CN114280440B - Photovoltaic direct-current arc fault identification device, identification method and photovoltaic system - Google Patents
Photovoltaic direct-current arc fault identification device, identification method and photovoltaic system Download PDFInfo
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Abstract
The invention discloses a photovoltaic direct current arc fault identification device, a photovoltaic direct current arc fault identification method and a photovoltaic system, wherein the identification device comprises: the differential current detection module is used for acquiring a current signal on a branch between the output side of the photovoltaic array and the input side of the inverter by adopting a differential detection method; the signal processing module comprises a band-pass filter circuit, a logarithm detection unit and an amplifying circuit, wherein the logarithm detection unit carries out logarithm processing on the filtered current signal, and the amplifying circuit is configured to amplify the signal output by the logarithm detection unit; the fault processing unit analyzes the signal to be detected output by the signal processing module, and acquires the current working state of the inverter according to the communication with the inverter so as to subtract an inverter interference signal from the signal to be detected and then judge the arc fault. The invention utilizes the logarithmic detection unit to collect high-frequency signals, the wide-frequency band signal measurement range covers the panoramic characteristic of the direct current electric arc, and the accuracy of the electric arc fault detection result is improved on the premise of good economy.
Description
Technical Field
The invention relates to the field of power electronics, in particular to a photovoltaic direct-current arc fault identification device, a photovoltaic direct-current arc fault identification method and a photovoltaic system.
Background
With the rapid development of new energy technology, photovoltaic systems are more and more widely applied, but due to the aging of solar photovoltaic panels and other reasons, direct current arc faults are easily generated inside the photovoltaic systems, so that fire disasters are caused, and life and property safety of the masses are threatened, so that detection of direct current arcs is necessary. The electrical characteristics of the dc arc include current, voltage, etc., but since the arc position is random, it is difficult to collect the voltage signal of the arc by using a sensor, which causes difficulty in collecting the arc voltage data, so that the method usually collects the dc arc current data for processing and analyzing.
The sampling frequency of the existing direct current arc current detection technology is mostly 300kHz and below, namely, only the low-frequency part of an arc signal is analyzed, and the analysis of the high-frequency part is abandoned, so that the detection of the direct current arc has certain limitation. For example, a PCI data acquisition card is used for detecting and analyzing a current signal, and the sampling frequency of the PCI data acquisition card is set to be 10 kHz; or the arc detection part comprises a hardware filter circuit, an ADC sampling part and a DSP digital processing part, wherein the hardware filter circuit filters signals below 20kHz to reduce the interference of noise of the inverter, an SM73201 sampling chip is used for arc data acquisition, the highest sampling rate of the chip is 250kHz, the sampling frequency in an experiment is set as 180kHz, the sampling data of each time is 1024 data points, and the frequency spectrum obtained after Fourier transform processing is symmetrical by taking 90kHz as a boundary, so that the frequency spectrum below 90kHz is only used for analysis, and the detection requirement on the arc is basically met. However, when an arc occurs, the high frequency content in the current is increased, and when other current detection methods are adopted, the chip sampling rate of 250kHz may not meet the requirements. The time domain method is adopted to detect the current signal, the high sampling frequency of more than 1MHz is needed, and obviously, the SM73201 sampling chip is not suitable for time domain detection. If the high-frequency signals are directly collected, the requirement on hardware is high, and the cost is also increased.
The siemens corporation patent application publication No. WO2021051401a1 describes an arc detection method that utilizes a plurality of band pass filters and other modules to collect a plurality of narrow band signals in the arc signal. Because the frequency of the alternating current power supply is low (50-60 Hz) and has periodic characteristics, and the load type of the alternating current arc generating circuit is limited and mostly is a power frequency load, the alternating current arc signal has certain regularity, the interference generated by the alternating current power supply is concentrated on a low-frequency part, and whether the alternating current arc fault exists can be detected by collecting a plurality of narrow-band signals above 100 kHz; however, the direct current arc signals are disordered, the direct current arc signal frequency band and the interference frequency band have overlapped parts, only narrow-band signals are collected, the characteristics of the direct current arc cannot be accurately reflected, the load of the photovoltaic direct current arc generation circuit is mainly an inverter, the working frequency of the inverter is above 20kHz, although the noise interference of the inverter can be ingeniously avoided by collecting a plurality of narrow-band signals, the characteristic frequency bands of partial direct current arc are ignored, and the arc detection method is suitable for the alternating current arc detection condition but not suitable for the detection of the direct current arc.
At present, no economical direct current arc current detection solution exists.
