CN110168384A - A kind of harmonic detecting method and Active Power Filter-APF - Google Patents

A kind of harmonic detecting method and Active Power Filter-APF Download PDF

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Publication number
CN110168384A
CN110168384A CN201780083210.3A CN201780083210A CN110168384A CN 110168384 A CN110168384 A CN 110168384A CN 201780083210 A CN201780083210 A CN 201780083210A CN 110168384 A CN110168384 A CN 110168384A
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coordinate system
theta
harmonic
transformation matrix
current component
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刘晓红
刘鹏飞
唐疑军
邓向钖
吴壬华
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Shenzhen Shinry Technologies Co Ltd
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Shenzhen Shinry Technologies Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof

Abstract

The embodiment of the invention discloses a kind of harmonic detecting method and Active Power Filter-APFs, this method comprises: Active Power Filter-APF APF determines the phase angle θ of network voltage using phaselocked loop；Detect the load current I of power grida、Ib、Ic, by the load current Ia、Ib、IcI under from abc coordinate system transformation to α β coordinate systemα、iβ；Transformation matrix is determined according to the n times harmonic wave of required extraction and the θ, using the transformation matrix by the iα、iβI under the α β coordinate system transformation to dq coordinate systemd、iq, the idInclude DC component INdAnd AC compounentThe iqInclude DC component INqAnd AC compounentThe N is the integer more than or equal to 1；Filter out the idAC compounentObtain the INd, filter out the iqAC compounentObtain the INq, by the INdWith the INqInverse transformation is carried out, n times harmonic current is obtained.Using the technical solution of the embodiment of the present invention, harmonic current can be quickly detected, it is convenient and simple.

Description

Harmonic detection method and active power filter Technical Field
The invention relates to the technical field of power networks, in particular to a harmonic detection method and an active power filter.
Background
With the rapid development of power electronic technology, the application of nonlinear loads causes harmonic pollution of a power grid, and the normal and stable operation of a power system and various electrical appliances is seriously damaged. The problem to be solved first for the treatment of harmonic pollution is a harmonic detection method.
Harmonic detection is a premise for handling harmonic problems, and is also one of key technologies for realizing harmonic compensation by an Active Power Filter (APF).
At present, the commonly used harmonic detection methods mainly include an instantaneous reactive power theory and a harmonic detection method based on Fourier transform. The harmonic detection method based on the instantaneous reactive power theory has the advantages of simple principle and high dynamic response speed, but the detection precision of the harmonic detection method is greatly influenced by a filter. The defects of frequency spectrum leakage, fence phenomenon and the like easily occur when the Fourier transform and a plurality of other improved Fourier transforms are adopted to detect the power grid harmonic waves. The instantaneous reactive power theory of the three-phase circuit is a main basic theory of APF development, and the active power filter is a novel power electronic device for dynamically inhibiting harmonic waves and compensating reactive power, can compensate harmonic waves with variable sizes and frequencies and reactive power with variable sizes and frequencies, and can overcome the defects of traditional harmonic wave inhibition and reactive power compensation methods such as a passive filter.
Currently, the method for detecting the harmonic wave by the active power filter is slow, and the response speed is also further improved.
Disclosure of Invention
The embodiment of the invention provides a harmonic detection method and an active power filter, which can quickly detect harmonic current and are convenient and simple.
A first aspect of an embodiment of the present invention provides a harmonic detection method, where the method includes:
the active power filter APF determines a phase angle theta of the power grid voltage by using a phase-locked loop;
detecting a load current I of a power networka、Ib、IcApplying the load current Ia、Ib、IcI transformed from abc to αβ coordinate systemα、iβ；
Determining a transformation matrix according to the N-th harmonic waves to be extracted and the theta, and utilizing the transformation matrix to convert the iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqThe said idContaining a direct current component INdAnd an alternating current component ofqContaining a direct current component INqAnd an alternating current component, said N being an integer greater than or equal to 1;
filtering out the idIs obtained from the alternating current component ofNdFiltering out the iqIs obtained from the alternating current component ofNqIntroduction of said INdAnd said INqAnd performing inverse transformation to obtain N-th harmonic current.
