CN112763853A - System for detecting and positioning short-circuit fault of alternating-current micro-grid in grid-connected mode and working method thereof - Google Patents
System for detecting and positioning short-circuit fault of alternating-current micro-grid in grid-connected mode and working method thereof Download PDFInfo
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Abstract
The invention relates to a detection and positioning system for short-circuit faults of an alternating-current micro-grid in a grid-connected mode and a working method thereof, and provides a radiation-type alternating-current micro-grid, which comprises a measurement module, a communication module and a micro-grid protection system module; the measuring module comprises a plurality of signal acquisition devices and a plurality of signal processing devices; the measurement module is connected with the communication module, and the communication module is connected with the microgrid protection system module and used for transmitting the current signals collected and processed by the measurement module to the microgrid protection system module through the communication module; the invention selects the proper wavelet energy spectrum value of the current as the fault judgment threshold value to judge whether the micro-grid has short-circuit fault, thereby achieving the early detection of the micro-grid short-circuit fault. And positioning the short-circuit fault area of the micro-grid by using the size of the first peak value of the wavelet energy spectrum waveform of the fault current measured at the detection point.
Description
Technical Field
The invention relates to the field of microgrid fault detection, in particular to a detection and positioning system for an alternating current microgrid short-circuit fault in a grid-connected mode and a working method thereof.
Background
At present, with the increasing exhaustion of fossil energy and the deterioration of the environment, the development of renewable energy and the protection of the environment are key ways for ensuring the realization of sustainable development of the whole human. Renewable energy sources such as photovoltaic provide electrical energy to humans in the form of distributed power sources. In order to enable the power generated by the distributed power supply to meet the requirements of human beings on the quality of electric energy and grid connection, the micro-grid technology is developed. Although the micro-grid technology can provide important support for the development of resource-saving and environment-friendly power systems, at present, a plurality of unsolved key technologies still limit the development of micro-grids. The micro-grid short-circuit fault detection and protection technology is one of key technologies for limiting the development of micro-grids. A microgrid is a multi-source power supply network, and therefore the power flow inside the microgrid is not completely consistent with that of a traditional power grid. And the generated energy of the distributed power supply can not directly supply power to the load generally, but can be converted by the power electronic converter to be used by the load and be merged into a large power grid. Therefore, the short-circuit fault characteristics of the micro-grid are not completely consistent with those of the traditional power grid, and a method suitable for detecting and identifying the short-circuit fault of the micro-grid needs to be researched.
At present, most of the short-circuit fault detection methods for micro-grids proposed by scholars at home and abroad directly utilize short-circuit fault characteristic quantities such as short-circuit current and the like. Such as by using the phase angle or amplitude difference of the sequence components of the fault current as a characteristic quantity of the short-circuit fault to detect the short-circuit fault. Although it is relatively simple to directly use fault characteristic quantities such as short-circuit current, the short-circuit fault can be detected and positioned after the fault is developed, so that it is difficult to detect and quickly position the short-circuit fault in an early stage. Traveling waves can be commonly used for fault detection in ac micro-grids, and fault detection is also relatively fast. However, the method has the problems of detection of reflected waves, high requirements on time accuracy and data synchronism and the like, and meanwhile, the traveling wave is difficult to apply to a low-voltage microgrid with a short line. The detection and positioning of the short-circuit fault are also a research trend by analyzing and processing the node information in the universe by using a communication technology and a complex intelligent algorithm. If students utilize the communication technology to obtain the information of output current, position, control strategy and the like of the distributed power supply in real time, and an intelligent algorithm is utilized to realize the detection and fault location of the fault. These are similar to integrated protection schemes, but the accuracy is high, but the amount of information processing is large, and therefore the time required for fault detection and localization is also long. In summary, the method for detecting and locating the short-circuit fault of the ac microgrid at home and abroad at present mainly determines the occurrence of the short-circuit fault in the microgrid and locates the short-circuit fault by analyzing and processing the collected electrical information of all nodes in the whole microgrid area by using the steady-state value of the electrical quantity after the short-circuit fault occurs or by using a complex algorithm. Therefore, early detection and rapid localization of short-circuit faults are difficult to achieve. The research of applying wavelet analysis to the early detection of the traditional power grid short-circuit fault has been carried out for many years, but no literature report is found on the research of applying the wavelet energy spectrum algorithm to the early detection and positioning of the micro-power grid short-circuit fault.
