KR20210122342A - Apparatus and method of estimating frequency - Google Patents

Abstract

Disclosed is a frequency estimation apparatus to estimate a frequency quickly and accurately. According to the present invention, the frequency estimation apparatus comprises: a phasor conversion unit converting each phase voltage signal into a complex signal; a discrete Fourier transform (DFT) update unit performing a discrete Fourier transform on the complex signal transformed by the phasor conversion unit to generate an updated N-point DFT value; a modified periodogram calculation unit using the updated DFT value output from the DFT update unit to calculate a modified periodogram value; a peak index detection unit detecting a peak index value of the modified periodogram value obtained through the modified periodogram calculation unit; a frequency estimation unit using the modification periodogram value generated by the modified periodogram calculation unit and the peak index detected by the peak index detection unit to detect a frequency correction factor; and a frequency calculation unit calculating a frequency through the frequency correction factor estimated through the frequency estimation unit.

Description

Frequency estimation apparatus and method {APPARATUS AND METHOD OF ESTIMATING FREQUENCY}

The present invention relates to an apparatus and method for estimating a frequency, and more particularly, estimating a frequency using only a sample value of a voltage signal of a power system, but estimating the frequency quickly and precisely by analytically removing the effect of an asymmetry between phases It relates to a frequency estimation apparatus and method.

Frequency in the power system is a representative measure that reflects the balance between the grid load and the amount of power generation in the power system. Frequency is one of the important factors for the stable operation of the power system, and must be precisely measured for large-capacity ESS control, in addition to protection relays for wide area blackout prevention, generator turbine protection, and distributed power independent operation detection.

This frequency measurement is generally performed in a power monitoring device such as a phasor measurement unit (PMU) or a protection relay (Relay). The limiting performance is proposed in the IEEE60255-118.1:2018 standard.

In the conventional three-phase power system frequency estimation method, the three-phase voltage information is Clarke-transformed to transform it into an orthogonal complex component, and then the zero-crossing technique is applied to the signal, or the method of finding the peak point after spectrum transformation through discrete Fourier transform. It was mainly used because of its computational efficiency and simplicity.

In addition, least squares method, Kalman filter method, Newton method, artificial neural network method, etc. can be used for the systematic frequency estimation.

However, the frequency estimation methods derived based on the power system equilibrium state have a problem in that when the symmetry of the three-phase power system is broken, the effect of the transient state is not taken into account in the estimation equation, and thus the precision of frequency estimation is lowered. In an actual power system, the symmetry between power phases may be broken by various dynamic transients such as sudden load changes or faults. It is inappropriate to be used for protection and control of the power system because it exceeds the limit of frequency estimation precision required by the standard. In a situation where the power system is not stable due to supply and demand imbalance and accidents, if the system frequency is not accurately identified, the control and protection algorithms may not operate properly, leading to additional damage or large-scale blackout. A possible frequency estimation algorithm is needed.

The interphase asymmetry caused by the dynamic transient of the power system appears as an antiphase component as a result of Clarke transform. To precisely remove the effect of the interphase asymmetry, additional derivation of the asymmetric signal parameter is required, but the characteristics of the nonlinear unbalanced signal difficulties exist because of

In order to remove the estimation error due to unbalance, a method of limiting the number of parameters required for frequency estimation or using a more simplified signal model has been proposed, but there is a disadvantage in that the estimation performance is limited.

In addition, methods have been proposed to apply an additional filter such as PLL or to remove the influence of interphase asymmetry through the time-domain relationship of the spectral peak points, but there is a problem in that the frequency estimation is delayed.

The background technology of the present invention is disclosed in 'frequency estimation apparatus and recording medium recording the method' of Korean Patent Registration No. 10-1034469 (2011.05.04) (2019.07.22).

The present invention was devised to improve the above problems, and an object according to an aspect of the present invention is to estimate the frequency using only sample values of the voltage signal of the power system, but analytically remove the influence of the phase asymmetry phenomenon. An object of the present invention is to provide a frequency estimation apparatus and method for estimating a frequency quickly and precisely.