In an alternative implementation manner, the transformation matrix is determined according to the N-th harmonic to be extracted and the theta, and the i is converted by the transformation matrixα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqThe method comprises the following steps:
determining the N-th harmonic to be extracted, and determining the transformation matrix according to the theta and the N, wherein the transformation matrix is
Will i isαAnd said iβTransforming from the αβ coordinate system to the i in the dq coordinate systemdAnd said iqThe concrete formula is as follows:
wherein the content of the first and second substances,
in an optional implementation, before the determining the transformation matrix according to θ and N, the method further includes:
obtaining sin (N-1) theta, sin theta, cos (N-1) theta and cos theta;
calculating the cosN theta and the sinN theta by the following specific formula:
said determining said transformation matrix in dependence on said θ comprises:
constructing the transformation matrix from the cosN θ and the sinN θ.
In an alternative implementation, the filtering the idIs obtained from the alternating current component ofNdFiltering out the iqIs obtained from the alternating current component ofNqThe method comprises the following steps:
filtering the i with a butterworth second order low pass filterdIs obtained from the alternating current component ofNdFiltering said i by said butterworth second order low pass filterqIs obtained from the alternating current component ofNqThe cut-off frequency of the butterworth second order low pass filter is set to 50 Hz.
In an alternative implementation, the method comprisesSaid I isNdAnd said INqThe inverse transformation is carried out to obtain the N-th harmonic current, and the method comprises the following steps:
subjecting the said INdAnd said INqDown-converting from the dq coordinate system to i in the αβ coordinate systemNαAnd iNβThe concrete formula is as follows:
will i isNαAnd said iNβTransforming to the abc coordinate system, wherein the specific formula is as follows:
wherein, the INaThe said INbThe said INcIs the Nth harmonic current in the power grid.
A second aspect of an embodiment of the present invention provides an active power filter, including:
the phase-locked loop comprises a phase-locked loop, a current transformer, a low-pass filter and a digital signal processor;
the phase-locked loop, the current transformer and the low-pass filter are respectively connected with the digital signal processor;
the phase-locked loop determines a phase angle theta of the power grid voltage and sends the theta to the digital signal processor; the current transformer detects the load current I of the power grida、Ib、IcApplying the load current Ia、Ib、IcSending to the digital signal processor; the digital signal processor converts the load current Ia、Ib、IcI transformed from abc to αβ coordinate systemα、iβDetermining a transformation matrix according to the N-th harmonic to be extracted and the theta, and utilizing the transformation matrix to convert the iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqA 1 to idAnd said iqIs sent to the low pass filter, wherein the idContaining a direct current component INdAnd an alternating current component ofqContaining a direct current component INqAnd an alternating current component, said N being an integer greater than or equal to 1; the low-pass filter filters the idIs obtained from the alternating current component ofNdFiltering out the iqIs divided intoIn an amount to obtain said INqIntroduction of said INdAnd said INqSending to the digital signal processor; the digital signal processor converts the INdAnd said INqAnd performing inverse transformation to obtain N-th harmonic current.
In an alternative implementation, the digital signal processor is specifically configured to determine the nth harmonic to be extracted, and determine the transformation matrix according to θ and N, where the transformation matrix is
Will i isαAnd said iβTransforming from the αβ coordinate system to the i in the dq coordinate systemdAnd said iqThe concrete formula is as follows:
wherein the content of the first and second substances,
in an optional implementation manner, the digital signal processor is further configured to obtain sin (N-1) θ, sin θ, cos (N-1) θ, cos θ, before the determining the transformation matrix according to θ and N;
calculating the cosN theta and the sinN theta by the following specific formula:
constructing the transformation matrix from the cosN θ and the sinN θ.
