CN101527456A - Composite detection method for active filter - Google Patents

Abstract

The invention relates to a composite detection method for an active filter. The method comprises the following steps: a, after the frequency doubling of ea, obtaining a sine signal sin m omega t and a corresponding cosine signal cos m omega t sharing the same phase with the ea through a phase locked loop and sine and cosine generating circuits, and consequently obtaining a transformation matrix Cm; b, converting network side three-phase currents isa, isb and isc into currents i alpha and i beta in a static two-phase coordinate system through 3/2 transformation, and then passing the currents i alpha and i beta through the transformation matrix Cm so as to obtain the reactive and active current components p<m> and q<m> of harmonics of powers in the coordinate system; c, filtering the reactive and active current components p<m> and q<m> through an LPF filtering to obtain reactive and active components *<m> and *<m> of m-th harmonic, passing the reactive and active components*<m> and *<m> of the m-th harmonic through a transformation matrix Cm<-1> to evaluate currents i alpha m and i beta m in the two-phase coordinate system, and then finally obtaining m-th harmonic currents iam, ibm and icm through 2/3 transformation; and d, taking an A phase as an example to count an instruction current: iac<*> is equal to ia minus iaf plus f(iam).

Description

Composite detection method for active filter

Technical field

The present invention relates to the active power filtering technical field, a kind of specifically composite detection method for active filter.

Background technology

Along with the continuous development of modern industry, nonlinear loads such as high power electronic equipment are used widely, and the harmonic pollution problem that brings electrical network is also more and more serious.Therefore, employing APF (Active Power Filter-APF, Active Power Filter) inhibition harmonic wave has become key subjects in the power electronic technology.Figure 1 shows that the schematic diagram that the most basic Active Power Filter-APF system constitutes.Among the figure, Us represents AC power, and load is a nonlinear load, and it produces harmonic wave.

The basic principle of APF is from load current i _LIn isolate harmonic current components i _LhThe command signal of offset current will be produced then after its reversed polarity effect $i_C^{*}=-i_{\mathrm{Lh}}.$ The offset current i according to the main circuit generation of current tracking control circuit _CShould follow the tracks of i _C ^*Principle, calculate the trigger impulse of each switching device of main circuit.This pulse acts on main circuit behind drive circuit, produce offset current i _CBecause, $i_C\&ap;i_C^{*},$ So, $i_S=i_L-i_C=i_L-i_C^{*}=i_L-i_{\mathrm{Lh}}.$ Be source current i _SIn only contain fundametal compoment, thereby reach the purpose of harmonic carcellation.Therefore, to the harmonic current precise real-time detection be the important step of APF.

At present, the harmonic current of parallel connection type APF detects the i that mainly is based on the instantaneous reactive theory _p-i _qMethod, the method can well detect the harmonic content in the load current, and the ring control method that stagnates is adopted in the generation of electric current, instantaneous reactive theory and control method principle thereof are seen Fig. 2.

I among Fig. 2 _a, i _b, i _cEach phase current instantaneous value for three-phase three-wire circuit; e _aIt is the instantaneous voltage of a phase; i _Af, i _Bf, i _CfBe fundamental current; i ^* _Ac, i ^* _Bc, i ^* _CcBe harmonic current; PLL is a phase-locked loop; LPF is a low pass filter.

This method by phase-locked loop and just, cosine generation circuit obtains and supply voltage e _aSynchronous sinusoidal signal and corresponding cosine signal.This two signals and i _a, i _b, i _cCalculate fundamental active current and fundamental reactive current i together _p, i _q

$\left[\begin{array}{c}{i}_p\\ i_q\end{array}\right]=C_{\mathrm{pq}}{C}_{32}\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]$

Wherein, $C_{\mathrm{pq}}=\left[\begin{array}{cc}-\sin \mathrm{\&omega;t}& \cos \mathrm{\&omega;t}\\ \cos \mathrm{\&omega;t}& \sin \mathrm{\&omega;t}\end{array}\right],$ ${\mathrm{<figure-callout\; id="32"\; label="C"\; filenames="A20081000807000102.png,A20081000807000103.png"\; state="\{\{state\}\}">C</figure-callout>}}_{32}=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right].$

Draw i through LPF filtering then _p, i _qDC component i _p, i _q

By i _p, i _qCan calculate i _Af, i _Bf, i _Cf,

$\left[\begin{array}{c}{i}_{\mathrm{af}}\\ i_{\mathrm{bf}}\\ i_{\mathrm{cf}}\end{array}\right]=C_{23}{C}_{\mathrm{pq}}^{-1}\left[\begin{array}{c}{\stackrel{\&OverBar;}{i}}_p\\ {\stackrel{\&OverBar;}{i}}_q\end{array}\right]$

