CN103219747A - Method for realizing high efficiency and high reliability of photovoltaic grid-connected micro inverted power supply - Google Patents
Method for realizing high efficiency and high reliability of photovoltaic grid-connected micro inverted power supply Download PDFInfo
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Abstract
The invention discloses a method for realizing high efficiency and high reliability of a photovoltaic grid-connected micro inverted power supply. The current is controlled through two-phase complementation. The two-phase output current is superposed, and then the energy is transmitted to the power grid. According to the method, an electrolytic capacitor is not required, the output voltage or the operating voltage at two ends of a photovoltaic cell panel is stable in a relatively stable external environment under the condition that the illumination is stable, implementation of maximum power point tracking (MPPT) is guaranteed, the output power of the cell panel is maximized, and high reliability and high conversion efficiency can be realized.
Description
Technical field
The present invention relates to solar energy power generating, the miniature inverter of photovoltaic power generation grid-connecting especially, specifically a kind of method that realizes grid-connected miniature inverter high efficiency and high reliability.
Background technology
At present, in the new energy development field, solar energy power generating is present main developing direction.And the low conversion efficiency of solar cell itself is one of the principal element that can not popularize at present of restriction photovoltaic generation.As an important ring of solar photovoltaic generation system, the research and development that high conversion efficiency, high reliability are incorporated into the power networks with inverter have been subjected to extensive attention in recent years.Wherein, photovoltaic power generation grid-connecting can promote the extensive use based on space solar generatings such as building roof, body of wall and electric wire are dried with the very suitable middle-size and small-size solar power system of miniature inverter.But the exploitation with miniature inverter of being incorporated into the power networks also exists and improves conversion efficiency and improve the conflicting key technical problem that waits of reliability, and purpose of the present invention will solve this technical barrier exactly.
There is the peak power output working point in photovoltaic cell, and the peak power output working point changes with environmental factors such as illumination.For realizing that peak power output point is followed the tracks of (MPPT) and power output maximizes, the voltage at cell panel two ends needs constant relatively.This load current that just the requires cell panel just input current of inverter is constant.But, the electric current that high efficiency single-stage inverter outputs to electrical network need and line voltage with homophase frequently, promptly the power output of inverter is sinusoidal wave variation.If ignore the energy loss of inverter transfer process, the power output of photovoltaic cell should equate with the inverter power output.This output voltage that just the causes photovoltaic cell just input voltage of inverter is that sinusoidal fluctuation changes, and MPPT can not be realized.In order to solve this contradiction, the simplest way is the Da Rong value capacitor C in that is connected in parallel at the two ends of cell panel, as shown in Figure 1.For being easy to realize MPPT, capacitance C required and that connect is provided by following formula:
Wherein, Pdc is the photovoltaic battery panel peak power output, and Udc is the average voltage on the electric capacity, and f is the AC network frequency, and Δ u is voltage fluctuation peak～peak value that maximum can be allowed.For typical 200 watts of power output photovoltaic modules, Udc=35V supposes Δ u=2V, and so, in order to obtain the utilance of photovoltaic cell 98%, minimum capacitance is 7.6mF.For big capacitance like this, have only with electrochemical capacitor usually and realize.Yet electrochemical capacitor has only the longest 7000 hours life-span at 105 ° of C operational environments, is 16000 hours when 75 ° of C.During cell panel and miniature inverter (AC module) work is to be exposed under the environment at sunshine, the heat that self produces when adding inverter work, and it is normal that its ambient temperature reaches 75 ° of C.Calculated in 8 hours if work every day by photovoltaic system, electrochemical capacitor life-span of 75 ° of C environmental works less than 6 years, far can not be complementary with the life-span of photovoltaic cell more than 20 years itself.Assessment is based on the average time (MTBF) between losing efficacy average time (MTFF) and lost efficacy for the first time to the inverter reliability of products.At present, be applied to the miniature inverter life of product of AC module in 5～10 years.Be that MTFF is 5 years, MTBF is 10 years.Using long-life thin-film capacitor, to replace electrochemical capacitor should be to prolong the inverter effective way in useful life.Because hull cell has 80000 hours life-span under same working temperature.Calculated in 8 hours by working every day, its life-span can reach 27 years.Yet problem is not so simple.Because the unit appearance value of thin-film capacitor is lower,, almost be unpractical with thin-film capacitor for the electric capacity of mF level from aspects such as cost and volumes.
Summary of the invention
The objective of the invention is at the problems referred to above, propose a kind of method that realizes grid-connected miniature inverter high efficiency and high reliability, carry out Current Control by the two-phase complementation.
