CN101710718A - Working method of grid-connected photovoltaic power generation system - Google Patents

Abstract

The invention relates to a grid-connected photovoltaic power generation system which consists of a phase-locked loop, a current transformator, a repetitive controller and a PWM generator. The invention also relates to a working method of the grid-connected photovoltaic power generation system, comprising the steps of: (1) acquiring network voltage phase position and grid-connected current; (2) designing the repetitive controller; (3) setting the modulation ratio, switch frequency and sampling times within unit cycle of an inverter; and (4) sending the output of the repetitive controller into the PWM generator, completing the switch operation for the inverter, and finally finishing grid-connected control for solar photovoltaic power generation. The invention has the advantages that the output waveform is greatly improved, the grid-connected current harmonic content is low, the total harmonic distortion is less than 1%, dc component is not contained, the power factor of the inverter is high, all indexes such as electrical energy quality and the like is in accordance with the requirement of grid-connected engineering technology, and the invention has application prospect.

Description

A kind of method of work of grid-connected photovoltaic power generation system

(1) technical field

The present invention is used for solar grid-connected photovoltaic generation industry, belongs to the method for work of power electronic technology and control theory crossing domain, particularly a kind of grid-connected photovoltaic power generation system.

(2) background technology

Along with the aggravation of world energy sources anxiety and environmental pollution, the utilization of renewable resource gets most of the attention.And solar energy is general, abundant with it, cleaning becomes the focus that people utilize.Now, solar energy is finished from replenishing the transition of the energy to alternative energy source.At present, the solar energy utilization mainly contains two kinds of forms: heat utilization and photovoltaic generation utilization.Wherein, being under the jurisdiction of the grid-connected of generating utilization is the development trend that solar energy utilizes.

Photovoltaic system mainly is made of solar battery array and necessary Technics of Power Electronic Conversion equipment two parts.In grid-connected photovoltaic system, the tracking Control of electrical network is directly connected to the quality of power supply of output and the operational efficiency of system, be the core and the key problem in technology of system.The various control methods of using respectively have self-defect now, can not take into account response speed, control index, system design and stability.For example: PID control dynamic response is fast, but the output waveform distortion is serious; Though dead-beat control method is control in real time, current response is fast, and the output voltage electric current does not contain specific subharmonic, and the switching frequency of power device is unfixing, can cause the current spectrum broad, may cause indirect Harmonic Interference, causes the filter circuit difficult design.Sliding-Mode Control Based shows the insensitivity of system parameter variations and load disturbance and robustness and has good dynamic characteristic.But Sliding-Mode Control Based exists desirable sliding formwork diverter surface to be difficult to choose, control the weakness such as influence that effect is subjected to sample frequency, it also exists in high dither phenomenon and the design need know the boundary of systematic uncertainty parameter and disturbance, and shake such as can't accurately locate at system.In view of this, employing has inhibiting repetition control technology to design net-connected controller to periodic disturbance, on the one hand it can eliminate the wave distortion that the dead time effect by inverter self causes, it also has certain inhibitory action to the harmonic wave that nonlinear-load causes simultaneously.So designing combining inverter based on the repetition control technology has certain prospect.

(3) summary of the invention

The object of the present invention is to provide a kind of method of work of grid-connected photovoltaic power generation system, it makes above-mentioned said employing have inhibiting repetition control technology to design net-connected controller to periodic disturbance and becomes a reality, not only the direct current that photovoltaic cell can be sent is converted to alternating current, and can to frequency, voltage, electric current, phase place, meritorious and idle, etc. control, having determined to send into the quality of power supply of electrical network and concerned the system capacity conversion efficiency, is a kind of new technology that is used for solar grid-connected photovoltaic generation industry.

Technical scheme of the present invention: a kind of grid-connected photovoltaic power generation system is characterized in that it is made up of phase-locked loop, current transformer, repetitive controller and PWM generator; The output of said current transformer and phase-locked loop is connected two inputs of repetitive controller respectively, and the output of repetitive controller inserts the PWM generator, and four road IGBT control input ends are received in the output of PWM generator.