In an alternative implementation, the low-pass filter is a butterworth second-order low-pass filter;
the low-pass filter is specifically used for filtering the idIs obtained from the alternating current component ofNd(ii) a Filtering out the iqIs obtained from the alternating current component ofNq，The cut-off frequency of the butterworth second order low pass filter is set to 50 Hz.
In an alternative implementation, the digital signal processor is specifically configured to couple the INdAnd said INqDown-converting from the dq coordinate system to i in the αβ coordinate systemNαAnd iNβThe concrete formula is as follows:
will i isNαAnd said iNβTransforming to the abc coordinate system, wherein the specific formula is as follows:
wherein, the INaThe said INbThe said INcIs the Nth harmonic current in the power grid.
According to the technical scheme, the embodiment of the invention has the following advantages: firstly, the phase angle of the voltage of the power grid is determined according to the phase-locked loop, and the load current I of the power grid is measureda、Ib、IcI transformed from abc to αβ coordinate systemα、iβ(ii) a Determining a transformation matrix according to the N-th harmonic waves to be extracted and the theta, and utilizing the transformation matrix to convert the iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iq(ii) a Finally, filtering out the idIs obtained from the alternating current component ofNdFiltering out the iqIs obtained from the alternating current component ofNqIntroduction of said INdAnd said INqAnd performing inverse transformation to obtain N-th harmonic current. According to the embodiment of the invention, the dq axis component of the harmonic current can be quickly detected by changing the coordinate system and filtering the load current, and then the component is subjected to inverse transformation to obtain the harmonic current, so that the method is quick and convenient.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the background art of the present invention, the drawings required to be used in the embodiments or the background art of the present invention will be described below.
FIG. 1 is a schematic flow chart of a harmonic detection method according to an embodiment of the present invention;
FIG. 2 is a comparison of waveforms in the q-axis before and after filtering of the load current according to an embodiment of the present invention;
FIG. 3 is a schematic flow chart of another harmonic detection method disclosed in the embodiments of the present invention;
FIG. 4 is a schematic flow chart of another harmonic detection method disclosed in the embodiments of the present invention;
fig. 5 is a schematic structural diagram of an active power filter according to an embodiment of the present invention.
Detailed Description
The embodiments of the present invention will be described below with reference to the drawings.
In one aspect, an embodiment of the present invention provides a harmonic detection method, as shown in fig. 1, including:
101. the active power filter APF determines a phase angle theta of the power grid voltage by using a phase-locked loop;
the active power filter can detect the load current through the current transformer, and carry out calculation through an internal digital signal processor to extract harmonic components in the load current. The phase-locked loop is a feedback control circuit and is characterized in that: the frequency and phase of the oscillation signal inside the loop are controlled by an externally input reference signal. Phase-locked loops are commonly used in closed-loop tracking circuits because they allow for automatic tracking of the output signal frequency versus the input signal frequency. In the working process of the phase-locked loop, when the frequency of the output signal is equal to that of the input signal, the output voltage and the input voltage keep a fixed phase difference value, namely the phase of the output voltage and the phase of the input voltage are locked. The phase angle θ of the network voltage can thus be determined using a phase locked loop.
102. Detecting a first load current I of a power networkaA second load current IbA third load current IcApplying the load current Ia、Ib、IcA fourth load current i transformed from the abc coordinate system to the first coordinate systemαA fifth load current iβ；
The first coordinate system is αβ coordinate system in the embodiment of the invention, the first load current I of the power grid can be detected by using a current transformeraA second load current IbA third load current IcThe current transformer is based on the electromagnetic induction principle and consists of a closed iron core and a winding, and can be used for converting a large current in an alternating current circuit into a small current with a certain proportion for measurement, wherein the abc coordinate system is a three-phase static coordinate system, the αβ coordinate system is a two-phase static coordinate system, and the load current I isa、Ib、IcCorresponding to the phase angle θ, that is, the load current and the phase angle at the same time. In the embodiment of the present invention, the order of detecting the phase angle and detecting the load current is not specified, and the phase angle may be detected first and then the load current may be detectedThe load current may be measured, the phase angle and the load current may be detected at the same time, or the phase angle may be detected after the load current is detected.
