CN112881776A - Rapid extraction method of harmonic current - Google Patents
Rapid extraction method of harmonic current Download PDFInfo
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- CN112881776A CN112881776A CN202110043102.1A CN202110043102A CN112881776A CN 112881776 A CN112881776 A CN 112881776A CN 202110043102 A CN202110043102 A CN 202110043102A CN 112881776 A CN112881776 A CN 112881776A
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Abstract
The invention relates to and belongs to the technical field of signal processing, in particular to a method for quickly extracting harmonic current, which comprises the following steps of A) collecting a load current signal of harmonic to be collected; the load current signal is a three-phase load current signal; B) carrying out abc/dq conversion on the load current signal, and calculating an active component and a reactive component of the load current signal; C) calculating the summation average value of the active components of the input signals; D) carrying out dq/abc conversion on the summation average value of the active component of the input signal to obtain the fundamental component of the load current signal; E) and performing signal difference on the fundamental component and the load current to obtain a harmonic component in the load current signal. The substantial effects of the invention are as follows: the invention can extract specific subharmonic component after improving the comb filter and gain part of the traditional MAF. GMAF reduces the extracted dynamic response time without obvious loss of precision, can avoid redundant zero points and reduce storage units.
Description
Technical Field
The invention belongs to the technical field of signal processing, and particularly relates to a method for quickly extracting harmonic current.
Background
With the access of renewable energy sources and power electronics to the power grid, the problem of harmonic pollution is more serious. The multi-port energy router is used as a control core of a new generation of power network, can flexibly manage and control power accessed to a power grid, promotes the consumption of renewable energy sources, improves the power quality of the power distribution network, and the harmonic current extraction method is used as an important branch for realizing a harmonic compensation function, has important significance on harmonic suppression and is mainly divided into a time domain method and a frequency domain method. The frequency domain method is mainly based on a discrete Fourier method, a fast discrete Fourier method and an iterative discrete Fourier method based on Fourier transform, but the Fourier transform method occupies a large amount of storage space of a digital controller, is large in calculation amount and is low in real-time performance. In the time domain method, a PQ power theory method and a synchronous dq rotation method are common, the PQ power theory method is only suitable for ideal grid working conditions, and the synchronous dq rotation method is more suitable for harmonic current detection under various non-ideal grid conditions. However, a Low Pass Filter (LPF) used for harmonic extraction in the synchronous dq rotation method is greatly affected by a cutoff frequency and an order, a dynamic response time of the Filter is long, and a real-time compensation effect is poor.
Chinese patent CN107782965A, published 2018, 03 and 09, discloses a novel harmonic current detection method, which is a harmonic current detection method based on the theory of input observers, and includes the steps of firstly, taking a measured current signal and components of each frequency thereof as state quantities, constructing a linear time-varying state space model, and then, designing an observer based on the state space model to perform online observation on unknown state variables, thereby implementing information extraction of each frequency component. The novel current harmonic detection method overcomes the limitation that the detection methods such as instantaneous reactive power and the like can only detect total harmonic current, can simultaneously detect harmonic components of each designated frequency, has the advantages of high detection speed, high precision, good dynamic tracking performance, good anti-interference performance and the like, has good practicability, and has certain reference value for APF harmonic detection research.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: a method for fast extracting harmonic current with small space and short dynamic response time is provided
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a fast extraction method of harmonic current comprises the following steps:
A) collecting a load current signal of harmonic waves to be collected; the load current signal is a three-phase load current signal;
B) carrying out abc/dq conversion on the load current signal, and calculating an active component and a reactive component of the load current signal;
C) calculating the summation average value of the active components of the input signals;
D) carrying out dq/abc conversion on the summation average value of the active component of the input signal to obtain the fundamental component of the load current signal;
E) and performing signal difference on the fundamental component and the load current to obtain a harmonic component in the load current signal.
The three-phase load current signals are subjected to abc/dq conversion and then subjected to active component optimization filtering, so that more accurate multi-wave components of the load current signals are obtained, and multiple harmonics of the three-phase load current are extracted. The invention is based on GMAF, namely a generalized moving average filter, and optimizes filtering to obtain a faster harmonic current extraction algorithm.
Preferably, in step a), the number of sampling points of the load current in each fundamental wave period is equal.
The number of the collection points of the three-phase load current needs to be kept equal in each fundamental wave period, and feasibility is provided for subsequent calculation.
