Long Lam - Photo: Tomas van Dijk
Batteries represent half of the value of electric cars. Yet, until recently, no one could clearly assess a battery’s state of health.
Long Lam (MSc) won the best thesis prize for e-mobility, awarded by Urgenda, a sustainability organisation, on 11 November – Sustainability Day. Jury president Auke Hoekstra (MSc) appreciates the clarity that Lam brought to the condition of batteries, and hopes that Lam’s battery model will now remove much of the uncertainty that is presently holding lease companies back from including electric vehicles in their fleets.
“In his Master’s thesis, Lam created a simple battery model that we can use for electro-technical modelling of electric vehicles,” says his supervisor, Dr Pavol Bauer (EEMCS). “It’s unique. No one had done that before.”
The model describes a battery’s state of health, its voltage, capacity and resistance, as a function of its history. Lam tested his model against an actual Li-ion battery in interrupted charging and discharging sessions lasting more than one hour. The two lines – theory and practice – coincided beautifully. The maximum deviation was only 14 millivolts.
“There are chemical battery models, electro-technical and mathematical,” says Lam, who extracted the knowledge from the chemical models and translated it into an electro-technical model. He had to simplify processes to obtain a formula that could be handled and also had to contend with non-linear behaviour.
“There are a lot of fables about batteries,” Bauer adds. “People say you have to charge and discharge batteries to the maximum. We have shown that this is not true.” This used to be true for Nickel-cadmium batteries, but the wisdom has lingered. Li-ion batteries in fact thrive best when used between 30 and 60 percent of their maximum charge.
Charging frequently, and in small doses, is best for the batteries. Coincidence or not, it’s also what contactless power transfer (CPT), as developed by Lam’s former fellow student Swagat Chopra (MSc), offers. Chopra’s thesis was also nominated for the e-mobility thesis prize. The jury apparently appreciates Bauer’s Delft e-mobility programme.
As part of his prize, Lam will be allowed to drive an electric Tesla sports car for a weekend. He says he’ll wait until spring to make the most of it: accelerating, speeding and driving down the batteries. Why are fun things always detrimental?
