CN111563231B - Method for accurately evaluating output characteristics of half photovoltaic module under shadow shielding condition - Google Patents
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Abstract
The invention discloses a method for accurately evaluating the output characteristics of a half-sheet photovoltaic module under the shadow shielding condition, which comprises the steps of summing the voltages V of all half-sheet solar cells on each cell string according to the serial circuit of the half-sheet solar cells in the cell string, with unchanged current I, to obtain each half-sheet cell stringI‑VA curve; judging whether a bypass diode for protecting the half-cell string is conducted or not to obtain each half-cell string after correctionI‑VA curve; according to the parallel circuit of the battery string in the half-sheet photovoltaic module, the voltage V is unchanged, and the current of each parallel partISumming to obtain the whole half photovoltaic module under the shadow conditionI‑VAndP‑Va curve. The invention can rapidly and simply simulate and analyze the I-V and P-V output characteristics under the shadow shielding of the half-piece photovoltaic module, and has practical significance for on-line monitoring of the mismatch of the photovoltaic system formed by the half-piece photovoltaic module, real-time tracking of the maximum power of the half-piece photovoltaic module and improvement of the power generation benefit of the photovoltaic system.
Description
Technical Field
The invention relates to a method for accurately evaluating output characteristics of a half photovoltaic module under a shadow shielding condition, and belongs to the technical field of photovoltaic power generation.
Background
Generally, a photovoltaic power generation system is formed by a plurality of half-sheet photovoltaic modules, and the half-sheet photovoltaic modules are formed by packaging solar cells with fixed sheets, so that the photovoltaic power generation system can fully utilize solar resources under ideal conditions to generate huge energy and environmental benefits. However, in practical situations, due to the existence of shadow masks in the installation environment, the power generation of half-sheet photovoltaic modules can be strongly disturbed by these local shadows.
The bypass diode connected in parallel inside the component solves the problem of mismatch caused by shadow among the components to a certain extent, but simultaneously causes the discontinuity of the integral output of the component, namely, the I-V output characteristic curve of the half photovoltaic component generates steps at the state point before and after the on-off state of the bypass diode, and the P-V output characteristic of the photovoltaic group string generates peak value at the state point; in summary, once the bypass diode in the half-sheet photovoltaic module is turned on, a plurality of power peaks occur in the P-V output characteristic. In order to make a half photovoltaic module output the maximum power at the current moment, tracking for a plurality of power peaks is particularly important, and some efficient MPPT tracking devices must have the function of evaluating the module output characteristics under the shadow condition and then tracking the maximum power.
As the efficiency of the crystalline silicon solar cell is more and more close to the bottleneck, the half-piece photovoltaic module realizes cost reduction and efficiency enhancement, and on one hand, the packaging efficiency of the half-piece photovoltaic module is improved; on the other hand, the battery piece is sliced, for example, the whole solar battery is cut into half pieces to manufacture a half piece of photovoltaic module, so that the resistance loss is effectively reduced.
Conventional monolithic assemblies are such that all of the monolithic solar cells are connected in a purely serial fashion, while half of the photovoltaic assemblies typically have twice the number of cells as the monolithic assemblies. In order to avoid additional increase of the voltage of the half photovoltaic module, the cost of the photovoltaic system and hidden danger of grid connection are increased, and the solar cells are usually connected in series and then in parallel, so that the output current and the output voltage of the module are unchanged. Then, the evaluation of the output characteristics under shadow conditions becomes more complicated, just as the internal circuitry of the half-cell photovoltaic module changes. Previous evaluation methods for whole-sheet assemblies under re-shading conditions are no longer applicable to half-sheet photovoltaic assemblies with series and parallel circuits.
In view of the above, the output characteristics of each half cell must be solved more accurately to obtain the I-V and P-V output characteristics of the half photovoltaic module under the shadow condition, so as to realize real-time tracking of the maximum power of the half photovoltaic module, realize on-line monitoring of the mismatch of the photovoltaic system and improve the photovoltaic power generation benefit.
Disclosure of Invention
Aiming at the prior art, after the solar cells are cut in half, when the parallel connection relation of each cell is processed in a series-parallel circuit of the half-piece photovoltaic module, the same voltage point cannot be found, so that the current points cannot be summed up to evaluate the output characteristics of the half-piece photovoltaic module under the conditions of shadow shielding and the like; in the past, the half-sheet photovoltaic module is regarded as a whole-sheet module for evaluation, the parallel circuit characteristic is inaccurate, the performance advantage of the half-sheet photovoltaic module under the mismatch condition cannot be evaluated, and the method is inconsistent with actual measurement.
