CN112067887A - Method for calculating phase quantity under condition of sampling value loss based on filter orthogonal characteristic - Google Patents

Abstract

The present disclosure provides a phasor calculation method in the case of loss of sampling values based on the quadrature characteristics of the filter; wherein, the first solution is to find the position of the symmetrical point in the filter according to the position of the lost sampling point in the sampling value sequence; The coefficients of the symmetrical points in the quadrature filter are set to zero to obtain a modified quadrature filter; the modified quadrature filter is applied to the sample value sequence to obtain an accurate phasor calculation result. Scheme 2: Connect the sampling point sequences before and after the missing point end to end to form a pseudo-continuous sampling value sequence; calculate the corresponding orthogonal filter coefficients according to the length of the pseudo-continuous sampling sequence; apply the orthogonal filter to the pseudo-continuous sampling sequence Sequence of sampled values to obtain accurate phasor calculations. In the case of loss of sampled values, the solution described in the present disclosure maximizes the calculation accuracy of the filtered phasor by ensuring the orthogonality of the filter.

Description

Phasor Calculation Method in Case of Loss of Sampled Values Based on Orthogonal Characteristics of Filters

technical field

The present disclosure belongs to the technical field of power system automation, and in particular, relates to a phasor calculation method in the case of loss of sampling values based on the quadrature characteristics of filters.

Background technique

The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

In the relay protection, monitoring and other functions of substations, it is necessary to use the phasors of voltage and current for calculation and analysis; among them, the phasors of voltage and current generally use a continuous sequence of sampling values of voltage and current, which is calculated by a filter. . In a smart substation, the sampled values of voltage and current are collected by the merging unit (MU), then sorted into SAV (SAmpledValue, or SV for short) messages, and transmitted to the relay protection, monitoring and other intelligent equipment (IEDs) through the communication network .

During the transmission of SAV packets, some packets may be delayed, out of order, or even lost due to congestion or failure of the communication network. Because functions such as relay protection and monitoring have high requirements on real-time performance, it is difficult to perform complex error correction processing for various transmission errors of SAV messages, so they are often treated as data loss. When a large number of SAV packets are continuously lost, the relay protection and monitoring functions can only take blocking measures to avoid erroneous judgments and actions; The substation hopes that in this case, the relay protection and monitoring functions can achieve their functions as far as possible, so the phasor calculation method in IEDs is required to have a certain ability to resist the loss of sampling values.

The inventor found that, in order to cope with the loss of the sampled value, the current general method is to replace the lost sampled value with an estimated value, and the subsequent filtering and phasor calculation methods have not changed in any way. Among them, the simplest processing method is to replace the lost sample value with a 0 value. Although this processing method is simple in algorithm, it causes the accuracy of the subsequent phasor calculation results to be very poor, so it is rarely applied in practice; in addition, some Researchers have also studied various methods such as polynomial approximation, spline interpolation, curve fitting, etc. However, these methods are difficult to use in real-time applications due to their computational complexity. The Lagrangian polynomial interpolation method (referred to as the pull-type interpolation method) is more common in practical applications, especially the linear and quadratic pull-type interpolation methods have been widely used. Among them, the first-order pull-type interpolation is a commonly used linear interpolation. Its calculation is simple, but the effect is not good in the case of continuous loss of multiple points; the quadratic pull-type interpolation, also known as parabolic interpolation, is more effective than linear interpolation. , but the coefficients of its interpolation formula need to be calculated in real time according to different point loss situations, which increases the computational burden of IEDs.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present disclosure provides a phasor calculation method in the case of loss of sampled values based on the orthogonal characteristic of the filter; in the case of loss of sampled values, the solution ensures the orthogonality of the filter, thereby maximizing the It can greatly improve the calculation accuracy of the filtered phasor.

According to a first aspect of the embodiments of the present disclosure, there is provided a phasor calculation method in the case of loss of sampling values based on the quadrature characteristic of the filter, including:

Obtain message data containing voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Find the position of the symmetrical point in the filter for the position of the missing sampling point in the sampling value sequence;

The coefficients of the symmetrical points in a pair of orthogonal filters are set to zero, and the coefficients of the orthogonal filters are normalized to obtain the modified orthogonal filter;

Applying the modified quadrature filter to the sampled value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

Further, the pair of quadrature filters includes a sine filter and a cosine filter.

Further, use the sine filter to calculate the imaginary part X _I of the fundamental wave phasor:

Among them, N is the number of sampling points in each power frequency cycle, and x(k), k=1,...,N is the sequence of sampling values.