Above-mentioned said phase-locked loop is to obtain electric network voltage phase and it is sent into an input of repetitive controller, it is the inner and controlled required reference signal of standard sine signal multiplication at controller, make inverter output voltage, frequency, phase place must be consistent with line voltage, accomplish to be incorporated into the power networks with unity power factor.

Above-mentioned said current transformer is used to detect the size of grid-connected current and it is considered as the other end that external disturbance is input to repetitive controller, in the hope of reducing systematic error.

A kind of method of work of grid-connected photovoltaic power generation system is characterized in that being made of following steps:

(1) at first gather electric network voltage phase and grid-connected current: with the multiply each other reference signal of controlled input of the sine wave of the voltage-phase that obtains and standard 50Hz, it and the grid-connected current that is regarded as disturbing signal insert repetitive controller as input together; Through the just modulation signal of controlled inverter of repetitive controller internal arithmetic, this signal is sent in the PWM generator, with triangular wave relatively, produce four road signals that drive inverter.This is incorporated into the power networks and carries out under input power and this prerequisite of power output balance, guarantees system stability work thus;

(2) design repetitive controller: traditional control method is mixed use with repetitive control, conventional state space method of average modeling is adopted in the inverter modeling that contains filter, on this model based, design repetitive controller, the final accurate control that realizes combining inverter.

(3) modulation ratio m, the switching frequency f of setting inverter _cAnd the value of the interior sampling number N of unit period, wherein, U _01mBe inverter output fundamental voltage amplitude, U _dBe the inverter direct-flow side magnitude of voltage

U _01m≈m×U _d

$N=\frac{f_c}{50}$

(4) the PWM generator is sent in the output of repetitive controller, the latter will produce four road IGBT drive signals and finish switching manipulation to inverter, the final realization becomes alternating current to send into electrical network the dc inverter of photovoltaic cell output, finishes the control of being incorporated into the power networks of solar energy power generating.

The design repetitive controller may further comprise the steps in the above-mentioned said step (2):

I. at first row write out the inverter transfer function P (z) that contains filter.To the inverter that has second order filter state space method of average modeling, the dead resistance of supposing inductance is r, and then the transfer function of filter is

$\mathrm{\Φ}\left(s\right)=\frac{\frac{1}{\mathrm{sc}}}{\mathrm{sL}+r+\frac{1}{\mathrm{sc}}}$

$=\frac{1}{{{\mathrm{<figure-callout\; id="2"\; label="Lc\; S"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">Lc</figure-callout>}}_S}^2+\mathrm{rcs}+1}$

To just obtain P (z) behind the following formula Z-transformation, conversion method is: num=[1], den=[L*C, r*C, 1], [numd dend]=c2dm (num, den, 5e-5, ' zoh ').

Ii. design of Compensator

Compensator is provided with at controlling object P (z), and its target is to make controlled object zero phase-shift, unit gain, and to high-frequency signal decay as far as possible, its form is: c (z)=K _rz ^kc ₁(z) c ₂(z).At the bode of the preceding controlled device P (z) that will draw earlier of design c (z) figure, come design compensation device C (z) according to bode figure.

C ₁(z) be a second-order low-pass filter, it will satisfy two conditions: the first, and damping ratio ξ is greater than 1; The second, cut-off angular frequency ω _cWill with the resonance angular frequency ω of P (z) _rQuite.Like this, C ₁Transfer function just can write out into:

$c_1\left(s\right)=\frac{{\mathrm{\&omega;}}_r^2}{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+2\&times;\mathrm{\&xi;}\&times;{\mathrm{\&omega;}}_r+{\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}$

At last this formula is carried out Z-transformation, transform method is the same.

C ₁(z) resonance peak that can not full remuneration P (z), this moment, remainder was by C ₂(z) finish, its form is:

$C_2\left(z\right)=\frac{\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i{z}^i+\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i{z}^{-i}}{2\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i+a_0}$

Finally to make C ₂(z) first trough is in the resonance angular frequency ω of P (z) _rNear.

Iii.Z ^kBe used for compensating the phase place of controlled system, the value of k be one greater than 0 natural number.At last by K _rFinish gain compensation, K _rValue be greater than zero less than one, the same K of value of Q (z) _rAbove several steps of process are finished design of Compensator.

