CN112415266B - Active power filter load harmonic current extraction method - Google Patents
Active power filter load harmonic current extraction method Download PDFInfo
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- CN112415266B CN112415266B CN202010318436.0A CN202010318436A CN112415266B CN 112415266 B CN112415266 B CN 112415266B CN 202010318436 A CN202010318436 A CN 202010318436A CN 112415266 B CN112415266 B CN 112415266B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
- G01R23/165—Spectrum analysis; Fourier analysis using filters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/20—Active power filtering [APF]
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Abstract
The invention relates to the field of power technology application, in particular to a method for extracting load harmonic current of an active power filter, which comprises the following steps: dividing load current into fundamental wave and harmonic wave, defining instantaneous values of sinusoidal current and sinusoidal voltage, so as to obtain instantaneous fundamental wave active power and instantaneous fundamental wave reactive power by means of calculation, and calculating arithmetic average of a basic period to eliminate AC component so as to obtain correspondent active power value, reactive power value and compound vision power; step two: inducing the PCC voltage filtered by the feedback second-order generalized integrator into complex fundamental voltage, and obtaining the amplitude and phase of the PCC voltage by using a vector method; step three: obtaining the amplitude and the corresponding phase of the fundamental wave load current; step four: under the condition that the fundamental wave load current is known, the load harmonic current is obtained by subtracting the load fundamental wave current from the load current, so that the extraction precision is ensured, and meanwhile, the good dynamic performance is also ensured.
Description
Technical Field
The invention relates to the field of power technology application, in particular to a method for extracting load harmonic current of an active power filter.
Background
The harmonic detection precision is used as the first link of active power filter control, the performance of the harmonic detection precision determines the compensation precision of the SAPF in steady state and the response speed in dynamic state, the traditional detection method is to detect fundamental wave current based on instantaneous reactive power theory, then subtract fundamental wave active power to obtain harmonic instructions, the inherent contradiction exists between low-pass filtering performance and delay, the cut-off frequency of the low-pass filter is generally selected in a compromise way, but the inherent defects of delay and performance still exist, and in the dynamic state, the delay of the low-pass filter in the algorithm can cause a certain fundamental wave active error between the harmonic instructions obtained in dynamic state and the actual value, and the direct current side of the SAPF in dynamic state is easy to generate great fluctuation, and the traditional harmonic extraction method mainly comprises the following steps:
1) The method based on the instantaneous reactive theory generally transforms the load current into a synchronous or static coordinate system through coordinate transformation, at the moment, the fundamental component of the load current is transformed into direct current, the harmonic component is displayed as alternating current, and then the fundamental component and the harmonic component are separated through a Low Pass Filter (LPF); however, the algorithm has a certain delay depending on the performance of the LPF when separating the fundamental wave and the harmonic wave, and the active current is injected in the dynamic process, so that the harmonic wave detection and the application occasion of the detection result are greatly damaged.
2) The FFT algorithm can calculate the frequency spectrum of all frequency points in the Nyquist frequency, the calculation speed is faster than that of DFT (discrete Fourier transform) to extract the frequency spectrum of all frequency points, but when only the frequency spectrum of partial frequency points is required, such as 50 times less characteristic harmonic waves in most power applications, the DFT algorithm can calculate the required harmonic frequency spectrum, so that the time required by the algorithm is smaller, the required data memory quantity is relatively smaller, and meanwhile, compared with the FFT, the DFT has the advantages of more flexible sampling rate and conversion point selection, better instantaneity, easier control, simpler operation, more convenient programming implementation in a chip and the like.
3) The SDFT (sliding window discrete Fourier transform) algorithm is the optimization of the DFT algorithm, and the DFT algorithm operation is evenly distributed in each sampling period in a sliding iteration mode, so that the calculated amount is further reduced, but the SDFT algorithm also has the defect that a fundamental wave period is required to be delayed in a dynamic process.
Disclosure of Invention
The invention provides the active power filter load harmonic current extraction method which ensures the extraction precision and good dynamic performance at the same time.
In order to solve the technical problems, the invention provides a method for extracting load harmonic current of an active power filter, which comprises the following steps:
step one: establishing a circuit for extracting load harmonic current of an active power filter, dividing the load current into fundamental waves and harmonic waves, defining instantaneous values of sinusoidal current and sinusoidal voltage, calculating to obtain instantaneous fundamental wave active power and instantaneous fundamental wave reactive power, and calculating arithmetic average of a basic period to eliminate alternating current components, thereby obtaining corresponding active power value, reactive power value and compound vision power;
step two: inducing the PCC voltage filtered by the feedback second-order generalized integrator into complex fundamental wave voltage through the calculated active power value and reactive power value, and obtaining the amplitude and phase of the PCC voltage by using a vector method;
step three: the same processing as the second step is carried out on the compound vision power to obtain the amplitude value and the corresponding phase of the fundamental wave load current;
step four: by the above steps, an instantaneous fundamental current is obtained, and thus, in the case where the fundamental load current is known, a load harmonic current is calculated by subtracting the load fundamental current from the load current.
