I have following problem:
I want to estimate battery parameters of 2RC network. I have data from discharge test. To estimate those parameters I want to use curve fitting toolbox, as many did in the literature. I am using following function:
y(x)= a + b*exp(-c*x) + d*exp(-f*x) ; y - terminal voltage ; x - time.
For some reason I have the error like in the topic:
"Inf computed by model function, fitting cannot continue. Try using or tightening upper and lower bounds on coefficients."
I have very large number of data (10k array for 1 parameter) so I decided to pay attention just to one iteration (relaxation zone, just after the pulse current). The error disappeared, but the fit created by the function y(x) is very, very poor. Basically, it is straight line, where it is supposed to be exponential I believe. R-square: -1.776e-15...
Using the function proposed by the toolbox, that is: y2(x) = a*exp(b*x) + c*exp(d*x) looks more promising and R-square value is 0.998 the actual fit shown on the plot is not so accurate, I'd say.
Below, I attached the screen of the interface. Any help would be extremely appreaciated