The technical scheme adopted in the invention is as follows:
definition of several terms in the present invention:
half-cell battery: the dicing saw is used for cutting the whole solar cell into half pieces, so that the solar cell has more advantages.
Half-sheet assembly: the photovoltaic module is formed by connecting half solar cells in series and parallel. The mainstream half-sheet assembly consists of 144 half-sheet solar cells. Under the normal non-shadow and other mismatch working conditions, the solar module can be equivalently used as a conventional whole photovoltaic module formed by connecting 72 whole solar cells in series.
Battery string: the series connection battery pieces controlled by each diode, and the half-piece photovoltaic assembly has 6 battery strings.
Battery domain: the three diodes are used for controlling the parallel connected battery pieces, and the half-piece photovoltaic assembly shares two battery domains.
Row: when half photovoltaic module vertical arrangement, the direction that the subassembly minor face is located. The opposite is true when arranged laterally.
The columns are: when the half photovoltaic modules are vertically arranged, the long sides of the modules are positioned in the direction. The opposite is true when arranged laterally.
I-V curve: the power generation performance of the half-sheet photovoltaic module under certain irradiance and certain module temperature is shown.
A method for accurately evaluating output characteristics of a half photovoltaic module under shadow shielding conditions comprises the following specific steps:
s1, obtaining five parameters required by an output characteristic equation for representing the half photovoltaic module according to nameplate parameters on the back of the half photovoltaic module;
s2, converting five parameters of the half-piece photovoltaic module into five parameters representing the electrical characteristics of each half-piece solar cell according to the number of the half-piece solar cells in the half-piece photovoltaic module;
s3, correcting the photo-generated current I in the five parameters according to the proportion of shadow shielding on the half solar cell ph Obtaining five parameters representing the electric characteristics of the half solar cells shielded by the shadow, and substituting the five parameters of the half solar cells which are not shielded by the shadow and the five parameters of the half solar cells shielded by the shadow into the output characteristic equation of the half photovoltaic module to obtain an I-V curve of each half solar cell;
s4, summing the voltages V of all the half solar cells on each battery string according to the series circuit of the half solar cells in the battery strings, wherein the current I is unchanged, so as to obtain an I-V curve of each half battery string; judging whether the bypass diode for protecting the half-cell strings is conducted or not according to the principle that the bypass diode is conducted when the bypass diode is subjected to reverse voltage of 0.7V, and obtaining an I-V curve of each corrected half-cell string; and summing the current I of each parallel part according to the parallel circuit of the battery string in the half-piece photovoltaic module, wherein the voltage V is unchanged, so as to obtain I-V and P-V curves of the whole half-piece photovoltaic module under the shadow condition.
Preferably, the specific steps of the step S1 are as follows:
s1-1, acquiring electric performance parameters of the half photovoltaic module and the number N of half solar cells under four standard measurement conditions from a nameplate attached to the back of the half photovoltaic module s The electrical performance parameters of the half-sheet photovoltaic module comprise an open circuit voltage V oc Short-circuit current I sc Maximum power point voltage V mpp And maximum power point current I mpp ；
S1-2, listing an output characteristic equation of the half photovoltaic module, wherein the equation is shown in a formula (1):
in the formula (1), I ph Is a photo-generated current; i o Reverse saturation dark current for the diode; n is a diode management thinking factor; r is R s Is a series resistor; n (N) s The number of the half solar cells; k is Boltzmann constant, 1.38 x 10 -23 J/K; q is the charge number, 1.6x10 -19 C；T c The temperature of the half solar cell is 298.15K by adopting Kelvin temperature; r is R sh Is a parallel resistor; i and V are the operating current and operating voltage, respectively;
s1-3, an open circuit voltage V known from step S1-1 oc Short-circuit current I sc Maximum power point voltage V mpp Maximum power point current I mpp The five unknown parameters in the extraction equation of the output characteristic equation of the half photovoltaic module are the five parameters of the half photovoltaic module, wherein the five parameters of the half photovoltaic module comprise I ph, half-sheet photovoltaic module ，I o, half piece photovoltaic module ，n Half-sheet photovoltaic module ，R s, half piece photovoltaic module ，R sh, half piece photovoltaic module 。
Preferably, the specific steps of the step S2 are as follows:
