CN112881776B - Method for rapidly extracting harmonic current - Google Patents
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- CN112881776B CN112881776B CN202110043102.1A CN202110043102A CN112881776B CN 112881776 B CN112881776 B CN 112881776B CN 202110043102 A CN202110043102 A CN 202110043102A CN 112881776 B CN112881776 B CN 112881776B
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Abstract
The invention relates to a method for rapidly extracting harmonic current, which belongs to the technical field of signal processing and comprises the following steps of A) collecting a load current signal of a harmonic to be collected; the load current signal is a three-phase load current signal; b) Performing abc/dq conversion on the load current signal, and calculating an active component and a reactive component of the load current signal; c) Calculating a sum average of active components of the input signal; d) Performing dq/abc conversion on the sum average value of the active components of the input signal to obtain a fundamental component of the load current signal; e) And carrying out signal difference on the fundamental wave component and the load current to obtain a harmonic wave component in the load current signal. The invention has the following substantial effects: the invention can extract specific subharmonic components after improving the comb filter and gain part of the traditional MAF. The GMAF reduces the extracted dynamic response time on the premise of not obviously losing the precision, and can avoid redundant zero points and reduce storage units.
Description
Technical Field
The invention relates to the technical field of signal processing, in particular to a method for rapidly extracting harmonic current.
Background
The problem of harmonic pollution is more serious as renewable energy and power electronics are connected into the power grid. The multiport energy router is used as a control core of a new generation power network, can flexibly manage and control power after being accessed into a power grid, promotes the consumption of renewable energy sources and improves the power quality of a power distribution network, and the harmonic current extraction method is used as an important branch for realizing a harmonic compensation function, has important significance for harmonic suppression and is mainly divided into a time domain method and a frequency domain method. The frequency domain method is mainly a discrete Fourier method, a fast discrete Fourier method and an iterative discrete Fourier method based on Fourier transformation, but the Fourier transformation method has large occupied amount of storage space, large calculated amount and low real-time performance for a digital controller. In the time domain method, a PQ power theory method and a synchronous dq rotation method are common, wherein the PQ power theory method is only suitable for the working condition of an ideal power grid, and the synchronous dq rotation method is more suitable for harmonic current detection under various non-ideal power grid conditions. However, a Low Pass Filter (LPF) for harmonic extraction in the synchronous dq rotation method is greatly affected by the cut-off frequency and the order, and the dynamic response time of the Filter is long and the real-time compensation effect is poor.
The Chinese patent CN107782965A, publication date 2018, 03 and 09, discloses a novel harmonic current detection method, which is based on the theory of an input observer. The novel current harmonic detection method overcomes the limitation that the detection methods such as instantaneous reactive power and the like can only detect the total harmonic current, can detect the harmonic component of each appointed frequency at the same time, has the advantages of high detection speed, high precision, good dynamic tracking performance and anti-interference performance and the like, has good practicability, and has a certain reference value for APF harmonic detection research.
Disclosure of Invention
The invention aims to solve the technical problems that: provides a method with small occupied space and short dynamic response time for fast harmonic current extraction
In order to solve the technical problems, the invention adopts the following technical scheme: a method for rapidly extracting harmonic current comprises the following steps:
a) Collecting a load current signal of a harmonic wave to be collected; the load current signal is a three-phase load current signal;
b) Performing abc/dq conversion on the load current signal, and calculating an active component and a reactive component of the load current signal;
c) Calculating a sum average of active components of the input signal;
d) Performing dq/abc conversion on the sum average value of the active components of the input signal to obtain a fundamental component of the load current signal;
e) And carrying out signal difference on the fundamental wave component and the load current to obtain a harmonic wave component in the load current signal.
The three-phase load current signal is subjected to abc/dq conversion and then is subjected to optimized filtering of active components, so that more accurate several wave components of the load current signal are obtained, and multiple harmonics of the three-phase load current are extracted. The invention is based on GMAF, namely generalized moving average filter, optimizes the filtering, and obtains a faster harmonic current extraction algorithm.
Preferably, in step a), the load current is equal in the number of sampling points per fundamental period.
The number of the collection points of the three-phase load current is required to be kept equal in the period of each base wave, and feasibility is provided for subsequent calculation.