Disclosure of Invention
The invention aims to provide an arc fault identification device and an arc fault identification method with better economy, which can comprehensively collect direct current arc current signals to complete the task of direct current arc current detection, improve the accuracy of arc fault detection and solve the problem that the existing direct current arc fault detection only collects low-frequency signals and abandons high-frequency signals or only collects narrow-band signals to cause incomplete arc characteristic detection.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a photovoltaic direct current arc fault identification device comprises a differential current detection module, a signal processing module and a fault processing unit, wherein the differential current detection module is configured to collect current signals on a branch between an output side of a photovoltaic array and an input side of an inverter by adopting a differential detection method;
the signal processing module is configured to process the current signal acquired by the differential current detection module to obtain a signal to be detected, and comprises a band-pass filter circuit and an amplification module, wherein the band-pass filter circuit is configured to filter the current signal acquired by the differential current detection module, the amplification module comprises a logarithmic detection unit and an amplification circuit, the logarithmic detection unit is configured to perform logarithmic processing on the filtered current signal, and the amplification circuit is configured to amplify the signal output by the logarithmic detection unit;
The fault processing unit is configured to analyze the signal to be detected output by the signal processing module, and if it is determined that an arc fault exists, send a control instruction to the inverter, wherein the control instruction is configured to disconnect a grid-connected circuit of the inverter.
Further, the amplifying module further comprises an a/D conversion module configured to process the filtered current signal and/or the current signal output by the amplifying circuit.
Further, the input end of the a/D conversion module is connected to one or more switches, and the amplification module further includes a control unit configured to control the one or more switches at the input end of the a/D conversion module to be turned on or off by:
if the amplitude of the current signal output by the amplifying circuit is between a preset first threshold and a preset second threshold, wherein the first threshold is higher than the second threshold, the control unit controls the conduction of a corresponding switch in one or more paths of switches at the input end of the A/D conversion module;
if the amplitude of the current signal output by the amplifying circuit is higher than the first threshold value or lower than the second threshold value, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off.
Furthermore, the input end of the logarithm detection unit is connected with a multi-way switch, and the multi-way switch is matched with the plurality of photovoltaic panel sets of the photovoltaic array in series.
Further, the fault processing unit is in bidirectional communication with the inverter, and before the fault processing unit determines the arc fault, the fault processing unit acquires the current working state of the inverter from the inverter so as to match a preset interference signal corresponding to the current working state of the inverter;
and the fault processing unit removes an interference signal matched with the current working state of the inverter from the signal to be detected output by the signal processing module and then judges whether an arc fault exists.
Further, the step of analyzing the to-be-detected signal output by the signal processing module by the fault processing unit includes:
s1, the fault processing unit receives the signal to be detected output by the signal processing module;
s2, judging whether the sampling time of the signal to be detected reaches a preset time window threshold value, if so, executing S3-S7; otherwise, returning to execute S1-S2;
s3, processing the signal to be detected into one-dimensional current data;
s4, inquiring the current working state of the inverter, and removing an interference signal matched with the current working state of the inverter from the one-dimensional current data;
S5, extracting characteristic values of the current data from which the interference signals are removed, and normalizing the extracted characteristic data;
s6, inputting the data after normalization processing into an arc detection model of a pre-trained one-dimensional convolutional neural network to obtain a detection result corresponding to the current time window, if the detection result is an arc fault, executing a self-increasing algorithm on the flag bit value and updating the flag bit value stored after self-increasing, otherwise executing a self-decreasing algorithm on the flag bit value and updating the flag bit value stored after self-decreasing;
s7, judging whether the current zone bit value reaches a preset zone bit threshold value, if so, executing S8, otherwise, resetting the sampling time to 0 and then returning to execute S1-S2;
s8, the fault processing unit sends a control instruction to the inverter, and the control instruction is configured to disconnect a grid-connected circuit of the inverter.
Further, the differential current detection module comprises a current transformer, positive and negative buses are connected from the photovoltaic array, and both the positive and negative buses penetrate through the current transformer; or,
the differential current detection module comprises a first current transformer, a second current transformer and a differential module, and a positive bus and a negative bus are connected from the photovoltaic array, wherein the positive bus is connected to one end of the differential module after penetrating through the first current transformer, and the negative bus is connected to the other end of the differential module after penetrating through the second current transformer.
Further, the logarithmic detection unit is a logarithmic detection chip, and the signal bandwidth range of the logarithmic detection chip satisfies 1kHz to 10 MHz.
Further, the band-pass filter circuit is an active band-pass filter circuit including a resistor, a capacitor, and an operational amplifier, or,
the band-pass filter circuit is an RLC band-pass filter circuit.
According to another aspect of the invention, a photovoltaic system is provided, comprising a photovoltaic array, an inverter and a photovoltaic dc arc fault identification device as described above.
According to another aspect of the present invention, there is provided a photovoltaic dc arc fault identification method, including the steps of:
p1, collecting current signals on a branch between the output side of the photovoltaic array and the input side of the inverter by adopting a differential detection method;
p2, processing the current signal obtained by differential detection by the signal processing module to obtain a signal to be detected;
p3, analyzing the signal to be detected, wherein the analyzing step comprises the following steps S1-S6:
s1, the fault processing unit receives the signal to be detected output by the signal processing module;
s2, judging whether the sampling time of the signal to be detected reaches a preset time window threshold value, if so, executing S3-S6; otherwise, returning to execute S1-S2;
S3, processing the signal to be detected into one-dimensional current data;
s4, inquiring the current working state of the inverter, and removing an interference signal matched with the current working state of the inverter from the one-dimensional current data;
s5, extracting characteristic values of the current data from which the interference signals are removed, and normalizing the extracted characteristic data;
s6, inputting the data after normalization processing into an arc detection model of a pre-trained one-dimensional convolutional neural network to obtain a detection result corresponding to the current time window; and
and the fault processing unit judges whether the arc fault exists according to the detection results corresponding to the time windows.