Preferably, the circuit for extracting the harmonic current of the load of the active power filter comprises a direct-current side voltage control circuit, a phase-locked loop circuit, a reference harmonic current extraction circuit and a current controller, wherein the reference harmonic current extraction circuit and the current controller are composed of the direct-current side voltage control circuit and a load-related harmonic current reference generator.
Preferably, in step one, the instantaneous values defining the sinusoidal current i (t) and the sinusoidal voltage u (t) are expressed as:
the phase difference between the two is:
therefore, the load side instantaneous power is:
the above formula is expressed as:
the first part of the above equation describes the instantaneous fundamental active power and the second part describes the instantaneous fundamental reactive power, and calculating the arithmetic average of one fundamental period from the above equation can eliminate the ac component, thereby obtaining the corresponding active power value:
to determine the fundamental reactive power, a 90 ° phase shifted quadrature component of the voltage is required:
according to the following formula:
the reactive power is obtained as follows:
the calculation of the active and reactive power of the fundamental wave is done with a moving average filter of N values corresponding to the times of the fundamental wave period, so that the calculation is not affected by the harmonics in the load current, since the harmonics appear as integer multiples of the fundamental wave and are eliminated by the moving average filter;
calculating the active and reactive power P of fundamental wave 1,L,μ And Q 1,L,μ They can be seen as a power of double vision:
S 1，L，u ＝P 1，L，u +j·Q 1，L，u
preferably, in the second step, the PCC voltage filtered by the feedback second-order generalized integrator may be summarized as a complex fundamental voltage:
u 1，PCC，u ＝u 1，PCC，u +j·u 1，PCC，u
using the vector method, the amplitude and phase of these two quantities can be determined, which is for PCC voltage:
preferably, in the third step, the same processing as in the second step is performed on the multi-view power, and the amplitude of the fundamental load current is:
the corresponding phases are:
preferably, in the fourth step, the instantaneous fundamental current is obtained by the following steps:
in the case of known fundamental load currents, the load harmonic current can be calculated by subtracting the load fundamental current from the load current:
i L，H，u (t)＝i L，u (t)-i L，1，u (t)。
by adopting the technical scheme, the invention has the beneficial effects that: the method provided by the invention can accurately extract the harmonic current in the load, and the harmonic current extraction result can reach a steady state in a basic period after the load current is changed for the first time, so that the extraction precision is ensured, and meanwhile, the good dynamic performance is also ensured.
Drawings
FIG. 1 is a control block diagram of an active power filter of the present invention;
FIG. 2 is a block diagram of a power calculation circuit according to the present invention;
FIG. 3 is a block diagram of a vector calculation circuit for complex power and complex fundamental voltage in accordance with the present invention;
FIG. 4 is a waveform diagram showing the dynamic performance of harmonic current extraction according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and detailed description:
as shown in figure 1, the invention provides a method for extracting harmonic current of an active power filter load, which comprises direct-current side voltage control, a phase-locked loop, reference harmonic current extraction and a current controller, wherein the reference harmonic current extraction and the current controller are composed of direct-current side voltage control and load-related harmonic current reference generation, and the basic idea of the current reference generation is to divide load current into fundamental waves i L,1,μ And harmonic i H,L,μ :
i L,u (t)＝i L,1,u (t)+i L,H,u (t)；
The extraction method comprises the following steps:
the instantaneous values defining the sinusoidal current i (t) and the sinusoidal voltage u (t) are expressed as:
the phase difference between the two is:
therefore, the load side instantaneous power is:
the above formula is expressed as:
the first part of the equation above describes instantaneous fundamental active power and the second part describes instantaneous fundamental reactive power. Calculating an arithmetic average of one fundamental period from the above equation may eliminate the alternating current component, thereby obtaining a corresponding active power value:
to determine the fundamental reactive power, a 90 ° phase shifted quadrature component of the voltage is required:
according to the following formula:
the reactive power is obtained as follows:
thus, the power calculation can be implemented as shown in the structure of fig. 2, the quadrature component of the voltage being provided by a feedback second-order generalized integrator, which is tuned to the fundamental frequency, since the phase-locked loop can also adapt to frequency variations, since the PCC voltage only changes slowly, only a low dynamic behavior is required to filter the PCC voltage and the feedback second-order generalized integrator can tune a very narrow strip, thus both providing a voltage without harmonics;
the calculation of the active and reactive power of the fundamental wave is done with a moving average filter of N values corresponding to the times of the fundamental wave period, so that the calculation is not affected by the harmonics in the load current, since the harmonics appear as integer multiples of the fundamental wave and are eliminated by the moving average filter;
can calculate the active and reactive power P of fundamental wave 1,L,μ And Q 1,L,μ They can be seen as complex apparent power:
S 1，L，u ＝P 1，L，u +j·Q 1，L，u
similarly, the PCC voltage filtered by the feedback second-order generalized integrator can be generalized to a complex fundamental voltage:
u 1，PCC，u ＝u 1，PCC，u +j·u 1，PCC，u
as shown in fig. 3, the complex view power and complex fundamental voltage provide the inputs of the current reference power supply;
using the vector method, the amplitude and phase of these two quantities can be determined, which is for PCC voltage:
the amplitude of the fundamental load current is similarly processed for the compound view power:
the corresponding phases are:
it is thus possible to obtain an instantaneous fundamental current of:
in the case of known fundamental load currents, the load harmonic current can be calculated by subtracting the load fundamental current from the load current:
i L,H,u (t)＝i L,u (t)-i L,1,u (t)。
the dynamic performance of harmonic current extraction is shown in figure 4, the method provided by the invention can accurately extract the harmonic current in the load, and in a basic period after the load current is changed for the first time, the harmonic current extraction result can reach a steady state, and the experimental result shows that the method has the characteristic of rapidly and accurately extracting the load harmonic current.