Disclosure of Invention
In view of this, the present invention provides a system for detecting and locating a short-circuit fault of an ac microgrid in a grid-connected mode and a working method thereof, so as to realize early detection of the short-circuit fault of the microgrid in the grid-connected mode. And the relation between the first peak value of the wavelet energy spectrum waveform of the fault current and the distance from the short-circuit point to the detection point is utilized to realize the quick positioning of the short-circuit fault area of the micro-grid.
The invention is realized by adopting the following scheme: a detection and positioning system for short-circuit faults of an alternating-current micro-grid in a grid-connected mode provides a radiation-type alternating-current micro-grid, and comprises a measurement module, a communication module and a micro-grid protection system module; the measuring module comprises a plurality of signal acquisition devices and a plurality of signal processing devices; the measurement module is connected with the communication module, the communication module is connected with the microgrid protection system module, and the communication module is used for transmitting the current signals collected and processed by the measurement module to the microgrid protection system module through the communication module, judging whether the microgrid has a short-circuit fault or not through the microgrid protection system module and judging an area where the microgrid has the short-circuit fault; every signal acquisition device all is connected with a signal processing device for the current signal transmission who gathers signal acquisition device arrives signal processing device handles, and through with the communication module that signal processing device connects arrives the current signal transmission after handling little electric wire netting protection system module, little electric wire netting protection system module carries out wavelet energy spectrum transform to current signal, judges little electric wire netting whether to take place short circuit fault through the wavelet energy spectrum value of comparison current and the big or small relation of fault detection threshold value, when little electric wire netting takes place short circuit fault, little electric wire netting protection system module judges the area that little electric wire netting took place short circuit fault through the first peak value of fault current wavelet energy spectrum waveform.
Further, the signal acquisition device adopts a current sensor.
Further, the invention provides a working method of a detection and positioning system for short-circuit faults of an alternating current micro-grid based on a grid-connected mode, which comprises the following steps:
step S1: dividing the feeder into a first type feeder and a second type feeder according to the number of nodes on each feeder of the radiation type alternating current micro-grid; the first feeder line only contains one node, and the second feeder line contains two or more nodes;
step S2: the method comprises the steps that each feeder line is taken as a minimum unit of the micro-grid, a detection point is arranged at the connection point of each feeder line and a common bus, a signal acquisition device at the detection point acquires a current signal, the acquired current signal is transmitted to a signal processing device, the current signal is converted into an acquisition signal required by a micro-grid protection system module, and then the acquisition signal is transmitted to the micro-grid protection system module through a communication module;
step S3: performing wavelet energy spectrum transformation on the current signal through the microgrid protection system module to obtain a wavelet energy spectrum value of the current;
step S4: the method comprises the steps that the maximum value of a current wavelet energy spectrum value obtained at a detection point when a single-phase short-circuit fault occurs at the tail end of a feeder line and the initial phase angle of the fault is 150 degrees is used as an upper limit, the maximum value of the current wavelet energy spectrum value obtained at the detection point when a load on the feeder line is put in or cut off is used as a lower limit, and a proper fault judgment threshold value is selected between the upper limit and the lower limit to judge whether the short-circuit fault occurs on the feeder line;
step S5: judging whether the microgrid has a short-circuit fault, if the wavelet energy spectrum value of the current is smaller than a fault judgment threshold value, not generating the short-circuit fault, otherwise, executing a step S6;
step S6: when the micro-grid has a short-circuit fault, if the feeder line is a first type feeder line, the circuit breaker on the feeder line is directly disconnected; if the feeder line is a second type feeder line, the second type feeder line comprises two or more nodes, so that the second type feeder line is divided into different areas according to different node positions; and taking the reduced value of the first peak value of the wavelet energy spectrum waveform of the short-circuit fault current at each node with the fault initial phase angle of 150 degrees as a different fault area judgment threshold value for judging a short-circuit fault area on the feeder line.
Further, the specific content of the wavelet energy spectrum value of the current obtained by performing wavelet energy spectrum transformation on the current signal in step S3 is as follows: taking the derivative function of the cubic B spline function as a wavelet mother function, and obtaining a dyadic wavelet transform formula of a discrete signal f (x) by recursion according to a Mallat algorithm as shown in a formula (1):
let E2jx (t) is the energy of the detail in the j-th scale, and the wavelet energy time spectrum of the signal is:
E2jx(t)＝|W2jx(t)|2(2) wherein j is 4.
