calculating V experimental of a solar cell using newton rapson calculations

hello every one i have this calcculation that i have been doing for a while but i have no answers. i am trying to get the 62 values of V in the code below; i am using matlab 2018a

% Program different values of V  for Iexp

clc
close all
global       s Vt_T  Iexp  V  
Iscn = 3.8;             %Nominal short-circuit voltage [A] 
Vocn = 21.1;            %Nominal array open-circuit voltage [V] 
Imp = 3.5;              %Array current @ maximum power point [A] 
Vmp = 17.1;             %Array voltage @ maximum power point [V] 
Pmax_e = Vmp*Imp;       %Array maximum output peak power [W] 
Kv = -80e-3;            %Voltage/temperature coefficient [V/K] 
Ki = .003;              %Current/temperature coefficient [A/K] 
Ns = 36;                %Nunber of series cells 
Gn = 1000;              %Nominal irradiance [W/m^2] @ 25oC
Tn = 25 + 273.15;       %Nominal operating temperature [K]

% Constants
k = 1.3806503e-23;   %Boltzmann [J/K]
q = 1.60217646e-19;  %Electron charge [C]
% a1 = 1.0; % Diode ideality factor (n) 
Eg =1.12; % Band gap energy; 1. 12eV (Si) , 1. 42 (GaAs) 
Vt_T=k*Tn/q; % Define thermal potential (Vt) at temp Ta

% Data values

Iexp = [3.81 3.81 3.81 3.81 3.81 3.80 3.80 3.80 3.80 3.80 3.80 3.75 3.70 3.65 3.60 3.55 3.50 3.45 ...
    3.40 3.35 3.30 3.25 3.20 3.15 3.10 3.05 3.00 2.95 2.90 2.85 2.80 2.75 2.70 2.65 2.60 2.55 2.50 ...
    2.40 2.30 2.20 2.10 2.00 1.90 1.80 1.70 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 ...
    0.50 0.40 0.30 0.20 0.10 0.00];

Iph=3.86;
I0=1e-9;
Rs=0.33;
n=1.04;
Rp=117.99;

V = zeros(1,size(Iexp,2));    % Current vector
s=1;
for i=s:500
    for j = 1 : size(Iexp,2) %Calculates for all voltage data values 
        % Solves g = V - f(I,V) = 0 with Newton-Raphson
        g(j) = 117.99 * 3.86 - 117.99 * 1.0e-9*(exp((V(j) + 0.33*Iexp(j))/(1.04*Ns*Vt_T)) - 1)-...
            (117.99 + 0.33)*Iexp(j)-V(j);
        while (abs(g(j)) > 0.01)
            g(j) = 117.99 * 3.86 - 117.99 * 1.0e-9*(exp((V(j) + 0.33*Iexp(j))/(1.04*Ns*Vt_T)) - 1)-...
                (117.99 + 0.33)*Iexp(j)-V(j);
            glin(j) = - 117.99*1.0e-9*(exp((V(j) + 0.33*Iexp(j)))/(1.04*Ns*Vt_T))-1; %#ok<*SAGROW>
            V_(j) = V(j) - g(j)/glin(j);
            V(j) = V_(j);   
        end  
    end
end
fprintf('=========== optimal parameters using LSE=========\n');
fprintf('\t V = %.2f\n',V);

Answer 1

[Leepakshi]

Hi Fopa,

As per my understanding, we can try correcting below points in code to get desired solution:

1. The for i = s:500 loop repeats the whole calculation 500 times. Try remove Outer Loop:Delete for i = s:500.
2. The function (g(j)) and its derivative (glin(j)) are not correctly set up for the PV equation. Loop Over Each Current Value i.e. use for j = 1:length(Iexp) and solve for each voltage separately.
3. The while loop can run forever if convergence is not reached. Properly define the function and derivative for the PV equation.
4. Always starting with V(j) = 0 can slow or prevent convergence. Try add Maximum Iteration Count:E.g., max_iter = 100 to avoid infinite loops.
5. The code tries to solve for all voltages together, but each current value should be solved one at a time. Try starting with a value closer to expected voltage (e.g., V(j) = Vocn).

Hope this will help!

Thanks