The load current I is measureda、Ib、IcI transformed from abc to αβ coordinate systemα、iβThe formula (c) is as follows:
103. determining a transformation matrix according to the Nth harmonic to be extracted and the phase angle theta, and using the transformation matrix to convert the fourth load current iαA fifth load current iβA sixth load current i transformed from the first coordinate system to the dq coordinate systemdA seventh load current iqI abovedContaining a direct current component INdAnd the alternating current component iqContaining a direct current component INqAnd an alternating current component, wherein N is an integer of 1 or more;
in the embodiment of the invention, the digital information processor can determine the extracted harmonic waves as required. For example, if the digital information processor determines that the pollution of the 7 th harmonic in the power grid is serious, the 7 th harmonic is extracted, i.e., N is 7. The dq coordinate system is a two-phase synchronous rotation coordinate system.
In an alternative implementation, the transformation matrix is determined according to the N-th harmonic to be extracted and the θ, and the i is transformed by using the transformation matrixα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqThe method comprises the following steps:
determining the N-th harmonic to be extracted, and determining the transformation matrix according to the theta and the N, wherein the transformation matrix is
Mixing the above iαAnd the above iβConverting the αβ coordinate system into the i coordinate system in the dq coordinate systemdAnd the above iqThe concrete formula is as follows:
wherein N is an integer of 1 or more.
In the embodiment of the invention, the transformation matrix can be determined according to the N-th harmonic wave to be extracted and the theta, and the transformation matrix is utilized to extract the harmonic waveI aboveαAnd the above iβConverting the αβ coordinate system into the i coordinate system in the dq coordinate systemdAnd the above iqAnd the calculation is simple and quick.
104. Filtering the sixth load current idObtain the above-mentioned eighth load current INdFiltering out the seventh load current iqThe alternating component of (b) obtains the ninth load current INqSetting the above-mentioned eighth load current INdAnd the ninth load current INqAnd performing inverse transformation to obtain N-th harmonic current.
I abovedContaining a direct current component INdAnd an alternating current component i as described aboveqContaining a direct current component INqAnd an alternating current component namely
In the embodiment of the invention, a low-pass filter can be used for filtering the idThe alternating current component of (A) is obtained as described aboveNdFiltering out iqThe alternating current component of (A) is obtained as described aboveNq。
In an alternative implementation, the i may be filtered out using a butterworth second order low pass filterdThe alternating current component of (A) is obtained as described aboveNdFiltering out iqThe alternating current component of (A) is obtained as described aboveNqThe cutoff frequency of the butterworth second order low pass filter is set to 50 Hz. Fig. 2 is a comparison graph of waveforms of the load current before and after filtering on the q-axis, and as shown in fig. 2, the butterworth second-order low-pass filter can effectively filter out harmonic components, i.e., the above-mentioned alternating current components, of the sixth load current and the seventh load current on the q-axis.
In the embodiment of the invention, the Butterworth second-order low-pass filter is adopted, the cut-off frequency is set to be 50Hz, the cut-off frequency can be set to be higher, and the dynamic response is faster.
In an alternative implementation, the harmonic current may be obtained by using a coordinate system transformation, which is as follows: the above general formula INdAnd the above-mentioned INqThe inverse transformation is carried out to obtain the N-th harmonic current, and the method comprises the following steps:
mixing the above INdAnd the above-mentioned INqDown-converting from said dq coordinate system to said αβ coordinate systemI ofNαAnd iNβThe concrete formula is as follows:
mixing the above iNαAnd the above iNβTransforming to the abc coordinate system, the specific formula is as follows:
wherein, the above-mentioned INaThe above-mentioned INbThe above-mentioned INcThe harmonic current of the Nth order in the power grid.
