CN112881799A - FFT (fast Fourier transform) -based harmonic detection method for ground power system - Google Patents
FFT (fast Fourier transform) -based harmonic detection method for ground power system Download PDFInfo
- Publication number
- CN112881799A CN112881799A CN202110061016.3A CN202110061016A CN112881799A CN 112881799 A CN112881799 A CN 112881799A CN 202110061016 A CN202110061016 A CN 202110061016A CN 112881799 A CN112881799 A CN 112881799A
- Authority
- CN
- China
- Prior art keywords
- frequency
- harmonic
- phase
- power system
- formula
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
Abstract
The invention provides a harmonic detection method of an electric power system based on FFT (fast Fourier transform), which is characterized in that the frequency change rate is set as the result of the difference quotient operation of the fundamental frequency measured at the previous time and the current time, the frequency change rate of the embodiment is used for correcting the normalized frequency correction value measured at the current time, and the corrected frequency, amplitude and phase are calculated through a frequency correction formula, an amplitude correction formula and a phase correction formula, so that the finally obtained frequency, amplitude and phase are more in line with the actual result, and the method can be further suitable for the power grid environment with dynamically changed frequency; and the frequency measured in the previous time is used for calculating the frequency change rate of the current time, so that the calculation time is shortened by half.
Description
Technical Field
The invention relates to the technical field of harmonic detection, in particular to a harmonic detection method of a power system based on FFT (fast Fourier transform).
Background
The harmonic wave not only reduces the efficiency of the power grid, but also forms resonant circulation, and even burns out the motor in serious cases. The harmonics are suppressed using fourier analysis. The FFT analysis method decomposes the detected periodic harmonic signals through fast FFT to obtain the amplitude and phase of each subharmonic, passes the to-be-eliminated subharmonic component through a band-pass filter or a Fourier transformer to obtain a required error signal, and then performs inverse Fourier transform on the error signal to obtain a compensation signal. The method can not separate active current and reactive current, and requires strict synchronous sampling and equal-interval sampling, otherwise, the barrier effect and the frequency spectrum leakage phenomenon can occur, thereby influencing the detection accuracy.
The measurement method under asynchronous sampling can be divided into a constant-rate sampling method and a self-adaptive sampling method from the aspect of a sampling mode, but the conventional constant-rate sampling method cannot adjust the sampling frequency in real time according to the change of the power grid frequency to realize synchronous sampling, and the measurement precision is sharply reduced when the power grid frequency is dynamically changed, so that in order to solve the problems, the invention provides a power system harmonic detection method based on FFT (fast Fourier transform). in the method, FFT is carried out on two windowed ground time domain sequences by a phase difference correction method, and the phase difference of corresponding peak spectral lines is utilized to correct the frequency, the amplitude and the phase to obtain synchronous data, and the method can be suitable for the power grid environment with dynamically changed frequency.
Disclosure of Invention
In view of the above, the invention provides a power system harmonic detection method based on FFT transformation, which performs FFT on two segments of windowed time domain sequences by a phase difference correction method and corrects frequency, amplitude and phase by using corresponding peak spectral line ground phase difference to obtain synchronous data, and can adapt to a power grid environment with dynamically changing frequency.
The technical scheme of the invention is realized as follows: the invention provides a harmonic detection method of an electric power system based on FFT (fast Fourier transform), which comprises the following steps of:
s1, carrying out FFT (fast Fourier transform) on the acquired asynchronous data to obtain a frequency spectrum sequence, and deriving a normalized frequency correction value from the frequency spectrum sequence;
and S2, correcting the normalized frequency correction quantity based on the frequency change rate, and substituting the corrected normalized frequency correction quantity into a frequency correction formula, an amplitude correction formula and a phase correction formula to obtain the frequency, the amplitude and the phase of the K-th harmonic.
On the basis of the above technical solution, preferably, S1 specifically includes the following steps:
s101, determining the phase of a harmonic signal, and shifting the harmonic signal to the left in the time domain for a time length t0Determining the translated phase;
and S102, subtracting the phase before translation and the phase after translation to obtain the phase difference of the two signals, and deducing a normalized frequency correction value according to the phase difference.
On the basis of the above technical solution, preferably, in S102, the phase difference between the two signals obtained by subtracting the phases before and after translation is:
Δφk＝2πfkt0；
in the formula, delta phikThe phase difference of the two signals is obtained; f. ofkFrequency at the k harmonic; t is t0The time length of the second segment signal shift.
