solar cell equation

[SPECTRE]

I am implementing the mathematical model of a solar cell, with the ideal solar cell equation as my basis. This is to be part of a simulation of a PV system that includes a solar cell, an MPPT algorithm, and a DC-DC converter. I am familiar with NI's toolkit for I-V characterization of PV cells, and I am using the *lvm files for voltage as inputs to my VI. However, it seems that I am getting incorrect values in the XY graph, especially at the y-axis. Can anyone knowledgeable with PV cells take a look at my VI? I have included the VI and the *lvm file I used. Thanks in advance.

[Anjelica-W]

Based on the equation in your VI, the dataflow of the functions looks correct. I ran an array of sample voltages into the input of the multiplier that starts the equation and received outputs that correspond to the equation you provided. As a result of the numbers selected for the values of the constants, it seems that small values of voltage will give a current of 0.5

Where did you get the values of voltages from in the .lvm file? I would recommend looking into how your inputs are being acquired to ensure you are starting out with values you expect.

[SPECTRE]

Hello and thanks for answering! The values in the lvm files were obtained from NI's toolkit for I-V characterization. As to how the inputs are entered, I read in here http://forums.ni.com/t5/LabVIEW/photovoltaic-Characterization-with-Solartoolkit-Hardware/m-p/1767400 that the voltage must be entered in ascending order of magnitude. I attached the toolkit's  Open circuit voltage/short circuit current VI to my own VI, but the curves still do not look right. I am now thinking that I need a better equation to accurately model the solar cell.

Many thanks,

SPECTRE

[Anjelica-W · Accepted solution]

Have you tried using the VIs provided by the toolkit without any modifications to compare to the values you are receiving?

Do you receive the correct values when you manually input constants to the equation?

I found a tutorial that might be helpful about the I-V toolkit pertaining to photovoltaic cells.

http://zone.ni.com/devzone/cda/tut/p/id/7230

Hope this helps!

[SPECTRE]

Yes, I have tried using the VIs without modifying anything. The values I get from the toolkit VIs were different from what I got.

However, when I tried entering values manually, and turning off autoscale for the axes, I got a squarlish looking, somewhat more accurate graph. The I-V graph I got was definitely more like the expected I-V curve solar cells. Attached is the resulting I-V graph.