CN111965408A - AC-DC hybrid power grid fault zero-sequence voltage amplitude detection method based on morphological filter - Google Patents
AC-DC hybrid power grid fault zero-sequence voltage amplitude detection method based on morphological filter Download PDFInfo
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Abstract
The invention relates to the technical field of power distribution network fault detection, and discloses an alternating current-direct current hybrid power grid fault zero-sequence voltage amplitude detection method based on a morphological filter, which comprises the following steps of S1: designing a generalized morphological filter, and constructing a generalized open-close filter and a closed-open filter by adopting an algorithm of selecting structural elements with different sizes and through cascade open-close operation; s2: and detecting the fault voltage drop depth of the power signal by using S transformation on the basis of the filtering of the generalized form filter in S1. Compared with the prior art, the invention uses the generalized form filter, improves the signal anti-jamming capability, considers the time-shifting deviation generated in the fault voltage drop detection, adds the adjustment factor, ensures that the fault zero-sequence voltage can be converted under the action of window functions of different adjustment factors, and improves the precision of the fault zero-sequence voltage amplitude detection.
Description
Technical Field
The invention relates to the technical field of power distribution network fault detection, in particular to an alternating current-direct current hybrid power grid fault zero sequence voltage amplitude detection method based on a morphological filter.
Background
With the large-scale access of various distributed power sources and the application of an alternating current and direct current hybrid power distribution technology, a power distribution network is transformed from a traditional single-power radiation type alternating current power grid into a complex network with multiple power sources for parallel power supply and alternating current and direct current hybrid operation, fault transient response and fault characteristic quantity of the complex network present new characteristics, and therefore fault judgment and positioning of various distributed energy alternating current and direct current hybrid power grids face new challenges. The morphological filter is an important signal processing method, and the morphological filter expands and corrodes the detected electric power signal by selecting structural elements with different lengths and shapes, so that the interference component in the detected electric power signal is effectively filtered, and the detection precision of the fault characteristic quantity of the complex power distribution network is guaranteed.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a method for detecting the zero sequence voltage amplitude of the fault of an alternating current-direct current hybrid power grid based on a morphological filter.
The technical scheme is as follows: the invention provides a method for detecting a fault zero sequence voltage amplitude of an alternating current-direct current hybrid power grid based on a morphological filter, which comprises the following steps:
s1: designing a generalized morphological filter, and constructing a generalized open-close filter and a closed-open filter by adopting an algorithm of selecting structural elements with different sizes and through cascade open-close operation;
the generalized on-off filter can be expressed as:
the generalized on-off filter can be expressed as:
wherein, FOC(x (n)) represents a generalized open-close filter, x (n) represents the signal to be filtered, n is the number of sampling points,
g1、g2respectively representing two structural elements,. representing a closed operation,
representing an open operation;
s2: and detecting the amplitude of the zero sequence voltage by using S transformation on the basis of the filtering of the generalized morphological filter in S1.
Furthermore, the selection of the structural elements directly influences the filtering effect of the generalized morphological filter, and the standard for measuring the filtering effect is the signal-to-noise ratio and the root-mean-square error;
selected structuring element SNRchooseThe conditions are satisfied as follows:
root Mean Square Error (RMSE) of selected structural elementschooseThe conditions are satisfied as follows:
wherein, i is 1.2.3 … n, n is the number of sampling points, tiFor each sampling instant, f (t)i) For the original fault grid voltage,
is the filtered fault grid voltage.
Further, the step of detecting the amplitude of the zero sequence voltage by using S transformation in S2 includes:
step 1: reading voltage parameters, initialization factors and storage space;
step 2: assigning the factors from 0 to 10 by 0.1 step length, and calculating a window function W (tau-t, f) and a transformed zero sequence voltage amplitude extraction quantity S (tau, f) in each step;
wherein, tau is time and is used for controlling the translation of the window function on a time axis, X (t) is a zero sequence voltage signal to be converted, and f is frequency;
and step 3: and giving the amplitude of the zero sequence voltage according to the finally obtained image. .
Has the advantages that:
when the generalized form filter is used, the anti-interference capability of the signal is improved. Considering that time shifting deviation can be generated in zero sequence voltage detection, the adjustment factor is added, the fault zero sequence voltage can be ensured to be converted under the action of window functions of different adjustment factors, and the precision of fault zero sequence voltage amplitude detection is improved.
Drawings
FIG. 1 is a decision diagram for detecting zero sequence voltage amplitude of a fault of an AC/DC hybrid power grid based on a morphological filter;
FIG. 2 is a flow chart of the algorithm for the S-transform;
FIG. 3 is a graph of a post-fault grid voltage waveform;
FIG. 4 is a diagram of a grid voltage waveform after being filtered by a generalized morphology filter;
FIG. 5 is a waveform diagram after filtering by a 100Hz low pass filter;
FIG. 6 is a zero sequence voltage waveform diagram;
fig. 7 is a diagram of zero sequence voltage amplitude detected by S transformation.
Detailed Description
The following will more clearly and completely describe the detailed embodiments of the present invention in conjunction with the attached drawings in the examples of the present invention.