The present invention has been described in detail by way of specific examples, but these should not be construed as limiting the invention. Many variations and modifications may be made by one skilled in the art without departing from the principles of the invention, which is also considered to be within the scope of the invention.
Claims (5)
1. The method for extracting the load harmonic current of the active power filter is characterized by comprising the following steps of:
step one: establishing a circuit for extracting load harmonic current of an active power filter, dividing the load current into fundamental waves and harmonic waves, defining instantaneous values of sinusoidal current and sinusoidal voltage, calculating to obtain instantaneous fundamental wave active power and instantaneous fundamental wave reactive power, and calculating arithmetic average of a basic period to eliminate alternating current components, thereby obtaining corresponding active power value, reactive power value and compound vision power;
step two: inducing the PCC voltage filtered by the feedback second-order generalized integrator into complex fundamental wave voltage through the calculated active power value and reactive power value, and obtaining the amplitude and phase of the PCC voltage by using a vector method;
step three: the same processing as the second step is carried out on the compound vision power to obtain the amplitude value and the corresponding phase of the fundamental wave load current;
step four: obtaining instantaneous fundamental wave current through the steps, and under the condition that the fundamental wave load current is known, subtracting the load fundamental wave current from the load current to obtain load harmonic current;
in the second step, the PCC voltage filtered by the feedback second-order generalized integrator is generalized to a complex fundamental voltage:
u1，PCC，u＝u1，PCC，u+j·u1，PCC，u，
the amplitude and phase of these two quantities are determined using a vector method, which is for PCC voltage:
2. the method of claim 1, wherein the circuit for active power filter load harmonic current extraction comprises a dc side voltage control, a phase locked loop, a reference harmonic current extraction and current controller, the reference harmonic current extraction and current controller being comprised of a dc side voltage control and a load dependent harmonic current reference generation.
3. The method of claim 1, wherein in step one, instantaneous values defining a sinusoidal current i (t) and a sinusoidal voltage u (t) are expressed as:
the phase difference between the two is:
therefore, the load side instantaneous power is:
the above formula is expressed as:
the first part of the above equation describes the instantaneous fundamental active power and the second part describes the instantaneous fundamental reactive power, and calculating the arithmetic average of one fundamental period from the above equation can eliminate the ac component, thereby obtaining the corresponding active power value:
to determine the fundamental reactive power, a 90 ° phase shifted quadrature component of the voltage is required:
according to the following formula:
the reactive power is obtained as follows:
the calculation of the active and reactive power of the fundamental wave is done with a moving average filter of N values corresponding to the times of the fundamental wave period, so that the calculation is not affected by the harmonics in the load current, since the harmonics appear as integer multiples of the fundamental wave and are eliminated by the moving average filter;
calculating the active and reactive power P of fundamental wave 1,L,μ And Q 1,L,μ They are considered as power of double vision:
S1，L，u＝P1，L，u+j·Q1，L，u。
4. the method for extracting harmonic current from active power filter load according to claim 1, wherein in step three, the complex view power is processed as in step two, and the amplitude of the fundamental load current is:
the corresponding phases are:
5. the method of claim 1, wherein in step four, the instantaneous fundamental current is obtained by:
in the case of known fundamental load currents, the load harmonic current can be calculated by subtracting the load fundamental current from the load current:
i L，H，u (t)＝i L，u (t)-i L，1，u (t)。
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