Further, the specific content of the area where the micro-grid short-circuit fault occurs when the micro-grid protection system module judges whether the micro-grid short-circuit fault occurs and judges that the micro-grid short-circuit fault occurs is as follows: after the micro-grid protection system module obtains the current signal, detecting and updating zero-crossing point information of the current signal, and simultaneously performing wavelet energy spectrum transformation on the current signal under a fourth scale to obtain a wavelet energy spectrum value of the current; then comparing the wavelet energy spectrum value of the current with a fault judgment threshold value, when the wavelet energy spectrum value of the current is smaller than the fault judgment threshold value, determining that no short-circuit fault occurs on a feeder line of the microgrid, and continuing to perform zero crossing point detection and wavelet energy spectrum transformation on the current; when the current wavelet energy spectrum value is larger than the fault judgment threshold value, the short-circuit fault is considered to occur on the feeder line of the microgrid, and if the feeder line is the first type of feeder line, the breaker on the feeder line is directly disconnected; if the feeder line is a second type feeder line, the microgrid protection system module needs to detect an initial phase angle of a short-circuit fault and the type of the short-circuit fault; after the initial fault phase angle and the fault type are determined, a proper fault area judgment threshold value can be selected, meanwhile, 1ms is delayed to detect the first peak value of the wavelet energy spectrum waveform of the fault current and carry out reduction, so that a reduced value when the initial fault phase angle is 150 degrees is obtained, then the reduced value is compared with the fault area judgment threshold value, a threshold value interval is judged according to the fault area where the reduced value is located, the area where the short-circuit fault is located is judged, then the breaker of the corresponding area is disconnected, and therefore the short-circuit fault area is positioned and eliminated.
Further, the initial phase angle for detecting the short-circuit fault is referred to the time difference between the occurrence time of the short-circuit fault and the zero-crossing time of the current, that is, the ratio of the time difference to 10ms of the two is equal to the ratio of the initial phase angle of the fault to 180 degrees; judging the type of the short-circuit fault by detecting the occurrence of positive sequence, negative sequence and zero sequence components in the fault current; when the zero sequence component of the current is detected, the occurrence of the ground short-circuit fault is considered, when the zero sequence component without the current and the negative sequence component are detected, the occurrence of the two-phase short-circuit fault is considered, and when only the positive sequence component of the current is detected, the occurrence of the three-phase short-circuit fault is considered.
Further, in step S6, the calculation method of the reduced value is: with E4max1Expressed as: defining a new parameter E4 'as a first peak value of a wavelet energy spectrum E4 waveform obtained after fourth scale transformation of fault current after short-circuit fault occurs'max1＝Ke/E4max1In which K iseIs a magnification factor; at fault initial phase angle thetacAt 150 DEG E4'max1Is a reference value KbOrder of reduced value E4 "max1＝KrKb. Wherein
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, a wavelet energy spectrum algorithm is applied to short-circuit protection of the AC micro-grid, so that the early detection of the short-circuit fault of the AC micro-grid in a grid-connected mode is realized, and the rapid and accurate positioning of the short-circuit fault area of the AC micro-grid in the grid-connected mode is realized.
Drawings
Fig. 1 is a structural diagram of a method for detecting and positioning a short circuit of a microgrid according to an embodiment of the present invention.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As shown in fig. 1, the embodiment provides a system for detecting and locating a short-circuit fault of an ac microgrid in a grid-connected mode, and provides a radiation-type ac microgrid, which includes a measurement module, a communication module, and a microgrid protection system module; the measuring module comprises a plurality of signal acquisition devices and a plurality of signal processing devices; the measurement module is connected with the communication module, the communication module is connected with the microgrid protection system module, and the communication module is used for transmitting the current signals collected and processed by the measurement module to the microgrid protection system module through the communication module, judging whether the microgrid has a short-circuit fault or not through the microgrid protection system module and judging an area where the microgrid has the short-circuit fault; every signal acquisition device all is connected with a signal processing device for the current signal transmission who gathers signal acquisition device arrives signal processing device handles, and through with the communication module that signal processing device connects arrives the current signal transmission after handling little electric wire netting protection system module, little electric wire netting protection system module carries out wavelet energy spectrum transform to current signal, judges little electric wire netting whether to take place short circuit fault through the wavelet energy spectrum value of comparison current and the big or small relation of fault detection threshold value, when little electric wire netting takes place short circuit fault, little electric wire netting protection system module judges the area that little electric wire netting took place short circuit fault through the first peak value of fault current wavelet energy spectrum waveform.