Preferably, in step B), the method for obtaining the active and reactive components of the load current comprises:
wherein, Ik+Is a positive sequence harmonic component, Ik-Is a negative sequence harmonic component, θk+Is a positive sequence harmonic component phase angle, thetak-Is the negative sequence harmonic component phase angle.
Preferably, after the load current signal is subjected to abc/dq conversion, the positive sequence harmonic component of the load current signal decreases by one order, and the negative sequence harmonic component of the load current signal increases by one order.
Preferably, the 6k ± 1 th harmonic generated by the load current signal in the three-phase rectifying load is represented as a 6k harmonic component after abc/dq conversion.
Preferably, in step C), the method of calculating the average value of the input signal includes:
the active component of the load current signal passes through a generalized moving average filter, and the input signal is subjected to the operation of calculating the average value in a fundamental wave period:
where x (T) is the input signal sequence of the generalized moving average filter, y (T) is the output signal sequence of the generalized moving average filter, TWIs the sliding window period of the generalized moving average filter.
The specific improvement mode of the GMAF-based harmonic current extraction algorithm comprises the following steps: the comb filter of the traditional MAF is improved; improvement of the gain λ of a conventional MAF.
Preferably, in step C), the method for passing the real component of the load current signal through the generalized moving average filter includes:
passing the three-phase rectified load current through the transfer function H of the generalized moving average filterGMAF(z) performing a filtering process with a transfer function HGMAF(z) is:
and obtaining the difference between the direct current component of the load current signal and the load current component to extract the mk subharmonic component.
Where N is the number of points sampled per fundamental period of the input signal, λGIs the gain of the filter.
After one period of summation and averaging, the GMAF can filter the mk subharmonic component, and the mk subharmonic component can be extracted after the difference between the obtained direct current component and the original load current is made.
The substantial effects of the invention are as follows: the invention can extract specific subharmonic component after improving the comb filter and gain part of the traditional MAF. GMAF reduces the extracted dynamic response time without obvious loss of precision, can avoid redundant zero points and reduce storage units.
Drawings
Fig. 1 is a schematic step diagram of a harmonic current fast extraction method according to the first embodiment.
Detailed Description
The following is a more detailed description of the embodiments of the present invention, with reference to the accompanying drawings.
As shown in fig. 1, a method for fast extracting harmonic current includes the following steps,
the method comprises the following steps: the system obtains load current through current transformer sampling, and makes the number of sampling points of the load current in each fundamental wave period equal.
Step two: carrying out abc/dq conversion on the load current to obtain active and reactive components of the load current:
wherein, Ik+Is a positive sequence harmonic component, Ik-Is a negative sequence harmonic component, θk+Is a positive sequence harmonic component phase angle, thetak-Is the phase angle of the harmonic component with negative sequence, and k is an integer.
Step three: the obtained active component passes through GMAF, namely a generalized moving average filter.
The method for passing the active component of the load current signal through the generalized moving average filter comprises the following steps:
passing the three-phase rectified load current through the transfer function H of the generalized moving average filterGMAF(z) performing a filtering process with a transfer function HGMAF(z) is:
obtaining the difference between the direct current component of the load current signal and the load current component to extract the mk subharmonic component;
where N is the number of points sampled per fundamental period of the input signal, λGIs the gain of the filter.
In a fundamental wave period, carrying out an average value operation on an input signal to obtain a direct current component:
where x (T) is the input signal sequence of the generalized moving average filter, y (T) is the output signal sequence of the generalized moving average filter, TWIs the sliding window period of the generalized moving average filter.
Step four: the direct current component obtained after GMAF is subjected to dq/abc conversion to obtain a corresponding fundamental wave component;
step five: the obtained fundamental component is subtracted from the original load current, and then the specific subharmonic component in the load current can be extracted.
The embodiment realizes the extraction of mk subharmonics by improving the algorithm structure of the traditional MAF.
MAF carries out average operation on input signals in a fundamental wave period, the accumulated value of alternating current components is zero, and only direct current components are reserved as a result. The transfer function of MAF in discrete domain can be regarded as cascaded three parts, H, of input signal passing through the first partc(Z) introducing N uniformly distributed zero points in a unit circle of a Z domain, wherein the zero points are positioned at integral harmonic frequencies, and filtering integral harmonic components; the H (Z) of the input signal passing through the second part is essentially a pole introduced in the Z-domain unit circle, and the pole introduced in the part is connected with the H of the first partc(Z) zero-pole cancellation is realized, namely the direct current component filtered out in the first part is restored in the part, so that the direct current component is extracted; the input signal passes through the third section λ, ensuring unity gain and zero phase shift of the output signal.
