CN117277960A - Method and device for detecting direct-current side fault arc of distributed photovoltaic module - Google Patents
Method and device for detecting direct-current side fault arc of distributed photovoltaic module Download PDFInfo
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Abstract
The invention discloses a method and a device for detecting a direct-current side fault arc of a distributed photovoltaic module, and belongs to the technical field of photovoltaic power generation and operation and maintenance. The invention realizes the judgment of the arcing phenomenon through the frequency domain characteristic and the time domain characteristic of the current signal, and compared with the prior art, the invention realizes the judgment of the arcing phenomenon through the current high-frequency noise, and improves the accuracy of the judgment of the arcing phenomenon. The current signal is divided into different current gears, and the arc discharge phenomenon is judged according to the different current gears, so that the accuracy of arc discharge phenomenon judgment is further improved.
Description
Technical Field
The invention relates to the technical field of photovoltaic power generation and operation and maintenance, in particular to a method and a device for detecting a direct-current side fault arc of a distributed photovoltaic module.
Background
In a photovoltaic power generation system, direct current arc discharge can occur due to poor contact between wires or aging of wires, and the like, so that a fire disaster is very easy to occur in a photovoltaic power station after long-time arc discharge, and casualties and property loss are caused.
In the prior art, the arc discharge detection equipment is usually adopted manually to detect the position of the line where arc discharge is easy to occur, and the working principle of the detection equipment is as follows: and judging whether an arc discharge phenomenon occurs or not by monitoring current high-frequency noise in real time.
However, if the arc discharge phenomenon occurs, the arc discharge phenomenon is determined only by current high-frequency noise, which may cause a misjudgment problem, thereby affecting the accuracy of the arc discharge phenomenon determination.
Disclosure of Invention
In order to solve the problems in the prior art, the embodiment of the invention provides a method and a device for detecting a direct-current side fault arc of a distributed photovoltaic module. The technical scheme is as follows:
in a first aspect, a method for detecting a fault arc on a direct current side of a distributed photovoltaic module is provided, which is characterized by comprising the following steps:
dividing a current signal into different current gears according to the current magnitude;
detecting whether the standard deviation, the signal peak value and the signal change rate of a current signal meet a time domain detection threshold value of a current gear, if so, judging that the time domain arcing is met;
performing fast Fourier transform on the circuit signal to obtain a plurality of harmonic values, judging whether the harmonic quantity meeting the frequency domain detection threshold value of the current gear in which the harmonic value is positioned in the plurality of harmonic values meets a quantity threshold value, if so, judging that the frequency domain arcing is met;
if the time domain arcing and the frequency domain arcing are simultaneously satisfied, determining that an arcing event occurs;
detecting the number of arcing events in a preset time after initial arcing, comparing the number with the preset number, judging that arcing faults occur if the number is larger than the preset number, and judging that accidental arcing occurs if the number is not larger than the preset number.
Optionally, the method further comprises:
and after 25s after the current signal is detected, continuing to execute the step of detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold values corresponding to the different gear currents.
Optionally, the method further comprises:
the different current gears are set to be large current (more than 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A).
Optionally, the method further comprises:
and setting the quantity threshold values corresponding to the different current gears.
Optionally, detecting the number of arcing events within a preset time after starting the arcing further includes:
if the arcing event is not detected within the preset time, resetting the number of the arcing events; and
and if the arcing fault is judged to occur, resetting the number of the arcing events.
In a second aspect, there is provided a distributed photovoltaic module dc side fault arc detection apparatus, the apparatus comprising:
the current signal acquisition module is used for dividing the current signal into different current gears according to the current magnitude;
the time domain detection module is used for detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold value of the current gear, and if so, judging that the time domain arcing is met;
the frequency domain detection module is used for carrying out fast Fourier transform on the circuit signal to obtain a plurality of harmonic values, judging whether the number of the harmonic waves meeting the frequency domain detection threshold value of the current gear in the plurality of harmonic values meets a number threshold value, and judging that the frequency domain arcing is met if the number of the harmonic waves meets the number threshold value;
the arcing fault judging module is used for judging that an arcing event occurs when the time domain arcing and the frequency domain arcing are simultaneously satisfied;
the arc discharge fault judging module is also used for detecting the number of arc discharge events in the preset time after the initial arc discharge, comparing the number with the preset number, judging that the arc discharge fault occurs if the number is larger than the preset number, and judging that the arc discharge fault occurs accidentally if the number is not larger than the preset number.