In this embodiment, the signal acquisition device employs a current sensor.
Preferably, the embodiment further provides a working method of the detection and positioning system based on the short-circuit fault of the alternating-current microgrid in the grid-connected mode, and the working method comprises the following steps:
step S1: dividing the feeder into a first type feeder and a second type feeder according to the number of nodes on each feeder of the radiation type alternating current micro-grid; the first feeder line only contains one node, and the second feeder line contains two or more nodes;
step S2: the method comprises the steps that each feeder line is taken as a minimum unit of the micro-grid, a detection point is arranged at the connection point of each feeder line and a common bus, a signal acquisition device at the detection point acquires a current signal, the acquired current signal is transmitted to a signal processing device, the current signal is converted into an acquisition signal required by a micro-grid protection system module, and then the acquisition signal is transmitted to the micro-grid protection system module through a communication module;
step S3: performing wavelet energy spectrum transformation on the current signal through the microgrid protection system module to obtain a wavelet energy spectrum value of the current;
step S4: the method comprises the steps that the maximum value of a current wavelet energy spectrum value obtained at a detection point when a single-phase short-circuit fault occurs at the tail end of a feeder line and the initial phase angle of the fault is 150 degrees is used as an upper limit, the maximum value of the current wavelet energy spectrum value obtained at the detection point when a load on the feeder line is put in or cut off is used as a lower limit, and a proper fault judgment threshold value is selected between the upper limit and the lower limit to judge whether the short-circuit fault occurs on the feeder line; (the proper fault judgment threshold is that the selected threshold is not more than 0.8 time of the upper limit value, is not less than 1.2 times of the lower limit value and is proper, and the rest is improper.)
Step S5: judging whether the microgrid has a short-circuit fault, if the wavelet energy spectrum value of the current is smaller than a fault judgment threshold value, not generating the short-circuit fault, otherwise, executing a step S6;
step S6: when the micro-grid has a short-circuit fault, if the feeder line is a first type feeder line, the circuit breaker on the feeder line is directly disconnected; if the feeder line is a second type feeder line, the second type feeder line comprises two or more nodes, so that the second type feeder line is divided into different areas according to different node positions; and taking the reduced value of the first peak value of the wavelet energy spectrum waveform of the short-circuit fault current at each node with the fault initial phase angle of 150 degrees as a different fault area judgment threshold value for judging a short-circuit fault area on the feeder line.
In this embodiment, the specific content of the wavelet energy spectrum value of the current obtained by performing wavelet energy spectrum transformation on the current signal in step S3 is as follows: taking the derivative function of the cubic B spline function as a wavelet mother function, and obtaining a dyadic wavelet transform formula of a discrete signal f (x) by recursion according to a Mallat algorithm as shown in a formula (1):
let E2jx (t) is the energy of the detail in the j-th scale, and the wavelet energy time spectrum of the signal is:
E2jx(t)＝|W2jx(t)|2(2) wherein j is 4.
The higher the decomposition scale of the wavelet energy spectrum is, the more obvious the singularity of the fault signal is, but the more complicated the calculation is, the wavelet energy spectrum transformation at the fourth scale is selected by the embodiment to analyze the short-circuit fault current waveform.
In this embodiment, the specific contents of the area where the microgrid protection system module determines whether the microgrid has a short-circuit fault and determines that the microgrid has the short-circuit fault are as follows: after the micro-grid protection system module obtains the current signal, detecting and updating zero-crossing point information of the current signal, namely a module Z, and simultaneously performing wavelet energy spectrum transformation on the current signal under a fourth scale to obtain a wavelet energy spectrum value of the current; then comparing the wavelet energy spectrum value of the current with a fault judgment threshold value, when the wavelet energy spectrum value of the current is smaller than the fault judgment threshold value, determining that no short-circuit fault occurs on a feeder line of the microgrid, and continuing to perform zero crossing point detection and wavelet energy spectrum transformation on the current; when the current wavelet energy spectrum value is larger than the fault judgment threshold value, the short-circuit fault is considered to occur on the feeder line of the microgrid, and if the feeder line is the first type of feeder line, the breaker on the feeder line is directly disconnected; if the feeder line is a second type feeder line, the microgrid protection system module needs to detect an initial phase angle of a short-circuit fault and the type of the short-circuit fault; after the initial phase angle and the fault type of the fault are determined, a proper fault area judgment threshold value can be selected, meanwhile, 1ms is delayed to detect a first peak value of a fault current wavelet energy spectrum waveform and carry out reduction, so that a reduced value when the initial phase angle of the fault is 150 degrees is obtained, the reduced value is compared with the fault area judgment threshold value, a threshold value interval is judged according to the fault area where the reduced value is located, the area where the short-circuit fault is located is judged, then a breaker of the corresponding area is disconnected, and therefore the short-circuit fault area is positioned and eliminated
The method is characterized in that a regression value obtained by actual detection and calculation at a detection point is compared with a fault area judgment threshold value, and a threshold value interval where the regression value is located is judged, so that the area where the fault occurs is located.