Further, the step of analyzing the to-be-detected signal in step P3 further includes: in step S6, if the detection result corresponding to the current time window is an arc fault, performing a self-increasing algorithm on the flag bit value and updating the flag bit value stored after self-increasing, otherwise performing a self-decreasing algorithm on the flag bit value and updating the flag bit value stored after self-decreasing, and then performing S7;
s7, judging whether the current zone bit value reaches a preset zone bit threshold value, if so, executing S8, otherwise, resetting the sampling time to 0 and then returning to execute S1-S2;
S8, the fault processing unit sends a control instruction to the inverter, and the control instruction is configured to disconnect a grid-connected circuit of the inverter.
Further, the step S5 of extracting the characteristic value from the current data after the interference signal is removed includes: and analyzing and extracting power spectral density characteristic information of the current data.
Further, in step P1, a differential current detection module is used to collect a current signal on a branch between an output side of the photovoltaic array and an input side of the inverter, where the differential current detection module includes a current transformer, positive and negative buses are connected from the photovoltaic array, and both the positive and negative buses pass through the current transformer; or,
the differential current detection module comprises a first current transformer, a second current transformer and a differential module, and a positive bus and a negative bus are connected from the photovoltaic array, wherein the positive bus is connected to one end of the differential module after penetrating through the first current transformer, and the negative bus is connected to the other end of the differential module after penetrating through the second current transformer.
Further, the signal processing module includes a band-pass filter circuit and an amplifying module, wherein the band-pass filter circuit is configured to filter the current signal collected by the differential current detection module, the amplifying module includes a logarithmic detection unit, an amplifying circuit, a control unit and an a/D conversion module, the logarithmic detection unit is configured to perform logarithmic processing on the filtered current signal, and the amplifying circuit is configured to amplify the signal output by the logarithmic detection unit;
The A/D conversion module is configured to process the filtered current signal and/or the current signal output by the amplifying circuit;
the input end of the A/D conversion module is connected with one or more switches, and the control unit is configured to control the one or more switches at the input end of the A/D conversion module to be switched on or switched off in the following way:
if the amplitude of the current signal output by the amplifying circuit is between a preset first threshold and a preset second threshold, wherein the first threshold is higher than the second threshold, the control unit controls the conduction of a corresponding switch in one or more paths of switches at the input end of the A/D conversion module;
if the amplitude of the current signal output by the amplifying circuit is higher than the first threshold value or lower than the second threshold value, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off.
The technical scheme provided by the invention has the following beneficial effects:
a. the method comprises the steps that a differential detection method is adopted to collect current signals on a branch between the output side of a photovoltaic array and the input side of an inverter, so that common-mode current noise in positive and negative buses of the photovoltaic array can be effectively eliminated, and therefore direct-current arc fault signals are effectively extracted;
b. The detection frequency of the logarithmic detection unit can reach the MHz level, the measurement range can be greatly increased, the panoramic characteristic of the direct current electric arc is covered, the collection of high-frequency signals can not be abandoned on the premise of good economy, and the incomplete detection problem of the electric arc characteristic is avoided.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be 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 application, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a schematic diagram of a connection structure of a photovoltaic dc arc fault identification device connected between a photovoltaic array and an inverter according to an exemplary embodiment of the present invention;
fig. 2 is a schematic structural diagram of a signal processing module in a photovoltaic dc arc fault identification apparatus according to an exemplary embodiment of the present invention;
fig. 3 is a schematic structural diagram of an amplifying module in a signal processing module according to an exemplary embodiment of the present invention;
FIG. 4 is a schematic diagram of a circuit structure of a first differential current detection module according to an exemplary embodiment of the present invention;
FIG. 5 is a schematic diagram of a circuit configuration of a second differential current sensing module provided in an exemplary embodiment of the invention;
fig. 6 is a schematic diagram of an overall connection structure of a first band-pass filter circuit in a photovoltaic dc arc fault identification apparatus in a signal processing module according to an exemplary embodiment of the present invention;
FIG. 7 is a schematic diagram of a second band pass filter circuit in a signal processing module provided in an exemplary embodiment of the invention;
fig. 8 is a schematic flowchart of the arc fault determination by the fault processing unit of the photovoltaic dc arc fault identification apparatus according to the exemplary embodiment of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solutions of the present invention, 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. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, apparatus, article, or device that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or device.
In the field of arc detection, a time domain method is adopted to detect current signals, and high sampling frequency of more than 1MHz is required, so that the SM73201 and other sampling chips are not suitable for time domain detection obviously; if the high-frequency signal is directly collected, the requirement on hardware is high, and the cost is greatly increased. The invention aims to provide a solution which can simultaneously acquire a low-frequency signal and a high-frequency signal and has better economical efficiency to complete the task of detecting the direct current arc current.
