CN105743123A - LCL-LC based active damping parameter design method for grid-connected system - Google Patents

Abstract

The invention discloses a capacitor voltage feedback LCL-LC based controller parameter and active damping parameter design method for a grid-connected system. The design method is on the basis of taking control delay into consideration, and ensures stable phase margin (PM), gain margin (GM) and error of amplitude (EA) of the system, configures a reasonable parameter selection domain, and chooses reasonable controller parameters and active damping coefficients from the parameter selection domain. By adoption of the method, the LCL-LC filter resonance can be effectively restrained, and the stability and the dynamic response performance of the photovoltaic grid-connected system are both effectively improved.

Description

A kind of grid-connected system active damping Parameters design based on LCL-LC

Technical field

The invention belongs to the new forms of energy distributed power generation in power system and control technical field, meter and one consider system and control to prolong Time, electric network impedance adaptability and the LCL-LC type grid-connected system controller of grid disturbance and active damping Parameters design, make Obtain whole photovoltaic parallel in system and there is stronger stability and robustness.

Background technology

The growing energy resource consumption in the whole world substantially increases the demand of the regenerative resource such as wind-force, solar energy.Grid-connected inverse Become device as the linking equipment of photovoltaic battery panel and electrical network, dynamic between its stability analysis and itself and distributed generation system Response problem is paid close attention to the most widely.But, photovoltaic parallel in system generally uses DC-DC with DC-AC two-stage type inverse Become device, cause in output voltage containing substantial amounts of harmonic component so that inject and comprise a large amount of inverter switching device inside the electric current of electrical network Higher hamonic wave at frequency.Subtract accordingly, it would be desirable to install a low pass filter between photovoltaic combining inverter and electrical network unit The higher hamonic wave of little injection electrical network points of common connection (Point of Common Coupling, PCC).

Tradition L-type wave filter needs bigger filter inductance could meet the resultant distortion rate index of networking electric current, is therefore greatly increased System cost, reduces the response speed of electric current loop.Comparing with L-type wave filter, LCL type wave filter has stronger high frequency Harmonic inhibition capability, but some specific frequency harmonic wave show impedance close to zero.Compared to LCL type wave filter, LLCL Mode filter is in hgher efficiency and control the simplest on the premise of inverter side inductance is identical, but weakens multiple resonance peak needs Multiple LC branch roads, global design can become more complicated.The LCL-LC mode filter of up-to-date proposition combines LCL and LLCL The advantage of mode filter, can bypass the harmonic current at switching frequency, therefore have more preferable filtering performance.Meanwhile, LCL-LC mode filter cost is relatively low, is more suitable for jumbo photovoltaic parallel in system, has very vast potential for future development.

Grid-connected inverting system based on LCL-LC wave filter is too much due to parameter, and each parametric relationship is complicated and more difficult design.Shen Please publication No. be the parameter designing side that the Chinese patent of CN103825438A proposes a kind of LCL-LC mode filter main circuit Method, but to system control parameters and the method for designing of wave filter active damping not mentioned.Additionally, ChenLei Bao et al. exists Entitled " the Step-by-Step controller design for LCL-type that IEEE Transactions on Power Electronics delivers Grid-connected inverter with capacitor-current-feedback active-damping " article propose one utilize electricity The controller Multiple-step mode method of capacitance current feedback, although this most understandable based on LCL type filter system Parameters design, But do not account for controlling the impact of delay on system；Fei Li et al. sends out at IEEE Transactions on Power Electronics Entitled " An LCL-LC filter for grid-connected converter:topology, parameter, the and analysis's " of table Article proposes decoupling LCL-LC mode filter, the parameter designing of LCL-LC mode filter is decomposed into traditional LCL filtering Device parameter designing and the parameter designing of LC branch road, but this method has still pertained only to LCL-LC mode filter main circuit parameter The problem designed and do not solve to control parameter designing.It is therefore desirable to research one meets electrical network practical situation and has strong The LCL-LC type photovoltaic combining inverter active damping Parameters design of robustness.

