CN103926456A - Flicker value calculation method based on improved FFT and inverter - Google Patents

Abstract

The invention relates to a flicker value calculation method based on improved FFT and an inverter. In order to solve the technical problems, the flicker value calculation method based on the improved FFT and the inverter are provided, and high-precision flicker value calculation is achieved. According to the technical scheme, the method includes the steps that (1), all phases of voltage signals are sampled to obtain a voltage sampled sequence; (2), a voltage root-mean-square value is calculated according to sampling length per semi-circle wave, so that a voltage root-mean-square value sequence is obtained; (3), the average value of the voltage root-mean-square value sequence is calculated, and the average value is subtracted from each voltage root-mean-square value, so that a new voltage root-mean-square value sequence is obtained; the new voltage root-mean-square value sequence is windowed, FFT is performed, and amplitude frequency is corrected through double spectrum line interpolation operation; (5), curve fitting is performed on voltage fluctuation and fluctuation frequency discrete points; (6), please see the formula in the specification, a transient flicker value P is calculated; (7), the steps from one to six are repeated, all transient flicker values P within ten minutes are calculated, and according to the formula in the specification, a short-time flicker value Pst is calculated. The flicker value calculation method and inverter are used for the field of electric power technologies.

Description

Calculation of Short Term Flicker Severity and inverter based on improving FFT

Technical field

The present invention relates to signal processing technology field, particularly a kind of Calculation of Short Term Flicker Severity and inverter based on improving FFT, is mainly applicable to power technology field.

Background technology

Along with the increase of non-linear in electrical network and impact load, voltage fluctuation phenomenon is also more and more serious, has caused serious impact to commercial production and social life.Voltage fluctuation is a series of relatively quick or phenomenons that continuously change of rms voltage.Voltage flicker is the evaluation index of weighing the voltage fluctuation extent of injury, is harmful result that voltage fluctuation causes, is the sensitivity response of human eye to the fluctuation of incandescent lamp illumination.Therefore voltage fluctuation and flickering are carried out to Real-Time Monitoring, i.e. Measurement accuracy voltage flicker index---instantaneous flicker value P, short time flicker value P _stwith long-time flickering value P _lt, for inhibition and the improvement of voltage fluctuation and flickering provides foundation, significant.

In recent years, the computing method of flickering value become the research of international academic community and engineering circles heat subject, successively having application number is 201110124225.4 " a kind of method of measuring electric network voltage flicker ", application number is 201210363581.6 " a kind of flickering real-time computing technique ", the patent No. is the open and mandates such as 201320070102.1 " a kind of voltage fluctuation and flicker pick-up unit based on energy operator and Spectrum Correction ", these patents or patent documentation can be realized the calculating to electric network voltage flicker value, but these existing patents or patent documentation or only calculate instantaneous flicker value, or adopt the fluctuation of IEC normal voltage and vibration frequency discrete point to carry out interpolation, but do not solve voltage fluctuation and fluctuation voltage frequency accidental correspondence problem, or adopt the method for FFT still not solve spectral leakage and the fence effect problem that FFT brings, and general voltage fluctuation and vibration frequency have diversity and randomness, therefore be difficult to realize high-precision flicker measurement and analysis.

Summary of the invention

The technical problem to be solved in the present invention is: the problem for above-mentioned existence provides a kind of Calculation of Short Term Flicker Severity and inverter based on improving FFT, to overcome spectrum component and the fluctuation amplitude problem that prior art flickering calculated amount is large, cannot accurately obtain voltage flicker signal, and cannot realize high-precision flicker measurement and problem analysis.

Another object of the present invention is: provide a kind of and can realize the inverter that high precision flickering value is measured.