In the embodiment of the invention, N-order harmonic current can be obtained by performing matrix operation on the filtered load current twice, and the calculation is simple.
In the embodiment of the invention, the load current I of the power grid is determined according to the phase angle of the voltage of the power grid determined by the phase-locked loopa、Ib、IcI transformed from abc to αβ coordinate systemα、iβ(ii) a Determining transformation matrix according to N-th harmonic and theta, and transforming the i by using the transformation matrixα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iq(ii) a Finally, filtering out idThe alternating current component of (A) is obtained as described aboveNdFiltering out iqThe alternating current component of (A) is obtained as described aboveNqThe above-mentioned INdAnd the above-mentioned INqAnd performing inverse transformation to obtain N-th harmonic current. According to the embodiment of the invention, the dq axis component of the harmonic current can be quickly detected by changing the coordinate system and filtering the load current, and then the component is subjected to inverse transformation to obtain the harmonic current, so that the method is quick and convenient.
The embodiment of the invention provides a method for constructing a transformation matrix, which comprises the following specific steps: before said determining said transformation matrix according to said θ and said N, said method further comprises:
obtaining sin (N-1) theta, sin theta, cos (N-1) theta and cos theta;
calculating the cosN theta and the sinN theta, wherein the specific formula is as follows:
the determining the transformation matrix according to θ includes:
the transformation matrix is constructed from cosnTheta and sinnTheta.
In the embodiment of the invention, cosnTheta and sinnTheta can be obtained by utilizing the N-1 th harmonic wave and the fundamental wave, repeated table look-up is not needed, and the method can be realized by simple multiplication operation according to the previous result.
Referring to fig. 3, fig. 3 is a schematic flow chart of another harmonic detection method disclosed in the embodiment of the present invention, including:
301. the active power filter APF determines a phase angle theta of the power grid voltage by using a phase-locked loop;
302. detecting a first load current I of a power networkaA second load current IbA third load current Ic；
303. The load current I is measureda、Ib、IcA fourth load current i transformed from the abc coordinate system to the first coordinate systemαA fifth load current iβThe concrete formula is as follows:
the first coordinate system is αβ coordinate system.
304. Determining N-th harmonic waves to be extracted according to a preset rule;
the active power filter may sequentially perform detection according to a sequence of detecting harmonics set by a user, for example, the user may set harmonic detection to be performed cyclically according to a sequence of 3 th harmonic, 5 th harmonic, 7 th harmonic, 11 th harmonic, and 3 rd harmonic. The active power filter can determine the N-th harmonic waves required to be extracted at the current moment according to the pollution degree of each harmonic wave at the current moment. The active power filter may determine the N-th harmonic to be extracted according to the received detection instruction, for example, the active power filter detects the 7 th harmonic after receiving an instruction for detecting the 7 th harmonic sent by the control device.
305. Determining a transformation matrix based on the phase angle theta and the N, the transformation matrix being
306. Applying the fourth load current iαAnd the fifth load current iβA sixth load current i converted from the first coordinate system to the dq coordinate systemdAnd a seventh load current iqThe concrete formula is as follows:
wherein the content of the first and second substances,
307. filtering the sixth load current i by using a butterworth second-order low-pass filterdObtain an eighth load current INdFiltering out the seventh load current iqObtains a ninth load current INq；
The cut-off frequency of the butterworth second order low pass filter is set to 50 Hz.
308. The eighth load current INdAnd the ninth load current INqA first current i down-converted from said dq coordinate system to said first coordinate systemNαAnd a second current iNβThe concrete formula is as follows:
applying the first current iNαAnd the second current iNβTransforming to the abc coordinate system, the specific formula is as follows:
wherein the third current INaThe fourth current INbThe fifth current INcThe harmonic current of the Nth order in the power grid.
