KR20170006067A

KR20170006067A - Apparatus for estimating frequency of power system

Info

Publication number: KR20170006067A
Application number: KR1020150096461A
Authority: KR
Inventors: 임영빈
Original assignee: 엘에스산전 주식회사
Priority date: 2015-07-07
Filing date: 2015-07-07
Publication date: 2017-01-17

Abstract

According to an embodiment, a device for estimating frequency of a power system includes: an analog digital converting unit which receives analog data to be detected from the power system, and converts the received analog data into digital data; and a frequency estimating unit which obtains sampling data by sampling digital data converted through the analog and digital converting unit, and estimates the frequency of the power system by using a result value through discrete Fourier conversion of the obtained sampling data.

Description

[0001] APPARATUS FOR ESTIMATING FREQUENCY OF POWER SYSTEM [0002]

The present invention relates to a frequency estimation apparatus for a power system, and more particularly to a frequency estimation apparatus for a power system capable of accurately estimating a frequency of a power system in accordance with a variable sampling frequency using a magnitude of a discrete Fourier transform (DFT) &Lt; / RTI >

Generally, a power monitoring device such as a protection relay or a phasor measurement unit (PMU) is equipped with a frequency estimating device for estimating a frequency for a voltage or current input from a power supply device.

In the protection relay, the frequency estimating device is used for fault diagnosis, stability determination and fault determination of the system, and the phaser measuring device uses the measured frequency information as basic data for monitoring the state of the system and operating the stable power system.

A conventional frequency estimating apparatus estimates a frequency for a signal input through a zero-crossing method.

1 to 3 are diagrams for explaining a frequency estimation method according to the related art.

As shown in FIG. 1, the frequency estimation method using the conventional zero crossing method detects a time point (T1, T2) crossing a zero point in a signal waveform of an inputted voltage or current, (Tn-1, Tn) at a predetermined interval, as shown in FIG. 2, and calculates the frequency of the sampled two points Tn-1 , Tn) is assumed to be linear, and then a zero intersection point Tzc is calculated using a linear equation.

However, the frequency estimation method using the zero-point crossing method has a problem that it is difficult to accurately detect the zero crossing point, and a large error occurs between the calculated frequency and the actual frequency. In order to reduce the error as described above, it is possible to use a secondary or cubic interpolation method that assumes a waveform between the sampled two points Tn-1 and Tn as a quadratic function or a cubic function.

However, when the second or third interpolation method is used, the amount of computation increases exponentially as the degree increases. This increase in the amount of computation is a large burden on the frequency estimation apparatus.

In addition, the zero crossing method has a very weak structure with respect to the noise included in the original signal. That is, when a signal including noise is applied, as shown in FIG. 3, since a plurality of zero crossing points Tzc1, Tzc2, and Tzc3 may be generated, it is difficult to detect a zero crossing point.

According to an embodiment of the present invention, there is provided a frequency system estimating apparatus for a power system capable of variably setting a sampling frequency of a digital signal according to a user's selection and reflecting the frequency calculation of the system in accordance with the set sampling frequency do.

In the embodiment of the present invention, harmonics and noise are removed through a discrete Fourier transform on a digital signal, and the frequency of the grid power can be estimated based on the size of the fundamental wave according to the removed discrete Fourier transform result A frequency estimation apparatus for a power system is provided.

It is to be understood that the technical objectives to be achieved by the embodiments are not limited to the technical matters mentioned above and that other technical subjects not mentioned are apparent to those skilled in the art to which the embodiments proposed from the following description belong, It can be understood.

An apparatus for estimating a frequency of a power system according to an embodiment includes an analog-digital converter for receiving analog data detected from a power system and converting the received analog data into digital data; And a frequency estimator for estimating a frequency of the power system by sampling the digital data converted by the analog-to-digital converter, wherein the frequency estimator samples the digital data to obtain sampling data, A discrete Fourier transformer for performing a discrete Fourier transform on the sampled values obtained through the sampling value obtaining unit and detecting a magnitude of a fundamental wave according to the discrete Fourier transform; And a frequency detector for detecting the frequency of the power system using the magnitude of the fundamental wave detected through the Fourier transformer.

Also, the size of the fundamental wave decreases as the frequency of the power system decreases.

The fundamental wave is a signal of 60 Hz.

