Background
The arc fault identification technology analyzes one or more parameters by collecting various parameters in a line and applying different methods, so as to judge whether an arc fault is generated in the line. But arc faults are characterized by randomness, concealment, complexity and the like, so that the arc faults are difficult to identify.
At present, there are three types of methods for detecting series arc faults by researchers at home and abroad. The first is a detection method based on a mathematical model. The second is a detection method based on the physical characteristics of the arc. The third is a detection method based on arc current and voltage waveforms. Due to the complexity and randomness of the arc faults, the existing arc model has difficulty in accurately and comprehensively expressing the dynamic characteristics of the arc faults when the arc faults occur. When the characteristics of arc sound, arc light, temperature and the like during arc combustion are used for identifying the arc, the characteristics are limited by the installation quantity and the positions of the sensors, and the detection effect is greatly reduced for the hidden arc. At present, arc detection by using waveform characteristics is mainstream.
In a known conventional arc detection method, extracted arc current waveform feature data is input to a classifier such as a support vector machine to be classified, and a classification result is obtained. However, the load conditions of different lines are very different and can change frequently, resulting in poor training effect and failure to meet the requirements. Therefore, an Extreme Learning Machine (ELM) algorithm of dynamic online sequence is adopted to detect the arc fault in the line.
The ELM can be regarded as an improved feedforward neural network, and compared with a traditional machine learning network, the ELM of the dynamic online sequence has the following advantages in arc fault detection that (1) the training speed of the extreme learning machine is nearly thousands of times faster than that of the traditional neural network (such as BP algorithm). (2) Extreme learning machines have been verified to have better universality. (3) The ELM is combined with a dynamic online sequence, online learning can be realized, and the method has strong adaptability to power grid systems with different load intensities and real-time changes.
Disclosure of Invention
In order to overcome the defects that the existing arc fault identification process is low in identification precision, poor in adaptability when the load condition changes and more in false detection and missing detection situations, the invention provides the arc fault identification algorithm of the extreme learning machine of the dynamic online sequence, and the arc fault identification algorithm can adapt to different power grid load environments through an online learning method.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method for series arc fault identification of an extreme learning machine based on a dynamic online sequence, the method comprising the steps of:
step 1) noise reduction of current waveform sampling data
Acquiring waveform sampling data of current in a power grid by using a high-speed sampling mutual inductance sensor, taking three adjacent sampling points as a group, adopting a pre-mean filtering algorithm, replacing the numerical value of a first point with the mean value of the group, adding a new point and discarding an old point;
step 2) real-time data segmentation interception
Intercepting the current real-time signal obtained in the step 1) by taking n current cycles as a period, namely intercepting data by adopting a window with an nT period as a length;
step 3) waveform data calculation and processing
After waveform data are obtained in the step 2), extracting time threshold characteristic root mean square error, integral energy value and period average value difference, extracting inter-harmonic factors and wavelet high-frequency components of frequency domain characteristic parts, and performing normalization processing on the characteristics;
step 4) ELM fault arc identification
Based on an ELM algorithm, arc identification is converted into a fault classification problem, weights from an input layer to a hidden layer are randomly given, and after the weights from the input layer to the hidden layer exist, the weights from the hidden layer to an output layer are obtained according to a least square method, so that fault arc identification is realized.
Further, the process of the step 4) is as follows:
4.1 selection of arc Fault database N at initialization stage
0Group data
Wherein
Randomly generating an input weight matrix w
iBias matrix b
iAn activation function f (), where i ═ 1, 2.,
learning method calculation according to ELM
Calculating an output weight matrix beta
0=M
0H
0T
0Wherein M is
0=(H
0H
0)
-1,
Obtaining Y ═ H
kβ
0Calculating the error between the normal output and the sample label
i=|Y
i-Tag |, with maximum error distance ∈ being counted
maxMinimum error distance of epsilon
minSetting a margin parameter
Calculating to obtain a judgment threshold value epsilon
b=k*(ε
max-ε
min);
4.2, after the initialization stage shown in 4.1 is completed, accessing the system into a fault arc detection line, and inputting the normalized numerical value real-time data obtained in the step 3);
firstly, the output value Y is calculated as Hkβ0. At this time epsiloni=|Y-Tag|;
When epsiloni≤εbJudging the sample to be in a normal running state, and marking a normal label on the sample to enter online learning;
when epsiloni>εbWhen the power grid is in error, warning is given, the power grid condition is manually checked, if the power grid condition is in error, a normal label is marked, and the power grid condition is used as a new sample to enter online learning;
recording a new sample set
At this point, a new sample set hidden layer output matrix is calculated:
calculating a new output weight matrix:
when k is k +1, completing one-time online sequence training;
4.3 repeat step 4.2 after new data is obtained, and perform a new training round.