Summary of the invention

The main object of the present invention is, overcomes the deficiencies in the prior art, proposes one meter and system controls time delay, electric network impedance is fitted The LCL-LC type photovoltaic combining inverter active damping Parameters design of answering property and grid disturbance so that whole grid-connected system System has stronger stability and robustness.

For solving above-mentioned technical problem, concrete technical scheme of the present invention is:

A kind of LCL-LC type photovoltaic grid inverter controller parameter based on capacitance voltage feedback and active damping parameter are provided Method for designing.The method is on the basis of considering to control time delay, ensure that the Phase margin (PM) of system stability, amplitude Nargin (GM) and amplitude error (E_A) it is restraining line, construct rational parameter field, in order to therefrom select rational parameter.Concrete bag Include following steps:

S1, on the basis of considering to control time delay, sets up LCL-LC type photovoltaic combining inverter control based on capacitance voltage feedback The mathematical model of circuit processed；The mathematical model drawn is utilized to obtain ratio resonance (Proportional Resonant, PR) controller Parameter K_pAnd K_rAssociated expression.

S2, sets up photovoltaic synchronization inverter system cut-off frequency f_cWith damping proportional coefficient K_ucMathematical model；To ensure system PM, GM and E of stability_AFor restrictive condition, mathematical model is utilized to find out qualified f_cWith K_ucParameter field, and from In select suitable f_cWith K_ucValue.

S3, according to the f obtained in S2_cWith K_ucValue also utilizes K in S1_pAnd K_rAssociated expression, be finally calculated K_p And K_r。

S4, the parameter designed by verification.

Further, step S1 is set up the number of LCL-LC type photovoltaic combining inverter control circuit based on capacitance voltage feedback Learn model and obtain parameter K of PR controller_pAnd K_rThe concretely comprising the following steps of mathematic(al) representation: grid-connected in LCL-LC type In inverter, the open-loop transfer function of main circuit and the transmission function of PR controller can be expressed as respectively:

$G_L\left(s\right)=\frac{G_c\left(s\right)G_d\left(s\right)K_{PWM}(1+L_r{C}_r{s}^2)}{s^5{L}_1{L}_2{L}_r{C}_r{C}_f+s^3(D_1+D_2+L_r{C}_r{L}_2{K}_{uc}{G}_d(s\left)K_{PWM}\right)+s\left(K_{uc}{G}_d\right(s)K_{PWM}{L}_2+L_1+L_2)}---\left(1\right)$

$G_c\left(s\right)=K_p+K_r\frac{2{\mathrm{\ω}}_{c}s}{s^2+2{\mathrm{\ω}}_{c}s+{\mathrm{\ω}}_0^2}---\left(2\right)$

Wherein, L₁For the inverter side inductance value of LCL-LC type photovoltaic combining inverter, L₂For LCL-LC type photovoltaic grid-connected inversion The net side inductance value of device, L_rFor the series resonant circuit inductance value of LCL-LC type photovoltaic combining inverter, C_fFor LCL-LC type The filtering capacitance of photovoltaic combining inverter, C_rSeries resonant circuit capacitance for LCL-LC type photovoltaic combining inverter.K_PWM For the transmission function of PWM rectifier, may be defined as U_dc/U_tri, wherein U_dcFor DC bus-bar voltage, U_triFor triangular carrier Voltage magnitude.D₁And D₂Expression formula be respectively as follows:

D₁=L₁L₂(C_r+C_f) (3)

D₂=L_rC_r(L₁+L₂) (4)

G_dS () is the control time delay of system, contain computation delay, sampling Continuous Approximation and PWM time delay.Additionally, zeroth order is protected Holder can introduce the time delay process of about 0.5 sampling time, therefore G_dS () can be expressed as:

$G_d\left(s\right)=e^{-1.5s\·T_s}---\left(5\right)$

The steady-state error of combining inverter includes amplitude error E_AWith phase error δ, PR controller can eliminate fundamental frequency f₀ The static error at place, i.e. phase error is negligible, therefore, in fundamental frequency f₀Place, amplitude error E_AWith PR control The transmission function of device can be expressed as:

$E_A=\left|\frac{1}{G_c\left(j2{\mathrm{\πf}}_0\right)}\right|\·\frac{V_g(K_{uc}+1)}{I_{ref}{K}_{PWM}}---\left(6\right)$

G_c(j2πf₀)≈K_p+K_r (7)

Wherein, V_gFor the three-phase line voltage of three-phase rectifier, I_refFor reference current amplitude, K_ucFor controller damping proportional coefficient.

