Distance measurement type distance protection method and system for sending-out system of direct-driven wind power plant

Abstract

The invention discloses a distance measurement type distance protection method and system for a direct-driven wind power plant sending-out system, and the method comprises the steps: collecting the voltage and current of a conventional system side of the direct-driven wind power plant sending-out system, specifically, respectively collecting the A, B and C three-phase voltage and current data of the conventional system side, and carrying out the phase-mode transformation and Park transformation of the collected voltage and current, the phase-mode transformation matrix can adopt a Clark transformation matrix; when the protection starting condition is met, protection starting is carried out; performing phase selection according to the fault zero and negative sequence current phase difference and the fault positive and negative sequence current phase difference; determining equivalent impedance in the simplified fault network according to a phase selection result; iteratively solving the fault distance and the transition resistance, and solving the fault distance and the transition resistance value in the fault network according to the voltage and current data of the grid-side system in combination with an opposite-end fan system control equation; and comparing the calculated fault distance with a setting value, and judging whether an internal fault occurs or not.

Description

Background Art

[0002] In 2022, my country's wind power grid-connected installed capacity will increase by 37.63 million kilowatts. By the end of December 2022, the total installed capacity of wind power in the country will exceed 360 million kilowatts. Permanent magnet direct-drive wind turbines without gearboxes have gradually increased their share in wind power due to their high power generation efficiency and good reliability.

[0003] In the context of the booming development of renewable energy today, direct-drive wind farms, as typical representatives of power electronics-intensive power systems, have injected a large amount of clean energy into the power grid with their high efficiency and direct drive characteristics. However, the complex control strategies and highly power electronics characteristics of such systems have led to profound changes in their fault response characteristics compared to traditional synchronous generator-based power systems, which undoubtedly poses a more severe challenge to the protection and control of power systems.

[0004] Traditional distance protection schemes are often based on the classic power system model at the beginning of their design, which simplifies the peer system into an RL model with a resistor (R) and an inductor (L) in series. This model has shown good adaptability and effectiveness when dealing with traditional power grids dominated by synchronous generators. However, its limitations are clearly revealed when facing new power systems such as direct-drive wind farms. Direct-drive wind farms are directly connected to the power grid through power electronic converters. They have fast dynamic response speed and high control flexibility, making it difficult for traditional RL models to accurately describe their fault characteristics, which in turn affects the accuracy and reliability of distance protection. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a distance measurement protection method and system for a direct-driven wind farm transmission system in response to the deficiencies in the above-mentioned prior art. By utilizing the control characteristics of the direct-driven wind turbine and combining it with a fault compound sequence network, a distance measurement protection principle suitable for a direct-driven wind farm transmission system that does not require the opposite-end voltage and current information is proposed. This is used to solve the technical problem that when the single-ended distance protection principle of the traditional synchronous machine system transmission line is applied to the wind turbine system transmission line, the equivalent model of the wind turbine system is different, resulting in low adaptability of the protection principle.

[0006] The present invention adopts the following technical solutions:

[0007] A distance measurement protection method for a direct-drive wind farm transmission system comprises the following steps:

[0008] Collect the voltage and current of the conventional system side of the direct-drive wind farm transmission system, specifically collect the three-phase voltage and current data of A, B, and C on the conventional system side respectively, perform phase mode transformation and Park transformation on the collected voltage and current, and the phase mode transformation matrix can adopt the Clark transformation matrix;

[0009] When the protection start conditions are met, the protection starts;

[0010] Phase selection is performed based on the phase difference between the zero-sequence and negative-sequence currents of the fault and the phase difference between the positive-sequence and negative-sequence currents of the fault;

[0011] Determine the equivalent impedance in the simplified fault network according to the phase selection result;

[0012] Iteratively solve the fault distance and transition resistance. According to the voltage and current data of the grid-side system and the control equation of the opposite wind turbine system, the fault distance and transition resistance values ​​are solved in the fault network.

[0013] Compare the calculated fault distance with the set value to determine whether an in-zone fault has occurred.