In the present embodiment, the fault region determination threshold is each of the values of the first peak of the wavelet energy spectrum waveform of the fault current at the time of occurrence of the short-circuit fault at each node known in the line. And comparing the actual detection and calculation values of the detection points during the fault with the fault area judgment threshold value, and positioning the position area of the fault point by judging the threshold value section in which the detection points are positioned.
In this embodiment, the calculation method of the reduced value in step S6 is as follows: with E4max1Expressed as: defining a new parameter E4 'as a first peak value of a wavelet energy spectrum E4 waveform obtained after fourth scale transformation of fault current after short-circuit fault occurs'max1＝Ke/E4max1In which K iseIs a magnification factor; at fault initial phase angle thetacE4 'at 150 DEG'max1Is a reference value KbOrder of reduced value E4 "max1＝KrKb. Wherein
In this embodiment, the initial phase angle for detecting the short-circuit fault is referred to as a time difference between a time when the short-circuit fault occurs and a zero-crossing time of the current, that is, a ratio of the time difference to 10ms of the two is equal to a ratio of the initial phase angle of the fault to 180 degrees; judging the type of the short-circuit fault by detecting the occurrence of positive sequence, negative sequence and zero sequence components in the fault current; when the zero sequence component of the current is detected, the occurrence of the ground short-circuit fault is considered, when the zero sequence component without the current and the negative sequence component are detected, the occurrence of the two-phase short-circuit fault is considered, and when only the positive sequence component of the current is detected, the occurrence of the three-phase short-circuit fault is considered.
The detection and positioning technology of the short-circuit fault of the microgrid is one of key technologies for limiting the development of practical engineering of the microgrid. By utilizing the advantages of wavelet analysis in the aspect of signal change trend extraction, the wavelet energy spectrum algorithm can be applied to early detection and positioning of the short-circuit fault of the microgrid. The method is a method adopted by most of the existing microgrid short-circuit fault detection methods, and comprises the steps of setting a fault judgment threshold in a protection system, comparing a function value detected by the protection system in real time with the fault judgment threshold, and making a reasonable protection decision. Therefore, the embodiment selects the appropriate wavelet energy spectrum value of the current as the fault determination threshold value to determine whether the short-circuit fault occurs in the microgrid, so as to achieve early detection of the short-circuit fault of the microgrid. The first peak value of the wavelet energy spectrum waveform of the fault current measured at the detection point of the microgrid is related to the distance from the short-circuit point to the detection point, so that the positioning of the short-circuit fault area of the microgrid is realized by using the size of the first peak value of the wavelet energy spectrum waveform of the fault current measured at the detection point.
Preferably, in the embodiment, the wavelet energy spectrum algorithm is used for analyzing the current at the detection point of the microgrid, and the short-circuit fault characteristic quantity is extracted, so that the early detection of the short-circuit fault of the microgrid in the grid-connected mode is realized. And the relation between the first peak value of the wavelet energy spectrum waveform of the fault current and the distance from the short-circuit point to the detection point is utilized to realize the quick positioning of the short-circuit fault area of the micro-grid.
Preferably, in this embodiment, the module 1 in fig. 1 is a measurement module. The output of the module 1 is a current signal of the microgrid under various operating states, and the signal is transmitted to the microgrid protection system module 2 after being transmitted by the communication module C.