The frequency detector may store a table of magnitude variation of the fundamental wave according to a frequency change of the power system and may determine a frequency of a power system corresponding to a magnitude of the fundamental wave obtained through the discrete Fourier transformer, .

The sampling frequency acquiring unit may further include a sampling frequency setting unit for setting a sampling frequency for sampling the digital data by the sampling value acquiring unit, wherein the sampling frequency acquiring unit acquires a sampling frequency, which is variably set by the sampling frequency setting unit, And obtains the sampling value.

In addition, the size of the fundamental wave changes according to a sampling frequency set through the sampling frequency setting unit.

In addition, the table of the magnitude variation of the fundamental wave according to the frequency change of the power system is classified according to the sampling frequency that can be set through the sampling frequency setting unit.

In addition, when the power system frequency is the first frequency, the size of the first fundamental wave appearing when the first sampling frequency is set through the sampling frequency setting unit is smaller than the size of the first fundamental wave when the second sampling frequency is set through the sampling frequency setting unit Is equal to the size of the second fundamental wave.

If the power system frequency is a second frequency lower than the first frequency, the size of the third fundamental wave appearing when the first sampling frequency is set through the sampling frequency setting unit is smaller than the size of the first fundamental wave The fourth fundamental wave having a size smaller than the second fundamental wave when the second sampling frequency is set through the sampling frequency setting unit is smaller than a difference between the size of the first fundamental wave and the size of the third fundamental wave, Is larger than the difference between the magnitude of the second fundamental wave and the magnitude of the fourth fundamental wave.

According to the embodiment of the present invention, the sampling frequency of the digital signal can be variably set according to the user's selection, and the frequency calculation is reflected according to the set sampling frequency, Structure can be provided to increase flexibility of frequency estimation, thereby improving user satisfaction.

According to an embodiment of the present invention, an analog signal for voltage / current data is converted into a digital signal, a harmonic or a noise included in the digital signal is removed through discrete Fourier transform , It is possible to reduce a frequency estimation error caused by the harmonics or noise, and thus the product reliability can be improved.

In addition, according to the embodiment of the present invention, the frequency estimation rate can be increased by tableizing the magnitude of the output signal according to the discrete Fourier transform of the digital signal according to the systematic frequency and the sample frequency, It is possible to drastically reduce the amount of computation required for the operation.

1 to 3 are diagrams for explaining a frequency estimation method according to the related art.
4 is a block diagram illustrating a configuration of a power system frequency estimation apparatus according to an embodiment of the present invention.
FIG. 5 is a block diagram showing a detailed configuration of the frequency estimator 130 shown in FIG.
6 is a view for explaining a variable sampling method according to a variable sampling frequency according to an embodiment of the present invention.
7 is a diagram illustrating an original signal and a noise composite signal according to an embodiment of the present invention.
FIGS. 8 and 9 show the magnitudes of the fundamental waves obtained by the discrete Fourier transform (DFT) according to the embodiment of the present invention.
10 to 12 are diagrams showing changes in the magnitude of the fundamental wave according to the change of the grid frequency according to the embodiment of the present invention.
FIG. 13 is a flowchart for explaining a step of creating a table according to an embodiment of the present invention.
FIG. 14 is a flowchart illustrating a method of estimating a frequency of a power system according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions in the embodiments of the present invention, which may vary depending on the intention of the user, the intention or the custom of the operator. Therefore, the definition should be based on the contents throughout this specification.

Combinations of the steps of each block and flowchart in the accompanying drawings may be performed by computer program instructions. These computer program instructions may be embedded in a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus so that the instructions, which may be executed by a processor of a computer or other programmable data processing apparatus, Thereby creating means for performing the functions described in the step. These computer program instructions may be stored in a computer-usable or computer-readable memory capable of directing a computer or other programmable data processing apparatus to implement a function in a particular manner. And, as described above, it is also possible for the instructions stored in the computer-usable or computer-readable memory to produce an article of manufacture containing instruction means for performing the functions described in each block or flowchart of the drawings. Computer program instructions may also be stored on a computer or other programmable data processing equipment so that a series of operating steps may be performed on a computer or other programmable data processing equipment to create a computer- It is also possible for the instructions to perform the processing equipment to provide steps for executing the functions described in each block and flowchart of the drawings.