The technical solution adopted in the present invention is: the Calculation of Short Term Flicker Severity based on improving FFT, is characterized in that comprising the following steps:

S1, three-phase voltage, after signal condition, are completed the slide block of each phase voltage signal are sampled by A/D converter, obtain voltage sample sequence u (i);

S2, with every half cycles sampling length H, calculate primary voltage root-mean-square value, obtain one group of rms voltage sequence U in a period of time _r(N), N is rms voltage number;

S3, calculating U _r(N) the mean value U of sequence, and deduct mean value U with each rms voltage, obtain one group of new rms voltage ordered series of numbers U _rms(N);

S4, to new rms voltage ordered series of numbers U _rms(N) windowing, and carry out FFT conversion, obtain the amplitude versus frequency characte U of each sampled point _f(k), then by double spectral line interpolation computing, carry out frequency amplitude correction, obtain revised amplitude U ' _f(k);

S5, voltage fluctuation in IEC standard and vibration frequency discrete point are carried out curve fitting, make the correspondence of voltage fluctuation and fluctuation voltage frequency there is continuity, obtain instantaneous flicker value P and be the funtcional relationship of 1 o'clock magnitude of a voltage fluctuation and vibration frequency;

S6, according to formula calculate instantaneous flicker value P, in formula, du _kfor instantaneous flicker value P is 1 o'clock corresponding frequencies f(k) corresponding magnitude of a voltage fluctuation, l is that after FFT, 0～35Hz is interior for calculating the amplitude number of instantaneous flicker value P, U ' _f(k) be revised amplitude;

S7, repeating step S1-S6, calculate each instantaneous flicker value P in 10 minutes, successively then according to formula calculate short time flicker value P _st, in formula, P _0.1, P ₁, P ₃, P ₁₀, P ₅₀be respectively the instantaneous flicker value of 10min voltage fluctuation cumulative probability function (CPF) curve ordinate 0.1%, 1%, 3%, 10%, 50% correspondence.

Described Calculation of Short Term Flicker Severity also comprises step S8, by each short time flicker value P recording in Measuring Time section _stk, calculate long-time flickering value,

$P_{\mathrm{lt}}=\sqrt[3]{\frac{1}{N}\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{\left(P_{\mathrm{stk}}\right)}^3}$

In formula, N=12, Measuring Time is 2h.

In described step S4, to new rms voltage ordered series of numbers U _rms(N) add Hanning window, obtain

x _w(i)＝U _rms(i)w _R(i)

In formula, w _r(i)=0.5-0.5cos (2 π i/N) (N=0,1 ..., i-1) be Hanning window.

In described step S4, the amplitude computing formula of sampled point is

A＝N ^-1·(y ₁+y ₂)·(2.3562+1.1554·α ²+0.3261·α ⁴+0.0789·α ⁶)

In formula, α=k ₀-k ₁-0.5, α span is [0.5,0.5], k ₁and k ₂be respectively peak point k ₀near the maximum spectral line of amplitude and time maximum spectral line, wherein, k ₁≤ k ₀≤ k ₂(k ₂=k ₁+ 1), k ₁and k ₂the amplitude of these 2 spectral lines is respectively y ₁and y ₂.

In described step S5, instantaneous flicker value P is that the funtcional relationship of 1 o'clock magnitude of a voltage fluctuation and vibration frequency is

$d\left(f\right)=\left\{\begin{array}{c}0.4448-0.1021\&CenterDot;(f-4.5176)+{1.4392\&CenterDot;10}^2\&CenterDot;{(f-4.5176)}^2-{1.2643\&CenterDot;10}^{-3}\&CenterDot;{(f-4.5176)}^3+{2.523110}^{-3}\&CenterDot;{(f-4.5176)}^4-{5.2723\&CenterDot;10}^{-4}\&CenterDot;{(f-4.5176)}^5\\ -{3.426410}^{-4}\&CenterDot;{(f-4.5176)}^6+{6.98701\&CenterDot;10}^{-5}\&CenterDot;{(f-4.5176)}^7+{2.0723\&CenterDot;10}^{-5}\&CenterDot;{(f-4.5176)}^8-4.2991\&CenterDot;{10}^{-6}\&CenterDot;{(f-4.5176)}^9\\ (0\mathrm{Hz}\&le;f<8.8\mathrm{Hz})\\ 0.4802+4.9051\&CenterDot;{10}^{-2}\&CenterDot;(f-16.3947)+1.6352\&CenterDot;{10}^{-3}\&CenterDot;{(f-16.3947)}^2-1.3387\&CenterDot;{10}^{-5\&CenterDot;}{3.257410}^{-6}\&CenterDot;{(f-16.3947)}^4-{1.5261\&CenterDot;10}^{-6}\&CenterDot;{(f-16.3947)}^5.\\ +{1.9572\&CenterDot;10}^{-7}\&CenterDot;{(f-16.3947)}^6+{8.9703\&CenterDot;10}^{-9}\&CenterDot;{(f-16.3947)}^7-8.2591\&CenterDot;{10}^{-10}\&CenterDot;{(f-16.3947)}^8-{2.4563\&CenterDot;10}^{-12}\&CenterDot;{(f-16.3947)}^9\\ (8.8\mathrm{Hz}\&le;f\&le;25\mathrm{Hz})\\ 0.0000386657\&CenterDot;f^3+0.0008733115\&CenterDot;f^2-0.0077651392\&CenterDot;f+0.0264286726(25\mathrm{Hz}<f\&le;35\mathrm{Hz})\end{array}\right.$