Technical scheme of the present invention is:
A kind of method that realizes grid-connected miniature inverter high efficiency and high reliability superposes the back to the electrical network transmission of power with two-phase output current Iout1 and Iout2, specifically may further comprise the steps:
(a), photovoltaic battery panel is I0 at the output current of peak power output point, the load current of photovoltaic battery panel is set to two-phase I1 and I2, and its size is represented with following formula:
I1=I0*|sin(2πft)|...(2) I2=I0*[1-|sin(2πft)|]...(3)
Wherein, f is a mains frequency, and t is the time, and absolute value representation I1 and I2 are not less than zero, and sinusoidal wave negative half period is become positive half cycle, and promptly the frequency of I1 and I2 is 2f, and the total load current of cell panel is
I1+I2=I0*[|sin(2πft)|+1-|sin(2πft)|]=I0...(4)
(b), at the output of photovoltaic battery panel thin-film capacitor in parallel than low-capacitance, in one-period T, I1 is carried out integration, obtain
I1*T=2I0*T/π=0.637I0*T...(5)
Promptly the first phase transmission current I1 accounts for 63.7% of total transmission current, and I2 accounts for 36.3%, and I2 has only 57% of I1.(c), in one-period T, from relation of equal quantity, I2 is also represented with SIN function, promptly
I2=(π/2-1)*I0|sin(2πft)|=0.57I0|sin(2πft)|...(6)
(d), the control signal reference voltage V sw1 of I1 obtains according to grid ac voltage, is 2 times of mains frequency, and in the positive and negative half period of electrical network and the line voltage same-phase, the control signal reference voltage of I2 and Vsw1 complementation, promptly
Vsw1=Vm*|sin(2πft)|...(8) Vsw2=Vm*[1-|sin(2πft)|]...(9)
Wherein Vm is the value that the electrical network crest voltage dwindles several times, and f is a mains frequency;
Because I1 and line voltage homophase and present the half-sinusoid waveform, the inverter first phase output current Iout1 is delivered directly to electrical network by the switch control identical with mains frequency, positive-negative half-cycle each with 2 switches;
(e), the second phase output current Iout2 is stored on the capacitor C link of low-capacitance, again by HF switch step-down mode with first mutually output current Iout1 superpose, realize to the electrical network transmission of power.According to (6) and (8) formula, the electrorheological of Clink being gone up storage changes the half-sinusoid electric current with the frequency homophase with Iout1 into, and promptly the second phase output current conversion high frequency SPWM switch control reference voltage from Clink is
Vsb=0.57Vsw1...(10);
Two-phase output current Iout1 and Iout2 are superposeed the back to the electrical network transmission of power.
Beneficial effect of the present invention:
The present invention is by superposeing the back to the electrical network transmission of power to the two-phase output current.This method does not need to use electrochemical capacitor, can realize high reliability and high conversion efficiency simultaneously.
Description of drawings
Fig. 1 is that traditional single-stage is changed miniature inverter topology schematic diagram.
Fig. 2 is the topological structure schematic diagram of the miniature inverter of two-phase complementary current that adopts of the present invention.
Embodiment
The present invention is further illustrated below in conjunction with drawings and Examples.
As shown in Figure 2, a kind of photovoltaic battery panel of establishing is I0 at the output current of peak power output point, if the load current of photovoltaic battery panel is set to two-phase I1 and I2, and its size is represented with following formula:
I1=I0*|sin(2πft)|...(2) I2=I0*[1-|sin（2πft）|]...(3）
Wherein, f is a mains frequency, and t is the time, and absolute value representation I1 and I2 become positive half cycle to sinusoidal wave negative half period never less than zero, and promptly the frequency of I1 and I2 is 2f.So, the total load current of cell panel is
I1+I2=I0*[|sin(2πft)|+1-|sin(2πft)|]=I0...(4)
The output current of photovoltaic battery panel and its load current equate in other words, have guaranteed that its operating voltage is constant and the time irrelevant.Therefore, in theory, even the photovoltaic battery panel two ends are without shunt capacitance, its output voltage or operating voltage also are being stable as illumination under the stable situation under the metastable external environment condition, this just guaranteed MPPT be easy to realize and the cell panel power output maximizes.And in fact because I1 and I2 are discontinuous high-frequency pulse currents, the output of photovoltaic battery panel also needs thin-film capacitor than low-capacitance in parallel.If in one-period T, I1 is carried out integration, just can obtain
I1*T=2I0*T/π=0.637I0*T...(5)
Promptly the first phase transmission current I1 accounts for 63.7% of total transmission current, and I2 accounts for 36.3%, and I2 has only 57% of I1.If in one-period T, from relation of equal quantity, I2 is also represented with SIN function, promptly
I2=(π/2-1)*I0|sin(2πft)|=0.57I0|sin(2πft)|...(6)
If conventional method shown in Figure 1, the load of cell panel is single-phase sinusoidal current I1=Isin, and the mean value in one-period will equal I0.So:
Isin=1.57I0|sin(2πft)|…(7)
The control signal reference voltage V sw1 of I1 obtains according to grid ac voltage among the present invention, is 2 times of mains frequency, and in the positive and negative half period of electrical network and the line voltage same-phase.And the control signal reference voltage of I2 and Vsw1 complementation, promptly
Vsw1=Vm*|sin(2πft)|...(8) Vsw2=Vm*[1-|sin(2πft)|]...(9)
Wherein Vm is the value that the electrical network crest voltage dwindles several times, and f is a mains frequency.That is to say that Vsw1 is big in each cycle, Vsw2 is just little, and vice versa.At any time, Vsw1+Vsw2=Vm is invariable.Because I1 and line voltage homophase and be the half-sinusoid waveform, the inverter first phase output current Iout1 just can control by the switch identical with mains frequency and be delivered directly to electrical network so.But second mutually can not realize so that then its output current need be stored in earlier on the capacitor C link of a low-capacitance, again by HF switch step-down mode with first mutually output current Iout1 superpose, realize to the electrical network transmission of power.