Also, each block or each step may represent a module, segment, or portion of code that includes one or more executable instructions for executing the specified logical function (s). It should also be noted that in some alternative embodiments, the functions mentioned in the blocks or steps may occur out of order. For example, two blocks or steps shown in succession may in fact be performed substantially concurrently, or the blocks or steps may sometimes be performed in reverse order according to the corresponding function.

4 is a block diagram illustrating a configuration of a power system frequency estimation apparatus according to an embodiment of the present invention.

Referring to FIG. 4, the power system frequency estimation apparatus includes an analog signal output unit 110, an analog-to-digital conversion unit 120, and a frequency estimation unit 130.

The analog signal output unit 110 obtains state information of the power system and outputs the obtained state information.

The analog signal output unit 110 includes a voltage detector PT and a current detector CT that detect the voltage and current of the power system and output analog data of the detected voltage and current.

The analog signal output unit 110 may further include a filter for removing aliasing included in each signal output from the voltage detector PT and the current detector CT.

The analog-to-digital conversion unit 120 converts the analog data output through the analog signal output unit 110 into digital data.

Preferably, the analog-to-digital converter 120 receives analog voltage data or analog current data output through the analog signal output unit 110, and converts the received analog voltage data or analog current data into digital data And outputs the converted signal to the frequency estimating unit 130.

The frequency estimator 130 receives the digital data output from the analog-to-digital converter 120 and acquires the frequency of the power system using the received digital data.

Preferably, the frequency estimator 130 samples the received digital data, obtains a sampling value according to the sampling, performs a discrete Fourier transform (DFT) on the obtained sampling value, And estimates the frequency of the power system based on the detected magnitude of the fundamental wave.

At this time, the frequency estimating unit 130 sets the sampling frequency of the digital data to obtain the sampling and sampling values.

The sampling frequency means a sampling rate, and the number of data sampled in one period is determined according to the sampling frequency.

For example, the sampling frequency may include 32 samples / cycle to obtain 32 sampled data within a period based on 60 Hz and 64 samples / cycle to obtain 64 sampled data within the period .

When the sampling frequency is set, the frequency estimator 130 obtains a sampling value of the digital data from the set sampling frequency, and when the sampling value is obtained, the frequency estimator 130 performs a frequency discretization process using a discrete Fourier transform (DFT) And removes the disturbance included in the raw sampled value.

The frequency estimator 130 detects the magnitude of the fundamental wave (60 Hz) with respect to the signal from which the disturbance is removed through the discrete Fourier transform (DFT), and based on the magnitude value of the detected fundamental wave (60 Hz) Estimate the frequency.

For this purpose, the frequency estimator 130 tabulates and stores magnitude values of the fundamental wave (60 Hz) varying according to the set sampling frequency and the grid frequency, and stores the magnitude values of the fundamental wave (60 Hz) And estimates a system frequency corresponding to the set sampling frequency based on the size value.

That is, the frequency estimator 130 acquires the grid frequency according to the set sampling frequency, based on the variable sampling frequency instead of the fixed sampling frequency.

In addition, the frequency estimator 130 may process the sampled values by a discrete Fourier transform (DFT) signal processing technique because the raw data for existing sampling values can be easily affected by various kinds of disturbances. And the size of the fundamental wave (60 Hz) output by the above processing is used as the input of the frequency tracking algorithm, thereby preventing the product reliability degradation and malfunction from various kinds of noise.

Hereinafter, the frequency estimator 130 will be described in more detail.

FIG. 5 is a block diagram showing a detailed configuration of the frequency estimator 130 shown in FIG.

5, the frequency estimation unit 130 includes a sampling frequency setting unit 131, a sampling value acquisition unit 132, a discrete Fourier transform unit 133, and a frequency detection unit 134.

The sampling frequency setting unit 131 sets a sampling frequency for sampling the digital data output through the analog-digital converter 120. [

The sampling frequency to be set may be determined by a sampling frequency setting signal input from the outside.

That is, the sampling frequency setting unit 131 sets a sampling frequency for sampling the digital data based on a sampling frequency setting signal input from a user. In other words, the frequency estimator 130 does not use the value obtained based on the fixed sampling frequency as the input value of the frequency estimation algorithm, but uses the value obtained based on the variable sampling frequency set by the sampling frequency setting unit 131 Value is used as an input value of the frequency estimation algorithm.