A frequency estimating apparatus according to an aspect of the present invention includes: a phasor converter for converting a voltage signal of each phase into a complex signal; a discrete Fourier transform update unit configured to perform a discrete Fourier transform on the complex signal transformed by the phasor transform unit to generate an updated N-point Discrete Fourier Transform (DFT) value; a modified periodogram calculation unit for calculating a modified periodogram value using the updated DFT value output from the discrete Fourier transform update unit; a peak index detector configured to detect a peak index value of the corrected periodogram value obtained through the modified periodogram calculator; a frequency estimator configured to detect a frequency correction factor using the corrected periodogram value generated by the corrected period calculator and the peak index detected by the peak index detector; and a frequency calculator configured to calculate a frequency through the frequency correction factor estimated by the frequency estimator.

The phasor transform unit of the present invention is characterized in that it converts the voltage signal of each phase into a complex signal through Clarke transform.

The discrete Fourier transform update unit of the present invention is characterized in that it uses a sliding DFT technique for the complex signal transformed by the phasor transform unit.

The discrete Fourier transform update unit of the present invention is updated by using the complex value updated by the sliding DFT technique and the complex value before the time output by the sliding DFT technique with respect to the plurality of signals transformed by the phasor transform unit. It is characterized in that the point DFT value is generated.

The discrete Fourier transform update unit of the present invention is characterized in that it updates the DFT spectrum value using a rectangular window with respect to the complex signal transformed by the phasor transform unit.

The discrete Fourier transform update unit of the present invention applies a Rife-Vincent (RV) window to the complex signal transformed by the phasor transform unit, and updates the DFT spectrum value every time a sample is received. .

The modified periodogram calculator of the present invention calculates the corrected periodogram value through the periodogram difference between the periodogram of the spectrum calculated with a complex input and the periodogram of the spectrum calculated with a complex-conjugated complex input. .

The modified period calculation unit of the present invention is characterized in that the spectrum calculated by the complex conjugated complex input is obtained by symmetrical the spectrum calculated by the complex input by using symmetry on the DFT spectrum.

The frequency estimator of the present invention estimates a scale parameter using a corrected periodic diagram updated with a current input voltage value and a previously estimated frequency correction factor, and compensates a negative image component on the corrected periodic diagram through the scale parameter to obtain a positive After obtaining an image component, an interpolation method is applied to the positive image component to analyze a relationship between DFT points, and then, the frequency correction factor is detected using the relationship between the DFT points.

A frequency estimation method according to an aspect of the present invention comprises the steps of: converting, by a phasor converter, a voltage signal of each phase into a complex signal; generating, by a discrete Fourier transform updater, an updated N-point Discrete Fourier Transform (DFT) value by performing a discrete Fourier transform on the complex signal transformed by the phasor transform; calculating, by a modified periodogram calculator, a modified periodogram value using the updated DFT value output from the discrete Fourier transform updater; detecting, by a peak index detection unit, a peak index value of the corrected periodicity value obtained through the modified periodicity calculation unit; detecting, by a frequency estimator, a frequency correction factor, a corrected periodogram value generated by the corrected period calculator and a peak index detected by the peak index detector; and calculating, by the frequency calculator, a frequency using the frequency correction factor estimated by the frequency estimator.

In the step of converting the voltage signal of each phase into a complex signal of the present invention, the phasor converter converts the voltage signal of each phase into a complex signal through Clarke transform.

In the step of generating the updated N-point Discrete Fourier Transform (DFT) value of the present invention, the discrete Fourier transform update unit uses a sliding DFT technique for the complex signal transformed by the phasor transform unit.

In the step of generating the updated N-point Discrete Fourier Transform (DFT) value of the present invention, the discrete Fourier transform update unit includes a complex value updated by a sliding DFT technique with respect to the plurality of signals transformed by the phasor transform unit; It is characterized in that the updated N-point DFT value is generated by using the complex value before the time output by the sliding DFT technique.

In the step of generating the updated N-point Discrete Fourier Transform (DFT) value of the present invention, the discrete Fourier transform update unit updates a DFT spectrum value using a rectangular window for the complex signal transformed by the phasor transform unit. characterized in that

In the step of generating the updated N-point Discrete Fourier Transform (DFT) value of the present invention, the discrete Fourier transform update unit Rife-Vincent (RV) window for the complex signal transformed by the phasor transform unit. It is characterized in that the DFT spectrum value is updated every time a sample is received by applying .

In the step of generating the modified periodogram value of the present invention, the modified periodogram calculating unit through the periodogram difference between the periodogram of the spectrum calculated by the complex input and the periodogram of the spectrum calculated by the complex-conjugated complex input It is characterized in that the corrected periodogram value is calculated.