Superiority of the present invention: build the emulation check that system model carries out at the design and show, using the grid-connected system that repeats control technology improves a lot aspect output waveform, the grid-connected current harmonic content is little, and total percent harmonic distortion is less than 1%, and does not contain flip-flop.From the effect that is incorporated into the power networks, inverter power factor height, power quality indexes meets the engineering requirement of being incorporated into the power networks.So, more than reasonable in design feasible, big than the conventional apparatus advantage, certain application prospect is arranged.

(4) description of drawings

Fig. 1 is the integrated circuit structural representation of the related a kind of grid-connected photovoltaic power generation system of the present invention.

Fig. 2 is the repetition control circuit structural representation of the inverter in the related a kind of grid-connected photovoltaic power generation system of the present invention.

Fig. 3 is the inverter circuit structural representation in the related a kind of grid-connected photovoltaic power generation system of the present invention.

Fig. 4 is the penalty function bode figure of design of Compensator in the step (2) in the method for work of the related a kind of grid-connected photovoltaic power generation system of the present invention.

Fig. 5 repeats control circuit internal structure schematic diagram for the combining inverter of making during the design repetitive controller in the embodiment in the method for work of the related a kind of grid-connected photovoltaic power generation system of the present invention under MATLAB.

Fig. 6 uses schematic diagram for photovoltaic combining inverter in the embodiment in the method for work of the related a kind of grid-connected photovoltaic power generation system of the present invention.

R is a sinusoidal reference signal among the figure, and y is an inverter output voltage, and e is an error signal, and d is periodic disturbance, and Z-N is the cycle delay link, and N is the sampling number of a primitive period, and C (z) is for repeating the compensator of control loop, and P (z) is a controlling object.

Get L=0.47mh, c=20 μ F, the dead resistance r=0.9 Ω of inductance

(5) embodiment:

Embodiment: a kind of grid-connected photovoltaic power generation system (see figure 1) is characterized in that it is made up of phase-locked loop, current transformer, repetitive controller and PWM generator; The output of said current transformer and phase-locked loop is connected two inputs of repetitive controller respectively, and the output of repetitive controller inserts the PWM generator, and four road IGBT control input ends are received in the output of PWM generator.

Said phase-locked loop is to obtain electric network voltage phase and it is sent into an input of repetitive controller, it is the inner and controlled required reference signal of standard sine signal multiplication at controller, make inverter output voltage, frequency, phase place must be consistent with line voltage, accomplish to be incorporated into the power networks with unity power factor.

Said current transformer is used to detect the size of grid-connected current and it is considered as the other end that external disturbance is input to repetitive controller, in the hope of reducing systematic error.

A kind of method of work of grid-connected photovoltaic power generation system is characterized in that being made of following steps:

Two-stage type photovoltaic generating system with Fig. 1 form is an example, selects Pmppt=300W for use, Uoc=80V, Isc=5.9A, Umppt=62V, the photovoltaic module of Imppt=4.8A.DC converter is finished maximal power tracing and output voltage adjustment among the figure, makes that inverter direct-flow side voltage is 440V.

(1) at first gathers electric network voltage phase and grid-connected current.With the multiply each other reference signal of controlled input of the sine wave of the voltage-phase that obtains and standard 50Hz, it and the grid-connected current that is regarded as disturbing signal insert repetitive controller as input together.

(2) design repetitive controller.Shown in the repetitive controller internal structure (see figure 2) that is designed.

I. at first row write out inverter transfer function P (z) (see figure 3) that contains filter.To the inverter that has second order filter state space method of average modeling, get L=0.47mH, the dead resistance r=0.9 Ω of c=20 μ F inductance, then the transfer function of filter is

$\mathrm{\&Phi;}\left(s\right)=\frac{\frac{1}{\mathrm{sc}}}{\mathrm{sL}+r+\frac{1}{\mathrm{sc}}}$

$=\frac{1}{{{\mathrm{<figure-callout\; id="2"\; label="Lc\; S"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">Lc</figure-callout>}}_S}^2+\mathrm{rcs}+1}$

$=\frac{1}{9.4\&times;{10}^{-9}s+1.8\&times;{10}^{-5}s+1}$

P (z) will just be obtained behind the following formula Z-transformation

$p\left(z\right)=\frac{0.126z+0.122}{z^2-1.6606z+0.9087}$

Ii. design of Compensator

Compensator is provided with at controlling object P (z), and its target is to make controlled object zero phase-shift, unit gain, and to high-frequency signal decay as far as possible, its form is: c (z)=K _rz ^kc ₁(z) c ₂(z).Bode figure (see figure 4) at the preceding controlled device P (z) that will draw earlier of design c (z).