(1) Measurement module (module 1): for different microgrid structures, the selection of detection points is different, and further the short-circuit fault detection and positioning methods are also different. The embodiment is applicable to a radiation type alternating current microgrid. For a radiating type alternating current micro-grid, the feeders can be divided into a first type feeder and a second type feeder according to the number of nodes on each feeder. The first feeder line only contains one node, so for the first feeder line protection system, only the short-circuit fault needs to be detected, and then the short-circuit device is disconnected to eliminate the short-circuit fault. The second feeder line contains two or more nodes, so that the fault area needs to be positioned for the second feeder line. In the embodiment, each feeder line of the micro-grid is used as a minimum unit, and the detection points are arranged at each feeder lineThe connection point of the feeder line and the common bus. And the measuring module at the detection point collects and processes the current signal. Through signal acquisition devices with current sensors as cores, i.e. modules M1-MnCollecting current signals, wherein the collected current signals need to pass through a signal processing device, namely a module N1～NnThe current signal is subjected to scaling, biasing, current-voltage signal conversion and the like, and then can be supplied to the protection module for use. The current signal collected by the measuring module is transmitted to the protection module through the communication module C.
Preferably, in the present embodiment, the signal processing apparatus is configured by using a conventional general voltage generation and bias circuit. Only the current signal is converted into a voltage signal without noise reduction processing. Because the single chip microcomputer in the protection system can only collect voltage signals of 0 to + 3.3V.
Preferably, in this embodiment, the module of the microgrid protection system is a dsPIC33EP256MC502 single chip microcomputer.
(2) Protection system module (module 2): according to research, in the embodiment, the maximum value of the current wavelet energy spectrum value obtained at the detection point when the single-phase short-circuit fault occurs at the tail end of the feeder line and the initial fault phase angle is 150 degrees is taken as the upper limit, the maximum value of the current wavelet energy spectrum value obtained at the detection point when the load on the feeder line is put in or cut off is taken as the lower limit, and a proper fault judgment threshold value is selected between the two upper and lower limits to judge whether the short-circuit fault occurs on the feeder line. The second feeder line has two or more nodes, so that the second feeder line can be divided into different areas according to different node positions. In the embodiment, the reduced value of the first peak value of the wavelet energy spectrum waveform of the short-circuit fault current at each node with the fault initial phase angle of 150 degrees is used as a different fault area determination threshold value for determining a short-circuit fault area on a feeder line. The protection system realizes early detection of the short-circuit fault of the microgrid and positioning of the fault area through the fault judgment threshold and the fault area judgment threshold.
After the protection system module obtains the current signal, the zero-crossing point information of the current signal is detected and updated, namely shown by a module Z, and simultaneously the wavelet energy spectrum value of the current, namely shown by a module E, is obtained by performing wavelet energy spectrum transformation on the current signal under a fourth scale. Then comparing the wavelet energy spectrum value of the current with a fault judgment threshold value, namely as shown in a module D, when the wavelet energy spectrum value of the current is smaller than the fault judgment threshold value, determining that no short-circuit fault occurs on a feeder line of the microgrid, and returning to the previous step to continue carrying out zero crossing point detection and wavelet energy spectrum transformation on the current; and when the current wavelet energy spectrum value is larger than the fault judgment threshold value, the short-circuit fault is considered to occur on the feeder line of the microgrid. If the feeder is the first type feeder, the breaker on the feeder, namely the module R, is directly disconnected at the moment. If the feeder line is the second type feeder line, the protection system needs to detect the initial phase angle of the short-circuit fault, namely the phase angle shown by the module P, and the type of the short-circuit fault, namely the type shown by the module L. The initial phase angle for detecting a short-circuit fault is referenced to the time difference between the moment when the short-circuit fault occurs and the zero-crossing moment of the current, i.e. the ratio of the time difference to 10ms equals the ratio of the initial phase angle of the fault to 180 degrees. The present embodiment determines the type of the short-circuit fault by detecting the occurrence of the positive sequence, negative sequence, and zero sequence components in the fault current. When the zero sequence component of the current is detected, the occurrence of the ground short-circuit fault is considered, when the zero sequence component without the current and the negative sequence component are detected, the occurrence of the two-phase short-circuit fault is considered, and when only the positive sequence component of the current is detected, the occurrence of the three-phase short-circuit fault is considered. After the initial phase angle and the fault type of the fault are determined, a suitable fault region decision threshold, that is, the first peak of the wavelet energy spectrum waveform of the fault current considered to occur in the embodiment shown in block X, is selected within 1ms after the wavelet energy spectrum value of the current is greater than the fault decision threshold. Therefore, when a proper fault area judgment threshold value is selected, 1ms is delayed to detect the first peak value of the fault current wavelet energy spectrum waveform and carry out reduction, and the reduction value when the initial fault phase angle is 150 degrees is obtained, namely the reduction value is shown in a module Y. And then comparing the reduced value with a fault area judgment threshold value, namely as shown in a module W, judging the area where the short-circuit fault is located according to the magnitude relation between the reduced value and the fault area judgment threshold value, and then disconnecting the breaker of the corresponding area, namely as shown in a module R, so that the short-circuit fault area can be positioned and eliminated.