Then can be obtained the mathematic(al) representation of Kr by formula (6) and formula (7) is:

$K_r=\frac{V_g(K_{uc}+1)}{E_A{I}_{ref}{K}_{PWM}}-K_p---\left(8\right)$

When the value of cut-off frequency fc is more than the value of 10 times of fundamental frequencies, PR controller is at the frequency not less than cut-off frequency fc Amplitude can be approximated to be K_p, therefore, K_pCan be expressed as:

$K_P=\frac{2{\mathrm{\πf}}_c(K_{uc}{K}_{PWM}{L}_2+L_1+L_2)}{K_{PWM}}---\left(9\right)$

Further, described step S2 is set up ensure that PM, GM and E of system stability_AFor restrictive condition Cut-off frequency f_cWith damping proportional coefficient K_ucThe concretely comprising the following steps of mathematical model:

In LCL-LC type photovoltaic combining inverter, phase frequency curve is in high-frequency resonant frequency f_r2Place is through-180 °, when frequency is f_r2 Time, magnitude margin GM can be expressed as:

GM=-20lg | G_L(j2πf_r2)| (10)

According to the expression formula of open-loop transfer function in formula (1), convolution (10), the damping proportional coefficient with GM as restrictive condition K_{uc_GM}Can be expressed as:

$K_{uc\_GM}=\frac{32{\mathrm{\π}}^5{f}_{r2}^5{C}_f{C}_r{L}_r{L}_1{L}_2+2{\mathrm{\πf}}_c(L_1+L_2)(4{\mathrm{\π}}^2{f}_{r2}^2{L}_r{C}_r-1){10}^{\frac{GM}{20}}-8{\mathrm{\π}}^3{f}_{r2}^3(D_1+D_2)+2{\mathrm{\πf}}_{r2}(L_1+L_2)}{2{\mathrm{\πf}}_c{K}_{PWM}{G}_d\left(s\right)L_2(1-4{\mathrm{\π}}^2{f}_{r2}^2{L}_r{C}_r){10}^{\frac{GM}{20}}+8{\mathrm{\π}}^3{f}_{r2}^3{L}_r{C}_r{K}_{PWM}{G}_d\left(s\right)L_2-2{\mathrm{\πf}}_{r2}{K}_{PWM}{G}_d\left(s\right)L_2}---\left(11\right)$

Wherein, high-frequency resonant frequency f_r2Expression formula be:

$f_{r2}=\sqrt{\frac{D_1+D_2+\sqrt{D_3+D_4+D_5}}{D_6}}---\left(12\right)$

$D_3=L_1^2{L}_2^2{(C_r+C_f)}^2---\left(13\right)$

$D_4=L_r^2{C}_r^2{(L_1+L_2)}^2---\left(14\right)$

D₅=2L₁L₂L_rC_r(L₁+L₂)(C_r-C_f) (15)

D₆=2L₁L₂C_rC _f(16)

At cut-off frequency f_cPlace, Phase margin PM can be expressed as:

Wherein ω_c=2 π f_c.According to step S1 Chinese style (8) and (9), the damping proportional coefficient with PM as restrictive condition can be obtained K_{uc_PM}:

$K_{uc\_PM}=\frac{G_{EA}{K}_{PWM}{G}_d\left(s\right)-V_g{G}_{PM}+G_{EA}2{\mathrm{\πf}}_c(L_1+L_2)}{(V_g{G}_{PM}-G_{EA}2{\mathrm{\πf}}_c{K}_{PWM}{G}_d(s\left)L_2\right)}---\left(18\right)$

