Curve Fit for PhotoVoltaic

[chtan23]

I had tried but i just couldn't solve my problem .

I am new to Labview.

So i need some help form you guys here.

I have and equation

I = Isc - Io((exp(q*(V+(I*Rs))/(k*T))-1) -((V+I*Rs)/Rp))

This is a standard Photovoltaic equation

All values could be obtained except for Rs and Rp

Therefore a curve fitting equation method is needed to solve the both constants (Rs and Rp)

A set of data of I and V  has already been obtained from the actual PV system. Therefore the IV graph could the drawn.The equation for the IV graph is the above.

How to solve Rs and Rp . I tried but failed. As you see I parameter is also on the Left Hand Side of the equation. Help me please i have been stuck on this for some time now

[chrisger]

hi there

try the "Curve Fitting" express VI. you can find it at "Mathematics"->"Curve Fitting" (it's the vi with the light blue frame). open it, switch to "nonlinear" and configure it. when the result is satisfying for your needs right click on the vi's icon in the diagram and select "Open Front Panel" and confirm "Convert". then you'll be able to look inside the vi and see how it's done.

[devchander]

I have done an application in past that acquires, plots and derieves the V-I curve for a photovoltaic cell and also derieves Series and Parallel resistances

Right now, I do not have labVIEW on my sytem and cannot open that VI and search for that section.

I also could not locate the documentation of that application.

But I clearly remember having refered to some material that showed up in google to derieve Series and parallel Resistances. ( again I cannot recall which particular site)

Do some search on google and u must be able to find those direct equations.

Message Edited by devchander on 07-17-2006 04:02 AM

[chtan23]

Hey devchander ,I am really glad that you had done what i am doin now. Could you please help me find the files you had done, to give me a head start in my work.

I am really stuck at this and it has been driving me nuts. I was only able to master exponential and polynomial curvefitting tools thru the examples given.

Unfortunately I could not master the non linear  curve fitting tool which i think is able to solve the Rs and Rp . Any comments ?

[devchander]

As I told in my previous mail, I really want to give you a better solutution, but presently I am not in position.

Shall try to find a system where LabVIEW is installed and open those VI's and pass the VI's

but it willl take time, hope your requirement can wait

regards

Dev

[chtan23]

Thanks man will be waitin for ya .....

Anyway as the problem above.

The I is also located in the left hand side do you think nonlinear curve fit is able to solve a problem like this ? 

[devchander]

The I is also located in the left hand side do you think nonlinear curve fit is able to solve a problem like this ? 

All labview curve fit VI's take input in terms of set of points (X and Y)

So, sorry pal, I am not sure how to answer your question!

but will try to give those equations I had used asap

[DFGray]

If you have not done so yet, I would strongly urge you to pick up a copy of Numerical Recipes in C, by Press et. al. and read the chapters on curve fitting, especially non-linear curve fitting.  You can find the book at most libraries, so you don't need to buy it.  It has a fairly good explanation of all the pertinent algorithms and how they work.  This will be invaluable, because there are a number of nasty pitfalls to nonlinear curve fitting.  You will find LabVIEW has the tools to do any of the techniques in the book.  Most of the algorithms are already implemented, so you just need to plug in your data.  But you need to know how.  Read the book.  Good luck.  Let us know if you are still having problems.

[chtan23]

Hi Chrisger and Everyone , I had already tried non linear curve fitting. Unfortunately i dont know how to post my program here.

THe problem with it is that the y parameter i located both in the left and right hand side of the equation.

Can someone please help me out ?

[chtan23]

Below is the attached picture of of my program