[Solved] Lithium Battery Cell - 1RC ECM model mistake? Why is SOC lower than 0.5 despite the inital charge being more than half (15/27) of the Battery capacity?

[EDIT: Solved]

So I was looking at the model "Lithium Battery Cell - One RC-Branch Equivalent Circuit" see https://de.mathworks.com/help/simscape/ug/lithium-battery-cell-one-rc-branch-equivalent-circuit.html

and used a matlab block for determining the SOC via coulomb counting.

There I noticed a difference between the SOCs.

Looking back into the initlization flie it uses the following lines

% Battery capacity
Capacity_LUT = [
    28.0081   27.6250   27.6392]; %Ampere*hours
% Charge deficit
Qe_init = 15.6845; %Ampere*hours

but when running the modell it starts roughly at 0.45 SOC.

The SOC calculating block is a Simscape function block called "Em_table" using lines like:

outputs
SOC = {1,'1'}   %SOC:right
C = {31,'A*hr'} %C_age:right

variables(Access=private)
Qe = {value=Qinit, priority=priority.high}; % Charge deficit

equations
% Charge deficit calculation, preventing SOC>1
if Qe<0 && i>0
    Qe.der == 0;
else
    Qe.der == -i;
end

% Perform the capacity table lookup
C == tablelookup(Temp_Table,C_Table,T,...
    interpolation=linear,extrapolation=nearest)
SOC == 1 - Qe/C

Can someone perhaps point out what I am failing to see or could there indeed be an issue with the example model?

one suspicion I have is related to the "C = {31,'A*hr'}" , but changing that to around 27 A*hr didnt seem to change the SOC results.

Answer 1

[Christian]

Nevermind I missed the

Qe.der == -i;

that makes sense then with

SOC == 1 - Qe/C
SOC == 1 - (-Qinit)/C