CN112763797B - Background harmonic voltage current frequency spectrum correction method and device - Google Patents
Background harmonic voltage current frequency spectrum correction method and device Download PDFInfo
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Abstract
The invention discloses a background harmonic voltage spectrum correction method and a device, wherein the background harmonic voltage spectrum correction method carries out fast Fourier decomposition on voltage measurement information and current measurement information through the obtained voltage measurement information and current measurement information to obtain fundamental wave information and each harmonic information in a power grid; on the basis, the ratio of each harmonic impedance to the fundamental impedance is calculated, whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not is preliminarily judged according to the ratio of the harmonic impedance to the fundamental impedance, and whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not is finally judged according to the calculated ratio of the harmonic voltage to the fundamental voltage so as to determine the harmonic voltage information contained in the background harmonic voltage frequency spectrum, the analysis result of the background harmonic voltage frequency spectrum can be comprehensively corrected, and the accuracy of the background harmonic monitoring result of the power transmission system is improved. The invention also correspondingly provides a background harmonic current frequency spectrum correction method and a background harmonic current frequency spectrum correction device.
Description
Technical Field
The invention relates to the technical field of harmonic detection, in particular to a background harmonic current and voltage frequency spectrum correction method and device.
Background
With the wide application of power electronic technology in power systems, each link of power generation, power transmission, power distribution and power utilization of the power systems presents power electronization characteristics. In recent years, in order to meet the requirements of national economy and social development on electric power, a long-distance, large-capacity and high-voltage direct-current transmission technology is rapidly developed, so that the power electronic characteristics of a power transmission network are obvious, the nonlinear characteristics are enhanced, the problems of harmonic propagation and amplification of the power transmission network occur, and the safe and stable operation of a large power grid is influenced.
The direct current converter station is used as an important harmonic source of a power transmission network, characteristic harmonics and non-characteristic harmonics can be generated, and the amplitude of the characteristic harmonics and the amplitude of the non-characteristic harmonics are increased along with the increase of direct current transmission power. The characteristic harmonic can be well suppressed by reasonably designing the alternating current filter, but the non-characteristic harmonic is usually suppressed by only adopting a small number of low-order tuning filters. Under a specific power grid structure and an operation mode, non-characteristic harmonic waves can be injected into a power transmission network, spread and amplified in the power transmission network, so that the voltage and current of a system are distorted, the normal operation of system equipment is influenced, and the safety production accidents of the power grid are caused. When multiple loops of direct current are fed into a power grid, the situation that multiple harmonic sources coexist can occur, and the harmonic sources are mutually influenced and spread or superposed in the power transmission network, so that the harmonic problem of the alternating-current and direct-current series-parallel power transmission network is more complicated. In addition, in recent years, as the flexible direct current transmission technology is applied to the large scale of the power transmission network, the harmonic problem of the power transmission network also presents new characteristics of high frequency and wide frequency domain.
In order to solve the problem of harmonic propagation and amplification caused by power electronization of the power transmission network, the harmonic detection of the power transmission network is firstly carried out. The traditional detection algorithm mainly comprises a fast Fourier transform method, a wavelet transform method, a Hilbert-Huang transform method and the like. The harmonic wave of the power transmission network has the characteristics of the harmonic wave, and is mainly reflected in high harmonic frequency, wide frequency band and high-precision synchronous detection. This is because the dc transmission technology is continuously developed, and different dc projects adopt different power electronic technologies, so that not only up to 50 harmonics but also as few harmonics may occur in the system, and the system is spread over a wide range of transmission networks.
The inventor finds that, in the process of implementing the invention, the harmonic detection algorithms are not optimized for the harmonic characteristics of the power transmission network, so that the obtained background harmonic spectrum is not accurate.
Disclosure of Invention
The embodiment of the invention provides a background harmonic current and voltage frequency spectrum correction method and device, which can effectively solve the problem that the obtained background harmonic frequency spectrum in the prior art is not accurate.
An embodiment of the present invention provides a background harmonic voltage spectrum correction method, including the following steps:
step S1, acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
step S2, performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
step S3, obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
step S4, calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
step S5, preliminarily judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the q-th harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
step S6, calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
step S7, finally judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
step S8, judging whether voltage spectrum correction detection of all harmonics is finished, if so, selecting all harmonic voltages contained in the background harmonic voltage spectrum to obtain a corrected background harmonic voltage spectrum, and finishing all steps; otherwise, go to step S9;
step S9, let q be q +1, perform voltage spectrum correction detection of the next harmonic, and repeat steps S4 to S8 until voltage spectrum correction detection of all harmonics is completed.
Preferably, the obtaining of the fundamental impedance and each harmonic impedance according to the voltage fourier series and the current fourier series specifically includes:
calculating the fundamental impedance from the voltage Fourier series and the current Fourier series by:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively;
calculating respective harmonic impedances from the voltage Fourier series and the current Fourier series by:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
Preferably, the preliminary judgment of whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the qth harmonic impedance to the fundamental impedance specifically includes:
when the ratio of the q-th harmonic impedance to the fundamental impedance is greater than a first preset impedance ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is preliminarily determined to contain the harmonic voltage; alternatively, the first and second electrodes may be,
and when the ratio of the q-th harmonic impedance to the fundamental impedance is smaller than a second preset impedance ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is preliminarily judged to contain the harmonic voltage.