Wherein G_PMAnd G_EARepresent the transmission function relevant with corresponding Phase margin and amplitude error, concrete expression formula respectively As shown in formula (19) and (20):

G_PM=tan (PM+180 °) (ω_c-4π²ω_cL_rC_r) (19)

G_EA=E_AI_ref(π-4π³L_rC_r) (20)

According to the K shown in formula (11) and formula (18)_ucAnd f_cRelational expression, cut-off frequency f can be drawn_cWith damping proportional coefficient K_ucGraph of relation, can ensure that PM, GM and E of system stability_AFor restraining line, construct qualified parameter Territory, and then therefrom choose rational cut-off frequency f_cWith damping proportional coefficient K_uc。

The invention have the benefit that

The present invention proposes that a kind of novel to carry out the LCL-LC type of selection control parameter by structure Reasonable Parameters territory grid-connected inverse Become device and control Parameters design.The method is with PM, GM and E_ADetermine parameter field for restrictive condition, consider control time delay While the control parameter of system and active damping feedback is combined, adjust parameter at any time also according to different parameter fields Optimize systematic function so that total system rate still has Shandong, the strongest ground in the case of electric network impedance change and voltage ripple of power network Rod.

Accompanying drawing explanation

Fig. 1. for using the grid-connected circuit diagram of LCL-LC filtering.

Fig. 2. for the parameter designing flow chart of LCL-LC type photovoltaic combining inverter of the present invention.

Fig. 3. for the control block diagram of the active damping method based on capacitance voltage feedback containing PR.

Fig. 4. the cut-off frequency f that Phase margin of serving as reasons, magnitude margin and amplitude error are limited_cAnd K_ucScope schematic diagram.

Fig. 5. for K_p、K_ucAnd f_cThe relation curve of three.

Fig. 6. for working as E_AWhen taking different value, K_r、K_pAnd K_ucThe relation curve of three.

Fig. 7. for the Bode diagram of LCL-LC type photovoltaic combining inverter transmission function.

Fig. 8. for photovoltaic combining inverter by saltus step semi-load to fully loaded transient emulation oscillogram.

Fig. 9. for the simulation waveform figure under conditions of the damping proportional coefficient different when capacitance voltage feeds back.

Detailed description of the invention

Below in conjunction with the accompanying drawings embodiments of the invention are elaborated: Fig. 1 is the grid-connected of employing LCL-LC mode filter Circuit diagram, the DC-DC booster circuit being connected with photovoltaic battery panel by the voltage increase in DC bus to applicable photovoltaic grid-connected inversion After the reasonable rated voltage of device, H bridge DC-AC inverter utilize MPPT maximum power point tracking (Maximum Power Point Tracking, MPPT) algorithm generation sinusoidal current, sinusoidal current injects electrical network after LCL-LC mode filter filters, at PCC Voltage by phaselocked loop sample-synchronous.The flow chart implementing step is shown in Fig. 2.If Fig. 3 is active resistance based on capacitance voltage feedback The control block diagram of Buddhist nun's method, reference current i_refTransmission function through PR controller, PWM rectifier and main circuit, it is considered to Control time delay, by feedback capacity voltage u_c, finally give the electric current i injecting electrical network_g。

The parameter of form 1 three-phase inverter

Form 2LCL-LC filter parameter

S1, makes triangular carrier voltage magnitude U_triIt is 1, K_PWMFor the transmission function of PWM inverter, can be obtained by following formula:

K_PWM=U_dc/U_tri=650 (1)

According to main circuit relevant parameter and K_PWMValue, try to achieve parameter K of PR controller_pAnd K_rAssociated expression be:

$K_P=\frac{2{\mathrm{\πf}}_c(K_{uc}{K}_{PWM}{L}_2+L_1+L_2)}{K_{PWM}}=\frac{2{\mathrm{\πf}}_c(0.072K_{uc}+0.0006)}{360}---\left(2\right)$

$K_r=\frac{V_g(K_{uc}+1)}{E_A{I}_{ref}{K}_{PWM}}-K_p=\frac{220(K_{uc}+1)}{7200E_A}-K_p---\left(3\right)$

S2, selects rational system stability index and performance indications: 30 °≤PM≤60 °, 3dB≤GM≤12dB, E_A=0.2%.