Adopt described method to carry out the inverter of flickering value calculating; it is characterized in that: it comprises solar module, startup and monitoring shutdown module, electric current and voltage sampling module A, MPPT control module, digital control unit, inversion converter, filtration module, isolating switch, electric current and voltage sampling module B; and digital signal processing and control module; wherein

Start and monitoring shutdown module, for monitoring the start and stop state of solar module, and status information is delivered to digital control unit;

Electric current and voltage sampling module A, for obtaining the voltage and current signal of solar module output, and is delivered to digital control unit;

Digital control unit, receive on the one hand the solar module start and stop state that startup and monitoring shutdown module are carried, the voltage and current signal of carrying according to electric current and voltage sampling module A on the other hand obtains the output power of solar module, start and stop state and the output power of comprehensive solar module, output control signals to MPPT control module;

MPPT control module, the control signal sending over according to digital control unit, makes solar module be operated in its maximum power point;

Inversion converter, for the converting direct-current power into alternating-current power that solar module is exported;

Filtration module, is connected with inversion converter output terminal, for converting the alternating voltage of output to pure power frequency sine wave;

Isolating switch, input end is connected with filtration module output terminal, and output terminal is connected with three-phase power line, and control signal input end is connected with control module with digital signal processing, according to the control signal of control signal input end, control its break-make, realize the break-make of inversion converter and three-phase power line;

Electric current and voltage sampling module B, for aforementioned power frequency sine wave is sampled, and transmits it to digital signal processing and control module;

Digital signal processing and control module, by serial ports, be connected with digital control unit, by I/O mouth, be connected with isolating switch, outputing control signals on the one hand inversion converter controls it and carries out inversion, the sampled signal that receiver voltage current sample module B transmits on the other hand, and it is carried out to the calculating of voltage flicker value, then according to result of calculation, output control signals to its break-make of breaker control.

Described inverter also comprises communication module and the human-computer interaction module being connected with control module with digital signal processing.

It is the digital signal processor of TMS320LF2407 that described digital control unit and digital signal processing and control module all adopt model.

The invention has the beneficial effects as follows: the present invention is by the added Hanning window interpolation FFT algorithms to improve spectrum leakage and the fence effect that exist in the Calculation of Short Term Flicker Severity based on FFT, by more accurate curve, solve fluctuation voltage frequency and voltage fluctuation randomness correspondence problem, thereby improved the accuracy that flickering value is calculated.In addition, the method has been simplified the flicker measurement process of International Electrotechnical Commission (International Electrotechnical Commission, IEC), has reduced calculated amount, is convenient to realize, and apparatus structure is simple, is convenient to commercialization.Inverter of the present invention is sampled by electric current and voltage, can the grid-connected end of high-precision Real-Time Monitoring and the quality of power supply of user side, and for grid-connected and power quality controlling provide reliable foundation.

Accompanying drawing explanation

Fig. 1 is flickering value calculation flow chart of the present invention.

Fig. 2 is the amplitude versus frequency characte figure of each common window function.

The matched curve figure of each frequency and magnitude of a voltage fluctuation when Fig. 3 is P=1 of the present invention.

Fig. 4 is the structural representation of inverter of the present invention.

