Thermal Modeling Key to Optimizing EV Range

September 25, 2017

Kami Buchholz

Image depicts CAD-embedded thermal management of a battery pack in an electrified vehicle. (Mentor)

For potential EV buyers, it's all about the driving range. And for EV engineers tasked with increasing that range, it's all about improving power efficiency through thermal management and electro-thermal modeling.

Mentor's Wally Rhines talks about electro-thermal modeling during his keynote address at Mentor's 2017 Integrated Electrical Solution Forum. (Mentor photo)

That's according to Walden (Wally) Rhines, President and CEO of Mentor, who spoke with Automotive Engineering following his keynote at his company's 2017 Integrated Electrical Solutions Forum - Automotive, in Plymouth, MI.

Rhines explained that until recently, thermal analysis "was done by thermal engineering specialists who used very advanced software in order to evaluate the thermal characteristics of a design,” he said. That product development approach meant a particular design could hit a roadblock weeks to months into a program before a potential thermal problem was detected by a thermal engineering specialist.

“If you flunk the ‘thermal gate’ in the design, you go back and re-do the electrical design,” Rhines noted.

Thermal management considerations are now routinely being considered by design engineers, a trend that has evolved rapidly. "You can save an enormous amount of time by having general feedback of where you’re going in terms of thermal-electrical tradeoffs as early as possible,” he observed.

In EV development, the operating state of batteries is vital information, especially from an optimization perspective. A 10º C difference in battery temperature can extend a battery's lifespan by up to three years, Rhines explained. Improving thermal efficiency can improve battery performance by as much as 20%. Thermal simulation is crucial for determining what will happen under a specific condition.

The battery is not only a limiter in terms of driving range—it's also "the real limiter in terms of the overall cost of an electric vehicle because the battery is more expensive than any traditional automotive sub-system,” said Rhines.

Simulation models of an energy storage system are important on a number of fronts.

“It’s about the efficiency of getting the power from the battery to the wheels. If it’s heat being generated instead of usable power, that’s a battery output loss,” Rhines, said, noting there are also reliability issues associated with higher battery temperatures.

Simulation tools can improve the power efficiency and performance of the battery, which in turn improves the efficiency of the electric vehicle, according to Rhines.

“I believe virtualization tools will determine the winners for system design. Electrification and autonomous driving will accelerate that process because it will be impossible not to adopt virtual design tools for the design and verification process of vehicles of the future,” Rhines asserted.

Genevieve Cullen, President of the Electric Drive Transportation Assoc., noted the declining cost of automotive-spec lithium battery cells. “It was widely seen that the incremental cost of a Li-ion battery was about $1000 per kW·h in 2010, and now market analysts put it south of $300 per kW·h,” Cullen said. There are approximately 40 light-duty passenger EV models in the U.S. market today.

“By 2020, the number of passenger vehicle models, plug-in and all-electric, will likely triple,” she predicted.