[0014] Preferably, the protection start condition is:

[0015]

[0016] Where: 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.

[0017] Preferably, the phase selection is performed according to the phase difference between the zero-sequence current and the negative-sequence current and the phase difference between the positive-sequence current and the negative-sequence current of the fault as follows:

[0018]

[0019] Among them, α is the phase difference of the zero-negative sequence current of the fault, is the fault zero-sequence current, β is the phase difference between the positive and negative sequence currents, is the fault positive sequence current, is the fault negative sequence current.

[0020] Preferably, the equivalent impedance is as follows:

[0021]

[0022] Among them, R f is the transition resistance at the fault point, Z Gk1 , Z Gk2 , Z Gk0 Z sk1 , Z sk2 , Z sk0 They represent the positive and negative zero-sequence impedance of the line from the fault point to the protection installation location, Z sk1 , Z sk2 , Z sk0 Respectively represent the positive and negative zero-sequence impedance of the fault point to the opposite line, Z GT1 , Z GT2 , Z GT0Represent the positive and negative zero-sequence components of the grid-side system impedance, Z sT1 , Z sT2 , Z sT0 They represent the positive and negative zero-sequence components of the wind turbine side system impedance, including the collector line impedance, transformer impedance, etc., Z′ S Represents the total impedance from the fault point to the opposite end system, Z′ G Indicates the total impedance from the fault point to the grid-side system.

[0023] Preferably, the iterative solution of the fault distance and the transition resistance is specifically:

[0024] The chord cutting method is used for iterative solution; the calculated value of the grid-side voltage and current is equal to the measured value to obtain the iterative solution result, and the voltage and current data of the fan system are used. The current data is obtained by the fan system control equation through the fan system voltage. The calculated value of the grid-side voltage and current is obtained according to the fault network. The iterative solution equation group is an equation group containing the opposite terminal voltage, fault distance, and transition resistance. The initial value of the opposite terminal voltage selects the voltage value of the measuring point, and the initial values ​​of the fault distance and transition resistance select 0.5pu and 50Ω.

[0025] Preferably, the chord-cut iterative algorithm is calculated as follows:

[0026]

[0027] Among them, f ij (k) is the iterative equation, f i (k) is the function equation, x j (k) is the k-times iterative solution of the equation, Δx j (k) is the correction value of the solution to the equation, h is the step size, z j is the iteration coefficient, ε1, ε2 are minimum values, x * is an approximate solution to the equation.

[0028] Preferably, the fan system control equation is specifically:

[0029]

[0030] Among them, i d is the d-axis component of the port current, i q is the q-axis component of the port current, P is the active power output in normal state, u d is the d-axis component of the port voltage, I max is the total current limit, K is the reactive current proportional coefficient, is the per unit value of the voltage reference value, is the per unit value of the d-axis component of the port voltage, I N is the rated current, iqlim is the reactive current limit, and It is the upper and lower boundary values ​​of voltage index in the dynamic reactive power regulation stage.

[0031] Preferably, the grid-side voltage and current calculation values ​​obtained according to the fault network are as follows:

[0032]

[0033] in, To protect the calculated value of the current at the installation location, is the voltage value of the fan side port, is the current value of the fan side port, Z S ' is the total impedance from the fault point to the wind turbine system, Z f is the equivalent impedance of the fault point, is the calculated value of the current at the protection installation, Z G ' is the total impedance from the fault point to the grid-side system.

[0034] Preferably, determining whether an intra-area fault occurs is specifically as follows:

[0035] When 0≤d≤l, a fault occurs in the zone and the protection trips, otherwise the protection does not operate.

[0036] In a second aspect, an embodiment of the present invention provides a distance-measuring distance protection system for a direct-drive wind farm transmission system, comprising:

[0037] The acquisition module collects the voltage and current of the conventional system side of the direct-drive wind farm transmission system. Specifically, the three-phase voltage and current data of A, B, and C on the conventional system side are collected respectively, and the collected voltage and current are subjected to phase mode transformation and Park transformation. The phase mode transformation matrix can adopt the Clark transformation matrix.