6 is a view for explaining a variable sampling method according to a variable sampling frequency according to an embodiment of the present invention.

Generally, in the frequency estimation algorithm, a sampling value is obtained according to one fixed sampling frequency, and the obtained sampling value is used as common input values of various different algorithms.

In other words, the conventional single sampling method uses sampling data obtained at one sampling rate set in the frequency estimation controller as input data of several signal processing algorithms.

At this time, the algorithm may include algorithms 1 through 4, each of which requires a different resolution.

Here, Resolution refers to the minimum change in the analog input to change the digital output value by one level.

Here, if the algorithm 1 is an algorithm requiring the highest resolution, the sampling frequency of the algorithm 1 is selected as a single sampling frequency, and the same sampling frequency as that of the algorithm 1 is also set in the algorithms 2 to 4.

Sampling data obtained based on the same sampling frequency is commonly applied to algorithms 2 to 4 which can sufficiently compute even with a small amount of sampling data as compared with the algorithm 1. [ In this case, in the conventional single sampling method, a large amount of sampling data is applied to an algorithm that can be calculated with a small amount of data, which increases the calculation amount of the frequency estimation controller.

Accordingly, in the present invention, a variable sampling frequency method is used to supplement the existing single sampling frequency method.

Referring to FIG. 6, the variable sampling frequency system includes digital data 210, a sampling frequency 1 220, a sampling frequency 2 230, a sampling value 1 240, a sampling value 2 250, ), Algorithm 2 (270), algorithm 3 (280), and algorithm 4 (290).

The digital data 210 is a signal output through the analog-to-digital converter 120.

Sampling frequency 1 220 is the sampling frequency to be applied to algorithm 1 260 and algorithm 2 270 and sampling frequency 2 230 is the sampling frequency to be applied to algorithm 3 280 and algorithm 4 290, Frequency 1 and sampling frequency 2 are different frequencies.

The sampling value 1 240 is sampling data obtained by applying the sampling frequency 1 220 to the digital data 210 and the sampling value 2 250 is sampling data for the digital data 210, Is sampling data obtained by applying sampling frequency 2 (230) different from frequency 1 (220).

The sampling value 1 240 obtained by applying the sampling frequency 1 220 is an input value of the algorithm 1 260 and the algorithm 2 270 and the sampling value 2 obtained by applying the sampling frequency 2 230 (250) is used as the input values of Algorithm 3 (280) and Algorithm 4 (290).

The variable sampling frequency method has a sampling frequency corresponding to a plurality of sampling rates as described above. The sampling frequency 1 (220) is higher than the sampling frequency 2 (230) and the sampling frequency 2 (230) is branched from the sampling frequency 1 (220). Therefore, the number of sampling data of one period generated by the sampling frequency 1 (220) is larger than the number of sampling data of one period generated by the sampling frequency 2 (230).

Accordingly, a sampling value 2 (250) obtained through a small number of sampling data to which the sampling frequency 2 (230) is applied is input to the algorithm 3 280 and the algorithm 4 290 which can be operated with a relatively low resolution The amount of computation of the controller can be reduced.

At this time, algorithms that desire high resolution are algorithms that precisely desire data to a decimal point, and algorithms that desire low resolution are algorithms that acquire only physical size rather than data precision. Accordingly, the developer appropriately selects the resolution according to the characteristics of the algorithm, and uses variable sampling according to the selected resolution.

Accordingly, in the present invention, the calculation amount of the frequency estimation unit 130, which performs many algorithms, is minimized to enable more efficient management.

In the present invention, sampling data is obtained using only one fixed sampling frequency. However, in the present invention, it is not necessary to perform much computation according to each algorithm characteristic (for example, data for drawing a wave waveform ) Algorithms do not need to increase the amount of computation with unnecessarily large amounts of data.

That is, the unnecessary calculation amount causes an overflow of the frequency estimating unit 130, which causes a secondary damage of a product malfunction due to data loss and error.

Therefore, in the present invention, the sampling frequency to be applied to various algorithms can be variably set, and the system frequency is obtained by utilizing data stored in different tables according to the set sampling frequency.

The sampling value acquisition unit 132 samples the digital data output through the analog-digital conversion unit 120 according to the sampling frequency set through the sampling frequency setting unit 131 to obtain sampling data, And obtains a sampling value according to the sampling data.

