Disclosure of Invention
The invention aims to provide an arc detection method based on wavelet decomposition and a neural network, and aims to solve the problem of low detection efficiency of fault arcs of a low-voltage distribution network in the prior art.
In order to achieve the above object, the present invention provides an arc detection method based on wavelet decomposition and neural network, comprising:
obtaining a current period current differential waveform sequence according to the difference between the background current waveform sequence and the current period current waveform sampling sequence, and performing discrete wavelet transform processing on the current period current differential waveform sequence to obtain the characteristic quantity of fault arc detection;
inputting the characteristic quantity detected by the fault arc into a trained error back propagation neural network for secondary classification, outputting the probability of the fault arc generated by a line, and if the probability of the fault arc generated by the output line is greater than a threshold value, judging that the line generates the fault arc.
Preferably, the discrete wavelet transform processing on the current period current difference waveform sequence to obtain the characteristic quantity of fault arc detection includes:
acquiring an initial scale function and an initial wavelet function according to the characteristics of a current waveform when a line generates a fault arc;
respectively constructing a high-pass filter and a low-pass filter of the initial scale function and the initial wavelet function;
and filtering the input signal by adopting the high-pass filter and the low-pass filter to obtain the characteristic quantity of the fault arc detection on the required frequency band, wherein the characteristic quantity of the fault arc detection comprises a scale coefficient and a wavelet coefficient of wavelet decomposition.
Preferably, before the difference is made from the background current waveform sequence and the current period current waveform sampling sequence, the method further comprises:
sampling a current waveform of a line in normal and steady-state operation to obtain a periodic current waveform sampling sequence in normal and steady-state operation;
and calculating the expectation of the periodic current waveform sampling sequence in normal steady-state operation to obtain the background current waveform sequence.
Preferably, before the difference is made from the background current waveform sequence and the current period current waveform sampling sequence, the method further comprises:
and sampling the current waveform of the line in the current period according to the sampling frequency of 200kHz to obtain a current waveform sampling sequence in the current period.
Preferably, the filtering the input signal by using the high-pass filter and the low-pass filter to obtain the characteristic quantity of the fault arc detection on the required frequency band includes:
and performing discrete convolution on the current period current difference waveform sequence and the low-pass filter and the high-pass filter respectively to obtain a scale coefficient and a wavelet coefficient of the wavelet decomposition respectively.
The invention also provides an arc detection device based on wavelet decomposition and a neural network, which comprises:
the acquisition module is used for carrying out difference according to the background current waveform sequence and the current period current waveform sampling sequence, acquiring a current period current differential waveform sequence, and carrying out discrete wavelet transform processing on the current period current differential waveform sequence to acquire the characteristic quantity of fault arc detection;
and the detection module is used for inputting the characteristic quantity detected by the fault arc into a trained error back propagation neural network for secondary classification, outputting the probability of generating the fault arc by the line, and if the probability of generating the fault arc by the output line is greater than a threshold value, judging that the line generates the fault arc.
Preferably, the obtaining module is further configured to obtain an initial scale function and an initial wavelet function according to characteristics of a current waveform when the line generates a fault arc;
respectively constructing a high-pass filter and a low-pass filter of the initial scale function and the initial wavelet function;
and filtering the input signal by adopting the high-pass filter and the low-pass filter to obtain the characteristic quantity of the fault arc detection on the required frequency band, wherein the characteristic quantity of the fault arc detection comprises a scale coefficient and a wavelet coefficient of wavelet decomposition.
Preferably, the method further comprises a first determining module, configured to:
sampling a current waveform of a line in normal and steady-state operation to obtain a periodic current waveform sampling sequence in normal and steady-state operation;
and calculating the expectation of the periodic current waveform sampling sequence in normal steady-state operation to obtain the background current waveform sequence.
Preferably, the first determining module is further configured to:
and sampling the current waveform of the line in the current period according to the sampling frequency of 200kHz to obtain a current waveform sampling sequence in the current period.
Preferably, the obtaining module is further configured to:
and performing discrete convolution on the current period current difference waveform sequence and the low-pass filter and the high-pass filter respectively to obtain a scale coefficient and a wavelet coefficient of the wavelet decomposition respectively.
Compared with the prior art, the invention has the beneficial effects that:
and comparing with the prior art that time domain waveforms are directly used as the input of the neural network, and the characteristic quantity of the fault arc detection is used as the input of the trained error back propagation neural network, so that the output result of the neural network is more accurate.
