CN109212311B - Novel real-time subharmonic detection method for comb filtering - Google Patents
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Abstract
The invention discloses a novel real-time subharmonic detection method of comb filtering, which measures amplitude signals of single harmonic waves by enabling the output of each second-order integrator to be a pair of orthogonal signals; in a specific process, the output of each second-order integrator is added and subtracted from the input of the system, so that the influence of other subharmonics can be eliminated, and the steady-state precision of the system is ensured; therefore, the redundant decoupling link of the traditional multiple second-order generalized integrator based on the band-pass filter is eliminated, the calculation burden is reduced, and the response speed of the system is increased.
Description
Technical Field
The invention belongs to the technical field of current harmonic control of active power filters, and particularly relates to a novel real-time fractional harmonic detection method for comb filtering.
Background
With the development of power electronic technology, the application of nonlinear load causes the problem of power grid harmonic pollution, and because the rapid extraction of specified subharmonics plays an important role in the aspects of power quality evaluation, power grid synchronization, harmonic compensation and the like, various methods for detecting and extracting harmonics are proposed in order to solve the increasingly serious harmonic problem. These methods are generally classified into a time domain method and a frequency domain method.
The frequency domain method is generally a fourier transform-based method, and discrete fourier transform converts time domain signals into frequency domain signals, which have obvious characteristics, such as simplicity, good selectivity, high steady-state accuracy, and the like. The fast fourier transform is an improved form of discrete fourier transform to reduce the amount of computation, and is widely used for harmonic monitoring and measurement. The Chinese invention patent ' a harmonic current compensation method based on fast Fourier transform ' (publication number: 102412579A) ' discloses a harmonic current compensation method based on FFT, which comprises the steps of respectively carrying out FFT analysis on load current and output current of a current converter, then calculating load current amplitude and output current amplitude errors of the current converter, load current phase and output current phase errors of the current converter, respectively correcting harmonic current amplitude and phase instructions according to the errors, and finally reconstructing the harmonic current amplitude/phase to obtain a harmonic current instruction of a chain type current converter. However, the dynamic response of the system is very slow, the frequency sensitivity is low, and harmonic amplitude signals cannot be extracted, so that the method is not suitable for rapidly detecting harmonics.
On the other hand, typical time domain methods include an instantaneous power theory (PQ power theory), a band-pass filter-based second-order generalized integrator method, a DQ coordinate system fundamental wave/harmonic control theory, a multi-reference coordinate system method, an adaptive notch filter method, a series delay signal elimination method, an advanced kalman filter method, and the like. These time-domain methods can effectively extract harmonic components, but there are some limitations. The Chinese invention patent ' a calculation method for fractional harmonic compensation of multiple synchronous rotating coordinate systems APF ' (publication number: 104466966A) ' discloses a calculation method for fractional harmonic compensation of multiple synchronous rotating coordinate systems APF, which promotes each harmonic current to be processed independently and response quickly to ensure that each harmonic compensation is set independently. However, the method increases the complexity and the calculation amount of the system, cannot detect amplitude signals, and is not suitable for quickly selecting harmonic extraction. The Chinese invention patent ' a frequency self-adaptive real-time subharmonic detection method ' (publication number: 103487652A) ' discloses a frequency self-adaptive real-time subharmonic detection method, which is characterized in that a phase-locked loop is used for carrying out phase locking on the voltage of a power grid to obtain the voltage frequency of the power grid, the system control frequency is adjusted according to the voltage frequency of the power grid, the number of sampling points in the fundamental wave period of the power grid is kept unchanged when the frequency of the voltage of the power grid fluctuates, the frequency self-adaptive function of an nth harmonic band-pass filter is realized, and then the input quantity of the nth harmonic band-pass filter is subjected to subtraction operation to eliminate the mutual interference among the subharmonics. The method has high detection precision, but has large calculation amount, can not calculate harmonic amplitude signals, and is not suitable for fractional rapid detection of harmonic.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a novel real-time subharmonic detection method for comb filtering.
