CN113740672A - Method for detecting arc fault of photovoltaic module array based on K-line graph - Google Patents
Method for detecting arc fault of photovoltaic module array based on K-line graph Download PDFInfo
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- CN113740672A CN113740672A CN202110795201.5A CN202110795201A CN113740672A CN 113740672 A CN113740672 A CN 113740672A CN 202110795201 A CN202110795201 A CN 202110795201A CN 113740672 A CN113740672 A CN 113740672A
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- 238000001514 detection method Methods 0.000 claims abstract description 10
- 238000005070 sampling Methods 0.000 claims abstract description 6
- 230000012447 hatching Effects 0.000 claims description 6
- 239000007787 solid Substances 0.000 claims description 6
- 230000000007 visual effect Effects 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 4
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/129—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of components or parts made of semiconducting materials; of LV components or parts
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
- H02S50/10—Testing of PV devices, e.g. of PV modules or single PV cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
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Abstract
The application provides a photovoltaic module array arc fault detection method based on a K line graph, which comprises the following steps: step 1: sampling and detecting initial current data; step 2: grouping the sampled initial current data, and constructing a K line graph according to the initial value, the maximum value, the minimum value and the end value of the current in each group of current data; and step 3: and calculating the length of each group of K lines, and judging whether an arc fault occurs according to the length of the K lines. According to the photovoltaic module array arc fault detection method based on the K line graph, the K line graph is drawn by grouping the initial current data, and simple and visual photovoltaic module array arc fault detection is achieved.
Description
Technical Field
The invention belongs to the field of power system fault detection, and particularly relates to a photovoltaic module array arc fault detection method based on a K-line graph.
Background
The photovoltaic power generation system comprises a large number of photovoltaic modules, and the conditions of module aging, line aging, connection looseness and the like can occur in long-term operation, so that an arc fault occurs in a photovoltaic module array. The arc fault may be a series type or a parallel type arc fault. Series type arc fault occurrences are typically generated by a broken wire, the ends of which are close enough to generate an arc; or a relatively poor electrical connection. Parallel type arc faults occur between conductors of different potentials, including for example between a power conductor and ground. Unlike parallel arc faults, series arc faults generally do not produce an increase in current as the fault is connected in series with the load. In fact, series arc faults may result in a slight reduction in load current and are not detected by the normal overload and overcurrent protection of conventional protection devices. The ac fault arc current waveform has the following characteristics in the time domain: because the fault arc is similar to a resistive load, the current amplitude is slightly reduced compared with normal operation; there is a "flat shoulder" of random length near the current zero crossing; the current waveform change rate is increased, and sudden changes with random magnitude and time exist; the symmetry of the waveform is broken. According to the time domain characteristics of the fault arc, most of the existing fault arc detection methods and protection circuits use the 'flat shoulder' time, the average value, the maximum value, the minimum value and the variable quantity of the current change rate of adjacent half-cycle current exceeding the threshold value as the composite criterion for judging the fault arc. The method needs more criteria, is easily interfered by power supply and load change of the power electronic switch, and has higher misjudgment rate. On the other hand, the method for analyzing the frequency domain characteristics of the fault arc based on discrete Fourier transform, wavelet transform and the like has good effect, but has high requirements on hardware circuits of the protection device, and is difficult to popularize and use in a large range.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a photovoltaic module array arc fault detection method based on a K-line diagram.
The embodiment of the application discloses a method for detecting arc faults of a photovoltaic module array based on a K-line graph, which comprises the following steps:
step 1: sampling and detecting initial current data;
step 2: grouping the sampled initial current data, and constructing a K line graph according to the initial value, the maximum value, the minimum value and the end value of the current in each group of current data;
and step 3: and calculating the length of each group of K lines, and judging whether an arc fault occurs according to the length of the K lines.
Preferably, the initial value is replaced by the mean of the first n bits of each group, and the end value is replaced by the mean of the last n bits of the sampled data of each group;
preferably, the bottom of each group of K-line graph entities is the smaller of the initial value and the end value, the top of each group of K-line graph entities is the larger of the initial value and the end value, the top of the upper hatched line is the maximum value, the bottom of the lower hatched line is the minimum value, the solid part of each group of K-line graph entities represents that the end value is larger than the initial value, and the solid part of each group of K-line graph entities represents that the end value is smaller than the initial value;
preferably, step 2 further comprises: constructing a maximum value fitting curve of the collected current according to the top ends of the upper hatching lines of all the grouped K line graphs, constructing a minimum value fitting curve of the collected current according to the bottom ends of the lower hatching lines of all the grouped K line graphs, constructing an initial value fitting curve of the collected current according to the initial values of all the grouped K line graphs, and constructing an end value fitting curve of the collected current according to the end values of all the grouped K line graphs;
preferably, step 3 comprises: and the length of the K line is an absolute value of the difference between the initial value and the ending value of each group of data, if the length of the K line is greater than a threshold value, the arc fault is judged to be generated, otherwise, the arc fault is not generated.
The beneficial effect of this application is: according to the photovoltaic module array arc fault detection method based on the K line graph, the K line graph is drawn by grouping the initial current data, and simple and visual photovoltaic module array arc fault detection is achieved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic flow chart of a method for detecting an arc fault of a photovoltaic module array based on a K-line graph according to an embodiment of the present application.