In an embodiment of the present invention, there is provided a photovoltaic dc arc fault identification apparatus, as shown in fig. 1, which includes a differential current detection module, a signal processing module and a fault processing unit, and the following detailed description is made for the differential current detection module, the signal processing module and the fault processing unit:
and the differential current detection module is configured to adopt a differential detection method to acquire a current signal on a branch between the output side of the photovoltaic array and the input side of the inverter, namely the photovoltaic array is used as a power supply, and the output direct current of the photovoltaic array flows into the differential current detection module and then enters the inverter for grid-connected operation. The benefits of this are: in a photovoltaic system, when a direct current arc fault occurs, direct currents of a positive bus and a negative bus of a photovoltaic power supply simultaneously comprise a fault arc current signal and an inverter common mode current noise signal, wherein the inverter common mode current noise is related to a PWM control strategy, so that the common mode current noise generally has periodic repeatability within a certain time scale, and the direct current arc signal does not have the repetition rule. Therefore, the differential current detection method is adopted to carry out differential processing on the signals, so that common mode current noise in the positive bus and the negative bus can be effectively eliminated/reduced, and a direct current arc fault signal can be effectively extracted. There are two specific embodiments: in one embodiment, referring to fig. 4, the differential current detection module includes a current transformer, and positive and negative bus bars are connected from the photovoltaic array, and both the positive and negative bus bars pass through the current transformer, and the principle is as follows: because the noise signal of the inverter has certain regularity, the magnetic field generated in the mutual inductor can be offset, the noise signal of the inverter in the current signal induced by the mutual inductor is greatly inhibited, the direct current arc signal is disordered, the magnetic field generated in the mutual inductor cannot be offset, and the current signal induced by the mutual inductor still contains the arc signal; in another embodiment, referring to fig. 5, the differential current detection module includes a first current transformer, a second current transformer, and a differential module, and positive and negative buses are connected from the photovoltaic array, wherein the positive bus is connected to one end of the differential module after passing through the first current transformer, and the negative bus is connected to the other end of the differential module after passing through the second current transformer, and the principle is as follows: because the noise signal of the inverter has certain regularity, the signal almost disappears after the subtraction, and the direct current arc signal is disordered, so the signal does not disappear after the subtraction, and the purpose of inhibiting the noise signal of the inverter is achieved.
A signal processing module configured to process the current signal collected by the differential current detection module to obtain a signal to be detected, see fig. 2, where the signal processing module includes a band-pass filter circuit and an amplification module, where the band-pass filter circuit is configured to filter the current signal collected by the differential current detection module, and the prior art collects multiple segments of narrow-band current signals for analysis due to difficulty in removing noise interference of an inverter, and ignores a part of a dc arc characteristic frequency band although the noise frequency band of the inverter is avoided skillfully, so that the accuracy of dc arc detection is reduced; and the current signal that difference current detection module gathered passes through band-pass filter circuit and gathers broadband signal, and this broadband signal has covered direct current arc panorama characteristic, avoids neglecting partly direct current arc characteristic frequency channel, and consequently, the direct current arc testing result accuracy degree in this embodiment is higher. Referring to fig. 3, the amplification module includes a logarithmic detection unit and an amplification circuit, the logarithmic detection unit is configured to perform logarithmic processing on the filtered current signal, the logarithmic detection function of the embodiment is mainly realized by a logarithmic detection chip, the working voltage of the logarithmic detection chip satisfies 3.3V-5V, the signal bandwidth satisfies 1k-10MHz, the typical current value is 7.5mA, the measurement range is greatly increased, the sampling frequency reaches the MHz level, the power consumption is low, and the economic requirement is satisfied; the amplification circuit is configured to amplify the signal output by the logarithmic detection unit; the differential current detection module is used for filtering data acquired by the differential current detection module through a band-pass filter circuit contained in the signal processing module, the amplification module is used for processing current signals, specifically, a logarithmic detection unit and an amplification circuit are adopted, the logarithmic detection unit acquires the current signals by utilizing the function of carrying out logarithmic processing on the filtered current data to enlarge the sampling range, the amplification circuit can enable the characteristics of the current signals to be more obvious, meanwhile, logarithmic detection can reflect the signal intensity, direct current arc faults can be identified quickly, the fault arc identification and protection speed is improved, the logarithmic detection method can reflect the current signal change trend, and the detection characteristics of the macroscopic level are represented. In one embodiment, the input end of the logarithm detection unit is connected with a multi-way switch, the multi-way switch is matched with a plurality of photovoltaic panel sets of the photovoltaic array in a string manner, circuits can be switched randomly through the multi-way switch, different circuits can be connected, the photovoltaic system can be better adapted to the situation that the photovoltaic system comprises a plurality of groups of photovoltaic panel sets in a string manner, meanwhile, the purpose of respectively detecting a plurality of paths of current signals can be achieved by only adopting one path of logarithm detection unit, and the economy is better. Band-pass filter circuit is the active band-pass filter circuit including resistance, electric capacity and operational amplifier, refers to fig. 6, and band-pass filter circuit and logarithm detection chip cooperate, more can improve the direct current electric arc detection degree of accuracy: the current signals output by the differential current detection module are sent to an active band-pass filter circuit formed by C1, C2, R1, R2, R3, R4, R5 and an operational amplifier in the figure 6, so that unnecessary signals are filtered; the active band-pass filter circuit needs to use an operational amplifier, and an RLC band-pass filter circuit can also be used if the cost is further reduced, as shown in fig. 7. Then the current data flows into a logarithm detection chip, the chip carries out logarithm processing on the current signal, the current data output by the chip is amplified by an amplification module and then is sent into a fault processing unit to analyze the power spectral density of the signal so as to carry out preprocessing on arc data, and then whether an arc exists or not is judged by using an algorithm, which is specifically referred to below.
