CN103235181A - Harmonic detection method based on wavelet transformation and instantaneous reactive power theory - Google Patents

Abstract

The invention discloses a harmonic detection method based on wavelet transformation and the instantaneous reactive power theory, and belongs to the technical field of signal processing. The harmonic detection method includes obtaining instantaneous active power and instantaneous reactive power of power grid detection amount on the basis of the reactive power theory, processing the instantaneous active power and the instantaneous reactive power of the power grid detection amount by means of wavelet transformation to find out direct-current components of the instantaneous active power and the instantaneous reactive power of the power grid detection amount so as to obtain a reference value of the power grid detection amount, and eliminating harmonic components in the power grid detection amount. By means of wavelet transformation for describing time-frequency variation of the power grid detection amount, astable signals can be well analyzed, adaptive filtering of a power system can be achieved easily, and anti-jamming capability of the power system is improved.

Description

Harmonic detecting method based on wavelet transformation and instantaneous reactive power theory

Technical field

The invention discloses the harmonic detecting method based on wavelet transformation and instantaneous reactive power theory, belong to the technical field that signal is handled.

Background technology

The Japan scholar has proposed " three-phase circuit instantaneous reactive power theory " in nineteen eighty-three, this theoretical breakthrough traditional power definition based on mean value, concepts such as instantaneous reactive power, instantaneous active power have systematically been provided, based on the harmonic wave of this theory and reactive current detection method at APF (ActivePowerFilter, Active Power Filter-APF) obtains successful application in, greatly promoted the development of APF.It is comparatively practical, most widely used at present a kind of detection method.Its algorithm principle figure as shown in Figure 1.

For voltage the circuit of harmonic components (distortion), i are arranged _p, i _qOperation method can obtain testing result more accurately.The performance of the LPF low-pass filtering module of ip-iq algorithm has determined the performance that harmonic wave detects, and the present invention utilizes wavelet transformation to realize the LPF module.Fourier transform is a kind of or fully in time domain, the fully conversion of the overall situation of using at frequency domain, be only applicable to the analysis of steady-state signal, and can not describe the time-frequency localization property of signal, and this character character of the most basic and most critical of unstable signal exactly.

Summary of the invention

Technical matters to be solved by this invention is the deficiency at the above-mentioned background technology, and the harmonic detecting method based on wavelet transformation and instantaneous reactive power theory is provided.

The present invention adopts following technical scheme for achieving the above object:

Harmonic detecting method based on wavelet transformation and instantaneous reactive power theory specifically comprises the steps:

Step 1 is transformed into the electrical network detection limit under the static rectangular coordinate system of two-phase, obtains the component of electrical network detection limit on the static rectangular coordinate of two-phase;

Step 2 is transformed into the described electrical network detection limit of step 1 under the meritorious idle coordinate system at the component on the static rectangular coordinate of two-phase, obtains electrical network detection limit instantaneous active power, instantaneous reactive power;

Step 3, utilize small wave converting method treatment step 2 described electrical network detection limit instantaneous active powers, instantaneous reactive power to obtain the instantaneous meritorious wavelet conversion coefficient of electrical network detection limit, instantaneous reactive wavelet conversion coefficient, according to the instantaneous meritorious wavelet coefficient of described electrical network detection limit, instantaneous reactive wavelet conversion coefficient electrical network detection limit instantaneous active power, instantaneous reactive power reconstruct are obtained flip-flop in described electrical network detection limit instantaneous active power, the instantaneous reactive power;

Step 4 obtains electrical network detection limit reference value to the described electrical network detection limit of step 3 instantaneous active power, instantaneous reactive power flip-flop inverse transformation, and the difference of electrical network detection limit and electrical network detection limit reference value is harmonic component.

In the described harmonic detecting method based on wavelet transformation and instantaneous reactive power theory, the electrical network detection limit is three phase network voltage or three phase network electric current.

The present invention adopts technique scheme, have following beneficial effect: the time-frequency time-frequency that utilizes wavelet transformation to describe the electrical network detection limit changes, can analyze unstable signal well, be easy to realize the auto adapted filtering of electric system energy, improve the antijamming capability of electric system.

Description of drawings

Fig. 1 is the harmonic detecting method synoptic diagram based on the three-phase circuit instantaneous reactive power theory.

Fig. 2 is the harmonic detecting method synoptic diagram based on wavelet transformation and instantaneous reactive power theory.