FIG. 2 is a diagram of a loop current over time when an arc occurs in a conventional DC device according to an embodiment of the present disclosure;
FIG. 3 is a graph of loop current over time during arcing in a photovoltaic array provided by an embodiment of the present application;
FIG. 4 is a K-line graph of a loop current when an arc occurs in a conventional DC device according to an embodiment of the present disclosure;
fig. 5 is a K-line graph of a loop current when an arc occurs in a photovoltaic array according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
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 invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
Please refer to fig. 1, a schematic flow chart of a method for detecting an arc fault of a photovoltaic module array based on a K-line diagram according to an embodiment of the present application includes:
step 1: sampling and detecting initial current data;
step 2: grouping the sampled initial current data, and constructing a K line graph according to the initial value, the maximum value, the minimum value and the end value of the current in each group of current data;
further, the initial value of the current of each group is replaced by the mean value of the first n bits of each group, and the end value is replaced by the mean value of the last n bits of the sampled data of each group.
Further, the bottom of each group of K-line graph entities is the smaller of the initial value and the end value, the top of each group of K-line graph entities is the larger of the initial value and the end value, the top of the upper hatched line is the maximum value, the bottom of the lower hatched line is the minimum value, the solid part of each group of K-line graph entities represents that the end value is larger than the initial value, and the solid part of each group of K-line graph entities represents that the end value is smaller than the initial value.
Further, in order to more intuitively represent the overall trend of the initial current data, a maximum value fitting curve of the collected current is constructed according to the top ends of the upper hatching lines of all the grouped K line graphs, a minimum value fitting curve of the collected current is constructed according to the bottom ends of the lower hatching lines of all the grouped K line graphs, an initial value fitting curve of the collected current is constructed according to the initial values of all the grouped K line graphs, and an end value fitting curve of the collected current is constructed according to the end values of all the grouped K line graphs.
And step 3: and calculating the length of each group of K lines, and judging whether an arc fault occurs according to the length of the K lines.
Further, the length of the K line is the height of the solid part in each group of K line graphs, that is, the absolute value of the difference between the initial value and the ending value of each group of current data. And judging whether an arc fault occurs according to the length of the K line and the difference value of the initial value and the ending value of the current, if the length of the K line is greater than a threshold value, judging that the arc fault occurs, otherwise, not generating the arc fault.
To further explain the principles of the present invention, the present application also provides an example of the invention in connection with a specific application of the present system.
FIG. 2 is a diagram of a loop current over time when an arc occurs in a conventional DC device according to an embodiment of the present disclosure; fig. 3 is a graph of a loop current over time when an arc occurs in a photovoltaic array according to an embodiment of the present disclosure. Taking the collection of the string branch current of the photovoltaic module for 5s as an example, the sampling rate is 200kHz, a time window is selected to be 0.165s, the waveform of 5s is divided into 30 groups of K lines, n =100 is selected, and the corresponding time is 0.5ms, as shown in fig. 4 and 5, the K line graph of each time window includes information of an initial value, a maximum value, a minimum value and an end value of the waveform in 0.165 s. The length (difference between the initial value and the end value) of each K line is calculated and is represented by L, if L is larger than a threshold value a, the arc is judged to be generated, and if the L is false, the arc is judged to be absent. The current has small fluctuation under the normal condition, the fluctuation is large and the decline is obvious when the arc fault occurs, the larger the initial current is, the larger the decline amplitude is, the current decline amplitude is larger than a certain value through experimental data analysis, and the current fluctuation is normally far smaller than the value, and the current is named as a threshold value a, so that whether the arc is generated is judged by using L larger than the threshold value a.
In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. The meaning of "plurality" is two or more unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (5)
1. A photovoltaic module array arc fault detection method based on a K-line graph is characterized by comprising the following steps:
step 1: sampling and detecting initial current data;
step 2: grouping the sampled initial current data, and constructing a K line graph according to the initial value, the maximum value, the minimum value and the end value of the current in each group of current data;
and step 3: and calculating the length of each group of K lines, and judging whether an arc fault occurs according to the length of the K lines.
2. The method for detecting the arc fault of the photovoltaic module array based on the K-line graph is characterized in that the initial value is replaced by the mean value of the first n bits of each group, and the end value is replaced by the mean value of the last n bits of sampling data of each group.
3. The method for detecting the arc fault of the photovoltaic module array based on the K-line graph is characterized in that the step 2 comprises the following steps: the bottom of each group of K-line graph entities is the smaller of the initial value and the ending value, the top of each group of K-line graph entities is the larger of the initial value and the ending value, the top of the upper hatched line is the maximum value, the bottom of the lower hatched line is the minimum value, the solid part of each group of K-line graph entities represents that the ending value is greater than the initial value, and the hollow part of each group of K-line graph entities represents that the ending value is less than the initial value.
4. The method for detecting the arc fault of the photovoltaic module array based on the K-line graph is characterized in that the step 2 further comprises the following steps: and constructing a maximum value fitting curve of the collected current according to the top ends of the upper hatching lines of all the grouped K line graphs, constructing a minimum value fitting curve of the collected current according to the bottom ends of the lower hatching lines of all the grouped K line graphs, constructing an initial value fitting curve of the collected current according to the initial values of all the grouped K line graphs, and constructing an end value fitting curve of the collected current according to the end values of all the grouped K line graphs.
5. The method for detecting the arc fault of the photovoltaic module array based on the K-line graph is characterized in that the step 3 comprises the following steps: and the length of the K line is an absolute value of the difference between the initial value and the ending value of each group of data, if the length of the K line is greater than a threshold value, the arc fault is judged to be generated, otherwise, the arc fault is not generated.
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