Robyn Jackey is the go-to guy for automotive battery modeling at The MathWorks, and with electrical loads increasing in vehicles, customers are keeping him busy. More of his time than I would have expected is spent modeling conventional lead acid batteries than those with exotic chemistries, but The MathWorks makes provision for both.
“Automakers want the optimum-size battery and alternator, so as not to add cost or increase fuel consumption unnecessarily,” Jackey says. “The alternator has to be big enough to keep the battery charged and the battery big enough to handle the idle times when the alternator can’t provide enough current.”
Jackey’s primary battery right-sizing tool is an equivalent circuit model fed with customers’ constant current and voltage data at a variety of temperatures. That data is used with optimization routines to parameterize the battery model, which control engineers can then put into their system level model. Jackey says the equivalent circuit model approximates lead acid battery performance pretty closely and has also been used to simulate a lithium polymer battery.
“To develop and verify control algorithms, engineers need a battery model that can run fast, be accurate, and be developed quickly, based on a defined process,” Jackey says. Engineers who design battery packs for hybrid and electric vehicles, on the other hand, want the ability to model chemical reactions and do in-depth analysis.
Those kinds of detailed models are slow to run, and thus are not appropriate for control applications, but Jackey says that engineers who need them and also want the benefits of model-based design can use co-simulation tools to link custom-developed or third-party battery models with control models in the MATLAB/Simulink environment.
“Battery technology is ever changing. Model-based design eliminates repetitive cycles, and if you have an accurate simulation before building a test vehicle, you can reduce development time and cost.” A technical paper is available for those who want more detail on the battery simulation model.