Fig. 3 is the original a phase current waveform figure that contains harmonic wave.

Fig. 4 is the original a phase current harmonic content synoptic diagram that contains harmonic wave.

Fig. 5 is detected harmonic components synoptic diagram.

Fig. 6 is a phase current figure behind the removal harmonic components.

Fig. 7 is the harmonic content synoptic diagram of a phase current behind the removal harmonic components.

Embodiment

Be elaborated below in conjunction with the technical scheme of accompanying drawing to invention:

As shown in Figure 2, the harmonic detecting method based on wavelet transformation and instantaneous reactive power theory of the present invention for detection of the harmonic wave of three phase network voltage or three phase network electric current, to detect the three phase network electric current for example, specifically comprises the steps: below

Step 1 is with the three phase network current i _a, i _b, i _cBe transformed under the static rectangular coordinate system of two-phase, obtain three phase network voltage or the three phase network electric current component i on the static rectangular coordinate of two-phase _α, i _β

Step 2 is in conjunction with a phase line voltage, synchronous sinusoidal signal sin ω t and corresponding cosine signal-cos ω t, the component i on the static rectangular coordinate of two-phase with the described three phase network voltage of step 1 or three phase network electric current _α, i _βBe transformed under the meritorious idle coordinate system, obtain the instantaneous active power i of three phase network voltage or three phase network electric current _p, instantaneous reactive power i _qSynchronous sinusoidal signal sin ω t and corresponding cosine signal-cos ω t can be obtained by hardware circuit, also can adopt the method for tabling look-up to obtain.In actual applications, people are more prone to look-up table.This method realizes by software, namely under sample frequency, just setting up, table of natural cosines, is stored in the sequential cells of storer, and before next sampling instant arrived, CPU took out data in the corresponding storage unit of storer earlier.

Step 3 utilizes small wave converting method to handle the instantaneous active power i of three phase network electric current _p, instantaneous reactive power i _q, obtain flip-flop in the instantaneous active power, instantaneous reactive power of three phase network electric current

Utilize formula (1) to do wavelet transformation:

Any L ²(R) continuous wavelet transform of the function f in the space (t) is defined as

${\mathrm{WT}}_f(a,\mathrm{\&tau;})=\frac{1}{\sqrt{a}}{\&Integral;}_{-\&infin;}^{\&infin;}f\left(t\right)\mathrm{\&psi;}*\left\{\frac{t-\mathrm{\&tau;}}{a}\right\}\mathrm{dt}=<f\left(t\right),{\mathrm{\&Psi;}}_{\mathrm{a\&tau;}}\left(t\right)>---\left(1\right),$

In the formula (1): WT _f(a τ) is wavelet conversion coefficient, and a is scale factor, and τ is shift factor,

Be wavelet basis, ψ _{A τ}(t) Fourier transform φ (ω) satisfies the admissibility condition:

$C_{\mathrm{\&Psi;}}=\underset{R}{\&Integral;}\frac{{\left|\mathrm{\&phi;}\left(\mathrm{\&omega;}\right)\right|}^2}{\mathrm{\&omega;}}\mathrm{d\&omega;}<\&infin;---\left(2\right)$

Because wavelet basis has a and two parameters of τ, therefore, (t) launches under wavelet basis with function f, mean with a function of time project to two dimension time-the yardstick plane on, the relation of reflection function on T/F.Among the present invention, make the function f (t) in the formula (1) be the instantaneous active power i of three phase network electric current _p, instantaneous reactive power i _q, obtain the instantaneous active power i of three phase network electric current _pWavelet conversion coefficient

Instantaneous reactive power i _qWavelet coefficient

Utilize formula (3) to the instantaneous active power i of three phase network electric current _pWavelet conversion coefficient

Instantaneous reactive power i _qWavelet coefficient

Reconstruct obtains flip-flop in the instantaneous active power, instantaneous reactive power of three phase network electric current

$\stackrel{\&OverBar;}{i_p}=\frac{1}{C_{\mathrm{\&psi;}}}{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}\frac{1}{a^2}W{T}_f{(a,\mathrm{\&tau;})}_{i_p}\mathrm{\&psi;}\left(\frac{t-\mathrm{\&tau;}}{a}\right)\mathrm{dad\&tau;}$

