CN102818995A - Variable frequency and high speed sampling handheld photovoltaic cell tester and method for achieving same - Google Patents

Abstract

The invention discloses a variable frequency and high speed sampling handheld photovoltaic cell tester and a method for achieving the same. The tester is designed by using a field programmable gate array (FPGA) chip EP2C8T144C6 combined with an analog-to-digital converter (ADC) chip AD9245-40, current voltage sampling points (P1 and P2) access to an input end of a cascade circuit to a programmable amplifier chip, an output end of the cascade circuit is accessed to an analog input port of the AD9245-40, and a 14-bit output of the AD9245-40 is accessed to an input/output (I/O) input port of the EP2C8T144C6. According to the variable frequency and high speed sampling handheld photovoltaic cell tester and the method for achieving the same, the highest sampling rate can achieve 32 MHz, a variable frequency sampling method is used, the problem of unreasonable data distribution is solved, the data redundancy is reduced, an obtained a voltage-current (I-V) curve is smooth, and relevant parameters are accurate and stable.

Description

A kind of frequency-conversion high-speed sampling hand-held photovoltaic cell tester and its implementation

Technical field

The invention belongs to the manual testing device field, be specifically related to a kind of frequency-conversion high-speed sampling hand-held photovoltaic cell tester and its implementation.

Background technology

At present, known employing electric capacity is based on as the photovoltaic cell component tester of electronic load that MCU designs, and sampling rate is very limited.And it adopts the at the uniform velocity method of sampling; The current-voltage sampling rate is constant in whole sampling process, and according to charging voltage-time curve, and charging current-time curve can be known; Sampling at the uniform velocity can make sampling number excessively intensive at electric current-voltage (on the curve of I-V) near the place of open-circuit voltage; So not only wasted limited sampled point, make the sampling number of curve main part more sparse, and intensive sampling point ADC can't differentiate.So after the filtering, the line smoothing degree is relatively poor, and the error of some important parameters that obtain from curve is bigger.

Summary of the invention

In order to obtain accurate more acquisition parameter and more level and smooth I-V curve and the redundancy that reduces data, the present invention adopts FPGA to design, and generates special-purpose sampling module with FPGA; Improve the high sampling rate of system greatly, and adopted the method for frequency-change sampling, solved the irrational problem of DATA DISTRIBUTION; Reduced data redundancy; The I that obtains-V curve is more smooth, and correlation parameter is more accurate, and is stable.

The technical solution adopted for the present invention to solve the technical problems is: a kind of frequency-conversion high-speed sampling hand-held photovoltaic cell tester; Comprise electric capacity, current/voltage collection point (P1, P2), MOS switching tube (S1, S2, S3), fpga chip, ADC chip, program control amplification chip; It is characterized in that; The cascade circuit input end of described program control amplification chip is inserted in described current/voltage collection point (P1, P2); The output of cascade circuit inserts the analog input port of described ADC chip, and 14 outputs of described ADC chip insert the I/O input port of described fpga chip; The cascade amplification coefficient of described three the MOS switching tubes of described fpga chip Control current voltage acquisition (S1, S2, S3), said program control amplification chip, and the sampling clock that said ADC chip is provided.

The method that realizes described frequency-conversion high-speed sampling hand-held photovoltaic cell tester is divided into four-stage:

Phase one is a charging voltage less than period of 70% of open-circuit voltage, and SF is set at: F1=(1000/Tcharge) * 4, and Tcharge is charging T.T.;

Subordinate phase is a charging voltage greater than 70% and charging current of open-circuit voltage stage of 65% greater than short-circuit current, is set at F2=F1 * 4;

Phase III be charging current short-circuit current 65% and 33% between stage, SF is set at F3=F1;

Stage is a charging current less than stage of 33% of short-circuit current, and 40 points of the every collection of SF reduce by half once, finish up to the sampling time.

The invention has the beneficial effects as follows, solved the irrational problem of DATA DISTRIBUTION, reduce data redundancy, the I that obtains-V curve is more smooth, and correlation parameter is more accurate, and is stable.Repeatable comparative result is: the maximum power point electric current repeatability that obtains of at the uniform velocity sampling is 5.5%, and the maximum power point voltage repeatability is 5.9%, and the peak power repeatability is 1.41%, and the fill factor, curve factor repeatability is 1.41%; The maximum power point electric current repeatability that the speed change sampling obtains is 2.7%, and the maximum power point voltage repeatability is 2.8%, and the peak power repeatability is 0.37%, and the fill factor, curve factor repeatability is 0.37%.

Description of drawings

Below in conjunction with accompanying drawing the present invention is described further.

Fig. 1 is an overall design block diagram of the present invention.

Fig. 2 is current/voltage acquisition principle figure of the present invention.

Fig. 3 is that current/voltage of the present invention is gathered structural drawing.

Fig. 4 is a process flow diagram of realizing the inventive method.

Accompanying drawing 2 signs: PV is a photovoltaic cell, and S1, S2, S3 are the MOS switching tube, and R1 is a current sampling resistor, and R2 is a capacitor discharge resistance, and R3, R4 are voltage sample resistance, and C is an electric capacity, and P1, P2 are respectively the current/voltage acquisition node.

Accompanying drawing 4 sign: U ₀Be charging voltage, U ₁Be open-circuit voltage, I ₀Be charging current, I ₁Be short-circuit current, F1, F2, F3 are SF.