[0038] Startup module, when the protection start conditions are met, the protection starts;

[0039] Phase selection module, which selects phases according to the phase difference between zero-sequence and negative-sequence currents and the phase difference between positive-sequence and negative-sequence currents;

[0040] A simplification module determines the equivalent impedance in the simplified fault network according to the phase selection result;

[0041] Iterative module, iteratively solves the fault distance and transition resistance, according to the voltage and current data of the grid-side system, combined with the control equation of the opposite wind turbine system, solves the fault distance and transition resistance value in the fault network;

[0042] The judgment module compares the calculated fault distance with the setting value to determine whether an in-zone fault occurs.

[0043] 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 distance measurement protection method for a direct-drive wind farm transmission system when executing the computer program.

[0044] 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 distance measurement distance protection method for a direct-drive wind farm transmission system.

[0045] Compared with the prior art, the present invention has at least the following beneficial effects:

[0046] A distance measurement protection method for the transmission system of a direct-driven wind farm utilizes the control characteristics of the direct-driven wind turbine, combines the fault composite sequence network, calculates the fault distance and transition resistance according to the voltage and current relationship under the corresponding fault type according to the phase selection results of the power frequency sequence component phase selection element, and judges the fault inside and outside the area by the fault distance. The protection principle takes into account the control characteristics of the power electronic power supply of the direct-driven wind farm, and realizes the single-ended distance protection of the transmission system of the direct-driven wind farm.

[0047] Furthermore, the instantaneous voltage is used as the protection start criterion, which takes advantage of the fact that the wind farm is a weak source and it is difficult to support the voltage when the system is short-circuited, so the protection can be started quickly.

[0048] Furthermore, the phase selection using the zero-negative sequence current phase difference and the positive-negative sequence current phase difference can reliably determine the fault phase and provide support for the calculation of the fault distance and transition resistance after the fault.

[0049] Furthermore, by utilizing the negative sequence current suppression strategy of the wind turbine system, a simplified fault network is adopted to replace the fault composite sequence network, and a function of the voltage and current at the measuring point with respect to the fault distance, transition resistance and the voltage and current at the wind turbine system port is established, so that the protection principle has higher reliability.

[0050] Furthermore, the low voltage ride-through control strategy of the direct-drive wind turbine system is used to characterize the port fault current with the fault voltage at the wind turbine port, and the fault distance is obtained by iteratively solving the calculated value and measured value of the electrical quantity at the measuring point. The protection does not rely on communication, but only uses the single-end electrical quantity and the control characteristics of the opposite-end wind turbine system to protect the entire length of the line.

[0051] Furthermore, by comparing the set value and the fault distance iteration result to determine whether an in-zone fault has occurred, the protection principle can reliably distinguish between in-zone and out-zone faults, thus providing a guarantee for the safe and stable operation of the direct-drive wind turbine delivery system.

[0052] 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.

[0053] In summary, the present invention can realize the distance measurement protection of the direct-drive wind farm transmission line, fully utilizes the control characteristics of the direct-drive wind turbine system, negative sequence current suppression and low penetration characteristics, establishes the function of the measuring point voltage and current and the fault distance, and iteratively solves the fault distance zone inside and outside the zone. The protection reliability is high, and the adaptability problem of the single-ended distance protection principle of the traditional synchronous machine system transmission line in the wind turbine system transmission line is solved.

[0054] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] 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.

[0056] Figure 1 To simplify the fault network diagram;

[0057] Figure 2 is a flow chart of the method of the present invention;

[0058] Figure 3 Send out system topology diagram for direct-drive wind farm;

[0059] Figure 4 A schematic diagram of a computer device provided by an embodiment of the present invention;

[0060] Figure 5 The present invention is a block diagram of an electronic device provided according to an embodiment. DETAILED DESCRIPTION

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The present invention provides a distance measurement distance protection method for a direct-drive wind farm transmission system, which measures and calculates the instantaneous voltage and current in real time, compares the instantaneous voltage with the starting value, and starts the protection when the starting condition is met. The fault phase is selected according to the power frequency sequence component phase selection element, and the equivalent impedance of the fault network is calculated according to the phase selection result. The voltage-current relationship is obtained according to the fault network, and the fault distance and transition resistance are comprehensively solved in combination with the wind turbine control equation. If the obtained fault distance is less than the total length of the line, it is judged that a fault occurs in the area, and the protection action trips; if the obtained fault distance is greater than the total length of the line, it is judged that the fault occurs outside the area, and the phase protection is reset.