Preferably, the step of finally judging whether the background harmonic voltage spectrum contains the harmonic voltage according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude specifically includes:
and when the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude is smaller than a preset voltage amplitude ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is determined to contain the harmonic voltage.
Another embodiment of the present invention provides a method for correcting a background harmonic current spectrum, including the steps of:
step S1, acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
step S2, performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
step S3, obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
step S4, calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
step S5, preliminarily judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the q-th harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
step S6, calculating the ratio of the harmonic current amplitude to the fundamental current amplitude;
step S7, finally judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the harmonic current amplitude to the fundamental current amplitude;
step S8, judging whether the current spectrum correction detection of all harmonics is finished, if so, selecting all harmonic currents contained in the background harmonic current spectrum to obtain a corrected background harmonic current spectrum, and finishing all steps; otherwise, go to step S9;
step S9, let q be q +1, perform current spectrum correction detection of the next harmonic, and repeat steps S4 to S9 until current spectrum correction detection of all harmonics is completed.
Preferably, the fundamental impedance is calculated according to the voltage fourier series and the current fourier series by the following formula:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively;
calculating respective harmonic impedances from the voltage Fourier series and the current Fourier series by:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
Preferably, the preliminary judgment of whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the qth harmonic impedance to the fundamental impedance specifically includes:
when the ratio of the q-th harmonic impedance to the fundamental impedance is larger than a first preset impedance ratio, the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, the background harmonic current frequency spectrum is preliminarily judged to contain the harmonic current; alternatively, the first and second electrodes may be,
and when the ratio of the q-th harmonic impedance to the fundamental impedance is smaller than a second preset impedance ratio, the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, the background harmonic current frequency spectrum is preliminarily judged to contain the harmonic current.
Preferably, the step of finally judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the harmonic current amplitude to the fundamental current amplitude specifically includes:
and when the ratio of the harmonic current amplitude to the fundamental current amplitude is smaller than a preset current amplitude ratio, determining that the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, determining that the background harmonic current frequency spectrum contains the harmonic current.
Another embodiment of the present invention provides a background harmonic voltage spectrum correction apparatus, including:
a measurement information acquisition module for executing step S1, namely acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
a fourier calculating module for performing step S2: performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
an impedance calculation module for executing step S3: obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
an impedance ratio calculation module for executing step S4: calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
a first determining module, configured to perform step S5: preliminarily judging whether a background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the qth harmonic impedance to the fundamental impedance, and if so, executing a step S6; otherwise, go to step S8;
a magnitude ratio calculation module, configured to perform step S6: calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
a second determining module, configured to execute step S7: finally judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
a harmonic voltage detection module for executing step S8: judging whether voltage spectrum correction detection of all harmonic waves is finished, if so, selecting all harmonic wave voltages contained in the background harmonic wave voltage spectrum to obtain a corrected background harmonic wave voltage spectrum, and finishing all steps; otherwise, go to step S9;
a round correction module for executing step S9: let q be q +1, the voltage spectrum correction detection of the next harmonic is performed, and steps S4 to S8 are repeated until the voltage spectrum correction detection of all harmonics is completed.
Another embodiment of the present invention provides a background harmonic current spectrum correction apparatus, including:
a measurement information acquisition module for executing step S1, namely acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
a fourier calculating module for performing step S2: performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
an impedance calculation module for executing step S3: obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
an impedance ratio calculation module for executing step S4: calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
a first determining module, configured to perform step S5: preliminarily judging whether a background harmonic current frequency spectrum contains the harmonic current according to the ratio of the qth harmonic impedance to the fundamental impedance, and if so, executing a step S6; otherwise, go to step S8;
a magnitude ratio calculation module, configured to perform step S6: calculating the ratio of the harmonic current amplitude to the fundamental current amplitude;
a second determining module, configured to execute step S7: finally judging whether the background harmonic current frequency spectrum contains the harmonic current or not according to the ratio of the harmonic current amplitude to the fundamental current amplitude;
a harmonic current detection module for executing step S8: judging whether the current spectrum correction detection of all harmonic waves is finished, if so, selecting all harmonic waves contained in the background harmonic wave current spectrum to obtain a corrected background harmonic wave current spectrum, and finishing all steps; otherwise, go to step S9;
a round correction module for executing step S9: let q be q +1, current spectrum correction detection of the next harmonic is performed, and steps S4 to S8 are repeated until current spectrum correction detection of all harmonics is completed.