according to the five parameters of the half-sheet photovoltaic module obtained in the step S1-3 and the number N of the half-sheet solar cells in the half-sheet photovoltaic module s Converting five parameters of the half-sheet photovoltaic module into five parameters of each half-sheet solar cell, wherein the five parameters of each half-sheet solar cell comprise: i ph, half-cell ，I o, half-cell ，n Half-cell battery ，R s, half-cell ，R sh, half-cell battery Wherein I ph, half-cell ＝I ph, half-sheet photovoltaic module /2；I o, half-cell ＝I o, half piece photovoltaic module /2；n Half-cell battery ＝n Half-sheet photovoltaic module ；R s, half-cell ＝R s, half piece photovoltaic module ×2；R sh, half-cell battery ＝R sh, half piece photovoltaic module ×2。
Preferably, the specific steps of the step S3 are as follows:
s3-1, simulating the output characteristics of a single half solar cell under different shielding ratios of 5%, 10%, 15% and 20% … …% and the output characteristics of a half photovoltaic module under the 100% shielding of 1, 2, 1 row and 2 row solar cells, and correcting the photo-generated current I in five parameters according to the ratio of shadow shielding on the half solar cell ph Obtaining five parameters representing the electric characteristics of the half-cell shielded by the shadow, and generating the photo-generated current I of the half-cell shielded by the shadow ph Can be expressed as: :
I ph, shielding battery ＝a×I ph, half-cell ， (2)；
In the formula (2), a is a shading proportion coefficient, a is 0.001 at minimum, a is 1 at maximum, and the larger the shading area is, the smaller the shading proportion coefficient a is, namely the I of the half-piece solar cell is represented ph The smaller.
S3-2, substituting the five parameters of the half-cell which is not blocked by the shadow and is obtained in the step S2 and the five parameters of the half-cell which is blocked by the shadow and is obtained in the step S3-1 into a formula (1) respectively to obtain an I-V curve of each half-cell.
Preferably, in the step S3-2, the data points on the I-V curve are obtained in two ways, the first is from-b-bxI ph Traversing the working current I to obtain different working voltages V corresponding to the same current; the second is from-b-bXV oc And traversing the working voltage V to obtain different working currents I corresponding to the same voltage, wherein the value of the parameter b is 1.2.
Preferably, the specific steps of the step S4 are as follows:
s4-1, numbering all the half-solar cells, and respectively marking two parallel battery domains as a battery domain I and a battery domain II according to the internal circuit structure of the half-photovoltaic module; dividing a battery string connected in series in a battery domain I into a battery string 1, a battery string 2 and a battery string 3, and dividing a battery string connected in series in a battery domain II into a battery string 4, a battery string 5 and a battery string 6; the bypass diode connected in parallel with the battery string 1 and the battery string 4 is denoted as a diode I, the bypass diode connected in parallel with the battery string 2 and the battery string 5 is denoted as a diode II, and the bypass diode connected in parallel with the battery string 3 and the battery string 6 is denoted as a diode III; finally, the serial number of any half solar cell in the half photovoltaic module is obtained;
s4-2, calculating the output characteristics of each half solar cell according to the first method for obtaining the data points on the I-V curve in the step S3-2, and respectively adding the voltages of all half solar cells in the cell strings 1, 2, 3, 4, 5 and 6, wherein the current is kept unchanged to obtain the I-V curve of each cell string;
s4-3, processing the voltage value on the I-V curve of each battery string, and completely replacing the data of the bypass diode on voltage with the voltage value smaller than or equal to the corresponding battery string with-0.7V to obtain an updated I-V curve of each battery string;
s4-4, respectively adding the voltages of 3 battery strings connected in series in the battery domain I and the battery domain II, and keeping the current unchanged to obtain an I-V curve of each battery domain;
s4-5, redrawing the I-V curves of the battery domain I and the battery domain II by adopting the second mode in the S3-2, wherein the specific steps are as follows: firstly, new voltage data traversed at the same voltage interval are listed, secondly, old voltages with the first voltage value being more than or equal to and the last voltage value being less than or equal to the new voltage value on the original curve are found out respectively, finally, the current in the old voltage range is added and averaged to be used as the current value corresponding to the new voltage value, and finally, two groups of updated I-V curves of the battery domain I and the battery domain II are obtained;
and S4-6, adding the current of the I-V curve of the battery domain I and the current of the I-V curve of the battery domain II updated by the S4-5, and keeping the voltage unchanged to obtain the I-V curve and the P-V curve of the half photovoltaic module.
