CN105548688A - Method and system for realizing frequency measurement on basis of zero initial phase reference cosine function sequence - Google Patents

Abstract

The invention relates to a method and a system for realizing frequency measurement on the basis of a zero initial phase reference cosine function sequence. According to the method, a real frequency mixing sequence and an imaginary frequency mixing sequence are acquired, digital filtering and integration of the real frequency mixing sequence and the imaginary frequency mixing sequence are carried out, a real frequency integration value and an imaginary frequency integration value are acquired, the phase of the zero initial phase reference cosine function modulation sequence is acquired according to the real frequency integration value and the imaginary frequency integration value, and the frequency of an electric power signal is acquired according to the phase. Through the method, the frequency of the electric power signal is acquired, and accuracy of frequency measurement on the electric power signal can be improved.

Description

Method and system for measuring frequency according to zero initial phase reference cosine function sequence

Technical Field

The invention relates to the technical field of power systems, in particular to a method and a system for measuring frequency according to a zero initial phase reference cosine function sequence.

Background

Frequency measurement, phase measurement, amplitude measurement and the like of the power system are measurements of sinusoidal parameters in nature. The Fourier transform is a basic method for realizing sinusoidal parameter measurement and has wide application in power systems. However, with the development of sinusoidal parameter measurement technology, the problems of fourier transform are more prominent, and it is difficult to further meet the requirement of the power system on high accuracy calculation of sinusoidal parameters.

In the aspect of measuring sinusoidal parameters of the power system, there are some improved parameter measuring methods, such as a zero-crossing method, a filter-based measuring method, a wavelet transform-based measuring method, a neural network-based measuring method, a DFT (discrete fourier transform) -transform-based measuring method, and the like. Because the rated power frequency of the power grid is near 50Hz (Hertz), the power grid belongs to a sine frequency with lower frequency, and interference exists in an actual power signal, such as harmonic interference, similar white noise interference generated by random fluctuation in a small range of power load, and the like, under the interference environment, the measurement accuracy of the algorithms is not high.

Disclosure of Invention

In view of the above, it is necessary to provide a method and a system for performing frequency measurement according to a zero initial phase reference cosine function sequence, which can improve the accuracy of power signal frequency measurement.

In order to solve the technical problems, the invention adopts the following technical scheme:

a method for measuring frequency according to zero initial phase reference cosine function sequence includes the following steps:

obtaining a preliminary sequence length according to the lower limit of the power signal frequency range, a preset sampling frequency and a preset integer signal period number;

sampling the power signal according to the length of the preliminary sequence to obtain a preliminary sequence of the power signal;

carrying out frequency initial measurement on the initial sequence to obtain an initial frequency of the power signal, and obtaining a reference frequency according to the initial frequency;

obtaining the unit cycle sequence length of the power signal according to the preset sampling frequency and the reference frequency;

multiplying the preset integer signal period number and the unit period sequence length to obtain a preprocessing sequence length;

acquiring a preprocessing sequence from the preliminary sequence of the power signal according to the length of the preprocessing sequence;

performing comb filtering processing on the preprocessing sequence to obtain a comb filtering sequence, wherein the length of the comb filtering sequence is the residual length of the preprocessing sequence after the comb filtering processing;

determining a ratio integer of the length of the comb filtering sequence to the length of the unit period sequence, and obtaining a preset sequence length according to the ratio integer and the length of the unit period sequence, wherein the ratio integer is an odd number, and the preset sequence length is an odd number;

obtaining a first forward sequence from the comb filtering sequence according to the preset sequence length and a preset starting point, and obtaining a first inverse pleat sequence according to the first forward sequence;

obtaining a first positive phase from the first forward sequence and a first anti-phase from the first anti-aliasing sequence;

obtaining a first average initial phase according to the first positive phase and the first negative phase;

obtaining a phase comparison value according to the first average initial phase and a preset phase value, and obtaining a new initial point according to the phase comparison value, the preset initial point and the unit cycle sequence length;

obtaining a second forward sequence from the comb filtering sequence according to the preset sequence length and the new starting point, and obtaining a second inverse pleat sequence according to the second forward sequence;

obtaining a second positive phase from the second forward sequence and a second anti-phase from the second anti-aliased sequence;

obtaining a second average initial phase according to the second positive phase and the second negative phase;

adding the second forward sequence and the second inverse pleat sequence to obtain a sum sequence, and obtaining a cosine function modulation sequence according to the sum sequence and a cosine function value of the second average initial phase;

outputting from the central point of the cosine function modulation sequence to obtain a zero initial phase reference cosine function modulation sequence;

multiplying the zero initial phase reference cosine function modulation sequence by a discrete cosine function of a reference frequency and a discrete sine function of the reference frequency respectively to obtain a real frequency mixing sequence and an imaginary frequency mixing sequence;

respectively carrying out digital filtering on the real frequency mixing sequence and the virtual frequency mixing sequence to obtain a real frequency filtering sequence and a virtual frequency filtering sequence;

respectively integrating the real-frequency filtering sequence and the virtual-frequency filtering sequence to obtain a real-frequency integral value and a virtual-frequency integral value;

and obtaining the phase of the zero initial phase reference cosine function modulation sequence according to the real frequency integral value and the virtual frequency integral value, and obtaining the frequency of the electric power signal according to the phase.

A system for frequency measurement based on a zero initial phase reference cosine function sequence, comprising:

the preliminary sequence length determining module is used for obtaining a preliminary sequence length according to the lower limit of the power signal frequency range, a preset sampling frequency and a preset integer signal period number;

the preliminary sequence acquisition module is used for sampling the electric power signal according to the length of the preliminary sequence to obtain a preliminary sequence of the electric power signal;

a reference frequency determining module, configured to perform frequency initial measurement on the preliminary sequence to obtain a preliminary frequency of the power signal, and obtain a reference frequency according to the preliminary frequency;

a unit cycle sequence length determining module, configured to obtain a unit cycle sequence length of the power signal according to the preset sampling frequency and the reference frequency;

the preprocessing sequence length determining module is used for multiplying the preset integer signal period number and the unit period sequence length to obtain a preprocessing sequence length;

the preprocessing sequence acquisition module is used for acquiring a preprocessing sequence from the preliminary sequence of the power signal according to the length of the preprocessing sequence;

the comb filtering sequence determining module is used for carrying out comb filtering processing on the preprocessing sequence to obtain a comb filtering sequence, wherein the length of the comb filtering sequence is the residual length of the preprocessing sequence after the comb filtering processing;

a preset sequence length determining module, configured to determine a ratio integer between the comb filtering sequence length and the unit period sequence length, and obtain a preset sequence length according to the ratio integer and the unit period sequence length, where the ratio integer is an odd number, and the preset sequence length is an odd number;

a first sequence obtaining module, configured to obtain a first forward sequence from the comb filtering sequence according to the preset sequence length and a preset starting point, and obtain a first anti-aliasing sequence according to the first forward sequence;

