To protect the startup threshold.

3. The time domain model identification and pilot protection method for wind power low-frequency transmission line according to claim 1 is characterized in that the actual Line differential current i cdφ The calculation is as follows: Among them, i cdφt is the measured φ phase differential current, u cdφ is the measured φ phase differential voltage, k l is the compensation coefficient, k l =-3L n / (L+3L n ), L is the inductance of the shunt reactor, L n is the inductance of the small neutral point reactor, u cd0 is the zero-sequence differential voltage.

4. The method for time domain model identification and pilot protection of wind power low-frequency transmission lines according to claim 3 is characterized in that: Shunt reactor current i mAl ,i mBl ,i mCl With phase voltage u mA ,u mB ,u mC The calculation is as follows: Among them, L n is the inductance of the small neutral point reactor.

5. The method for time domain model identification and pilot protection of wind power low-frequency transmission line according to claim 1 is characterized in that: The voltage and current of the opposite end are calculated using the voltage and current of the local end; the first-order derivative of the differential current change and the second-order derivative of the differential voltage change are determined, and the correlation coefficient of the differential current and voltage is obtained as follows: The calculation of the opposite terminal voltage and current is specifically based on the Berelon model; Calculate the first-order derivative of the differential current change and the second-order derivative of the differential voltage change; Based on the measured data of the first-order derivative of the φ phase differential current and the second-order derivative of the differential voltage.

6. The method for time domain model identification and pilot protection of wind power low-frequency transmission line according to claim 5 is characterized in that: The first-order derivative of the differential current change and the second-order derivative of the differential voltage change are calculated as follows: Among them, Δi mφ is the change in current flowing into the line at the φ phase at the m end; Δi nφt Δu is the current change measured by the n-terminal φ phase; mφ is the voltage change of the phase φ at the m end; Δu nφcal , Δu n0cal is the calculated change of the φ-phase voltage and zero-sequence voltage at the n-terminal.

7. The method for time domain model identification and pilot protection of wind power low-frequency transmission line according to claim 5 is characterized in that: The correlation coefficient of the differential current and voltage is calculated as follows: r φ =ρ(Δi c ′ dφ ,D c ″ dφ ) Among them, ρ(x,y) is the correlation coefficient, N E is the end point of the data window, N S is the starting point of the data window, x(k) is the kth value of the discrete data sequence x, y(k) is the kth value of the discrete data sequence y, ρ φ is the phase correlation coefficient, Δi c ' dφ is the first-order derivative of the φ phase differential current change, Δu c ″ dφ is the second-order derivative of the φ phase differential voltage change, and ρ is the function for calculating the correlation coefficient.

8. The method for time domain model identification and pilot protection of wind power low-frequency transmission line according to claim 1 is characterized in that: The fault phase line judgment conditions are as follows: r φ <p set Among them, ρ set is the threshold, ρ φ It is the measured data of the second derivative of the differential voltage.

9. The method for time domain model identification and pilot protection of wind power low-frequency transmission lines according to claim 1 is characterized in that: When no fault occurs in this phase, if the timing is less than the upper limit of the cycle calculation time, it will be delayed to the next sampling moment and return to re-acquire the actual line differential current; if the timing is greater than the upper limit of the cycle calculation time, it will be judged as an out-of-zone fault and the phase protection will be reset; the upper limit of the cycle calculation time is 20ms.

10. A wind power low-frequency transmission line time domain model identification pilot protection system, characterized in that: include: The acquisition module collects the voltage and current of the offshore wind power low-frequency transmission line, specifically, respectively collects the three-phase voltage and current data of the local end A, B, and C and the three-phase current data of the opposite end, and performs phase-mode transformation on the collected voltage. The phase-mode transformation matrix can adopt the Clark transformation matrix; Judgment module, protection starts when the set conditions are met; The processing module eliminates the current flowing into the shunt reactor from the collected current data, and obtains the actual line differential current by subtracting the shunt reactor current from the measured current; A calculation module, using the voltage and current of the local terminal to calculate the voltage and current of the opposite terminal; Determine the first-order derivative of the differential current change and the second-order derivative of the differential voltage change, and obtain the correlation coefficient of the differential current and voltage; The output module compares the calculated differential current-voltage correlation coefficient with the set value, and when the fault phase line discrimination condition is met, it is determined that the corresponding phase is faulty.

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