In the step of generating the modified periodogram value of the present invention, the modified period calculation unit obtains the spectrum calculated with the complex conjugated complex input by symmetrically using the symmetry on the DFT spectrum to obtain the spectrum calculated with the complex input characterized in that

In the step of detecting the frequency correction factor of the present invention, the frequency estimator estimates a scale parameter using the corrected periodicity value updated with the current input voltage value and the previously estimated frequency correction factor, and uses the scale parameter to be negative. After compensating the image component on the corrected periodogram to obtain a positive image component, applying interpolation on the positive image component to analyze the relationship between DFT points, and then using the relationship between the DFT points to detect the frequency correction factor characterized in that

A frequency estimation apparatus and method according to an aspect of the present invention estimates a frequency using only a sample value of a voltage signal of a power system, but estimates the frequency quickly and precisely by analytically removing the effect of the phase asymmetry phenomenon.

A frequency estimating apparatus and method according to another aspect of the present invention cancels the influence of the interference of the phase values of the normal component and the antiphase component of a power signal to analytically compensate the asymmetry effect, and through this, the peak on the periodogram Iteratively estimates the current frequency by analyzing the relationship between the points and the surrounding points, and maintains precision even in the dynamic transient section that appears according to failures and load fluctuations in the power system.

The frequency estimation apparatus and method according to another aspect of the present invention enable high-precision frequency estimation even in a dynamic transient section, so that the concept of protection and blocking can be applied to a faster and more detailed section than before.

The frequency estimation apparatus and method according to another aspect of the present invention can satisfy the estimation precision required by the latest PMU standard (IEEE60255-118.1:2018) even on a signal of a power system whose phase symmetry is broken, so the reliability of the power system is improved can do.

1 is a block diagram of a frequency estimation apparatus according to an embodiment of the present invention.
2 is a flowchart of a frequency estimation method according to an embodiment of the present invention.
3 is a diagram illustrating a spectrum of a modified periodogram according to an embodiment of the present invention.
4 is a diagram illustrating an example in which the present embodiment is applied to a frequency relay.
5 is a diagram illustrating an example in which the present embodiment is applied to a PMU.

Hereinafter, an apparatus and method for estimating a frequency according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, the terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to intentions or customs of users and operators. Therefore, definitions of these terms should be made based on the content throughout this specification.

Implementations described herein may be implemented in, for example, a method or process, an apparatus, a software program, a data stream, or a signal. Although discussed only in the context of a single form of implementation (eg, only as a method), implementations of the discussed features may also be implemented in other forms (eg, in an apparatus or a program). The apparatus may be implemented in suitable hardware, software and firmware, and the like. A method may be implemented in an apparatus such as, for example, a processor, which generally refers to a computer, a microprocessor, a processing device, including an integrated circuit or programmable logic device, or the like. Processors also include communication devices such as computers, cell phones, portable/personal digital assistants (“PDAs”) and other devices that facilitate communication of information between end-users.

1 is a block diagram of a frequency estimation apparatus according to an embodiment of the present invention.

Referring to FIG. 1 , the frequency estimation apparatus according to an embodiment of the present invention includes a phasor transform unit 10 that converts a voltage signal of each phase into a complex signal, and a discrete Fourier transform complex signal converted by the phasor transform unit 10 A discrete Fourier transform update unit 20 that transforms to generate an updated N-point Discrete Fourier Transform (DFT) value, and a modified periodogram using the updated DFT value output from the discrete Fourier transform update unit 20 ), a modified periodogram calculator 30 for generating ) a frequency estimator 50 that detects a frequency correction factor using the corrected periodogram value generated by and the peak index detected by the peak index detector 40, and the frequency estimated through the frequency estimator 50 and a frequency calculator 60 for calculating a frequency through the correction factor.

The operation and operation of the present embodiment configured as described above will be described in detail with reference to FIGS. 2 and 3 .

FIG. 2 is a flowchart of a frequency estimation method according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a spectrum of a modified periodic diagram according to an embodiment of the present invention.

Referring to FIG. 2 , first, the phasor converter 10 converts a voltage signal of each phase into a complex signal ( S10 ).

In this embodiment, voltage signals of phases a, b, and c measured by a phasor measurement unit (PMU) are used as shown in Equation 1 for frequency estimation of a three-phase power system instead of a single-phase power system.

은 신호의 주파수,

은 현재 시간,

는 샘플링 간격이다.