In the invention, the specific improvement mode of the GMAF-based harmonic current extraction algorithm is as follows:
(1) the comb filter for a conventional MAF is improved:
reconfiguring GMAFj2πkThe zero, the new comb filter is of the form:
when m is 6, the 6k harmonic is extracted, and the dynamic response time becomes 1/6.
(2) Improvement of the gain λ of a conventional MAF:
in order to realize the unit gain of the direct current component, the gain in the GMAF algorithm is adjusted, and the adjusted gain is as follows:
the following can be obtained:
(3) after one period of summation and averaging, the GMAF can filter the mk subharmonic component, and the mk subharmonic component can be extracted after the difference between the obtained direct current component and the original load current is made.
The amplitude response of MAF at 50Hz integer multiple harmonic frequencies is zero and the amplitude response of GMAF at 6k harmonic frequencies is zero, both achieving unity gain and zero phase displacement.
Experiments may show that the dynamic response time of the harmonic current extraction based on MAF is about 20ms of one fundamental period and the dynamic response time of the harmonic current extraction based on GMAF is about 1/6 of MAF, both in case of sudden change of three-phase rectifying load and in case of sudden change of harmonics
After the comb filter and the gain part of the traditional MAF are improved, the specific subharmonic component can be extracted by configuring m. For example, when m is 6 for a three-phase rectifying load, GMAF reduces the extracted dynamic response time to 1/6 MAF, i.e., 3.3ms, without significant loss of accuracy, and can avoid redundant zeros and reduce memory cells.
The above embodiment is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the technical scope of the claims.
Claims (7)
1. A method for quickly extracting harmonic current is characterized by comprising the following steps:
A) acquiring a load current signal of harmonic waves to be acquired, wherein the load current signal is a three-phase load current signal;
B) carrying out abc/dq conversion on the load current signal, and calculating an active component and a reactive component of the load current signal;
C) calculating the summation average value of the active components of the input signals;
D) carrying out dq/abc conversion on the summation average value of the active component of the input signal to obtain the fundamental component of the load current signal;
E) and performing signal difference on the fundamental component and the load current to obtain a harmonic component in the load current signal.
2. The method for fast extracting harmonic current according to claim 1,
in the step A), the sampling points of the load current in each fundamental wave period are equal.
3. The method for fast extracting harmonic current according to claim 2,
in step B), the method for obtaining the active and reactive components of the load current comprises:
wherein, Ik+Is a positive sequence harmonic component, Ik-Is a negative sequence harmonic component, θk+Is the phase angle of the positive sequence harmonic component, thetak-Is the negative sequence harmonic component phase angle.
4. The method for fast extracting harmonic current according to claim 3,
after the load current signal is subjected to abc/dq conversion, the positive sequence harmonic component of the load current signal is reduced by one order, and the negative sequence harmonic component of the load current signal is increased by one order.
5. The method of claim 4, wherein the harmonic current is extracted rapidly
The 6k +/-1 harmonic generated by the load current signal on the three-phase rectifying load is represented as a 6k harmonic component after being subjected to abc/dq conversion.
6. The method of claim 1, wherein the harmonic current is extracted rapidly
In step C), the method for calculating the average value of the input signal includes:
the active component of the load current signal passes through a generalized moving average filter, and the input signal is subjected to the operation of calculating the average value in a fundamental wave period:
where x (T) is the input signal sequence of the generalized moving average filter, y (T) is the output signal sequence of the generalized moving average filter, TWIs the sliding window period of the generalized moving average filter.
7. The method for fast extracting harmonic current according to claim 6, wherein in step C), the method for passing the active component of the load current signal through the generalized moving average filter includes:
passing the three-phase rectified load current through the transfer function H of the generalized moving average filterGMAF(z) performing a filtering process with a transfer function HGMAF(z) is:
obtaining the difference between the direct current component of the load current signal and the load current component to extract the mk subharmonic component; where N is the number of points sampled per fundamental period of the input signal, λGIs an increase of a filterIt is beneficial to.
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| CN113964848A (en) * | 2021-12-20 | 2022-01-21 | 昆山帝森华途工业物联网科技有限公司 | Reactive current extraction module of APF control system |
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