Compared with the prior art, the invention has the following beneficial effects:
according to the background harmonic voltage spectrum correction method provided by the embodiment of the invention, the voltage measurement information and the current measurement information are subjected to fast Fourier decomposition through the obtained voltage measurement information and current measurement information, so that fundamental wave information and each harmonic wave information in a power grid are obtained; on the basis, the ratio of each harmonic impedance to the fundamental impedance is calculated, whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not is preliminarily judged according to the ratio of the harmonic impedance to the fundamental impedance, and whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not is finally judged according to the calculated ratio of the harmonic voltage to the fundamental voltage so as to determine the harmonic voltage information contained in the background harmonic voltage frequency spectrum, so that the analysis result of the background harmonic voltage frequency spectrum can be comprehensively corrected, and the accuracy of the background harmonic monitoring result of the power transmission system is improved. Another embodiment of the present invention provides a background harmonic current spectrum calibration method, which uses the obtained voltage measurement information and current measurement information, performing fast Fourier decomposition on the voltage measurement information and the current measurement information to obtain fundamental wave information and each harmonic wave information in the power grid, on the basis, the ratio of each harmonic impedance to the fundamental impedance is calculated, whether the background harmonic current frequency spectrum contains the harmonic current is preliminarily judged according to the ratio of the harmonic impedance to the fundamental impedance, and further finally judges whether the background harmonic current frequency spectrum contains the harmonic current or not by calculating the ratio of the obtained harmonic current to the fundamental current, the harmonic current information contained in the background harmonic current frequency spectrum is determined, the analysis result of the background harmonic current frequency spectrum can be comprehensively corrected, and the accuracy of the background harmonic monitoring result of the power transmission system is improved. The embodiment of the invention also correspondingly provides a background harmonic voltage spectrum correction device and a background harmonic current spectrum correction device.
Drawings
Fig. 1 is a schematic flow chart illustrating a method for correcting a background harmonic voltage spectrum according to an embodiment of the present invention;
FIG. 2 is a schematic flow chart of a background harmonic current spectrum correction method according to another embodiment of the present invention;
FIG. 3 is a connection diagram of an experimental apparatus used in a background harmonic correction experiment provided by the present invention;
FIG. 4 is a block diagram of a background harmonic voltage spectrum correction apparatus according to another embodiment of the present invention;
fig. 5 is a block diagram of a background harmonic current spectrum correction apparatus according to another embodiment of 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 drawings in 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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a flow chart of a background harmonic voltage spectrum correction method according to an embodiment of the present invention is schematically shown.
The background harmonic voltage spectrum correction method provided by the embodiment of the invention comprises the following steps:
step S1, acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
step S2, performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
step S3, obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
step S4, calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
step S5, preliminarily judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the q-th harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
step S6, calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
step S7, finally judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
step S8, judging whether voltage spectrum correction detection of all harmonics is finished, if so, selecting all harmonic voltages contained in the background harmonic voltage spectrum to obtain a corrected background harmonic voltage spectrum, and finishing all steps; otherwise, go to step S9;
step S9, let q be q +1, perform voltage spectrum correction detection of the next harmonic, and repeat steps S4 to S8 until voltage spectrum correction detection of all harmonics is completed.
As an alternative embodiment, in the step S1 "acquiring voltage measurement information of the measurement point and current measurement information of the measurement point", the acquired voltage measurement information of the measurement point may be acquired by a voltage sensor, and the acquired current measurement information of the measurement point may be acquired by a current sensor.
As an alternative embodiment, in step S2 ", performing fast fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage fourier series and a current fourier series, where the voltage fourier series includes a fundamental voltage amplitude and each harmonic voltage amplitude, and the current fourier series includes a fundamental current amplitude and each harmonic current amplitude", the principle and method for obtaining the fundamental voltage amplitude (or the fundamental current amplitude) and each harmonic voltage amplitude (or the fundamental current amplitude) according to the fast fourier transform are as follows:
let x (N) be M-point finite length measurement sequence, i.e. there is a measurement value within 0 ≦ N ≦ M-1, then it can define the N-point discrete Fourier transform of x (N) (N ≧ M, when N > M, make up N-M zero values):
the matrix expression is as follows:
XN＝WNxN
the fast Fourier transform is a fast algorithm of discrete Fourier transform, not a new transform, and can improve the operation speed in the sense of magnitude order and realize the real-time analysis and calculation of harmonic waves. Performing fast Fourier series decomposition on the voltage signal measurement value and the current signal measurement value, and calculating to obtain a voltage Fourier series (comprising voltage amplitude and frequency information) and a current Fourier series (comprising current amplitude and frequency information)
Wherein u is0、i0Voltage direct current components and current direct current components are respectively, and n is the harmonic frequency; u. ofn、inRespectively the nth harmonic voltage,An nth harmonic current amplitude; w is a0Is the fundamental frequency;
the first phase of the nth harmonic voltage and the first phase of the nth harmonic current are respectively.