And the fault processing unit is configured to analyze the signal to be detected output by the signal processing module, and if the arc fault is determined to exist, a control instruction is sent to the inverter, and the control instruction is configured to disconnect a grid-connected circuit of the inverter. In an embodiment of the invention, the fault processing unit adopts a single chip, that is, the single chip processing unit communicates with the inverter to obtain the current working state of the inverter, and because different states have different interferences, under the premise of obtaining the current working state of the inverter, an interference signal of the current working state of the inverter can be removed during signal processing, so as to facilitate the judgment of whether a direct current arc exists or not, for example, obtaining that the inverter is currently in a PWM modulation mode, the single chip processing unit inquires the interference frequency in the pre-stored PWM modulation mode, removes the interference signal matched with the current working state of the inverter from the signal to be detected processed by the signal processing module according to the interference frequency, and then judges whether the arc fault exists or not, so that the arc characteristics are comprehensively analyzed, the arc detection is well promoted, and the detection accuracy is improved, if the arc fault exists, the single chip sends an instruction to the inverter to disconnect the grid-connected circuit, so that the circuit is protected. The photovoltaic direct current arc fault identification method and device collect arc current signals.
In an embodiment of the present invention, the amplifying module further includes a second processing mode, that is, the amplifying module further includes an a/D conversion module, the a/D conversion module can better retain signal details, and is configured to process the filtered current signal and/or the current signal output by the amplifying circuit, and the a/D conversion mode can collect a real-time signal, can reflect a change of the current signal in details, and represents a detection characteristic at a microscopic level. The former method using the logarithmic detection unit and the amplification circuit embodies the detection characteristics of the macroscopic level, when the fault characteristics are detected macroscopically, the a/D conversion module does not need to be selected, when the fault characteristics are not detected macroscopically, the a/D conversion module is further selected, that is, whether the a/D conversion module is used or not is controlled according to the result of the macroscopically detecting, as shown in fig. 3, the input end of the a/D conversion module is connected with one or more switches, the amplification module further comprises a control unit, and if the a/D conversion module is needed, the control unit controls the conduction of the one or more switches at the input end of the a/D conversion module; if the A/D conversion module is not needed, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off. Specifically, if the amplitude of the current signal output by the amplifying circuit is between a preset first threshold and a preset second threshold, where the first threshold is higher than the second threshold, the control unit controls the conduction of a corresponding switch in one or more switches at the input end of the a/D conversion module; if the amplitude of the current signal output by the amplifying circuit is higher than the first threshold value or lower than the second threshold value, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off. The first threshold value may be selected to have a value at a timing of about 33% higher than the current normal signal, and the second threshold value may be selected to have a value at a timing of about 25% lower than the current normal signal. The control unit mainly judges whether the amplitude of the current signal reaches the range between the first threshold and the second threshold, and the control unit can be realized by a hardware circuit or a software mode. The multi-way switch can be connected in front of the A/D conversion module, lines can be switched randomly so that a plurality of photovoltaic panel sets connected with the photovoltaic array can be connected, the photovoltaic system is better suitable for the condition that the photovoltaic system comprises a plurality of sets of photovoltaic arrays, meanwhile, the purpose of respectively detecting multi-way current signals can be achieved by only adopting one A/D conversion module, and the economy is good.
