CN102135567A - Real-time frequency tracking and harmonic measuring method for AC sampling of power system - Google Patents

Abstract

The invention discloses a real-time frequency tracking and harmonic measuring method for the AC sampling of a power system, which is characterized by comprising the steps: an AC sampling input is made to enter an analog-to-digital converter at a fixed sampling rate; the analog-to-digital converter at the fixed sampling rate respectively outputs a first segment of digital signals with the length of N points and a second segment of digital signals with the length of N points to enter a first fast Fourier module; the first fast Fourier module outputs phase angles of the highest frequency components of the first segment of digital signals with the length of N points and the second segment of digital signals with the length of N points, and sends the phase angles into a phase discriminator one after another; the phase discriminator outputs a correction frequency, and sends the correction frequency into a digital signal reconstruction filter; the digital signal reconstruction filter performs digital reconstruction sampling on the first segment of digital output signals with the length of N points, of the analog-to-digital converter at the fixed sampling rate, according to the correction frequency, and sends an obtained N-point reconstruction sampling signal into a second fast Fourier module; the phase angle output of the highest frequency component of the second fast Fourier module is sent into the phase discriminator; the third segment of digital signals with the length of N points, of the analog-to-digital converter, enter the first fast Fourier module; and the phase discriminator judges the phase angle based on accuracy requirements, and outputs a correction frequency to a digital signal reconstruction filter. After the iterations of the process reach M, the output of the second fast Fourier module is the values of respective subharmonic components of the AC sampling signal, and the output frequency of the phase discriminator is the frequency of the AC sampling signal.

Description

A kind of electric power system alternating current sampling real-time frequency is followed the tracks of and harmonic measuring method

Technical field

The invention belongs to AC sampling and measure applied technical field, relate more specifically to electric system industrial frequency AC sampled measurements real-time frequency and follow the tracks of and the harmonic measure technology.

Background technology

Fast development along with electric system, the power network capacity constantly increases, structure is increasingly sophisticated, it is very important that the robotization of monitoring in real time in the electric system, dispatching just seems, and digital collection is the important step that realizes robotization, especially how the electric weight of the simulation of each in the acquisition system accurately and rapidly is the focus that work about electric power person pays close attention to always.According to the difference of sampled signal, can be divided into direct current sampling and AC sampling 2 big classes.The direct current sampling is the DC voltage that alternating voltage, current signal is converted into 0～5V, and the major advantage of this method is that algorithm is simple, is convenient to filtering, but invest bigger, safeguard complexity, can't realize the live signal collection, thereby be restricted in application on power system.AC sampling be of ac is converted into ± 5V (or gather, and major advantage is that real-time is good, and phase distortion is little, small investment, is convenient to safeguard by 0～5V) alternating voltage; Its shortcoming is the algorithm complexity, and precision is difficult to improve, and the A/D slewing rate is had relatively high expectations.Along with the development of microcomputer technology, AC sampling has the trend that progressively replaces the direct current sampling with its excellent ratio of performance to price.

Summary of the invention

The objective of the invention is the A/D slewing rate to be had relatively high expectations for the data acquisition that overcomes electric power power frequency component ac electric, precision is difficult to the shortcoming of conventional AC Sampling techniques such as improving, and a kind of real-time frequency-tracking and high-precision AC quantity measuring method fast is provided.

A kind of electric power system alternating current sampling real-time frequency of the present invention is followed the tracks of and harmonic measuring method is achieved by the following technical solution, and the described real-time synchronous AC method of sampling comprises that step is as follows:

1, gets AC sampling input 1 and enter fixed sample rate analog to digital converter 2.

2, fixed sample rate analog to digital converter 2 is exported the digital signal of first section N point length respectively, second section N point length digital signal enters the first fast Fourier module (FFT) 3, the digital signal of first section N point length of the first fast Fourier module (FFT), 3 outputs, the highest frequency component phase angle 8 of second section N point length digital signal are successively sent into phase detector 4, and phase detector 4 output calibration frequencies 10 are sent into digital signal reconfigurable filter 5.

3, digital signal reconfigurable filter 5 carries out the digital reconstruction sampling according to the digital output signal 12 of first section N point length of proofreading and correct 10 pairs of fixed sample rate analog to digital converters 2 of back frequency, and the N point reconstructed sample signal that obtains is sent into the second fast Fourier module 6.