Further, use the cosine filter to calculate the real part X _R of the fundamental wave phasor:

Among them, N is the number of sampling points in each power frequency cycle, and x(k), k=1,...,N is the sequence of sampling values.

Further, the coefficients of the sine filter and the cosine filter satisfy the quadrature condition:

According to a second aspect of the embodiments of the present disclosure, there is provided another phasor calculation method in the case of loss of sampled values based on the quadrature characteristic of the filter, including:

Obtain message data containing voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Connect the sampling point sequence before and after the missing point end to end to form a pseudo-continuous sampling value sequence;

Calculate the corresponding orthogonal filter coefficients according to the length of the pseudo-continuous sampling sequence;

Applying the quadrature filter to the pseudo-continuous sample value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

According to a third aspect of the embodiments of the present disclosure, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory and running on the memory. When the processor executes the program, the above-mentioned filter-based quadrature is implemented The phasor calculation method in the case of missing sample values of a characteristic.

According to a fourth aspect of the embodiments of the present disclosure, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the above-mentioned case where the sampling value is lost based on the orthogonal characteristic of the filter is realized. phasor calculation method.

Compared with the prior art, the beneficial effects of the present disclosure are:

(1) The scheme of the present disclosure obtains the phasor calculation result by modifying the coefficients of the symmetrical points in the orthogonal filter, and using the modified orthogonal filter to act on the sampling value sequence. The calculation method of the scheme is simple and does not require a large number of operations;

(2) The scheme of the present disclosure maintains the orthogonal characteristic of the filter, and ensures the accuracy of the phasor calculation result to the greatest extent in the case of loss of sampling points;

(3) Scheme 1 described in the present disclosure is suitable for various sampling point loss forms. At the same time, since the filtering effect is greatly affected by the number of lost points, scheme 1 is most suitable for applications with small electrical harmonics, such as normal and stable power systems. under working conditions;

(4) The second solution described in the present disclosure is suitable for the situation of continuous point loss, the filtering effect of harmonics is good, and it can be applied to the situation where the harmonics are relatively large or the power system is disturbed.

Description of drawings

The accompanying drawings that constitute a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation of the present application.

FIG. 1(a) and FIG. 1(b) are respectively a schematic diagram of coefficients of a full-cycle Fourier filter (sine filter and cosine filter) and an example diagram of symmetrical coefficients (N=80) described in Embodiment 1 of the present disclosure. ;

2(a) and FIG. 2(b) are respectively schematic diagrams of amplitude-frequency characteristics of filters (sine filter and cosine filter) in the case of missing two-point sample values described in Embodiment 1 of the present disclosure;

3(a) and FIG. 3(b) are respectively schematic diagrams of amplitude-frequency characteristics of filters (sine filter and cosine filter) in the case of missing five-point sampling values described in Embodiment 1 of the present disclosure;

FIG. 4( a ) and FIG. 4( b ) are respectively schematic diagrams of amplitude-frequency characteristics of filters (sine filter and cosine filter) in the case of missing ten-point sample values described in Embodiment 2 of the present disclosure.

Detailed ways

The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

According to the idea of quadrature filter, to calculate the phasor of the electrical quantity, two mutually orthogonal filters w _c and ws _s are required to act on the sampling sequence x of the electrical quantity respectively, so as to obtain the real part X _R and the imaginary part X of the phasor _I , as follows:

where M is the data window length of the filter. The filter coefficients need to satisfy the following orthogonal conditions:

_ec and _es are the normalization coefficients of the filter:

If w _c and w _s take the cosine function and the sine function respectively, and M takes the sampling length N of a power frequency cycle, it is a commonly used full-cycle Fourier fundamental wave filter:

Among them, N is the number of sampling points in each power frequency cycle, and x(k), k=1,...,N is the sequence of sampling values. The sine filter coefficients and cosine filter coefficients satisfy the quadrature condition:

Taking the 80-point sampling per power frequency cycle commonly used in smart substations as an example (N=80), the filter coefficients are drawn as shown in Figures 1(a) and 1(b). It can be seen from the figures:

The sine function is centrally symmetric about the 40th point; the cosine function is axisymmetric about the 40th point; it is precisely because of the above two symmetrical properties that the sine filter and the cosine filter meet the orthogonal conditions;

Further generalization, as long as w _s and w _c satisfy center symmetry and axis symmetry, respectively, they are a pair of orthogonal filters.

In the sine filter and cosine filter, the symmetrical points on both sides of the 40th point are set to 0, and the above symmetry conditions are still satisfied;

For the sine filter and the cosine filter, as long as the number of coefficients on both sides of the 40th point is equal, even if the total number of coefficients is less than 80 points, the above symmetry condition is still satisfied.