High-frequency resonant frequency f is tried to achieve according to converter main circuit parameter_r2Value be:

$f_{r2}=\sqrt{\frac{D_1+D_2+\sqrt{D_3+D_4+D_5}}{D_6}}=16kHz---\left(4\right)$

Wherein,

D₁=L₁L₂(C_r+C_f)=1.6 × 10^-12 (5)

D₂=L_rC_r(L₁+L₂)=1 × 10^-13 (6)

$D_3=L_1^2{L}_2^2{(C_r+C_f)}^2=2.56\×{10}^{-24}---\left(7\right)$

$D_4=L_r^2{C}_r^2{(L_1+L_2)}^2=1\×{10}^{-25}---\left(8\right)$

D₅=2L₁L₂L_rC_r(L₁+L₂)(C_r-C_f)=-6.5 × 10^-26 (9)

D₆=2L₁L₂C_rC_f=2.7 × 10^-17 (10)

The transmission function G of Phase margin is tried to achieve according to converter main circuit parameter_PMTransmission function G with amplitude error_EAExpression Formula is respectively as follows:

G_PM=tan (PM+180 °) (ω_c-4π²ω_cL_rC_r)=tan (PM+180 °) (2 π f_c-1.36×10^-9π³f_c) (11)

G_EA=E_AI_ref(π-4π³L_rC_r)=20E_A(π-6.8×10^-10π³) (12)

Draw at PM, GM and E_AK under Xian Zhiing_ucAnd f_cGraph of relation such as Fig. 4, and select the cutoff frequency at A point Rate f_cWith damping proportional coefficient K_ucNumerical value, i.e. f_c=2150Hz, K_uc=-0.28.K_ucAnd f_cGraph of relation can be by formula (13) (14) draw:

$K_{uc\_GM}=\frac{32{\mathrm{\π}}^5{f}_{r2}^5{C}_f{C}_r{L}_r{L}_1{L}_2+2{\mathrm{\πf}}_c(L_1+L_2)(2{\mathrm{\π}}^2{f}_{r2}^2{L}_r{C}_r-1){10}^{\frac{GM}{20}}-8{\mathrm{\π}}^3{f}_{r2}^3(G_1+G_2)+2{\mathrm{\πf}}_{r2}(L_1+L_2)}{2{\mathrm{\πf}}_c{K}_{PWM}{G}_d\left(s\right)L_2(1-4{\mathrm{\π}}^2{f}_{r2}^2{L}_r{C}_r){10}^{\frac{GM}{20}}+8{\mathrm{\π}}^3{f}_{r2}^3{L}_r{C}_r{K}_{PWM}{G}_d\left(s\right)L_2-2{\mathrm{\πf}}_{r2}{K}_{PWM}{G}_d\left(s\right)L_2}---\left(13\right)$

$K_{uc\_PM}=\frac{G_{EA}{K}_{PWM}{G}_d\left(s\right)-V_g{G}_{PM}+G_{EA}2{\mathrm{\πf}}_c(L_1+L_2)}{(V_g{G}_{PM}-G_{EA}2{\mathrm{\πf}}_c{K}_{PWM}{G}_d(s\left)L_2\right)}---\left(14\right)$

S3, the numerical value f that will choose in S2_c=2150Hz, K_uc=-0.28 substitutes into the formula (2) in S1 and (3), tries to achieve K_pAnd K_rPoint It is not:

K_p=0.49 (15)

K_r=40 (16)