Optionally, the current signal acquisition module is further configured to:
and after 25s after the current signal is detected, continuing to execute the step of detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold values corresponding to the different gear currents.
Optionally, the current signal acquisition module is further configured to:
the different current gears are set to be large current (more than 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A).
Optionally, the frequency domain detection module is further configured to:
and setting the quantity threshold values corresponding to the different current gears.
Optionally, the arc discharge fault judging module is further configured to:
if the arcing event is not detected within the preset time, resetting the number of the arcing events; and
and if the arcing fault is judged to occur, resetting the number of the arcing events.
The technical scheme provided by the invention has at least the following beneficial effects:
1. the arcing phenomenon judgment is realized through the frequency domain characteristics and the time domain characteristics of the current signals, and compared with the arcing phenomenon judgment realized through current high-frequency noise in the prior art, the accuracy of the arcing phenomenon judgment is improved.
2. The current signal is divided into different current gears, and the arc discharge phenomenon is judged according to the different current gears, so that the accuracy of arc discharge phenomenon judgment is further improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic flow chart of a method for detecting a fault arc on a direct current side of a distributed photovoltaic module according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a harmonic arc discharge misjudgment provided by an embodiment of the present invention;
FIG. 3 is a schematic drawing of an arc discharge fault provided by an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a dc side fault arc detection device for a distributed photovoltaic module according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1, a method for detecting a fault arc on a direct current side of a distributed photovoltaic module is provided, which includes the following steps:
101. dividing a current signal into different current gears according to the current magnitude;
specifically, the current signal of the direct current side of the photovoltaic system is collected, and the signal collection module is located between the junction box and the inverter of the direct current side of the photovoltaic system.
Preferably, in practical application, different current steps are set to be large current (above 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A), and the setting of the current steps is merely exemplary, and the embodiment of the present invention does not limit the specific current steps.
102. Detecting whether the standard deviation, the signal peak value and the signal change rate of a current signal meet a time domain detection threshold value of a current gear, if so, judging that the time domain arcing is met;
specifically, the standard deviation of the current signal is the difference between the arithmetic mean value of the signal at each moment in a certain period of time and the current value corresponding to the sampling point, taking the square root, accumulating all the sampling points, dividing the sampling points after opening the root, and expressing the result as
In the aboveIs the average of the signal; sigma is the standard deviation of the signal, N is the sampling point number in a certain time, and in the method, the sampling point number is 2048; i.e r Refers to the ith value of the signal;
the signal peak of the current signal refers to the instantaneous value of the maximum signal within a certain time, and is specifically expressed as
I max ＝max{i r } (3)
In which I max Is the signal peak;
the rate of change of the current signal refers to the ratio of the amount of change of the current signal at two times to the time interval of the two times, specifically expressed as
Wherein V is the rate of change of the signal, i r+1 、i r For the (r+1) th and (r) th sequence values in the signal, and t r+1 t r Is the time value corresponding to the former two.
Corresponding standard deviation threshold values, signal peak value threshold values and change rate threshold values are respectively set for different current gears; the high current, the medium low current and the low current respectively have corresponding standard deviation threshold values, signal peak value threshold values and change rate threshold values;
comparing the standard deviation with a standard deviation threshold;
comparing the obtained signal peak value with a signal peak value threshold value;
comparing the obtained change rate with a change rate threshold;
and if the standard deviation is greater than or equal to the standard deviation threshold value, the signal peak value is greater than or equal to the signal peak value threshold value and the signal peak value is greater than or equal to the signal peak value threshold value, judging that the time domain arcing is satisfied.
The standard deviation threshold, the signal peak threshold, and the change rate threshold in the above process may be obtained by:
for standard deviation:
taking the average value of the maximum value of the standard deviation of the normal state and the minimum value of the standard deviation of the fault arc state as a standard deviation threshold; the standard deviation threshold may be determined by obtaining the ratio of the standard deviations in the two states, and the method of determining the standard deviation threshold by obtaining the ratio of the standard deviations in the two states is not limited in the embodiment of the present invention.
Similarly, the signal peak threshold and the rate of change threshold can be obtained in the same manner as described above.