Embodiment

As shown in Figure 1, the Calculation of Short Term Flicker Severity of the present embodiment based on improving FFT, method by calculating voltage effective value is extracted voltage flicker signal, utilize Hanning window function to improve fft analysis to voltage flicker signal, provided the matched curve of voltage fluctuation and fluctuation voltage frequency simultaneously, solved voltage fluctuation and fluctuation voltage frequency accidental correspondence problem, improved the accuracy that flickering value is calculated, concrete steps are as follows:

S1, three-phase voltage, after signal condition, are completed the slide block of each phase voltage signal are sampled by A/D converter, obtain voltage sample sequence u (i), sample frequency f _s=12.8K.

S2, with every half cycles sampling length H, calculate primary voltage root-mean-square value, obtain one group of rms voltage sequence U in a period of time _r(N);

$U_r\left(N\right)=\sqrt{\frac{1}{N}\underset{i=1}{\overset{H}{\mathrm{\&Sigma;}}}{u}^2\left(i\right)},$ In formula, H=128.

S3, calculating U _r(N) the mean value U of sequence;

in formula, N=512, is rms voltage number.

S4, with each rms voltage, deduct mean value U, obtain one group of new rms voltage ordered series of numbers U _rms(N);

U _rms(i)＝U _r(i)-U。

S5, by the simulation analysis (as shown in Figure 2) to conventional window function, select to the better Hanning window of spectral leakage inhibition, to new rms voltage ordered series of numbers U _rms(N) add Hanning window, obtain

x _w(i)＝U _rms(i)w _R(i)

In formula, w _r(i)=0.5-0.5cos (2 π i/N) (N=0,1 ..., i-1) be Hanning window.

S6, the sequence after windowing is carried out to FFT conversion,

$U_f\left(k\right)=\underset{i=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{U}_{\mathrm{rms}}\left(i\right)w_R\left(i\right)e^{-j\frac{2\mathrm{\&pi;k}}{N}i}.$

S7, discrete series is carried out to interpolation arithmetic

When signal is carried out to non-synchronous sampling, crest frequency f ₀k ₀f does not drop on discrete spectral line frequency, occurs fence effect, and the present embodiment is eliminated by the method for double spectral line interpolation.If k ₁and k ₂be respectively peak point k ₀near the maximum spectral line of amplitude and time maximum spectral line, wherein, k ₁≤ k ₀≤ k ₂(k ₂=k ₁+ 1), k ₁and k ₂the amplitude of these 2 spectral lines is respectively y ₁=| X (k ₁Δ f) | and y ₂=| X (k ₂Δ f) |, get intermediate variable α=k ₀-k ₁-0.5, α span is [0.5,0.5], and the expression formula by discrete Fourier transformation can obtain

$\mathrm{\&beta;}=\frac{\left|W_R\left(\frac{2\mathrm{\&pi;}(-\mathrm{\&alpha;}+0.5)}{N}\right)\right|-\left|W_R\left(\frac{2\mathrm{\&pi;}(-\mathrm{\&alpha;}-0.5)}{N}\right)\right|}{\left|W_R\left(\frac{2\mathrm{\&pi;}(-\mathrm{\&alpha;}+0.5)}{N}\right)\right|+\left|W_R\left(\frac{2\mathrm{\&pi;}(-\mathrm{\&alpha;}-0.5)}{N}\right)\right|}$

The inverse function of note formula α is α=h ^-1(β).Utilize curve polyfit () function call α=h ^-1(β) approximating polynomial,

α＝1.5·β

By β, can obtain parameter alpha, frequency correction formula is

F ₀=k ₀Δ f=(α+k ₁+ 0.5) Δ f, in formula for discrete frequency interval,

To k ₁and k ₂two spectral lines are weighted on average, just obtain amplitude computing formula,

$\begin{array}{c}{A}_0=\frac{A_1\left|W_R\left(\frac{2\mathrm{\&pi;}(k_1-k_0)}{N}\right)\right|+A_2\left|W_R\left(\frac{2\mathrm{\&pi;}(k_2-k_0)}{N}\right)\right|}{\left|W_R\left(\frac{2\mathrm{\&pi;}(k_1-k_0)}{N}\right)\right|+\left|W_R\left(\frac{2\mathrm{\&pi;}(k_2-k_0)}{N}\right)\right|}\\ =\frac{2(y_1+y_2)}{\left|W_R\left(\frac{2\mathrm{\&pi;}(-\mathrm{\&alpha;}+0.5)}{N}\right)\right|+\left|W_R\left(\frac{2\mathrm{\&pi;}(-\mathrm{\&alpha;}-0.5)}{N}\right)\right|}\end{array}$

N is larger, and amplitude correction formula can be reduced to

A=N ^-1(y ₁+ y ₂) (2.3562+1.1554 α ²+ 0.3261 α ⁴+ 0.0789 α ⁶), in formula, N is the data amount check of being FFT, N=512 herein,

Utilize this formula to carry out interpolation arithmetic and obtain revised amplitude U ' _f(k).