309. And controlling the inverter to generate harmonic current with the same magnitude as the load harmonic current and injecting the harmonic current with the opposite direction into the power grid.
Controlling inverter generation and I aboveNaThe above-mentioned INbThe above-mentioned INcHarmonic currents with equal magnitude and opposite directions are injected into a power grid, and the purpose of filtering is achieved.
According to the embodiment of the invention, the dq axis component of the harmonic current can be quickly detected by changing the coordinate system and filtering the load current, and then the component is subjected to inverse transformation to obtain the harmonic current, so that the method is quick and convenient. Harmonic current with the same magnitude and the opposite direction is injected into the power grid by controlling the inverter to generate the harmonic current with the same magnitude as the load harmonic current, so that harmonic pollution is eliminated.
Referring to fig. 4, fig. 4 is a schematic flow chart of another harmonic detection method disclosed in the embodiment of the present invention, including:
401. the active power filter APF determines a phase angle theta of the power grid voltage by using a phase-locked loop;
402. will load current Ia、Ib、IcI transformed from abc to αβ coordinate systemα、iβ；
403. Mixing the above iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iq；
404. Filtering out idIs obtained as the alternating component of INdFiltering out iqIs obtained as the alternating component of INq；
405. Mixing the above INdAnd the above-mentioned INqI down-converted from the dq coordinate system to the αβ coordinate systemNαAnd iNβ；
406. Mixing the above iNαAnd the above iNβTransforming to the abc coordinate system to obtain N-th harmonic current INa、INb、INc。
According to the embodiment of the invention, the dq axis component of the harmonic current can be quickly detected by changing the coordinate system and filtering the load current, and then the component is subjected to inverse transformation to obtain the harmonic current, so that the method is quick and convenient. Harmonic current with the same magnitude and the opposite direction is injected into the power grid by controlling the inverter to generate the harmonic current with the same magnitude as the load harmonic current, so that harmonic pollution is eliminated.
In two aspects, an embodiment of the present invention further provides an active power filter, as shown in fig. 5, including:
a phase-locked loop 501, a current transformer 502, a low-pass filter 503 and a digital signal processor 504;
the phase-locked loop 501, the current transformer 502, and the low-pass filter 503 are connected to the digital signal processor 504;
the phase-locked loop 501 determines a phase angle θ of the grid voltage, and sends θ to the digital signal processor 504; the current transformer 502 detects the load current I of the power grida、Ib、IcApplying the load current Ia、Ib、IcTo the digital signal processor 504; the digital signal processor 504 applies the load current Ia、Ib、IcTransformation from abc coordinate system to αβ coordinate systemiα、iβDetermining a transformation matrix according to the N-th harmonic and the theta, and using the transformation matrix to transform the iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqI abovedAnd the above iqIs sent to the low pass filter 503, where i isdContaining a direct current component INdAnd the alternating current component iqContaining a direct current component INqAnd an alternating current component, wherein N is an integer of 1 or more; the low pass filter 503 filters the idThe alternating current component of (A) is obtained as described aboveNdFiltering out iqThe alternating current component of (A) is obtained as described aboveNqThe above-mentioned INdAnd the above-mentioned INqTo the digital signal processor 504; the digital signal processor 504 converts the INdAnd the above-mentioned INqAnd performing inverse transformation to obtain N-th harmonic current.
The active power filter in the embodiment of the present invention can rapidly detect the harmonic current in the power grid, and the specific method is the same as the method in fig. 1, and will not be described in detail here.
