Distribution line inter-phase permanent fault identification method and system using SOP detection

Abstract

The invention discloses a distribution line inter-phase permanent fault identification method and system based on SOP detection, and relates to the technical field of active injection protection. Based on an active detection idea, when an inter-phase short-circuit fault occurs in a distribution line containing SOP, a fault current limiting control measure is firstly started; limiting the output current of the fault side converter to be zero so as to enable the fault to extinguish arc; secondly, injecting pilot frequency positive sequence detection signals to obtain response characteristics by adopting a constant current injection strategy; solving the permanent fault equivalent model, and carrying out permanent fault identification by utilizing voltage structure similarity based on a model identification idea; and finally, fault isolation and power supply recovery are carried out based on a fault property identification result. Additional injection equipment is not needed, the fault property can be effectively judged, the fault section can be quickly determined under the permanent fault, and the power supply reliability of a power distribution system can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of active injection protection, and in particular relates to a method and system for identifying permanent interphase faults of distribution lines using SOP detection. Background Art

[0002] At present, the flexible interconnected distribution network with intelligent soft switch (SOP, soft open point) as the core has the ability to balance feeder load, quickly recover from faults and quickly absorb new energy, and has been widely studied and initially demonstrated.

[0003] In order to improve the reliability of power supply, distribution lines are usually equipped with automatic reclosing devices. However, in the face of permanent faults, traditional automatic reclosing may cause the fault current to surge again, which may not only damage the equipment but also expand the scope of the fault. As an advanced power electronic switch, SOP has the ability to continuously control the feeder exchange power and inject detection signals. Based on the idea of ​​active detection fault recovery, SOP is used to inject detection signals to obtain response characteristics, thereby clarifying the nature of the fault and performing adaptive reclosing, which is of great significance to improving the operational reliability of the distribution network. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for identifying permanent interphase faults in distribution lines using SOP detection in response to the deficiencies in the above-mentioned prior art, obtain the response characteristics of the interphase circuit of the line after the fault, and judge the nature of the fault based on the model recognition idea, so as to solve the technical problem that the automatic reclosing switch overlaps with the permanent fault and causes secondary impact on the system.

[0005] The present invention adopts the following technical solutions: A method for identifying permanent phase-to-phase faults in a distribution line using SOP detection comprises the following steps: Establish an equivalent model of permanent fault between phases of feeder after power outage; When a short-circuit fault occurs on the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault. After a certain delay, a three-phase positive sequence detection signal with characteristic frequency is injected in a constant current injection mode; Based on the constant current injection method, the constructed feeder phase-to-phase permanent fault equivalent model is solved and the permanent fault judgment criterion is constructed; The fault nature is identified based on the permanent fault criterion, and the fault is isolated and the power supply is restored based on the fault nature identification result.

[0006] Preferably, the equivalent model of permanent fault between phases of feeder after power outage is established as follows: When a permanent phase fault occurs on the distribution line, the residual load is equivalent to RL Series model; the residual load is in parallel with the transition resistor and the residual compensation capacitor. The distribution line adopts the Π model equivalent to establish an equivalent model of permanent phase-to-phase fault of the feeder after power outage.

[0007] Preferably, the SOP fault side converter limits the output current to zero so that the fault arc is extinguished as follows: The outgoing line switch of the fault side substation trips, and other section switches and boundary switches on the feeder line lose pressure but do not trip. The converter on the non-fault side of SOP switches to U dc Q Control, the fault side converter starts the fault current limiting strategy after the protection action, the voltage outer loop and the phase-locked loop are tripped, and the inner loop current reference value is given to suppress the output current to zero in the form of inner loop control.

[0008] Preferably, the fault current limiting strategy is activated 5 to 10 ms after the protection action.

[0009] Preferably, the three-phase positive sequence detection signal of the characteristic frequency injected in a constant current injection manner is specifically: The converter extracts the current signal at a specific frequency, sets a negative feedback link based on PI control, and implements current effective value negative feedback tracking based on the controller, so that the current effective value is equal to the preset reference value, and injects a positive sequence detection signal with a certain amplitude in a constant current injection manner.