Preferably, in the step S3-1, when the shielding ratio of the single solar cell is 100%, the shielding ratio coefficient a=0.001.
The beneficial effects are that: the invention provides an accurate evaluation method of a half-sheet photovoltaic module under shadow shielding, which can calculate an I-V curve of the half-sheet photovoltaic module under mismatch conditions such as shadow shielding and the like, evaluate the advantages of the half-sheet photovoltaic module in resisting shadow shielding and hot spots compared with a whole-sheet module, and has important significance for popularization and application of the half-sheet photovoltaic module, mismatch on-line monitoring of a photovoltaic system, real-time tracking of maximum power and improvement of power generation benefits of the half-sheet photovoltaic system.
Drawings
FIG. 1 is a flow chart of a method for accurately evaluating a half-sheet photovoltaic module of the present invention under shadow masking.
FIG. 2 is an I-V graph of a single cell under normal conditions versus occluded.
Fig. 3 is a schematic diagram of the internal structure of a conventional half-sheet photovoltaic module.
Fig. 4 shows the output characteristics (actual measurement and calculation) of half-sheet photovoltaic modules under shadow mismatch conditions.
Fig. 5 is an output characteristic (measured) of the whole wafer assembly under the same shadow mismatch condition.
Detailed Description
In order to better understand the technical solutions in the present application, the following description will clearly and completely describe the technical solutions in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, shall fall within the scope of the present application.
In this embodiment, the half-sheet photovoltaic module selected is 144 half-sheet photovoltaic modules, which corresponds to the layout size of 72 whole-sheet modules, and the structural schematic diagram is shown in fig. 3. The whole cell area is 158.75mm by 158.7mm, and the half cell area is 158.75mm by 79.35mm.
As shown in fig. 1, the invention provides a precise evaluation method of a half-sheet photovoltaic module under shadow shielding, which mainly comprises the following steps:
s1, obtaining five parameters required by an output characteristic equation for representing the half photovoltaic module according to nameplate parameters on the back of the half photovoltaic module;
s1-1, acquiring the electrical property of the half photovoltaic module under four standard measurement conditions from a nameplate attached to the back surface of the half photovoltaic moduleEnergy parameter and number of half solar cells N s As shown in table 1, the electrical performance parameters of the half-sheet photovoltaic module include: open circuit voltage V oc =47.74, short-circuit current I sc =10.03, maximum power point voltage V mpp =39.39, maximum power point current I mpp =9.42, half cell number N s =144; four electrical performance parameters of the half-cell under standard conditions (STC) are shown in the second row of table 1, and are respectively: v (V) oc ＝0.663；I sc ＝5.015；V mpp ＝0.547；I mpp ＝4.71；
TABLE 1
Half photovoltaic module electrical performance parameter under standard condition and calculated half solar cell electrical performance parameter
* "72" is the number of half cells in series; "0.001" is an occlusion scaling factor a, the more shadows are occluded, the smaller the value of a is; and 2 is that the whole battery is cut into two halves.
S1-2, listing an output characteristic equation of the half photovoltaic module, wherein the output characteristic equation is shown in a formula (1):
wherein I is ph Is a photo-generated current; i o Reverse saturation dark current for the diode; n is a diode management thinking factor; r is R s Is a series resistor; n (N) s The number of the half solar cells; k is Boltzmann constant, 1.38 x 10 -23 J/K; q is the charge number, 1.6x10 - 19 C；T c The temperature of the battery piece is 298.15K by adopting Kelvin temperature; r is R sh Is a parallel resistor; i and V are the operating current and operating voltage, respectively.
