CN103746587A - Control damping method applied to the resonance inhibition of LLCL single-phase grid connected inverter - Google Patents

Abstract

The invention discloses a control damping method applied to the resonance inhibition of an LLCL single-phase grid connected inverter. The method comprises the steps of connecting resonance inhibition capacitors Cds at two ends of a filter capacitor Cf of an LLCL filter resonance inhibition branch circuit in parallel, and using a current icd flowing by the resonance inhibition capacitors Cds as a feedback control signal, wherein the feedback control signal is added into a control system of the grid connected inverter after being adjusted by a control damping adjuster. According to the control damping method applied to the resonance inhibition of the LLCL single-phase grid connected inverter, the loss and temperature rising problems of an element damping method are effectively solved, the resonance peak of the LLCL filter in the medium frequency band can be effectively inhibited, the filter performance of the LLCL filter is improved, the grid connected waveform and the harmonic content of the grid connected inverter are effectively improved and the grid connected performances of the single-phase grid connected inverter are improved.

Description

Be applied to the control damped method that LLCL single-phase grid-connected inverter resonance suppresses

Technical field

The invention belongs to the control technology field of grid-connected converter, relate in particular to the control damped method that a kind of LLCL of being applied to single-phase grid-connected inverter resonance suppresses.

Background technology

Voltage controlled grid-connected inverter has advantages of that output current harmonics content is low, power factor regulation and energy in bidirectional flow, volume is little and lightweight, therefore in the fields such as grid-connected system of the regenerative resources such as active power filtering, Electric Drive and solar energy, is widely used.

Combining inverter generally adopts high-frequency PWM modulation technique, may cause a large amount of higher harmonic currents to inject electrical network, can pollute line voltage, even have a strong impact on operation and the work of electric equipment, grid-connected current must be installed just after filtering can meet grid-connected standard, therefore, the selection of the grid-connected filter of combining inverter is particularly important with design.Grid-connected filter construction mainly contains L, LC, LCL and tetra-kinds of forms of LLCL.

Compare with L, LC, LCL mode filter, LLCL filter can better meet the requirement of combining inverter output filtering, and volume is less, and cost is lower.But LLCL filter belongs to Higher-Order Circuit network, has resonance peak at Mid Frequency, easily cause the unstable of closed-loop control system, therefore need to adopt effective resonance braking measure.

Conventional resonance suppressing method is element damped method at present, on the electric capacity of LLCL filter, series/parallel resistive element plays inhibitory action to resonance, this method does not need to increase extra control algolithm, realize simple, but series/parallel resistive element need to consume larger active power, the heat dissipation design of the system of giving is brought certain challenge, the excessive loss of resistive element resistance is larger, reduced generating efficiency, resistive element resistance is less than normal can be cut down because electrical network inductance causes more greatly resonance inhibition when light current net accesses.Meanwhile, add resistive element and can weaken filter to high-frequency harmonic fade performance.

Summary of the invention

The deficiency existing for prior art, the invention provides the control damped method that a kind of LLCL of being applied to single-phase grid-connected inverter resonance suppresses, the present invention suppresses resonance by introducing additional feedback controlled quentity controlled variable, resonance can be effectively suppressed, the larger drawback of element damped method resistive element loss can be avoided again.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

LLCL filtering single-phase grid-connected inverter circuit, comprises the combining inverter and the LLCL filter that are connected, and LLCL filter comprises by the filter inductance L connecting _fwith filter capacitor C _fthe resonance forming suppresses branch road, and resonance suppresses filter capacitor C in branch road _ftwo ends are only parallel with resonance and suppress capacitor C _d.

The control damped method that adopts above-mentioned LLCL filtering single-phase grid-connected inverter circuit, comprising:

(1) build and control damper regulator, guarantee that grid-connected current is consistent with grid-connected current under element damped method;

(2) by grid-connected current i _gwith grid-connected current fiducial value

make poor first difference that obtains, the first difference is through grid-connected current adjuster;

(3) resonance of flowing through suppresses capacitor C _dcurrent i _cdthrough controlling damper regulator, the output of grid-connected current adjuster and control damper regulator is poor, and export pwm pulse generator to;

(4) pwm pulse generator triggers opening or closing of single-phase grid-connected inverter switching device.

