CN110568254A - Method for accurately detecting attenuated direct-current component parameters in fault current - Google Patents
Method for accurately detecting attenuated direct-current component parameters in fault current Download PDFInfo
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Abstract
The invention relates to a method for accurately detecting an attenuated direct current component parameter in fault current. The method is characterized by comprising the following steps: (1) firstly, reducing the current in an equal ratio to reduce the three-phase alternating current to 0-300 mA; (2) performing AD sampling of alternating current, namely discretization of an analog signal; (3) performing Fourier pre-filtering on the discrete signals, and filtering all components which are not integer multiples of 50hz fundamental frequency signals; (4) carrying out fault curve fitting on the filtered alternating current signal, and finding a group of parameters on the basis of the fault model to ensure that the fault curve is most fit with the fitted curve, so that the error value is kept to be minimum; (5) and (4) filtering the attenuation direct current component added by the fault through the parameters of the fault model obtained in the step (4) to obtain the true effective value of the non-fault current. The invention provides a method for accurately detecting the parameter value of the attenuation direct current component in the alternating current fault of a power grid.
Description
Technical Field
the invention relates to a method for accurately detecting an attenuated direct current component parameter in fault current.
Background
In order to ensure the stability of the power system and protect modules processed by the power system, and the like, enterprises often use a Fourier transform method or a two-point product method to perform simple current judgment, and if abnormal phenomena occur, a protection device is started. The detection method of Fourier transform comprises the steps of discretizing an acquired alternating current signal, then carrying out frequency domain conversion on the discretized signal, filtering out all components except 50hz in a frequency domain, considering that the 50hz component is a true effective value in the power grid alternating current, and considering that a circuit has a fault and carrying out protection action if the energy occupation ratio of the components except 50hz is higher than a certain threshold value. The detection method of the two-point product method is characterized in that an acquired alternating current signal is discretized, then the discretized signal is sampled at a quarter period, then true effective values of two sampling points are directly calculated, and if a large mutation of a derivative of two points is found, a circuit is considered to be in fault, and protection action is carried out.
Both methods can detect a current fault, but cannot obtain specific parameters of an additional current signal caused by the current fault. 1, an accurate current true effective value cannot be obtained once the current fails; 2. once the current fails, specific current fault parameters cannot be obtained, and higher-level algorithm analysis cannot be performed.
Disclosure of Invention
the invention aims to provide a method for accurately detecting parameters of an attenuated direct current component in fault current, which can quantize the component of the fault, accurately filter out the precision influence generated by the fault after the current fails and obtain the fault parameter information as much as possible.
a method for accurately detecting a parameter of an attenuated direct current component in a fault current is characterized by comprising the following steps:
(1) Firstly, reducing the current in an equal ratio to reduce the three-phase alternating current to 0-300 mA;
(2) Performing AD sampling of alternating current, namely discretization of an analog signal;
(3) Performing Fourier pre-filtering on the discrete signals, and filtering all components which are not integer multiples of 50hz fundamental frequency signals;
(4) carrying out fault curve fitting on the filtered alternating current signal, namely establishing a fault model, and finding a group of parameters on the basis of the fault model to ensure that the fault curve is most fit with the fitted curve, so that the error value is kept to be minimum;
(5) And (4) filtering the attenuation direct current component added by the fault through the parameters of the fault model obtained in the step (4) to obtain a true effective value of the non-fault current, and carrying out quantitative analysis on the fault.
the step (1) is specifically that firstly, the high-precision current transformer is used for conversion, the secondary output of the transformer is connected with an operational amplifier I/V conversion circuit to improve the load capacity of the transformer, the transformer works in a zero-load state, the converted voltage is sent to an AD sampling module to carry out discretization of an analog signal,
The proportional transformation of the current can be calculated using the above formula based on the voltage division and shunting action of the resistors.
The step (2) is to perform discretization sampling on the signal after geometric reduction, and for the sampling times which are more than 16 times of sampling within 20ms, in the invention, a successive approximation method is adopted to perform AD sampling, the sampling points are 16 points, namely the sampling frequency is 800hz, then the discretized signal is stored as a matrix and stored by two dimensions, the first dimension is the sampling time, the second dimension is the signal sampled at the time, and the matrix is a 2 x 16 matrix.
the step (3) can decompose the periodic function into constant DC component and various higher harmonic components according to the concept of Fourier series
Wherein n is harmonic order, n is 0,1,2, … …; a isnand bnThe amplitudes of the cosine term and sine term of each harmonic can be obtained according to the principle of Fourier seriesnAnd bnAre respectively as
based on this, only the energy characteristics of the 50hz component are preserved.