And then calculate i ^* _Ac, i ^* _Bc, i ^* _Cc, promptly

$\left[\begin{array}{c}{i}_{\mathrm{ac}}^{*}\\ i_{\mathrm{bc}}^{*}\\ i_{\mathrm{cc}}^{*}\end{array}\right]=\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]-\left[\begin{array}{c}{i}_{\mathrm{af}}\\ i_{\mathrm{bf}}\\ i_{\mathrm{cf}}\end{array}\right]$

Though i based on the instantaneous reactive theory _p-i _qMethod can well detect the harmonic content in the load current, but has the variation and the phase shift of amplitude after the filtering of the electric current of output process output filter.If the load current rate of change is very big, the rate of change of APF instruction current is also very big, and output filter will make the compensation effect of APF have a greatly reduced quality this moment.

Summary of the invention

The objective of the invention is time delay and phase shift, and propose a kind of composite detection method for active filter in order to solve output filter.

The technical scheme that realizes the foregoing invention purpose is as follows:

Composite detection method for active filter comprises the steps:

A. with e _aAfter the frequency multiplication by phase-locked loop and just, cosine generation circuit obtains and e _aSynchronous sinusoidal signal sin m ω t and corresponding cosine signal co s m ω t, thus conversion battle array C obtained _m,

$C_m=\left[\begin{array}{cc}-\sin \mathrm{m\&omega;t}& \cos \mathrm{m\&omega;t}\\ \cos \mathrm{m\&omega;t}& \sin \mathrm{m\&omega;t}\end{array}\right];$

B. with net side three-phase current i _Sa, i _SbAnd i _ScThrough 3/2 conversion, be for conversion into the current i under static two phase coordinate systems _αAnd i _β, again with biphase current i _αAnd i _βThrough conversion battle array C _mDraw the idle and active current component p of the each harmonic under this coordinate system ^mAnd q ^m,

$\left[\begin{array}{c}{p}^m\\ q^m\end{array}\right]=C_m{C}_{32}\left[\begin{array}{c}{i}_{\mathrm{sa}}\\ i_{\mathrm{sb}}\\ i_{\mathrm{sc}}\end{array}\right];$

C. will gain merit and reactive current component p ^mAnd q ^mDraw the meritorious and idle component p of m subharmonic through LPF filtering ^mAnd q ^m, through conversion battle array C _m ^-1Obtain two phase coordinate system current i _{α m}And i _{β m}, finally obtain m subharmonic current i through 2/3 conversion again _Am, i _BmAnd i _Cm

D. establishing the instantaneous fundamental current of three-phase that the load-side electric current loop calculates is i _Af, i _BfAnd i _Cf, actual measurement grid side m subharmonic current is i _Am, i _BmAnd i _Cm, the actual measurement load current is i _a, i _bAnd i _c, then instruction current is:

$i_{\mathrm{ac}}^{*}=i_a-i_{\mathrm{af}}+f\left(i_{\mathrm{am}}\right)$

i ^* _bc＝i _b-i _bf+f(i _bm)

i ^* _cc＝i _c-i _cf+f(i _cm)。

In above-mentioned formula, get function f (x)=kx, obtain k value more excellent under the different loads size by emulation and experiment, and tabulation is for routine call.

The present invention has following advantage:

1, adopts composite detection method can reduce the adverse effect that the time delay that causes because of the filtering link and phase shift bring, thereby improve the compensation effect of active filter;

2, the load-side detection method is optimized, has reduced amount of calculation.

Description of drawings

Fig. 1 is existing Filter Structures schematic diagram

Fig. 2 is the schematic diagram of existing control method

Fig. 3 is a composite detection method for active filter schematic diagram of the present invention

Embodiment

The invention will be further described below in conjunction with the drawings and specific embodiments.