[0069] See also Figure 2 The present invention provides a distance-measuring distance protection method for a direct-drive wind farm transmission system, comprising the following steps:

[0070] S1. Collecting the voltage and current of the conventional system side of the direct-drive wind farm transmission system, specifically collecting the three-phase voltage and current data of A, B, and C on the conventional system side, performing phase mode transformation and Park transformation on the collected voltage and current, and the phase mode transformation matrix can adopt the Clark transformation matrix;

[0071] S2. Determine whether the protection is activated by formula (1). If formula (1) is satisfied, the protection is activated;

[0072]

[0073] Where: 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.

[0074] S3, select the fault phase according to the sequence component phase selection element, specifically, select the phase according to the phase difference between the zero-sequence current and the negative-sequence current and the phase difference between the positive-sequence current and the negative-sequence current, the expressions are shown in equations (2) and (3);

[0075]

[0076] S4. Determine the equivalent impedance in the simplified fault network based on the phase selection result. The specific simplified fault network is as follows: Figure 1 As shown, the equivalent impedance expression under different fault types is shown in formula (4);

[0077]

[0078] Where Rf is the transition resistance at the fault point, Z Gk1 , Z Gk2 , Z Gk0 Z sk1 , Zsk2 , Z sk0 They represent the positive and negative zero-sequence impedance of the line from the fault point to the protection installation location, Z sk1 , Z sk2 , Z sk0 Respectively represent the positive and negative zero-sequence impedance of the fault point to the opposite line, Z GT1 , Z GT2 , Z GT0 Represent the positive and negative zero-sequence components of the grid-side system impedance, Z sT1 , Z sT2 , Z sT0 They represent the positive and negative zero-sequence components of the wind turbine side system impedance, including the collector line impedance, transformer impedance, etc. S ' represents the total impedance from the fault point to the opposite end system, Z G ' represents the total impedance from the fault point to the grid-side system.

[0079] S5, iteratively solving the fault distance and transition resistance, according to the voltage and current data of the grid-side system, combined with the control equation of the opposite wind turbine system, solving the fault distance and transition resistance value in the fault network;

[0080] The chord cutting method is used for iterative solution; the specific chord cutting method iteration algorithm is shown in formula (5), and the equation to be solved based on the chord cutting method is shown in formula (6). The calculated value of the grid-side voltage and current is equal to the measured value to obtain the iterative solution result. In order to solve formula (6), the voltage and current data of the fan system are needed. The fan system control equation is shown in formula (7). From formula (7), it can be seen that the current data can be obtained from the fan system voltage, as shown in formula (8). According to the fault network, the grid-side voltage and current calculation value expression is shown in formula (9). Therefore, the iterative solution equation group is an equation group containing the opposite terminal voltage, fault distance, and transition resistance. The initial value of the opposite terminal voltage is the voltage value of the measuring point, and the initial value of the fault distance and transition resistance is 0.5pu and 50Ω.

[0081]

[0082]