a first positive and negative phase determination module for obtaining a first positive phase from the first forward sequence and a first negative phase from the first deconvolution sequence;

a first average initial phase determining module, configured to obtain a first average initial phase according to the first positive phase and the first negative phase;

a new starting point determining module, configured to obtain a phase comparison value according to the first average initial phase and a preset phase value, and obtain a new starting point according to the phase comparison value, the preset starting point, and the unit cycle sequence length;

a second sequence obtaining module, configured to obtain a second forward sequence from the comb filtering sequence according to the preset sequence length and the new starting point, and obtain a second inverse-folding sequence according to the second forward sequence;

a second forward-reverse phase determination module, configured to obtain a second positive phase according to the second forward sequence and obtain a second reverse phase according to the second deconvolution sequence;

a second average initial phase determining module, configured to obtain a second average initial phase according to the second positive phase and the second negative phase;

a cosine function modulation sequence determining module, configured to add the second forward sequence and the second inverse-pleated sequence to obtain a sum sequence, and obtain a cosine function modulation sequence according to the sum sequence and a cosine function value of the second average initial phase;

the zero initial phase modulation sequence acquisition module is used for outputting from the center point of the cosine function modulation sequence to acquire a zero initial phase reference cosine function modulation sequence;

a mixing sequence determining module, configured to multiply the zero initial phase reference cosine function modulation sequence by a discrete cosine function of a reference frequency and a discrete sine function of the reference frequency, respectively, to obtain a real-frequency mixing sequence and an imaginary-frequency mixing sequence;

a filtering sequence determining module, configured to perform digital filtering on the real-frequency mixing sequence and the virtual-frequency mixing sequence, respectively, to obtain a real-frequency filtering sequence and a virtual-frequency filtering sequence;

an integral value determining module, configured to integrate the real-frequency filtering sequence and the virtual-frequency filtering sequence, respectively, to obtain a real-frequency integral value and a virtual-frequency integral value;

and the power signal frequency determining module is used for obtaining the phase of the zero initial phase reference cosine function modulation sequence according to the real frequency integral value and the virtual frequency integral value and obtaining the frequency of the power signal according to the phase.

The invention provides a frequency measurement method and a frequency measurement system according to a zero initial phase reference cosine function sequence, a real frequency mixed sequence and an imaginary frequency mixed sequence are obtained, then digital filtering and integration are carried out on the real frequency mixed sequence and the imaginary frequency mixed sequence, a real frequency integral value and an imaginary frequency integral value are obtained, the phase of the zero initial phase reference cosine function modulation sequence is obtained according to the real frequency integral value and the imaginary frequency integral value, and the frequency of an electric power signal is obtained according to the phase. The frequency of the power signal is obtained by the method, so that the accuracy of measuring the frequency of the power signal can be obviously improved.

Drawings

FIG. 1 is a schematic flow chart illustrating an embodiment of a method for frequency measurement according to a zero initial phase reference cosine function sequence according to the present invention;

FIG. 2 is a schematic diagram of the amplitude-frequency characteristics of the comb filtering process in the frequency domain according to the present invention;

FIG. 3 is a diagram illustrating a comb filter sequence, a first forward sequence, and a first anti-aliasing sequence according to the present invention;

FIG. 4 is a graphical illustration of a zero initial phase reference point according to the present invention;

fig. 5 is a schematic structural diagram of an embodiment of a frequency measurement system according to a zero initial phase reference cosine function sequence.

Detailed Description

In order to further explain the technical means and effects of the present invention, the following description of the present invention with reference to the accompanying drawings and preferred embodiments will be made for clarity and completeness.

As shown in fig. 1, a method for performing frequency measurement according to a zero initial phase reference cosine function sequence includes the steps of:

s101, obtaining a preliminary sequence length according to the lower limit of the power signal frequency range, a preset sampling frequency and a preset integer signal period number;

s102, sampling the electric power signal according to the length of the preliminary sequence to obtain the preliminary sequence of the electric power signal;

s103, carrying out frequency initial measurement on the initial sequence to obtain an initial frequency of the power signal, and obtaining a reference frequency according to the initial frequency;

s104, obtaining the unit cycle sequence length of the power signal according to the preset sampling frequency and the reference frequency;

s105, multiplying the preset integer signal period number by the unit period sequence length to obtain a preprocessing sequence length;

s106, acquiring a preprocessing sequence from the preliminary sequence of the power signal according to the length of the preprocessing sequence;

s107, performing comb filtering processing on the preprocessing sequence to obtain a comb filtering sequence, wherein the length of the comb filtering sequence is the residual length of the preprocessing sequence after the comb filtering processing;

s108, determining a ratio integer of the length of the comb filtering sequence to the length of the unit period sequence, and obtaining a preset sequence length according to the ratio integer and the length of the unit period sequence, wherein the ratio integer is an odd number, and the preset sequence length is an odd number;

s109, obtaining a first forward sequence from the comb filtering sequence according to the preset sequence length and a preset starting point, and obtaining a first inverse pleat sequence according to the first forward sequence;

s110, obtaining a first positive phase according to the first forward sequence, and obtaining a first reverse phase according to the first reverse pleat sequence;

s111, obtaining a first average initial phase according to the first positive phase and the first negative phase;

s112, obtaining a phase comparison value according to the first average initial phase and a preset phase value, and obtaining a new initial point according to the phase comparison value, the preset initial point and the unit cycle sequence length;

s113, according to the preset sequence length and the new starting point, obtaining a second forward sequence from the comb filtering sequence, and according to the second forward sequence, obtaining a second inverse pleat sequence;

s114, obtaining a second positive phase according to the second positive sequence, and obtaining a second reverse phase according to the second reverse-folding sequence;

s115, obtaining a second average initial phase according to the second positive phase and the second negative phase;

s116, adding the second forward sequence and the second inverse pleat sequence to obtain a sum sequence, and obtaining a cosine function modulation sequence according to the sum sequence and a cosine function value of the second average initial phase;

s117, outputting from the center point of the cosine function modulation sequence to obtain a zero initial phase reference cosine function modulation sequence;

s118, multiplying the zero initial phase reference cosine function modulation sequence by a discrete cosine function of a reference frequency and a discrete sine function of the reference frequency respectively to obtain a real frequency mixing sequence and an imaginary frequency mixing sequence;

s119, respectively carrying out digital filtering on the real frequency mixing sequence and the virtual frequency mixing sequence to obtain a real frequency filtering sequence and a virtual frequency filtering sequence;

s120, integrating the real-frequency filtering sequence and the virtual-frequency filtering sequence respectively to obtain a real-frequency integral value and a virtual-frequency integral value;

and S121, obtaining the phase of the zero initial phase reference cosine function modulation sequence according to the real frequency integral value and the virtual frequency integral value, and obtaining the frequency of the electric power signal according to the phase.