S8, voltage fluctuation in IEC standard and vibration frequency discrete point are carried out curve fitting (as shown in Figure 3), make the correspondence of voltage fluctuation and fluctuation voltage frequency there is continuity, obtain instantaneous flicker value P and be the funtcional relationship of 1 o'clock magnitude of a voltage fluctuation and vibration frequency,

$d\left(f\right)=\left\{\begin{array}{c}0.4448-0.1021\&CenterDot;(f-4.5176)+{1.4392\&CenterDot;10}^2\&CenterDot;{(f-4.5176)}^2-{1.2643\&CenterDot;10}^{-3}\&CenterDot;{(f-4.5176)}^3+{2.523110}^{-3}\&CenterDot;{(f-4.5176)}^4-{5.2723\&CenterDot;10}^{-4}\&CenterDot;{(f-4.5176)}^5\\ -{3.426410}^{-4}\&CenterDot;{(f-4.5176)}^6+{6.98701\&CenterDot;10}^{-5}\&CenterDot;{(f-4.5176)}^7+{2.0723\&CenterDot;10}^{-5}\&CenterDot;{(f-4.5176)}^8-4.2991\&CenterDot;{10}^{-6}\&CenterDot;{(f-4.5176)}^9\\ (0\mathrm{Hz}\&le;f<8.8\mathrm{Hz})\\ 0.4802+4.9051\&CenterDot;{10}^{-2}\&CenterDot;(f-16.3947)+1.6352\&CenterDot;{10}^{-3}\&CenterDot;{(f-16.3947)}^2-1.3387\&CenterDot;{10}^{-5\&CenterDot;}{3.257410}^{-6}\&CenterDot;{(f-16.3947)}^4-{1.5261\&CenterDot;10}^{-6}\&CenterDot;{(f-16.3947)}^5.\\ +{1.9572\&CenterDot;10}^{-7}\&CenterDot;{(f-16.3947)}^6+{8.9703\&CenterDot;10}^{-9}\&CenterDot;{(f-16.3947)}^7-8.2591\&CenterDot;{10}^{-10}\&CenterDot;{(f-16.3947)}^8-{2.4563\&CenterDot;10}^{-12}\&CenterDot;{(f-16.3947)}^9\\ (8.8\mathrm{Hz}\&le;f\&le;25\mathrm{Hz})\\ 0.0000386657\&CenterDot;f^3+0.0008733115\&CenterDot;f^2-0.0077651392\&CenterDot;f+0.0264286726(25\mathrm{Hz}<f\&le;35\mathrm{Hz})\end{array}\right.$

S9, according to the definition of voltage fluctuation, 2 times of correspondences of each frequency amplitude the peak-to-peak value of this frequency sinusoidal voltage fluctuation, i.e. the magnitude of a voltage fluctuation △ U of this frequency _f(k),

ΔU _f(k)＝2×|U' _f(k)|

Instantaneous flicker value P can be by magnitude of a voltage fluctuation △ U _f(k) divided by producing 1 unit instantaneous flicker in this frequency

The magnitude of a voltage fluctuation du of value _kafter quadratic sum realize,

$P=\underset{k=1}{\overset{l}{\mathrm{\&Sigma;}}}{\left[\frac{2\&times;{U^{\&prime;}}_f\left(k\right)|}{{\mathrm{du}}_k}\right]}^2=\underset{k=1}{\overset{l}{\mathrm{\&Sigma;}}}{\left[\frac{\mathrm{\&Delta;}{U}_f\left(k\right)}{{\mathrm{du}}_k}\right]}^2,$

In formula, du _kfor instantaneous flicker value P is 1 o'clock corresponding frequencies f(k) corresponding magnitude of a voltage fluctuation, the funtcional relationship that can set up by step S8 obtains, and l is that after FFT, 0～35Hz is interior for calculating the amplitude number of instantaneous flicker value P, determines U ' according to sample frequency _f(k) be revised amplitude.