Above-mentioned grid-connected current adjuster adopts grid-connected current adjuster transfer function G (s) to realize.

Above-mentioned control damper regulator adopts controls damper regulator transfer function

wherein, s is complex frequency domain variable; C _dfor being parallel to filter capacitor C _fthe resonance at two ends suppresses the capacitance of electric capacity; R _dfor equivalent resistance.

Compared with prior art, the present invention has the following advantages:

1, the filter capacitor C that suppresses branch road in LLCL filter resonance _ftwo ends parallel resonance suppresses capacitor C _d, sample streams suppresses capacitor C through resonance _delectric current make feedback signal, adopt to control damped method equivalence, alternative elements damped method, eliminated the resonance peak of LLCL filter Mid Frequency.

2, compare with the LLCL filter based on element damped method, the present invention can avoid the power dissipation concerns of resistive element, reduces combining inverter distribute heat, thereby reduces combining inverter heat radiation cost, improves electric energy grid connection efficiency simultaneously.

3, adopt grid-connected current i _gouter shroud is controlled, the resonance of flowing through suppresses capacitor C _dthe current i of branch road _cdthe double-current ring control strategy that interior ring is controlled, makes control system increase a current inner loop, can improve the dynamic responding speed of electric current output, realizes better the unity power factor of grid-connected current and voltage on line side.

4, can effectively suppress the harmonic current components in grid-connected current, effectively improve filtering performance and and the network electric energy quality of LLCL filter.

Accompanying drawing explanation

Fig. 1 is LLCL filtering single-phase grid-connected inverter circuit structure diagram of the present invention;

Fig. 2 is LLCL filtering single-phase grid-connected inverter control block diagram of the present invention;

Fig. 3 is the flow chart that method is controlled in damping of the present invention;

Fig. 4 is grid-connected current i _gto combining inverter output voltage u _btransfer function Bode diagram;

Fig. 5 is grid-connected current i in traditional LLCL filtering single-phase grid-connected inverter _gsimulation waveform and spectrum analysis figure, wherein, figure (a) is grid-connected current i _gsimulation waveform, figure (b) is grid-connected current i _gspectrum analysis figure;

Fig. 6 is grid-connected current i in LLCL filtering single-phase grid-connected inverter of the present invention _gsimulation waveform and spectrum analysis figure, wherein, figure (a) is grid-connected current i _gsimulation waveform, figure (b) is grid-connected current i _gspectrum analysis figure.

Embodiment

The symbol relating in accompanying drawing and literary composition and label declaration:

E-combining inverter DC voltage; u _b-combining inverter output voltage; i _b-combining inverter output current; S _a1, S _a2, S _b1, S _b2-power switch pipe; L _b-inverter side reactor; L _g-network reactor; C _f-resonance suppresses branch road filter capacitor; L _f-resonance suppresses branch road filter inductance; i _f-filter inductance L flows through _felectric current; C _d-be parallel to filter capacitor C _fthe resonance at two ends suppresses electric capacity; i _cd-the resonance of flowing through suppresses capacitor C _delectric current; R _dthe resistance element of-control damped method equivalence; u _g-line voltage; i _g-grid-connected current; G (s)-grid-connected current adjuster transfer function; G _rd(s)-control damper regulator transfer function; G _pWM(s)-pwm pulse generator equivalent transfer function.