S1-3, an open circuit voltage V known from step S1-1 oc Short-circuit current I sc Maximum power point voltage V mpp Maximum power point current I mpp The five unknown parameters in the extraction equation of the output characteristic equation of the half photovoltaic module are the five parameters of the half photovoltaic module, wherein the five parameters of the half photovoltaic module comprise I ph, half-sheet photovoltaic module ，I o, half piece photovoltaic module ，n Half-sheet photovoltaic module ，R s, half piece photovoltaic module ，R sh, half piece photovoltaic module As shown in the first row of table 2:
TABLE 2
Five parameters of characteristic equation of half photovoltaic module and five parameters of calculated characteristic equation of solar cell under standard condition
S2, converting five parameters of the half-piece photovoltaic module into five parameters representing the electrical characteristics of each half-piece solar cell according to the number of the half-piece solar cells in the half-piece photovoltaic module; namely, according to the five parameters of the half-sheet photovoltaic module obtained in the step S1-3 and the number N of the half-sheet solar cells in the half-sheet photovoltaic module s Converting five parameters of the half-sheet photovoltaic module into five parameters of each half-sheet solar cell, wherein the five parameters of each half-sheet solar cell comprise: i ph, half-cell ，I o, half-cell ，n Half-cell battery ，R s, half-cell ，R sh, half-cell battery Wherein I ph, half-cell ＝I ph, half-sheet photovoltaic module /2；I o, half-cell ＝I o, half piece photovoltaic module /2；n Half-cell battery ＝n Half-sheet photovoltaic module ；R s, half-cell ＝R s, half piece photovoltaic module /72×2；R sh, half-cell battery ＝R sh, half piece photovoltaic module 72 x 2, in particular as shown in the second row of table 2.
S3, correcting the photo-generated current I in the five parameters according to the proportion of shadow shielding on the half solar cell ph Obtaining five parameters representing the electric characteristics of the half-cell shielded by the shadow, and substituting the five parameters of the half-cell not shielded by the shadow and the five parameters of the half-cell shielded by the shadow into the half-photovoltaic group respectivelyAnd obtaining the I-V curve of each half solar cell by the piece output characteristic equation.
The method comprises the following specific steps:
s3-1, simulating the output characteristics of a single half solar cell under different shielding ratios of 5%, 10%, 15% and 20% … …% and the output characteristics of a half photovoltaic module under the shielding of 100% of 1, 2, 1 row and 2 row solar cells, wherein the influence of shadow on the solar cell is mainly light receiving rate, and the light generated current I of the half solar cell is shielded by the shadow ph Can be expressed as:
I ph, shielding battery ＝a×I ph, half-cell ， (2)；
Wherein a is a shading proportion coefficient, the minimum is 0.001, the maximum is 1, and the larger the shading area is, the smaller the coefficient a is, which represents the I of the solar cell ph The smaller. In this embodiment, the half cell is 100% blocked; the shielding number is 4; the numbers of the shielding battery pieces are respectively 2-13,2-14,3-13 and 3-14, and the photo-generated current I of the shielding battery pieces ph Becomes 0.001 xI ph . The specific parameters are shown in the third row of table 2.
S3-2, substituting the five parameters of the batteries which are not blocked by the shadow and the five parameters of the batteries which are blocked by the shadow into the formula (1) respectively to obtain an I-V curve of each half solar battery. There are two ways to obtain the data points on the I-V curve, the first is from-b-bxI ph Traversing the working current I to obtain different working voltages V corresponding to the same current (namely, taking the working current I at intervals of.01); the second is from-b-bXV oc And traversing the working voltage V to obtain different working currents I corresponding to the same voltage (namely, taking the working voltage V at intervals of.01), wherein the value of the parameter b is 1.2, and the aim is to consider curve areas with negative voltage and current. As shown in fig. 2.