Further preferably, the frequency change rate in S2 is the result of subtracting the previously measured fundamental frequency from the currently measured fundamental frequency and dividing the result by the time interval between the two measurements.
Further preferably, the corrected normalized frequency correction amount in S2 is:
in the formula,. DELTA.mkThe corrected normalized frequency correction value is obtained; n is the number of sampling points of each section of signal; l is the number of points of the second section of signal translation; f. ofkFrequency at the k harmonic; f. ofsIs the sampling rate; m iskNormalized peak spectral frequency.
Further preferably, the frequency correction formula is:
further preferably, the amplitude correction formula is:
in the formula, AkIs the amplitude of the k harmonic; a. themkThe amplitude of a peak spectral line in a harmonic signal spectrum; wnorm(Δmk) Is Δ mkThe fourier transform function of (a).
Further preferably, the phase correction formula is:
in the formula (I), the compound is shown in the specification,
is the phase of the k harmonic; i iskAnd RkRespectively, normalized frequency is mkTime Wnorm(Δmk) The imaginary and real parts of the function.
Compared with the prior art, the FFT-transformation-based harmonic detection method for the ground power system has the following beneficial effects:
(1) setting the frequency change rate as the result of the difference quotient operation of the fundamental frequency measured at the previous time and the current time, correcting the normalized frequency correction value measured at the current time by using the frequency change rate of the embodiment, and calculating the corrected frequency, amplitude and phase by using a frequency correction formula, an amplitude correction formula and a phase correction formula, wherein the finally obtained frequency, amplitude and phase are more in line with the actual result, thereby being capable of adapting to the power grid environment with dynamically changed frequency;
(2) and the frequency measured in the previous time is used for calculating the frequency change rate of the current time, so that the calculation time is shortened by half.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of the harmonic detection method of the power system based on FFT transformation according to the present invention;
fig. 2 is a specific flowchart of step S1 in the FFT transform-based power system harmonic detection method according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
For constant-rate sampling, a method in a frequency domain needs to derive corresponding frequency, amplitude and phase correction formulas, each correction formula is related to a normalized frequency correction value, but the existing method does not consider the situation that the grid frequency change rate is not zero in the process of deriving a normalized frequency correction value calculation formula, so that the measurement precision is seriously reduced in the frequency dynamic process, and in order to solve the problem, as shown in fig. 1, the embodiment provides a power system harmonic detection method based on FFT transformation, which comprises the following steps:
s1, carrying out FFT (fast Fourier transform) on the acquired asynchronous data to obtain a frequency spectrum sequence, and deriving a normalized frequency correction value from the frequency spectrum sequence; as shown in fig. 2, the method specifically includes the following steps:
s101, determining the phase of a harmonic signal, and shifting the harmonic signal to the left in the time domain for a time length t0Determining the translated phase;
and S102, subtracting the phase before translation and the phase after translation to obtain the phase difference of the two signals, and deducing a normalized frequency correction value according to the phase difference. The phase difference of the two signals obtained by subtracting the phases before and after translation is as follows: delta phik＝2πfkt0(ii) a In the formula, delta phikThe phase difference of the two signals is obtained; f. ofkFrequency at the k harmonic; t is t0The time length of the second segment signal shift. Deriving the normalized frequency correction amount from the phase difference can be achieved using prior art techniques, and will not be described in further detail herein. In this embodiment, the calculated normalized frequency correction amount is further corrected to be suitable for the frequency dynamic process.
And S2, correcting the normalized frequency correction quantity based on the frequency change rate, and substituting the corrected normalized frequency correction quantity into a frequency correction formula, an amplitude correction formula and a phase correction formula to obtain the frequency, the amplitude and the phase of the K-th harmonic.
Wherein, the frequency change rate is the result of subtracting the fundamental frequency measured last time from the fundamental frequency measured last time and dividing the result by the time interval of two measurements. Since the frequency change rate is an important parameter in the field of power harmonic measurement technology, in this embodiment, the frequency change rate is a result of performing a difference quotient operation on the fundamental frequency measured at the previous time and the current time. The frequency change rate of the present embodiment is used to correct the normalized frequency correction amount of the current measurement, and the corrected frequency, amplitude and phase are calculated by the frequency correction formula, amplitude correction formula and phase correction formula. In this embodiment, the frequency measured in the previous time is used for calculating the frequency change rate of this time, so that the calculation time is shortened by half.