The sampling value is a digital value (voltage value) at each sampling point in the digital data over one period according to the sampling frequency.

The sampling value acquisition unit 132 acquires a different number of sampling values according to the set sampling frequency.

That is, when the sampling frequency according to 32 samples / cycle is set, the sampling value acquiring unit 132 acquires 32 sampling values in one cycle based on 60 Hz. When the sampling frequency according to 64 samples / cycle is set, , 64 samples are obtained in one cycle.

Also, even if the same sampling frequency is set, the sampling value acquiring unit 132 acquires a different number of sampling values in one cycle according to the frequency of the system. For example, if the frequency of the system is lowered from 60 Hz to 59 Hz, 55 Hz, and 50 Hz, the number of sampling values obtained in one period increases.

At this time, if the frequency of the system is lowered, the increase width of the number of sampling values obtained by the 32 samples / cycle is larger than the increase width of the number of sampling values obtained by the 64 samples / cycle.

The discrete Fourier transformer 133 performs discrete Fourier transform (DFT) on the sampling value obtained through the sampling value obtaining unit 132 to extract the size of the fundamental wave.

At this time, the fundamental wave has a frequency of 60 Hz.

The discrete Fourier transform (DFT) may be performed on the basis of a sampling frequency set by the sampling frequency setting unit 131 and a sampling value obtained through the sampling value obtaining unit 132 according to the sampling frequency. .

The processing technique for the discrete Fourier transform (DFT) is a technique well known in the art to which the present invention belongs, and a detailed description thereof will be omitted.

The discrete Fourier transformer 133 performs the discrete Fourier transform (DFT) on the basis of the sampling value obtained through the sampling value acquiring unit 132 and the number of the sampling values, .

That is, if the sampling is performed according to the variable sampling frequency as described above, various sampling rate requirements may be improved in the field, such as the efficiency of the frequency estimator 130 and the reduction of the calculation amount. However, in the conventional zero crossing method of estimating the frequency of the system using the number of sampling values per cycle, it is not possible to accurately measure the frequency of the system in accordance with the variable sampling frequency.

In addition, the conventional frequency measurement is calculated based on the number of sampling values per cycle, and the sampling value means a value obtained by converting an analog value into a digital value through the analog-digital conversion unit 120.

However, when a large amount of noise is mixed with the analog value, many white noise, harmonics, and various noises may be mixed with the analog value, so that accurate digital data acquisition is difficult and calculation The frequency measurement is also not accurate.

Therefore, the discrete Fourier transform unit 133 eliminates a method using an analog sample value that is inferior to the noise for the conventional frequency estimation, removes various kinds of noise except the fundamental wave through the discrete Fourier transform (DFT) So that more accurate frequency measurement can be performed.

Since the magnitudes of the fundamental waves obtained through the discrete Fourier transform unit 133 are the same even if the sampling frequency is variable, the grid frequency can be estimated based on the magnitudes of the fundamental waves.

7 is a diagram illustrating an original signal and a noise composite signal according to an embodiment of the present invention.

Referring to FIG. 7, in the case of obtaining 32 sampling values per one cycle based on the digital data of 60 Hz, the original signal data as shown in FIG. 7 (a) should be substantially obtained.

However, various noise may be mixed in the original signal, so that a noise synthesis signal as shown in FIG. 7 (b) is obtained although the signal as in (a) should be obtained.

Therefore, it is difficult to accurately obtain digital data using the noise synthesis signal as shown in FIG. 7 (b), and the system frequency estimation to be calculated based on the noise synthesis signal is not accurately performed.

FIGS. 8 and 9 show the magnitudes of the fundamental waves obtained by the discrete Fourier transform (DFT) according to the embodiment of the present invention.

8 shows that the sampling is performed based on the sampling frequency according to 32 samples / cycle, with respect to the original signal without noise. That is, the figure at the top of FIG. 8 shows a sine wave of 32 samples.

8 shows a composite signal when a disturbance such as noise is synthesized in the original signal.

8 shows the magnitude of the fundamental wave obtained by performing discrete Fourier transform (DFT) on the synthesized synthesized signal.

9 shows that the sampling is performed based on the sampling frequency according to 64 samples / cycle with respect to the original signal without noise. That is, the figure at the top of FIG. 9 shows a sine wave of 64 samples.