Further, discrete convolution is carried out on the current period current difference waveform sequence and a low-pass filter and a high-pass filter which are formed by a scale function and a wavelet function respectively, a scale coefficient and a wavelet coefficient of wavelet decomposition are obtained respectively, the influence of background noise on the waveform characteristics of the fault arc current is avoided, the execution time of an algorithm is reduced, and the accuracy of fault arc detection is improved.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be understood that the step numbers used herein are for convenience of description only and are not intended as limitations on the order in which the steps are performed.
It is to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The terms "comprises" and "comprising" indicate the presence of the described features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "and/or" refers to and includes any and all possible combinations of one or more of the associated listed items.
Referring to fig. 1, an embodiment of the present invention provides an arc detection method based on wavelet decomposition and a neural network, including the following steps:
s101: and obtaining a current period current differential waveform sequence according to the difference between the background current waveform sequence and the current period current waveform sampling sequence, and performing discrete wavelet transform processing on the current period current differential waveform sequence to obtain the characteristic quantity of fault arc detection.
Specifically, the current waveform during normal and steady operation of the line is sampled, a periodic current waveform sampling sequence during normal and steady operation is obtained, the expectation of the periodic current waveform sampling sequence during normal and steady operation is calculated, and the background current waveform sequence is obtained.
The characteristic frequency of the current waveform when the line is generating fault arc is usually distributed in the range of 1kHz-100 kHz. From the nyquist sampling theorem: sampling frequency f
sMust be equal to or greater than the highest frequency component of interest of the signal under testNyquist frequency f
N) Twice, the sampling frequency f is selected
sAt 200kHz, the frequency band of interest of the detected signal has no spectrum aliasing, and the number of sampling points of the waveform in each period is calculated according to the frequency f of the normal operation of the line
Sampling the current waveform of the line in normal steady state operation with a sampling period of N
TTo obtain N
TPeriodic current waveform sampling sequence for normal steady-state operation of individual line
Wherein the sequence of each cycle is
According to the calculation of N
TMathematical expectation of periodic current waveform sampling sequence during normal steady-state operation of individual line
As a background current waveform sequence
Sampling the current waveform of the line in the current period according to the sampling frequency of 200kHz to obtain the current waveform sampling sequence in the current period
Sampling sequence of current waveform of current cycle
Waveform sequence with background current
Making difference to obtain current differential waveform sequence R of current period
c=C
c-Y as input signal for wavelet decomposition, enabling filtering of background noise.
Referring to fig. 2 and 3, in particular, the coiflet1 wavelet is selected as the wavelet function Ψ (t) and the scaling function according to the characteristics of the current waveform when the line generates the fault arc
The following were used:
1) the fault arc duration of the line is usually very short, but can generate huge heat effect, the temperature can reach 3000-5000 ℃ during arc burning, and the standard regulation of UL1699 in the United states: when the arc fault circuit breaker detects 8 half-cycles of fault arcs in 500ms, the circuit breaker needs to execute tripping action to cut off a circuit, so that the arc detection algorithm has high real-time requirements, discrete wavelet transformation needs to be adopted, and a wavelet function with high vanishing moment is selected to enable the transformed signal energy to be more concentrated, reduce the complexity of the algorithm and improve the detection real-time property.
2) Because the electric arc is usually scattered in the sporadic flash waves among normal currents, the electric arc current waveform has a plurality of burrs similar to high-frequency pulses relative to the normal current waveform, a wavelet function with a short tight support set needs to be selected, the local time-frequency characteristic of the wavelet function is improved, the detection of a catastrophe point and a singular point is facilitated, and the wavelet function with good symmetry is selected as much as possible to avoid signal phase distortion after wavelet transformation.
3) In order to avoid signal phase distortion after wavelet transformation, a wavelet function with good symmetry is selected as much as possible.
Therefore, an initial scale function and an initial wavelet function are obtained according to the characteristics of a current waveform when a line generates a fault arc, a high-pass filter and a low-pass filter of the initial scale function and the initial wavelet function are respectively constructed, multiple filtering processing is carried out by adopting the high-pass filter and the low-pass filter, the characteristic quantity of fault arc detection on a required frequency band is obtained, the characteristic quantity of fault arc detection comprises a scale coefficient and a wavelet coefficient of wavelet decomposition, specifically, according to the analysis, the initial scale function and the wavelet function are selected, the high-pass filter and the low-pass filter are respectively constructed, multiple filtering is carried out on an original signal, and a coiflet1 wavelet on the required frequency band is determined as a small waveletWave function Ψ (t) and scale function

The coiflet1 wavelet has biarthogonality, compactness and approximate symmetry, filter length 6,
support length 5, wavelet function vanishing
moment order 2, and scale function vanishing
moment order 1.