As an optional implementation manner, in step S3 ", obtaining a fundamental impedance and each harmonic impedance according to the voltage fourier series and the current fourier series, specifically:
calculating the fundamental impedance from the voltage Fourier series and the current Fourier series by:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively;
calculating respective harmonic impedances from the voltage Fourier series and the current Fourier series by:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
It can be understood that m harmonics, which are respectively expressed as a 1 st harmonic and a 2 nd harmonic, can be obtained from the voltage measurement information after fourier transform, where it should be noted that the m harmonics are not necessarily consecutive harmonics, and if 4 harmonics are generated, that is, 3 th harmonic, 5 th harmonic, 7 th harmonic, and 9 th harmonic, the 1 st harmonic corresponds to the 3 rd harmonic.
As an alternative implementation, the step S4 "calculating the ratio of the q-th harmonic impedance to the fundamental impedance" specifically includes:
wherein the content of the first and second substances,
is the ratio of the q-th harmonic impedance to the fundamental impedance.
As an optional implementation manner, in step S5 ", preliminarily determine whether the background harmonic voltage spectrum contains the harmonic voltage according to a ratio of the qth harmonic impedance to the fundamental impedance, specifically:
when the ratio of the q-th harmonic impedance to the fundamental impedance is greater than a first preset impedance ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is preliminarily determined to contain the harmonic voltage; alternatively, the first and second electrodes may be,
and when the ratio of the q-th harmonic impedance to the fundamental impedance is smaller than a second preset impedance ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is preliminarily judged to contain the harmonic voltage.
In this embodiment, if
The following conditions are satisfied:
determining that the background harmonic voltage spectrum does not contain the qth harmonic voltage, performing step S8; otherwise, it is preliminarily determined that the background harmonic voltage spectrum contains the qth harmonic voltage, and step S6 is executed.
Wherein, alpha 1 is a larger positive number, and is generally 5; α 2 is a small positive number, typically taken to be 0.2.
As an alternative implementation, the step S6 "calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude" is specifically obtained by the following formula:
wherein the content of the first and second substances,
is the ratio of the voltage amplitude of the q-th harmonic wave to the voltage amplitude of the fundamental wave.
As an optional implementation manner, in step S7 ", finally, whether the background harmonic voltage spectrum contains the harmonic voltage is determined according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude, specifically:
and when the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude is smaller than a preset voltage amplitude ratio, the background harmonic voltage spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage spectrum contains the harmonic voltage.
In this embodiment, if
The following conditions are satisfied:
then the background harmonic voltage spectrum can be judged not to contain the q-th harmonic voltage; otherwise, the background harmonic voltage spectrum can be judged to contain the q-th harmonic voltage.
Wherein, β 1 is a small positive number, which can be selected according to the practical power grid and different restrictions on harmonic voltage, and the value range is generally 0.1% -0.2%.
Referring to fig. 2, it is a schematic flow chart of a background harmonic current spectrum correction method according to another embodiment of the present invention.
The embodiment of the invention provides a background harmonic current frequency spectrum correction method, which comprises the following steps:
step S1, acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
step S2, performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
step S3, obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
step S4, calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
step S5, preliminarily judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the q-th harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
step S6, calculating the ratio of the harmonic current amplitude to the fundamental current amplitude;
step S7, finally judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the harmonic current amplitude to the fundamental current amplitude;
step S8, judging whether the current spectrum correction detection of all harmonics is finished, if so, selecting all harmonic currents contained in the background harmonic current spectrum to obtain a corrected background harmonic current spectrum, and finishing all steps; otherwise, go to step S9;
in step S9, current spectrum correction detection of the next harmonic is performed, and steps S4 to S9 are repeated until current spectrum correction detection of all harmonics is completed.
In an alternative embodiment, in the step S1 "acquiring voltage measurement information of the measurement point and current measurement information of the measurement point", the acquired voltage measurement information of the measurement point is acquired by a voltage sensor, and the acquired current measurement information of the measurement point is acquired by a current sensor.
As an alternative embodiment, in step S2 ", performing fast fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage fourier series and a current fourier series, where the voltage fourier series includes a fundamental voltage amplitude and each harmonic voltage amplitude, and the current fourier series includes a fundamental current amplitude and each harmonic current amplitude", the principle and method for obtaining the fundamental voltage amplitude (or the fundamental current amplitude) and each harmonic voltage amplitude (or the fundamental current amplitude) according to the fast fourier transform are as follows:
let x (N) be M-point finite length measurement sequence, i.e. there is a measurement value within 0 ≦ N ≦ M-1, then it can define the N-point discrete Fourier transform of x (N) (N ≧ M, when N > M, make up N-M zero values):
the matrix expression is as follows:
XN＝WNxN
the fast Fourier transform is a fast algorithm of discrete Fourier transform, not a new transform, and can improve the operation speed in the sense of magnitude order and realize the real-time analysis and calculation of harmonic waves. Performing fast Fourier series decomposition on the voltage signal measurement value and the current signal measurement value, and calculating to obtain a voltage Fourier series (comprising a voltage amplitude and frequency information) and a current Fourier series (comprising a current amplitude and frequency information)
Wherein u is0、i0Voltage direct current components and current direct current components are respectively, and n is the harmonic frequency; u. ofn、inThe amplitude values of the nth harmonic voltage and the nth harmonic current are respectively; w is a0Is the fundamental frequency;
the first phase of the nth harmonic voltage and the first phase of the nth harmonic current are respectively.