$i_q=\frac{1}{C_{\mathrm{\&psi;}}}{\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="130411123801.png"\; state="\{\{state\}\}">a</figure-callout>}}^2}{\mathrm{WT}}_f{(a,\mathrm{\&tau;})}_{i_q}\mathrm{\&psi;}\left(\frac{t-\mathrm{\&tau;}}{a}\right)\mathrm{dad\&tau;}$ （3）；

Step 4 is to instantaneous active power, the instantaneous reactive power flip-flop of three phase network electric current

Inverse transformation obtains the reference value i of three phase network electric current _Af, i _Bf, i _Cf, the three phase network current i _a, i _b, i _cWith three phase network current reference value i _Af, i _Bf, i _CfMake difference and obtain harmonic component.

We experimentize to the ip-iq algorithm based on wavelet transformation: adopt the three-phase current that contains 7 subharmonic as input, detection algorithm validity.

$U_a=\sqrt{2}*220*\sin \left(\mathrm{wt}\right)---\left(4\right),$

I _a=100*sin(wt+π/6)+20*sin(2wt+π/6)+15*sin(3wt+π/6) （5），

+12*sin(4wt+π/6)+10*sin(5wt+π/6)+8*sin(6wt+π/6)+5*sin(7wt+π/6)

I _b=100*sin((wt-2π/3)+π/6)+20*sin(2(wt-2π/3)+π/6)

+15*sin(3(wt-2π/3)+π/6)+12*sin(4(wt-2π/3)+π/6) （6），

+10*sin(5(wt-2π/3)+π/6)+8*sin(6(wt-2π/3)+π/6)

+5*sin(7(wt-2π/3)+π/6)

I _c=100*sin((wt+2π/3)+π/6)+20*sin(2(wt+2π/3)+π/6)+

15*sin(3(wt+2π/3)+π/6)+12*sin(4(wt+2π/3)+π/6) （7），

+10*sin(5(wt+2π/3)+π/6)+8*sin(6(wt+2π/3)+π/6)

+5*sin(7(wt+2π/3)+π/6)

Adopt the db4 wavelet basis to make 8 layers of wavelet decomposition in the experiment, 1024 points of each cycle sampling.The original a phase current waveform that contains harmonic wave as shown in Figure 3, the original a phase current harmonic content that contains harmonic wave is as shown in Figure 4.Detected harmonic components as shown in Figure 5, remove behind the harmonic components a phase current as shown in Figure 6, remove the harmonic content of a phase current behind the harmonic components as shown in Figure 7.The algorithm that can be got us by the result can detect harmonic current well accurately.

In sum, the time-frequency time-frequency that harmonic detecting method based on wavelet transformation and reactive power theory of the present invention utilizes wavelet transformation to describe the electrical network detection limit changes, can analyze unstable signal well, be easy to realize the auto adapted filtering of electric system energy, improved the antijamming capability of electric system.

Claims (2)

1. based on the harmonic detecting method of wavelet transformation and instantaneous reactive power theory, it is characterized in that, specifically comprise the steps:

Step 1 is transformed into the electrical network detection limit under the static rectangular coordinate system of two-phase, obtains the component of electrical network detection limit on the static rectangular coordinate of two-phase;

Step 2 is transformed into the described electrical network detection limit of step 1 under the meritorious idle coordinate system at the component on the static rectangular coordinate of two-phase, obtains electrical network detection limit instantaneous active power, instantaneous reactive power;

Step 3, utilize small wave converting method treatment step 2 described electrical network detection limit instantaneous active powers, instantaneous reactive power to obtain the instantaneous meritorious wavelet conversion coefficient of electrical network detection limit, instantaneous reactive wavelet conversion coefficient, according to the instantaneous meritorious wavelet coefficient of described electrical network detection limit, instantaneous reactive wavelet conversion coefficient electrical network detection limit instantaneous active power, instantaneous reactive power reconstruct are obtained flip-flop in described electrical network detection limit instantaneous active power, the instantaneous reactive power;

Step 4 obtains electrical network detection limit reference value to the described electrical network detection limit of step 3 instantaneous active power, instantaneous reactive power flip-flop inverse transformation, and the difference of electrical network detection limit and electrical network detection limit reference value is harmonic component.

2. the harmonic detecting method based on wavelet transformation and instantaneous reactive power theory according to claim 1 is characterized in that, described electrical network detection limit is three phase network voltage or three phase network electric current.

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