The step (4) is specifically to obtain a large number of signal samples of the fault function, analyze the signal samples, fit the functions of the fundamental frequency component and some integral harmonic components according to the principle of minimum error, and the matrix form is that y (i) ═ A (i) X
in the formula
Assume that the sampled value of the transient is: z (i), then our goal is to minimize the sum of squared residuals:
Expanding the attenuation non-periodic component term into Taylor series and taking the first three terms
A (i) and X are each
A(i)＝[1，iTs，(iTs)2，sin(ωiTs)，cos(ωiTs)，…sin(nωiTs)，cos(nωiTs)]
Obtaining a parameter matrix and an input matrix of the model, wherein X has dimension number m, and when i is 1,2
A×X＝Y
All elements in the X vector are obtained through the formula, and the fundamental wave and the second harmonic wave are calculated:
After the parameter values are obtained, the non-periodic component of the current after the fault, namely the specific parameter of the attenuated direct current component can be obtained, and the parameter data of the non-periodic component of the fault current with high quality can be obtained according to the data collection of the specific parameter.
And (5) specifically, after the fitting parameters of the step (4) are obtained, the energy contribution and all parameters of the desired function are obtained, the signal of the non-periodic component is subtracted at each sampling point, the finally obtained signal is the signal with the non-periodic component filtered, and the signal is used for performing true effective value calculation to obtain the true effective value of the current alternating current.
the invention provides a method for accurately detecting the parameter value of the attenuation direct current component in the alternating current fault of a power grid, which can be used in the microcomputer comprehensive protection to determine the degree of the fault after the fault is generated, and is suitable for being used in the microcomputer comprehensive protection, a transformer substation and the environment needing detailed information analysis on the circuit fault. The method can provide fault information as much as possible for a system to analyze and decide after a circuit has a fault, carry out parameter approximation in a Taylor expansion and curve fitting mode, carry out pre-filtering through Fourier series, quickly detect the fault within 25ms through an embedded platform and obtain fault related technical parameters, and can better and more stably realize various functions of automatic detection, automatic adaptation and the like by matching with a big data analysis algorithm and an intelligent algorithm.
The beneficial effects of the invention also include: 1. the components of the fault may be quantified; 2. the precision influence generated by the fault can be accurately filtered after the current has the fault; 3. as much fault parameter information as possible is available that can provide a high quality data analysis basis for advanced algorithms.
Drawings
FIG. 1 is a voltage sampling diagram of one cycle before and after conversion in current scaling according to the present invention;
FIG. 2 is a graph comparing data and frequency before and after filtering in accordance with the present invention.
Detailed Description
The invention provides a method for accurately detecting an attenuated direct current component parameter in fault current, which comprises the following steps:
(1) firstly, reducing the current in an equal ratio to reduce the three-phase alternating current to 0-300 mA;
(2) Performing AD sampling of alternating current, namely discretization of an analog signal;
(3) performing Fourier pre-filtering on the discrete signals, and filtering all components which are not integer multiples of 50hz fundamental frequency signals;
(4) Carrying out fault curve fitting on the filtered alternating current signal, namely establishing a fault model, and finding a group of parameters on the basis of the fault model to ensure that the fault curve is most fit with the fitted curve, so that the error value is kept to be minimum;
(5) And (4) filtering the attenuation direct current component added by the fault through the parameters of the fault model obtained in the step (4) to obtain a true effective value of the non-fault current, and carrying out quantitative analysis on the fault.
The method comprises the following specific steps:
1. Current scaling:
Before signal processing, current scaling is performed. The circuit function is firstly converted by a high-precision current transformer, the secondary output of the transformer is connected with an operational amplifier I/V conversion circuit to improve the load capacity of the transformer, and the transformer works in a zero-load state. The converted voltage is sent to an AD sampling module to carry out discretization of an analog signal.
The proportional transformation of the current can be calculated by the above formula according to the voltage division and the shunt action of the resistor, that is, the input of 110V can obtain a difference of 0.75 through the conversion of the circuit, the maximum voltage which can be sampled by the AD sampling of the straight surface is 3.3V, and the maximum difference is 3.3V-1.65V to 1.65V because of the alternating current and the intermediate point is 1.65V, and the maximum voltage which can be sampled is 242V. The voltage sampling one cycle before and after the conversion is shown in fig. 1.
2. Discretization of analog signals:
The signal after the geometric reduction is subjected to discretization sampling, the original analog signal can be restored to a certain degree if the sampling times are more than 16 times within 20ms, AD sampling is carried out in a successive after all method mode in the invention, and the sampling points are 16 points, namely the sampling frequency is 800 hz.