Example 1:

The purpose of this embodiment is to provide a phasor calculation method in the case of loss of sampled values based on the quadrature characteristic of the filter.

According to the signal processing theory of power engineering, it can be known that the phasor of an electrical quantity is calculated by filtering and calculating the sampling value sequence of electrical quantity through a pair of orthogonal digital filters, and the obtained results are respectively used as the real part of the electrical quantity phasor and imaginary part, thus realizing the real-time calculation of the phasor. The orthogonality of the two digital filters is of great significance to the accuracy of the phasor calculation results.

When the sample value is lost, for the phasor calculation, it can be regarded that the digital filter coefficient corresponding to the lost point is equal to 0. Then, according to the situation of missing points, the digital filter at this time often no longer satisfy the orthogonality. In order to maintain the orthogonal characteristic of the filter, this patent proposes to find the symmetrical point of the coefficient corresponding to the missing point in the digital filter, and artificially set the coefficient of the symmetrical point to zero, thereby ensuring the orthogonality of the digital filter, and The corrected pair of quadrature filters acts on the sampling value sequence with missing points, and the obtained results are used as the real part and imaginary part of the electrical phasor, so as to maximize the phasor calculation in the case of missing sampling points accuracy.

Based on the above analysis, the present embodiment provides a phasor calculation method in the case of loss of sampling values based on the quadrature characteristics of the filter, including:

Obtain message data containing voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Find the position of the symmetrical point in the filter for the position of the missing sampling point in the sampling value sequence;

The coefficients of the symmetrical points in a pair of orthogonal filters are set to zero, and the coefficients of the orthogonal filters are normalized to obtain the modified orthogonal filter;

Applying the modified quadrature filter to the sampled value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

Further, the steps of obtaining the position of the symmetrical point are as follows:

At any point k of the filter coefficient sequence, its symmetry point is (N-k+1). If the coefficients of the kth point and the (N-k+1)th point in the filter are set to 0 at the same time, the filter still satisfies the quadrature condition of the above formula; where N is the length of the filter coefficient sequence.

Further, taking the commonly used full-cycle Fourier algorithm to calculate the fundamental wave phasor as an example, it uses a pair of orthogonal filters of sine and cosine to calculate the real part X _R and the imaginary part X _I of the fundamental wave phasor:

Among them, N is the number of sampling points in each power frequency cycle, and x(k), k=1,...,N is the sequence of sampling values. The sine filter coefficients and cosine filter coefficients satisfy the quadrature condition:

Taking the 80-point sampling per power frequency cycle commonly used in smart substations as an example (N=80), the filter coefficients are drawn as shown in Figures 1(a) and 1(b). As can be seen from the figure, at any point k of the filter coefficient sequence, its symmetry point is (N-k+1). If the coefficients of the kth point and the (N-k+1)th point in the filter are set to 0 at the same time, the filter still satisfies the quadrature condition of the above formula.

In order to prove the practicability of the scheme described in this example, the specific experimental data is used to prove it here:

Experiment 1:

Taking the full-cycle Fourier algorithm with N=80 as an example, in the sampling value of one cycle, assuming that the sampling values of the 4th and 5th points are lost, the implementation steps of the phasor calculation are as follows:

Step 1: Receive SAV packets through IEDs (intelligent monitoring devices), and analyze the loss of sampling points;

Step 2: The analysis shows that the 4th and 5th sampling points are lost, then according to the position of the lost point in the sampling value sequence, the serial numbers of the symmetrical points in the filter are found to be 76 and 77;

Step 3: Set the coefficients 76 and 77 in the sine and cosine filters to zero to obtain the modified sine and cosine filters;

Step 4: Apply the modified sine and cosine filters to the sequence of sampled values to obtain the phasor calculation result.

The amplitude-frequency characteristics of the modified filter are shown in Figure 2(a) and Figure 2(b). As a comparison, the amplitude-frequency characteristics of the full-cycle Fourier filter after linear interpolation and parabolic interpolation are also drawn in the figure; As can be seen from the figure, the phasor calculation method proposed in the present disclosure ensures that the filter has an amplitude-frequency characteristic of 1 at the power frequency (50 Hz), and has the best comprehensive filtering effect, so the phasor calculation accuracy is high.

