CN111965408A - A detection method for fault zero-sequence voltage amplitude of AC-DC hybrid grid based on morphological filter - Google Patents

Abstract

The invention relates to the technical field of distribution network fault detection, and discloses a method for detecting the fault zero-sequence voltage amplitude of an AC-DC hybrid power grid based on a morphological filter. The algorithm of the element constructs a class of generalized open-closed filters and closed-open filters by cascading opening and closing operations; S2: On the basis of the filtering of the generalized morphological filter in S1, the S transform is used to detect the fault voltage of the power signal. drop in depth. Compared with the prior art, the present invention uses a generalized morphological filter to improve the anti-interference ability of the signal. Considering that the time-shift deviation will occur in the fault voltage drop detection, an adjustment factor is added to ensure that the fault zero-sequence voltage can be adjusted between different adjustment factors. The down-conversion under the action of the window function improves the detection accuracy of the fault zero-sequence voltage amplitude.

Description

A morphological filter-based detection of zero-sequence voltage amplitude in AC-DC hybrid grid faults test method

technical field

The invention relates to the technical field of distribution network fault detection, in particular to a method for detecting the fault zero-sequence voltage amplitude of an AC/DC hybrid power grid based on a morphological filter.

Background technique

With the large-scale access of multiple types of distributed power sources and the application of AC-DC hybrid power distribution technology, the distribution network has evolved from a traditional single-power source radiating AC power grid to a complex network with multiple power sources in parallel and AC-DC hybrid operation. , its fault transient response and fault feature quantity present new characteristics, which makes the fault judgment and location of multi-type distributed energy AC-DC hybrid grid face new challenges. The morphological filter is an important signal processing method. It expands and corrodes the measured power signal by selecting structural elements of different lengths and shapes, so as to effectively filter out the interference components in the measured power signal and ensure the complex configuration. Detection accuracy of power grid fault feature quantities.

SUMMARY OF THE INVENTION

Purpose of the invention: The purpose of the present invention is to propose a method for detecting the fault zero-sequence voltage amplitude of an AC/DC hybrid power grid based on a morphological filter. The generalized morphological filter is used to expand and corrode the grid voltage through suitable structural elements, so as to improve the performance of the grid voltage. The accuracy of the grid voltage detection, the grid voltage after filtering out harmonics is subjected to S-transformation to obtain the amplitude of the zero sequence voltage.

Technical solution: The present invention provides a method for detecting the fault zero-sequence voltage amplitude of an AC/DC hybrid power grid based on a morphological filter. The detection method includes the following steps:

S1: Design a generalized morphological filter, adopt the algorithm of selecting structural elements of different sizes, and construct a class of generalized open-closed filter and closed-open filter by cascading opening and closing operations;

The generalized open-closed filter can be expressed as:

The generalized closed-open filter can be expressed as:

g₁、g₂分别代表两个结构元素，·代表闭运算，

代表开运算；Among them, F _OC (x(n)) represents the generalized open-closed filter, x(n) represents the signal to be filtered, n is the number of sampling points,

g ₁ , g ₂ represent two structural elements respectively, · represents a closed operation,

represents the open operation;

S2: On the basis of filtering by the generalized morphological filter in S1, use S transform to detect the amplitude of the zero-sequence voltage.

Further, the selection of the structural elements directly affects the filtering effect of the generalized morphological filter, and the criterion for measuring the filtering effect is the signal-to-noise ratio and the root mean square error;

The selected structuring element signal-to-noise ratio SNR _choose meets the following conditions:

The conditions for the selected structural element root mean square error RMSE _choose are:

为滤波后的故障电网电压。Among them, i=1.2.3...n, n is the number of sampling points, t _i is each sampling time, f(t _i ) is the original fault grid voltage,

is the filtered fault grid voltage.

Further, the step of detecting the amplitude of the zero-sequence voltage using S transform in the S2 includes:

Step 1: Read voltage parameters, initialization factors and storage space;

Step 2: Assign a value to the factor from 0 to 10 with a step size of 0.1, and calculate the window function W(τ-t,f) and the transformed zero-sequence voltage amplitude extraction amount S(τ,f) in each step;

Among them, τ is the time, which is used to control the translation of the window function on the time axis, X(t) is the zero-sequence voltage signal to be transformed, and f is the frequency;

Step 3: According to the final obtained image, the magnitude of the zero-sequence voltage is given. .