9 shows a composite signal when a disturbance such as noise is synthesized in the original signal.

9 shows the magnitude of the fundamental wave obtained by performing discrete Fourier transform (DFT) on the synthesized synthesized signal.

That is, when the system frequency is 60 Hz, the number of sampling values obtainable with respect to the digital data is determined by the sampling frequency. In other words, when the sampling frequency is set to 32 samples / cycle, 32 sampling values are obtained in one cycle, and when the sampling frequency is set to 64 samples / cycle, 64 sampling values are obtained in one cycle.

At this time, the calculation formula of the discrete Fourier transform (DFT) includes the number of sampling values obtained by the sampling frequency.

Therefore, when the system frequency is 60 Hz, the magnitude of the fundamental wave obtained when the sampling frequency is set to 32 samples / cycle and the magnitude of the fundamental wave obtained when the sampling frequency is set to 64 samples / cycle are equal to each other.

That is, when the system frequency is 60 Hz, the size of the fundamental wave obtained when the sampling frequency is set to 32 samples / cycle is 13,200 V, and when the sampling frequency is set to 64 samples / cycle, 13 and 200 V, respectively.

In other words, as shown in FIGS. 8 and 9, different sampling frequencies (samples / cycles) are respectively set, and the second to fifteenth order harmonics are synthesized to 30% of fundamental wave to generate a frequency estimation table, And the frequency of the synthesized signal due to the variable sampling frequency is estimated through the frequency estimation table.

8 and 9, even when the disturbance is synthesized in the original signal regardless of the sampling frequency, the fundamental wave according to the discrete Fourier transform (DFT) at 60 Hz is equal to 13,200 V and is output. When the system frequency is 60 Hz, the fundamental waves obtained through the discrete Fourier transform (DFT) are equal to each other irrespective of the sampling frequency.

That is, if the discrete Fourier transform (DFT) is performed on the assumption that the system frequency is 60 Hz, the number of sampling values according to the sampling frequency is included in the calculation formula for the discrete Fourier transform (DFT) Are the same as each other.

However, when the system frequency decreases from 60 Hz to 59 Hz, 55 Hz, and 50 Hz, the number of sampling values obtained in one cycle becomes larger than the number of sampling values obtained when the frequency is 60 Hz, The size is also reduced.

In other words, with the sampling frequency set to 32 samples / cycle, the number of sampled values obtained when the system frequency is 60 Hz is 32, but as the system frequency decreases from 60H to 59 Hz, 55 Hz and 50 Hz, The number of values is also increased.

At this time, the number of sampling values obtained in the one cycle is increased according to the change of the system frequency, and the discrete Fourier transform (DFT) is performed according to the number of the sampling values. Change.

More specifically, as the grid frequency decreases, the size of the fundamental wave obtained through the discrete Fourier transform unit 133 also decreases.

At this time, the decrease width of the fundamental wave at the sampling frequency of 64 samples is larger than the decrease width of the fundamental wave at the 32 samples.

Accordingly, the magnitude of the fundamental wave when the grid frequency is 60 Hz appears at 64 samples / cycle and the same value at 32 samples / cycle. However, as the grid frequency decreases, the magnitude of the fundamental wave also decreases. At this time, since the decrease width in the sample / cycle is larger than the decrease width in 32 samples / cycle, Size also appears differently.

Accordingly, when the magnitude of the fundamental wave is detected through the discrete Fourier transformer 133, the frequency detector 134 detects the magnitude of the fundamental wave and the sampling frequency set through the sampling frequency setting unit 131 in the pre- And extracts a system frequency corresponding to the system frequency.

To this end, the frequency detector 134 stores a magnitude value of a fundamental wave according to a discrete Fourier transform (DFT) varying according to a sampling frequency and a grid frequency as a table, and sets the sampling frequency setting unit 131) and a grid frequency corresponding to a magnitude value of the fundamental wave to estimate the grid frequency.

10 to 12 are diagrams showing changes in the magnitude of the fundamental wave according to the change of the grid frequency according to the embodiment of the present invention.

Referring to FIG. 10, in the state where the sampling frequency is set to 32 samples / cycle, the fundamental frequency according to the discrete Fourier transform (DFT) is 13,200 V when the system frequency is 60 Hz, The magnitude of the fundamental wave according to the discrete Fourier transform (DFT) decreases to 13,161V.