Experiment 2:

Taking the full-cycle Fourier algorithm with N=80 as an example, in the sampled values of one cycle, assuming that five sampled values from the 33rd to 37th are lost, the implementation steps of the phasor calculation are as follows:

Step 1: IEDs receive SAV packets and analyze the loss of sampling points;

Step 2: The analysis shows that the 33rd to 37th sampling points are lost, then according to the position of the lost point in the sampling value sequence, find the serial numbers of the symmetrical points in the filter as 44 to 48;

Step 3: Set the 44th to 48th coefficients in the sine and cosine filters to zero to obtain the modified sine and cosine filters;

Step 4: Apply the modified sine and cosine filters to the sequence of sampled values to obtain the phasor calculation result.

The amplitude-frequency characteristics of the modified filter are shown in Fig. 3(a) and Fig. 3(b). As a comparison, the figure also plots the amplitude-frequency characteristics of the full-cycle Fourier filter after linear interpolation and parabolic interpolation. As can be seen from the figure, the phasor calculation method proposed in the present disclosure ensures that the filter has an amplitude-frequency characteristic of 1 at the power frequency (50 Hz), and has the best comprehensive filtering effect, so the phasor calculation accuracy is high.

Embodiment 2:

The purpose of this embodiment is to provide another phasor calculation method in the case of loss of sampled values based on the quadrature characteristic of the filter.

According to the properties of the orthogonal characteristics of the filters, if the two filters satisfy the orthogonal characteristics, even if the filter data window is less than the length of one power frequency cycle, it can achieve a better filtering effect. This phasor calculated from a sampling sequence shorter than one power frequency period is called a small vector.

Based on the above technical concept, the present embodiment proposes a phasor calculation method in the case of loss of sampling values based on the quadrature characteristics of the filter, including:

Obtain message data containing voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Connect the sampling point sequence before and after the missing point end to end to form a pseudo-continuous sampling value sequence;

Calculate the corresponding orthogonal filter coefficients according to the length of the pseudo-continuous sampling sequence;

Applying the quadrature filter to the pseudo-continuous sample value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

Further, the sampling point sequence before and after the missing point is connected end to end, specifically including:

Assuming that a total of q sampling points from point k to point k+q-1 are lost, the sampling sequence of (k+q~N) and the sampling sequence of (1~k-1) can be connected end to end, forming a length of A pseudo-consecutive sampling sequence of N-q:

[x(N-k-q),...,x(N),x(1),...,x(k-1)]

Then the phasor (small vector) can be calculated by using an orthogonal filter of length N-q.

Further, taking the commonly used full-cycle Fourier algorithm to calculate the fundamental wave phasor as an example, it uses a pair of orthogonal filters of sine and cosine to calculate the real part X _R and the imaginary part X _I of the fundamental wave phasor:

Among them, N is the number of sampling points in each power frequency cycle, and x(k), k=1,...,N is the sequence of sampling values. The sine filter coefficients and cosine filter coefficients satisfy the quadrature condition:

In order to prove the practicability of the scheme described in the present disclosure, it is proved by specific experimental data here:

Experiment 3:

Taking the full-cycle Fourier algorithm with N=80 as an example, in the sampled values of one cycle, assuming that the 59th to 68th sampled values are lost, the implementation steps of the phasor calculation are as follows:

Step 1: IEDs receive SAV packets and analyze the loss of sampling points;

Step 2: The analysis shows that the 59th to 68th sampling points are lost, then the sampling sequence number of the pseudo-continuous sampling sequence is: [69,70,…,80,1,2,…,58], a total of 70 sampling points;

Step 3: Calculate the filter coefficients and normalization coefficients of the orthogonal filter with 70 coefficients;

Step 4: Apply a quadrature filter with 70 coefficients to the pseudo-continuous sampling sequence to obtain the phasor calculation result.

Further, the amplitude-frequency characteristics of the filter with 70 coefficients are shown in Figure 4 (a) and Figure 4 (b); as a comparison, the figure also draws the linear interpolation and parabolic interpolation. Amplitude frequency characteristics. As can be seen from the figure, the phasor calculation method proposed in this patent ensures that the filter has an amplitude-frequency characteristic of 1 at the power frequency (50Hz), and has the best comprehensive filtering effect, so the phasor calculation accuracy is high.

Embodiment three:

The purpose of this embodiment is to provide an electronic device.

An electronic device, comprising, a memory, a processor and a computer program stored on the memory to run, the processor implements the following steps when executing the program, including:

Obtain the message data containing the sequence of voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Find the position of the symmetrical point in the filter for the position of the missing sampling point in the sampling value sequence;

Set the coefficients of the symmetrical points in a pair of orthogonal filters to zero to obtain the modified orthogonal filter;

Applying the modified quadrature filter to the sampled value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

/or

Obtain message data containing voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Connect the sampling point sequence before and after the missing point end to end to form a pseudo-continuous sampling value sequence;

Calculate the corresponding orthogonal filter coefficients according to the length of the pseudo-continuous sampling sequence;

Applying the quadrature filter to the pseudo-continuous sample value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

Embodiment 4:

The purpose of this embodiment is to provide a computer-readable storage medium.