The actual power signal is a sinusoidal signal mainly composed of fundamental wave components, and if not specifically stated, the power signal refers to the fundamental wave signal, and the power signal frequency refers to the fundamental wave frequency. For step S101, the power system frequency range is generally 45Hz (Hertz) -55Hz, so the lower limit f of the power signal frequency range_minMay be taken to be 45 Hz. Presetting integer signal period number C_2πCan be set according to actual needs, for example, C_2πTaken as 17. The preliminary sequence length may be calculated according to equation (1):

$N_{start}=\left(\mathrm{int}\right)\frac{C_{2\mathrm{\π}}f}{f_{min}}---\left(1\right)$

wherein N is_startIs the preliminary sequence length; (int) represents rounding; c_2πIs a preset integer signal period number; f. of_minThe lower limit of the frequency range of the power signal, in Hz; f is the preset sampling frequency in Hz.

For step S102, the power signal can be expressed by a cosine function signal of a single fundamental frequency, and then the initial sequence is formula (2):

wherein, X_start(n) is a preliminary sequence; a is the signal amplitude in v; omega_iIs the signal frequency, T is the sampling interval time, f is the preset sampling frequency, the unit Hz, n is the sequence discrete number,for the initial phase of the preliminary sequence, N_startIs the preliminary sequence length.

For step S103, a frequency preliminary measurement may be performed on the preliminary sequence by a zero-crossing method, a filtering-based algorithm, a wavelet transform algorithm, a neural network-based algorithm, a DFT transform-based frequency algorithm, or a phase difference-based frequency algorithm to obtain a preliminary frequency ω_o. In one embodiment, the reference frequency ω_s＝ω_o。

For step S104, in one embodiment, the length of the unit cycle sequence of the power signal is calculated as formula (3):

$N_{2\mathrm{\π}}=\left(\mathrm{int}\right)\frac{2\mathrm{\π}f}{{\mathrm{\ω}}_s}---\left(3\right)$

wherein N is_2πIs the length of the unit period sequence; (int) is an integer; f is a preset sampling frequency in Hz; omega_sIs the reference frequency. The unit period sequence length integer has an error within 1 sampling interval.

For step S105, the pre-processing sequence length is formula (4):

N_set＝C_2πN_2π(4)

wherein N is_setIs the length of the preprocessing sequence; c_2πIs a preset integer signal period number; n is a radical of_2πIs the unit period sequence length.

For step S106, in one embodiment, a pre-processing sequence is obtained, which is equation (5):

wherein, X_set(n) is a pretreatment sequence, X_start(N) is a preliminary sequence, N_setIs the length of the preprocessing sequence.

In the process of frequency mixing, the generated frequency mixing interference frequency seriously influences the calculation accuracy of sinusoidal parameters, and the factors generated by the frequency mixing interference frequency can be effectively inhibited from the source by comb filtering.

For step S107, 2 input sequences with different starting points are subtracted, so as to obtain a comb-shaped frequency-domain amplitude-frequency filtering characteristic, which is referred to as comb filtering processing for short. Defining the interval of 2 input sequences as the comb filter parameter, the single-stage comb filter process is expressed as equation (6):

$\begin{array}{c}{X}_L\left(n\right)=\frac{1}{2}{X}_{\mathrm{set}}\left(n\right)-\frac{1}{2}{X}_{\mathrm{set}}(N_L+n)\\ n=\mathrm{0,1,2,3},.......,N_{\mathrm{set}}-N_L-1\\ N_L=\left(\mathrm{int}\right)\left(0.5N_{2\mathrm{\π}}\right)\end{array}---\left(6\right)$

wherein, X_L(n) is a single stage comb filter output sequence; x_set(n) is a pre-treatment sequence; x_set(N_L+ N) is from N_LAn initial pre-treatment sequence; n is a radical of_L2 sequence interval or single stage comb filter parameters; n is a radical of_setIs the length of the preprocessing sequence; n is a radical of_2πIs the unit period sequence length. Comb filter parameter N_LTaking the value as the length N of the sequence of unit periods_2π0.5 times of the harmonic wave, even harmonic waves can be suppressed and sub harmonic waves can be attenuated.

In one embodiment, the pre-processing sequence may be comb filtered by a comb filter. Because the reference frequency has an error and the comb filtering parameters have integer errors, in order to improve the comb filtering effect, comb filtering processing can be performed through an 8-level comb filter, which is expressed as formula (7):

wherein, X_8L(n) is an 8-stage comb filter or comb filter sequence; filter [8, N ]_L,X_set(n)]Middle 8 represents a comb filter with 8, N_LFor single-stage comb filter parameters, X_set(n) is a pre-treatment sequence; k_L(ω_i) Processing at signal frequency omega for comb filtering_iThe dimensionless amplitude gain of (a), T is the sampling interval time;for comb filteringInitial phase of the sequence; n is a radical of_setIs the length of the preprocessing sequence.

The comb filtering process requires the use of a unit period sequence length N_2π4 times the length of the sequence. The amplitude-frequency characteristics of the comb filtering process in the frequency domain are shown in fig. 2.

For step S108, in one embodiment, the integer ratio is set to be an odd number, and the integer ratio of the comb-filtered sequence length to the unit period sequence length is determined as formula (8):

wherein k is an integer of the ratio, N_setFor pre-processing the sequence length, N_LAs a single-stage comb filter parameter, N_2πIs the unit period sequence length.

In one embodiment, the preset sequence length is set to be an odd number, and the preset sequence length is calculated as equation (9):

wherein N is a preset sequence length, k is the ratio integer, N_2πIs the unit period sequence length.

For step S109, in an embodiment, the preset starting point may be 0.5 times the length of the unit cycle sequence, and the first forward sequence is represented by equation (10):

wherein, X_8L(n) is an 8-stage comb filter sequence, X_+start(n) is a first forward sequence, P_startIn order to be a preset starting point,N_2πis the unit period sequence length, (int) is an integer, A is the signal amplitude, and the unit v, omega_iIs the signal frequency, K_L(ω_i) Processing at signal frequency omega for comb filtering_iT is the sampling interval time, n is the sequence discrete number,is the initial phase of the first forward sequence, and N is the preset sequence length.

In one embodiment, the first anti-pleat sequence is of formula (11):

$\begin{array}{c}{X}_{-\mathrm{start}}(-n)=X_{+\mathrm{start}}(N-n)=\mathrm{AK}\left({\mathrm{\ω}}_i\right)\cos (-{\mathrm{\ω}}_i\mathrm{Tn}+\mathrm{\β}1)\\ n=\mathrm{0,1,2,3},.....,N-1\end{array}---\left(11\right)$

wherein, X_-start(-n) is the first deconvolution sequence, X_+start(n) is the first forward sequence, A is the signal amplitude in v, ω_iFor signal frequency, T is the sampling interval time, N is the sequence discrete number, β 1 is the first unwrapped sequence initial phase, and N is the predetermined sequence length, the graphical representation of the comb filter sequence, the first forward sequence and the first unwrapped sequence is shown in FIG. 3.