S10, repeating step S1-S7, calculate each instantaneous flicker value P in 10 minutes, successively then according to formula calculate short time flicker value P _st, in formula, P _0.1, P ₁, P ₃, P ₁₀, P ₅₀be respectively the instantaneous flicker value of 10min voltage fluctuation cumulative probability function (CPF) curve ordinate 0.1%, 1%, 3%, 10%, 50% correspondence.

S11, by each short time flicker value P recording in Measuring Time section _stk, calculate long-time flickering value,

$P_{\mathrm{lt}}=\sqrt[3]{\frac{1}{N}\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{\left(P_{\mathrm{stk}}\right)}^3}$

In formula, N=12, Measuring Time is 2h.

The Zhejiang Province Electric Power Research Institute test point of take is foundation, and the STR3030DN power quality analyzer calibrating installation of Henan Xing Chuan development in science and technology company limited of take is standard, and the test data that adopts the present embodiment computing method to obtain is as shown in table 1.

Table 1

As can be seen from the above table, the flickering value error that adopts the present embodiment computing method to obtain is less, has realized high-precision flickering value and has calculated.

As shown in Figure 4; the inverter that adopts preceding method to carry out the calculating of flickering value; comprise solar module 1, startup and monitoring shutdown module 2, electric current and voltage sampling module A3, MPPT control module 4, digital control unit 5, inversion converter 6, filtration module 7, isolating switch 8, electric current and voltage sampling module B9, digital signal processing and control module 10, communication module 11 and human-computer interaction module 12; wherein

Start and monitoring shutdown module 2, for monitoring the start and stop state of solar module 1, and status information is delivered to digital control unit 5;

Electric current and voltage sampling module A3, for obtaining the voltage and current signal of solar module 1 output, and is delivered to digital control unit 5;

Digital control unit 5, receive on the one hand the solar module 1 start and stop state that startup and monitoring shutdown module 2 are carried, the voltage and current signal of carrying according to electric current and voltage sampling module A3 on the other hand obtains the output power of solar module 1, start and stop state and the output power of comprehensive solar module 1, output control signals to MPPT control module 4;

MPPT(MPPT maximum power point tracking) control module 4, and the control signal sending over according to digital control unit 5 makes solar module 1 be operated in its maximum power point;

Inversion converter 6, for the converting direct-current power into alternating-current power that solar module 1 is exported;

Filtration module 7, is connected with inversion converter 6 output terminals, for converting the alternating voltage of output to pure power frequency sine wave;

Isolating switch 8, input end is connected with filtration module 7 output terminals, and output terminal is connected with three-phase power line, and control signal input end is connected with control module 10 with digital signal processing, according to the control signal of control signal input end, control its break-make, realize the break-make of inversion converter 6 and three-phase power line;

Electric current and voltage sampling module B9, for aforementioned power frequency sine wave is sampled, and transmits it to digital signal processing and control module 10;

Digital signal processing and control module 10, by serial ports, being connected with digital control unit 5, (data that send over according to digital control unit realize man-machine interface, the management of the aspects such as communication), by I/O mouth, be connected with isolating switch 8, it carries out inversion to inversion converter 6 controls to export on the one hand pwm control signal, the sampled signal that receiver voltage current sample module B9 transmits on the other hand, and it is carried out to the calculating of voltage flicker value, then according to result of calculation, output control signals to isolating switch 8 and control its break-make (according to user's requirement setting, for example flickering value is excessive, electric network voltage flicker is serious, control power supply or stop grid-connected etc.).

Communication module 11, is connected with control module 10 with digital signal processing, for realizing input and output and the function such as communicating by letter.

Human-computer interaction module 12, is connected with control module 10 with digital signal processing, for realizing data, shows.

It is the digital signal processor of TMS320LF2407 that described digital control unit 5 and digital signal processing and control module 10 all adopt model.

In practical application, utilize the present embodiment inverter, can monitor on the one hand the quality of power supply of the electric energy of grid-connected end, for host's electrical network also provides clean electric energy to check on, on the other hand, also the quality of power supply that can Real-Time Monitoring user side, for electrical network power quality controlling provides foundation.