A computer-readable storage medium on which a computer program is stored, and when the program is executed by a processor, realizes the following steps, including:

Obtain the message data containing the sequence of voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Find the position of the symmetrical point in the filter for the position of the missing sampling point in the sampling value sequence;

Set the coefficients of the symmetrical points in a pair of orthogonal filters to zero to obtain the modified orthogonal filter;

Applying the modified quadrature filter to the sampled value sequence to obtain an accurate phasor calculation result;

Analyze the voltage and current of the substation according to the calculated phasors;

/or

Obtain message data containing voltage and current sampling values;

Parse the message data, and analyze the loss of sampling points;

Connect the sampling point sequence before and after the missing point end to end to form a pseudo-continuous sampling value sequence;

Calculate the corresponding orthogonal filter coefficients according to the length of the pseudo-continuous sampling sequence;

Applying the quadrature filter to the pseudo-continuous sample value sequence to obtain an accurate phasor calculation result;

The voltage and current of the substation are analyzed according to the calculated phasors.

The phasor calculation method provided by the above-mentioned embodiments in the case of loss of sampled values based on the quadrature characteristic of the filter can be fully realized and has broad application prospects.

The above descriptions are only preferred embodiments of the present disclosure, and are not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included within the protection scope of the present disclosure.

Although the specific embodiments of the present disclosure have been described above in conjunction with the accompanying drawings, they do not limit the protection scope of the present disclosure. Those skilled in the art should understand that on the basis of the technical solutions of the present disclosure, those skilled in the art do not need to pay creative efforts. Various modifications or variations that can be made are still within the protection scope of the present disclosure.

Claims (10)

1. The phasor calculation method under the condition of sampling value loss based on the filter quadrature characteristic is characterized by comprising the following steps:

acquiring message data containing voltage and current sampling values;

analyzing the message data, and analyzing the loss condition of the sampling point;

searching the position of a symmetrical point in the filter according to the position of the lost sampling point in the sampling value sequence;

setting coefficients of symmetrical points in a pair of orthogonal filters to zero, and performing normalization processing on the coefficients of the orthogonal filters to obtain modified orthogonal filters;

applying the modified orthogonal filter to the sampling value sequence to obtain an accurate phasor calculation result;

and analyzing the voltage and the current of the transformer substation according to the calculated phasor.

2. The method for phasor calculation in the case of sample value loss based on filter quadrature characteristics of claim 1 wherein said pair of quadrature filters includes a sine filter and a cosine filter.

3. The method of claim 2, wherein the imaginary component X of the fundamental phasor is calculated using the sine filter_I：

N is the number of sampling points in each power frequency cycle, x (k), where k is 1.

4. The method of claim 2, wherein the cosine filter is used to calculate the real part X of the fundamental phasor_R：

N is the number of sampling points in each power frequency cycle, x (k), where k is 1.

5. The phasor calculation method in the case of a missing sample value based on the filter quadrature characteristic of claim 2, wherein the sine and cosine filter coefficients satisfy the quadrature condition:

6. the phasor calculation method under the condition of sampling value loss based on the filter quadrature characteristic is characterized by comprising the following steps:

acquiring message data containing voltage and current sampling values;

analyzing the message data, and analyzing the loss condition of the sampling point;

connecting sampling point sequences before and after the lost point end to form a pseudo-continuous sampling value sequence;

calculating corresponding orthogonal filter coefficients according to the length of the pseudo-continuous sampling sequence;

applying the orthogonal filter to a pseudo-continuous sampling value sequence to obtain an accurate phasor calculation result;

and analyzing the voltage and the current of the transformer substation according to the calculated phasor.

7. The method for phasor calculation in the case of sample value loss based on filter quadrature characteristics of claim 6, wherein said filter includes a sine filter and a cosine filter.

8. The method of claim 7, wherein the imaginary component X of the fundamental phasor is calculated using the sine filter_I：

Calculating the real part X of the fundamental phasor by using the cosine filter_R：

N is the number of sampling points in each power frequency cycle, x (k), where k is 1.

9. An electronic device comprising a memory, a processor and a computer program stored on the memory for execution, wherein the processor when executing the program implements the method for phasor calculation in case of loss of sample values based on filter quadrature characteristic as claimed in any of claims 1-8.

10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out a phasor calculation method in the event of a loss of sample values based on the filter quadrature characteristic as claimed in any one of claims 1 to 8.

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