CN105281666A - Method for improving test precision of solar cell radiation sensor - Google Patents

Abstract

The invention discloses a method for improving test precision of a solar cell radiation sensor. By analyzing the relations, between the solar cell area, adopted circuits and load resistances with the test precision, in the solar cell radiation sensor, a direction for the accurate design for the cost-effective solar radiation sensor is provided.

Description

A kind of method improving solar cell irradiation sensor measuring accuracy

Technical field

The present invention relates to a kind of method improving solar cell irradiation sensor measuring accuracy, belong to photovoltaic system technical field.

Background technology

Along with the development of photovoltaic system, the assessment of photovoltaic efficiency seems particularly important.Photovoltaic system efficiency refers generally to actual power and exports and the ratio arriving photovoltaic arrays surface irradiation total amount, irradiation accurate, Quick Measurement is most important to photovoltaic system efficiency evaluation.And the assessment of photovoltaic system mainly realizes by solar radiation sensor, one is made up of combination thermoelectric pile circuit, can comparatively accurate response radiation intensity, but can not embody the impact that radiation spectrum difference arrives on photovoltaic generation.Another kind then adopts solar cell as global solar radiation transducer, basically identical with the solar cell spectral response of photovoltaic generation, eliminates the impact of radiation spectrum difference on photovoltaic generation.

Making solar cell as the general principle of global radiation transducer is: irradiation intensity value is converted to short-circuit current value by solar cell, magnitude of voltage is converted into as load again by series connection precision resister, finally resistance is connected with single-chip microcomputer, the voltage signal that single-chip microcomputer gathers load two ends carries out computing (as shown in Figure 1), and irradiation value (LCD) in LCDs shows the most at last.The parameter relevant to measuring process is respectively: the magnitude of voltage U (unit: V) at load two ends, flows through the circuit values I (unit: A) of load, resistance value R (unit: Ω), irradiation intensity H (unit: W/m ²).

In solar radiation sensor circuit, AD conversion module is responsible for gathering solar cell load both end voltage, and converts this analog voltage signal to digital signal, and input single-chip microcomputer carries out computing.The several concepts relevant to transducer have:

1, the figure place of ADC (analog to digital converter)

The ADC of a n position represents that this ADC has a n power scale of 2.The ADC of 8, output be have 256 digital quantities altogether from 0 ~ 255, a namely 8 powers data scale of 2.

2, a reference source

A reference source, is also reference voltage, is an important indicator of ADC, and want accurate for the signal measurement of input ADC, so first a reference source want accurate, and the deviation of a reference source directly can cause the deviation of transformation result.

3, resolution

Resolution is digital quantity when changing a minimum scale, and the variable quantity of analog signal, is defined as full-scale range and 2 ⁿthe ratio of-1.Assuming that the electrical voltage system of 5.10V, use the ADC of 8 to measure, be so equivalent to 0 ~ 255 and have 256 scales altogether 5.10V has been divided into 255 parts, so resolution is exactly 5.10/255=0.02V.

Summary of the invention

Making in the process using solar cell as global radiation transducer, the guarantee of irradiation precision is particularly important.The present invention, by from the sample circuit design of irradiatometer and the reasonability two aspect deployment analysis of solar cell size Selection, provides a kind of method improving solar cell irradiation sensor measuring accuracy, thus ensures the precision of irradiatometer.

For achieving the above object, the technical solution used in the present invention is as follows:

Improve a method for solar cell irradiation sensor measuring accuracy, comprise the following steps:

1) suppose that in solar cell irradiation sensor, digital to analog converter figure place is n position, reference voltage is X, then the resolution x of sample circuit is:

$x=\frac{X}{2^n-1}---\left(1\right)$

2) establish certain moment irradiation changes delta H', change in voltage is Δ U, then, irradiation sensor minimum resolution Δ H is calculated by following relation:

$\frac{{\mathrm{\ΔH}}^{\′}}{\mathrm{\Δ}H}=\frac{\mathrm{\Δ}U}{x}---\left(2\right)$

3) according to formula (2), when sample circuit is determined, increase change in voltage Δ U, the value of irradiation sensor minimum resolution Δ H can be reduced, namely improve irradiation sensor measuring accuracy.