As an optional implementation manner, in step S3 ", obtaining a fundamental impedance and each harmonic impedance according to the voltage fourier series and the current fourier series, specifically:
calculating the fundamental impedance from the voltage Fourier series and the current Fourier series by:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively;
calculating respective harmonic impedances from the voltage Fourier series and the current Fourier series by:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
As an alternative implementation, the step S4 "calculating the ratio of the q-th harmonic impedance to the fundamental impedance" specifically includes:
wherein the content of the first and second substances,
is the ratio of the q-th harmonic impedance to the fundamental impedance.
As an optional implementation manner, in step S5 ", preliminarily determine whether the background harmonic current spectrum contains the harmonic current according to a ratio of the qth harmonic impedance to the fundamental impedance, specifically:
when the ratio of the q-th harmonic impedance to the fundamental impedance is larger than a first preset impedance ratio, the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, the background harmonic current frequency spectrum is preliminarily judged to contain the harmonic current; alternatively, the first and second electrodes may be,
and when the ratio of the q-th harmonic impedance to the fundamental impedance is smaller than a second preset impedance ratio, the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, the background harmonic current frequency spectrum is preliminarily judged to contain the harmonic current.
In this embodiment, if
The following conditions are satisfied:
then it can be determined that the background harmonic voltage spectrum does not contain the qth harmonic voltage, and step S8 is executed; otherwise, it is preliminarily determined that the background harmonic voltage spectrum contains the qth harmonic voltage, and step S6 is executed.
Wherein, alpha 1 is a larger positive number, and is generally 5; α 2 is a small positive number, typically taken to be 0.2.
As an alternative embodiment, the step S6 "calculating the ratio of the harmonic current amplitude to the fundamental current amplitude" is specifically obtained by the following formula:
wherein the content of the first and second substances,
is the ratio of the amplitude of the q-th harmonic current to the amplitude of the fundamental current.
As an optional implementation manner, the step of finally determining whether the background harmonic current spectrum contains the harmonic current according to the ratio of the harmonic current amplitude to the fundamental current amplitude in step S7 "is specifically:
and when the ratio of the harmonic current amplitude to the fundamental current amplitude is smaller than a preset current amplitude ratio, determining that the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, determining that the background harmonic current frequency spectrum contains the harmonic current.
In this embodiment, if
The following conditions are satisfied:
the background harmonic voltage spectrum does not contain the qth harmonic voltage; otherwise, determining that the background harmonic voltage spectrum contains the qth harmonic voltage.
Wherein, beta 2 is a small positive number, which can be selected according to the practical power grid and different restrictions on harmonic current, and the value range is generally 0.1-0.2%.
In order to better explain the flow of the present invention, the following takes a background harmonic correction experiment to explain the present invention in detail. The experiment simultaneously carries out correction test on the background harmonic voltage frequency spectrum and the background harmonic current frequency spectrum.
Referring to fig. 3, it is a connection diagram of an experimental apparatus used in the background harmonic correction experiment provided by the present invention; the harmonic source generator is adopted in the experiment, and is an all-Digital Power System Simulator (ADPSS) for simulating a harmonic source in an actual Power grid. The harmonic source generator is connected to the power amplifier, and converts the harmonic original signal (which is generally a weak current signal) generated by the harmonic source generator into a higher voltage and current signal for output as an actual harmonic source signal. The harmonic source signal is connected to different devices through a line and is used for obtaining measurement point voltage measurement information and current measurement information. The experiment took the following steps S1 'to S8':
step S1': and obtaining voltage measurement information and current measurement information of the measurement point. In the experiment, the voltage measuring points comprise a voltage measuring point 1, a voltage measuring point 2 and a voltage measuring point 3, and the current measuring points comprise a current measuring point 1, a current measuring point 2 and a current measuring point 3.
Step S2': and carrying out fast Fourier transform calculation on the voltage measurement information and the current measurement information to obtain fundamental voltage amplitude, fundamental current amplitude, each harmonic voltage amplitude and each harmonic current amplitude. During the experiment, the voltage measurement information of the voltage measurement point 1 and the current measurement information of the current measurement point 1 are subjected to Fourier transform calculation, the fundamental voltage frequency and the fundamental current frequency are both 50Hz, the harmonic voltage frequency is 1600Hz, 1800Hz, 100Hz and 400Hz respectively, the harmonic current frequency is 1600Hz, 1800Hz, 100Hz and 400Hz respectively, and the corresponding amplitudes of the harmonic voltages and the harmonic currents are shown in Table 1.
TABLE 1
Step S3': calculating fundamental wave impedance and each harmonic impedance according to the obtained voltage Fourier series and current Fourier series; wherein, the calculation formula of the fundamental wave impedance is as follows:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively.