In prior art, adopt the filter capacitor C that suppresses branch road in LLCL filter resonance _ftwo ends parallel resistance element R _dand capacitor C _delement damped method suppress the feature resonance of LLCL filter, but the present invention is only at filter capacitor C _ftwo ends parallel resonance suppresses capacitor C _d, remove resistive element R _d, in LLCL filter resonance, suppress the filter capacitor C of branch road _ftwo ends parallel resonance suppresses capacitor C _d, and suppress capacitor C with the resonance of flowing through _dcurrent i _cdas feedback control signal, feedback control signal, through controlling the control system that adds combining inverter after damper regulator regulates, is eliminated LLCL filter at the resonance peak of Mid Frequency, thereby improves the output of inverter.

See Fig. 1, LLCL filtering single-phase grid-connected inverter circuit of the present invention comprises single-phase grid-connected inverter and the LLCL filter being connected, and LLCL filter comprises network reactor L _g, inverter side reactor L _b, by the filter inductance L connecting _fwith filter capacitor C _fthe resonance forming suppresses branch road and newly-increased resonance suppresses branch road, and newly-increased resonance suppresses branch road for being connected in parallel on filter capacitor C _fthe resonance at two ends suppresses capacitor C _d.

The present invention adopts current transformer sample streams to suppress capacitor C through resonance _dcurrent i _cdas feedback signal, by controlling damped method equivalence, alternative elements damping R _d, the feature resonance of LLCL filter is suppressed, thus the filtering performance of raising LLCL filter, and then the grid-connected performance of raising single-phase grid-connected inverter.

See Fig. 2～3, damping control method of the present invention adopts grid-connected current i _gouter shroud is controlled, the resonance of flowing through suppresses capacitor C _dthe current i of branch road _cdthe double-current ring control strategy that interior ring is controlled, is specially: by current transformer acquisition stream through network reactor L _ggrid-connected current i _g, by grid-connected current i _gwith grid-connected current fiducial value

poor at the first subtracter, grid-connected current fiducial value

given in advance according to loading demand; Grid-connected current i _gwith grid-connected current fiducial value

difference through grid-connected current adjuster, export the second subtracter to, and suppress capacitor C through controlling the resonance of flowing through of damper regulator effect _dcurrent i _cdpoor in the second subtracter, difference exports pwm pulse generator to, and pwm pulse generator triggers opening or closing of single-phase grid-connected inverter switching device.

In this concrete enforcement, single-phase grid-connected inverter and pwm pulse circuit for generating are the conventional module of power electronics professional domain.Grid-connected current adjuster adopts pi regulator, by transfer function G (s), realizes, and grid-connected current adjuster transfer function G (s) can adopt known transfer function, at this, does not repeat.Control damper regulator by transfer function G _rd(s) realize.

To provide below and control the logical transfer function G of damper regulator _rdand derivation (s):

Suppose each physical quantity relating in the LLCL filtering single-phase grid-connected inverter circuit that adopts element damped method all use subscript " ' " represent, LLCL filtering single-phase grid-connected inverter control block diagram corresponding to element damped method is on the basis of Fig. 2, to remove to control damper regulator by transfer function G _rd(s)), and at resonance suppress capacitor C _dbranch road series resistance element R _d.

According to the LLCL filtering single-phase grid-connected inverter circuit based on element damped method and LLCL filtering single-phase grid-connected inverter circuit control block diagram of the present invention, can obtain the voltage of resonance inhibition branch road in LLCL filter;

$\left\{\begin{array}{c}{u}_f={\mathrm{sL}}_f\·i_f+\frac{1}{{\mathrm{sC}}_d}\·i_d\\ u_f^{\′}={\mathrm{sL}}_f\·i_f^{\′}+(R_d+\frac{1}{{\mathrm{sC}}_d})\·{i_d}^{\′}\end{array}\right.---\left(1\right)$

In formula (1):

U _ffor resonance in LLCL filtering single-phase grid-connected inverter circuit of the present invention suppresses branch voltage;

U _f' be that in the LLCL filtering single-phase grid-connected inverter circuit based on element damped method, resonance suppresses branch voltage;

I _ffor the filter inductance L that flows through in LLCL filtering single-phase grid-connected inverter circuit of the present invention _felectric current;

I _f' be the filter inductance L that flows through in the LLCL filtering single-phase grid-connected inverter circuit based on element damped method _felectric current;

I _cdin order to flow through in LLCL filtering single-phase grid-connected inverter circuit of the present invention, resonance suppresses capacitor C _delectric current;

I _cd' be the resonance inhibition capacitor C of flowing through in the LLCL filtering single-phase grid-connected inverter circuit based on element damped method _delectric current;

S is complex frequency domain variable, is a plural number, is conventional analysis circuit method.