Claims (8)

1. the Calculation of Short Term Flicker Severity based on improving FFT, is characterized in that comprising the following steps:

S1, three-phase voltage, after signal condition, are completed the slide block of each phase voltage signal are sampled by A/D converter, obtain voltage sample sequence u (i);

S2, with every half cycles sampling length H, calculate primary voltage root-mean-square value, obtain one group of rms voltage sequence U in a period of time _r(N), N is rms voltage number;

S3, calculating U _r(N) the mean value U of sequence, and deduct mean value U with each rms voltage, obtain one group of new rms voltage ordered series of numbers U _rms(N);

S4, to new rms voltage ordered series of numbers U _rms(N) windowing, and carry out FFT conversion, obtain the amplitude versus frequency characte U of each sampled point _f(k), then by double spectral line interpolation computing, carry out frequency amplitude correction, obtain revised amplitude U ' _f(k);

S5, voltage fluctuation in IEC standard and vibration frequency discrete point are carried out curve fitting, make the correspondence of voltage fluctuation and fluctuation voltage frequency there is continuity, obtain instantaneous flicker value P and be the funtcional relationship of 1 o'clock magnitude of a voltage fluctuation and vibration frequency;

S6, according to formula calculate instantaneous flicker value P, in formula, du _kfor instantaneous flicker value P is 1 o'clock corresponding frequencies f(k) corresponding magnitude of a voltage fluctuation, l is that after FFT, 0～35Hz is interior for calculating the amplitude number of instantaneous flicker value P, U ' _f(k) be revised amplitude;

S7, repeating step S1-S6, calculate each instantaneous flicker value P in 10 minutes, successively then according to formula calculate short time flicker value P _st, in formula, P _0.1, P ₁, P ₃, P ₁₀, P ₅₀be respectively the instantaneous flicker value of 10min voltage fluctuation cumulative probability function (CPF) curve ordinate 0.1%, 1%, 3%, 10%, 50% correspondence.

2. the Calculation of Short Term Flicker Severity based on improving FFT according to claim 1, is characterized in that: described Calculation of Short Term Flicker Severity also comprises step S8, by each short time flicker value P recording in Measuring Time section _stk, calculate long-time flickering value,

$P_{\mathrm{lt}}=\sqrt[3]{\frac{1}{N}\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{\left(P_{\mathrm{stk}}\right)}^3}$

In formula, N=12, Measuring Time is 2h.

3. the Calculation of Short Term Flicker Severity based on improving FFT according to claim 1, is characterized in that: in described step S4, to new rms voltage ordered series of numbers U _rms(N) add Hanning window, obtain

x _w(i)＝U _rms(i)w _R(i)

In formula, w _r(i)=0.5-0.5cos (2 π i/N) (N=0,1 ..., i-1) be Hanning window.

4. the Calculation of Short Term Flicker Severity based on improving FFT according to claim 1, is characterized in that: in described step S4, the amplitude computing formula of sampled point is

A＝N ^-1·(y ₁+y ₂)·(2.3562+1.1554·α ²+0.3261·α ⁴+0.0789·α ⁶)

In formula, α=k ₀-k ₁-0.5, α span is [0.5,0.5], k ₁and k ₂be respectively peak point k ₀near the maximum spectral line of amplitude and time maximum spectral line, wherein, k ₁≤ k ₀≤ k ₂(k ₂=k ₁+ 1), k ₁and k ₂the amplitude of these 2 spectral lines is respectively y ₁and y ₂.

5. the Calculation of Short Term Flicker Severity based on improving FFT according to claim 1, is characterized in that: in described step S5, instantaneous flicker value P is that the funtcional relationship of 1 o'clock magnitude of a voltage fluctuation and vibration frequency is