Because I1 and line voltage homophase and present the half-sinusoid waveform, the inverter first phase output current Iout1 just can be delivered directly to electrical network by the switch control identical with mains frequency so, and positive-negative half-cycle is respectively with 2 switches.But second mutually can not realize so that then its output current need be stored in earlier on the capacitor C link of a low-capacitance, again by HF switch step-down mode with first mutually output current Iout1 superpose, realize to the electrical network transmission of power.According to (6) and (8) formula, change the electrorheological that Clink goes up storage into and Iout1 with the half-sinusoid electric current of homophase frequently, promptly the second phase output current conversion high frequency SPWM switch control reference voltage from Clink is
Vsb=0.57Vsw1...(10)
Like this, just can realize two-phase output current stack back to the electrical network transmission of power.Therefore, the method that the present invention proposes realizes high reliability and high conversion efficiency simultaneously without electrochemical capacitor.Shown in Figure 2ly be based on miniature inverter topological structure of the present invention.
The part that the present invention does not relate to prior art that maybe can adopt all same as the prior art is realized.
Claims (1)
1. a method that realizes grid-connected miniature inverter high efficiency and high reliability superposes the back to the electrical network transmission of power with two-phase output current Iout1 and Iout2, it is characterized in that it may further comprise the steps:
(a), photovoltaic battery panel is I0 at the output current of peak power output point, the load current of photovoltaic battery panel is set to two-phase I1 and I2, and its size is represented with following formula:
I1=I0*|sin(2πft)|...(2) I2=I0*[1-|sin(2πft)|]...(3)
Wherein, f is a mains frequency, and t is the time, and absolute value representation I1 and I2 are not less than zero, and sinusoidal wave negative half period is become positive half cycle, and promptly the frequency of I1 and I2 is 2f, and the total load current of cell panel is
I1+I2=I0*[|sin(2πft)|+1-|sin(2πft)|]=I0...(4)
(b), at the output of photovoltaic battery panel thin-film capacitor in parallel than low-capacitance, in one-period T, I1 is carried out integration, obtain
I1*T=2I0*T/π=0.637I0*T...(5)
Promptly the first phase transmission current I1 accounts for 63.7% of total transmission current, and I2 accounts for 36.3%, and I2 has only 57% of I1.(c), in one-period T, from relation of equal quantity, I2 is also represented with SIN function, promptly
I2=(π/2-1)*I0|sin(2πft)|=0.57I0|sin(2πft)|...(6)
(d), the control signal reference voltage V sw1 of I1 obtains according to grid ac voltage, is 2 times of mains frequency, and in the positive and negative half period of electrical network and the line voltage same-phase, the control signal reference voltage of I2 and Vsw1 complementation, promptly
Vsw1=Vm*|sin(2πft)|...(8) Vsw2=Vm*[1-|sin(2πft)|]...(9)
Wherein Vm is the value that the electrical network crest voltage dwindles several times, and f is a mains frequency;
Because I1 and line voltage homophase and present the half-sinusoid waveform, the inverter first phase output current Iout1 is delivered directly to electrical network by the switch control identical with mains frequency, positive-negative half-cycle each with 2 switches;
(e), the second phase output current Iout2 is stored on the capacitor C link of low-capacitance, again by HF switch step-down mode with first mutually output current Iout1 superpose, realize to the electrical network transmission of power.According to (6) and (8) formula, the electrorheological of Clink being gone up storage changes the half-sinusoid electric current with the frequency homophase with Iout1 into, and promptly the second phase output current conversion high frequency SPWM switch control reference voltage from Clink is
Vsb=0.57Vsw1...(10);
Two-phase output current Iout1 and Iout2 are superposeed the back to the electrical network transmission of power.
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| WO2009145380A1 (en) * | 2008-05-30 | 2009-12-03 | Kunsan National University Industry-Academy Cooperation Foundation | A grid-interactive photovoltaic generation system with power quality control and energy saving |
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| WO2009145380A1 (en) * | 2008-05-30 | 2009-12-03 | Kunsan National University Industry-Academy Cooperation Foundation | A grid-interactive photovoltaic generation system with power quality control and energy saving |
| CN101714763A (en) * | 2009-09-03 | 2010-05-26 | 周德佳 | High-efficiency stable multifunctional single-stage photovoltaic single-phase grid-connected control method |
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| 宋影等: "高效两相交错Boost变换器在光伏发电系统中的应用", 《航空精密制造技术》 * |
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| CN104682750A (en) * | 2015-03-20 | 2015-06-03 | 南京工业大学 | High-efficiency and high-reliability photovoltaic grid-connected miniature inverter power supply |
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