[0010] Preferably, the injected positive sequence detection signal is specifically:

[0011] in, is the amplitude of the detection signal; is the angular frequency of the detection signal; is the initial phase of the detection signal; , and are the voltage magnitudes of the injected detection signals respectively.

[0012] Preferably, the single-frequency detection current amplitude is 3% to 5% of the maximum load current, and the single-frequency detection voltage is set to be less than or equal to 12.5% ​​of the rated voltage; the detection signal frequency is within the applicable frequency band of the phase-to-phase permanent fault equivalent model, and the initial phase of the detection signal can be set arbitrarily.

[0013] Preferably, the permanent fault criterion is constructed as follows: According to the feeder phase permanent fault equivalent model, write the frequency-different voltage and current phasor constraint equations, and then solve the parameters of the equivalent model; use the interior point method to solve the model under the objective function and its constraint conditions; The real and imaginary parts of the voltage phasor estimation and measured values ​​at the injection frequency are extracted to form a 4×2 matrix and , and the structural similarity index is used to measure the errors of the two matrices to determine the permanent fault identification criterion.

[0014] Preferably, the permanent fault identification criterion is:

[0015] in, is the similarity threshold, is the fluctuation threshold, is the mean value of the structural similarity index, is the total number of structural similarity indices, is the structural similarity index sequence, is the normalized mean absolute deviation, which is used to measure the degree of volatility.

[0016] In a second aspect, an embodiment of the present invention provides a distribution line phase-to-phase permanent fault identification system using SOP detection, comprising: Building modules to establish an equivalent model of permanent faults between phases of feeder after power outage; Fault module: when a short-circuit fault occurs on the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault; The injection module injects the three-phase positive sequence detection signal of the characteristic frequency in a constant current injection mode after a certain delay; The judgment module solves the constructed feeder phase-to-phase permanent fault equivalent model based on the constant current injection method and constructs the permanent fault judgment criterion; The identification module identifies the nature of the fault based on the permanent fault criterion, and performs fault isolation and power supply restoration based on the fault nature identification result.

[0017] In a third aspect, a computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for identifying permanent phase-to-phase faults of distribution lines using SOP detection are implemented.

[0018] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, comprising a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for identifying permanent inter-phase faults in distribution lines using SOP detection.

[0019] In a fifth aspect, a chip comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for identifying permanent interphase faults in distribution lines using SOP detection are implemented.

[0020] In a sixth aspect, an embodiment of the present invention provides an electronic device, comprising a computer program, which, when executed by the electronic device, implements the steps of the above-mentioned method for identifying permanent inter-phase faults in distribution lines using SOP detection.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: A method for identifying permanent interphase faults in distribution lines using SOP detection uses existing equipment to inject heterofrequency detection signals to determine the nature of the fault. It does not rely on additional injection equipment and can avoid secondary impacts on the system caused by overlapping permanent faults, which is conducive to accelerating power supply recovery.

[0022] Furthermore, an equivalent model of permanent interphase fault of feeder after power outage is established, which can accurately reflect the characteristics of interphase circuit of feeder after power outage within the applicable frequency band.

[0023] Furthermore, after the outgoing line switch of the fault-side substation trips, the SOP fault-side converter limits the output current to zero to extinguish the fault arc, so as to avoid interference of the fault arc in the determination of the fault nature.

[0024] Furthermore, the constant current injection strategy for starting the SOP fault-side converter can inject a three-phase positive-sequence detection signal with a certain characteristic frequency amplitude under different fault types, fault locations and transition resistances to obtain the feeder phase-to-phase loop response characteristics.

[0025] Furthermore, the single-frequency detection current amplitude is set to 3%~5% of the maximum load current, the single-frequency detection voltage is less than or equal to 12.5% ​​of the rated voltage, and the initial phase of the detection signal can be set arbitrarily so that the mutual inductor can collect signals for analysis while avoiding causing a large impact on the system.