The successive approximation conversion process is as follows: resetting each bit of the successive approximation register during initialization; when the conversion starts, the highest position 1 of the successive approximation register is firstly sent to a D/A converter, the analog quantity generated after the D/A conversion is sent to a comparator, called Vo, and is compared with the analog quantity Vi to be converted sent to the comparator, if Vo < Vi, the position 1 is reserved, otherwise, the position is cleared. Then, the second highest bit of the successive approximation register is set to be 1, new digital quantity in the register is sent to a D/A converter, the output Vo is compared with Vi, if Vo < Vi, the bit 1 is reserved, otherwise, the bit is cleared. This process is repeated until the lowest bit of the register is approached. And after the conversion is finished, the digital quantity in the successive approximation register is sent to a buffer register to obtain the output of the digital quantity. The successive approximation operation is performed under the control of a control circuit.
Storing the signals after dispersion as matrix storage, and storing in two dimensions, wherein the first dimension is sampling time; the second dimension is the signal after the time sampling, and the matrix is used as a 2 × 16 matrix as the operation data basis of the method invented later.
3. Fourier function filtering:
The basic idea of the fourier function is derived from the fourier series, and assuming that the sampled analog signal is a periodic time function, which may be a time function, or a non-sinusoidal function containing multiple harmonic components, the periodic function can be decomposed into a constant dc component and various higher harmonic components according to the concept of the fourier series, which can be expressed as
Wherein n is harmonic order, n is 0,1,2, … …; a isnand bnthe amplitudes of the cosine and sine terms of the respective harmonics.
From the principle of Fourier series, a can be obtainednAnd bnare respectively as
This algorithm for calculating the whole sampling period is called full cycle Fourier algorithm. The full-wave Fourier algorithm has strong filtering capability, can filter direct-current components and all integer subharmonic components, and has good stability. The fourier transform is derived from a periodic signal, and if there is an attenuated dc component in the sampled signal, the fourier algorithm will bring about a large calculation error.
4. and (3) fitting a fault curve:
When a large number of signal samples of the fault function are obtained and analyzed, it can be known that the signal samples of the fault function are basically formed by combining transient electric quantity and a certain non-periodic component. It is also the key point of the present invention, that is, the function of the fundamental frequency component and some whole harmonic components is fitted according to the principle of minimum error. The matrix form is y (i) ═ A (i) X
In the formula
Assume that the sampled value of the transient is: z (i), then our goal is to minimize the sum of squared residuals:
expanding the attenuation non-periodic component term into Taylor series and taking the first three terms
A (i) and X are each
A(i)＝[1，iTs，(iTs)2，sin(ωiTs)，cos(ωiTs)，…sin(nωiTs)，cos(nωiTs)]
Thus, a parameter matrix and an input matrix of the model are obtained, X has a dimension number of m, and when i is 1,2
A×X＝Y
All the elements in the X vector can be found by the above formula, but all unknowns need not be calculated in our invention. We can calculate only the fundamental wave and the second harmonic, that is, obtain:
after the parameter values are obtained, specific parameters of the non-periodic component of the current after the fault, namely the attenuation direct current component, can be obtained, and parameter data of the non-periodic component of the fault current with high quality can be obtained according to data collection of the specific parameters, so that data analysis can be carried out in the next step.
The emulation code implemented on MATLAB is as follows:
% coefficient of construction matrix
for i＝1:16
COEFF(1,i)＝1；
COEFF(2,i)＝i*(1/fs)；
COEFF(3,i)＝(i*(1/fs))^2；
COEFF(4,i)＝sin(100*pi*i*(1/fs))；
COEFF(5,i)＝cos(100*pi*i*(1/fs))；
end
% of coefficient matrix to obtain inverse pseudo matrix
InversePseudoMatrix_Coeff＝pinv(COEFF)；
% derived parameter matrix
Parameter_Matrix＝SourceData(:,5)'*InversePseudoMatrix_Coeff；
% derived fitted matrix
Least_Squares_Y＝Parameter_Matrix*COEFF；
5. And (3) filtering non-periodic component quantization fault parameters:
After the fitting parameters described above are obtained, the energy contribution and all parameters of the desired function can be obtained, and the signal of the non-periodic component is subtracted at each sampling point. The resulting signal is the signal filtered from the non-periodic components and can be used for true effective value calculation and the true effective value of the present alternating current can be obtained more accurately.
Claims (6)
1. A method for accurately detecting parameters of attenuated direct current components in fault current is characterized by comprising the following steps:
(1) Firstly, reducing the current in an equal ratio to reduce the three-phase alternating current to 0-300 mA;
(2) Performing AD sampling of alternating current, namely discretization of an analog signal;
(3) performing Fourier pre-filtering on the discrete signals, and filtering all components which are not integer multiples of 50hz fundamental frequency signals;
(4) carrying out fault curve fitting on the filtered alternating current signal, namely establishing a fault model, and finding a group of parameters on the basis of the fault model to ensure that the fault curve is most fit with the fitted curve, so that the error value is kept to be minimum;
(5) And (4) filtering the attenuation direct current component added by the fault through the parameters of the fault model obtained in the step (4) to obtain a true effective value of the non-fault current, and carrying out quantitative analysis on the fault.