,

,

는 각각 3상 전압 신호 정현파의 크기를 나타며

는 각 상의 초기 위상이다.here

is the frequency of the signal,

is the current time,

is the sampling interval.

,

,

represents the magnitude of the three-phase voltage signal sine wave, respectively.

is the initial phase of each phase.

As a result of converting the voltage signal into a complex signal as described above, the three-phase image component is removed, and a complex signal as shown in Equation 3 below is output.

이 되어, 회전하는 단일 신호만 존재하게 되지만, 불균형이면 역으로 회전하는 성분이 존재하게 된다. If the three phases of the power system are balanced,

Thus, there is only a single rotating signal, but if there is an imbalance, there is a component rotating in the opposite direction.

At this time, if the frequency estimation algorithm does not consider the component rotating in reverse, the estimation accuracy is deteriorated due to the influence of the component.

, 정상성분의 크기와 위상인

, 역상성분의 크기와 위상인

다섯 개의 언노운 파라미터(Unknown parameter)가 존재하기 때문에 해석적인 방법으로 주파수 추정식을 바로 유도하기는 상대적으로 어려울 수 있다.In the complex signal, the frequency of the signal is

, which is the magnitude and phase of the normal component

, which is the magnitude and phase of the antiphase component

Since there are five unknown parameters, it may be relatively difficult to directly derive a frequency estimation equation in an analytical way.

Accordingly, the discrete Fourier transform update unit 20 generates an updated N-point Discrete Fourier Transform (DFT) value by performing a discrete Fourier transform on the complex signal transformed by the phasor transform unit 10 ( S20 ).

The discrete Fourier transform update unit 20 outputs an updated N-point DFT value using the complex signal of Equation 3 output as a result of the phasor transform unit 10 .

In this case, in order to reduce the computational complexity, a sliding DFT technique that can be used for continuous input values may be applied, and it is divided into a case in which zero-padding is applied and a case in which zero-padding is not applied on the window. can get

A case in which zero-padding is applied and a case in which zero-padding is not applied to the window may be expressed as Equations 4 and 5, respectively.

Equations 4 and 5 above are equations that can be used in the case of a rectangular window that does not apply windowing.

Here, k is a DFT point index, L is the number (length) of used data, and N is the number of DFT points extended through zero-padding.

In this embodiment, a frequency estimation algorithm applicable not only to the rectangular window but also to other windowing shapes is included.

Rife-, which is a sin-based windowing that can be updated on the frequency domain as in Equations 6 and 7 below, rather than the general windowing method applied on the time-domain for computational efficiency By applying the Vincent (RV) window, the DFT spectrum value can be updated for every sample, and frequency estimation using the value can be implemented.

값은 상기한 수학식 4를 통해 업데이트된 값이고, DFT index 간의 간격을 나타내는

을 의미한다.here,

The value is a value updated through Equation 4 above, and represents the interval between DFT indices.

means

과 Sliding DFT 기법에 의해 출력되는 L 시간 전의

값(복소수 값)을 사용하여, 업데이트된 N-포인트 DFT 값을 생성하여 출력한다.As a result, the discrete Fourier transform update unit 20 receives the complex value of Equation 3 as the sliding DFT input.

and L time before output by the sliding DFT technique

Using the values (complex values), an updated N-point DFT value is generated and output.

The modified periodogram calculator 30 calculates a modified periodogram value using the updated DFT value output from the discrete Fourier transform updater 20 (S30).

That is, the modified periodogram calculator 30 calculates the corrected periodogram value using the updated spectrum input from the discrete Fourier transform updater 20 .

In the present embodiment, the corrected periodogram is a method for removing the influence of estimation error due to three-phase imbalance existing on the DFT spectrum, and the corrected periodogram can be calculated as in Equation 8 below.

의 주기도값인

과, 복소 켤레(complex-conjugated)된 복소수 입력으로 계산된 스펙트럼인

의 주기도값인

의 주기도값 간의 차를 통해 산출될 수 있다. The modified periodogram is a spectrum computed with a conventional complex input.

is the periodogram value of

and, a spectrum computed with a complex-conjugated complex input

is the periodogram value of

It can be calculated through the difference between the periodicity values of

은 신호의 스펙트럼 상 실제 주파수이고,

은 windowed 신호의 DTFT 결과로 나온 값이며, 적용된 윈도윙 방법에 따라 다음의 표 1과 같은 값이 출력된다. At this time,

is the actual frequency in the spectrum of the signal,

is a value obtained as a result of the DTFT of the windowed signal, and the values shown in Table 1 below are output according to the applied windowing method.