In an alternative implementation, the dsp 504 is specifically configured to determine the nth harmonic to be extracted, and determine the transformation matrix according to the θ and the N, where the transformation matrix is
Mixing the above iαAnd the above iβConverting the αβ coordinate system into the i coordinate system in the dq coordinate systemdAnd the above iqThe concrete formula is as follows:
wherein the content of the first and second substances,
in the embodiment of the present invention, a transformation matrix may be determined according to the N-th harmonic to be extracted and the θ, and the i may be transformed by using the transformation matrixαAnd the above iβConverting the αβ coordinate system into the i coordinate system in the dq coordinate systemdAnd the above iqAnd the calculation is simple and quick.
In an alternative implementation, the dsp 504 is further configured to obtain sin (N-1) θ, sin θ, cos (N-1) θ, and cos θ before the transformation matrix is determined according to the θ and the N;
calculating the cosN theta and the sinN theta, wherein the specific formula is as follows:
the transformation matrix is constructed from cosnTheta and sinnTheta.
In the embodiment of the invention, cosnTheta and sinnTheta can be obtained by utilizing the N-1 th harmonic wave and the fundamental wave, repeated table look-up is not needed, and the method can be realized by simple multiplication operation according to the previous result.
In an alternative implementation, the low-pass filter 503 is a butterworth second-order low-pass filter;
the low pass filter 503 is specifically configured to filter the idThe alternating current component of (A) is obtained as described aboveNd(ii) a Filtering out the iqIs obtained from the alternating current component ofNqThe cutoff frequency of the butterworth second order low pass filter is set to 50 Hz.
In the embodiment of the invention, the Butterworth second-order low-pass filter is adopted, the cut-off frequency is set to be 50Hz, and compared with a second-order RC low-pass filter, the cut-off frequency is set to be higher, and the dynamic response is faster.
In an alternative implementation, the digital signal processor 504 is specifically configured to apply the above INdAnd the above-mentioned INqI down-converted from the dq coordinate system to the αβ coordinate systemNαAnd iNβThe concrete formula is as follows:
mixing the above iNαAnd the above iNβTransforming to the abc coordinate system, the specific formula is as follows:
wherein, the above-mentioned INaThe above-mentioned INbThe above-mentioned INcThe harmonic current of the Nth order in the power grid.
In the embodiment of the invention, N-order harmonic current can be obtained by performing matrix operation on the filtered load current twice, and the calculation is simple.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

  1. A method of harmonic detection, comprising:
    the active power filter APF determines a phase angle theta of the power grid voltage by using a phase-locked loop;
    detecting a load current I of a power networka、Ib、IcApplying the load current Ia、Ib、IcI transformed from abc to αβ coordinate systemα、iβ；
    Determining a transformation matrix according to the N-th harmonic waves to be extracted and the theta, and utilizing the transformation matrix to convert the iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqThe said idContaining a direct current component INdAnd an alternating current component ofqContaining a direct current component INqAnd an alternating current component, said N being an integer greater than or equal to 1;
    filtering out the idIs obtained from the alternating current component ofNdFiltering out the iqIs obtained from the alternating current component ofNqIntroduction of said INdAnd said INqAnd performing inverse transformation to obtain N-th harmonic current.
  2. The method of claim 1, wherein a transformation matrix is determined according to the Nth harmonic to be extracted and the theta, and the i is transformed by the transformation matrixα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqThe method comprises the following steps:
    determining the N-th harmonic to be extracted, and determining the transformation matrix according to the theta and the N, wherein the transformation matrix is
    Will i isαAnd said iβTransforming from the αβ coordinate system to the i in the dq coordinate systemdAnd said iqTool for measuringThe volume formula is as follows:
    wherein the content of the first and second substances,
  3. the method of claim 2, wherein prior to determining the transformation matrix in terms of θ and N, the method further comprises:
    obtaining sin (N-1) theta, sin theta, cos (N-1) theta and cos theta;
    calculating the cosN theta and the sinN theta by the following specific formula:
    said determining said transformation matrix in dependence on said θ comprises:
    constructing the transformation matrix from the cosN θ and the sinN θ.
