CN103219747B - 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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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, especially the miniature inverter of photovoltaic power generation grid-connecting, specifically a kind of method realizing grid-connected miniature inverter high efficiency and high reliability.
Background technology
At present, in new energy development field, solar energy power generating is developing direction main at present.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 of the grid-connected inverter of high conversion efficiency, high reliability receive extensive attention in recent years.Wherein, the photovoltaic power generation grid-connecting very applicable middle-size and small-size solar power system of miniature inverter, can promote the extensive use doing etc. space solar power based on building roof, body of wall and electric wire.But also there is raising conversion efficiency and wait key technical problem with improvement reliability is conflicting in the exploitation of grid-connected Miniature inverter, object of the present invention will solve this technical barrier exactly.
There is peak power output working point in photovoltaic cell, and peak power output working point changes with environmental factors such as illumination.For realizing maximum output power point tracking (MPPT) and power output maximization, the voltage at cell panel two ends needs relative constancy.This just requires that the input current of the load current of cell panel i.e. inverter is constant.But the electric current that high efficiency single-stage invert power supply outputs to electrical network needs and the same homophase frequently of line voltage, and namely the power output of inverter is sinusoidal wave change.If ignore the energy loss of inverter transfer process, the power output of photovoltaic cell should be equal with inverter power output.This just causes the output voltage of photovoltaic cell i.e. the input voltage of inverter to be sinusoidal fluctuation changes, and MPPT can not be realized.In order to solve this contradiction, the simplest way is connected in parallel a large capacitance electric capacity Cin, as shown in Figure 1.For being easy to realize MPPT, the required and capacitance C connect is provided by following formula:
Wherein, Pdc is photovoltaic battery panel peak power output, and Udc is the average voltage on electric capacity, and f is AC network frequency, and Δ u is the maximum voltage fluctuation peak ~ peak value that can allow.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 so large capacitance, usually only have and realize with electrochemical capacitor.But electrochemical capacitor only has the life-span of the longest 7000 hours at 105 ° of C operational environments, it is 16000 hours when 75 ° of C.Cell panel and Miniature inverter (AC module) are under being exposed to sunshine environment when working, and the heat self produced when adding inverter work, it is normal that its ambient temperature reaches 75 ° of C.Within 8 hours, calculate if to work every day by photovoltaic system, electrochemical capacitor is less than 6 years in the life-span of 75 ° of C environmental works, far can not match with the photovoltaic cell life-span of more than 20 years itself.Lost efficacy average time (MTFF) based on first time and average time (MTBF) between losing efficacy to the reliability assessment of inverter product.At present, the Miniature inverter life of product of AC module is applied in 5 ~ 10 years.Namely MTFF is 5 years, and MTBF is 10 years.Applying long-life thin-film capacitor to replace electrochemical capacitor should be the effective way extending inverter useful life.Because hull cell has the life-span of 80000 hours under same working temperature.Within 8 hours, calculate by working every day, its life-span can reach 27 years.But problem is not so simple.Because the unit capacitance of thin-film capacitor is lower, from the aspect such as cost and volume, the electric capacity thin-film capacitor for mF level is almost unpractical.
Summary of the invention
The object of the invention is for the problems referred to above, propose a kind of method realizing grid-connected miniature inverter high efficiency and high reliability, carry out Current Control by two-phase complementation.
Technical scheme of the present invention is:
Realize a method for grid-connected miniature inverter high efficiency and high reliability, two-phase output current Iout1 and Iout2 superposed backward electrical grid transmission energy, specifically comprises the following steps:
A (), photovoltaic battery panel are 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 following formula represents:
I1=I0*|sin(2πft)|...(2) I2=I0*[1-|sin(2πft)|]...(3)
Wherein, f is mains frequency, and t is the time, and absolute value representation I1 and I2 is not less than zero, and the negative half period of sine wave is become positive half cycle, and namely 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 a photovoltaic battery panel thin-film capacitor compared with low-capacitance in parallel, in one-period T, integration is carried out to I1, obtains
I1*T=2I0*T/π=0.637I0*T...(5)
Namely first-phase transmission current I1 account for that 63.7%, I2 of total transmission current accounts for that 36.3%, I2 only has I1 57%.(c), from relation of equal quantity, I2 is also represented with SIN function in one-period T, namely
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, be 2 times of mains frequency, and in the positive and negative half period of electrical network, and line voltage same-phase, the control signal reference voltage of I2 and Vsw1 complementation, namely
Vsw1=Vm*|sin(2πft)|...(8) Vsw2=Vm*[1-|sin(2πft)|]...(9)
Wherein Vm is the value that electrical network crest voltage reduces several times, and f is mains frequency;
Present half-sinusoid waveform due to I1 and line voltage homophase, inverter first-phase output current Iout1 is delivered directly to electrical network by the switch control rule identical with mains frequency, and positive-negative half-cycle respectively uses 2 switches;
E (), second-phase output current Iout2 are stored on the electric capacity Clink of low-capacitance, then superposed by high frequency switching buck mode and first-phase output current Iout1, realize to electrical grid transmission energy.According to (6) and (8) formula, the ER effect that Clink stores is changed into and the sinusoidal half-wave current of Iout1 with frequency homophase, namely from the second-phase output current transduce high frequency SPWM switch control rule reference voltage of Clink is
Vsb=0.57Vsw1...(10);
Two-phase output current Iout1 and Iout2 is superposed backward electrical grid transmission energy.
Beneficial effect of the present invention:
The present invention is by superposing backward electrical grid transmission energy to two-phase output current.The method does not need to use electrochemical capacitor, can realize high reliability and high conversion efficiency simultaneously.