More preferably, the corrected normalized frequency correction amount is:
in the formula,. DELTA.mkThe corrected normalized frequency correction value is obtained; n is the number of sampling points of each section of signal; l is the number of points of the second section of signal translation; f. ofkFrequency at the k harmonic; f. ofsIs the sampling rate; m iskNormalized peak spectral frequency.
Further preferably, the frequency correction formula is:
further preferably, the amplitude correction formula is:
in the formula, AkIs the amplitude of the k harmonic; a. themkThe amplitude of a peak spectral line in a harmonic signal spectrum; wnorm(Δmk) Is Δ mkThe fourier transform function of (a).
Further preferably, the phase correction formula is:
in the formula (I), the compound is shown in the specification,
is the phase of the k harmonic; i iskAnd RkRespectively, normalized frequency is mkTime Wnorm(Δmk) The imaginary and real parts of the function.
The beneficial effect of this embodiment does: setting the frequency change rate as the result of the difference quotient operation of the fundamental frequency measured at the previous time and the current time, correcting the normalized frequency correction value measured at the current time by using the frequency change rate of the embodiment, and calculating the corrected frequency, amplitude and phase by using a frequency correction formula, an amplitude correction formula and a phase correction formula, wherein the finally obtained frequency, amplitude and phase are more in line with the actual result, thereby being capable of adapting to the power grid environment with dynamically changed frequency;
in this embodiment, the frequency measured in the previous time is used for calculating the frequency change rate of this time, so that the calculation time is shortened by half.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. The method for detecting the harmonic wave of the power system based on FFT (fast Fourier transform) is characterized by comprising the following steps of: the method comprises the following steps:
s1, carrying out FFT (fast Fourier transform) on the acquired asynchronous data to obtain a frequency spectrum sequence, and deriving a normalized frequency correction value from the frequency spectrum sequence;
and S2, correcting the normalized frequency correction quantity based on the frequency change rate, and substituting the corrected normalized frequency correction quantity into a frequency correction formula, an amplitude correction formula and a phase correction formula to obtain the frequency, the amplitude and the phase of the K-th harmonic.
2. The FFT transformation-based harmonic detection method for an electric power system of claim 1, wherein: the S1 specifically includes the following steps:
s101, determining harmonic signalsPhase and left-shifting the harmonic signal in time domain for a time length of t0Determining the translated phase;
and S102, subtracting the phase before translation and the phase after translation to obtain the phase difference of the two signals, and deducing a normalized frequency correction value according to the phase difference.
3. The FFT transformation-based harmonic detection method for an electric power system of claim 2, wherein: in S102, the phase difference between the two signals obtained by subtracting the phases before and after translation is:
Δφk＝2πfkt0；
in the formula, delta phikThe phase difference of the two signals is obtained; f. ofkFrequency at the k harmonic; t is t0The time length of the second segment signal shift.
4. The FFT transformation-based harmonic detection method for an electric power system of claim 1, wherein: the frequency change rate in S2 is the result of subtracting the previously measured fundamental frequency from the currently measured fundamental frequency and dividing by the time interval between the two measurements.
5. The FFT transform-based harmonic detection method for an electric power system of claim 4, wherein: the normalized frequency correction amount corrected in S2 is:
in the formula,. DELTA.mkThe corrected normalized frequency correction value is obtained; n is the number of sampling points of each section of signal; l is the number of points of the second section of signal translation; f. ofkFrequency at the k harmonic; f. ofsIs the sampling rate; m iskNormalized peak spectral frequency.
6. The FFT transformation-based harmonic detection method for an electric power system of claim 5, wherein: the above-mentionedThe frequency correction formula is:
7. the FFT transformation-based harmonic detection method for an electric power system of claim 5, wherein: the amplitude correction formula is as follows:
in the formula, AkIs the amplitude of the k harmonic; a. themkThe amplitude of a peak spectral line in a harmonic signal spectrum; wnorm(Δmk) Is Δ mkThe fourier transform function of (a).