Referring to FIG. 11, in the state where the sampling frequency is set to 32 samples / cycle, the fundamental frequency according to the discrete Fourier transform (DFT) when the system frequency is 60 Hz is 13,200 V, The magnitude of the fundamental wave according to the discrete Fourier transform (DFT) in the case of 59 Hz is 13,161 V, but the magnitude of the fundamental wave according to the discrete Fourier transform (DFT) when the system frequency is 55 Hz is further reduced to 13,038 V .

12, in the state where the sampling frequency is set to 32 samples / cycle, the magnitude of the fundamental wave according to the discrete Fourier transform (DFT) when the system frequency is 60 Hz is 13,200 V, The fundamental wave according to the discrete Fourier transform (DFT) at the frequency of 59 Hz is 13,161 V and the fundamental wave according to the discrete Fourier transform (DFT) at the frequency of 55 Hz is 13,038 V, The magnitude of the fundamental wave according to the discrete Fourier transform (DFT) that occurs when the frequency is 50 Hz is further reduced to 12,320 V.

Accordingly, the frequency detector 134 stores a magnitude value of the fundamental wave according to the discrete Fourier transform (DFT) represented by the sampling frequency and the change of the grid frequency as a table.

The above table may be as shown in Table 1.

Sampling frequency System frequency Basic Wave Size 32 samples / cycle

60Hz 13200V 59Hz 13161V 55Hz 13038V 50Hz 12320V

In addition, the frequency detector 134 may check the state of a change in the magnitude of the fundamental wave according to the system frequency, which occurs when the sampling frequency is 64 samples / cycle, It can be made into a table.

When the disturbance is synthesized into the signal data as described above, accurate frequency measurement can not be performed with the existing frequency estimation technique that counts the number of sampling data and counts the frequency, because the sample data is distorted or distorted due to the disturbance. Also, when the sampling frequency is variable, the number of sample data included in one period is variable, so that the conventional frequency estimation technique can not normally measure the frequency according to the variable sampling frequency. Therefore, in the present invention, accurate frequency estimation is performed according to the variable sampling frequency without using the number of sample data and robust to disturbance by using one period magnitude value.

That is, in order to overcome the structural contradiction that can not be removed when a disturbance occurs, in a method of counting the number of sampling data included in an existing one cycle and estimating the frequency, a data size (Magnitude ), And we propose a robust frequency estimation technique for the variable sampling data and the disturbance through this magnitude value. This method eliminates harmonics and disturbances by performing discrete Fourier transform (DFT) signal processing differently from the conventional method of estimating the frequency using a sample of a distorted original signal. In the present invention, the signal values processed corresponding to each frequency with the signal value in which the disturbance is removed as described above are tabularized to estimate the frequency.

FIG. 13 is a flowchart for explaining a step of generating a table according to an embodiment of the present invention. FIG. 14 is a flowchart for explaining a power system frequency estimation method according to an embodiment of the present invention.

First, the frequency estimator 130 receives the digital data output through the analog-digital converter 120 (operation 110).

The frequency estimator 130 sets a sampling frequency for sampling the received digital data (operation 120). The sampling frequency may be set to 32 samples / cycle or 64 samples / cycle.

Thereafter, the frequency estimator 130 activates a timer interrupt to acquire sample data according to the set sampling frequency (step 130).

In operation 140, the frequency estimator 130 samples the received digital data on the basis of the set sampling frequency in accordance with the activation of the timer interrupt, thereby obtaining a sampling value.

Thereafter, the frequency estimator 130 performs discrete Fourier transform on the obtained sampling value when the sampling value is obtained (operation 150).

Then, the frequency estimator 130 detects the magnitude of the fundamental wave of 60 Hz according to the discrete Fourier transform (operation 160).

Thereafter, the frequency estimator 130 stores the set sampling frequency, the predetermined system frequency, and the detected fundamental wave size in a table (operation 170).

The frequency estimator 130 sets a sampling frequency that is different from the previously set sampling frequency or a system frequency that is different from the previously set system frequency, (Steps 110-170), and stores the magnitude values of fundamental waves according to all the sampling frequencies and the grid frequencies in a table.

Referring to FIG. 14, the frequency estimator 130 receives digital data output through the analog-digital converter 120 (operation 210).

