How to set initial SOC value in simscape 1RC or 2RC equivalent circuit model (Lithim-Ion-Battery)

From time to time I use the 1RC or 2RC equivalent circuit model from the Simscape toolbox and parameterize it for some of the batteries used in my company.

For many simulations it makes sense to start with a certain initial SOC < 100%, say 80% or 50% for example or to have various diffeernt initial SOC's in a pack. I noticed that this can be set with some newer toolboxes like Simscape Battery.

As for in simscape I'm having a really hard time finding the right place/variable where I can set this value.

My first guess was that Qe_init is the value of choice since it can be multiplied by a charge deficit factor, but some recent simulation results got me wondering as they don't seem to make much sense. In addition, this factor also appears to vary from cell to cell.

Answer 1

[Javier Gazzarri]

Hello Jassir,

You are correct. Qe_init (charge deficit) is where you can set initial SOC. Please take into account that Qe has units of Ah (unlike SOC) and it ranges from 0 (fully charged) to the call's capacity (fully discharged). For example, a 1 Ah cell with a 0.25 Ah initial charge deficit is equivalent to an initial SOC of 75%.

Please let me know if this makes sense and if you need further help.

Javier

[Jassir Chaffai]

Hello Javier,

thanks for the confirmation and the explanation. Since I use simscape only once in a while and in my setup it is necessary to call my 1RC or 2RC parameters at each start I've got rather confusing results. Now I can say with confidence that this is more likely due to the call of parameter file which must be preloaded in the workspace and maybe was not or was simply updated by other parameters.

As it's already a year ago since I've used simscape more inetnsively I began to doubt some earlier "beliefs" a colleague who handed over a simulation setup just told me that Qe_init should be the parameter to set initial SOC. I've also figured out that the value set is related to the capacity of the cell. Now at least I've got clarity on that point this will help me also filter "simulation setup errors" from possible deviations due to phyiscs.

Thanks a lot!

Jassir