[0026] Furthermore, based on the model identification principle, a permanent fault criterion using voltage structure similarity is proposed, which can clearly reflect the model error and fault nature through the voltage error and is not affected by the transition resistance and fault location.

[0027] 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.

[0028] To sum up, the present invention does not rely on additional equipment. By injecting heterofrequency detection signals through SOP, the response characteristics of the phase-to-phase loop of the feeder are obtained for permanent fault identification, which can avoid the secondary impact on the system caused by overlapping permanent faults, and is conducive to accelerating power supply recovery; after the outgoing line switch trips, the SOP starts the fault current limiting strategy to extinguish the arc at the fault point, thereby avoiding the influence of the fault arc on the judgment of the nature of the fault; injecting a detection signal with a certain amplitude in the form of constant current injection can avoid causing a large impact on the system; based on the model recognition principle, permanent fault identification is performed by voltage structure similarity, which can effectively judge the nature of the fault, is not affected by the fault location and transition resistance, and quickly locates the fault section, which helps to improve the reliability of the distribution system.

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of an embodiment of a method for identifying permanent interphase faults in a power distribution line using SOP detection provided by the present invention; Figure 2 A topological diagram of a SOP-containing flexible interconnection power distribution system provided by the present invention; Figure 3 A schematic diagram of an equivalent model of permanent interphase fault of a power distribution line provided by the present invention; Figure 4 A schematic diagram of the fault current limiting and active injection control strategy provided by the present invention; Figure 5 A schematic diagram of the voltage and current waveforms at the SOP outlet side when a permanent two-phase short circuit fault occurs at the midpoint of the line L1 provided by the present invention; Figure 6 A schematic diagram of the result of distinguishing the nature of a fault when a permanent two-phase short circuit fault occurs at the midpoint of the line L1 provided by the present invention; Figure 7 A schematic diagram of a computer device provided by an embodiment of the present invention; Figure 8 The block diagram of a chip provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The present invention provides a method for identifying permanent interphase faults in distribution lines using SOP detection. In order to ensure system stability, a series of measures need to be taken immediately when a fault occurs; first, the fault current limiting control measure is started to achieve fault arc extinguishing by limiting the output current of the fault side converter to zero. Subsequently, a constant current injection strategy is adopted to inject a heterofrequency positive sequence detection signal into the system to obtain response characteristics. On this basis, the equivalent model of the permanent fault is solved, and the permanent fault is identified using model recognition technology and voltage structure similarity. Finally, fault isolation and power supply restoration operations are performed according to the identification results of the fault nature to ensure the safe operation of the power grid.

[0039] See also Figure 1 The present invention provides a method for identifying permanent interphase faults of distribution lines using SOP detection, comprising the following steps: S1. Establish an equivalent model of permanent interphase fault of feeder after power outage; When a permanent phase fault occurs on the distribution line, most nonlinear loads and high-power motor loads will be out of operation, and the residual load within a certain frequency band can be equivalent to RL Series model. The residual load is in parallel with the transition resistor and the residual compensation capacitor. The distribution line is equivalent to the Π model, and an equivalent model of permanent fault between phases of the distribution line can be established.

[0040] S2, propose a fault current limiting strategy; When a short-circuit fault occurs on the feeder on the SOP side, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault arc. Specifically: The outgoing line switch of the fault side substation trips, and other section switches and boundary switches on the feeder line lose pressure but do not trip, ensuring that the detection signal injected by the subsequent SOP has a circulation loop. At the same time, the converter on the non-fault side of the SOP switches to U dc Q Control, the fault side converter starts the fault current limiting strategy 5ms after the protection action, the voltage outer loop and the phase-locked loop are tripped, and the inner loop current reference value is given to suppress the output current to zero in the form of inner loop control.