8. The FFT transformation-based harmonic detection method for an electric power system of claim 5, wherein: the phase correction formula is:
in the formula (I), the compound is shown in the specification,
is the phase of the k harmonic; i iskAnd RkRespectively, normalized frequency is mkTime Wnorm(Δmk) The imaginary and real parts of the function.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110061016.3A CN112881799A (en) | 2021-01-18 | 2021-01-18 | FFT (fast Fourier transform) -based harmonic detection method for ground power system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110061016.3A CN112881799A (en) | 2021-01-18 | 2021-01-18 | FFT (fast Fourier transform) -based harmonic detection method for ground power system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN112881799A true CN112881799A (en) | 2021-06-01 |
Family
ID=76048800
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202110061016.3A Pending CN112881799A (en) | 2021-01-18 | 2021-01-18 | FFT (fast Fourier transform) -based harmonic detection method for ground power system |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN112881799A (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106918741A (en) * | 2017-03-02 | 2017-07-04 | 浙江大学 | It is applied to the adaptively sampled phase difference correction method of frequency wide swings power network |
| CN106970264A (en) * | 2017-03-02 | 2017-07-21 | 浙江大学 | A kind of improvement phase difference correction method for considering mains frequency rate of change |
-
2021
- 2021-01-18 CN CN202110061016.3A patent/CN112881799A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106918741A (en) * | 2017-03-02 | 2017-07-04 | 浙江大学 | It is applied to the adaptively sampled phase difference correction method of frequency wide swings power network |
| CN106970264A (en) * | 2017-03-02 | 2017-07-21 | 浙江大学 | A kind of improvement phase difference correction method for considering mains frequency rate of change |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN105738696B (en) | Full phase time shift phase difference frequency estimating methods and device | |
| CN108896820B (en) | Phase modulator startup protection phasor calculation method suitable for starting static frequency converter | |
| CN110837001B (en) | Method and device for analyzing harmonic waves and inter-harmonic waves in electric power system | |
| CN101261292A (en) | Base wave and harmonic detection method based on fiver item Rife-Vincent(1)window double spectral line interpolation FFT | |
| Wen et al. | Hanning self-convolution window and its application to harmonic analysis | |
| CN105137180B (en) | High-precision harmonic analysis method based on six four spectral line interpolations of Cosine Window | |
| CN109521275B (en) | Synchronous phasor determination method, system, device and readable storage medium | |
| CN103018555B (en) | High-precision electric power parameter software synchronous sampling method | |
| CN106018956B (en) | A kind of power system frequency computational methods of adding window spectral line interpolation | |
| CN105353215A (en) | Harmonic detection method based on Nuttall window four-spectral-line interpolation FFT (fast Fourier transform) | |
| CN108535613A (en) | A kind of voltage flicker parameter detection method based on combination window function | |
| CN110954746A (en) | Six-interpolation FFT algorithm based on four-term Nuttall cosine window | |
| CN108896944B (en) | Laboratory calibrator of synchronous measuring device and synchronous phasor measuring method thereof | |
| CN102495285B (en) | Method for estimating power harmonic wave parameter by using power gravity center of symmetric window function | |
| CN114460527B (en) | Correlation degree continuation Hilbert phase-shifting electronic transformer calibrator source tracing method and system | |
| CN109444539B (en) | Synchronous phasor measurement method based on Clark transformation | |
| CN112881799A (en) | FFT (fast Fourier transform) -based harmonic detection method for ground power system | |
| Jiao et al. | An approach for electrical harmonic analysis based on interpolation DFT | |
| CN106324342A (en) | Harmonic wave detecting method based on table look-up | |
| CN114487589A (en) | Power grid broadband signal self-adaptive measurement method, device and system | |
| CN111579868B (en) | Method and device for measuring higher harmonics | |
| Xu et al. | Harmonic parameter online estimation in power system based on Hann self-convolving window and equidistant two-point interpolated DFT | |
| CN113129912A (en) | Method for detecting single-tone signal | |
| CN108982966A (en) | Humorous phase angle analysis method based on linear correction algorithm | |
| CN110687350A (en) | Power grid voltage and current harmonic analysis method and system |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| TA01 | Transfer of patent application right |
Effective date of registration: 20220921 Address after: No. 488, QingWang Road, Donghu eco tourism scenic spot, Wuhan City, Hubei Province, 430000 Applicant after: Marketing Service Center (metering center) of State Grid Hubei Electric Power Co.,Ltd. Address before: No. 488, QingWang Road, Donghu eco tourism scenic spot, Wuhan City, Hubei Province, 430000 Applicant before: Marketing Service Center (metering center) of State Grid Hubei Electric Power Co.,Ltd. Applicant before: WUHAN GLORY ROAD INTELLIGENT TECHNOLOGY Co.,Ltd. |
|
| TA01 | Transfer of patent application right | ||
| RJ01 | Rejection of invention patent application after publication |
Application publication date: 20210601 |
|
| RJ01 | Rejection of invention patent application after publication |