In order to achieve the above object, the present invention provides a novel real-time sub-harmonic detection method for comb filtering, which is characterized by comprising the following steps:
(1) subtracting a measured signal v (Z) from a total harmonic output signal v (Z)' of the last-beat comb filter to obtain an error signal e (Z), wherein Z represents a Z domain operator;
(2) the error signal e (z) is added to the integral gain K of each second-order generalized integratorInThe products of the first and second order generalized integrators are respectively used as a first path of input signals of each second order generalized integrator connected in parallel in the comb filter, wherein n is 1,2, …, h, h is the number of the second order generalized integrators;
(3) general (n omega)2As a second path of input signal of the second-order generalized integrator, omega is the fundamental frequency; inputting the second path of input signal (n omega)2The product of the feedback signal x3 and the first input signal are added to obtain a signal x 1;
(4) integrating the signal x1 by a first integrator to obtain a signal x2, and integrating the signal x2 by a second integrator to obtain a feedback signal x 3;
(5) the feedback signals x3 and sin (n ω T)s) Multiplying to obtain quadrature signal qvn(z)'，TsA system control period; then the orthogonal signal qv is processedn(z)' and cos (n ω T)s) The product of-1 is summed with the signal x2 to obtain the individual single harmonic signals vn(z)'；
(6) The single harmonic signals v in the step (5) are respectively processednSquared (z)' and quadrature signal qvnAddition of the squares of (z)' and reopeningSquaring to obtain amplitude signal V of each single harmonicnm；
(7) Each single harmonic signal vn(z) 'to obtain a total harmonic output signal v (z)'.
The invention aims to realize the following steps:
the invention relates to a novel real-time subharmonic detection method of comb filtering, which measures amplitude signals of single harmonic waves by enabling the output of each second-order integrator to be a pair of orthogonal signals; in a specific process, the output of each second-order integrator is added and subtracted from the input of the system, so that the influence of other subharmonics can be eliminated, and the steady-state precision of the system is ensured; therefore, the redundant decoupling link of the traditional multiple second-order generalized integrator based on the band-pass filter is eliminated, the calculation burden is reduced, and the response speed of the system is increased.
Meanwhile, the novel real-time subharmonic detection method for comb filtering further has the following beneficial effects:
(1) on the premise of extracting the specified subharmonic, the dynamic characteristic and the smaller calculated amount of the system can be ensured;
(2) the steady-state error of the experimental result of the invention is low, even if the frequency of the power grid fluctuates greatly.
Drawings
Fig. 1 is a system block diagram of a novel comb-filtering real-time subharmonic detection method according to the present invention.
Fig. 2 is a system block diagram of a second order generalized integrator.
FIG. 3 is a block diagram of a system for measuring the amplitude of harmonics.
FIG. 4 is a steady-state accuracy test waveform measured by a real-time subharmonic detection method using comb filtering.
Fig. 5 is a graph showing experimental waveforms and corresponding amplitude signals for fundamental and 5 th harmonic components.
FIG. 6 is an experimental waveform of all harmonic components when the grid voltage jumps from 50Hz to 55 Hz.
FIG. 7 is an experimental waveform of all harmonic components when the grid voltage jumps from 50Hz to 45 Hz.
Fig. 8 is a transient experimental waveform of all harmonic components.
Fig. 9 is an experimental waveform of individual harmonic component extraction.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Examples
Fig. 1 is a system block diagram of a novel comb-filtering real-time subharmonic detection method according to the present invention.
In this embodiment, as shown in fig. 1, the method for detecting real-time subharmonic of comb filtering of the present invention includes the following steps:
s1, subtracting the measured signal v (Z) from the total harmonic output signal v (Z)' of the last comb filter to obtain an error signal e (Z), wherein Z represents a Z-domain operator;
s2, mixing the error signal e (z) with the integral gain K of each second-order generalized integratorInThe products of the first and second order generalized integrators are respectively used as a first path of input signals of each second order generalized integrator connected in parallel in the comb filter, wherein n is 1,2, …, h, h is the number of the second order generalized integrators;
s3 general (n omega)2As a second path of input signal of the second-order generalized integrator, omega is the fundamental frequency; inputting the second path of input signal (n omega)2The product of the feedback signal x3 and the first input signal are added to obtain a signal x 1;
s4, integrating the signal x1 by a first integrator to obtain a signal x2, and integrating the signal x2 by a second integrator to obtain a feedback signal x 3;
s5, feedback signals x3 and sin (n ω T)s) Multiplying to obtain quadrature signal qvn(z)'，TsA system control period; then the orthogonal signal qv is processedn(z)' and cos (n ω T)s) The product of-1 is summed with the signal x2 to obtain the individual single harmonic signals vn(z)'；
S6, converting each single harmonic signal v in the step S5nSquared (z)' and quadrature signal qvnAdding the squares of (z)' and then squaring to obtain amplitude signals V of each single harmonicnm；
S7, converting each single harmonic signal vn(z) 'to obtain a total harmonic output signal v (z)'.