[0041] S3. Propose a constant current injection strategy for characteristic frequency positive sequence signal; After a certain delay, the three-phase positive sequence detection signal of the characteristic frequency is injected in the form of constant current injection, specifically: The converter extracts the current signal at a specific frequency, sets a negative feedback link based on PI control, and implements negative feedback tracking of the current effective value based on the controller, so that the current effective value is equal to the preset reference value, thereby injecting a positive sequence detection signal with a certain amplitude in the form of constant current injection. At the same time, the detection voltage amplitude is limited to avoid a large impact on the system.

[0042] The injected positive sequence detection signal is specifically:

[0043] in, is the amplitude of the detection signal; is the angular frequency of the detection signal; is the initial phase of the detection signal; , and are the voltage magnitudes of the injected detection signals respectively.

[0044] When the detection current amplitude is too low, signal acquisition is more difficult, and when the amplitude is too high, it will cause overvoltage problems during transient faults or high-resistance faults. The single-frequency detection current amplitude can generally be selected as 3%~5% of the maximum load current (600A). At the same time, to avoid overvoltage problems, the single-frequency detection voltage should not be higher than 12.5% ​​of the rated voltage. The detection signal frequency should be within the applicable frequency band of the phase-to-phase permanent fault equivalent model and meet the requirements of SOP filter design and transformer transmission characteristics. The initial phase of the detection signal can be set arbitrarily.

[0045] S4. Construct permanent fault judgment criteria based on model identification; On the basis of active injection, the equivalent model of phase-to-phase permanent fault is solved and the permanent fault criterion is constructed, which is as follows: According to the feeder phase permanent fault equivalent model, the heterofrequency voltage and current phasor constraint equations are listed, and then the equivalent model parameters are solved. The specific nonlinear equations are:

[0046] in, , and , are the real and imaginary parts of the measured voltage and current phasors at different frequencies, respectively; , is the current coefficient, specifically

[0047] in, , They are:

[0048] The interior point method is used to solve the model under the objective function and its constraints, and its form is:

[0049] in, x is a column vector containing the model parameters, which are ; , are the real and imaginary parts of the voltage phasor estimate under the parameter estimation value; lb and ub for x The upper and lower limits of is a nonlinear constraint function used to speed up the iteration.

[0050] The actual parameters in the permanent fault model are difficult to obtain, and the nature of the fault cannot be accurately and effectively judged only by the estimated parameter values. The voltage error can be used to map the error between the parameter estimate and the actual parameter. In the case of a permanent fault, the actual model is consistent with the permanent fault model, and the final iteration error is small; in the case of a transient fault, the model cannot reflect the actual distribution system, and the final iteration error is large. Therefore, consider using the voltage error for permanent fault identification.

[0051] The real and imaginary parts of the voltage phasor estimation and measured values ​​at the injection frequency are extracted to form a 4×2 matrix and , and the structural similarity index (SSIM) measures the error between the two matrices, which is defined as:

[0052] in, and , and They are and The mean and standard deviation of is the covariance of A and B; In order to maintain a stable constant, the present invention sets .

[0053] The SSIM value range is [-1,1]. The higher the value, the higher the similarity of the two matrix structures. Conversely, the lower the similarity. and The permanent fault identification criterion is

[0054] in, is the similarity threshold, which can generally be set to 90%; It is the fluctuation threshold, which can generally be set to 5%.

[0055] S5. Perform fault isolation and power supply restoration based on the fault nature identification result.

[0056] In another embodiment of the present invention, a system for identifying permanent phase-to-phase faults in distribution lines using SOP detection is provided. The system can be used to implement the above-mentioned method for identifying permanent phase-to-phase faults in distribution lines using SOP detection. Specifically, the system for identifying permanent phase-to-phase faults in distribution lines using SOP detection includes a building module, a fault module, an injection module, a judgment module and an identification module.