For step S110, the calculation of the first positive phase and the first negative phase is based on the results of the quadrature mixing and integration calculation.

When the mixing interference frequency of the quadrature mixing is not considered, the quadrature mixing is expressed as equation (12), and the integral calculation is expressed as equation (13):

wherein R is_+start(n) is a first positive real-frequency mixing sequence, I_+start(n) is a first positive virtual audio mixing sequence, R_-start(-n) is the first inverse real mixing sequence, I_-start(-n) is the first inverse virtual mixing sequence, cos ([ omega ])_sTn) or cos (-omega)_sTn) is a discrete cosine function of the reference frequency sin (ω)_sTn) or sin (-omega)_sTn) is a discrete sine function of the reference frequency and omega is the signal frequency omega_iWith reference frequency omega_sFrequency ofThe difference, T is the sampling interval time, n is the sequence discrete number, K_L(ω_i) Processing at signal frequency omega for comb filtering_iIs used to obtain a non-dimensional amplitude gain of (c),the first forward sequence initial phase is β 1, and N is a predetermined sequence length.

Wherein R is_+startIs the first positive real-frequency integral value, unit dimensionless, I_+startIs the first positive imaginary frequency integral value, with dimensionless units, R_-startIs the first inverse real-frequency integral value, unit dimensionless, I_-startIs the first inverse virtual mixing integral value, the unit is dimensionless, omega is the signal frequency omega_iWith reference frequency omega_sT is the sampling interval time, N is the sequence discrete number, N is the preset sequence length,the first forward sequence initial phase, β 1 the first unwrapped sequence initial phase, and N the predetermined sequence length.

In one embodiment, the calculation of the first positive phase and the first negative phase is expressed by equation (14):

wherein the pH is_+startIs the first positive phase, PH_-startIs a first antiphase, R_+startIs the first positive real-frequency integral value, unit dimensionless, I_+startIs the first positive imaginary frequency integral value, with dimensionless units, R_-startIs the first inverse real-frequency integral value, unit dimensionless, I_-startIs firstInverse virtual-frequency mixing integral value with dimensionless unit and omega being signal frequency omega_iWith reference frequency omega_sT is the sampling interval time, N is the preset sequence length,the first forward sequence initial phase, β 1 is the first unwrapped sequence initial phase.

For step S111, in one embodiment, the first average initial phase calculation method, expressed as equation (15):

wherein the pH is_start-avgIs the first average initial phase, PH_+startIs the first positive phase, PH_-startIn order to be in a first opposite phase,the first forward sequence initial phase, β 1 is the first unwrapped sequence initial phase.

For step S112, in one embodiment, the preset phase value may be ± pi/4; the step of obtaining a phase comparison value according to the first average initial phase and the preset phase value may include:

if the first average initial phase is greater than or equal to 0 and less than or equal to pi/2, subtracting the first average initial phase according to pi/4 to obtain a phase comparison value;

and if the first average initial phase is greater than or equal to-pi/2 and less than or equal to 0, subtracting the first average initial phase according to-pi/4 to obtain a phase comparison value.

In particular formula (16):

${\mathrm{\ΔPH}}_{com}=\left\{\begin{array}{cc}\frac{\mathrm{\π}}{4}-{\mathrm{PH}}_{start-avg}& 0\≤{\mathrm{PH}}_{start-avg}\≤\frac{\mathrm{\π}}{2}\\ -\frac{\mathrm{\π}}{4}-{\mathrm{PH}}_{start-avg}& -\frac{\mathrm{\π}}{2}\≤{\mathrm{PH}}_{start-avg}\≤0\\ 0& {\mathrm{PH}}_{start-avg}=\±\frac{\mathrm{\π}}{2}\end{array}\right.---\left(16\right)$

wherein, △ PH_comIs the phase comparison value, in units of rad, PH_start-avgIs the first average initial phase.

In one embodiment, the new starting point is calculated as equation (17):

$P_{new}=P_{start}+\left(\mathrm{int}\right)\left(\frac{{\mathrm{\ΔPH}}_{com}}{2\mathrm{\π}}{N}_{2\mathrm{\π}}\right)---\left(17\right)$

wherein, P_newAs a new starting point, in dimensionless units, P_start△ PH as a predetermined starting point_comFor phase comparison, in units rad, N_2πIs the length of the unit period sequence, and (int) is an integer.

For step S113, the second forward sequence and the second reverse-pleated sequence are equation (18):

wherein, X_8L(n) is an 8-stage comb filter sequence, X_+end(n) is a second forward sequence, X_-end(-n) is the second deconvolution sequence, P_newAs a new starting point, unit dimensionless, K_L(ω_i) Processing at signal frequency omega for comb filtering_iIs used to obtain a non-dimensional amplitude gain of (c),for the initial phase of the second forward sequence, β 2 isInitial phase, ω, of the second unwrapped sequence_iIs the signal frequency, T is the sampling interval time, N is the sequence discrete number, and N is the preset sequence length.

As for step S114, the calculation method of the second positive phase and the second negative phase is based on the results of the quadrature mixing and digital filtering calculation. The digital filtering consists of a 6-stage rectangular window arithmetic mean filter of 2 filtering parameters.

When the mixing interference frequency of the quadrature mixing is not considered, the quadrature mixing is expressed as equation (19), and the filtering calculation of the 6-level rectangular window arithmetic mean filter of the 2 filtering parameters is expressed as equation (20):

wherein R is_+end(n) is a second positive real-frequency mixing sequence, I_+end(n) is a second positive virtual audio mixing sequence, R_-end(-n) is the second inverse real mixing sequence, I_-end(-n) is the second inverse virtual mixing sequence, cos ([ omega ])_sTn) or cos (-omega)_sTn) is a discrete cosine function of the reference frequency sin (ω)_sTn) or sin (-omega)_sTn) is a discrete sine function of the reference frequency, K_L(ω_i) Processing at signal frequency omega for comb filtering_iIs the signal frequency omega_iWith reference frequency omega_sFrequency difference of (a) ([ omega ])_iIs the signal frequency, T is the sampling interval time, n is the sequence discrete number,the first forward sequence initial phase, β 1 the first unwrapped sequence initial phase, and N the predetermined sequence length.

