How to use the overpotential in the parameterised battery for the simscape battery equivalent circuit? I am trying to use the molicell 21700 cell. I can run the R0 model.

The simscape equivalent circuit battery has a bunch of parameterized cells. I am using the molicelI NR_21700_P45B lithium ion battery. The in built data set has 101 state of charge breakpoints, and 7 temperature levels. So, the R0 value has a matrix of size 101x7. However, the overpotential (R1-C1, R2-C2, R3-C3) has the size 7x3. Obviously, when I run the model, I get the following error :

size of First polarization resistance, R1(SOC,T) must be equal to length of State of charge breakpoints for resistance, SOC by length of Temperature breakpoints for resistance, T.

I have read the model documentation clearly, there is a part where a hint of how to use the values properly is given: The software does not parameterize the change in series resistance with the battery cycle life and the dynamic RC network parameters. Instead, the software sums the net resistance of the RC network resistors to the series resistance of the specific parameterized data. To populate the RC parameter data, subtract the net RC network resistance from the series resistance data.

This description to me is not very clear. The model contains the following data heads: Instantaneous resistance, R0 (SOC, T), first polarization resistance R1(SOC, T) and Tau, if I use one time-constant dynamics, which are of my interest. There is nothing mentioned explicitly about a series resistance from which the net RC resistance is to be subtracted. A demonstration of how to use this will be useful.

Answer 1

[Vinay]

Hi @Tamoghna Bhattacharya,

The 'Battery Equivalent Circuit' uses the series resistance(R0) in series with the RC network. The RC network models the transient (dynamic) electrical behavior.The total resistance of this network is called the net RC resistance.

The software does not paramatrize the following parameters

1. Series resistance degradation over cycle life (R₀ change with N)
2. Dynamic behavior of the battery, represented by the RC network

The series resistance (R0)[Datasheet] in the parameterized model is a combined effect of:

• The instantaneous resistance (R0 from datasheet), and
• The net resistance of the RC network (transient part of the model)

To get only the transient resistance (for RC network), you must subtract:

​

So you extract the RC resistance by subtracting the measured or estimated instantaneous resistance from the datasheet's total series resistance.

I hope this helps!

[Ivan]

Hello Mr. Vinay,

I am actually having the same problem of Mr. Tamoghna for the same cell. I can´t run the simulations, because of the matrix size of the R1, Tau1, R2, Tau2 and so on... that are expected to be 101 x 7, but are only 7 x 3.

Now, as I am not an expert on the field, i am uncertain on the way forward, as the given 7x3 for R1 (as example) is based on only 3 values of temp. (which ones?).

How can i extrapolate 97 values of R1 for 7 different temperatures, when i have only a set of 7 SoCs over 3 unknown temperatures?

Should i reduce the SOC and temp. matrix to fit the R1/Tau1 matrix, would that produce releable enough data?

Thank you in advance for your time, and for understanding that i am a beginner!!

Kind Regards

Ivan T.

P.s. I had the same problem for the SoC estimator Kalman Filter, in that case i observed, most of the R1/Tau values pre-setting parameters where by coincidence similar to the Molicel cell. In anycase i solved the issue reduing the matrix of the Molicel Datatables to adjust according the matrix size in the estimator. As i do not have a lot of experience on this topic, I do ask myself, how well the estimator is going to work now with only 7 SoC points and 3 Temperatures.