[0057] Among them, the construction module establishes an equivalent model of permanent fault between phases of feeder after power outage; Fault module: when a short-circuit fault occurs on the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault; The injection module injects the three-phase positive sequence detection signal of the characteristic frequency in a constant current injection mode after a certain delay; The judgment module solves the constructed feeder phase-to-phase permanent fault equivalent model based on the constant current injection method and constructs the permanent fault judgment criterion; The identification module identifies the nature of the fault based on the permanent fault criterion, and performs fault isolation and power supply restoration based on the fault nature identification result.

[0058] In another embodiment of the present invention, a terminal device is provided, the terminal device includes a processor and a memory, 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., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions to implement corresponding method flows or corresponding functions; The processor described in the embodiment of the present invention can be used for the operation of the distribution line phase-to-phase permanent fault identification method using SOP detection, including: An equivalent model of permanent interphase fault of feeder after power outage is established; when a short-circuit fault occurs in the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault; after a certain delay, a three-phase positive-sequence detection signal of the characteristic frequency is injected in a constant current injection manner; based on the constant current injection method, the constructed equivalent model of permanent interphase fault of feeder is solved, and a permanent fault judgment criterion is constructed; the fault nature is identified based on the permanent fault judgment criterion, and the fault isolation and power supply restoration are performed based on the fault nature identification result.

[0059] See also Figure 7 , the terminal device is a computer device. 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 interphase permanent fault of the distribution line using the SOP detection 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 system for identifying the interphase permanent fault of the distribution line using the SOP detection in the embodiment are implemented. To avoid repetition, it is not described one by one here.

[0060] 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 7 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.

[0061] The processor 61 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 gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0062] 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.

[0063] 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.

[0064] See also Figure 8 , the terminal device is a chip, and the chip 600 of this embodiment includes a processor 622, which may be one or more, and a memory 632 for storing a computer program executable by the processor 622. The computer program stored in the memory 632 may include one or more modules each corresponding to a set of instructions. In addition, the processor 622 may be configured to execute the computer program to execute the above-mentioned distribution line phase-to-phase permanent fault identification method using SOP detection.

[0065] In addition, the chip 600 may further include a power supply component 626 and a communication component 650, wherein the power supply component 626 may be configured to perform power management of the chip 600, and the communication component 650 may be configured to implement communication, for example, wired or wireless communication, of the chip 600. In addition, the chip 600 may further include an input / output interface 658. The chip 600 may operate based on an operating system stored in the memory 632.

[0066] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It can be understood 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. 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. It should be noted that the computer-readable storage medium here can be a high-speed RAM memory, or a non-volatile memory (Non-VolatileMemory), such as at least one disk memory.

[0067] 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 interphase permanent faults of distribution lines using SOP detection in the above-mentioned embodiment; one or more instructions in the computer-readable storage medium are loaded and executed by the processor as follows: An equivalent model of permanent interphase fault of feeder after power outage is established; when a short-circuit fault occurs in the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault; after a certain delay, a three-phase positive-sequence detection signal of the characteristic frequency is injected in a constant current injection manner; based on the constant current injection method, the constructed equivalent model of permanent interphase fault of feeder is solved, and a permanent fault judgment criterion is constructed; the fault nature is identified based on the permanent fault judgment criterion, and the fault isolation and power supply restoration are performed based on the fault nature identification result.

[0068] 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.

[0069] See also Figure 1 , is an embodiment of the method for identifying permanent interphase faults of distribution lines using SOP detection provided by the present invention, and the specific steps are as follows: S1. When a short circuit occurs, the outgoing line switch of the fault-side substation trips, and the converter on the fault-side suppresses the output current to zero by means of inner loop control; S2. After a certain delay, a three-phase positive sequence detection signal with a characteristic frequency is injected in a constant current manner to obtain a response characteristic; S3, SOP outlet side FTU determines the nature of the fault according to the permanent fault judgment criteria and reports it to the main station; S4: If it is a transient fault, signal 1 is given, allowing reclosing and restoring power supply, otherwise go to step S5; S5, permanent fault signal 0, lock reclosing, then each FTU starts fault nature identification and reports to the master station; S6, check the branch line FTU report, if there is a branch line report 0, then the branch line has a permanent fault, isolate the branch line and go to step S9, otherwise go to step S7; S7, check the main line FTU reports, if all reports are 0, then the substation outlet side line has a permanent fault, isolate the faulty line and go to step S10, otherwise go to step S8; S8, determine the two adjacent trunk line FTUs with inconsistent reports, locate the fault section, isolate the faulty line and proceed to step S9; S9, allow the substation outgoing line circuit breaker to reclose, SOP switches to Vf control, restore power supply to the non-fault area, and end; S10, SOP switches to Vf control, restores power supply to non-faulty areas, and ends.