Preferably, in step B), the method for obtaining active and reactive components of the load current comprises:
wherein I is k+ As positive sequence harmonic component, I k- As negative sequence harmonic component, θ k+ Is the phase angle of positive sequence harmonic component, theta k- Is the phase angle of the negative sequence harmonic component.
Preferably, after the load current signal is subjected to abc/dq conversion, the positive sequence harmonic component of the load current signal decreases by a first order, and the negative sequence harmonic component of the load current signal increases by a first order.
Preferably, 6k±1 harmonics generated in the three-phase rectifying load by the load current signal are converted by abc/dq and are expressed as 6k harmonic components.
Preferably, in step C), the method of calculating the summed average value of the input signals comprises:
the active component of the load current signal passes through a generalized moving average filter, and in a fundamental wave period, the summation average value operation is carried out on the input signal:
where x (T) is the input signal sequence of the generalized moving average filter and y (T) is the output signal sequence of the generalized moving average filter, T W Is the sliding window period of the generalized moving average filter.
Specific improvement modes of the harmonic current extraction algorithm based on GMAF comprise: the comb filter of the traditional MAF is improved; improvement of gain lambda of conventional MAF.
Preferably, in step C), the method of passing the active component of the load current signal through a generalized moving average filter includes:
transfer function H of three-phase rectifying load current through generalized moving average filter GMAF (z) filtering, transfer function H GMAF (z) is:
the mk subharmonic component can be extracted by taking the difference between the DC component of the load current signal and the load current component.
Wherein N is the number of points sampled per fundamental period of the input signal, lambda G Is the gain of the filter.
After one period of summation and averaging, the GMAF can filter off the mk harmonic component, and the mk harmonic component can be extracted after the obtained direct current component is differenced from the original load current.
The invention has the following substantial effects: the invention can extract specific subharmonic components after improving the comb filter and gain part of the traditional MAF. The GMAF reduces the extracted dynamic response time on the premise of not obviously losing the precision, and can avoid redundant zero points and reduce storage units.
Drawings
Fig. 1 is a schematic diagram of a method for rapidly extracting harmonic current according to a first embodiment.
Detailed Description
The following description of the embodiments of the present invention will be made with reference to the accompanying drawings.
As shown in fig. 1, a method for rapidly extracting harmonic current includes the steps of,
step one: the system obtains the load current through sampling of the current transformer, and the sampling points of the load current in each fundamental wave period are equal.
Step two: the abc/dq conversion is carried out on the load current to obtain active and reactive components of the load current:
wherein I is k+ As positive sequence harmonic component, I k- As negative sequence harmonic component, θ k+ Is the phase angle of positive sequence harmonic component, theta k- Is the phase angle of the negative sequence harmonic component, and k is an integer.
Step three: the resulting active component is passed through a GMAF, 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:
transfer function H of three-phase rectifying load current through generalized moving average filter GMAF (z) filtering, transfer function H GMAF (z) is:
obtaining a difference between a direct current component and a load current component of a load current signal, and extracting an mk subharmonic component;
wherein N is the number of points sampled per fundamental period of the input signal, lambda G Is the gain of the filter.
In a fundamental wave period, carrying out summation 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 and y (T) is the output signal sequence of the generalized moving average filter, T W Is 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 component;
step five: the obtained fundamental component is differenced with the original load current, and 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 performs average value operation on the input signal in one fundamental wave period, the accumulated value of the alternating current component is zero, and only the direct current component is reserved as a result. The MAF transfer function in the discrete domain can be seen as a cascade of three parts, the input signal passing through H in the first part c (Z) introducing N evenly distributed zero points in a unit circle of a Z domain, wherein the zero points are positioned at the harmonic frequency of integer times, and filtering out the harmonic components of integer times; input letterThe number H (Z) passing through the second part essentially introduces a pole within the Z-domain unit circle, the pole introduced by this part being identical to the H of the first part c (Z) pole-zero cancellation is achieved, i.e. the DC component filtered out in the first part is reduced in this part, thereby extracting the DC component; the input signal passes through the third portion lambda ensuring unity gain and zero phase shift of the output signal.
In the invention, the specific improvement mode of the harmonic current extraction algorithm based on GMAF is as follows:
(1) The comb filter of the traditional MAF is improved:
reconfiguring z=e for GMAF j2πk The form of the new comb filter is as follows:
when m=6, the 6k harmonics can be extracted, and the dynamic response time becomes 1/6 of the original one.