The single-chip microcomputer algorithm for photovoltaic direct-current arc detection has various algorithms, and in recent years, the artificial intelligence algorithm is widely applied to arc detection due to high accuracy, so the artificial intelligence algorithm is adopted for arc fault detection in the embodiment; and the single chip processing unit is communicated with the inverter to obtain the current working state of the inverter, and interference signals of the current working state of the inverter can be removed during signal processing, so that the existence of the direct current arc can be conveniently judged. Referring to fig. 8, the specific steps of analyzing the to-be-detected signal output by the signal processing module by the fault processing unit include:
s1, the fault processing unit receives the signal to be detected output by the signal processing module;
s2, judging whether the sampling time of the signal to be detected reaches a preset time window threshold value, wherein the time window threshold value is generally 5ms or 10ms, and if yes, executing S3-S7; otherwise, returning to execute S1-S2;
s3, processing the signal to be detected into one-dimensional current data;
s4, inquiring the current working state of the inverter, and removing an interference signal matched with the current working state of the inverter from the one-dimensional current data;
s5, extracting characteristic values of the current data after the interference signals are removed, and performing normalization processing on the extracted characteristic data; the photovoltaic direct current arc fault current waveform is characterized by random high-frequency burrs in the time domain, and is characterized by slightly increased spectrum amplitude in a specific frequency band in the frequency domain. When the photovoltaic inverter is subjected to pulse width modulation, high-frequency noise in a similar frequency band is generated, and the amplitude of the high-frequency noise may be the same as or even higher than that of an arc signal. Therefore, it is difficult to distinguish between normal operation and arc faults based on the difference in amplitude, which makes it difficult to perform algorithm analysis after generating a spectrogram by frequency domain transformation using a fast fourier transform method. In the embodiment, the arc data are preprocessed by analyzing the power spectral density of the signal, so that the power spectral density has high sensitivity to the change of the signal and can essentially reflect the objective rule of the change of the signal. Due to system inertia, the noise of the photovoltaic inverter can be regarded as a steady random signal in a short time slot (such as 10ms), however, the direct current arc does not follow the rule, so the normal operation state and the direct current arc fault state of the photovoltaic system can be distinguished according to the stationarity of the signal, and after preprocessing, an algorithm is used for judging whether an arc exists or not, so the power spectral density characteristic information of the current data is analyzed and extracted as the extracted characteristic type in the step S5.
And S6, inputting the data after normalization processing into an arc detection model of a pre-trained one-dimensional convolutional neural network to obtain a detection result corresponding to the current time window, training the arc detection model by using a large amount of arc data in advance, and putting the arc detection model into use after ensuring accuracy. If the detection result is the arc fault, executing a self-increasing algorithm on the flag bit value and updating the flag bit value stored after self-increasing, otherwise executing a self-decreasing algorithm on the flag bit value and updating the flag bit value stored after self-decreasing;
s7, judging whether the current zone bit value reaches a preset zone bit threshold value, if so, executing S8, otherwise, resetting the sampling time to 0 and then returning to execute S1-S2;
s8, that is, when the detection result of the plurality of time windows is an arc fault and the flag bit is greater than the set value, the fault processing unit sends a control command to the inverter, where the control command is configured to disconnect a grid-connected circuit of the inverter and protect the circuit.
In this way, the photovoltaic array, the inverter, and the photovoltaic dc arc fault identification apparatus provided in the above embodiments may constitute a photovoltaic system.
The embodiment provides a photovoltaic direct current arc fault identification method, which comprises the following steps:
p1, collecting current signals on a branch between the output side of the photovoltaic array and the input side of the inverter by adopting a differential detection method;
p2, processing the current signal obtained by differential detection by the signal processing module to obtain a signal to be detected;
p3, analyzing the signal to be detected, wherein the analyzing step comprises the following steps S1-S6:
s1, the fault processing unit receives the signal to be detected output by the signal processing module;
s2, judging whether the sampling time of the signal to be detected reaches a preset time window threshold value, if so, executing S3-S6; otherwise, returning to execute S1-S2;
s3, processing the signal to be detected into one-dimensional current data;
s4, inquiring the current working state of the inverter, and removing an interference signal matched with the current working state of the inverter from the one-dimensional current data;
s5, extracting characteristic values of the current data after the interference signals are removed, and performing normalization processing on the extracted characteristic data;
s6, inputting the data after normalization processing into an arc detection model of a pre-trained one-dimensional convolutional neural network to obtain a detection result corresponding to the current time window; and
In order to improve the anti-interference capability of the model, the detection result of one time window is not used as the final output result, and it is necessary to determine whether an arc fault exists according to the detection results corresponding to multiple time windows, specifically, the step of analyzing the to-be-detected signal in step P3 further includes: in step S6, if the detection result corresponding to the current time window is an arc fault, performing a self-increasing algorithm on the flag bit value and updating the flag bit value stored after self-increasing, otherwise performing a self-decreasing algorithm on the flag bit value and updating the flag bit value stored after self-decreasing, and then performing S7;
s7, judging whether the current zone bit value reaches a preset zone bit threshold value, if so, executing S8, otherwise, resetting the sampling time to 0 and then returning to execute S1-S2;
s8, the fault processing unit sends a control instruction to the inverter, and the control instruction is configured to disconnect a grid-connected circuit of the inverter.
Further, in step P1, a differential current detection module is used to collect a current signal on a branch between an output side of the photovoltaic array and an input side of the inverter, where the differential current detection module includes a current transformer, positive and negative buses are connected from the photovoltaic array, and both the positive and negative buses pass through the current transformer; or,
The differential current detection module comprises a first current transformer, a second current transformer and a differential module, and positive and negative buses are connected out of the photovoltaic array, wherein the positive bus is connected to one end of the differential module after penetrating through the first current transformer, and the negative bus is connected to the other end of the differential module after penetrating through the second current transformer.