As shown in Figure 3, the present invention is on the basis of traditional harmonic current detecting method, for time delay and the phase shift that solves output filter, the composite detection method for active filter that proposes, the dotted line below is load-side current loop control (principle is consistent with Fig. 2) among the figure, and it goes out the current instruction value of needs compensation in every phase current: i according to the load-side current draw _a-i _Af, i _b-i _BfAnd i _c-i _CfThe dotted line top is the grid side current loop control, and it detects a few subharmonic that also leave by the system power of load-side current loop control compensation back from grid side.Specifically comprise the steps:

A. with e _aAfter the frequency multiplication by phase-locked loop and just, cosine generation circuit obtains and e _aSynchronous sinusoidal signal sin m ω t and corresponding cosine signal co s m ω t, thus conversion battle array C obtained _m,

$C_m=\left[\begin{array}{cc}-\sin \mathrm{m\&omega;t}& \cos \mathrm{m\&omega;t}\\ \cos \mathrm{m\&omega;t}& \mathrm{snm\&omega;t}\end{array}\right];$

B. with net side three-phase current i _Sa, i _SbAnd i _ScThrough 3/2 conversion, be for conversion into the current i under static two phase coordinate systems _αAnd i _β, again with biphase current i _αAnd i _βThrough conversion battle array C _mDraw the idle and active current component p of the each harmonic under this coordinate system ^mAnd q ^m,

$\left[\begin{array}{c}{p}^m\\ q^m\end{array}\right]=C_m{C}_{32}\left[\begin{array}{c}{i}_{\mathrm{sa}}\\ i_{\mathrm{sb}}\\ i_{\mathrm{sc}}\end{array}\right];$

C. will gain merit and reactive current component p ^mAnd q ^mDraw the meritorious and idle component p of m subharmonic through LPF filtering ^mAnd q ^m, through conversion battle array C _m ^-1Obtain two phase coordinate system current i _{α m}And i _{β m}, finally obtain m subharmonic current i through 2/3 conversion again _Am, i _BmAnd i _Cm

D. establishing the instantaneous fundamental current of three-phase that the load-side electric current loop calculates is i _Af, i _BfAnd i _Cf, actual measurement grid side m subharmonic current is i _Am, i _BmAnd i _Cm, the actual measurement load current is i _a, i _bAnd i _c, then instruction current is:

$i_{\mathrm{ac}}^{*}=i_a-i_{\mathrm{af}}+f\left(i_{\mathrm{am}}\right)$

i ^* _bc＝i _b-i _bf+f(i _bm)

i ^* _cc＝i _c-i _cf+f(i _cm)。

For reducing amount of calculation, get function f (x)=kx in actual applications, can obtain k value more excellent under the different loads size by emulation and experiment, and tabulation is for routine call.

The present invention is at the current changing rate larger part, and composite detection method is than the spine of the more effective inhibition electric current of conventional detection; The composite detection method of introducing net side detection method has better dynamic stability.

Claims (2)

1. composite detection method for active filter is characterized by, and comprises the steps:

A. with e _aAfter the frequency multiplication by phase-locked loop and just, cosine generation circuit obtains and e _aSynchronous sinusoidal signal sin m ω t and corresponding cosine signal co sm ω t, thus conversion battle array C obtained _m,

$C_m=\left[\begin{array}{cc}-\sin \mathrm{m\&omega;t}& \cos \mathrm{m\&omega;t}\\ \cos \mathrm{m\&omega;t}& \sin \mathrm{m\&omega;t}\end{array}\right];$

B. with net side three-phase current i _Sa, i _SbAnd i _ScThrough 3/2 conversion, be for conversion into the current i under static two phase coordinate systems _αAnd i _β, again with biphase current i _αAnd i _βThrough conversion battle array C _mDraw the idle and active current component p of the each harmonic under this coordinate system ^mAnd q ^m,

$\left[\begin{array}{c}{p}^m\\ q^m\end{array}\right]=C_m{C}_{32}\left[\begin{array}{c}{i}_{\mathrm{sa}}\\ i_{\mathrm{sb}}\\ i_{\mathrm{sc}}\end{array}\right];$

C. will gain merit and reactive current component p ^mAnd q ^mDraw the meritorious and idle component p of m subharmonic through LPF filtering ^mAnd q ^m, through conversion battle array C _m ^-1Obtain two phase coordinate system current i _{α m}And i _{β m}, finally obtain m subharmonic current i through 2/3 conversion again _Am, i _BmAnd i _Cm

D. establishing the instantaneous fundamental current of three-phase that the load-side electric current loop calculates is i _Af, i _BfAnd i _Cf, actual measurement grid side m subharmonic current is i _Am, i _BmAnd i _Cm, the actual measurement load current is i _a, i _bAnd i _c, then instruction current is:

$i_{\mathrm{ac}}^{*}=i_a-i_{\mathrm{af}}+f\left(i_{\mathrm{am}}\right)$

i ^* _bc＝i _b-i _bf+f(i _bm)

i ^* _cc＝i _c-i _cf+f(i _cm)

2. composite detection method for active filter according to claim 1 is characterized by: wherein in above-mentioned formula, get function f (x)=kx, obtain k value more excellent under the different loads size by emulation and experiment, and tabulation is for routine call.

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