The calculation formula of the harmonic impedance is as follows:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
In this experiment, the fundamental wave impedance and each harmonic impedance are calculated according to the fundamental wave, each harmonic voltage amplitude and each harmonic current amplitude in table 1, as shown in table 2, where the fundamental wave impedance is 10.3582 □.
TABLE 2
Step S4': and calculating the ratio of the q-th harmonic impedance to the fundamental impedance by the following calculation formula:
wherein the content of the first and second substances,
is the ratio of the q-th harmonic impedance to the fundamental impedance.
In this experiment, the ratio of the harmonic impedance to the fundamental impedance is calculated according to the fundamental wave, each harmonic voltage amplitude and each harmonic current amplitude in table 1, which is specifically referred to in table 2.
Step S5': judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not and whether the background harmonic voltage frequency spectrum contains the harmonic current or not according to the ratio of the harmonic impedance to the fundamental impedance, wherein the judging method comprises the following steps:
if it is
The following conditions are satisfied:
then, it can be determined that the background harmonic voltage spectrum does not contain the qth harmonic voltage and the background harmonic current spectrum does not contain the qth harmonic current, and step S8 is executed; otherwise, it is determined that the background harmonic voltage spectrum includes the qth harmonic voltage and the background harmonic current spectrum does not include the qth harmonic current, and step S6 is executed.
Wherein α 1 is a large positive number, typically 5; α 2 is a small positive number, typically taken to be 0.2.
In this experiment, the impedance ratio between the harmonic voltage with frequency of 100Hz and the harmonic current with frequency of 100Hz is 0.0324, which is a very small positive number, and satisfies the above conditions, so that the frequency spectrum of the background harmonic voltage does not include the harmonic voltage with frequency of 100Hz, and the frequency spectrum of the background harmonic current does not include the harmonic current with frequency of 100 Hz.
Step S6': calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude, wherein the calculation formula is as follows:
calculating the ratio of the harmonic current amplitude to the fundamental current amplitude, wherein the calculation formula is as follows:
wherein the content of the first and second substances,
are respectively asThe ratio of the q-th harmonic voltage amplitude to the fundamental voltage amplitude, and the ratio of the q-th harmonic current amplitude to the fundamental current amplitude.
In this experiment, the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude, to the ratio of the harmonic current amplitude to the fundamental current amplitude, is calculated according to the fundamental information, each harmonic voltage amplitude, and each harmonic current amplitude of table 1, as shown in table 3.
TABLE 3
Step S7': judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude, wherein the judging method comprises the following steps:
if it is
The following conditions are satisfied:
it can be determined that the background harmonic voltage spectrum does not contain the qth harmonic voltage.
Otherwise, the background harmonic voltage spectrum can be judged to contain the q-th harmonic voltage.
Judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the harmonic current amplitude to the fundamental current amplitude, wherein the judging method comprises the following steps:
if it is
The following conditions are satisfied:
it can be determined that the background harmonic current spectrum does not contain the qth harmonic current.
Otherwise, it can be determined that the background harmonic current spectrum contains the qth harmonic current.
Wherein, the beta 1 and the beta 2 are both small positive numbers, can be selected according to the practical power grid and different limits to harmonic voltage and harmonic current, and generally have a value range of 0.1 to 0.2 percent.
In this experiment, the amplitude ratio of the harmonic voltage with the frequency of 400Hz is 0.0579, the amplitude ratio of the harmonic current with the frequency of 400Hz is 0.0461, which is a very small positive number, and the above conditions are satisfied, so the background harmonic voltage spectrum does not include the harmonic voltage with the frequency of 400Hz, and the background harmonic current spectrum does not include the harmonic current with the frequency of 400 Hz.
Step S8': and (5) performing spectrum correction detection on all the harmonics, and finishing the spectrum correction. The obtained final background harmonic voltage frequency spectrum is 1800Hz and 1600Hz, and the final background harmonic current frequency spectrum is 1800Hz and 1600 Hz.
Referring to fig. 4, it is a block diagram of a background harmonic voltage spectrum correction apparatus according to another embodiment of the present invention.
The background harmonic voltage spectrum correction device 10 provided by the embodiment of the invention comprises:
a measurement information obtaining module 100, configured to perform step S1, namely, obtaining voltage measurement information of a measurement point and current measurement information of the measurement point;
a fourier calculating module 101, configured to execute step S2: performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
an impedance calculating module 102, configured to execute step S3: obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
an impedance ratio calculation module 103, configured to execute step S4: calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
the first determining module 104 is configured to execute step S5: judging whether a background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the qth harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
the amplitude ratio calculation module 105 is configured to execute step S6: calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
a second determination module 106, configured to perform step S7: judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
a harmonic voltage detection module 107, configured to execute step S8: judging whether voltage spectrum correction detection of all harmonic waves is finished, if so, selecting all harmonic wave voltages contained in the background harmonic wave voltage spectrum to obtain a corrected background harmonic wave voltage spectrum, and finishing all steps; otherwise, go to step S9;
a round correction module 108 for executing step S9: let q be q +1, the voltage spectrum correction detection of the next harmonic is performed, and steps S4 to S8 are repeated until the voltage spectrum correction detection of all harmonics is completed.
