CN112528211A - Method for fitting solar cell IV curve - Google Patents

Abstract

The invention discloses a solar cell IV curve fitting method, and belongs to the field of IV curve fitting. The method for obtaining the solar cell IV fitting curve realizes fitting of discrete I, V data originally collected by the solar cell through a plurality of sections of composite functions, obtains corresponding fitting functions through setting different data sections, and then combines the functions together to obtain an integrated smooth I-V data curve, thereby not only obtaining a test curve with high fitting precision, but also effectively avoiding the phenomenon of fitting curve oscillation.

Description

Method for fitting solar cell IV curve

Technical Field

The invention belongs to the field of IV curve fitting, and particularly relates to a solar cell IV curve fitting method.

Background

The model of the solar cell is a typical nonlinear transcendental function, and the characteristic parameters of the solar cell are difficult to solve through the function. The characteristic parameters of a solar cell are analyzed by engineering by collecting (I, V) data for a set of solar cells. However, the (I, V) data collected by the test circuit is a discrete set of test data, and noise data is inevitably included in the collected data due to the noise effect of the test circuit, resulting in deviation and fluctuation of the test data. In order to obtain a smooth I-V data curve, a curve fitting method is usually used to obtain a smooth curve, so that the smooth curve can be optimally fitted to the acquired data, and the fluctuation and noise of the acquired data can be avoided and reduced. The fitting algorithms adopted at present comprise an exponential function analytical method, a pseudo-Monte Carlo algorithm and the like, but because the algorithms have certain defects, or the fitting precision is low, or the algorithms are complex and the like, a polynomial fitting algorithm is mostly adopted in engineering application, but the polynomial fitting algorithm has the defects that the fitting precision is related to the polynomial order, and meanwhile, the phenomenon of fitting curve oscillation easily occurs.

Disclosure of Invention

In order to solve the problems, the invention provides a method for fitting the solar cell IV curve, which is reasonable in design, overcomes the defects of the prior art and has a good effect.

In order to achieve the purpose, the invention adopts the following technical scheme:

a fitting method of a solar cell IV curve comprises the steps of conducting segmentation analysis on a group of discrete solar cell I, V data collected by a test circuit, conducting polynomial fitting on different data segments to obtain corresponding polynomial fitting functions, integrating the polynomial fitting functions into a group of fitting functions, and finally obtaining a high-precision smooth I-V curve by utilizing the fitting function group.

Preferably, the method specifically comprises the following steps:

step 1: collecting discrete data of the solar cell by using a test circuit, wherein the number of collected points is n;

step 2: calculating I in collected data_i*V_iDividing the whole data acquisition segment into two segments from a first acquisition point to an mth acquisition point, and from an m +1 th acquisition point to an nth acquisition point, wherein i is 1-n;

and step 3: calculating a coefficient set f [ 1-15 ] of a 14-order polynomial fitting function according to the acquired data of the full data segment 1-n to obtain a fitting function 1, as shown in formula (1):

wherein, V_iRepresenting the voltage value, Inew, in the raw acquired data_iRepresenting the current value after 14-order polynomial fitting, wherein the value range of i is 1-n;

and 4, step 4: calculating a coefficient set h [ 1-15 ] of a 14-order polynomial fitting function corresponding to the data segment according to the data of the first segment of acquired data segment to obtain a fitting function 2, as shown in formula (2):

wherein, V_jRepresenting the voltage value, Inew, in the raw acquired data_jRepresenting the current value after 14-order polynomial fitting, wherein the value range of j is 1-m;

and 5: the fitting function 1 and the fitting function 2 are combined into a function group, data fitting is carried out on the function group corresponding to different data sections respectively, and finally a group of complete (Inew, V) fitting data is integrated, wherein the function group is shown as a formula (3):

wherein, Inew_iFor the fitted current value, V_iThe collected voltage value is m, the position of a data segmentation point is m, and the total number of collected data points is n;

step 6: and finally obtaining the solar cell I-V curve with high precision and smoothness according to the fitting function group.

The invention has the following beneficial technical effects:

the method realizes the fitting of discrete (I, V) data originally collected by the solar cell through a multi-section composite function, obtains corresponding fitting functions through setting different data sections, and then combines the functions together to obtain an integrated smooth I-V data curve; the invention can not only obtain the test curve with high fitting precision, but also effectively avoid the phenomenon of fitting curve oscillation.

Drawings

FIG. 1 is a schematic diagram of an equivalent circuit of a solar cell according to the present invention;

FIG. 2 is a diagram of originally collected discrete data according to example 1 of the present invention;

FIG. 3 is a schematic diagram of a 14 th order polynomial fit curve according to example 1 of the present invention;

FIG. 4 shows full data segment data according to example 2 of the present invention;

FIG. 5 is a schematic diagram of oscillation occurring by using a single 14 th order polynomial fitting curve according to embodiment 2 of the present invention;

FIG. 6 is a diagram illustrating a comparison between a multi-segment complex function fitted curve and a 14 th order polynomial fitted curve according to example 2 of the present invention.

Detailed Description

The method adopts a multi-section complex function method to fit the originally acquired (I, V) data to obtain a high-precision smooth I-V curve, and effectively solves the oscillation problem of the fitted curve.

The invention is described in further detail below with reference to the following figures and detailed description:

fig. 1 shows an equivalent circuit of a solar cell, and fig. 1 shows an equivalent circuit in the case of illumination.