S9, checking parameter.If Fig. 5 is K_p、K_ucAnd f_cThe relation curve of three.The numerical value K calculated_p=0.49 just position K in figure_pIn optimized scope, K is described_pDesign is correct.Fig. 6 is to work as E_AWhen taking different value, K_r、K_pAnd K_ucThree's Relation curve.The numerical value K calculated_r=40 are located just at the K in figure_rOptimized scope, illustrates K_rDesign is correct.Utilize this The parameter of bright Parameters design design carries out the Bode diagram such as figure of the transmission function of the LCL-LC type photovoltaic combining inverter drawn Shown in 7.The magnitude margin of this transmission function is 3.78dB, and Phase margin is 45.6 °, and cut-off frequency is 2.08kHz, shows this The LCL-LC grid-connected system inverter control Parameters design based on capacitance voltage feedback that invention is proposed can be good at protecting Demonstrate,prove stability and the dynamic characteristic of whole photovoltaic synchronization inverter system.Meanwhile, when the cut-off frequency of transmission function is with parameter designing The cut-off frequency selected is completely the same, also illustrate that the effectiveness of the Parameters design of the present invention.

For verifying the feasibility of institute of the present invention extracting method, exist according to the LCL-LC type photovoltaic synchronization inverter system shown in Fig. 1 Phantom has been built on Matlab/Simulink.When controlling parameters selection above-mentioned parameter, i.e. K_p=0.49, K_r=40 and K_uc= -0.28, the transient emulation waveform that photovoltaic combining inverter is extremely fully loaded with by saltus step semi-load is respectively as shown in Fig. 8 (a), (b).As seen from the figure, Inject the electric current i of electrical network_gRoot-mean-square value be 20.71A, and reference current value is 20.80A, so the steady-state error of this system is only It is 0.43%, and its overshoot is 5%, adjust time about 1.2ms.It can be seen that this system has good stability And dynamic response characteristic, illustrate that the Parameters design of the present invention is the most effective.

It is illustrated in figure 9 and chooses A point (K_uc=-0.28) B (K and outside Fig. 4 shaded region_uc=-0.34), C (K_uc=-0.37) 2 is K_ucCorresponding simulation result during value, (a), (b) and (c) represent K respectively_ucChoose emulation ripple during A, B, C point value Shape.As seen from the figure, K_ucWhen=-0.28, system is in steady statue；K_ucWhen=-0.34, the waveform of system occurs in that trickle Vibration；K_ucWhen=-0.37, system can not be in steady statue.Thus, it is also possible to find out the parameter utilizing the present invention Method for designing, on the basis of considering to control time delay, utilizes PM, GM and E_AFor restraining line, construct rational parameter field, And the parameter therefrom selected can ensure that stability and the dynamic response characteristic of system completely.

The foregoing is only the detailed description of the invention of the present invention, it will be appreciated by those skilled in the art that and disclosed herein In technical scope, the present invention can carry out various amendment, replace and change, therefore the present invention should not limited by above-mentioned example.

Those of ordinary skill in the art is it will be appreciated that embodiment described here is to aid in the former of the reader understanding present invention Reason, it should be understood that protection scope of the present invention is not limited to such special statement and embodiment.The ordinary skill of this area Personnel can according to these technology disclosed by the invention enlightenment make various other various concrete deformation without departing from essence of the present invention and Combination, these deformation and combination are the most within the scope of the present invention.

Claims (6)

1. a LCL-LC grid-connected system active damping parameter based on capacitance voltage feedback and controller parameter method for designing.

Control method the most according to claim 1, it is characterised in that setting up the mathematical model of LCL-LC type photovoltaic combining inverter control circuit based on capacitance voltage feedback, the open-loop transfer function of its main circuit and the transmission function of PR controller can be expressed as respectively

Wherein, L₁For the inverter side inductance value of LCL-LC type photovoltaic combining inverter, L₂For the net side inductance value of LCL-LC type photovoltaic combining inverter, L_rFor the series resonant circuit inductance value of LCL-LC type photovoltaic combining inverter, C_fFor the filtering capacitance of LCL-LC type photovoltaic combining inverter, C_rFor the series resonant circuit capacitance of LCL-LC type photovoltaic combining inverter, K_PWMFor the transmission function of PWM rectifier, may be defined as U_dc/U_tri, wherein U_dcFor DC bus-bar voltage, U_triFor triangular carrier voltage magnitude, D₁And D₂Expression formula be respectively