Preferably, in this embodiment, the module Z: the current zero crossing point detection module is a current zero crossing point detection general circuit. And a module E: and a current wavelet energy spectrum value calculation module. A module D: and the current wavelet energy spectrum value is compared with a fault judgment threshold value. A module R: a circuit breaker. And a module P: and the short-circuit fault initial phase angle detection module. A module L: and a short-circuit fault type detection module. A module X: a failure zone determination threshold module. And a module Y: and (4) reducing to a reduced value when the initial phase angle of the fault is 150 degrees. A module W: and a module for comparing the reduced value (module Y) with the fault area judgment threshold value.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (7)
1. A detection and positioning system for short-circuit faults of an alternating-current micro-grid in a grid-connected mode is characterized in that: providing a radiation type alternating current microgrid, which comprises a measuring module, a communication module and a microgrid protection system module; the measuring module comprises a plurality of signal acquisition devices and a plurality of signal processing devices; the measurement module is connected with the communication module, the communication module is connected with the microgrid protection system module, and the communication module is used for transmitting the current signals collected and processed by the measurement module to the microgrid protection system module through the communication module, judging whether the microgrid has a short-circuit fault or not through the microgrid protection system module and judging an area where the microgrid has the short-circuit fault; every signal acquisition device all is connected with a signal processing device for the current signal transmission who gathers signal acquisition device arrives signal processing device handles, and through with the communication module that signal processing device connects arrives the current signal transmission after handling little electric wire netting protection system module, little electric wire netting protection system module carries out wavelet energy spectrum transform to current signal, judges little electric wire netting whether to take place short circuit fault through the wavelet energy spectrum value of comparison current and the big or small relation of fault detection threshold value, when little electric wire netting takes place short circuit fault, little electric wire netting protection system module judges the area that little electric wire netting took place short circuit fault through the first peak value of fault current wavelet energy spectrum waveform.
2. The system for detecting and positioning the short-circuit fault of the alternating-current micro-grid in the grid-connected mode according to claim 1, wherein the system comprises: the signal acquisition device adopts a current sensor.
3. An operating method of the system for detecting and positioning the short-circuit fault of the alternating-current micro-grid in the grid-connected mode according to any one of claims 1 to 2, characterized in that: the method comprises the following steps:
step S1: dividing the feeder into a first type feeder and a second type feeder according to the number of nodes on each feeder of the radiation type alternating current micro-grid; the first feeder line only contains one node, and the second feeder line contains two or more nodes;
step S2: the method comprises the steps that each feeder line is taken as a minimum unit of the micro-grid, a detection point is arranged at the connection point of each feeder line and a common bus, a signal acquisition device at the detection point acquires a current signal, the acquired current signal is transmitted to a signal processing device, the current signal is converted into an acquisition signal required by a micro-grid protection system module, and then the acquisition signal is transmitted to the micro-grid protection system module through a communication module;
step S3: performing wavelet energy spectrum transformation on the current signal through the microgrid protection system module to obtain a wavelet energy spectrum value of the current;
step S4: the method comprises the steps that the maximum value of a current wavelet energy spectrum value obtained at a detection point when a single-phase short-circuit fault occurs at the tail end of a feeder line and the initial phase angle of the fault is 150 degrees is used as an upper limit, the maximum value of the current wavelet energy spectrum value obtained at the detection point when a load on the feeder line is put in or cut off is used as a lower limit, and a proper fault judgment threshold value is selected between the upper limit and the lower limit to judge whether the short-circuit fault occurs on the feeder line;
step S5: judging whether the microgrid has a short-circuit fault, if the wavelet energy spectrum value of the current is smaller than a fault judgment threshold value, not generating the short-circuit fault, otherwise, executing a step S6;
step S6: when the micro-grid has a short-circuit fault, if the feeder line is a first type feeder line, the circuit breaker on the feeder line is directly disconnected; if the feeder line is a second type feeder line, the second type feeder line comprises two or more nodes, so that the second type feeder line is divided into different areas according to different node positions; and taking the reduced value of the first peak value of the wavelet energy spectrum waveform of the short-circuit fault current at each node with the fault initial phase angle of 150 degrees as a different fault area judgment threshold value for judging a short-circuit fault area on the feeder line.