Wherein,R_+endthe second positive real frequency digital filtering final value is a unit dimensionless; i is_+endThe unit is a second positive virtual frequency digital filtering final value and is dimensionless; r_-endThe second inverse digital filtering final value is a unit dimensionless; i is_-endThe second inverse virtual frequency digital filtering final value is a unit dimensionless; k_L(ω_i) Processing at signal frequency omega for comb filtering_iIs the signal frequency omega_iWith reference frequency omega_sThe frequency difference of (2); k (omega) is the amplitude gain of the digital filtering at the frequency difference omega, and the unit is dimensionless; t is sampling interval time;is the second forward sequence initial phase, β 2 is the second inverse pleat sequence initial phase, N_D1For filtering parameter 1, i.e. for N_D1Adding the continuous discrete values, and then taking the arithmetic mean value of the continuous discrete values as the current filtering value to be output; n is a radical of_D2For filter parameter 2, i.e. for N_D2Adding the continuous discrete values, and then taking the arithmetic mean value of the continuous discrete values as the current filtering value to be output; n is a radical of_DThe sequence length is used for digital filtering, the number of the sequence length is the sum of filtering parameters of a 6-stage rectangular window arithmetic mean filter, and the sequence length is less than or equal to a preset sequence length N.

In one embodiment, the filter parameter N_D1The value is 1.5 times of the length of the unit period sequence of the reference frequency, so that the frequency mixing interference frequency generated by 1/3 subharmonic waves is deeply inhibited; filter parameter N_D2The value is 2 times of the length of the unit period sequence of the reference frequency, so that the frequency mixing interference frequency generated by direct current, 1/2 frequency division, subharmonic and the like is deeply inhibited. The 6-stage rectangular window arithmetic mean filter filtering calculation of 2 filtering parameters needs to use 10.5 times of the length of the signal period sequence.

Filter parameter N_D1And a filter parameter N_D2Calculated as formula (21):

$\begin{array}{c}{N}_{D1}=\left(\mathrm{int}\right)\left(1.5N_{2\mathrm{\π}}\right)\\ N_{D2}=2N_{2\mathrm{\π}}\end{array}---\left(21\right)$

wherein N is_D1Is a digital filtering parameter 1, the unit is dimensionless, (int) is an integer, N_D2For the digital filter parameter 2, unit dimensionless, N_2πIs the unit period sequence length.

In one embodiment, the calculation method of the second positive phase and the second negative phase is expressed by formula (22):

wherein the pH is_+endIs the second positive phase, PH_-endIs a second opposite phase, R_+endIs the second positive real frequency integral value, unitDimensionless, I_+endIs the second positive imaginary frequency integral value, with dimensionless units, R_-endIs the second inverse real-frequency integral value, unit dimensionless, I_-endIs the second inverse virtual mixing integral value, the unit is dimensionless, omega is the signal frequency omega_iWith reference frequency omega_sFrequency difference of (1), T is sampling interval time, N_DThe sequence length is used for the digital filtering,the second forward sequence initial phase, and β 2 the second unwrapped sequence initial phase.

For step S115, the second average initial phase calculation method, expressed as equation (23):

wherein the pH is_end-avgIs the second average initial phase, PH_+endIs the second positive phase, PH_-endIn order to be in the second opposite phase,the second forward sequence initial phase β 2 is the second forward sequence initial phase.

For step S116, the cosine function modulation sequence is expressed as equation (24):

wherein, X_cos(n) is a cosine function modulation sequence; AK (alkyl ketene dimer)_L(ω_i) Modulating the sequence amplitude for a cosine function in unit v;modulating the initial phase, K, of the sequence for the cosine function_L(ω_i) Is in the shape of a combThe filtering process being at the signal frequency omega_iOf dimensionless amplitude gain, omega_iIs the signal frequency, T is the sampling interval time, N is the sequence discrete number, N is the preset sequence length,the second forward sequence initial phase, and β 2 the second unwrapped sequence initial phase.

For step S117, in one embodiment, a zero initial phase reference cosine function modulation sequence is obtained, expressed as equation (25):

$\begin{array}{c}{X0}_{\cos }\left(n\right)=X_{\cos }(\frac{N-1}{2}+n)={\mathrm{AK}}_L\left({\mathrm{\ω}}_i\right)\cos \left({\mathrm{\ω}}_i{T}_{n}n\right)\\ n=\mathrm{0,1,2,3},.....,\frac{N-1}{2}-1\end{array}---\left(25\right)$

wherein, X0_cos(n) is zero initial phase reference cosine function modulation sequence, AK_L(ω_i) Modulating the amplitude of the sequence by cosine function in v, omega_iIs the signal frequency, K_L(ω_i) Processing at signal frequency omega for comb filtering_iT is the sampling interval time, N is the sequence discrete number, and N is the preset sequence length. The zero initial phase reference point graphical representation is shown in fig. 4.

For step S118, in one embodiment, real and imaginary mixed sequences are obtained, expressed as equation (26):

$\begin{array}{c}R\left(n\right)=X{O}_{\cos }\left(n\right)\cos \left({\mathrm{\ω}}_s\mathrm{Tn}\right)=U\cos \left(\mathrm{\ΩTn}\right)+U\cos \left[\right({\mathrm{\ω}}_i+{\mathrm{\ω}}_s\left)\mathrm{Tn}\right]\\ I\left(n\right)=X{O}_{\cos }\left(n\right)\sin \left({\mathrm{\ω}}_s\mathrm{Tn}\right)=-U\sin \left(\mathrm{\ΩTn}\right)+U\sin \left[\right({\mathrm{\ω}}_i+{\mathrm{\ω}}_s\left)\mathrm{Tn}\right]\\ U=\frac{{\mathrm{AK}}_L\left({\mathrm{\ω}}_i\right)}{2}\\ \mathrm{\Ω}={\mathrm{\ω}}_i-{\mathrm{\ω}}_s\\ n=\mathrm{0,1,2},.....,\frac{N-1}{2}-1\\ \left(26\right)\end{array}$

wherein R (n) is a real-frequency mixing sequence, I (n) is an imaginary-frequency mixing sequence, X0_cos(n) is zero initial phase reference cosine function modulation sequence, cos (omega)_sTn) is a discrete cosine function of the reference frequency sin (ω)_sTn) is a discrete sine function of the reference frequency, U is the common amplitude, and the unit v, omega is the signal frequency omega_iWith reference frequency omega_sT is the sampling interval time, N is the sequence discrete number, and 0.5(N-1) is the mixing sequence length. Wherein the frequency difference omega part is useful component, frequency (omega)_i+ω_s) In part, the mixing interference component.

For step S119, a filtering order of digital filtering is set, and in one embodiment, the real-frequency mixing sequence and the virtual-frequency mixing sequence may be digitally filtered by a rectangular window arithmetic mean filtering algorithm, respectively.