[0070] See also Figure 2 , is a topological diagram of a SOP-based flexible interconnection distribution system provided by the present invention. The typical topological structure of SOP is a back-to-back voltage source converter. During normal operation, one side of SOP adopts U dc Q Control to maintain the DC side voltage stability; the converter on the other side adopts PQ Control to achieve precise power control. After a feeder fault occurs, the outgoing line switch of the substation on the fault side trips, and other section switches and boundary switches on the feeder lose pressure but do not trip, providing a circulation loop for the subsequent injection of detection signals. Subsequently, the SOP starts the fault current limiting and active injection control strategy to obtain the response characteristics, and uses the voltage structure similarity based on the model recognition idea to identify permanent faults.

[0071] The system voltage level is 10kV, and the lengths of each section in the distribution system are: L 1= L 3= L 6= L 8=5 km, L 2=4 km, L 4= L 5= L 9=2.5 km, L 7=6km.

[0072] See also Figure 3 , is a schematic diagram of an equivalent model of permanent interphase fault of a distribution line provided by the present invention. R 1. L 1 are the equivalent resistance and inductance between phases of the distribution line, C 1 is half of the line phase equivalent capacitance, R 2. L 2 are the equivalent resistance and inductance of the phase-to-phase load, C 2 is the sum of the load-side interphase compensation capacitance and half of the line interphase equivalent capacitance, R f is the phase transition resistance, is the line voltage between the two fault phases, It is half of the current difference between the two phases of the fault.

[0073] See also Figure 4 , is a schematic diagram of the fault current limiting and active injection control strategy provided by the present invention. u s , i s are the voltage and current on the AC side of the converter respectively; U dc * , Q * and U dc , Q They are the reference value and actual value of DC voltage and reactive power respectively; u dq + , u dq - , i dq + , i dq - is the measured value of positive and negative sequence voltage and current of dq axis; i dq +* , i dq -* is the reference value of the positive and negative sequence current of the dq axis; u dq +* , u dq -* The positive and negative sequence voltage values ​​of the inner loop output dq axis; I 1. I 2. I 3. I 4 is the injection frequency current phasor amplitude; I det * and I det To inject the reference value and actual value of the detection current; u * det1 , u * det2 , u * det3 , u * det4 is an additional modulation wave at the injection frequency;u abc * is the output modulation wave.

[0074] See also Figure 5 , a schematic diagram of the voltage and current waveforms at the SOP outlet side when a permanent two-phase short circuit fault occurs at the midpoint of the line L1 provided by the present invention.

[0075] See also Figure 6 , a schematic diagram of the result of distinguishing the nature of a fault when a permanent two-phase short circuit fault occurs at the midpoint of line L1 provided by the present invention.

[0076] In summary, the present invention provides a method and system for identifying permanent interphase faults in distribution lines using SOP detection, which utilizes intelligent soft switching (SOP) technology, combined with active detection fault recovery and adaptive reclosing strategies, can significantly improve the operating reliability of the distribution network, promote the efficient use of clean energy, and conform to the development direction of building a new power system.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices, and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks 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.

[0085] 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.

[0086] 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 The steps for the functions specified in one or more boxes.