Further, the signal processing module in step P2 includes a band-pass filter circuit and an amplifying module, where the band-pass filter circuit is configured to filter the current signal collected by the differential current detection module, the amplifying module includes a logarithmic detection unit, an amplifying circuit, a control unit and an a/D conversion module, the logarithmic detection unit is configured to perform logarithmic processing on the filtered current signal, and the amplifying circuit is configured to amplify the signal output by the logarithmic detection unit;
the A/D conversion module is configured to process the filtered current signal and/or the current signal output by the amplifying circuit;
the input end of the A/D conversion module is connected with one or more switches, and the control unit is configured to control the one or more switches at the input end of the A/D conversion module to be switched on or switched off in the following way:
If the amplitude of the current signal output by the amplifying circuit is between a preset first threshold and a preset second threshold, wherein the first threshold is higher than the second threshold, the control unit controls the conduction of a corresponding switch in one or more paths of switches at the input end of the A/D conversion module;
if the amplitude of the current signal output by the amplifying circuit is higher than the first threshold value or lower than the second threshold value, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off.
The embodiment of the photovoltaic direct-current arc fault identification method and the embodiment of the photovoltaic direct-current arc fault identification device belong to the same concept, and the whole content of the embodiment of the photovoltaic direct-current arc fault identification device is incorporated into the embodiment of the photovoltaic direct-current arc fault identification method in a reference mode, so that the details are not repeated.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.
The foregoing is illustrative of the present disclosure and it will be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles of the disclosure, the scope of which is defined by the appended claims.
Claims (14)
1. The photovoltaic direct-current arc fault identification device is characterized by comprising a differential current detection module, a signal processing module and a fault processing unit, wherein the differential current detection module is configured to adopt a differential detection method to acquire current signals on a branch circuit between an output side of a photovoltaic array and an input side of an inverter;
the signal processing module is configured to process the current signal collected by the differential current detection module to obtain a signal to be detected, and the signal processing module includes a band-pass filter circuit and an amplification module, wherein the band-pass filter circuit is configured to filter the current signal collected by the differential current detection module, the amplification module includes a logarithmic detection unit, an amplification circuit, an a/D conversion module and a control unit, the logarithmic detection unit is configured to perform logarithmic processing on the filtered current signal, the amplification circuit is configured to amplify the signal output by the logarithmic detection unit, and the a/D conversion module is configured to process the filtered current signal and/or the current signal output by the amplification circuit;
The input end of the A/D conversion module is connected with one or more switches, and the control unit is configured to control the one or more switches at the input end of the A/D conversion module to be switched on or switched off in the following way: if the amplitude of the current signal output by the amplifying circuit is between a preset first threshold and a preset second threshold, wherein the first threshold is higher than the second threshold, the control unit controls the conduction of a corresponding switch in one or more paths of switches at the input end of the A/D conversion module; if the amplitude of the current signal output by the amplifying circuit is higher than the first threshold value or lower than a second threshold value, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off;
the fault processing unit is configured to analyze the signal to be detected output by the signal processing module, and if it is determined that an arc fault exists, send a control instruction to the inverter, wherein the control instruction is configured to disconnect a grid-connected circuit of the inverter.
2. The photovoltaic direct current arc fault identification device according to claim 1, wherein a multi-way switch is connected to an input end of the logarithmic detection unit, and the multi-way switch is adapted to a plurality of photovoltaic panel set strings of the photovoltaic array.
3. The photovoltaic direct-current arc fault identification device according to claim 1, wherein the fault processing unit is in bidirectional communication with the inverter, and before the fault processing unit determines an arc fault, the fault processing unit obtains a current working state of the inverter to match a preset interference signal corresponding to the current working state of the inverter;
and the fault processing unit removes an interference signal matched with the current working state of the inverter from the signal to be detected output by the signal processing module and then judges whether an arc fault exists.
4. The photovoltaic direct-current arc fault identification device according to claim 3, wherein the step of analyzing the signal to be detected output by the signal processing module by the fault processing unit comprises:
s1, the fault processing unit receives the signal to be detected output by the signal processing module;
s2, judging whether the sampling time of the signal to be detected reaches a preset time window threshold value, if so, executing S3-S7; otherwise, returning to execute S1-S2;
s3, processing the signal to be detected into one-dimensional current data;
s4, inquiring the current working state of the inverter, and removing an interference signal matched with the current working state of the inverter from the one-dimensional current data;
S5, extracting characteristic values of the current data from which the interference signals are removed, and normalizing the extracted characteristic data;
s6, inputting the data after normalization processing into an arc detection model of a pre-trained one-dimensional convolutional neural network to obtain a detection result corresponding to the current time window, if the detection result is an arc fault, executing a self-increment algorithm on the flag bit value and updating the flag bit value after self-increment, and if not, executing a self-decrement algorithm on the flag bit value and updating the flag bit value after self-decrement;
s7, judging whether the current zone bit value reaches a preset zone bit threshold value, if so, executing S8, otherwise, resetting the sampling time to 0 and then returning to execute S1-S2;
s8, the fault processing unit sends a control instruction to the inverter, and the control instruction is configured to enable a grid-connected circuit of the inverter to be disconnected.