Aforesaid step 3) in, in solar cell irradiation sensor, change in voltage Δ U is the voltage U at the load two ends of connecting at solar cell two ends, increases the concrete grammar that namely change in voltage Δ U improves the voltage U at load two ends, comprises the following steps:

3-1) for certain model solar cell, if irradiation intensity H, solar battery assembly efficiency η, solar cell area A are known, then the power output P of this solar cell is:

P＝H·A·η(3)

3-2) in conjunction with formula P=UI=U ²/ R, can obtain:

$U=\sqrt{P\·R}=\sqrt{H\·A\·\mathrm{\η}\·R}---\left(5\right)$

Wherein, I represents the electric current by load, and R represents load resistance;

If 3-3) irradiation intensity H, solar battery assembly efficiency η, load resistance resistance R determine, then according to formula (5), the area A of solar cell is larger, and the voltage U at load two ends is larger, and irradiation sensor precision is higher;

If the area A of irradiation intensity H, solar battery assembly efficiency η, solar cell is determined, then according to formula (5), load resistance resistance R is larger, and the voltage U at load two ends is larger, and irradiation sensor precision is higher.

Aforesaid step 3-3) in, described load resistance resistance R must meet:

Wherein, U _ocrepresent the open circuit voltage of solar cell, I _screpresent the short circuit current of solar cell.

Aforesaid step 3-3) in, due to the size restrictions of irradiation sensor solar cell used, the open-circuit voltage values of solar cell own within 10V, then solar cell connect load two ends voltage U must meet: U < 10V.

Aforesaid according to formula (1) and formula (2), obtain:

$\frac{{\mathrm{\&Delta;H}}^{\&prime;}}{\mathrm{\&Delta;}H}=\frac{\mathrm{\&Delta;}U}{\frac{X}{2^n-1}}$

According to above formula, when change in voltage Δ U can not increase, improve irradiation sensor digital to analog converter figure place n, the value of irradiation sensor minimum resolution Δ H can be reduced, namely improve irradiation sensor measuring accuracy.

The present invention proposes a kind of circuit design of simple solar radiation sensor, and by the relation with measuring accuracy such as analysis solar cell area, employing circuit, for the careful design of high performance-price ratio solar radiation sensor provides direction.

Accompanying drawing explanation

Fig. 1 is solar cell irradiation sensor fundamental diagram;

Fig. 2 is solar cell irradiation sensor internal circuit diagram of the present invention;

Fig. 3 is solar cell area and irradiation accuracy relation curve chart in embodiments of the invention.

Embodiment

Now in detail the present invention is described in further detail with embodiment by reference to the accompanying drawings.

As shown in Figure 2, solar cell irradiation sensor circuit of the present invention comprises single-chip microcomputer, digital to analog converter, GPS module and LCD1602 screen display.Wherein,

U1 in single-chip microcomputer and Fig. 2, is connected with LCD1602 screen display, digital to analog converter U2, GPS module.Have the irradiation instrument working procedure that programming is good in single-chip microcomputer U1, single-chip microcomputer U1 receives the digital signal that digital to analog converter U2 exports, and after the process of irradiation instrument working procedure calculates, then sends to LCD1602 screen display irradiation.

Digital to analog converter adopts PCF8951, the U2 namely in Fig. 2, and connecting the load resistance of solar cell, is input end of analog signal on the right side of Fig. 2.The analog voltage signal of input is converted to digital voltage signal input single-chip microcomputer U1 and calculates by digital to analog converter U2.

GPS module (omitting in Fig. 2) can automatic reception locating information, locating information is sent to wherein by single-chip microcomputer U1 serial ports, single-chip microcomputer plug-in can resolve the latitude in locating information, temporal information, and the necessary constant that latitude and time calculate as irradiation value participates in computing.

LCD1602 screen display comprises RP1 and RV1, and receive the irradiance data that will show that single-chip microcomputer U1 sends, and show on screen, the program package of support screen work is contained in single-chip microcomputer, forms the total program of irradiation instrument work with other program groups.

Solar cell irradiation sensor measuring accuracy is by the impact of following factor.

One, the impact of sample circuit precision

Suppose according to selected circuit requirement, Chip Microcomputer A/D converter voltage reference used is X, ADC figure place is n, then its resolution (when digital quantity changes a minimum scale, the variable quantity of analog signal) x is:

$x=\frac{X}{2^n-1}---\left(1\right)$

If certain moment irradiation changes delta H', change in voltage is Δ U, then, irradiation minimum resolution and irradiation precision Δ H are calculated by following relation:

$\frac{{\mathrm{\&Delta;H}}^{\&prime;}}{\mathrm{\&Delta;}H}=\frac{\mathrm{\&Delta;}U}{x}---\left(2\right)$