Embodiment

In Fig. 1, the major control module is controlled the whole process of measuring.Under the control of major control module, the environmental parameter acquisition module is gathered temperature and light intensity parameter, and display module can show open-circuit voltage, short-circuit current and the fill factor, curve factor of current tested battery; Initialization module is realized the program control amplification coefficient of electric current and voltage signal is carried out best configuration, thereby makes full use of the resolution of A/D, and measures the open-circuit voltage and the short-circuit current of photovoltaic cell; Size according to open-circuit voltage and short-circuit current calculates the duration of charging; And the initial sampled frequency, sampling module mainly is the frequency-change sampling of accomplishing signal, according to the process of charging; Different sampling rates is provided; The effect of memory module is after gathering completion, and in the Flash storer, this instrument of RS232 serial interface module realization is communicated by letter with PC with the data storage among the FIFO in the FPGA.

In Fig. 2, the duty of three MOS switching tubes (S1, S2, S3) control circuit realizes the measurement to photovoltaic cell PV open-circuit voltage, short-circuit current and I-V curve.When measuring short-circuit current; MOS switching tube S1 conducting; MOS switching tube S2 breaks off, and electric current directly flows back to negative pole from the positive pole of photovoltaic cell PV through current sampling resistor R1, because current sampling resistor R1 resistance is very little; Photovoltaic cell PV can be considered the state that is in short circuit, and can collect the size of short-circuit current this moment from current acquisition node P1.When measuring open-circuit voltage, MOS switching tube S1 and MOS switching tube S2 all break off, because the voltage acquisition resistance is bigger, photovoltaic cell PV can be regarded as open circuit, and can collect the size of open-circuit voltage this moment from voltage acquisition node P2.Before I-V curve is measured in charging to capacitor C, discharge to capacitor C, S3 conducting this moment, capacitor C is through 2 discharges of capacitor discharge resistance R.When measuring I-V curve, MOS switching tube S1 breaks off, MOS switching tube S2 conducting; MOS switching tube S3 breaks off; Photovoltaic cell PV charges to capacitor C, reaches the open-circuit voltage of photovoltaic cell PV up to the capacitor C terminal voltage, in this process; Carry out the high frequency sampling of electric current and voltage at current acquisition node P1 and voltage acquisition node P2, just can obtain I-V curve.

In Fig. 3; A kind of frequency-conversion high-speed sampling hand-held photovoltaic cell tester; Comprise electric capacity, current/voltage collection point (P1, P2), MOS switching tube, fpga chip, ADC chip, program control amplification chip PGA202, program control amplification chip PGA203; Described fpga chip is selected EP2C8T144C6 for use, and described ADC chip is selected AD9245-40 for use, and described EP2C8T144C6 combines described ADC chip AD9245-40 design.

The cascade circuit input end of described program control amplification chip is inserted in described current/voltage collection point (P1, P2); The output of cascade circuit inserts the analog input port of described ADC chip, and 14 outputs of described ADC chip insert the I/O input port of described fpga chip; The cascade amplification coefficient of described three the MOS switching tubes of described fpga chip Control current voltage acquisition (S1, S2, S3), said program control amplification chip, and the sampling clock that said ADC chip is provided.

Described program control amplification chip can be selected PGA202 and two kinds of models of PGA203 for use.

In Fig. 4, realize that the method for described frequency-conversion high-speed sampling hand-held photovoltaic cell tester is divided into four-stage:

Phase one is charging voltage U ₀Less than open-circuit voltage U ₁Period of 70%, SF is set at: F1=(1000/Tcharge) * 4, Tcharge is charging T.T.;

Subordinate phase is charging voltage U ₀Greater than open-circuit voltage U ₁70% and charging current I ₀Greater than short-circuit current I ₁Stage of 65%, be set at F2=F1 * 4;

Phase III is charging current I ₀At short-circuit current I ₁65% and 33% between stage, SF is set at F3=F1;

Stage is charging current I ₀Less than short-circuit current I ₁Stage of 33%, 40 points of the every collection of SF reduce by half once, finish up to the sampling time.

Claims (3)

1. frequency-conversion high-speed sampling hand-held photovoltaic cell tester; Comprise electric capacity, current/voltage collection point (P1, P2), MOS switching tube (S1, S2, S3), fpga chip, ADC chip, program control amplification chip; It is characterized in that; The cascade circuit input end of described program control amplification chip is inserted in described current/voltage collection point (P1, P2); The output of cascade circuit inserts the analog input port of described ADC chip, and 14 outputs of described ADC chip insert the I/O input port of described fpga chip.

2. frequency-conversion high-speed sampling hand-held photovoltaic cell tester according to claim 1; It is characterized in that; The cascade amplification coefficient of described three the MOS switching tubes of described fpga chip Control current voltage acquisition (S1, S2, S3), said program control amplification chip, and the sampling clock that said ADC chip is provided.

3. realize the method for the described frequency-conversion high-speed sampling of claim 1 hand-held photovoltaic cell tester, it is characterized in that, realize that the method for described frequency-conversion high-speed sampling hand-held photovoltaic cell tester is divided into four-stage:

Phase one is a charging voltage less than period of 70% of open-circuit voltage, and SF is set at: F1=(1000/Tcharge) * 4, and Tcharge is charging T.T.;

Subordinate phase is a charging voltage greater than 70% and charging current of open-circuit voltage stage of 65% greater than short-circuit current, is set at F2=F1 * 4;

Phase III be charging current short-circuit current 65% and 33% between stage, SF is set at F3=F1;

Stage is a charging current less than stage of 33% of short-circuit current, and 40 points of the every collection of SF reduce by half once, finish up to the sampling time.

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