4, phase detector 4 is sent in the highest frequency component phase angle of the second fast Fourier module 6 output 9, the digital signal of the 3rd section N point of analog to digital converter 2 length enters the first fast Fourier module 3, and output calibration frequency 10 was sent into digital signal reconfigurable filter 5 after phase detector 4 was judged according to accuracy requirement.

5, repeating step 2,3 and 4, reach predetermined iterations M after, 6 outputs 7 of the second fast Fourier module are the each harmonic component value of ac sampling signal, phase detector 4 output frequencies 10 are the frequency of ac sampling signal.

Description of drawings

Fig. 1 is a structural representation of the present invention.

Fig. 2 is a practical measuring examples that contains harmonic noise AC sampling input signal of the present invention.

Embodiment

Fig. 1 is the inventive method structural representation.The AC sampling input 1 of stable state electrical network is expressed as x (t), and its work frequency is expressed as f ₀Because harmonic interference and other factors disturb the frequency departure that is caused to make the frequency of power network signal fluctuation occur, analog to digital converter 1 is with fixed sample rate f ₀N times of speed the one-period signal of signal x (t) is sampled, digital length is the N point.Sampled signal is expressed as x _i(nT _s), n=0 wherein, 1,2, L N-1 is an integer, T _sBe sampling time interval.

Simulation power network signal x (t) is sampled, and getting two segment length on time shaft respectively all is that the numeral that N is ordered obtains x _m(n) and x _n(n), n=0,1,2, L N-1.Then with x _m(n) and x _n(n) send into first Fast Fourier Transform (FFT) (FFT) module 3, be output as X respectively _m(k) and X _n(k), k=0,1,2, L, N-1

M highest frequency component constantly is expressed as X _m(k), k is expressed as the frequency component of input signal.The initial phase that obtains the high frequency components of m moment N point input signal from fast Fourier transform module (FFT) output is:

${\mathrm{\θ}}_m\left(k\right)={\tan }^{-1}\left\{\frac{\mathrm{Im}\left[X_m\left(k\right)\right]}{\mathrm{Re}\left[X_m\left(k\right)\right]}\right\}---(1-1)$

In the formula, Im and Re represent real and imaginary part respectively.At the n of m after the moment constantly, fast Fourier transform module (FFT component) highest frequency component of N point numeral is expressed as X _n(k), its initial phase angle is:

${\mathrm{\θ}}_n\left(k\right)={\tan }^{-1}\left\{\frac{\mathrm{Im}\left[X_n\left(k\right)\right]}{\mathrm{Re}\left[X_n\left(k\right)\right]}\right\}---(1-2)$

Utilize these two phasing degree can obtain the tracking frequencies deviation

$f_{\mathrm{\Δ}}=\frac{{\mathrm{\θ}}_n\left(k\right)-{\mathrm{\θ}}_m\left(k\right)}{2\mathrm{\π}(n-m)}---(1-3)$

The minimum frequency deviation that obtains by (1-3) formula be frequency resolution far above the frequency resolution precision that conventional fast Fourier transform FFT obtains, have speed of convergence fast simultaneously.Fixed sampling frequency f ₀With fine frequency f _ΔAddition obtains the new frequency of power network signal:

f _new＝f ₀+f _Δ (1-4)

So just can obtain an estimation frequency value of approaching electrical network power frequency component frequency relatively, power network signal x (t) is pressed new sample rate f with latter two periodic signal _sSampling, wherein

f _s＝f _new·N (1-5)

From the output signal 13 of reconfigurable filter 5, get two sections N continuous and put digital signal, send into module 6 and be Fast Fourier Transform (FFT) FFT again, new sampling rate after (1-1) to (1-5) process of utilization obtains proofreading and correct, the iteration said process just can infinitely be approached the frequency of true power network signal, thereby the high precision real-time frequency that realizes AC sampling input signal 1 is followed the tracks of and measured.

Phase detector 2 estimations obtain new sample rate f _NewAfter, to entering analog to digital converter 2 AC sampling input 1 before by new sample rate f _NewCarry out resampling, this process realizes by reconfigurable filter 5.Reconfigurable filter 5 is a kind of digital signal reconfigurable filters, the output sampled signal 12 of analog to digital converter 2 is carried out numeral recover reconstruct.