Suppose according to selected circuit requirement, Chip Microcomputer A/D modular converter reference voltage used is 5.1V, ADC figure place is 8, then its resolution is: x=5 ÷ (2 ⁸-1)=0.02V, then, irradiation change precision Δ H is calculated by following relation:

$\frac{{\mathrm{\&Delta;H}}^{\&prime;}}{\mathrm{\&Delta;}H}=\frac{U}{0.02}$

To ensure the minimum value Δ H=1W/m that final irradiatometer irradiation intensity changes ²(namely when solar cell load both end voltage is 0.02V, corresponding irradiation intensity is 1W/m ²), then at standard test condition, (irradiation intensity is 1000W/m ²) under, the magnitude of voltage corresponding to load two ends is $U=\frac{x\&CenterDot;{\mathrm{\&Delta;H}}^{\&prime;}}{\mathrm{\&Delta;}H}-=\frac{1000W/m^2\&times;0.02V}{1W/m^2}=20V,$ And due to the size restrictions of irradiatometer solar cell used, the open-circuit voltage values of solar cell own is generally within 10V, then connect load both end voltage must be less than 10V.Therefore at current 8 ADC, when reference voltage 5.1V, the minimum change (resolution) of irradiatometer cannot reach 1W/m ².

ADC figure place is brought up to 10, and reference voltage is 5.1V, then resolution is corresponding irradiatometer minimum resolution is Δ H=1W/m ².In like manner under standard test condition, the voltage corresponding to load two ends is $U=\frac{1000W/m^2\&times;0.005V}{1W/m^2}=5V,$ The requirement of solar cell itself can be met.

As can be seen here, if solar cell connects load both end voltage, value is larger, and irradiatometer resolution is higher, but the size restrictions of solar cell load voltage can not infinitely increase; Now adopt the method improving irradiatometer ADC figure place, the resolution of final irradiatometer can be made also will to be improved.

Two, solar cell is on the impact of final irradiation precision

The area of solar cell determines the size of its power output, and the size of power output determines the magnitude of voltage at solar cell load two ends and flows through the current value size of load.

For certain model solar cell, if irradiation intensity H, solar battery assembly efficiency η, solar cell area A (or length of side) are known, then the power output (unit: W) of this battery is

P＝H·A·η(3)

Be such as 1000W/m at irradiation intensity ²under condition, selected solar battery assembly efficiency is 15%, solar cell size 80mm × 80mm, then assembly power output P=1000W/m ²× 80 × 80 × 10 ^-6m ²× 15%=0.96W.

Again by formula

P＝UI＝U ²/R(4)

Can be obtained by (3), (4):

$U=\sqrt{P\&CenterDot;R}=\sqrt{H\&CenterDot;A\&CenterDot;\mathrm{\&eta;}\&CenterDot;R}---\left(5\right)$

As can be seen here, improve irradiation precision, except improving ADC figure place, the value still improving load voltage U by following methods realizes, that is:

I. the solar cell that photovoltaic efficiency η is higher is selected, as 19%;

II. select rational solar cell size, suitably can increase the value of solar cell area A;

III. suitable load resistance is selected.

(1) area of solar cell is changed when load resistance resistance R determines

The determination of load resistor value first can measure the open circuit voltage U of solar cell _ocand short circuit current I _scsize, then exist load resistance is selected in scope.Such as, certain solar cell is recorded at 1000W/m ²u under condition _oc=6.05V, I _sc=0.2A, then can select the load resistance within the scope of 10 Ω ~ 15 Ω, ensure survey linear relationship between irradiation intensity and load voltage (electric current).If now get load resistance R=15 Ω, efficiency of solar cell 20%, getting ADC figure place is 12, then according to formula (5), can show that the relation between solar cell area and load voltage, irradiation precision is as shown in table 1 below:

The relation of table 1 solar cell area and load voltage, irradiation precision

Wherein, load voltage calculates according to formula (5), and irradiatometer minimum resolution Δ H presses calculate, here bearing power calculates by formula (3).

According to table 1, make solar cell area and irradiation accuracy relation curve chart as shown in Figure 3, as seen from Figure 3, when above-mentioned condition is constant, along with the increase of solar cell area, irradiatometer minimum resolution reduces, and means that irradiation precision is improved.