(2) Improvement of gain λ for 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 method can obtain:
(3) After one period of summation and averaging, the GMAF can filter off the mk harmonic component, and the mk harmonic component can be extracted after the obtained direct current component is differenced from the original load current.
The amplitude response of MAF at 50Hz integer multiple harmonic frequency is zero, the amplitude response of GMAF at 6k harmonic frequency is zero, both of which can realize unity gain and zero phase displacement.
Experiments have shown that the dynamic response time of the MAF-based harmonic current extraction is about 20ms for one fundamental period, and about 1/6 of that of the MAF, both in the case of abrupt three-phase rectifying load changes and in the case of abrupt harmonic changes
The invention can extract specific subharmonic components by configuring m after improving the comb filter and gain part of the traditional MAF. For example, when m=6 is configured for a three-phase rectifying load, the GMAF reduces the extracted dynamic response time to 1/6 of the MAF, i.e. 3.3ms, without significant loss of accuracy, and can avoid redundant zero points and reduce memory cells.
The above embodiment is only a preferred embodiment of the present invention, and is not limited in any way, and other variations and modifications may be made without departing from the technical aspects set forth in the claims.
Claims (3)
1. The rapid harmonic current extraction method is characterized by comprising the following steps of:
a) Collecting a load current signal of a harmonic wave to be collected, wherein the load current signal is a three-phase load current signal;
b) Performing abc/dq conversion on the load current signal, and calculating an active component and a reactive component of the load current signal;
c) Calculating a sum average of active components of the input signal;
d) Performing dq/abc conversion on the sum average value of the active components of the input signal to obtain a fundamental component of the load current signal;
e) The fundamental wave component and the load current are subjected to signal difference to obtain a harmonic wave component in a load current signal;
in step B), the method of obtaining active and reactive components of the load current comprises:
wherein I is k+ As positive sequence harmonic component, I k- As negative sequence harmonic component, θ k+ Is the phase angle of positive sequence harmonic component, theta k- Is the phase angle of the negative sequence harmonic component;
after a load current signal is subjected to abc/dq conversion, a positive sequence harmonic component of the load current signal is reduced by a first order, and a negative sequence harmonic component of the load current signal is increased by the first order;
in step C), the method of calculating the summed average of the input signals comprises:
the active component of the load current signal passes through a generalized moving average filter, and in a fundamental wave period, the summation average value operation is carried out on the input signal:
where x (T) is the input signal sequence of the generalized moving average filter and y (T) is the output signal sequence of the generalized moving average filter, T W A sliding window period that is a generalized moving average filter;
in step C), the method of passing the active component of the load current signal through a generalized moving average filter includes:
transfer function H of three-phase rectifying load current through generalized moving average filter GMAF (z) filtering, transfer function H GMAF (z) is:
obtaining a difference between a direct current component and a load current component of a load current signal, and extracting an mk subharmonic component;
wherein N is an input signalNumber of samples per fundamental period, lambda G Is the gain of the filter;
the specific improvement mode of the harmonic current extraction algorithm based on GMAF is as follows:
(1) The comb filter of the traditional MAF is improved:
reconfiguring z=e for GMAF j2πk The form of the new comb filter is as follows:
when m=6, the 6k harmonics can be extracted, and the dynamic response time becomes 1/6 of the original one;
(2) Improvement of gain λ for 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 method can obtain:
(3) After one period of summation and averaging, the GMAF can filter off the mk harmonic component, and the mk harmonic component can be extracted after the obtained direct current component is differenced from the original load current.
2. A method for rapidly extracting harmonic current according to claim 1, wherein,
in step a), the load current has equal sampling points per fundamental period.
3. The method for rapidly extracting harmonic current according to claim 2, wherein
The 6k + -1 subharmonic generated by the load current signal on the three-phase rectifying load is converted by abc/dq and then appears as a 6k subharmonic component.
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| CN104020351A (en) * | 2014-06-24 | 2014-09-03 | 哈尔滨同为电气股份有限公司 | Subharmonic detection method suitable for APF (Active Power Filter) under load unbalance system |
| CN110061615A (en) * | 2019-06-03 | 2019-07-26 | 上海理工大学 | The Stator Current Harmonic compensation method of inverter nonlinear characteristic |
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| CN110061615A (en) * | 2019-06-03 | 2019-07-26 | 上海理工大学 | The Stator Current Harmonic compensation method of inverter nonlinear characteristic |
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