For guaranteeing in element damped method and controlling under damped method, combining inverter grid-connected current is consistent, i.e. i _g=i _g', in conjunction with control block diagram, can obtain u _f=u _f'.

According to control block diagram, can obtain controlling unit should meet:

$\left\{\begin{array}{c}{i}_f=\left\{\right[(i_g^{*}-i_g)G\left(s\right)-G_{\mathrm{Rd}}\left(s\right)i_{\mathrm{cd}}]G_{\mathrm{PWM}}\left(s\right)-u_g\}\·\frac{1}{{\mathrm{sL}}_b}-i_g\\ {{i_f}^{\′}}_{}=\left\{\right[(i_g^{*}-{i_g}^{\′})G\left(s\right)-{i_{\mathrm{cd}}}^{\′}]G_{\mathrm{PWM}}\left(s\right)-u_g\}\·\frac{1}{{\mathrm{sL}}_b}-{i_g}^{\′}\end{array}\right.---\left(2\right)$

In formula (2),

I _gfor the LLCL filtering single-phase grid-connected inverter circuit reactor L of CEInet of the present invention _ggrid-connected current;

I _g' be the LLCL filtering single-phase grid-connected inverter circuit reactor L of CEInet based on element damped method _ggrid-connected current.

Convolution (1)～(2) can be released and control damper regulator transfer function G _rd(s) be:

$G_{\mathrm{Rd}}\left(s\right)=\frac{1}{{\mathrm{sR}}_d{C}_d+1}---\left(3\right)$

In formula (3), R _dfor equivalent resistance, artificially given.

According to adopting resonance to suppress capacitor C _dthe control damped method of current feedback, and in conjunction with LLCL filtering single-phase grid-connected inverter control block diagram, derive the transfer function of combining inverter grid-connected current in the present invention

for:

$G_{i_g\left(s\right)/U_b\left(s\right)}=\frac{{\mathrm{\&beta;}}_3{s}^3+{\mathrm{\&beta;}}_2{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="HDA0000460352420000031.png,HDA0000460352420000041.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+{\mathrm{\&beta;}}_{1}s+1}{{\mathrm{\&alpha;}}_4{s}^4+{\mathrm{\&alpha;}}_3{s}^3+{\mathrm{\&alpha;}}_2{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="HDA0000460352420000031.png,HDA0000460352420000041.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+{\mathrm{\&alpha;}}_{1}s}---\left(4\right)$

In formula (4):

β ₁＝C _dR _d、β ₂＝C _dL _f+C _fL _f、β ₃＝C _dC _fL _fR _d；

α ₁=L _g+L _b、α ₂＝C _dL _gR _d+C _dL _bR _d；

α ₃＝2*C _dL _fL _b+2*C _fL _fL _b+C _dL _gL _b+C _fL _gL _b；

α ₄＝C _dC _f(L _fL _g+L _fL _b+L _gL _b)R _d。

Derive the transfer function of traditional LLCL filtering single-phase grid-connected inverter grid-connected current based on element damped method

for:

$G_{i_g\left(s\right)/U_b\left(s\right)}^{*}=\frac{C_f{L}_f{s}^2+1}{(2*C_f{L}_f{L}_b+C_f{L}_g{L}_b)s^3+(L_g+L_b)s}---\left(5\right)$