Referring to fig. 5, it is a block diagram of a background harmonic current spectrum correction apparatus according to another embodiment of the present invention.
The background harmonic current spectrum correction device 20 provided by the embodiment of the present invention includes:
a measurement information obtaining module 200, configured to perform step S1, namely, obtaining voltage measurement information of a measurement point and current measurement information of the measurement point;
a fourier calculating module 201, configured to perform step S2: performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
an impedance calculating module 202, configured to execute step S3: obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
an impedance ratio calculation module 203, configured to execute step S4: calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
the first determining module 204 is configured to execute step S5: judging whether a background harmonic current frequency spectrum contains the harmonic current according to the ratio of the qth harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
a magnitude ratio calculation module 205, configured to execute step S6: calculating the ratio of the harmonic current amplitude to the fundamental current amplitude;
a second determination module 206, configured to perform step S7: judging whether the background harmonic current frequency spectrum contains the harmonic current or not according to the ratio of the harmonic current amplitude to the fundamental current amplitude;
a harmonic current detection module 207 for executing step S8: judging whether the current spectrum correction detection of all harmonic waves is finished, if so, selecting all harmonic waves contained in the background harmonic wave current spectrum to obtain a corrected background harmonic wave current spectrum, and finishing all steps; otherwise, go to step S9;
a round correction module 208, configured to execute step S9: let q be q +1, current spectrum correction detection of the next harmonic is performed, and steps S4 to S8 are repeated until current spectrum correction detection of all harmonics is completed.
It should be noted that the above-described device embodiments are merely illustrative, where the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. In addition, in the drawings of the embodiment of the apparatus provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, and may be specifically implemented as one or more communication buses or signal lines. One of ordinary skill in the art can understand and implement it without inventive effort.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (10)
1. A background harmonic voltage spectrum correction method is characterized by comprising the following steps:
step S1, acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
step S2, performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
step S3, obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
step S4, calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
step S5, preliminarily judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the q-th harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
step S6, calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
step S7, finally judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
step S8, judging whether voltage spectrum correction detection of all harmonics is finished, if so, selecting all harmonic voltages contained in the background harmonic voltage spectrum to obtain a corrected background harmonic voltage spectrum, and finishing all steps; otherwise, go to step S9;
step S9, let q be q +1, perform voltage spectrum correction detection of the next harmonic, and repeat steps S4 to S8 until voltage spectrum correction detection of all harmonics is completed.
2. The background harmonic voltage spectrum correction method according to claim 1, wherein the fundamental impedance and each harmonic impedance are obtained according to the voltage fourier series and the current fourier series, specifically:
calculating the fundamental impedance from the voltage Fourier series and the current Fourier series by:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively;
calculating respective harmonic impedances from the voltage Fourier series and the current Fourier series by:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
3. The method for correcting the frequency spectrum of the background harmonic voltage according to claim 1, wherein the preliminary judgment of whether the frequency spectrum of the background harmonic voltage contains the harmonic voltage is performed according to a ratio of the q-th harmonic impedance to the fundamental impedance, specifically:
when the ratio of the q-th harmonic impedance to the fundamental impedance is greater than a first preset impedance ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is preliminarily determined to contain the harmonic voltage; alternatively, the first and second electrodes may be,
and when the ratio of the q-th harmonic impedance to the fundamental impedance is smaller than a second preset impedance ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is preliminarily judged to contain the harmonic voltage.
4. The method according to claim 1, wherein the step of finally determining whether the background harmonic voltage spectrum contains the harmonic voltage according to a ratio of the harmonic voltage amplitude to the fundamental voltage amplitude comprises:
and when the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude is smaller than a preset voltage amplitude ratio, the background harmonic voltage frequency spectrum does not contain the harmonic voltage, otherwise, the background harmonic voltage frequency spectrum is determined to contain the harmonic voltage.
5. A background harmonic current spectrum correction method is characterized by comprising the following steps:
step S1, acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
step S2, performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
step S3, obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
step S4, calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
step S5, preliminarily judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the q-th harmonic impedance to the fundamental impedance, if so, executing step S6; otherwise, go to step S8;
step S6, calculating the ratio of the harmonic current amplitude to the fundamental current amplitude;
step S7, finally judging whether the background harmonic current frequency spectrum contains the harmonic current according to the ratio of the harmonic current amplitude to the fundamental current amplitude;
step S8, judging whether the current spectrum correction detection of all harmonics is finished, if so, selecting all harmonic currents contained in the background harmonic current spectrum to obtain a corrected background harmonic current spectrum, and finishing all steps; otherwise, go to step S9;
step S9, let q be q +1, perform current spectrum correction detection of the next harmonic, and repeat steps S4 to S9 until current spectrum correction detection of all harmonics is completed.