Accompanying drawing explanation
Fig. 1 is traditional single-stage conversion Miniature inverter topological structure schematic diagram.
Fig. 2 is the topological structure schematic diagram of the two-phase complementary current Miniature inverter that the present invention adopts.
Embodiment
Below in conjunction with drawings and Examples, the present invention is further illustrated.
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 following formula represents:
I1=I0*|sin(2πft)|...(2) I2=I0*[1-|sin（2πft）|]...(3）
Wherein, f is mains frequency, and t is the time, and absolute value representation I1 and I2 is never less than zero, and the negative half period of sine wave is become positive half cycle, and namely 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 is equal with its load current in other words, ensure that its operating voltage is constant, and the time has nothing to do.Therefore, in theory, even if photovoltaic battery panel two ends are without shunt capacitance, be also stable when its output voltage or operating voltage are as stable in illumination under metastable external environment condition, what this guarantees MPPT is easy to realization and the maximization of cell panel power output.And in fact because I1 and I2 is discontinuous high-frequency pulse current, the output of photovoltaic battery panel also needs a thin-film capacitor compared with low-capacitance in parallel.If carry out integration to I1 in one-period T, just can obtain
I1*T=2I0*T/π=0.637I0*T...(5)
Namely first-phase transmission current I1 account for that 63.7%, I2 of total transmission current accounts for that 36.3%, I2 only has I1 57%.If I2 is also represented with SIN function from relation of equal quantity in one-period T, namely
I2=(π/2-1)*I0|sin(2πft)|=0.57I0|sin(2πft)|...(6)
If the conventional method shown in Fig. 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)
In the present invention, 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 line voltage same-phase.And the control signal reference voltage of I2 and Vsw1 complementation, namely
Vsw1=Vm*|sin(2πft)|...(8) Vsw2=Vm*[1-|sin(2πft)|]...(9)
Wherein Vm is the value that electrical network crest voltage reduces several times, and f is mains frequency.That is within each cycle, Vsw1 is large, and Vsw2 is just little, and vice versa.At any time, Vsw1+Vsw2=Vm is invariable.Due to I1 and line voltage homophase and in half-sinusoid waveform, so inverter first-phase output current Iout1 just can be delivered directly to electrical network by the switch control rule identical with mains frequency.But second-phase then can not so realize, its output current needs first to be stored on the electric capacity Clink of a low-capacitance, then is superposed by high frequency switching buck mode and first-phase output current Iout1, realizes to electrical grid transmission energy.
Present half-sinusoid waveform due to I1 and line voltage homophase, so inverter first-phase output current Iout1 just can be delivered directly to electrical network by the switch control rule identical with mains frequency, and positive-negative half-cycle respectively uses 2 switches.But second-phase then can not so realize, its output current needs first to be stored on the electric capacity Clink of a low-capacitance, then is superposed by high frequency switching buck mode and first-phase output current Iout1, realizes to electrical grid transmission energy.According to (6) and (8) formula, the ER effect that Clink stores be changed into and the sinusoidal half-wave current of Iout1 with frequency homophase, namely from the second-phase output current transduce high frequency SPWM switch control rule reference voltage of Clink be
Vsb=0.57Vsw1...(10)
Like this, just can realize superposing backward electrical grid transmission energy to two-phase output current.Therefore, the method that the present invention proposes, without electrochemical capacitor, realizes high reliability and high conversion efficiency simultaneously.Based on miniature inverter topological structure of the present invention shown in Fig. 2.
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. realize a method for grid-connected miniature inverter high efficiency and high reliability, two-phase output current Iout1 and Iout2 superposed backward electrical grid transmission energy, it is characterized in that it comprises the following steps:
A (), photovoltaic battery panel are 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 following formula represents:
I1＝I0*|sin(2πft)|...(2) I2＝I0*[1-|sin(2πft)|]...(3)
Wherein, f is mains frequency, and t is the time, and absolute value representation I1 and I2 is not less than zero, and the negative half period of sine wave is become positive half cycle, and namely 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 a photovoltaic battery panel thin-film capacitor compared with low-capacitance in parallel, in one-period T, integration is carried out to I1, obtains
I1*T＝2I0*T/π＝0.637I0*T...(5)
Namely first-phase transmission current I1 account for that 63.7%, I2 of total transmission current accounts for that 36.3%, I2 only has I1 57%;
(c), from relation of equal quantity, I2 is also represented with SIN function in one-period T, namely
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, be 2 times of mains frequency, and in the positive and negative half period of electrical network, and line voltage same-phase, the control signal reference voltage V sw2 of I2 and Vsw1 complementation, namely
Vsw1＝Vm＊|sin(2πft)|...(8) Vsw2＝Vm＊[1-|sin(2πft)|]...(9)
Wherein Vm is the value that electrical network crest voltage reduces several times, and f is mains frequency;
Present half-sinusoid waveform due to I1 and line voltage homophase, inverter first-phase output current Iout1 is delivered directly to electrical network by the switch control rule identical with mains frequency, and positive-negative half-cycle respectively uses 2 switches;
E (), second-phase output current Iout2 are stored on the electric capacity Clink of low-capacitance, then superposed by high frequency switching buck mode and first-phase output current Iout1, realize to electrical grid transmission energy; According to (6) and (8) formula, the ER effect that Clink stores is changed into and Iout1 with the sinusoidal half-wave current of frequently homophase, namely from the second-phase output current transduce high frequency SPWM switch control rule reference voltage of Clink be Vsb=0.57Vsw1... (10);
Two-phase output current Iout1 and Iout2 is superposed backward electrical grid transmission energy.
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