Under the condition of illumination, the volt-ampere characteristic equation of the solar cell model is shown as the formula (4):

wherein, I and V are the output current and the output voltage of the solar cell respectively; i is_LIs a photo-generated current; i is_dIs a dark current; i is₀Is a diode reverse saturation current; q is the electron charge constant; k is the boltzmann constant; t is the junction temperature at test time; r_sIs a series resistor; r_shIs a parallel resistor.

Example 1

The (I, V) data set of solar cells under light conditions collected by the test circuit is a discrete set of data, as indicated by the dots in fig. 3. In order to obtain a smooth I-V curve, polynomial fitting is usually used in engineering to achieve the curve fit. Equation (5) below is a 14-order polynomial fitting function for the discrete data points in fig. 3 (the 14-order polynomial fitting function is used because the 14-order fitting accuracy substantially meets the engineering requirements), and the fitting curve is as shown in fig. 3. The collected (I, V) data and the 14 th order polynomial fitted current data are listed in the table in fig. 2.

Wherein, V_iThe value is the originally collected voltage value, Inewi is the fitted current value, and i is the total number of collected points from 1.

It can be seen from fig. 3 that the error between the 14 th-order fitting curve and the original collected data is small, and a smooth I-V fitting curve of the solar cell can be obtained.

Example 2

However, for some (I, V) data acquisitions, fitting the function with only a single polynomial tends to cause oscillations in the fitted curve, as shown in FIG. 5. In fig. 5, the dots are the original collected data, and the curve is a fitting curve obtained by applying a 14-order polynomial fitting function to the data of the whole data segment, and the fitting function is shown in formula (6). The collected (I, V) data and the 14 th order polynomial fitted current data are listed in the table in fig. 4.

Wherein, V_iThe value is the originally collected voltage value, Inewi is the fitted current value, and i is the total number of collected points from 1.

It can be seen from fig. 5 that the curves fitted with a single polynomial show oscillations.

The curve obtained by piecewise fitting the raw collected data in fig. 4 by the multi-segment complex function fitting method of the present invention is shown in fig. 6. In fig. 6, the diamond points are the original collected data, the smooth curve is the fitted curve obtained by fitting the full data segment data with a 14-order polynomial fitting function, and the curve with points is the fitted curve obtained by fitting the full data segment data with a multi-segment complex function. The fitting function group of the multi-section complex function fitting method is shown as the formula (7):

where m is the position of the segmentation point, which has a value of 54; n is the total number of collected points, and the value is 399.

As can be seen from FIG. 6, the method of the present invention uses a multi-segment complex function to fit the original sampling data, so that the oscillation phenomenon of the fitting curve can be effectively solved, and the fitting accuracy is improved.

It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make modifications, alterations, additions or substitutions within the spirit and scope of the present invention.

Claims (2)

1. A fitting method of a solar cell IV curve is characterized in that a group of discrete solar cell I, V data collected by a test circuit is subjected to sectional analysis, polynomial fitting is carried out on different data sections to obtain corresponding polynomial fitting functions, the polynomial fitting functions are integrated into a group of fitting functions, and a high-precision smooth I-V curve is finally obtained by utilizing the group of fitting functions.

2. The method for fitting the solar cell IV curve according to claim 1, comprising the following steps:

step 1: collecting discrete data of the solar cell by using a test circuit, wherein the number of collected points is n;

step 2: calculating I in collected data_i*V_iThe point m with the maximum value divides the whole data acquisition segment into two segmentsThe first section is from the first acquisition point to the mth acquisition point, and the second section is from the m +1 th acquisition point to the nth acquisition point, wherein i is 1-n;

and step 3: calculating a coefficient set f [ 1-15 ] of a 14-order polynomial fitting function according to the acquired data of the full data segment 1-n to obtain a fitting function 1, as shown in formula (1):

wherein, V_iRepresenting the voltage value, Inew, in the raw acquired data_iRepresenting the current value after 14-order polynomial fitting, wherein the value range of i is 1-n;

and 4, step 4: calculating a coefficient set h [ 1-15 ] of a 14-order polynomial fitting function corresponding to the data segment according to the data of the first segment of acquired data segment to obtain a fitting function 2, as shown in formula (2):

Inew_j＝h(1)+h(2)*V_j+h(3)*V_j ²+h(4)*V_j ³+h(5)*V_j ⁴+h(6)*V_j ⁵+h(7)*V_j ⁶+h(8)*V_j ⁷+h(9)*V_j ⁸+h(10)*V_j ⁹+h(11)*V_j ¹⁰+h(12)*V_j ¹¹+h(13)*V_j ¹²+h(14)*V_j ¹³+h(15)*V_j ¹⁴ (2)

wherein, V_jRepresenting the voltage value, Inew, in the raw acquired data_jRepresenting the current value after 14-order polynomial fitting, wherein the value range of j is 1-m;

and 5: the fitting function 1 and the fitting function 2 are combined into a function group, data fitting is carried out on the function group corresponding to different data sections respectively, and finally a group of complete (Inew, V) fitting data is integrated, wherein the function group is shown as a formula (3):

wherein, Inew_iFor the fitted current value, V_iThe collected voltage value is m, the position of a data segmentation point is m, and the total number of collected data points is n;

step 6: and finally obtaining the solar cell I-V curve with high precision and smoothness according to the fitting function group.

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