The frequency estimator 130 sets a sampling frequency for sampling the received digital data (step 220). The sampling frequency may be set to 32 samples / cycle or 64 samples / cycle.

Thereafter, the frequency estimator 130 activates a timer interrupt to acquire sample data according to the set sampling frequency (step 230).

In operation 240, the frequency estimator 130 performs sampling on the received digital data on the basis of the set sampling frequency in accordance with the activation of the timer interrupt, thereby obtaining a sampling value.

Thereafter, the frequency estimator 130 performs a discrete Fourier transform on the obtained sampling values when the sampling values are obtained (operation 250).

Then, the frequency estimator 130 detects a fundamental frequency of 60 Hz according to the discrete Fourier transform (step 260).

In step 270, the frequency estimator 130 detects a grid frequency corresponding to the set sampling frequency and the detected fundamental wave size in the pre-stored table.

The features, structures, effects and the like described in the embodiments are included in at least one embodiment and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects and the like illustrated in the embodiments can be combined and modified by other persons skilled in the art to which the embodiments belong. Accordingly, the contents of such combinations and modifications should be construed as being included in the scope of the embodiments.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. It can be seen that the modification and application of branches are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof.

110: Analog signal output section
120: Analog-to-digital conversion section
130: Frequency estimator
140: Sampling frequency setting unit
150: Sampling value obtaining unit
160: Discrete Fourier transform unit
170:

Claims

An analog-digital converter for receiving the analog data detected from the power system and converting the received analog data into digital data; And
A frequency estimator for sampling the digital data converted by the analog-digital converter to obtain sampling data, and estimating a frequency of the power system using a result value obtained through discrete Fourier transform of the obtained sampling data;
An apparatus for estimating the frequency of a power system.

The method according to claim 1,
The frequency estimator may include:
A sampling value obtaining unit for obtaining the sampling data by sampling the digital data and obtaining a sampling value for the obtained sampling data,
A discrete Fourier transform unit for performing discrete Fourier transform on the sampling value acquired through the sampling value obtaining unit and detecting the magnitude of the fundamental wave according to the discrete Fourier transform,
And a frequency detector for detecting the frequency of the power system using the magnitude of the fundamental wave detected through the discrete Fourier transformer
An apparatus for estimating the frequency of a power system.

3. The method of claim 2,
The size of the fundamental wave is,
And decreases as the frequency of the power system decreases
An apparatus for estimating the frequency of a power system.

3. The method of claim 2,
The basic wave includes:
Signal of 60Hz
An apparatus for estimating the frequency of a power system.

3. The method of claim 2,
Wherein the frequency detector comprises:
A table for a magnitude variation of the fundamental wave according to a frequency change of the power system,
And extracting from the table the frequency of the power system corresponding to the magnitude of the fundamental wave obtained through the discrete Fourier transform unit
An apparatus for estimating the frequency of a power system.

3. The method of claim 2,
And a sampling frequency setting unit for setting a sampling frequency for sampling the digital data by the sampling value obtaining unit,
The sample-and-
And the sampling value is obtained according to a sampling frequency variably set by the sampling frequency setting unit
An apparatus for estimating the frequency of a power system.

The method according to claim 6,
The size of the fundamental wave is,
And a sampling frequency setting unit
An apparatus for estimating the frequency of a power system.

8. The method of claim 7,
Wherein the frequency detector comprises:
A table for a magnitude change of the fundamental wave according to a frequency change of the power system,
Wherein the table for the size change of the fundamental wave according to the frequency change of the power system includes:
A sampling frequency setting unit configured to set a sampling frequency according to the sampling frequency,
An apparatus for estimating the frequency of a power system.

9. The method of claim 8,
If the power system frequency is the first frequency, the magnitude of the fundamental wave detected through the discrete Fourier transform unit is the same as the first magnitude regardless of the sampling frequency set through the sampling frequency
An apparatus for estimating the frequency of a power system.

9. The method of claim 8,
If the power system frequency is a second frequency lower than the first frequency,
Wherein the fundamental frequency of the fundamental wave detected through the discrete Fourier transform unit is reduced to a second size smaller than the first frequency according to a sampling frequency set through the sampling frequency setting unit,
The decreasing width,
As the sampling frequency to be set decreases,
An apparatus for estimating the frequency of a power system.