In practical application, the current signal is processed, and finally, the standard deviation, the signal peak value and the signal change rate of the representation current state are obtained. Firstly, characteristic values of four normal states and fault arc states are listed, a table is drawn for comparison, and standard deviation, signal peak value and signal change rate obtained by series fault arc current are compared with the standard deviation, signal peak value and signal change rate of normal current, so that the amplitude is greatly increased, and is tens of times or even tens of times of the normal current, and the normal current can be obviously distinguished. The characteristic values in the two states differ by several times to tens of times, so that whether an arc event occurs can be accurately represented through the standard deviation threshold value, the signal peak value threshold value and the change rate threshold value provided by the embodiment of the invention;
in addition, the arc burning process has strong randomness, and the current is disordered and stable, so that the result of the characteristic value has large fluctuation. In order to prove that the fault arc detection algorithm provided by the invention has no contingency, a large number of experiments are respectively carried out under the conditions of small current and large current to obtain standard deviation, signal peak value and signal change rate, under the normal state, the fluctuation range of the standard deviation, the signal peak value and the signal change rate is small, and under the fault arc state, the fluctuation range of the standard deviation, the signal peak value and the signal change rate is large, but the characteristic values under the two states are not crossed and have large intervals, and further, the standard deviation threshold value, the signal peak value threshold value and the change rate threshold value provided by the embodiment of the invention can accurately represent whether an arc event occurs or not; thereby improving the accuracy of arc event detection.
When arc discharge occurs, the arc current is continuously changed in the arc combustion process, the current value is in a descending trend, and the current amplitude is changed drastically in a short time, so that the current amplitude is an important reference for judging whether arc discharge occurs or not, and the arc event is detected based on the standard deviation of the current signal, the current signal peak value and the current signal change rate, so that the accuracy of arc event detection can be improved.
103. Performing fast Fourier transform on the circuit signal to obtain multiple harmonic values, judging whether the harmonic quantity meeting the frequency domain detection threshold value of the current gear in the multiple harmonic values meets the quantity threshold value, if so, judging that the frequency domain arcing is met;
specifically, the collected real-time current signal is reserved by a hardware filtering amplifying circuit to be 40kHz-100kHz current signal, and the current signal is converted into a frequency domain through windowing Fourier transformation to obtain a plurality of harmonic values. The multiple harmonic values of the embodiment of the invention are 5 th harmonic values, namely a minimum first harmonic value, a minimum second harmonic value, a minimum third harmonic value, a minimum fourth harmonic value and a minimum fifth harmonic value;
it should be noted that the number threshold corresponding to different current gear is also set, specifically:
the minimum first harmonic value, the minimum second harmonic value, the minimum third harmonic value, the minimum fourth harmonic value and the minimum fifth harmonic value are not required to be all in the threshold range, and the number of the required harmonic waves meeting the threshold is also different according to different signal current gears; specifically, in the high-current (above 8A) gear, if any four of the minimum first harmonic value, the minimum second harmonic value, the minimum third harmonic value, the minimum fourth harmonic value, and the minimum fifth harmonic value exceeds a current preset threshold, it is determined that an arc discharge event has occurred; and if any three of the minimum first harmonic value, the minimum second harmonic value, the minimum third harmonic value, the minimum fourth harmonic value and the minimum fifth harmonic value in the medium large current (4A-8A) gear, the medium small current (2.5A-4A) gear and the small current (0.5A-2.5A) gear exceed the current preset threshold value, determining that an arc discharge event occurs.
104. If the time domain arcing and the frequency domain arcing are simultaneously satisfied, determining that an arcing event occurs;
105. detecting the number of arcing events in a preset time after initial arcing, comparing the number with the preset number, judging that arcing faults occur if the number is larger than the preset number, and judging that accidental arcing occurs if the number is not larger than the preset number.
Current harmonic interference or very short duration arcing events may occur due to continuous long-term operation of the photovoltaic power generation system. As shown in fig. 2, when the harmonic interference exceeds the detection set threshold value at the time t2 to t3, it is determined as an arcing event, but the harmonic interference and other interference do not affect the photovoltaic power generation system, so an arcing fault determination module is added. The principle of the arc discharge fault judging module is shown in fig. 3, wherein the arc discharge faults mainly detected are divided into accidental arc discharge and arc discharge faults, the method is that the number of arc discharge events in a fixed short time after initial arc discharge is detected is compared with a preset number of times, for example, the time t0 is the initial arc discharge event P1, the number of arc discharge events detected in the time t0-t1 is compared with a preset value of the number of arc discharge events, and when the number of arc discharge events is greater than or equal to the preset value, the arc discharge faults are judged and the alarm is given; and when the number of arc discharge events is smaller than a preset value, judging that the arc discharge happens.