Fig. 2 is a practical measuring examples that contains harmonic noise AC sampling input signal that adopts the inventive method.The AC sampling input 1 of stable state electrical network is:

$x\left(t\right)=\sin \left(2\mathrm{\π}{f}_{0}t\right)+\frac{1}{3}\sin (3\×2\mathrm{\π}{f}_{0}t)+\frac{1}{5}\sin (5\×2\mathrm{\π}{f}_{0}t)+\frac{1}{7}\sin (7\×2\mathrm{\π}{f}_{0}t)$

F wherein ₀Get 52, N gets 128, implements following steps according to the inventive method:

1, gets AC sampling input 1 and enter fixed sample rate analog to digital converter 2.

2, fixed sample rate analog to digital converter 2 is exported the digital signal of first section N point length respectively, second section N point length digital signal enters the first fast Fourier module (FFT) 3, the digital signal of first section N point length of the first fast Fourier module (FFT), 3 outputs, the highest frequency component phase angle 8 of second section N point length digital signal are successively sent into phase detector 4, and phase detector 4 output calibration frequencies 10 are sent into digital signal reconfigurable filter 5.

3, digital signal reconfigurable filter 5 carries out the digital reconstruction sampling according to the digital output signal 12 of first section N point length of proofreading and correct 10 pairs of fixed sample rate analog to digital converters 2 of back frequency, and the N point reconstructed sample signal that obtains is sent into the second fast Fourier module 6.

4, phase detector 4 is sent in the highest frequency component phase angle of the second fast Fourier module 6 output 9, the digital signal of the 3rd section N point of analog to digital converter 2 length enters the first fast Fourier module 3, and output calibration frequency 10 was sent into digital signal reconfigurable filter 5 after phase detector 4 was judged according to accuracy requirement.

5, repeating step 2,3 and 4, reach 2.7e-12 through frequency-tracking after 3 iteration and measuring error, and each harmonic is measured maximum error 1e-15.

Claims (4)

1. an electric power system alternating current sampling real-time frequency is followed the tracks of and harmonic measuring method, and it is characterized in that: it is as follows that the method comprising the steps of:

(1) gets AC sampling input 1 and enter fixed sample rate analog to digital converter 2.

(2) fixed sample rate analog to digital converter 2 is exported the digital signal of first section N point length respectively, second section N point length digital signal enters the first fast Fourier module (FFT) 3, the digital signal of first section N point length of the first fast Fourier module (FFT), 3 outputs, the highest frequency component phase angle 8 of second section N point length digital signal are successively sent into phase detector 4, and phase detector 4 output calibration frequencies 10 are sent into digital signal reconfigurable filter 5.

(3) digital signal reconfigurable filter 5 carries out the digital reconstruction sampling according to the digital output signal 12 of first section N point length of proofreading and correct 10 pairs of fixed sample rate analog to digital converters 2 of back frequency, and the N point reconstructed sample signal that obtains is sent into the second fast Fourier module 6.

Phase detector 4 is sent in the highest frequency component phase angle output 9 of (4) second fast Fourier modules 6, the digital signal of the 3rd section N point of analog to digital converter 2 length enters the first fast Fourier module 3, and output calibration frequency 10 was sent into digital signal reconfigurable filter 5 after phase detector 4 was judged according to accuracy requirement.

(5) repeating step 2,3 and 4, reach predetermined iterations M after, 6 outputs 7 of the second fast Fourier module are the each harmonic component value of ac sampling signal, phase detector 4 output frequencies 10 are the frequency of ac sampling signal.

2. method according to claim 1 is characterized in that: predetermined iterations M is a positive integer, generally gets the M value and be 3 to 6 proper.

3. method according to claim 1 is characterized in that: the highest frequency component phase angle of the first fast Fourier module (FFT) 3 and the second fast Fourier module 6 is sent into phase detector 4, utilizes the difference of the phase angle of the two to obtain the tracking frequencies deviation.

4. method according to claim 1 is characterized in that: digital signal reconfigurable filter 5 is a sampling rate with emending frequency 10, and the digital signal of fixed sample rate analog to digital converter 2 outputs is carried out the variable Rate sampling.

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