ACCEPTED SOLUTION
Accepted Solutions
Werner Exinger escribió:
At least the error is now more meanigful - if you use trace error it says that the no solution was found and suggested to change TOL/CTOL (which didn't help) or provide different guess values. So if your equations are correct try the correct solution values as guess values to see if it would come to an solution.
The five reference parameters (a, Io, Iph, Rs, and Rp) can be
obtained by simultaneously solving Eq. (7) through Eq.
(11) using the Mathcad solve block (Given …. Find) and
by implementing the method of Conjugate Gradients.
The necessary guess values are easily determined as
follows:
The value Iph is approximately equal to the value of Isc
which can be used as a good guess value. Usually, the diode quality factor 1 ≤ a ≤ 1.5 . The reverse saturation current Io guess value can be obtained using the following equation.
A guess value for Rp can be obtained by evaluating Eq. 2 at
open circuit condition. Also, a guess value for Rs can be
obtained by evaluating Eq. 2 at short circuit condition and
assuming Rp→ ∞
Plotting theP–V andI–V curves requires solving (2) for I∈[0,Isc,n] and V∈[0,Voc,n]. Equation (2) does not have
a direct solution because I=f(V,I) and V=f(I,V).This transcendental equation must be solved by a numerical method and this imposes no difficulty.
I = f (I , V ) .........................................(14)
where f (I, V ) is the right side. By differentiating (14):
doing the same analogy for dV/dI we got the dP/dI.
this came from the reference of the model paper
Your sheet works for me using Find(), too, and comes up with the same solutions.
I found that Jaime's sheet would find a solution using Find() if Find() is evaluated symbolically. But the solution differs from yours! Its noticeable in your solution that Iph doesn't change.
Maybe, but in your sheet we get the same solutions using Find and MinErr (symbolic eval is not possible ere because of the units).
So I wonder if you have changed something else other than adding units and correcting the definition of Rs (which at the end only affects slightly the initial guess value for Rs).
I just tried and deleted all units in your sheet and it still evaluates using Find() - so obviously something else was changed, too.
This is what I get with your sheet and symbolic eval (numeric will give the same results as with units). Notice especially the difference in Io and a!
And the values are different from what I got with Jaimes's sheet and symbolic eval.
I have no explanation.
Obviously much dependent on the algorithm chosen (LM, CG)
Wonder what algorithm the symbolic eval choses - should not be an approximating numerical algorithm.
Wouldn't say that the results from the symbolic are best while I think they should be.
In your comparison you have to pull down the functions you evaluate a bit so the correct values are taken
hi Werner and Andy let me put the correct answer from the model paper 
thats the values from each parameter i use the last revision of my file and seems only working with the LM algorithm
Seems to me you don't have 5 independent equations with which to find the five unknowns. These last two:
provide basically the same information in a slightly different form (substitute one into the other and you get a trivial identity). I think you need a fifth, independent condition.
Alan
AlanStevens escribió:
Seems to me you don't have 5 independent equations with which to find the five unknowns. These last two:
provide basically the same information in a slightly different form (substitute one into the other and you get a trivial identity). I think you need a fifth, independent condition.
Alan
Hi Alan thanks for your comments, im using this method for my project becuse i want to use it as a predicted method , the five equations that i put it is from the model. It supposed works solving with the conjugated gradients method with mathcad solve block (Find,Given).