)의 영향이 제거될 수 있으며, 크기 성분 (

)의 영향이 수정된 주기도의 전체 주기도 상에 동일하게 적용됨으로써 해석적으로 신호 주파수

에 대한 주파수 추정식이 도출될 수 있게 된다.As described above, by applying the modified periodogram (hereinafter referred to as MP), the Phase component (

) can be eliminated, and the size component (

) is applied equally on the entire periodogram of the modified periodogram, so that analytically the signal frequency

It is possible to derive a frequency estimation equation for .

는 일일이 계산할 필요없이 DFT 스펙트럼상의 대칭성을 이용해 아래의 수학식 9와 같이

값을 대칭시켜 얻을 수 있다. Spectrum computed with complex-conjugated input

without having to calculate each one using the symmetry on the DFT spectrum as in Equation 9 below

It can be obtained by symmetrical values.

를 아래의 수학식 10을 통해 검출한다(S40).The peak index detection unit 40 detects a peak index that is a maximum value among the corrected periodogram values obtained through the corrected periodogram.

is detected through Equation 10 below (S40).

The frequency estimator 50 detects a frequency correction factor using the corrected periodogram value generated by the corrected period calculator and the peak index detected by the peak index detector 40 ( S50 ).

를 입력값을 사용하여 DFT 도메인상의 현재 주파수를 나타내는 주파수 보정 팩터(frequency correction factor)

를 출력한다.The frequency estimator 50 includes the corrected periodogram values obtained through the modified periodogram calculator 30 , and the peak index detection unit 40 .

A frequency correction factor representing the current frequency in the DFT domain using

to output

In the present embodiment, interpolation may be applied to obtain a signal frequency by analyzing the relationship between DFT point values for efficient frequency estimation on the modified periodogram. For smooth frequency estimation, a method of iteratively estimating from a previous calculated value may be used.

)을 추정할 수 있다. 여기서, 파라미터 M의 값은 수학식 8에서 현재 입력된 전압값으로 업데이트된 수정된 주기도값과 이전 추정된 주파수 보정 팩터

를 사용해서 수학식 11과 통해 추정 가능하다. More specifically, the frequency estimator 50 determines the variable M (

) can be estimated. Here, the value of the parameter M is the corrected periodicity value updated to the voltage value currently input in Equation (8) and the previously estimated frequency correction factor

It can be estimated through Equation 11 using

Referring to Equation (8), the corrected periodogram appears as a difference between two symmetric sinc components except for a common scale factor M. Therefore, accurate frequency estimation is impossible by simply finding the peak point.

Referring to FIG. 3 , the peak of the spectrum does not mean an actual frequency due to a negative-image component on the corrected periodogram.

값을 추정한 뒤 수정된 주기도상에서 보상하는 과정을 거치고, 보상된 결과로 얻은 포지티브-이미지(Positive-Image) 성분

값 상에 보간법(interpolation)을 적용하여 현재 주파수를 추정한다. Therefore, in order to solve this problem, the frequency estimator 50 determines the negative-image component's influence.

After estimating the value, it goes through the process of compensating on the corrected periodogram, and the positive-image component obtained as a result of the compensation

The current frequency is estimated by applying interpolation on the value.

값을 보상한

값은 C로 나타낼 수 있다.At this time, since it is enough to use three values around the peak point for frequency estimation, the peak value and its left and right periodograms are modified as shown in Equation 12.

compensated for

The value can be denoted by C.

Equations for each window for compensation are shown in Table 1 above.

에 대한 관계식이 도출될 수 있으며, 적용한 윈도윙 방법에 따라 다음과 같이 표현될 수 있다.Meanwhile, C0, C1, and C2 obtained as a result of Equation (12) are the peak values and left and right values of the periodogram in which only the normal component exists. Therefore, by using the relationship between the DFT points by applying the existing interpolation method, the frequency correction factor

A relational expression for can be derived and can be expressed as follows depending on the applied windowing method.

On the other hand, the frequency estimator 50 can estimate the frequency more precisely by repeating the above process.

통해 주파수를 계산한다(S60).The frequency calculation unit 60 calculates a frequency correction factor estimated through the frequency estimation unit 50 .

The frequency is calculated through (S60).