C ₁(z) be a second-order low-pass filter, it will satisfy two conditions: the first, and damping ratio ξ is greater than 1; The second, cut-off angular frequency ω _cWill with the resonance angular frequency ω of P (z) _rQuite.Here ξ gets 1.6, C ₁Transfer function just can write out into:

$c_1\left(s\right)=\frac{{\mathrm{\&omega;}}_r^2}{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+2\&times;\mathrm{\&xi;}\&times;{\mathrm{\&omega;}}_r+{\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}$

$c_1\left(s\right)=\frac{{10300}^2}{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+2\&times;1.6\&times;10300+{10300}^2}$

At last this formula is carried out Z-transformation

$c_1\left(z\right)=\frac{0.0805z+0.0468}{z^2-1.0652z+0.1924}$

C ₁(z) resonance peak that can not full remuneration P (z), this moment, remainder was by C ₂(z) finish, its form is:

$C_2\left(z\right)=\frac{\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i{z}^i+\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i{z}^{-\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="H2009102289528E00011.png,H2009102289528E00022.png"\; state="\{\{state\}\}">i</figure-callout>}}}{2\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i+a_0}$

Finally make C ₂(z) first trough is in the resonance angular frequency ω of P (z) _rNear.Here

Get $c_2\left(z\right)=\frac{z^6+2+z^{-6}}{4}$

Iii.Z ^kBe used for compensating the phase place of controlled system, the value of k be one greater than 0 natural number, be taken as 6 here.At last by K _rFinish gain compensation, K _rValue be greater than zero less than one, the same K of value of Q (z) _rThis routine K _r=Q (z)=0.9, above several steps of process are finished design of Compensator.

(3) modulation ratio m=0.8, the switching frequency f of setting inverter _cSampling number N=200 in=10KHz and the unit period, wherein, U _01mFor inverter output fundamental voltage amplitude is 311V, U _dBe inverter direct-flow side voltage 440V.

U _01m≈m×U _d

$N=\frac{f_c}{50}$

(4) the PWM generator is sent in the output of repetitive controller, the latter will produce four road IGBT drive signals and finish switching manipulation to inverter, the final realization becomes alternating current to send into electrical network the dc inverter of photovoltaic cell output, finishes the control of being incorporated into the power networks of solar energy power generating.

More than four designs of finishing repetitive controller, inverter control chart (see figure 5).With the combining inverter output current as disturbance, with line voltage same frequency, synchronous sinusoidal wave as with reference to signal, the previous designs content obtains final design drawing (see figure 6) in addition.Wherein, the control that repeats of inverter replaces with subsystem.Find by emulation: the grid-connected current harmonic content is little, and total percent harmonic distortion is less than 1%, and does not contain flip-flop.From the effect that is incorporated into the power networks, inverter power factor 97.9%, power quality indexes meets the engineering requirement of being incorporated into the power networks.

Claims (5)

1. grid-connected photovoltaic power generation system is characterized in that it is made up of phase-locked loop, current transformer, repetitive controller and PWM generator; The output of said current transformer and phase-locked loop is connected two inputs of repetitive controller respectively, and the output of repetitive controller inserts the PWM generator, and four road IGBT control input ends are received in the output of PWM generator.

2. according to the said a kind of grid-connected photovoltaic power generation system of claim 1, it is characterized in that said phase-locked loop is to obtain electric network voltage phase and it is sent into an input of repetitive controller, it is the inner and controlled required reference signal of standard sine signal multiplication at controller, make inverter output voltage, frequency, phase place must be consistent with line voltage, accomplish to be incorporated into the power networks with unity power factor.