Compared with the prior series arc fault detection technology, the invention has the following advantages:
the invention adopts an Extreme Learning Machine (ELM) algorithm with a dynamic sequence to identify the fault, and has the advantages of high learning and processing speed, good normalization performance and high identification accuracy compared with the traditional BP neural network algorithm.
The invention adopts a dynamic time sequence method on the basis of an Extreme Learning Machine (ELM), has stronger adaptability aiming at different loads of a power grid in the operation process and strong anti-interference capability, and is suitable for occasions needing long-time data monitoring.
The features of the root mean square error, the integral energy value, the period mean value difference, the partial inter-harmonic factor and the wavelet high-frequency component extracted by the method can be obtained by integrating, Fast Fourier Transform (FFT) and wavelet transform through the terminal, the calculation has low requirement on calculation power, and the calculation power can be integrated in a terminal collector to save cloud calculation power and transmission bandwidth.
The method tests the effect of series arc fault detection, can adaptively adjust the identification sensitivity under the conditions of different loads (1A and 5A), and has stronger anti-interference capability and real-time property under different conditions. The method can accurately identify the series arc fault and send out warning, and can utilize the real-time data online optimization model in normal operation to improve the accuracy.
Detailed Description
The invention will be described in detail with reference to the accompanying drawings: the present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
Referring to fig. 1, a method for series arc fault identification of an extreme learning machine based on a dynamic online sequence, the method comprising the steps of:
step 1) noise reduction of current waveform sampling data
The method comprises the steps that a mutual inductance sensor for high-speed sampling is used for obtaining waveform sampling data of current in a power grid, burrs exist in the data due to interference and the like, adjacent three sampling points are used as a group, a pre-mean filtering algorithm is adopted, the mean value of the group replaces the numerical value of a first point, a new point is added, and the old point is discarded, and the like;
step 2) real-time data segmentation interception
In order to facilitate the rapid processing of data and improve the real-time detection capability, 10(n is 10) current cycles are adopted as a period to intercept the current real-time signal obtained in the step 1), namely a window with the length of 10T period is adopted to intercept data;
step 3) waveform data calculation and processing
After waveform data are obtained in the step 2), extracting time threshold characteristic root mean square error, integral energy value and period average value difference, extracting inter-harmonic factors and wavelet high-frequency components of frequency domain characteristic parts, and performing normalization processing on the characteristics;
step 4) ELM fault arc identification
Based on an ELM algorithm, arc identification is converted into a fault classification problem, weights from an input layer to a hidden layer are randomly given, and after the weights from the input layer to the hidden layer exist, the weights from the hidden layer to an output layer can be obtained according to a least square method, so that fault arc identification is realized.
The process of the step 4) is as follows:
4.1 selection of arc Fault database N at initialization stage
0Group data
Wherein
Randomly generating an input weight matrix w
iBias matrix b
iAn activation function f (), where i ═ 1, 2.,
learning method calculation according to ELM
Calculating an output weight matrix beta
0=M
0H
0T
0Wherein M is
0=(H
0H
0)
-1,
Obtaining Y ═ H
kβ
0Calculating between normal output and sample labelError epsilon
i=|Y
i-Tag |, with maximum error distance ∈ being counted
maxMinimum error distance of epsilon
minSetting a margin parameter
Calculating to obtain a judgment threshold value epsilon
b=k*(ε
max-ε
min) The threshold parameter is not suitable to be set too small;
4.2, after the initialization stage shown in 4.1 is completed, accessing the system into a fault arc detection line, and inputting the normalized numerical value real-time data obtained in the step 3);
firstly, the output value Y is calculated as Hkβ0At this time εi=|Y-Tag|;
When epsiloni≤εbJudging the sample to be in a normal running state, and marking a normal label on the sample to enter online learning;
when epsiloni>εbWhen the power grid is in error, warning is given, the power grid condition is manually checked, if the power grid condition is in error, a normal label is marked, and the power grid condition is used as a new sample to enter online learning;
recording a new sample set
At this point, a new sample set hidden layer output matrix is calculated:
calculating a new output weight matrix:
when k is k +1, completing one-time online sequence training;
4.3 repeat step 4.2 after new data is obtained, and perform a new training round.
Finally, it should also be noted that the above-mentioned list is only one specific embodiment of the invention. It is obvious that the invention is not limited to the above embodiments, but that many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.