# PV module I-V curve Rs, Rsh, error,

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Emircan Han on 30 Jun 2017
Answered: Ibrahim Abouemira on 19 May 2019
Hi, my problem is when ı try to start these algorithm it's working. But when i try to change Rs value like different than 0 it's giving error.
"Error using plot. Non-numeric data is not supported in 'Line'"
I need to change value of Rs(manual), and I need to get I-V graph...
Thanks for helping
here is my code;
syms Vt Rp Rpmin Io Ipv V I Rp1 Pmax P Rs
Pmax=200.143;
Imp=7.61;
Vmp=26.3;
Iscn=8.21;
Vocn=32.9;
Ns=54;
q=1.60217646*(10^(-19));
K=1.3806503*(10^(-23));
ki=0.0032;
kv=-0.1230;
Tnom=298.15;
Gnom=1000;
a=1.3;
Vt=K*Tnom*Ns/q;
% for T G calculate Io , for Rs=0 Rpm,n
G=1000;
T=298.15;
Io=(Iscn+ki*(T-Tnom))/(exp((Vocn+kv*(T-Tnom))/(a*Vt))-1)
Rpmin= (Vmp/(Iscn-Imp))-((Vocn-Vmp)/Imp)
Rs=0;
Rp=Rpmin;
Ipvn= ((Rp+Rs)/Rp)*Iscn
Ipv=(Ipvn+ki*(T-Tnom))*(G/Gnom)
Rp1= (Vmp*(Vmp+Imp*Rs))/(Vmp*Ipv-Vmp*Io*exp(((Vmp+Imp*Rs)*q)/(Ns*a*K*T))+Vmp*Io-Pmax)
V=0:0.1:32.9;
I=Ipv-Io*exp((V+I*Rs)/(a*Vt))-((V+I*Rs)/Rp1)
plot(V,I)

John BG on 30 Jun 2017
Edited: John BG on 1 Jul 2017
Hi Emircan
your script doesn't work for Rs>0 because as soon as Rs is not null, you are attempting to pass a vector and and an implicit function to command plot, where plot expects just 2 vectors, let me explain:
You may just plot with V alone
plot(V)
It works with any value of Rs, but then the X axis labels have to be re-tagged accordingly.
The problem lays in the line previous to plot
I=Ipv-Io*exp((V+I*Rs)/(a*Vt))-((V+I*Rs)/Rp1)
Note that you have I on both sides of the equal.
The only way for MATLAB to accept plot(V,I) is to either first solve that equation and pass the solved equation, or correct any possible error like perhaps the equation that you really need is
I=Ipv-Io*exp((V+Io*Rs)/(a*Vt))-((V+Io*Rs)/Rp1)
or
I=Ipv-Io*exp((V+Ic*Rs)/(a*Vt))-((V+Ic*Rs)/Rp1)
Where Ic may be a collector current that requires additional equations prior attempting to solve I and then plot.
.
So omitting I in plot or correcting the I equation you should be able to plot.
.
Yet, for further assistance, would it be possible for you to show the circuit diagram?
is it a transistor bias that you are modelling? or a diode?
John BG

Emircan Han on 4 Jul 2017
Hello John,
Thank you very very much. I'm looking your codes and i was working on it since you sent and sorry just i could write you for thanks. It is really useful.
Emircan Han on 4 Jul 2017
and also one question, how can i see different values of Rp for Rs on graph.
for example, If just I need to see Rs=0 Rs=1 Rs=2 Rs=2.21 lines on graph, is it possible? and how can i see Rp values for these points?
Tabich Ouijdane on 18 Jun 2018
Hi John,
Please can you tell me if you used an external function f1 and f2? I did'nt really understand the for loop.

Walter Roberson on 30 Jun 2017
syms Vt Rp Rpmin Io Ipv V I Rp1 Pmax P Rs
So I starts as a symbolic variable.
I=Ipv-Io*exp((V+I*Rs)/(a*Vt))-((V+I*Rs)/Rp1)
When rs is 0 then all occurrences of the symbolic variable I are multiplied by 0 so the symbolic variable drops out of the equation. When rs is not 0 then the symbolic variable I stays in the equation giving a result that involves the symbolic variable I. Confusingly the result is then written to I.
When I is then used in the plot() it involves the symbolic variable I. That cannot be be plotted.
Question: why are you creating so many variables as symbolic and then overwriting them with numeric values? That confuses you and confuses us.

#### 1 Comment

Emircan Han on 30 Jun 2017
Actually if i put out Rs from symbolic values still it's not working. I see when Rs=0, I is dropping out. But when I put value for Rs also i need that I-V curve. So i know matlab lets me to do that but, how? where is problem?
or is there any other for my equations because thing is;
V has to be between "0 <= V <= 32.9"
and first i should see I-V curve for
"I=I=Ipv-Io*exp((V+I*Rs)/(a*Vt))-((V+I*Rs)/Rp1)"
then i should change Rs value
and i should check how that curve is changing.
also i need P-V curve for P=IxV equation. (I get it but Rs value is also problem for it)

Wissal EL FADIL on 3 Jul 2017
I think you should solve the output current equation using the Newton Raphson method and then you can proceed with the code. I am acctually working on the same thing and I am still struggling to find the solution of the current equation.

#### 1 Comment

Emircan Han on 4 Jul 2017
Hello Wissal,
John's codes are useful to see parameter values with good initial points. I could't find good Newton Raphson codes for PV equations but if you find some can you please share with me?

Ibrahim Abouemira on 19 May 2019