3. according to the said a kind of grid-connected photovoltaic power generation system of claim 1, it is characterized in that said current transformer is used to detect the size of grid-connected current and it is considered as the other end that external disturbance is input to repetitive controller, in the hope of reducing systematic error.

4. the method for work of an above-mentioned said grid-connected photovoltaic power generation system is characterized in that being made of following steps:

(1) at first gather electric network voltage phase and grid-connected current: with the multiply each other reference signal of controlled input of the sine wave of the voltage-phase that obtains and standard 50Hz, it and the grid-connected current that is regarded as disturbing signal insert repetitive controller as input together; Through the just modulation signal of controlled inverter of repetitive controller internal arithmetic, this signal is sent in the PWM generator, with triangular wave relatively, produce four road signals that drive inverter.This is incorporated into the power networks and carries out under input power and this prerequisite of power output balance, guarantees system stability work thus;

(2) design repetitive controller: traditional control method is mixed use with repetitive control, conventional state space method of average modeling is adopted in the inverter modeling that contains filter, on this model based, design repetitive controller, the final accurate control that realizes combining inverter.

(3) modulation ratio m, the switching frequency f of setting inverter _cAnd the value of the interior sampling number N of unit period, wherein, U _01mBe inverter output fundamental voltage amplitude, U _dBe the inverter direct-flow side magnitude of voltage

U _01m≈m×U _d

$N=\frac{f_c}{50}$

(4) the PWM generator is sent in the output of repetitive controller, the latter will produce four road IGBT drive signals and finish switching manipulation to inverter, the final realization becomes alternating current to send into electrical network the dc inverter of photovoltaic cell output, finishes the control of being incorporated into the power networks of solar energy power generating.

5. according to the method for work of the said a kind of grid-connected photovoltaic power generation system of claim 4, it is characterized in that the design repetitive controller may further comprise the steps in the said step (2):

I. at first row write out the inverter transfer function P (z) that contains filter.To the inverter that has second order filter state space method of average modeling, the dead resistance of supposing inductance is r, and then the transfer function of filter is

$\mathrm{\&Phi;}\left(s\right)=\frac{\frac{1}{\mathrm{sc}}}{\mathrm{sL}+r+\frac{1}{\mathrm{sc}}}$

$=\frac{1}{{{\mathrm{Lc}}_S}^2+\mathrm{rcs}+1}$

To just obtain P (z) behind the following formula Z-transformation, conversion method is: num=[1], den=[L*C, r*C, 1], [numd dend]=c2dm (num, den, 5e-5, ' zoh ');

Ii. design of Compensator

Compensator is provided with at controlling object P (z), and its target is to make controlled object zero phase-shift, unit gain, and to high-frequency signal decay as far as possible, its form is: c (z)=K _rz ^kc ₁(z) c ₂(z).At the bode of the preceding controlled device P (z) that will draw earlier of design c (z) figure, come design compensation device C (z) according to bode figure.

C ₁(z) be a second-order low-pass filter, it will satisfy two conditions: the first, and damping ratio ξ is greater than 1; The second, cut-off angular frequency ω _cWill with the resonance angular frequency ω of P (z) _rQuite.Like this, C ₁Transfer function just can write out into:

$c_1\left(s\right)=\frac{{\mathrm{\&omega;}}_r^2}{s^2+2\&times;\mathrm{\&xi;}\&times;{\mathrm{\&omega;}}_r+{\mathrm{\&omega;}}_r^2}$

At last this formula is carried out Z-transformation, transform method is the same.

C ₁(z) resonance peak that can not full remuneration P (z), this moment, remainder was by C ₂(z) finish, its form is:

$C_2\left(z\right)=\frac{\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i{z}^i+\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i{z}^{-i}}{2\underset{i=0}{\overset{m}{\mathrm{\&Sigma;}}}{a}_i+a_0}$

Finally to make C ₂(z) first trough is in the resonance angular frequency ω of P (z) _rNear;

Iii.Z ^kBe used for compensating the phase place of controlled system, the value of k be one greater than 0 natural number.At last by K _rFinish gain compensation, K _rValue be greater than zero less than one, the same K of value of Q (z) _rAbove several steps of process are finished design of Compensator.

Images