D₁=L₁L₂(C_r+C_f) (3)

D₂=L_rC_r(L₁+L₂) (4)

Control method the most according to claim 2, it is characterised in that G_dS () is the control time delay of system, contain computation delay, sampling Continuous Approximation and PWM time delay, additionally, zero-order holder can introduce the time delay process of about 0.5 sampling time, therefore G_dS () can be expressed as

The steady-state error of combining inverter includes amplitude error E_AWith phase error δ, PR controller can eliminate fundamental frequency f₀The static error at place, i.e. phase error is negligible, therefore, in fundamental frequency f₀Place, amplitude error E_ACan be expressed as with the transmission function of PR controller

G_c(j2πf₀)≈K_p+K_r (7)

Wherein, V_gFor the three-phase line voltage of three-phase rectifier, I_refFor reference current amplitude, K_ucFor controller damping proportional coefficient, then can be obtained K by formula (6) and formula (7)_rMathematic(al) representation be

As cut-off frequency f_cValue more than the value of 10 times of fundamental frequencies time, PR controller is not less than cut-off frequency f_cFrequency at amplitude can be approximated to be K_p, therefore, K_pCan be expressed as

In formula, V_gFor three-phase line voltage, I_refFor reference current amplitude, E_AFor systematic steady state error.

Control method the most according to claim 1 and 2, it is characterised in that select rational system stability index and performance indications: 30 °≤PM≤60 °, 3dB≤GM≤12dB, E_A=0.2%, to ensure PM, GM and E of system stability_AFor restrictive condition, set up photovoltaic synchronization inverter system cut-off frequency f_cWith damping proportional coefficient K_ucMathematical model.

The most according to claim 4, it is characterised in that in LCL-LC type photovoltaic combining inverter, phase frequency curve is in high-frequency resonant frequency f_r2Place is through-180 °, when frequency is f_r2Time, magnitude margin GM can be expressed as

GM=-20lg | G_L(j2πf_r2)| (10)

According to the expression formula of open-loop transfer function in formula (1), convolution (10), obtain the damping proportional coefficient K with GM as restrictive condition_{uc_GM}For

Wherein, high-frequency resonant frequency f_r2Expression formula be

Wherein

D₅=2L₁L₂L_rC_r(L₁+L₂)(C_r-C_f) (15)

D₆=2L₁L₂C_rC_f (16)

At cut-off frequency f_cPlace, Phase margin PM can be expressed as

Wherein ω_c=2 π f_c, the damping proportional coefficient K with PM as restrictive condition can be obtained_{uc_PM}

Wherein G_PMAnd G_EARepresent the transmission function relevant with corresponding Phase margin and amplitude error respectively, shown in concrete expression formula such as formula (19) and (20)

G_PM=tan (PM+180 °) (ω_c-4π²ω_cL_rC_r) (19)

G_EA=E_AI_ref(π-4π³L_rC_r) (20)

According to the K shown in formula (11) and formula (18)_ucAnd f_cRelational expression, cut-off frequency f can be drawn_cWith damping proportional coefficient K_ucGraph of relation, can ensure that PM, GM and E of system stability_AFor restraining line, construct qualified parameter field, and then therefrom choose rational cut-off frequency f_cWith damping proportional coefficient K_uc。

The most according to claim 5, it is characterised in that the f of acquisition_cWith K_ucThe K that value obtains after substituting into_pAnd K_rAssociated expression, be finally calculated PR controller parameter K_pAnd K_r, the parameter obtained is verified, verifies grid-connected inverting system PM, GM and f_cWhether meeting performance indications, if meeting grid-connected requirement, verification is passed through, and parameter designing completes；If systematic function is unsatisfactory for requirement, do not reach grid-connected conditions, return and reselect performance indications PM, GM and E_A, then be optimized, until parameter designing completes.