를 아래의 수학식 14을 이용하여 주파수 값으로 변환한다. That is, the frequency calculation unit 60 is a frequency correction factor resulting from the frequency estimation unit 50 .

is converted into a frequency value using Equation 14 below.

는 샘플링 주파수(sampling frequency)이다.here

is the sampling frequency.

Meanwhile, the present embodiment as described above may be applied to a frequency relay or a PMU. This will be described with reference to FIGS. 4 and 5 .

4 is a diagram illustrating an example in which the present embodiment is applied to a frequency relay.

Referring to FIG. 4 , when the frequency relay A/D-converts the estimated three-phase frequency from the power line and brings it, the frequency is estimated according to the present embodiment based on the converted three-phase voltage signal value.

System abnormality is judged by whether the estimated frequency value exceeds or falls short of a specific value (Threshold), and a trip signal, etc. can be sent to a circuit breaker based on the determined abnormality information.

Unlike the conventional frequency estimation algorithm, the present embodiment is not affected by the three-phase unbalance, thereby preventing malfunction of the frequency relay.

5 is a diagram illustrating an example in which the present embodiment is applied to a PMU.

Referring to FIG. 5 , when the frequency relay A/D converts the three-phase frequency estimate from the power line and brings it, a precision time synchronization algorithm such as PTP (Precision Time Protocol) guarantees the time at which the sample is measured and the measurement interval. This embodiment is performed based on the converted three-phase voltage signal value, and the frequency estimate tagged with visual information is sent to the central system through the network.

As described above, the frequency estimation apparatus and method according to an embodiment of the present invention estimate the frequency using only the sample value of the voltage signal of the power system, but estimate the frequency quickly and precisely by analytically removing the effect of the phase asymmetry phenomenon. .

Frequency estimation apparatus and method according to an embodiment of the present invention cancels the influence of the interference of the phase values of the normal component and the antiphase component of a power signal to analytically compensate the asymmetry effect, and through this, Iteratively estimates the current frequency by analyzing the relationship between the peak point and the peripheral point, and maintains precision even in the dynamic transient section that appears according to failures and load changes in the power system.

The frequency estimation apparatus and method according to an embodiment of the present invention enable high-precision frequency estimation even in a dynamic transient section, so that the concept of protection and blocking can be applied to a faster and more detailed section than before.

The frequency estimation apparatus and method according to an embodiment of the present invention can satisfy the estimation precision required by the latest PMU standard (IEEE60255-118.1:2018) even on a signal of a power system in which the symmetry between phases is broken, thereby improving the reliability of the power system can do.

Although the present invention has been described with reference to the embodiment shown in the drawings, this is merely exemplary, and it is understood that various modifications and equivalent other embodiments are possible by those skilled in the art. will understand Accordingly, the true technical protection scope of the present invention should be defined by the following claims.

10: phasor transform unit 20: discrete Fourier transform update unit
30: modified periodogram calculation unit 40: peak index detection unit
50: frequency estimator 60: frequency calculator

Claims (18)

