Background technology
Solar cell parameter comprises photogenerated current, reverse saturation current, and ideal factor, parallel resistance and series resistance, solar cell parameter extraction technology obtains broad research in photovoltaic field, because these parameters are to weigh the important evidence of solar cell quality; But the solar cell electric current output equation that comprises above parameter is a transcendental equation, cannot resolve and obtain each parameter.In order to address this problem, people put forward various solar cell parameter extracting method [(Xiao Wenbo etc., photoelectron # laser, 2012.23 (9): 1681), (L L Peng, et aL, JournaL of Power Sources, 2013,227(1): 131)], the target that all methods are pursued is easy and high-precision extraction solar cell parameter.
At this, we propose a kind of based on Lambert W function and fitting of a polynomial, set up the equation group of Analytical Solution solar cell photogenerated current, reverse saturation current, ideal factor, parallel resistance and 5 electrical parameters of series resistance, extract the new method of battery parameter.
Summary of the invention
The object of this invention is to provide a kind of solar cell parameter extracting method based on Lambert W function and fitting of a polynomial, this sun parameter extracting method only relies on solar cell wall scroll volt-ampere characteristic under illumination, can realize the extraction solar cell parameter of simple and degree of precision.
The present invention is achieved by the following technical solutions, and its characterization method step is:
(1) utilize Lambert W function by solar cell electric current output transcendental equation rear integration clear, obtain integral equation clear;
(2) to solar cell volt-ampere characteristic, divide three sections to carry out matching, obtain piecewise function;
(3) to above-mentioned piecewise function integration, obtain segmentation integral equation;
(4) choose measured value in solar cell volt-ampere characteristic, set up the equation group that subsection integral equation equates with integral equation clear, thus the sunny battery photogenerated current of Analytical Solution, reverse saturation current, ideal factor, parallel resistance and 5 electrical parameters of series resistance;
(5) by above-mentioned 5 electrical parameter substitution solar cell electric currents output transcendental equation, the volt-ampere characteristic under overall matching illumination, obtains root-mean-square error.
In step of the present invention (1), utilize Lambert W function by solar cell electric current output transcendental equation in clear and integral process, be take voltage as integration variable electric current be integrand.
In step step of the present invention (2), to solar cell volt-ampere characteristic, divide three sections to carry out matching, three sections of fitting functions are respectively an order polynomial, quadratic polynomial and quadratic polynomial.
In step of the present invention (4), set up in the equation group process that integral equation clear equates with subsection integral equation, need to choose measured value in volt-ampere characteristic.
In step of the present invention (5), by above-mentioned 5 electrical parameter substitution solar cell electric currents output transcendental equation overall situation matching volt-ampere characteristic, can obtain the root-mean-square error of evaluating extracting parameter effect.
Solar cell electric current output transcendental equation of the present invention is:
Utilize LambertW function solar cell electric current clear output transcendental equation, and to its integration, can obtain integral equation clear and be:
Solar cell volt-ampere characteristic is divided into three sections, carries out respectively an order polynomial, quadratic polynomial and cubic polynomial matching; Wherein first paragraph is a fitting of a polynomial, and matching voltage range is
; Second segment is quadratic polynomial matching, and matching voltage range is
; The 3rd section is quadratic polynomial matching, and matching voltage range is
.
Three sections of fitting functions are respectively:
To three sections of fitting functions respectively from 0 volt to
volt interval integral, can obtain segmentation integral equation and be respectively:
(4)
In above formula (1), (2), (3) and (4)
ifor solar cell output current,
i ph for photogenerated current; ,
i 0 for diode reverse saturation current
, Vfor solar cell output voltage,
r s for equivalent series resistance,
nfor Diode Ideality Factor,
v th thermal voltage constant,
r sh for equivalent parallel resistance,
i sc ,
v oc ,
i m with
v m be respectively electric current and the voltage at solar cell short circuit current, open circuit voltage, maximum power point place,
be respectively volt-ampere characteristic piecewise fitting coefficient,
fto obtain function after integration.
Choose measured value in solar cell volt-ampere characteristic, set up the equation group (being the equation group that formula (2) equates with formula (4)) that integral equation clear equates with subsection integral equation, thus the sunny battery photogenerated current of Analytical Solution, reverse saturation current, ideal factor, parallel resistance and 5 electrical parameters of series resistance; By 5 parameter substitution solar cell electric current output equations of the solar cell extracting, overall matching volt-ampere characteristic, obtains root-mean-square error.
Method of the present invention and traditional solar cell parameter extracting method relatively have following characteristics: 1, utilize Lambert W function solar cell electric current output transcendental equation clear and minute three sections of Function Fitting solar cell volt-ampere characteristic, can resolve the equation group that 5 electrical parameters such as battery photogenerated current are extracted in foundation simultaneously; 2, integration clear and minute three sections of Function Fitting means in the method, can avoid the accidental error of certain measurement data in volt-ampere characteristic to affect extracting parameter precision; 3, the method is simple and have the advantages that precision is higher, for solar cell parameter extraction at present provides an effective approach.
Embodiment
The present invention is a kind of method that only relies on solar cell wall scroll volt-ampere characteristic extraction battery parameter under illumination.
As an example, we utilize the method to propose 5 electrical parameters such as monomer and assembly solar cell photogenerated current.Test and fitting result are as shown in Figure 1 and Figure 2; Concrete operations are that the method for utilizing common making alive to survey electric current is measured the volt-ampere characteristic of solar cell; Then, sharp contents extraction solar cell parameter of the present invention; Finally, adopt volt-ampere characteristic under solar cell electric current output transcendental equation matching illumination.
From Fig. 1-2, measure and fitting result, can find out and coincide finely, for single solar cell, the photogenerated current extracting is 0.7637 ampere, and reverse saturation current is
ampere, ideal factor is 1.5736, and parallel resistance is 73.3281 ohm, and series resistance is 0.0366 ohm; For assembly solar cell, the photogenerated current extracting is 1.0372 amperes, and reverse saturation current is
ampere, ideal factor is 50.7886, and parallel resistance is 553.0657 ohm, and series resistance is 1.2530 ohm.Root-mean-square error for monomer and assembly solar cell is respectively 0.0046 ampere and 0.0181 ampere; From error, can find out very littlely, 5 parameters precisions that namely extract are higher.
Above example illustrates that the solar cell parameter extracting method that we propose is correct, and the method will obtain certain popularization in the middle of the research of current solar cell parameter extraction technology.
The above; it is only the embodiment in the present invention; but protection scope of the present invention is not limited to this; any people who is familiar with this technology is in the disclosed technical scope of the present invention; the conversion that can expect easily or replacement; all should be encompassed in of the present invention comprise scope within, therefore, protection scope of the present invention should be as the criterion with the protection range of claims.