Fig. 4 is grid-connected current i _gto combining inverter output voltage u _btransfer function

with

bode diagram, can be used for evaluating the fade performance of controller to combining inverter output harmonic wave, and in figure, solid line is the single-phase grid-connected filter transfer function of LLCL filtering based on controlling damped method

amplitude-versus-frequency curve, dotted line is traditional single-phase grid-connected filter transfer function of LLCL filtering based on element damped method amplitude-versus-frequency curve.As can be seen from the figure, traditional LLC L filter is close at the filtering performance of low-frequency range with LLCL filter of the present invention; But at Mid Frequency, traditional LLC L filter has larger resonance peak, and combining inverter is difficult to play attenuation at the harmonic voltage of this frequency range, even can produce amplification, make to inject the resonance band harmonic current that the electric current of electrical network comprises larger capacity, to electrical network, cause serious harmonic pollution.And LLCL filter of the present invention can well suppress resonance peak, effectively solve resonance problems, and then improved the filtering performance of LLCL filter.

For the feasibility of checking technical solution of the present invention, built a 1kW single-phase full bridge combining inverter, DC voltage 400V, line voltage 220V/50Hz, LLCL filter parameter: L _b=1.2mH, L _g=0.22mH, C _f=2 μ F, C _d=2 μ F, R _d=16.5 Ω, carrier frequency f _c=12kHz.In LLCL filtering single-phase grid-connected inverter in tradition based on element damped method, grid-connected current i _gfig. 5 is shown in waveform and spectrum analysis thereof, and wherein, figure (a) is grid-connected current i _goscillogram, figure (b) is grid-connected current i _gspectrum analysis figure, in the LLCL filtering single-phase grid-connected inverter of tradition based on element damped method, the fundamental voltage amplitude under 50Hz is 2.776, total harmonic distortion is 5.28%.The present invention is based in the LLCL filtering single-phase grid-connected inverter of controlling damped method grid-connected current i _gfig. 6 is shown in waveform and spectrum analysis thereof, and wherein, figure (a) is grid-connected current i _goscillogram, figure (b) is grid-connected current i _gspectrum analysis figure, in LLCL filtering single-phase grid-connected inverter of the present invention, the fundamental voltage amplitude under 50Hz is 2.981, total harmonic distortion is 0.78%.Comparison diagram 5 and 6 is known, the present invention is based on the LLCL filtering single-phase grid-connected inverter of controlling damped method, its grid-connected current i _gwaveform sine obviously promote, aberration rate effectively reduces.

Above embodiment will contribute to those skilled in the art further to understand the present invention, but not limit in any form the present invention.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, can also make some distortion and improvement.These all belong to protection scope of the present invention.

Claims (4)

1.LLCL filtering single-phase grid-connected inverter circuit, comprises the combining inverter and the LLCL filter that are connected, and LLCL filter comprises by the filter inductance L connecting _fwith filter capacitor C _fthe resonance forming suppresses branch road, it is characterized in that:

Described resonance suppresses filter capacitor C in branch road _ftwo ends are only parallel with resonance and suppress capacitor C _d.

2. adopt the control damped method of LLCL filtering single-phase grid-connected inverter circuit claimed in claim 1, comprise grid-connected current i _gwith grid-connected current fiducial value

make poor first difference that obtains, the first difference, through grid-connected current adjuster, is characterized in that:

Build and control damper regulator, guarantee that grid-connected current is consistent with grid-connected current under element damped method; The resonance of flowing through suppresses capacitor C _dcurrent i _cdthrough controlling damper regulator, the output of grid-connected current adjuster and control damper regulator is poor, and export pwm pulse generator to, pwm pulse generator triggers opening or closing of single-phase grid-connected inverter switching device.

3. control damped method as claimed in claim 2, is characterized in that:

Described grid-connected current adjuster adopts grid-connected current adjuster transfer function G (s) to realize.

4. control damped method as claimed in claim 2, is characterized in that:

Described control damper regulator adopts controls damper regulator transfer function

wherein, s is complex frequency domain variable; C _dfor being parallel to filter capacitor C _fthe resonance at two ends suppresses the capacitance of electric capacity; R _dfor equivalent resistance.

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