S4, summing the voltages V of all the half solar cells on each battery string according to the series circuit of the half solar cells in the battery strings, wherein the current I is unchanged, so as to obtain an I-V curve of each half battery string; judging whether the bypass diode for protecting the half-cell strings is conducted or not according to the principle that the bypass diode is conducted when the bypass diode is subjected to reverse voltage of 0.7V, and obtaining an I-V curve of each corrected half-cell string; and summing the current I of each parallel part according to the parallel circuit of the battery string in the half-piece photovoltaic module, wherein the voltage V is unchanged, so as to obtain I-V and P-V curves of the whole half-piece photovoltaic module under the shadow condition. The method comprises the following specific steps:
s4-1, numbering all the half-cells, and respectively marking two parallel partial cell domains as a cell domain I and a cell domain II according to the internal circuit structure of the half-cell photovoltaic module; dividing a battery string connected in series in a battery domain I into a battery string 1, a battery string 2 and a battery string 3, and dividing a battery string connected in series in a battery domain II into a battery string 4, a battery string 5 and a battery string 6; the bypass diode connected in parallel with the battery string 1 and the battery string 4 is denoted as a diode I, the bypass diode connected in parallel with the battery string 2 and the battery string 5 is denoted as a diode II, and the bypass diode connected in parallel with the battery string 3 and the battery string 6 is denoted as a diode III; finally, the serial number of any half solar cell in the half photovoltaic module is obtained; for example, the 24 th cell in the cell string 1, denoted as 1-24, is shown in fig. 3;
s4-2, calculating the output characteristics of each half solar cell according to the first method for obtaining the data points on the I-V curve in the step S3-2, and respectively adding the voltages of all half solar cells in the cell strings 1, 2, 3, 4, 5 and 6, wherein the current is kept unchanged to obtain the I-V curve of each cell string;
s4-3, processing the voltage value on the I-V curve of each battery string, and completely replacing the data of the bypass diode on voltage with the voltage value smaller than or equal to the corresponding battery string with-0.7V to obtain an updated I-V curve of each battery string; (here different output characteristics of the blocking and non-blocking cells and the turn-on and turn-off of the bypass diode are considered);
s4-4, respectively adding the voltages of 3 battery strings connected in series in the battery domain I and the battery domain II, and keeping the current unchanged to obtain an I-V curve of each battery domain; as in fig. 2 for the dashed and solid curves, the ordinate is unchanged and the abscissa is added (taking into account the negative region);
s4-5, considering that the battery domain I and the battery domain II are in a parallel structure, the current of the domain I and the current of the domain II need to be added, and the voltage remains unchanged. However, since only the field i is blocked, the voltages of the fields i and ii, which are obtained at the same current interval, are not equal in practice, and thus the currents of the two parallel parts cannot be superimposed at the same voltage interval. Therefore, to obtain the same voltage value, the second mode described in S3-2 is used to redraw the I-V curves of battery domain I and battery domain ii, and the specific steps are as follows: firstly, new voltage data traversed at the same voltage interval (0.01V) are listed, then, old voltages with the first voltage value being more than or equal to the old voltage value and the last voltage value being less than or equal to the new voltage value on an original curve (I-V curve of each battery domain obtained in S4-4) are found respectively, finally, current in the old voltage range is added and averaged to be used as current values corresponding to the new voltage value, and finally, two groups of updated I-V curves of the battery domain I and the battery domain II are obtained;
s4-6, adding the updated current of the battery domain I and the updated current of the battery domain II, and keeping the voltage unchanged to obtain an I-V curve and a P-V curve of the half-piece photovoltaic module. As in fig. 2 for the dashed and solid line portions, the abscissa is unchanged and the ordinate is added. (consider the negative area)
And verifying the I-V curve and the P-V curve of the obtained half photovoltaic module:
at irradiance of 1000W/m 2 Under the laboratory environment with the environmental temperature of 25+/-2 ℃ and the spectrum AM of 1.5, the black PVC plate is utilized to shade the battery position in the S30; and the output characteristics of the half-sheet photovoltaic module are measured by using a solar simulator of the German PASAN POWER. According to different shielding schemes in the step S3-1, the position of the PVC plate is adjusted, the temperature of the assembly is detected by using a temperature tester, and the assembly is tested once every 2 minutes after the temperature is stable. The measured I-V curve is compared to the simulated I-V curve plotted on a graph. Since the values are taken at current and voltage intervals of 0.01, there are more than 5000I-V data points. And the output characteristic curve of the half photovoltaic module is obtained finally, and the current and voltage