4. The working method of the system for detecting and positioning the short-circuit fault of the alternating-current micro-grid in the grid-connected mode according to claim 3, characterized in that: the specific content of the wavelet energy spectrum value of the current obtained by performing wavelet energy spectrum transformation on the current signal in step S3 is as follows: taking the derivative function of the cubic B spline function as a wavelet mother function, and obtaining a dyadic wavelet transform formula of a discrete signal f (x) by recursion according to a Mallat algorithm as shown in a formula (1):
order to
The energy of the detail in the j-th scale is obtained, and the wavelet energy time spectrum of the signal is:
5. The working method of the system for detecting and positioning the short-circuit fault of the alternating-current micro-grid in the grid-connected mode according to claim 3, characterized in that: the specific contents of the micro-grid protection system module for judging whether the micro-grid has the short-circuit fault and judging the area where the micro-grid has the short-circuit fault are as follows: after the micro-grid protection system module obtains the current signal, detecting and updating zero-crossing point information of the current signal, and simultaneously performing wavelet energy spectrum transformation on the current signal under a fourth scale to obtain a wavelet energy spectrum value of the current; then comparing the wavelet energy spectrum value of the current with a fault judgment threshold value, when the wavelet energy spectrum value of the current is smaller than the fault judgment threshold value, determining that no short-circuit fault occurs on a feeder line of the microgrid, and continuing to perform zero crossing point detection and wavelet energy spectrum transformation on the current; when the current wavelet energy spectrum value is larger than the fault judgment threshold value, the short-circuit fault is considered to occur on the feeder line of the microgrid, and if the feeder line is the first type of feeder line, the breaker on the feeder line is directly disconnected; if the feeder line is a second type feeder line, the microgrid protection system module needs to detect an initial phase angle of a short-circuit fault and the type of the short-circuit fault; after the initial fault phase angle and the fault type are determined, a proper fault area judgment threshold value can be selected, meanwhile, 1ms is delayed to detect the first peak value of the wavelet energy spectrum waveform of the fault current and carry out reduction, so that a reduced value when the initial fault phase angle is 150 degrees is obtained, then the reduced value is compared with the fault area judgment threshold value, a threshold value interval is judged according to the fault area where the reduced value is located, the area where the short-circuit fault is located is judged, then the breaker of the corresponding area is disconnected, and therefore the short-circuit fault area is positioned and eliminated.
6. The working method of the system for detecting and positioning the short-circuit fault of the alternating-current micro-grid in the grid-connected mode according to claim 3, characterized in that: the initial phase angle for detecting the short-circuit fault is referenced by the time difference between the occurrence time of the short-circuit fault and the zero-crossing time of the current, namely the ratio of the time difference of the two to 10ms is equal to the ratio of the initial phase angle of the fault to 180 degrees; judging the type of the short-circuit fault by detecting the occurrence of positive sequence, negative sequence and zero sequence components in the fault current; when the zero sequence component of the current is detected, the occurrence of the ground short-circuit fault is considered, when the zero sequence component without the current and the negative sequence component are detected, the occurrence of the two-phase short-circuit fault is considered, and when only the positive sequence component of the current is detected, the occurrence of the three-phase short-circuit fault is considered.
7. The working method of the system for detecting and positioning the short-circuit fault of the alternating-current micro-grid in the grid-connected mode according to claim 3, characterized in that: the calculation method of the reduced value in step S6 is: with E4max1Expressed as: defining a new parameter E4 'as a first peak value of a wavelet energy spectrum E4 waveform obtained after fourth scale transformation of fault current after short-circuit fault occurs'max1＝Ke/E4max1In which K iseIs a magnification factor; at fault initial phase angle thetacE4 'at 150 DEG'max1Is a reference value KbLet us calculate the value E4max1＝KrKb(ii) a Wherein
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