[0083] in, is the port current and port voltage of the power supply on the fan system side, u d is the d-axis component of the port voltage, which is the port voltage amplitude in the case of voltage orientation; δ is the phase angle of the port voltage relative to the reference point; i d 、i q is the component of the port current on the d and q axes, i d 、i q Determined by the fault ride-through control strategy, the low voltage ride-through control strategy is adopted here; and The upper and lower boundary values ​​of the voltage index in the dynamic reactive power regulation stage are generally 0.9 and 0.2; is the per unit value of the voltage reference value, generally That is 0.9;I N is the rated current value, K is the reactive current proportionality factor, usually 2; i qlim ,I max For the limit of reactive current and total current, generally P is the active power output in normal state. In the case of asymmetric voltage drop, the positive sequence d and q axis currents are still calculated according to the above formula, and the negative sequence current is generally controlled to 0; Zf is the equivalent impedance of the fault network, Z ST is the equivalent impedance of the transformer and collector line on the power supply side, is the current and voltage at the measuring point, is the grid-side equivalent potential, f ij (k) is the iterative equation, f i (k) is a functional equation, x j (k) is the k-times iterative solution of the equation, Δx j (k) is the correction value of the solution to the equation, h is the step size, z j is the iteration coefficient, ε1,ε2 are minimum values, take 10 -6 , x * is an approximate solution to the equation.

[0084] S6. Compare the calculated fault distance with the setting value to determine whether an internal fault has occurred. The specific fault discrimination formula is shown in formula (10). When formula (10) is satisfied, it can be considered that a fault has occurred in the area and the protection will trip. Otherwise, the protection will not operate.

[0085] 0≤d≤l (10)

[0086] 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".

[0087] In another embodiment of the present invention, a distance measurement type distance protection system for a direct-driven wind farm transmission system is provided. The system can be used to implement the above-mentioned distance measurement type distance protection method for a direct-driven wind farm transmission system. Specifically, the distance measurement type distance protection system for a direct-driven wind farm transmission system includes an acquisition module, a start-up module, a phase selection module, a simplification module, an iteration module and a judgment module.

[0088] Among them, the acquisition module collects the voltage and current of the conventional system side of the direct-drive wind farm transmission system, specifically collects the three-phase voltage and current data of A, B, and C on the conventional system side, performs phase mode transformation and Park transformation on the collected voltage and current, and the phase mode transformation matrix can adopt the Clark transformation matrix;

[0089] Startup module, when the protection start conditions are met, the protection starts;

[0090] Phase selection module, which selects phases according to the phase difference between zero-sequence and negative-sequence currents and the phase difference between positive-sequence and negative-sequence currents;

[0091] A simplification module determines the equivalent impedance in the simplified fault network according to the phase selection result;

[0092] Iterative module, iteratively solves the fault distance and transition resistance, according to the voltage and current data of the grid-side system, combined with the control equation of the opposite wind turbine system, solves the fault distance and transition resistance value in the fault network;

[0093] The judgment module compares the calculated fault distance with the setting value to determine whether an in-zone fault occurs.

[0094] 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 distance protection method of the direct-drive wind farm transmission system, including:

[0095] The voltage and current on the conventional system side of the direct-drive wind farm transmission system are collected, specifically, the three-phase voltage and current data of A, B, and C on the conventional system side are collected respectively, and the collected voltage and current are subjected to phase mode transformation and Park transformation. The phase mode transformation matrix can adopt the Clark transformation matrix; when the protection start condition is met, the protection is started; the phase is selected according to the phase difference between the zero-sequence current and the negative-sequence current of the fault and the phase difference between the positive-sequence current and the negative-sequence current of the fault; the equivalent impedance in the simplified fault network is determined according to the phase selection result; the fault distance and transition resistance are solved iteratively, and the fault distance and transition resistance values ​​are solved in the fault network according to the voltage and current data of the grid-side system and the control equation of the opposite wind turbine system; the calculated fault distance is compared with the set value to determine whether an intra-area fault occurs.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] The processor may load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the distance protection method for the direct-drive wind farm transmission system in the above embodiment; the processor may load and execute the following steps:

[0100] The voltage and current on the conventional system side of the direct-drive wind farm transmission system are collected, specifically, the three-phase voltage and current data of A, B, and C on the conventional system side are collected respectively, and the collected voltage and current are subjected to phase mode transformation and Park transformation. The phase mode transformation matrix can adopt the Clark transformation matrix; when the protection start condition is met, the protection is started; the phase is selected according to the phase difference between the zero-sequence current and the negative-sequence current of the fault and the phase difference between the positive-sequence current and the negative-sequence current of the fault; the equivalent impedance in the simplified fault network is determined according to the phase selection result; the fault distance and transition resistance are solved iteratively, and the fault distance and transition resistance values ​​are solved in the fault network according to the voltage and current data of the grid-side system and the control equation of the opposite wind turbine system; the calculated fault distance is compared with the set value to determine whether an intra-area fault occurs.