values are too large. For easier mapping, 200I-V data points were selected from matlab and I-V curves were plotted. The final results are shown in fig. 4, and the experimental results are basically consistent with the simulation results, so that the accuracy of the evaluation method is verified. P (P) 1 And P 2 Peak power point on the P-V curve in fig. 4, at P 1 On the left side of the point, the battery piece of the component which is not affected by shadow works normally, and two diodes of the half-piece photovoltaic component shadow battery are in a conducting state. At P 1 Point-P 2 In between, all three diodes in the assembly are not conducted and are in a cut-off state. The half-sheet photovoltaic module continuously outputs in a mode of reducing current at the moment, and the shadow shields the battery from becoming a load to consume energy. But the maximum power is P 2 At this point, therefore, the half-sheet photovoltaic module is now outputting maximum performance while the shadow cell consumes energy. However, if the previous method is adopted, the parallel circuit structure is not considered, and the calculation is carried out as a whole-piece assembly, as shown in fig. 5, the result can be seen to be quite different, the maximum power of the whole-piece assembly is 108W, and the maximum power of the half-piece photovoltaic assembly is 193W; the power output loss of the whole photovoltaic module is huge and is 2 times that of the half photovoltaic module. Obviously, in the shadow shielding mode, the half photovoltaic module has remarkable power generation performance advantage, and the practical significance of the method is shown.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (3)
1. The method for accurately evaluating the output characteristics of the half photovoltaic module under the shadow shielding condition is characterized by comprising the following specific steps:
s1, obtaining five parameters required in an output characteristic equation for representing the half photovoltaic module according to nameplate parameters on the back of the half photovoltaic module, wherein the specific method comprises the following steps of:
s1-1, acquiring electric performance parameters of the half photovoltaic module and the number N of half solar cells under four standard measurement conditions from a nameplate attached to the back of the half photovoltaic module s The electrical performance parameters of the half-sheet photovoltaic module comprise an open circuit voltage V oc Short-circuit current I sc Maximum power point voltage V mpp And maximum powerPoint current I mpp ；
S1-2, listing an output characteristic equation of the half photovoltaic module, wherein the equation is shown in a formula (1):
in the formula (1), I ph Is a photo-generated current; i o Reverse saturation dark current for the diode; n is a diode management thinking factor; r is R s Is a series resistor; n (N) s The number of the half solar cells; k is Boltzmann constant, 1.38 x 10 -23 J/K; q is the charge number, 1.6x10 -19 C；T c The temperature of the half solar cell is 298.15K by adopting Kelvin temperature; r is R sh Is a parallel resistor; i and V are the operating current and operating voltage, respectively;
s1-3, an open circuit voltage V known from step S1-1 oc Short-circuit current I sc Maximum power point voltage V mpp Maximum power point current I mpp The five unknown parameters in the extraction equation of the output characteristic equation of the half photovoltaic module are the five parameters of the half photovoltaic module, wherein the five parameters of the half photovoltaic module comprise I ph, half-sheet photovoltaic module ，I o, half piece photovoltaic module ，n Half-sheet photovoltaic module ，R s, half piece photovoltaic module ，R sh, half piece photovoltaic module ；
S2, converting five parameters of the half-piece photovoltaic module into five parameters representing the electrical characteristics of each half-piece solar cell according to the number of the half-piece solar cells in the half-piece photovoltaic module;
s3, correcting the photo-generated current I in the five parameters according to the proportion of shadow shielding on the half solar cell ph Obtaining five parameters representing the electric characteristics of the half solar cells shielded by the shadow, and substituting the five parameters of the half solar cells which are not shielded by the shadow and the five parameters of the half solar cells shielded by the shadow into the output characteristic equation of the half photovoltaic module to obtain an I-V curve of each half solar cell; the method comprises the following specific steps:
s3-1, simulating a single half-sheetOutput characteristics of solar cells under different shielding ratios of 5%, 10%, 15%, 20% … …% and output characteristics of half photovoltaic modules under the shielding of 1 piece, 2 piece, 1 string, 2 string, 1 row and 2 row of solar cells 100%, and photo-generated current I in five parameters is corrected according to the ratio of shadow shielding on half solar cells ph Obtaining five parameters representing the electric characteristics of the half-cell shielded by the shadow, and generating the photo-generated current I of the half-cell shielded by the shadow ph Can be expressed as:
I ph, shielding battery ＝a×I ph, half-cell ，(2)；
In the formula (2), a is a shading proportion coefficient, a is 0.001 at minimum, a is 1 at maximum, and the larger the shading area is, the smaller the shading proportion coefficient a is, namely the I of the half-piece solar cell is represented ph The smaller;