  4. A method according to any one of claims 1 to 3, wherein said filtering out said idIs obtained from the alternating current component ofNdFiltering out the iqIs obtained from the alternating current component ofNqThe method comprises the following steps:
    filtering the i with a butterworth second order low pass filterdIs obtained from the alternating current component ofNdFiltering said i by said butterworth second order low pass filterqIs obtained from the alternating current component ofNqThe cut-off frequency of the butterworth second order low pass filter is set to 50 Hz.
  5. The method of any one of claims 1 to 3, wherein said combining INdAnd said INqThe inverse transformation is carried out to obtain the N-th harmonic current, and the method comprises the following steps:
    subjecting the said INdAnd said INqDown-converting from the dq coordinate system to i in the αβ coordinate systemNαAnd iNβThe concrete formula is as follows:
    will i isNαAnd said iNβTransforming to the abc coordinate system, wherein the specific formula is as follows:
    wherein, the INaThe said INbThe said INcIs the Nth harmonic current in the power grid.
  6. An active power filter, comprising:
    the phase-locked loop comprises a phase-locked loop, a current transformer, a low-pass filter and a digital signal processor;
    the phase-locked loop, the current transformer and the low-pass filter are respectively connected with the digital signal processor;
    the phase-locked loop determines a phase angle theta of the power grid voltage and sends the theta to the digital signal processor; the current transformer detects the load current I of the power grida、Ib、IcApplying the load current Ia、Ib、IcSending to the digital signal processor; the digital signal processor converts the load current Ia、Ib、IcI transformed from abc to αβ coordinate systemα、iβDetermining a transformation matrix according to the N-th harmonic to be extracted and the theta, and utilizing the transformation matrix to convert the iα、iβI transformed from the αβ coordinate system to dq coordinate systemd、iqA 1 to idAnd said iqIs sent to the low pass filter, wherein the idContaining a direct current component INdAnd an alternating current component ofqContaining a direct current component INqAnd an alternating current component, said N being an integer greater than or equal to 1; the low-pass filter filters the idIs obtained from the alternating current component ofNdFiltering out the iqIs obtained from the alternating current component ofNqIntroduction of said INdAnd said INqSending to the digital signal processor; the digital signal processor converts the INdAnd said INqAnd performing inverse transformation to obtain N-th harmonic current.
  7. The active power filter of claim 6,
    the digital signal processor is specifically configured to determine the N-th harmonic to be extracted, and determine the transformation matrix according to θ and N, where the transformation matrix is
    Will i isαAnd said iβTransforming from the αβ coordinate system to the i in the dq coordinate systemdAnd said iqThe concrete formula is as follows:
    wherein the content of the first and second substances,
  8. the active power filter of claim 7,
    the digital signal processor is further used for obtaining sin (N-1) theta, sin theta, cos (N-1) theta and cos theta before determining the transformation matrix according to theta and N;
    calculating the cosN theta and the sinN theta by the following specific formula:
    constructing the transformation matrix from the cosN θ and the sinN θ.
  9. Active power filter according to any of claims 6 to 8, characterized in that the low-pass filter is a butterworth second order low-pass filter;
    the low-pass filter is specifically used for filtering the idIs obtained from the alternating current component ofNd(ii) a Filtering out the iqIs obtained from the alternating current component ofNqThe cut-off frequency of the butterworth second order low pass filter is set to 50 Hz.
  10. Active power filter according to any of claims 6 to 8,
    the digital signal processor is specifically used for converting the INdAnd said INqDown-converting from the dq coordinate system to i in the αβ coordinate systemNαAnd iNβThe concrete formula is as follows:
    will i isNαAnd said iNβTransforming to the abc coordinate system, wherein the specific formula is as follows:
    wherein, the INaThe said INbThe said INcIs the Nth harmonic current in the power grid.
CN201780083210.3A 2017-09-08 2017-09-08 A kind of harmonic detecting method and Active Power Filter-APF Pending CN110168384A (en)

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