As shown in fig. 1, a decision diagram of a fault zero-sequence voltage amplitude detection method for an ac/dc hybrid power grid based on a morphological filter mainly includes two steps, respectively:
step 1: a generalized morphological filter is designed.
The generalized morphological filter adopts an algorithm of selecting structural elements with different sizes and constructs a generalized open-close and closed-open filter through cascade open-close operation.
The generalized on-off filter can be expressed as:
the generalized on-off filter can be expressed as:
wherein, FOC(x (n)) represents a generalized open-close filter, x (n) represents the signal to be filtered, n is the number of sampling points,
g1、g2respectively representing two structural elements,. representing a closed operation,
representing an open operation;
the selection of the structural elements directly influences the filtering effect of the generalized morphological filter, and the criteria for measuring the filtering effect are signal-to-noise ratio (SNR) and Root Mean Square Error (RMSE).
The signal-to-noise ratio (SNR) can be expressed as:
the Root Mean Square Error (RMSE) can be expressed as:
where i is 1.2.3 … n, n is the number of sampling points, tiFor each sampling instant, f (t)i) Is the original power signal of the power supply,
is a filtered power signal.
SNR of the structural elementchooseThe conditions are satisfied as follows:
root Mean Square Error (RMSE) of structural elementchooseThe conditions are satisfied as follows:
wherein, i is 1.2.3 … n, n is the number of sampling points, tiFor each sampling instant, f (t)i) For the original fault grid voltage,
is the filtered fault grid voltage.
Step 2: and detecting the amplitude of the zero sequence voltage by using S transformation.
1) And reading the voltage parameter, the initialization factor and the storage space.
2) The adjustment factor is assigned from 0 to 10 in 0.1 steps, and a window function W (τ -t, f) and a transformed pressure drop extraction S (τ, f) are calculated at each step.
Wherein, tau is time and is used for controlling the translation of the window function on the time axis, X (t) is a zero sequence voltage signal to be converted, and f is frequency.
3) And giving the amplitude of the zero sequence voltage according to the finally obtained image.
As shown in fig. 3, the waveform of the original grid voltage in fig. 3 is taken as an example, which contains more harmonics. After filtering by the generalized morphological filter, the harmonic components are significantly reduced as shown in fig. 4. The original power grid voltage still has a large amount of harmonic waves after being filtered by the 100Hz low-pass filter, as shown in figure 5, so the generalized form filter has better filtering effect than the common filter. As shown in fig. 6, which is a waveform diagram of the zero sequence voltage, the amplitude of the zero sequence voltage obtained after S transformation is 0.3, as shown in fig. 7.
In summary, the invention improves the signal anti-interference capability when using the generalized morphological filter. Considering that time shifting deviation can be generated in zero sequence voltage detection, the adjustment factors are added, the fault zero sequence voltage can be ensured to be converted under the action of window functions of different adjustment factors, and the precision of fault zero sequence voltage amplitude detection is improved.
The above embodiments are merely illustrative of the technical concepts and features of the present invention, and the purpose of the embodiments is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (3)
1. A method for detecting the zero sequence voltage amplitude of an alternating current-direct current hybrid power grid fault based on a morphological filter is characterized by comprising the following steps:
s1: designing a generalized morphological filter, and constructing a generalized open-close filter and a closed-open filter by adopting an algorithm of selecting structural elements with different sizes and through cascade open-close operation;
the generalized on-off filter can be expressed as:
the generalized on-off filter can be expressed as:
wherein, FOC(x (n)) represents a generalized open-close filter, x (n) represents the signal to be filtered, n is the number of sampling points,
g1、g2respectively representing two structural elements,. representing a closed operation,
representing an open operation;
s2: and detecting the amplitude of the zero sequence voltage by using S transformation on the basis of the filtering of the generalized morphological filter in S1.
2. The alternating current-direct current hybrid power grid fault zero sequence voltage amplitude detection method based on the morphological filter is characterized in that the selection of the structural elements directly influences the filtering effect of the generalized morphological filter, and the standard for measuring the filtering effect is the signal-to-noise ratio and the root-mean-square error;
selected structuring element SNRchooseThe conditions are satisfied as follows:
root Mean Square Error (RMSE) of selected structural elementschooseThe conditions are satisfied as follows:
wherein, i is 1.2.3 … n, n is the number of sampling points, tiFor each sampling instant, f (t)i) For the original fault grid voltage,
is the filtered fault grid voltage.
3. The AC-DC hybrid power grid fault zero-sequence voltage amplitude detection method based on the morphological filter as claimed in claim 1, wherein the step of detecting the amplitude of the zero-sequence voltage by using S transformation in S2 comprises:
step 1: reading voltage parameters, initialization factors and storage space;
step 2: assigning the factors from 0 to 10 by 0.1 step length, and calculating a window function W (tau-t, f) and a transformed zero sequence voltage amplitude extraction quantity S (tau, f) in each step;
wherein, tau is time and is used for controlling the translation of the window function on a time axis, X (t) is a zero sequence voltage signal to be converted, and f is frequency;
and step 3: and giving the amplitude of the zero sequence voltage according to the finally obtained image.
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