Referring to fig. 4, 5 and 6, the wavelet function Ψ (t) and the scaling function are selected according to the above
Constructing a low-pass filter and a high-pass filter, in particular defining a low-pass filter h
nThe mathematical expression is
Defining a high-pass filter g
nThe mathematical expression is
Using a low-pass filter h
nAnd a high-pass filter g
nFor input signal R
cFiltering to obtain input signal R
cAre respectively connected with a low-pass filter h
nAnd a high-pass filter g
nRespectively making discrete convolution
And
wherein c is
j,n=R
cFiltered result c
j-1,kAnd d
j-1,kThe k scale coefficient and the k wavelet coefficient of the wavelet decomposition of the j-1 th layer, the j-1 th layer and the (j-n-1) th layer can be further calculated to form a one-dimensional vector s ═ c
j-n,k,d
j-n,k,...,d
j-1,k). The iterative process is to pass the input signal R through a filter
cIs gradually decomposed into different frequency bands, after the nth decomposition,
in order to approximate the frequency band range of the signal,
is the frequency band range of the detail signal. And (n-1) k wavelet coefficients d (j-n, k) and k scale coefficients c (j-1, k) obtained after wavelet decomposition are used as characteristic quantities for fault arc detection, and after normalization processing is carried out on the n x k coefficients, the n x k coefficients are directly used as n x k input parameters of the input layer of the neural network.
S102: inputting the characteristic quantity detected by the fault arc into a trained error back propagation neural network for secondary classification, outputting the probability of the fault arc generated by a line, and if the probability of the fault arc generated by the output line is greater than a threshold value, judging that the line generates the fault arc.
Referring to fig. 7, specifically, n × k input parameters calculated in the above steps are input into an input layer of a neural network, and n × k parameters are input into a trained error back propagation neural network, wherein the trained neural network is composed of an input layer, a hidden layer and an output layer, and a threshold p for controlling an arc fault circuit interrupting device (AFCI) to operate by a decision maker is determined according to a hazard level of a fault arc generated by the linetUnder the conventional strategy ptIf the damage degree of the fault arc generated by the line is not large and a conservative strategy is adopted, p is takent<0.5, so as to reduce the false action probability of AFCI, if the harmfulness of the fault arc generated by the circuit is larger, an aggressive strategy is adopted, and p is takent>And 0.5, reducing the probability of missed judgment of the fault arc event.
Inputting the characteristic quantity of fault arc detection into the trained error back propagation neural network for two classifications, outputting the probability of fault arc generation and the probability of normal operation of the circuit, and forming a 1 x 2 matrix [ p ] by the probability of fault arc generation and the probability of normal operation of the circuitf,pn]T,pfRepresenting the probability sum p of line fault arcingnRepresenting the probability of normal operation, if the output line is producing a fault arc, pfGreater than a threshold value ptAnd judging that the line generates fault arc.
The invention analyzes based on the differential waveform of the current waveform to be detected and the historical normal operation current waveform of the circuit, avoids the influence of background noise on the waveform characteristics of the fault arc current, improves the accuracy of fault arc detection, further balances the parameters of waveform symmetry, tight set length, filter length, vanishing moment order and the like, selects the coiflet1 wavelet as a wavelet base, ensures that the algorithm has low complexity and good real-time property, the phase distortion of the wavelet function is low, the high-frequency time-frequency characteristic is good, compared with the method of directly using the time domain waveform as the input of the neural network, the invention uses the wavelet function as the input of the neural network, the wavelet function simultaneously contains the time-frequency domain information of the waveform, improves the information entropy, ensures that the output result of the neural network is more accurate, the error back propagation neural network has the capacity of from the input to the output of complex nonlinear mapping, and is suitable for solving the problem of complex internal mechanism, and the network structure is simple, and the algorithm execution time is reduced.
Referring to fig. 8, another embodiment of the present invention provides an arc detection apparatus based on wavelet decomposition and neural network, including:
and the obtaining module 11 is configured to obtain a current period current differential waveform sequence by subtracting the background current waveform sequence from the current period current waveform sampling sequence, and perform discrete wavelet transform processing on the current period current differential waveform sequence to obtain a characteristic quantity of fault arc detection.
And the detection module 12 is configured to input the feature quantity detected by the fault arc into a trained error back propagation neural network to perform two classifications, output the probability that the line generates the fault arc, and determine that the line generates the fault arc if the probability that the output line generates the fault arc is greater than a threshold value.
For specific limitations of the arc detection apparatus based on wavelet decomposition and neural network, reference may be made to the above limitations of the arc detection method based on wavelet decomposition and neural network, and details are not repeated here. The modules in the above-mentioned arc detection device based on wavelet decomposition and neural network can be wholly or partially realized by software, hardware and combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.