6. The background harmonic current spectrum correction method of claim 5, wherein the fundamental impedance is calculated from the voltage fourier series and the current fourier series by the following formula:
wherein Z is1Is the fundamental impedance, u1、i1The amplitude of the fundamental wave voltage and the amplitude of the fundamental wave current are respectively;
calculating respective harmonic impedances from the voltage Fourier series and the current Fourier series by:
wherein Z isqIs the q-th harmonic impedance, uq、iqThe q harmonic voltage amplitude and the q harmonic current amplitude are respectively.
7. The method for correcting the background harmonic current spectrum according to claim 5, wherein the preliminary determination of whether the background harmonic current spectrum contains the harmonic current is performed according to a ratio of the qth harmonic impedance to the fundamental impedance, specifically:
when the ratio of the q-th harmonic impedance to the fundamental impedance is larger than a first preset impedance ratio, the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, the background harmonic current frequency spectrum is preliminarily judged to contain the harmonic current; alternatively, the first and second electrodes may be,
and when the ratio of the q-th harmonic impedance to the fundamental impedance is smaller than a second preset impedance ratio, the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, the background harmonic current frequency spectrum is preliminarily judged to contain the harmonic current.
8. The method according to claim 5, wherein the step of finally determining whether the background harmonic current spectrum contains the harmonic current according to a ratio of the harmonic current amplitude to the fundamental current amplitude comprises:
and when the ratio of the harmonic current amplitude to the fundamental current amplitude is smaller than a preset current amplitude ratio, determining that the background harmonic current frequency spectrum does not contain the harmonic current, otherwise, determining that the background harmonic current frequency spectrum contains the harmonic current.
9. A background harmonic voltage spectrum correction apparatus, comprising:
a measurement information acquisition module for executing step S1, namely acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
a fourier calculating module for performing step S2: performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
an impedance calculation module for executing step S3: obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
an impedance ratio calculation module for executing step S4: calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
a first determining module, configured to perform step S5: preliminarily judging whether a background harmonic voltage frequency spectrum contains the harmonic voltage according to the ratio of the qth harmonic impedance to the fundamental impedance, and if so, executing a step S6; otherwise, go to step S8;
a magnitude ratio calculation module, configured to perform step S6: calculating the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
a second determining module, configured to execute step S7: finally judging whether the background harmonic voltage frequency spectrum contains the harmonic voltage or not according to the ratio of the harmonic voltage amplitude to the fundamental voltage amplitude;
a harmonic voltage detection module for executing step S8: judging whether voltage spectrum correction detection of all harmonic waves is finished, if so, selecting all harmonic wave voltages contained in the background harmonic wave voltage spectrum to obtain a corrected background harmonic wave voltage spectrum, and finishing all steps; otherwise, go to step S9;
a round correction module for executing step S9: let q be q +1, the voltage spectrum correction detection of the next harmonic is performed, and steps S4 to S8 are repeated until the voltage spectrum correction detection of all harmonics is completed.
10. A background harmonic current spectrum correction apparatus, comprising:
a measurement information acquisition module for executing step S1, namely acquiring voltage measurement information of a measurement point and current measurement information of the measurement point;
a fourier calculating module for performing step S2: performing fast Fourier transform calculation on the voltage measurement information and the current measurement information respectively to obtain a voltage Fourier series and a current Fourier series, wherein the voltage Fourier series comprises fundamental voltage amplitude and each harmonic voltage amplitude, and the current Fourier series comprises fundamental current amplitude and each harmonic current amplitude;
an impedance calculation module for executing step S3: obtaining fundamental wave impedance and each harmonic impedance according to the voltage Fourier series and the current Fourier series;
an impedance ratio calculation module for executing step S4: calculating the ratio of the q-th harmonic impedance to the fundamental impedance, wherein q belongs to [1, m ], the initial value of q is equal to 1, and m is the number of harmonics;
a first determining module, configured to perform step S5: preliminarily judging whether a background harmonic current frequency spectrum contains the harmonic current according to the ratio of the qth harmonic impedance to the fundamental impedance, and if so, executing a step S6; otherwise, go to step S8;
a magnitude ratio calculation module, configured to perform step S6: calculating the ratio of the harmonic current amplitude to the fundamental current amplitude;
a second determining module, configured to execute step S7: finally judging whether the background harmonic current frequency spectrum contains the harmonic current or not according to the ratio of the harmonic current amplitude to the fundamental current amplitude;
a harmonic current detection module for executing step S8: judging whether the current spectrum correction detection of all harmonic waves is finished, if so, selecting all harmonic waves contained in the background harmonic wave current spectrum to obtain a corrected background harmonic wave current spectrum, and finishing all steps; otherwise, go to step S9;
a round correction module for executing step S9: let q be q +1, current spectrum correction detection of the next harmonic is performed, and steps S4 to S8 are repeated until current spectrum correction detection of all harmonics is completed.
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