2. a method for accurately detecting a parameter of a pad dc component in a fault current as claimed in claim 1, wherein: the step (1) is specifically that firstly, the high-precision current transformer is used for conversion, the secondary output of the transformer is connected with an operational amplifier I/V conversion circuit to improve the load capacity of the transformer, the transformer works in a zero-load state, the converted voltage is sent to an AD sampling module to carry out discretization of an analog signal,
The proportional transformation of the current can be calculated using the above formula based on the voltage division and shunting action of the resistors.
3. A method for accurately detecting a parameter of a pad dc component in a fault current as claimed in claim 1, wherein: the step (2) is to perform discretization sampling on the signal after geometric reduction, and for the sampling times which are more than 16 times of sampling within 20ms, in the invention, a successive approximation method is adopted to perform AD sampling, the sampling points are 16 points, namely the sampling frequency is 800hz, then the discretized signal is stored as a matrix and stored by two dimensions, the first dimension is the sampling time, the second dimension is the signal sampled at the time, and the matrix is a 2 x 16 matrix.
4. A method for accurately detecting a parameter of a pad dc component in a fault current as claimed in claim 1, wherein: the step (3) can decompose the periodic function into constant DC component and various higher harmonic components according to the concept of Fourier series
Wherein n is harmonic order, n is 0,1,2, … …; a isnAnd bnthe amplitudes of the cosine term and sine term of each harmonic can be obtained according to the principle of Fourier seriesnAnd bnare respectively as
Based on this, only the energy characteristics of the 50hz component are preserved.
5. a method for accurately detecting a parameter of a pad dc component in a fault current as claimed in claim 1, wherein: step (4) is specifically to obtain a large number of signal samples of the fault function, analyze the signal samples, fit the functions of the fundamental frequency component and some integral harmonic components according to the principle of minimum error, and form a matrix of the functions
y(i)＝A(i)X
in the formula
assume that the sampled value of the transient is: z (i), then our goal is to minimize the sum of squared residuals:
Expanding the attenuation non-periodic component term into Taylor series and taking the first three terms
A (i) and X are each
A(i)＝[1，iTs，(iTs)2，sin(ωiTs)，cos(ωiTs)，…sin(nωiTs)，cos(nωiTs)]
obtaining a parameter matrix and an input matrix of the model, wherein X has dimension number m, and when i is 1,2
A×X＝Y
All elements in the X vector are obtained through the formula, and the fundamental wave and the second harmonic wave are calculated:
after the parameter values are obtained, the non-periodic component of the current after the fault, namely the specific parameter of the attenuated direct current component can be obtained, and the parameter data of the non-periodic component of the fault current with high quality can be obtained according to the data collection of the specific parameter.
6. A method for accurately detecting a parameter of a pad dc component in a fault current as claimed in claim 1, wherein: and (5) specifically, after the fitting parameters of the step (4) are obtained, the energy contribution and all parameters of the desired function are obtained, the signal of the non-periodic component is subtracted at each sampling point, the finally obtained signal is the signal with the non-periodic component filtered, and the signal is used for performing true effective value calculation to obtain the true effective value of the current alternating current.
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| CN110970878A (en) * | 2019-12-24 | 2020-04-07 | 宁夏凯晨电气集团有限公司 | Method for improving band-limited time current quick-break precision based on mean filtering |
| CN112198361A (en) * | 2020-10-12 | 2021-01-08 | 宁夏凯晨电气集团有限公司 | Electric singular point monitoring device based on frequency energy ratio |
| CN115184673A (en) * | 2022-09-13 | 2022-10-14 | 山东大学 | Attenuated direct current accurate transient calculation method based on 90-degree phasor rotator |
| CN117517755A (en) * | 2024-01-08 | 2024-02-06 | 石家庄科林电气股份有限公司 | Method for rapidly determining alternating current component in electric quantity and protection measurement and control safety device |
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| CN117517755B (en) * | 2024-01-08 | 2024-03-19 | 石家庄科林电气股份有限公司 | Method for rapidly determining alternating current component in electric quantity and protection measurement and control safety device |
| CN117970039A (en) * | 2024-04-01 | 2024-05-03 | 山东大学 | Distribution line fault moment detection method |
| CN117970039B (en) * | 2024-04-01 | 2024-06-04 | 山东大学 | Distribution line fault moment detection method |
| CN118050588A (en) * | 2024-04-16 | 2024-05-17 | 锐曜石医疗科技(苏州)有限公司 | Electric fault detection method for ultrasonic cutting knife |
| CN118050588B (en) * | 2024-04-16 | 2024-06-21 | 锐曜石医疗科技(苏州)有限公司 | Electric fault detection method for ultrasonic cutting knife |
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