Beneficial effects:

When the generalized morphological filter is used in the present invention, the anti-interference ability of the signal is improved. Considering the time-shift deviation in the zero-sequence voltage detection, an adjustment factor is added to ensure that the fault zero-sequence voltage can be transformed under the action of the window function of different adjustment factors, which improves the detection accuracy of the fault zero-sequence voltage amplitude.

Description of drawings

Figure 1 is a decision-making diagram for detecting the zero-sequence voltage amplitude of faults in an AC-DC hybrid grid based on a morphological filter;

Fig. 2 is the algorithm flow chart of S transform;

Figure 3 is the grid voltage waveform diagram after the fault;

Fig. 4 is the grid voltage waveform diagram filtered by the generalized morphological filter;

Figure 5 is a waveform diagram filtered by a 100Hz low-pass filter;

Figure 6 is a zero-sequence voltage waveform diagram;

Fig. 7 is a zero-sequence voltage amplitude diagram detected by S-transformation.

Detailed ways

The specific embodiments of the patent of the present invention will be more clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

As shown in Figure 1, the decision diagram of the detection method of fault zero-sequence voltage amplitude of AC-DC hybrid grid based on morphological filter, the detection method mainly includes two steps, namely:

Step 1: Design a generalized morphological filter.

The generalized morphological filter is a kind of generalized open-closed and closed-open filter constructed by using an algorithm that selects structural elements of different sizes and through cascading open-close operations.

The generalized open-closed filter can be expressed as:

The generalized closed-open filter can be expressed as:

g₁、g₂分别代表两个结构元素，·代表闭运算，

代表开运算；Among them, F _OC (x(n)) represents the generalized open-closed filter, x(n) represents the signal to be filtered, n is the number of sampling points,

g ₁ , g ₂ represent two structural elements respectively, · represents a closed operation,

represents the open operation;

The selection of structural elements directly affects the filtering effect of the generalized morphological filter, and the criteria for measuring the filtering effect are the signal-to-noise ratio (SNR) and the 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:

为滤波后的电力信号。In the formula, i=1.2.3...n, n is the number of sampling points, t _i is each sampling time, f(t _i ) is the original power signal,

is the filtered power signal.

The conditions for the SNR _choose to be satisfied by the structuring element signal-to-noise ratio SNR choose are:

The selected structural element root mean square error RMSE _choose meets the following conditions:

为滤波后的故障电网电压。Among them, i=1.2.3...n, n is the number of sampling points, t _i is each sampling time, f(t _i ) is the original fault grid voltage,

is the filtered fault grid voltage.

Step 2: Use S transform to detect the amplitude of the zero-sequence voltage.

1) Read voltage parameters, initialization factors and storage space.

2) The adjustment factor is assigned a value from 0 to 10 with a step size of 0.1, and the window function W(τ-t, f) and the transformed pressure drop extraction amount S(τ, f) are calculated in each step.

Among them, τ is the time, which is used to control the translation of the window function on the time axis, X(t) is the zero-sequence voltage signal to be transformed, and f is the frequency.

3) According to the final obtained image, the magnitude of the zero-sequence voltage is given.

As shown in FIG. 3 , taking the waveform diagram of the original grid voltage in FIG. 3 as an example, it contains many harmonics. After filtering by the generalized morphological filter, as shown in Figure 4, the harmonic components are significantly reduced. After the original grid voltage is filtered by the 100Hz low-pass filter, there are still a lot of harmonics, as shown in Figure 5. Therefore, the generalized morphological filter has better filtering effect than the ordinary filter. As shown in Figure 6, the waveform of the zero-sequence voltage is obtained after S transformation, and the amplitude of the zero-sequence voltage is 0.3, as shown in Figure 7.

To sum up, when the generalized morphological filter is used in the present invention, the anti-interference capability of the signal is improved. Considering the time-shift deviation in the zero-sequence voltage detection, an adjustment factor is added to ensure that the fault zero-sequence voltage can be transformed under the action of the window function of different adjustment factors, which improves the detection accuracy of the fault zero-sequence voltage amplitude.

The above-mentioned embodiments are only intended to illustrate the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with the art to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention. All equivalent transformations or 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, F_OC(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 SNR_chooseThe conditions are satisfied as follows:

root Mean Square Error (RMSE) of selected structural elements_chooseThe conditions are satisfied as follows:

wherein, i is 1.2.3 … n, n is the number of sampling points, t_iFor 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.

Images