Fig. 2 is a system block diagram of a second order generalized integrator.
The phase checking circuit specifically comprises two integrators and a phase checking module. The output x2 of the first integrator is used as the input of the second integrator, the sum of the output x3 of the second integrator and the error signal is used as the input of the first integrator, and at the moment, the sum of the output x3 of the second integrator and the error signal is verified by the phase verification module to obtain a harmonic signal v, wherein the sum of the output x3 and the output x2 of the second integrator is used as the input of the first integratorn(z)' with quadrature signal qvn(z)'。
FIG. 3 is a block diagram of a system for measuring the amplitude of harmonics.
As shown in FIG. 3, the square of the quadrature signal obtained in FIG. 2 is added to the square of the harmonic signal, and then squared to obtain the amplitude signal V of each single harmonicnm。
FIG. 4 is a steady-state accuracy test waveform measured by a real-time subharmonic detection method using comb filtering.
An experimental platform is built in a laboratory environment, fig. 4 is a steady-state waveform of an experiment, and it can be seen from fig. 4 that a real-time subharmonic detection method based on comb filtering extracts a signal which is almost coincident with an input signal, and an error curve is basically 0, so that the method is proved to have the characteristic of high steady-state precision.
Fig. 5 is a fundamental and 5 th harmonic component experimental waveform and corresponding amplitude signal.
Fig. 5 shows fundamental and 5 th harmonic components and corresponding amplitude signals, verifying that harmonic signals can be extracted separately and their amplitude signals found.
FIG. 6 is an experimental waveform of all harmonic components when the grid voltage jumps from 50Hz to 55 Hz.
When the voltage of the power grid jumps from 50Hz to 55Hz, all harmonic components show that the steady-state performance of the system is still very good even if the frequency of the power grid jumps greatly to the high frequency.
FIG. 7 is an experimental waveform of all harmonic components when the grid voltage jumps from 50Hz to 45 Hz.
When the voltage of the power grid jumps from 50Hz to 45Hz, all harmonic components show that the steady-state performance of the system is still very good even if the frequency of the power grid jumps greatly to the low frequency.
Fig. 8 is a transient experimental waveform of all harmonic components.
As shown in fig. 8, transient waveforms of all harmonic components are extracted, and it can be seen from the figure that one cycle time is required to reach a steady state.
Fig. 9 is an experimental waveform of individual harmonic component extraction.
As shown in fig. 9, the dynamic characteristics of the method of the present invention are better because a period of time is required from a transient state to a steady state when the individual harmonic components are extracted.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (1)
1. A novel comb filtering real-time subharmonic detection method is characterized by comprising the following steps:
(1) subtracting a measured signal v (Z) from a total harmonic output signal v (Z)' of the last-beat comb filter to obtain an error signal e (Z), wherein Z represents a Z domain operator;
(2) the error signal e (z) is added to the integral gain K of each second-order generalized integratorInThe products of the first and second order generalized integrators are respectively used as a first path of input signals of each second order generalized integrator connected in parallel in the comb filter, wherein n is 1,2, …, h, h is the number of the second order generalized integrators;
(3) general (n omega)2Second output as second order generalized integratorAn input signal, omega is the fundamental frequency; inputting the second path of input signal (n omega)2The product of the feedback signal x3 and the first input signal are added to obtain a signal x 1;
(4) integrating the signal x1 by a first integrator to obtain a signal x2, and integrating the signal x2 by a second integrator to obtain a feedback signal x 3;
(5) the feedback signals x3 and sin (n ω T)s) Multiplying to obtain quadrature signal qvn(z)'，TsA system control period; then the orthogonal signal qv is processedn(z)' and cos (n ω T)s) The product of-1 is summed with the signal x2 to obtain the individual single harmonic signals vn(z)'；
(6) The single harmonic signals v in the step (5) are respectively processednSquared (z)' and quadrature signal qvnAdding the squares of (z)' and then squaring to obtain amplitude signals V of each single harmonicnm；
(7) Each single harmonic signal vn(z) 'to obtain a total harmonic output signal v (z)'.
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