Optionally, the method further comprises:
after the current signal is detected for 25 seconds, the step of detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold corresponding to different gear currents is continuously executed, so that erroneous judgment is avoided.
Optionally, detecting the number of arcing events within a preset time after starting the arcing further includes:
if the arcing event is not detected within the preset time, resetting the number of arcing events; and if the arcing fault is judged to occur, resetting the number of arcing events.
Referring to fig. 4, there is provided a distributed photovoltaic module dc side fault arc detection apparatus, the apparatus comprising:
the current signal acquisition module is used for dividing the current signal into different current gears according to the current magnitude;
the time domain detection module is used for detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold value of the current gear, and if so, judging that the time domain arcing is met;
the frequency domain detection module is used for carrying out fast Fourier transform on the circuit signal to obtain a plurality of harmonic values, judging whether the number of the harmonic waves meeting the frequency domain detection threshold value of the current gear in the plurality of harmonic values meets a number threshold value, and if so, judging that the frequency domain arcing is met;
the arcing fault judging module is used for judging that an arcing event occurs when the time domain arcing and the frequency domain arcing are simultaneously satisfied;
the arc discharge fault judging module is also used for detecting the number of arc discharge events in the preset time after the initial arc discharge, comparing the number with the preset number, judging that the arc discharge fault occurs if the number is larger than the preset number, and judging that the arc discharge fault occurs accidentally if the number is not larger than the preset number.
Optionally, the current signal acquisition module is further configured to:
and after 25s after the current signal is detected, continuing to execute the step of detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold corresponding to different gear currents.
Optionally, the current signal acquisition module is further configured to:
different current gears are set to be large current (more than 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A).
Optionally, the frequency domain detection module is further configured to:
and setting the quantity threshold values corresponding to different current gears.
Optionally, the arc discharge fault judging module is further configured to:
if the arcing event is not detected within the preset time, resetting the number of arcing events; and
and if the arcing fault is judged to occur, resetting the number of arcing events.
According to the technical scheme provided by the embodiment of the invention, through different current gears, large current (more than 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A), a time domain detection module and a frequency domain detection module are used for simultaneous calculation and analysis, when arc faults occur according to current magnitude judgment, a time domain value under the corresponding current gear is judged to be compared with a time domain threshold value, and when the time domain value exceeds the time domain arcing condition is met; judging a frequency domain value under the corresponding current gear, and when the frequency domain value exceeds a frequency domain threshold value of the corresponding current gear, meeting a frequency domain arcing condition of the corresponding current gear; finally, judging whether the values in the time domain and the frequency domain exceed the threshold value in the corresponding current gear, if one or both of the values do not meet the threshold value, judging that an arc discharge event does not occur, and returning to the starting stage to continue detection; if the current signal is simultaneously satisfied, judging that the current signal is an accidental arc discharge or arc discharge fault, continuing to perform arc discharge fault judgment, judging that the number of arc discharge events in a fixed short time after initial arc discharge is compared with the preset number, judging that the arc discharge fault occurs if the number exceeds the preset number, and returning to a starting stage if the number exceeds the preset number, so that arc discharge phenomenon judgment is realized through the frequency domain characteristics and the time domain characteristics of the current signal, and compared with the prior art, the arc discharge phenomenon judgment is realized through current high-frequency noise, and the accuracy of arc discharge phenomenon judgment is improved. The current signal is divided into different current gears, and the arc discharge phenomenon is judged according to the different current gears, so that the accuracy of arc discharge phenomenon judgment is further improved.
The above specific embodiments may be combined with each other and some embodiments may not be repeated for the same or similar concepts or processes.
Any combination of the technical features of the above embodiments may be performed (as long as there is no contradiction between the combination of the technical features), and for brevity of description, all of the possible combinations of the technical features of the above embodiments are not described; these examples, which are not explicitly written, should also be considered as being within the scope of the present description.
