Electric Vehicle Charging

[Justinli]

I recently finished designing a GUI design for an electric car charging pile, and I'm thinking about what to use to simulate this charging process. Do I need a row of battery packs? Or does anyone have another better solution?

 

[D.A.(Tony)Stewart]

Batteries have simplified equivalent circuits of (R+C)//(R2+C2) where R is the ESR*C time constant for long term time constants and the other for short term changes and CV mode decay current. But you only need good specs to get started to validate and/or simulate a design for DVT. But then ESR rises rapidly with DoD and other non-linear effects. You want environmental specs to fill a page of parameters in the design to verify all assumptions.

But if you are just making a marketing GUI brochure, show a variety target vehicles with transparent views of batteries and show how it is spark free on disconnect.

 

[Justinli]

I didn't intend to make a particularly complete and large project, I initially intended to use many small components to simulate the functionality I wanted to achieve. For example, I will use a coin machine module to simulate the charging function, so it's not really simulating a car charging.

Someone gave me the suggestion to design an additional power supply circuit.

 

[RCinFLA]

The picture you showed is not a charger. It is a charging port.

It is an AC outlet that communicates with EV so EV charger in vehicle does not pull too much AC current from the given charging port AC outlet.
The picture appears to show some charge level info reported to it by communications from the vehicle's charger/battery system.

 

[d123]

Hi,

Useful battery models are very complicated and have e.g. IEEE papers dedicated to them by teams of accomplished engineers who want to publish/divulge their version; e.g., the link is for the Min Chen and Gabriel Rincon Mora's rather complete one on battery models, if you want to have a look for ideas - that or make the basic/simplistic model of rc + parallel r x number of cells for a 'this is how it would theoretically work (on a reduced scale and not very accurate)'. Another approach for a simple, small-scale approximation to what you want to demonstrate (if I've understood your posts) is maybe you could look for a li-ion battery charger IC design note by an IC manufacturer that comes with a model and its own simulation file. AD or TI, et al, at least, should have several of such to choose from and copy/adapt if needs must.

An Accurate Electrical Battery Model Capable of Predicting Runtime and I–V Performance

 

[d123]

Hi,

More (li-ion) battery model papers with pictures.

Going back to your first, and then second, post(s) - I see no point in entering the complicated territory of charge balancing between multiple cells/packs (unless you really want/need/have to), one single cell model for a simulation to show the purpose might/will spare you from a lot of design and simulation time and/or misery, IMO. A row of battery packs will require a lot of sensing and control circuitry to balance the charging between the cells and also between the packs... Personally, I'd take the weasel-way-out and only model/include one cell, or at most two, especially as you say 'I initially intended to use many small components to simulate the functionality I wanted to achieve' - I designed a theoretically functional discrete single li-ion cell charging/discharging circuit (very, very interesting and fun to do) and it is a lot of components and a couple of workarounds to get the waveforms you need/expect to see in the simulation results. It's loads of ICs like logic, op amps and comparators, transistors, sensors, passives, the odious battery model, and so on to control: the battery has temperature limits/limitations both ends, limits on depth of discharge, requires the pre-charge current, the charge current, has a voltage cut-off at both ends. A coulumb counter would be good/vital to add realism (not just voltage has reached lower or upper limit) but that is in and of itself also a lot of parts to do discrete design. Simulating with an MCU presumably takes out a lot of the design work? Those are the reasons why I think a 'one cell proof of concept' would be the way to go with your project.

 

[FvM]

If I understand the original post right, it just wants a minimal behavioral model of a car battery charger interface involving state of charge, charging power negotiation, power demand during charge and update of state of charge according to the actual power input. No actual relation to physical battery models and e.g. cell voltage or charge balancing.

 

[D.A.(Tony)Stewart]

Hi,

More (li-ion) battery model papers with pictures.

Going back to your first, and then second, post(s) - I see no point in entering the complicated territory of charge balancing between multiple cells/packs (unless you really want/need/have to), one single cell model for a simulation to show the purpose might/will spare you from a lot of design and simulation time and/or misery, IMO. A row of battery packs will require a lot of sensing and control circuitry to balance the charging between the cells and also between the packs... Personally, I'd take the weasel-way-out and only model/include one cell, or at most two, especially as you say 'I initially intended to use many small components to simulate the functionality I wanted to achieve' - I designed a theoretically functional discrete single li-ion cell charging/discharging circuit (very, very interesting and fun to do) and it is a lot of components and a couple of workarounds to get the waveforms you need/expect to see in the simulation results. It's loads of ICs like logic, op amps and comparators, transistors, sensors, passives, the odious battery model, and so on to control: the battery has temperature limits/limitations both ends, limits on depth of discharge, requires the pre-charge current, the charge current, has a voltage cut-off at both ends. A coulumb counter would be good/vital to add realism (not just voltage has reached lower or upper limit) but that is in and of itself also a lot of parts to do discrete design. Simulating with an MCU presumably takes out a lot of the design work? Those are the reasons why I think a 'one cell proof of concept' would be the way to go with your project.

Although these articles went into greater depth than I did they arrived at similar 2nd order models except they used exponential factors with SoC where I estimated a single 18650 cell is about 10 kFarads with a primary ESR of about 25 to 200 mOhms depending on C charge rate multiplier. (similar to CCR in acid batteries)

Justin certainly doesn't need this complexity to model a charger except use a wide range of RC values for ramping up current slowly until ESR drops to a safe thermal value for losses.

I haven't compared yet to their reports. TL/DR yet.
TY for the attached.