5. The photovoltaic dc arc fault identification device of claim 1, wherein the differential current detection module comprises a current transformer through which positive and negative bus bars are connected from the photovoltaic array; or,
the differential current detection module comprises a first current transformer, a second current transformer and a differential module, and a positive bus and a negative bus are connected from the photovoltaic array, wherein the positive bus is connected to one end of the differential module after penetrating through the first current transformer, and the negative bus is connected to the other end of the differential module after penetrating through the second current transformer.
6. The photovoltaic direct current arc fault identification device according to claim 1, wherein the logarithmic detection unit is a logarithmic detection chip, and a signal bandwidth range of the logarithmic detection chip satisfies 1kHz to 10 MHz.
7. The photovoltaic direct current arc fault identification device of claim 1, wherein the band-pass filter circuit is an active band-pass filter circuit comprising a resistor, a capacitor and an operational amplifier, or,
the band-pass filter circuit is an RLC band-pass filter circuit.
8. A photovoltaic system comprising a photovoltaic array, an inverter and a photovoltaic DC arc fault identification apparatus as claimed in any one of claims 1 to 7.
9. A photovoltaic direct current arc fault identification method is characterized by comprising the following steps:
p1, collecting current signals on a branch between the output side of the photovoltaic array and the input side of the inverter by adopting a differential detection method;
p2, processing the current signal obtained by differential detection by the signal processing module to obtain a signal to be detected; the signal processing module comprises a band-pass filter circuit and an amplifying module, wherein the band-pass filter circuit is configured to filter acquired current signals, the amplifying module comprises a logarithmic detection unit, an amplifying circuit, a control unit and an A/D conversion module, the logarithmic detection unit is configured to carry out logarithmic processing on the filtered current signals, and the amplifying circuit is configured to amplify signals output by the logarithmic detection unit; the A/D conversion module is configured to process the filtered current signal and/or the current signal output by the amplifying circuit; the input end of the A/D conversion module is connected with one or more switches, and the control unit is configured to control the one or more switches at the input end of the A/D conversion module to be switched on or switched off in the following modes: if the amplitude of the current signal output by the amplifying circuit is between a preset first threshold and a preset second threshold, wherein the first threshold is higher than the second threshold, the control unit controls the conduction of a corresponding switch in one or more paths of switches at the input end of the A/D conversion module; if the amplitude of the current signal output by the amplifying circuit is higher than the first threshold or lower than a second threshold, the control unit controls one or more switches at the input end of the A/D conversion module to be switched off;
And P3, analyzing the signal to be detected, and if the arc fault is determined to exist, sending a control command to the inverter, wherein the control command is configured to disconnect a grid-connected circuit of the inverter.
10. The method for identifying a photovoltaic direct current arc fault as claimed in claim 9, wherein the step of analyzing in step P3 includes the following steps S1-S6:
s1, the fault processing unit receives the signal to be detected output by the signal processing module;
s2, judging whether the sampling time of the signal to be detected reaches a preset time window threshold value, if so, executing S3-S6; otherwise, returning to execute S1-S2;
s3, processing the signal to be detected into one-dimensional current data;
s4, inquiring the current working state of the inverter, and removing an interference signal matched with the current working state of the inverter from the one-dimensional current data;
s5, extracting characteristic values of the current data after the interference signals are removed, and performing normalization processing on the extracted characteristic data;
s6, inputting the data after normalization processing into an arc detection model of a pre-trained one-dimensional convolutional neural network to obtain a detection result corresponding to the current time window; and
and the fault processing unit judges whether an arc fault exists according to the detection results corresponding to the time windows.
11. The method for identifying the photovoltaic direct-current arc fault according to claim 10, wherein the step of analyzing the signal to be detected in step P3 further comprises: in step S6, if the detection result corresponding to the current time window is an arc fault, performing a self-increment algorithm on the flag bit value and updating the flag bit value stored after self-increment, otherwise performing a self-decrement algorithm on the flag bit value and updating the flag bit value stored after self-decrement, and then performing S7;
s7, judging whether the current zone bit value reaches a preset zone bit threshold value, if so, executing S8, otherwise, resetting the sampling time to 0 and then returning to execute S1-S2;
s8, the fault processing unit sends a control instruction to the inverter, and the control instruction is configured to enable a grid-connected circuit of the inverter to be disconnected.
12. The method for identifying the photovoltaic direct-current arc fault as claimed in claim 9, wherein the step S5 of extracting the characteristic value of the current data after the interference signal is removed includes: and analyzing and extracting power spectral density characteristic information of the current data.
13. The pv dc arc fault identification method according to claim 9, wherein in step P1, a differential current detection module is used to collect current signals on a branch between an output side of the pv array and an input side of the inverter, wherein the differential current detection module comprises a current transformer, positive and negative buses are connected from the pv array, and both the positive and negative buses pass through the current transformer; or,
The differential current detection module comprises a first current transformer, a second current transformer and a differential module, and a positive bus and a negative bus are connected from the photovoltaic array, wherein the positive bus is connected to one end of the differential module after penetrating through the first current transformer, and the negative bus is connected to the other end of the differential module after penetrating through the second current transformer.
14. The photovoltaic direct current arc fault identification method of claim 13, wherein the band pass filter circuit of the signal processing module is configured to filter the current signal collected by the differential current detection module.
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