[0087] 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 identifying permanent phase-to-phase faults in a distribution line using SOP detection, characterized in that: The following steps are involved: Establish an equivalent model of permanent fault between phases of feeder after power outage; When a short-circuit fault occurs on the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault. After a certain delay, a three-phase positive sequence detection signal with characteristic frequency is injected in a constant current injection mode; Based on the constant current injection method, the constructed feeder phase-to-phase permanent fault equivalent model is solved and the permanent fault judgment criterion is constructed; The fault nature is identified based on the permanent fault criterion, and the fault is isolated and the power supply is restored based on the fault nature identification result.

2. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 1, characterized in that, The equivalent model of permanent fault between phases of feeder after power outage is established as follows: When a permanent phase fault occurs on the distribution line, the residual load is equivalent to RL Series model; the residual load is in parallel with the transition resistor and the residual compensation capacitor. The distribution line adopts the Π model equivalent to establish an equivalent model of permanent phase-to-phase fault of the feeder after power outage.

3. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 1, characterized in that, The converter on the fault side of SOP limits the output current to zero to extinguish the fault arc. Specifically: The outgoing line switch of the fault side substation trips, and other section switches and boundary switches on the feeder line lose pressure but do not trip. The converter on the non-fault side of SOP switches to U dc Q Control, the fault side converter starts the fault current limiting strategy after the protection action, the voltage outer loop and the phase-locked loop are tripped, and the inner loop current reference value is given to suppress the output current to zero in the form of inner loop control.

4. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 3, characterized in that, The fault current limiting strategy starts 5~10ms after the protection action.

5. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 1, characterized in that: The three-phase positive sequence detection signal injected with characteristic frequency by constant current injection is specifically: The converter extracts the current signal at a specific frequency, sets a negative feedback link based on PI control, and implements current effective value negative feedback tracking based on the controller, so that the current effective value is equal to the preset reference value, and injects a positive sequence detection signal with a certain amplitude in a constant current injection manner.

6. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 5, characterized in that: The injected positive sequence detection signal is specifically: in, is the amplitude of the detection signal; is the angular frequency of the detection signal; is the initial phase of the detection signal; , and are the voltage magnitudes of the injected detection signals respectively.

7. The method for identifying permanent interphase faults in a power distribution line using SOP detection according to claim 5, characterized in that: The single-frequency detection current amplitude is 3%~5% of the maximum load current, and the single-frequency detection voltage is set less than or equal to 12.5% ​​of the rated voltage; the detection signal frequency is within the applicable frequency band of the phase-to-phase permanent fault equivalent model, and the initial phase of the detection signal can be set arbitrarily.

8. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 1, characterized in that: The specific criteria for constructing permanent faults are: According to the feeder phase permanent fault equivalent model, write the frequency-different voltage and current phasor constraint equations, and then solve the parameters of the equivalent model; use the interior point method to solve the model under the objective function and its constraint conditions; The real and imaginary parts of the voltage phasor estimation and measured values ​​at the injection frequency are extracted to form a 4×2 matrix and , and the structural similarity index is used to measure the errors of the two matrices to determine the permanent fault identification criterion.

9. The method for identifying permanent phase-to-phase faults of distribution lines using SOP detection according to claim 8, characterized in that: The permanent fault identification criteria are: in, is the similarity threshold, is the fluctuation threshold, is the mean value of the structural similarity index, is the total number of structural similarity indices, is the structural similarity index sequence, is the normalized mean absolute deviation, which is used to measure the degree of volatility.

10. A distribution line phase-to-phase permanent fault identification system using SOP detection, characterized in that: include: Building modules to establish an equivalent model of permanent faults between phases of feeder after power outage; Fault module: when a short-circuit fault occurs on the feeder on one side of the SOP, the converter on the fault side of the SOP limits the output current to zero to extinguish the fault; The injection module injects the three-phase positive sequence detection signal of the characteristic frequency in a constant current injection mode after a certain delay; The judgment module solves the constructed feeder phase-to-phase permanent fault equivalent model based on the constant current injection method and constructs the permanent fault judgment criterion; The identification module identifies the nature of the fault based on the permanent fault criterion, and performs fault isolation and power supply restoration based on the fault nature identification result.

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