(2) in the fixed situation of solar cell size, suitable load resistance is selected

According to above-mentioned conclusion, solar cell area is larger, and under certain radiation parameter, it can be supplied to the voltage of load, electric current (can also say power output) is larger.Know according to formula (5), load resistor value is also the variable determining irradiation precision, if now determined solar cell size, if selected solar cell size 70mm*70mm, at 1000W/m ²u under condition _oc=6.05V, I _sc=0.2A, efficiency of solar cell 20%, getting ADC figure place is 12, and now H, A, η are definite value, and load voltage U is relevant with load resistance R.For the determination of load resistance R, can first utilize obtain the maximum occurrences R of a R _m, then according to this R _mtake advantage of in certain proportion, in like manner obtained the relation of irradiation precision and load voltage by computational analysis.According to above parameter, obtain R _m=30.25 Ω, then:

Relation between table 2 load resistance and load voltage, irradiation precision

Wherein, load voltage calculates according to formula (5), and irradiation precision Δ H presses calculate, here $x=\frac{5.1}{2^{12}-1}=\mathrm{0.001.}$

Be not difficult to find by his-and-hers watches 2 analysis, actual loading resistance is larger, and load both end voltage is larger, and irradiation precision is higher.But the value of load resistance R is not infinitely to increase, when load resistor value is too high, the voltage at load two ends, between electric current and irradiation value, lose significantly linear relationship itself, and then cause irradiatometer accurately can not measure the irradiation value in this moment.Now according to related data, select to meet resistance value in scope can ensure load voltage, linear relationship between electric current and irradiation.

Claims (5)

1. improve a method for solar cell irradiation sensor measuring accuracy, it is characterized in that, comprise the following steps:

1) suppose that in solar cell irradiation sensor, digital to analog converter figure place is n position, reference voltage is X, then the resolution x of sample circuit is:

$x=\frac{X}{2^n-1}---\left(1\right)$

2) establish certain moment irradiation changes delta H', change in voltage is Δ U, then, irradiation sensor minimum resolution Δ H is calculated by following relation:

$\frac{{\mathrm{\&Delta;H}}^{\&prime;}}{\mathrm{\&Delta;}H}=\frac{\mathrm{\&Delta;}U}{x}---\left(2\right)$

3) according to formula (2), when sample circuit is determined, increase change in voltage Δ U, the value of irradiation sensor minimum resolution Δ H can be reduced, namely improve irradiation sensor measuring accuracy.

2. a kind of method improving solar cell irradiation sensor measuring accuracy according to claim 1, it is characterized in that, described step 3) in, in solar cell irradiation sensor, change in voltage Δ U is the voltage U at the load two ends of connecting at solar cell two ends, increase the concrete grammar that namely change in voltage Δ U improves the voltage U at load two ends, comprise the following steps:

3-1) for certain model solar cell, if irradiation intensity H, solar battery assembly efficiency η, solar cell area A are known, then the power output P of this solar cell is:

P＝H·A·η(3)

3-2) in conjunction with formula P=UI=U ²/ R, can obtain:

$U=\sqrt{P\&CenterDot;R}=\sqrt{H\&CenterDot;A\&CenterDot;\mathrm{\&eta;}\&CenterDot;R}---\left(5\right)$

Wherein, I represents the electric current by load, and R represents load resistance;

If 3-3) irradiation intensity H, solar battery assembly efficiency η, load resistance resistance R determine, then according to formula (5), the area A of solar cell is larger, and the voltage U at load two ends is larger, and irradiation sensor precision is higher;

If the area A of irradiation intensity H, solar battery assembly efficiency η, solar cell is determined, then according to formula (5), load resistance resistance R is larger, and the voltage U at load two ends is larger, and irradiation sensor precision is higher.

3. a kind of method improving solar cell irradiation sensor measuring accuracy according to claim 2, is characterized in that, described step 3-3) in, described load resistance resistance R must meet:

Wherein, U _ocrepresent the open circuit voltage of solar cell, I _screpresent the short circuit current of solar cell.

4. a kind of method improving solar cell irradiation sensor measuring accuracy according to claim 2, it is characterized in that, described step 3-3) in, due to the size restrictions of irradiation sensor solar cell used, the open-circuit voltage values of solar cell own within 10V, then solar cell connect load two ends voltage U must meet: U < 10V.

5. a kind of method improving solar cell irradiation sensor measuring accuracy according to claim 1, is characterized in that, according to formula (1) and formula (2), obtains:

$\frac{{\mathrm{\&Delta;H}}^{\&prime;}}{\mathrm{\&Delta;}H}=\frac{\mathrm{\&Delta;}U}{\frac{X}{2^n-1}}$

According to above formula, when change in voltage Δ U can not increase, improve irradiation sensor digital to analog converter figure place n, the value of irradiation sensor minimum resolution Δ H can be reduced, namely improve irradiation sensor measuring accuracy.