In one embodiment, the number of filtering stages of the digital filtering can be set to 5, and the digital filtering parameter is 1 time of the length of the unit period sequence, so as to carry out deep suppression on the subharmonic mixing interference frequency. Regardless of the mixing interference frequency, the expressions of the real-frequency filtering sequence and the imaginary-frequency filtering sequence are expressed as equation (27):

$\begin{array}{c}{R}_D\left(n\right)=\frac{1}{N_D}\underset{n}{\overset{N_D-1}{\Σ}}\frac{1}{N_D}\underset{n}{\overset{N_D-1}{\Σ}}\frac{1}{N_D}\underset{n}{\overset{N_{D1}-1}{\Σ}}\frac{1}{N_D}\underset{n}{\overset{N_D-1}{\Σ}}\frac{1}{N_D}\underset{n}{\overset{N_D-1}{\Σ}}R\left(n\right)\\ ={\mathrm{UK}}_D\left(\mathrm{\Ω}\right)\cos (\mathrm{\Ω}Tn+\mathrm{\α}(\mathrm{\Ω}\left)\right)\end{array}$

wherein R is_D(n) is a real frequency filtering sequence; i is_D(n) is an imaginary frequency filter sequence; r (n) is a real frequency mixing sequence; i (n) is a virtual frequency mixing sequence; u is a public amplitude and a unit v; n is a radical of_DAs filter parameters of rectangular-windowed arithmetic mean filter algorithms, i.e. for N_DAdding the continuous discrete values, and then taking the arithmetic mean value of the continuous discrete values as the current filtering value to be output; t is sampling interval time; n is a radical of_2πIs the length of the unit period sequence; k_DThe unit is dimensionless, the amplitude gain of the digital filtering at the frequency difference omega is α omega is the phase shift of the digital filtering at the frequency difference omega, M is the length of the output sequence of the digital filtering, 0.5N-1 is the length of the input sequence of the digital filtering, and N is the length of the preset sequence.

For step S120, in one embodiment, the length of the digital filtering output sequence is an integration length, and a real-frequency integration value and an imaginary-frequency integration value are obtained, which are expressed by equation (28):

$\begin{array}{c}{R}_D=\frac{1}{M}\underset{n}{\overset{M-1}{\mathrm{\Σ}}}{R}_D\left(n\right)=U\left[\frac{2\sin \left(\frac{\mathrm{\ΩT}{N}_D}{2}\right)}{\mathrm{\ΩT}{N}_D}{]}^5\right[\frac{2\sin \left(\frac{\mathrm{\ΩTM}}{2}\right)}{\mathrm{\ΩTM}}\left]\cos \right[\frac{\mathrm{\ΩT}({5N}_D+M)}{2}]\\ I_D=\frac{1}{M}\underset{n}{\overset{M-1}{\mathrm{\Σ}}}{I}_D\left(n\right)=-U\left[\frac{2\sin \left(\frac{\mathrm{\ΩT}{N}_D}{2}\right)}{\mathrm{\ΩT}{N}_D}{]}^5\right[\frac{2\sin \left(\frac{\mathrm{\ΩTM}}{2}\right)}{\mathrm{\ΩTM}}\left]\sin \right[\frac{\mathrm{\ΩT}(5N_D+M)}{2}]\\ M=\frac{N-1}{2}-5N_D\\ n=\mathrm{0,1,2,3},....,M-1---\left(28\right)\end{array}$

wherein R is_DIs the real frequency integral value; i is_DIs the virtual frequency integral value; r_D(n) is a real frequency filtering sequence; i is_D(n) is an imaginary frequency filter sequence; t is sampling interval time, and M is integration length; n is a radical of_DFiltering parameters of a rectangular window arithmetic mean filtering algorithm; 0.5(N-1) is the digital filtering input sequence length; and N is a preset sequence length.

For step S121, in one embodiment, the phase of the zero initial phase reference cosine function modulation sequence is obtained, expressed as equation (29):

$PH=-\arctan \left(\frac{I_D}{R_D}\right)=\frac{\mathrm{\Ω}T(5N_D+M)}{2}---\left(29\right)$

wherein PH is the phase of the zero initial phase reference cosine function modulation sequence, I_DIs a virtual frequency integral value, R_DThe value is the real frequency integral value, and M is the integral length; n is a radical of_DIs the filter parameter of the rectangular window arithmetic mean filter algorithm.

In one embodiment, the power signal frequency is obtained according to the phase of the zero initial phase reference cosine function modulation sequence, and is expressed by equation (30):

${\mathrm{\ω}}_i=\frac{2PH}{T(5N_D+M)}+{\mathrm{\ω}}_s---\left(30\right)$

wherein, ω is_iFor the frequency of the power signal, PH is the phase of the zero initial phase reference cosine function modulation sequence, T is the sampling interval time, M is the integration length, N is the integral length_DFilter parameter, omega, for a rectangular window arithmetic mean filter algorithm_sIs the reference frequency.

Based on the same inventive concept, the invention also provides a system for measuring frequency according to the zero initial phase reference cosine function sequence, and the following describes the specific implementation mode of the system in detail with reference to the attached drawings.

As shown in fig. 5, a system for performing frequency measurement according to a zero initial phase reference cosine function sequence includes:

a preliminary sequence length determining module 101, configured to obtain a preliminary sequence length according to a lower limit of a power signal frequency range, a preset sampling frequency, and a preset integer signal cycle number;

a preliminary sequence obtaining module 102, configured to sample an electric power signal according to the length of the preliminary sequence, so as to obtain a preliminary sequence of the electric power signal;

a reference frequency determining module 103, configured to perform frequency initial measurement on the preliminary sequence to obtain a preliminary frequency of the power signal, and obtain a reference frequency according to the preliminary frequency;

a unit cycle sequence length determining module 104, configured to obtain a unit cycle sequence length of the power signal according to the preset sampling frequency and the reference frequency;

a preprocessing sequence length determining module 105, configured to multiply the preset integer signal cycle number and the unit cycle sequence length to obtain a preprocessing sequence length;

a preprocessing sequence obtaining module 106, configured to obtain a preprocessing sequence from the preliminary sequence of the power signal according to the length of the preprocessing sequence;

a comb filtering sequence determining module 107, configured to perform comb filtering processing on the pre-processing sequence to obtain a comb filtering sequence, where the length of the comb filtering sequence is a remaining length of the pre-processing sequence after the comb filtering processing;

a preset sequence length determining module 108, configured to determine a ratio integer between the comb filtering sequence length and the unit period sequence length, and obtain a preset sequence length according to the ratio integer and the unit period sequence length, where the ratio integer is an odd number, and the preset sequence length is an odd number;

a first sequence obtaining module 109, configured to obtain a first forward sequence from the comb filtering sequence according to the preset sequence length and a preset starting point, and obtain a first anti-aliasing sequence according to the first forward sequence;

a first positive and negative phase determining module 110, configured to obtain a first positive phase according to the first forward sequence and obtain a first negative phase according to the first anti-aliasing sequence;

a first average initial phase determining module 111, configured to obtain a first average initial phase according to the first positive phase and the first negative phase;

a new starting point determining module 112, configured to obtain a phase comparison value according to the first average initial phase and a preset phase value, and obtain a new starting point according to the phase comparison value, the preset starting point, and the unit cycle sequence length;