[0101] See also Figure 4 , 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 distance protection method of the direct-driven wind farm transmission system in the embodiment is realized. 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 distance protection system of the direct-driven wind farm transmission system in the embodiment are realized. To avoid repetition, it is not described one by one here.

[0102] 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 4 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] See also Figure 5 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.

[0109] 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 2 Follow the steps shown in .

[0110] 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 .

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] Experimental verification:

[0116] In order to verify the correctness of the proposed protection scheme, a simulation model of the direct-drive wind farm transmission system is built in PSCAD. Figure 3 , the line parameters are: positive sequence resistance r1 = 1.7816 × 10 -5 Ω / km; positive sequence reactance x1=3.1388×10 -4 Ω / km; zero sequence resistance r0=2.9522×10 -4 Ω / km; zero-sequence reactance x0=1.0398×10 -3 Ω / km; voltage level 220kV; line length 100km; wind farm capacity 100MW, its low voltage ride through control parameters K=2,I max =3kA, negative sequence current is controlled to 0; the series inductance of the grid-side power supply is 0.1H.

[0117] In order to verify that the proposed distance protection scheme can reliably distinguish between internal and external faults, a fault is set at a distance of 10 km from the protection range. The measured fault distances are shown in Table 1. The required fault distances are all greater than the total length of the line.

[0118] Table 1 Ranging results for faults at 10 km outside the protection range

[0119]

[0120] Table 2 Distance measurement results for different fault types and transition resistances in the fault zone

[0121]

[0122]

[0123] In order to verify that the protection scheme can operate correctly under different fault types and transition resistances, different fault types and transition resistances are set for simulation under fault conditions within the zone. Table 2 shows the fault distance and transition resistance measured by ranging and the relative error.

[0124] In summary, the present invention provides a distance measurement distance protection method and system for a direct-drive wind farm transmission system. By utilizing the control characteristics of the opposite direct-drive wind turbine system, a function of the electrical quantity of the measuring point related to the fault distance is established, and the chord cut method is used to iteratively solve the fault distance, thereby realizing distance protection for the line. A single-ended distance protection principle suitable for the direct-drive wind turbine transmission line is proposed, which has high reliability and provides a guarantee for the safe and stable operation of the system.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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 including an instruction device, which implements the process Figure 1A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0134] 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 in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0135] 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 distance measurement protection method for a direct-drive wind farm transmission system, characterized in that: The following steps are involved: Collect the voltage and current of the conventional system side of the direct-drive wind farm transmission system, specifically collect the three-phase voltage and current data of A, B, and C on the conventional system side respectively, perform phase mode transformation and Park transformation on the collected voltage and current, and the phase mode transformation matrix can adopt the Clark transformation matrix; When the protection start conditions are met, the protection starts; Phase selection is performed based on the phase difference between the zero-sequence and negative-sequence currents of the fault and the phase difference between the positive-sequence and negative-sequence currents of the fault; Determine the equivalent impedance in the simplified fault network according to the phase selection result; Iteratively solve the fault distance and transition resistance. According to the voltage and current data of the grid-side system and the control equation of the opposite wind turbine system, the fault distance and transition resistance values ​​are solved in the fault network. Compare the calculated fault distance with the set value to determine whether an in-zone fault has occurred.

2. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 1 is characterized in that: The protection start 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 distance measurement protection method for the direct-drive wind farm transmission system according to claim 1 is characterized in that: The phase selection is performed according to the phase difference between the zero-sequence current and the negative-sequence current and the phase difference between the positive-sequence current and the negative-sequence current of the fault as follows: Among them, α is the phase difference of the zero-negative sequence current of the fault, is the fault zero-sequence current, β is the phase difference between the positive and negative sequence currents, is the fault positive sequence current, is the fault negative sequence current.

4. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 1 is characterized in that: The equivalent impedance is as follows: Among them, R f is the transition resistance at the fault point, Z Gk1 , Z Gk2 , Z Gk0 Z sk1 , Z sk2 , Z sk0 They represent the positive and negative zero-sequence impedance of the line from the fault point to the protection installation location, Z sk1 , Z sk2 , Z sk0 Respectively represent the positive and negative zero-sequence impedance of the fault point to the opposite line, Z GT1 , Z GT2 , Z GT0 Represent the positive and negative zero-sequence components of the grid-side system impedance, Z sT1 , Z sT2 , Z sT0 They represent the positive and negative zero-sequence components of the wind turbine side system impedance, including the collector line impedance, transformer impedance, etc. S ′ represents the total impedance from the fault point to the opposite end system, Z′ G Indicates the total impedance from the fault point to the grid-side system.

5. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 1 is characterized in that: The iterative solution of fault distance and transition resistance is as follows: The chord cutting method is used for iterative solution; the calculated value of the grid-side voltage and current is equal to the measured value to obtain the iterative solution result, and the voltage and current data of the fan system are used. The current data is obtained by the fan system control equation through the fan system voltage. The calculated value of the grid-side voltage and current is obtained according to the fault network. The iterative solution equation group is an equation group containing the opposite terminal voltage, fault distance, and transition resistance. The initial value of the opposite terminal voltage selects the voltage value of the measuring point, and the initial values ​​of the fault distance and transition resistance select 0.5pu and 50Ω.

6. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 5 is characterized in that: The calculation of the chord cutting iterative algorithm is as follows: Among them, f ij (k) is the iterative equation, f i (k) is the function equation, x j (k) is the k-times iterative solution of the equation, Δx j (k) is the correction value of the solution to the equation, h is the step size, z j is the iteration coefficient, ε1, ε2 are minimum values, x * is an approximate solution to the equation.

7. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 5 is characterized in that: The fan system control equation is as follows: Among them, i d is the d-axis component of the port current, i q is the q-axis component of the port current, P is the active power output in normal state, u d is the d-axis component of the port voltage, I max is the total current limit, K is the reactive current proportional coefficient, is the per unit value of the voltage reference value, is the per unit value of the d-axis component of the port voltage, I N is the rated current, i qlim is the reactive current limit, and It is the upper and lower boundary values ​​of voltage index in the dynamic reactive power regulation stage.

8. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 5 is characterized in that: The calculated values ​​of grid-side voltage and current based on the fault network are as follows: in, To protect the calculated value of the current at the installation location, is the voltage value of the fan side port, is the current value of the fan side port, Z S ' is the total impedance from the fault point to the wind turbine system, Z f is the equivalent impedance of the fault point, is the calculated value of the current at the protection installation, Z G ' is the total impedance from the fault point to the grid-side system.

9. The distance measurement protection method for the direct-drive wind farm transmission system according to claim 1 is characterized in that: The specific methods for judging whether an in-area fault occurs are: When 0≤d≤l, a fault occurs in the zone and the protection trips, otherwise the protection does not operate.

10. A distance measuring protection system for a direct-drive wind farm transmission system, characterized in that: include: The acquisition module collects the voltage and current of the conventional system side of the direct-drive wind farm transmission system. Specifically, the three-phase voltage and current data of A, B, and C on the conventional system side are collected respectively, and the collected voltage and current are subjected to phase mode transformation and Park transformation. The phase mode transformation matrix can adopt the Clark transformation matrix. Startup module, when the protection start conditions are met, the protection starts; Phase selection module, which selects phases according to the phase difference between zero-sequence and negative-sequence currents and the phase difference between positive-sequence and negative-sequence currents; A simplification module determines the equivalent impedance in the simplified fault network according to the phase selection result; Iterative module, iteratively solves the fault distance and transition resistance, according to the voltage and current data of the grid-side system, combined with the control equation of the opposite wind turbine system, solves the fault distance and transition resistance value in the fault network; The judgment module compares the calculated fault distance with the setting value to determine whether an in-zone fault occurs.

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