$d\left(f\right)=\left\{\begin{array}{c}0.4448-0.1021\&CenterDot;(f-4.5176)+{1.4392\&CenterDot;10}^2\&CenterDot;{(f-4.5176)}^2-{1.2643\&CenterDot;10}^{-3}\&CenterDot;{(f-4.5176)}^3+{2.523110}^{-3}\&CenterDot;{(f-4.5176)}^4-{5.2723\&CenterDot;10}^{-4}\&CenterDot;{(f-4.5176)}^5\\ -{3.426410}^{-4}\&CenterDot;{(f-4.5176)}^6+{6.98701\&CenterDot;10}^{-5}\&CenterDot;{(f-4.5176)}^7+{2.0723\&CenterDot;10}^{-5}\&CenterDot;{(f-4.5176)}^8-4.2991\&CenterDot;{10}^{-6}\&CenterDot;{(f-4.5176)}^9\\ (0\mathrm{Hz}\&le;f<8.8\mathrm{Hz})\\ 0.4802+4.9051\&CenterDot;{10}^{-2}\&CenterDot;(f-16.3947)+1.6352\&CenterDot;{10}^{-3}\&CenterDot;{(f-16.3947)}^2-1.3387\&CenterDot;{10}^{-5\&CenterDot;}{3.257410}^{-6}\&CenterDot;{(f-16.3947)}^4-{1.5261\&CenterDot;10}^{-6}\&CenterDot;{(f-16.3947)}^5.\\ +{1.9572\&CenterDot;10}^{-7}\&CenterDot;{(f-16.3947)}^6+{8.9703\&CenterDot;10}^{-9}\&CenterDot;{(f-16.3947)}^7-8.2591\&CenterDot;{10}^{-10}\&CenterDot;{(f-16.3947)}^8-{2.4563\&CenterDot;10}^{-12}\&CenterDot;{(f-16.3947)}^9\\ (8.8\mathrm{Hz}\&le;f\&le;25\mathrm{Hz})\\ 0.0000386657\&CenterDot;f^3+0.0008733115\&CenterDot;f^2-0.0077651392\&CenterDot;f+0.0264286726(25\mathrm{Hz}<f\&le;35\mathrm{Hz})\end{array}\right.$

6. one kind adopts the inverter that method is carried out the calculating of flickering value described in claim 1-5 any one; it is characterized in that: it comprises solar module (1), startup and monitoring shutdown module (2), electric current and voltage sampling module A(3), MPPT control module (4), digital control unit (5), inversion converter (6), filtration module (7), isolating switch (8), electric current and voltage sampling module B(9); and digital signal processing and control module (10); wherein

Start and monitoring shutdown module (2), for monitoring the start and stop state of solar module (1), and status information is delivered to digital control unit (5);

Electric current and voltage sampling module A(3), for obtaining the voltage and current signal of solar module (1) output, and be delivered to digital control unit (5);

Digital control unit (5), receive on the one hand solar module (1) the start and stop state that startup and monitoring shutdown module (2) are carried, on the other hand according to electric current and voltage sampling module A(3) voltage and current signal carried obtains the output power of solar module (1), start and stop state and the output power of comprehensive solar module (1), output control signals to MPPT control module (4);

MPPT control module (4), the control signal sending over according to digital control unit (5), makes solar module (1) be operated in its maximum power point;

Inversion converter (6), for the converting direct-current power into alternating-current power that solar module (1) is exported;

Filtration module (7), is connected with inversion converter (6) output terminal, for converting the alternating voltage of output to pure power frequency sine wave;

Isolating switch (8), input end is connected with filtration module (7) output terminal, output terminal is connected with three-phase power line, control signal input end is connected with control module (10) with digital signal processing, according to the control signal of control signal input end, control its break-make, realize the break-make of inversion converter (6) and three-phase power line;

Electric current and voltage sampling module B(9), for aforementioned power frequency sine wave is sampled, and transmit it to digital signal processing and control module (10);

Digital signal processing and control module (10), by serial ports, be connected with digital control unit (5), by I/O mouth, be connected with isolating switch (8), outputing control signals on the one hand inversion converter (6) controls it and carries out inversion, receiver voltage current sample module B(9 on the other hand) sampled signal transmitting, and it is carried out to the calculating of voltage flicker value, then according to result of calculation, output control signals to isolating switch (8) and control its break-make.

7. inverter according to claim 6, is characterized in that: described inverter also comprises communication module (11) and the human-computer interaction module (12) being connected with control module (10) with digital signal processing.

8. inverter according to claim 6, is characterized in that: it is the digital signal processor of TMS320LF2407 that described digital control unit (5) and digital signal processing and control module (10) all adopt model.