a phasor converter converting each phase voltage signal into a complex signal;
a discrete Fourier transform update unit configured to perform a discrete Fourier transform on the complex signal transformed by the phasor transform unit to generate an updated N-point Discrete Fourier Transform (DFT) value;
a modified periodogram calculation unit for calculating a modified periodogram value using the updated DFT value output from the discrete Fourier transform update unit;
a peak index detector configured to detect a peak index value of the corrected periodogram value obtained through the modified periodogram calculator;
a frequency estimator configured to detect a frequency correction factor using the corrected periodogram value generated by the corrected period calculator and the peak index detected by the peak index detector; and
and a frequency calculator configured to calculate a frequency using the frequency correction factor estimated by the frequency estimator. According to claim 1, wherein the phasor conversion unit
A frequency estimator, characterized in that the voltage signal of each phase is converted into a complex signal through Clarke transform. The method of claim 1, wherein the discrete Fourier transform update unit
The frequency estimation apparatus according to claim 1, wherein a sliding DFT technique is used for the complex signal transformed by the phasor transform unit. The method of claim 1, wherein the discrete Fourier transform update unit
For the plurality of signals transformed by the phasor transform unit, an updated N-point DFT value is generated using a complex value updated by a sliding DFT technique and a complex value before a time output by the sliding DFT technique frequency estimation device. 5. The method of claim 4, wherein the discrete Fourier transform update unit
The frequency estimating apparatus according to claim 1, wherein the DFT spectrum value is updated using a rectangular window with respect to the complex signal transformed by the phasor transform unit. 5. The method of claim 4, wherein the discrete Fourier transform update unit
The frequency estimation apparatus according to claim 1, wherein the DFT spectrum value is updated every time a sample is received by applying a Rife-Vincent (RV) window to the complex signal converted by the phasor transform unit. The method of claim 1, wherein the modified periodogram calculator
A frequency estimating apparatus, characterized in that the corrected periodogram value is calculated through the periodogram difference between the periodogram of the spectrum calculated with a complex input and the periodogram of the spectrum calculated with the complex-conjugated complex input. The method of claim 7, wherein the modified period calculator
The frequency estimating apparatus according to claim 1, wherein the spectrum calculated with the complex conjugated complex input is obtained by symmetrical the spectrum calculated with the complex input using symmetry on the DFT spectrum. The method of claim 1, wherein the frequency estimator
A positive image component is obtained by estimating a scale parameter using the corrected periodicity value updated with the current input voltage value and a previously estimated frequency correction factor, and compensating for a negative image component on the corrected periodogram through the scale parameter, An apparatus for estimating a frequency, characterized in that after analyzing a relationship between DFT points by applying an interpolation method on a positive image component, the frequency correction factor is detected using the relationship between the DFT points. converting the voltage signal of each phase into a complex signal by a phasor converter;
generating, by a discrete Fourier transform updater, an updated N-point Discrete Fourier Transform (DFT) value by performing a discrete Fourier transform on the complex signal transformed by the phasor transform;
calculating, by a modified periodogram calculator, a modified periodogram value using the updated DFT value output from the discrete Fourier transform updater;
detecting, by a peak index detection unit, a peak index value of the corrected periodicity value obtained through the modified periodicity calculation unit;
detecting, by a frequency estimator, a frequency correction factor, a corrected periodogram value generated by the corrected period calculator and a peak index detected by the peak index detector; and
and calculating, by the frequency calculator, a frequency through the frequency correction factor estimated by the frequency estimator. 11. The method of claim 10, wherein in the step of converting the voltage signal of each phase into a complex signal,
The phasor transform unit converts the voltage signal of each phase into a complex signal through Clarke transform. 11. The method of claim 10, wherein in the step of generating the updated N-point Discrete Fourier Transform (DFT) value,
The frequency estimation method according to claim 1, wherein the discrete Fourier transform update unit uses a sliding DFT technique on the complex signal transformed by the phasor transform unit. 11. The method of claim 10, wherein in the step of generating the updated N-point Discrete Fourier Transform (DFT) value,
The discrete Fourier transform update unit is an N-point DFT value updated by using the complex value updated by the sliding DFT method and the complex value before the time output by the sliding DFT method with respect to the plurality of signals transformed by the phasor transform unit Frequency estimation method, characterized in that for generating. 14. The method of claim 13, wherein in generating the updated N-point Discrete Fourier Transform (DFT) value,
The frequency estimation method according to claim 1, wherein the discrete Fourier transform update unit updates a DFT spectrum value using a rectangular window with respect to the complex signal transformed by the phasor transform unit. 14. The method of claim 13, wherein in generating the updated N-point Discrete Fourier Transform (DFT) value,
The discrete Fourier transform update unit applies a Rife-Vincent (RV) window to the complex signal transformed by the phasor transform unit, and updates the DFT spectrum value every time a sample is received. Frequency estimation method . 11. The method of claim 10, wherein in generating the modified periodogram value,
The modified periodogram calculator calculates the corrected periodogram value through the periodogram difference between the periodogram of the spectrum calculated by the complex input and the periodogram of the spectrum calculated by the complex-conjugated complex input . 17. The method of claim 16, wherein in generating the modified periodogram value,
The frequency estimation method, characterized in that the corrected period calculator obtains the spectrum calculated with the complex conjugated complex input by using symmetry on the DFT spectrum to symmetrically obtain the spectrum calculated with the complex input. 11. The method of claim 10, wherein in the step of detecting the frequency correction factor,
The frequency estimator estimates a scale parameter by using the corrected periodicity value updated with the current input voltage value and the previously estimated frequency correction factor, and compensates the negative image component on the modified periodic diagram through the scale parameter to obtain a positive image component After obtaining, interpolation is applied to the positive image component to analyze the relationship between DFT points, and then, the frequency correction factor is detected using the relationship between the DFT points.

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