s3-2, substituting five parameters of the half-cell which is not blocked by shadow and is obtained in the step S2 and five parameters of the half-cell which is blocked by shadow and is obtained in the step S3-1 into a formula (1) respectively to obtain an I-V curve of each half-cell, wherein two ways of obtaining data points on the I-V curve are adopted, and the first method is that the data points are obtained from-b-b multiplied by I ph Traversing the working current I to obtain different working voltages V corresponding to the same current; the second method is from-b-bXV oc Traversing the working voltage V to obtain different working currents I corresponding to the same voltage, wherein the value of the parameter b is 1.2;
s4, summing the voltages V of all the half solar cells on each battery string according to the series circuit of the half solar cells in the battery strings, wherein the current I is unchanged, so as to obtain an I-V curve of each half battery string; judging whether the bypass diode for protecting the half-cell strings is conducted or not according to the principle that the bypass diode is conducted when the bypass diode is subjected to reverse voltage of 0.7V, and obtaining an I-V curve of each corrected half-cell string; according to the parallel circuit of the battery string in the half-sheet photovoltaic module, the voltage V is unchanged, and the current I of each parallel part is summed to obtain I-V and P-V curves of the whole half-sheet photovoltaic module under the shadow condition, the specific method is as follows:
s4-1, numbering all the half-solar cells, and respectively marking two parallel battery domains as a battery domain I and a battery domain II according to the internal circuit structure of the half-photovoltaic module; dividing a battery string connected in series in a battery domain I into a battery string 1, a battery string 2 and a battery string 3, and dividing a battery string connected in series in a battery domain II into a battery string 4, a battery string 5 and a battery string 6; the bypass diode connected in parallel with the battery string 1 and the battery string 4 is denoted as a diode I, the bypass diode connected in parallel with the battery string 2 and the battery string 5 is denoted as a diode II, and the bypass diode connected in parallel with the battery string 3 and the battery string 6 is denoted as a diode III; finally, the serial number of any half solar cell in the half photovoltaic module is obtained;
s4-2, calculating the output characteristics of each half solar cell according to the first method for obtaining the data points on the I-V curve in the S3-2, respectively adding the voltages of all half solar cells in the cell strings 1, 2, 3, 4, 5 and 6, and keeping the current unchanged to obtain the I-V curve of each cell string;
s4-3, processing the voltage value on the I-V curve of each battery string, and completely replacing the data of the bypass diode on voltage with the voltage value smaller than or equal to the corresponding battery string with-0.7V to obtain an updated I-V curve of each battery string;
s4-4, respectively adding the voltages of 3 battery strings connected in series in the battery domain I and the battery domain II, and keeping the current unchanged to obtain an I-V curve of each battery domain;
s4-5, redrawing the I-V curves of the battery domain I and the battery domain II according to the second method for obtaining the data points on the I-V curves described in the S3-2, wherein the specific steps are as follows: firstly, new voltage data traversed at the same voltage interval are listed, secondly, old voltages with the first voltage value being more than or equal to and the last voltage value being less than or equal to the new voltage value on the original curve are found out respectively, finally, the current in the old voltage range is added and averaged to be used as the current value corresponding to the new voltage value, and finally, two groups of updated I-V curves of the battery domain I and the battery domain II are obtained;
and S4-6, adding the current of the I-V curve of the battery domain I and the current of the I-V curve of the battery domain II updated by the S4-5, and keeping the voltage unchanged to obtain the I-V curve and the P-V curve of the half photovoltaic module.
2. The method for accurately evaluating the output characteristics of a half-sheet photovoltaic module under a shadow masking condition according to claim 1, wherein the specific steps of S2 are as follows:
according to the five parameters of the half-sheet photovoltaic module obtained in the step S1-3 and the number N of the half-sheet solar cells in the half-sheet photovoltaic module s Converting five parameters of the half-sheet photovoltaic module into five parameters of each half-sheet solar cell, wherein the five parameters of each half-sheet solar cell comprise: i ph, half-cell ，I o, half-cell ，n Half-cell battery ，R s, half-cell ，R sh, half-cell battery Wherein I ph, half-cell ＝I ph, half-sheet photovoltaic module /2；I o, half-cell ＝I o, half piece photovoltaic module /2；n Half-cell battery ＝n Half-sheet photovoltaic module ；R s, half-cell ＝R s, half piece photovoltaic module ×2；R sh, half-cell battery ＝R sh, half piece photovoltaic module ×2。
3. The method for accurately evaluating the output characteristics of a half-photovoltaic module under a shadow mask condition according to claim 1, wherein in S3-1, when the mask ratio of the single-piece solar cell is 100%, the mask ratio coefficient a=0.001.
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