RC circuit parameter's calculation - formal method needed!

Dear all,

I am calculatiing paramaters for RC circuits from HPPC data. I am new to the field and do not fully understand how it work and online sources quite confuses.

So I really need a formal way to calculation R0, R1, C1 mathematically, not the code or simulation in order to verify if simulation is correct with the input in look up table.

I used this default simulation from mathlab (does not change anything), just ran it.

openExample('simscape/LithiumBatteryCellOneRCBranchEquivalentCircuitExample')

After getting simulation, I get the the data and calculated again. Here is how I get it

Ro( Ohmic resitance) = Ohmic drop at begin of pulse/ Current = V_A - V_B/ I

R1( Transient Resistant) = Voltage change in voltage relaxation after ohmic jump /Current = V_E - V_D /I

Then using curve fitting with data from D to E to find constant time tau

C1 = tau/R1

However, after I calculated and check it with look uptable, R0 is matched, R1 is totally different.

How exactly can I calculate these paramters? I don;t have issue with simulation set up or coding since I work directly on default set up, just need to know the method!

Thank you in advance!

Answer 1

[Xiangchun]

Hi @Thanh,

When you hand calculate R1 from the voltage relaxation curve, using the following statement:

R1( Transient Resistant) = Voltage change in voltage relaxation after ohmic jump /Current = V_E - V_D /I,

please note that we essentially want to determine R1 by R1 = V_{R1} / I_{R1}, where V_{R1} = V_E - V_D. Please note that unlike the calculation of R0, the total current of I is split between resistance R1 and capacitor C1. I_{R1} deos not equal to I, which is I = I_{R1} + I_{C1}.

To get the I_{R1} from the model and simulation, we can either use a Current Sensor connected in series with C1 to measure it or use a Probe to get the current from the C1 component. To do these, we need to look under the mask of the "Lithium Cell 1RC."

By the way, there is a better block doing equivalent circuit model provided by Simscape Battery, Battery Equivalent Circuit - Battery model with electro-thermal dynamics and optional faults - MATLAB. Please feel free to check it out.

Best wishes,

Xiangchun