a second sequence obtaining module 113, configured to obtain a second forward sequence from the comb filtering sequence according to the preset sequence length and the new starting point, and obtain a second inverse-folding sequence according to the second forward sequence;

a second positive and negative phase determination module 114, configured to obtain a second positive phase according to the second forward sequence and a second inverse phase according to the second inverse-folding sequence;

a second average initial phase determining module 115, configured to obtain a second average initial phase according to the second positive phase and the second negative phase;

a cosine function modulation sequence determining module 116, configured to add the second forward sequence and the second inverse-pleated sequence to obtain a sum sequence, and obtain a cosine function modulation sequence according to the sum sequence and a cosine function value of the second average initial phase;

a zero initial phase modulation sequence obtaining module 117, configured to output from the cosine function modulation sequence center point to obtain a zero initial phase reference cosine function modulation sequence;

a mixing sequence determining module 118, configured to multiply the zero initial phase reference cosine function modulation sequence by a discrete cosine function of a reference frequency and a discrete sine function of the reference frequency, respectively, to obtain a real-frequency mixing sequence and an imaginary-frequency mixing sequence;

a filtering sequence determining module 119, configured to perform digital filtering on the real-frequency mixing sequence and the virtual-frequency mixing sequence, respectively, to obtain a real-frequency filtering sequence and a virtual-frequency filtering sequence;

an integral value determining module 120, configured to integrate the real-frequency filtering sequence and the virtual-frequency filtering sequence, respectively, to obtain a real-frequency integral value and a virtual-frequency integral value;

and the power signal frequency determining module 121 is configured to obtain a phase of the zero initial phase reference cosine function modulation sequence according to the real frequency integral value and the virtual frequency integral value, and obtain a frequency of the power signal according to the phase.

In one embodiment, the mixing sequence determination module 118 may determine the mixing sequence according to the expression r (n) ═ X0_cos(n)cos(ω_sTn) obtaining a real frequency mixing sequence R (n), wherein X0_cos(n) is zero initial phase reference cosine function modulation sequence, cos (omega)_sTn) is a discrete cosine function of the reference frequency, ω_sFor reference frequency, T is the sampling interval time, n is the sequence discrete number,

the mixing sequence determination module 118 may determine the mixing sequence according to the expression i (n) ═ X0_cos(n)sin(ω_sTn) obtaining a virtual-frequency mixing sequence I (n), wherein X0_cos(n) is a zero initial phase reference cosine function modulation sequence, sin (ω)_sTn) is a discrete sine function of the reference frequency, ω_sFor reference frequency, T is the sampling interval time, n is the sequence discrete number, $n=0,1,2,\mathrm{.....},\frac{N-1}{2}-1.$

in one embodiment, the filtering sequence determination module 119 may perform digital filtering on the real and virtual mixing sequences respectively through a rectangular window arithmetic mean filtering algorithm.

In one embodiment, the power signal frequency determination module 121 may be according to the expressionObtaining the phase PH of the zero initial phase reference cosine function modulation sequence, wherein R_DAs a real-frequency integral value, I_DIs the virtual frequency integral value.

In one embodiment, the power signal frequency determination module 121 may be according to the expressionObtaining a frequency omega of an electrical power signal_iPH is the phase of the zero initial phase reference cosine function modulation sequence, T is the sampling interval time, M is the integral length, N is_DFilter parameter, omega, for a rectangular window arithmetic mean filter algorithm_sIs the reference frequency.

Other technical features of the system of the present invention are the same as those of the method of the present invention, and are not described herein again.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A method for measuring frequency according to zero initial phase reference cosine function sequence is characterized by comprising the following steps:

obtaining a preliminary sequence length according to the lower limit of the power signal frequency range, a preset sampling frequency and a preset integer signal period number;

sampling the power signal according to the length of the preliminary sequence to obtain a preliminary sequence of the power signal;

carrying out frequency initial measurement on the initial sequence to obtain an initial frequency of the power signal, and obtaining a reference frequency according to the initial frequency;

obtaining the unit cycle sequence length of the power signal according to the preset sampling frequency and the reference frequency;

multiplying the preset integer signal period number and the unit period sequence length to obtain a preprocessing sequence length;

acquiring a preprocessing sequence from the preliminary sequence of the power signal according to the length of the preprocessing sequence;

performing comb filtering processing on the preprocessing sequence to obtain a comb filtering sequence, wherein the length of the comb filtering sequence is the residual length of the preprocessing sequence after the comb filtering processing;

determining a ratio integer of the length of the comb filtering sequence to the length of the unit period sequence, and obtaining a preset sequence length according to the ratio integer and the length of the unit period sequence, wherein the ratio integer is an odd number, and the preset sequence length is an odd number;

obtaining a first forward sequence from the comb filtering sequence according to the preset sequence length and a preset starting point, and obtaining a first inverse pleat sequence according to the first forward sequence;

obtaining a first positive phase from the first forward sequence and a first anti-phase from the first anti-aliasing sequence;

obtaining a first average initial phase according to the first positive phase and the first negative phase;

obtaining a phase comparison value according to the first average initial phase and a preset phase value, and obtaining a new initial point according to the phase comparison value, the preset initial point and the unit cycle sequence length;

obtaining a second forward sequence from the comb filtering sequence according to the preset sequence length and the new starting point, and obtaining a second inverse pleat sequence according to the second forward sequence;

obtaining a second positive phase from the second forward sequence and a second anti-phase from the second anti-aliased sequence;

obtaining a second average initial phase according to the second positive phase and the second negative phase;

adding the second forward sequence and the second inverse pleat sequence to obtain a sum sequence, and obtaining a cosine function modulation sequence according to the sum sequence and a cosine function value of the second average initial phase;

outputting from the central point of the cosine function modulation sequence to obtain a zero initial phase reference cosine function modulation sequence;

multiplying the zero initial phase reference cosine function modulation sequence by a discrete cosine function of a reference frequency and a discrete sine function of the reference frequency respectively to obtain a real frequency mixing sequence and an imaginary frequency mixing sequence;

respectively carrying out digital filtering on the real frequency mixing sequence and the virtual frequency mixing sequence to obtain a real frequency filtering sequence and a virtual frequency filtering sequence;

respectively integrating the real-frequency filtering sequence and the virtual-frequency filtering sequence to obtain a real-frequency integral value and a virtual-frequency integral value;

and obtaining the phase of the zero initial phase reference cosine function modulation sequence according to the real frequency integral value and the virtual frequency integral value, and obtaining the frequency of the electric power signal according to the phase.

2. The method of claim 1, wherein the frequency measurement is performed according to an expression in accordance with the zero initial phase reference cosine function sequenceObtaining the phase PH of the zero initial phase reference cosine function modulation sequence, wherein R_DAs a real-frequency integral value, I_DIs the virtual frequency integral value.