The invention has been described above with particularity and detail in connection with general description and specific embodiments. It should be noted that it is obvious that several variations and modifications can be made to these specific embodiments without departing from the spirit of the present invention, which are all within the scope of protection of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.
It should be noted that: when the distributed photovoltaic module direct-current side fault arc detection device provided in the above embodiment executes the distributed photovoltaic module direct-current side fault arc detection method, only the division of the above functional modules is used for illustration, in practical application, the above functional allocation can be completed by different functional modules according to needs, that is, the internal structure of the device is divided into different functional modules, so as to complete all or part of the functions described above. In addition, the embodiments of the device and the method for detecting a fault arc on a direct current side of a distributed photovoltaic module provided in the foregoing embodiments belong to the same concept, and detailed implementation processes of the device and the method embodiments are detailed in the method embodiments, and are not repeated here.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program for instructing relevant hardware, where the program may be stored in a computer readable storage medium, and the storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (10)
1. The method for detecting the direct-current side fault arc of the distributed photovoltaic module is characterized by comprising the following steps of:
dividing a current signal into different current gears according to the current magnitude;
detecting whether the standard deviation, the signal peak value and the signal change rate of a current signal meet a time domain detection threshold value of a current gear, if so, judging that the time domain arcing is met;
performing fast Fourier transform on the circuit signal to obtain a plurality of harmonic values, judging whether the harmonic quantity meeting the frequency domain detection threshold value of the current gear in which the harmonic value is positioned in the plurality of harmonic values meets a quantity threshold value, if so, judging that the frequency domain arcing is met;
if the time domain arcing and the frequency domain arcing are simultaneously satisfied, determining that an arcing event occurs;
detecting the number of arcing events in a preset time after initial arcing, comparing the number with the preset number, judging that arcing faults occur if the number is larger than the preset number, and judging that accidental arcing occurs if the number is not larger than the preset number.
2. The method according to claim 1, wherein the method further comprises:
and after 25s after the current signal is detected, continuing to execute the step of detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold values corresponding to the different gear currents.
3. The method according to claim 2, wherein the method further comprises:
the different current gears are set to be large current (more than 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A).
4. A method according to claim 3, characterized in that the method further comprises:
and setting the quantity threshold values corresponding to the different current gears.
5. The method of claim 4, wherein detecting the number of arcing events within a preset time after initiating arcing further comprises:
if the arcing event is not detected within the preset time, resetting the number of the arcing events; and
and if the arcing fault is judged to occur, resetting the number of the arcing events.
6. A distributed photovoltaic module dc side fault arc detection device, the device comprising:
the current signal acquisition module is used for dividing the current signal into different current gears according to the current magnitude;
the time domain detection module is used for detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold value of the current gear, and if so, judging that the time domain arcing is met;
the frequency domain detection module is used for carrying out fast Fourier transform on the circuit signal to obtain a plurality of harmonic values, judging whether the number of the harmonic waves meeting the frequency domain detection threshold value of the current gear in the plurality of harmonic values meets a number threshold value, and judging that the frequency domain arcing is met if the number of the harmonic waves meets the number threshold value;
the arcing fault judging module is used for judging that an arcing event occurs when the time domain arcing and the frequency domain arcing are simultaneously satisfied;
the arc discharge fault judging module is also used for detecting the number of arc discharge events in the preset time after the initial arc discharge, comparing the number with the preset number, judging that the arc discharge fault occurs if the number is larger than the preset number, and judging that the arc discharge fault occurs accidentally if the number is not larger than the preset number.
7. The apparatus of claim 6, wherein the current signal acquisition module is further configured to:
and after 25s after the current signal is detected, continuing to execute the step of detecting whether the standard deviation, the signal peak value and the signal change rate of the current signal meet the time domain detection threshold values corresponding to the different gear currents.
8. The apparatus of claim 6, wherein the current signal acquisition module is further configured to:
the different current gears are set to be large current (more than 8A), medium large current (4A-8A), medium small current (2.5A-4A) and small current (0.5A-2.5A).
9. The apparatus of claim 8, wherein the frequency domain detection module is further configured to:
and setting the quantity threshold values corresponding to the different current gears.
10. The apparatus of claim 9, wherein the arcing fault determination module is further configured to:
if the arcing event is not detected within the preset time, resetting the number of the arcing events; and
and if the arcing fault is judged to occur, resetting the number of the arcing events.
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