3. The method of claim 1, wherein the real and imaginary audio mixing sequences are digitally filtered by a rectangular window arithmetic mean filtering algorithm.

4. According to claimThe method of claim 3, wherein the frequency measurement is performed according to an expressionObtaining a frequency omega of an electrical power signal_iPH is the phase of the zero initial phase reference cosine function modulation sequence, T is the sampling interval time, M is the integral length, N is_DFilter parameter, omega, for a rectangular window arithmetic mean filter algorithm_sIs the reference frequency.

5. The method according to any one of claims 1 to 4, wherein the frequency measurement is performed according to a zero initial phase reference cosine function sequence:

according to the expression R (n) ═ X0_cos(n)cos(ω_sTn) obtaining a real frequency mixing sequence R (n), wherein X0_cos(n) is zero initial phase reference cosine function modulation sequence, cos (omega)_sTn) is a discrete cosine function of the reference frequency, ω_sFor reference frequency, T is the sampling interval time, n is the sequence discrete number,

according to the expression I (n) ═ X0_cos(n)sin(ω_sTn) obtaining a virtual-frequency mixing sequence I (n), wherein X0_cos(n) is a zero initial phase reference cosine function modulation sequence, sin (ω)_sTn) is a discrete sine function of the reference frequency, ω_sFor reference frequency, T is the sampling interval time, n is the sequence discrete number,

6. a system for performing frequency measurement based on a zero initial phase reference cosine function sequence, comprising:

the preliminary sequence length determining module is used for obtaining a preliminary sequence length according to the lower limit of the power signal frequency range, a preset sampling frequency and a preset integer signal period number;

the preliminary sequence acquisition module is used for sampling the electric power signal according to the length of the preliminary sequence to obtain a preliminary sequence of the electric power signal;

a reference frequency determining module, configured to perform frequency initial measurement on the preliminary sequence to obtain a preliminary frequency of the power signal, and obtain a reference frequency according to the preliminary frequency;

a unit cycle sequence length determining module, configured to obtain a unit cycle sequence length of the power signal according to the preset sampling frequency and the reference frequency;

the preprocessing sequence length determining module is used for multiplying the preset integer signal period number and the unit period sequence length to obtain a preprocessing sequence length;

the preprocessing sequence acquisition module is used for acquiring a preprocessing sequence from the preliminary sequence of the power signal according to the length of the preprocessing sequence;

the comb filtering sequence determining module is used for carrying out comb filtering processing on the preprocessing sequence to obtain a comb filtering sequence, wherein the length of the comb filtering sequence is the residual length of the preprocessing sequence after the comb filtering processing;

a preset sequence length determining module, configured to determine a ratio integer between the comb filtering sequence length and the unit period sequence length, and obtain a preset sequence length according to the ratio integer and the unit period sequence length, where the ratio integer is an odd number, and the preset sequence length is an odd number;

a first sequence obtaining module, configured to obtain a first forward sequence from the comb filtering sequence according to the preset sequence length and a preset starting point, and obtain a first anti-aliasing sequence according to the first forward sequence;

a first positive and negative phase determination module for obtaining a first positive phase from the first forward sequence and a first negative phase from the first deconvolution sequence;

a first average initial phase determining module, configured to obtain a first average initial phase according to the first positive phase and the first negative phase;

a new starting point determining module, configured to obtain a phase comparison value according to the first average initial phase and a preset phase value, and obtain a new starting point according to the phase comparison value, the preset starting point, and the unit cycle sequence length;

a second sequence obtaining module, configured to obtain a second forward sequence from the comb filtering sequence according to the preset sequence length and the new starting point, and obtain a second inverse-folding sequence according to the second forward sequence;

a second forward-reverse phase determination module, configured to obtain a second positive phase according to the second forward sequence and obtain a second reverse phase according to the second deconvolution sequence;

a second average initial phase determining module, configured to obtain a second average initial phase according to the second positive phase and the second negative phase;

a cosine function modulation sequence determining module, configured to add the second forward sequence and the second inverse-pleated sequence to obtain a sum sequence, and obtain a cosine function modulation sequence according to the sum sequence and a cosine function value of the second average initial phase;

the zero initial phase modulation sequence acquisition module is used for outputting from the center point of the cosine function modulation sequence to acquire a zero initial phase reference cosine function modulation sequence;

a mixing sequence determining module, configured to multiply the zero initial phase reference cosine function modulation sequence by a discrete cosine function of a reference frequency and a discrete sine function of the reference frequency, respectively, to obtain a real-frequency mixing sequence and an imaginary-frequency mixing sequence;

a filtering sequence determining module, configured to perform digital filtering on the real-frequency mixing sequence and the virtual-frequency mixing sequence, respectively, to obtain a real-frequency filtering sequence and a virtual-frequency filtering sequence;

an integral value determining module, configured to integrate the real-frequency filtering sequence and the virtual-frequency filtering sequence, respectively, to obtain a real-frequency integral value and a virtual-frequency integral value;

and the power signal frequency determining module is used for obtaining the phase of the zero initial phase reference cosine function modulation sequence according to the real frequency integral value and the virtual frequency integral value and obtaining the frequency of the power signal according to the phase.

7. The system of claim 6, wherein the power signal frequency determination module is based on an expressionObtaining the phase PH of the zero initial phase reference cosine function modulation sequence, wherein R_DAs a real-frequency integral value, I_DIs the virtual frequency integral value.

8. The system of claim 6, wherein the filter sequence determination module digitally filters the real and imaginary audio mixing sequences using a rectangular window arithmetic mean filter algorithm.

9. The system of claim 8, wherein the power signal frequency determination module is based on an expressionObtaining a frequency omega of an electrical power signal_iPH is the phase of the zero initial phase reference cosine function modulation sequence, T is the sampling interval time, M is the integral length, N is_DFilter parameter, omega, for a rectangular window arithmetic mean filter algorithm_sIs the reference frequency.

10. The system according to any one of claims 6 to 9, wherein:

the mixing sequence determining module is based onThe expression r (n) ═ X0_cos(n)cos(ω_sTn) obtaining a real frequency mixing sequence R (n), wherein X0_cos(n) is zero initial phase reference cosine function modulation sequence, cos (omega)_sTn) is a discrete cosine function of the reference frequency, ω_sFor reference frequency, T is the sampling interval time, n is the sequence discrete number, $n=0,1,2,\mathrm{.....},\frac{N-1}{2}-1;$

the mixing sequence determination module is according to expression i (n) ═ X0_cos(n)sin(ω_sTn) obtaining a virtual-frequency mixing sequence I (n), wherein X0_cos(n) is a zero initial phase reference cosine function modulation sequence, sin (ω)_sTn) is a discrete sine function of the reference frequency, ω_sFor reference frequency, T is the sampling interval time, n is the sequence discrete number, $n=0,1,2,\mathrm{.....},\frac{N-1}{2}-1.$