Better battery management could halve hybrid battery size

The size of the battery in hybrid vehicles could be cut in half with no change in range or performance if a new ARPA-E effort comes to fruition.

Researchers at Eaton Corp.'s Innovation Center in Southfield, Mich. will work with a team from the National Renewable Energy Laboratory (NREL) on the project which is getting part of its $2.5 million funding from Dept. of Energy’s Advanced Research Projects Agency – Energy (ARPA-E).

"Battery management today uses the notion of state-of-charge and might let the battery range from 40 to 60% charged," says Eaton Manager of Intelligent Truck Vehicle Technology and Innovation Ben Saltsman. "The battery might have a large capacity but its usable energy is much smaller than its capacity." Currently vehicle makers must limit the amount of recharge current to the battery in the interest of prolonging battery life -- large charging currents heat up the battery and shorten its life. And battery life is an issue when replacements can cost car owners several thousand dollars.

Saltsman says NREL's electrochemical models of battery behavior will help optimize recharging strategies. "We aim to come up with dynamic battery controls that will allow expanding the usable state of charge," he says. "We might get a usable state-of-charge of 20 to 80% without reducing battery life."

Another aspect of the work pertains to predictive powertrain controls. Conventional vehicles already use these schemes to realize features such as predictive cruise control. Here the vehicle might anticipate a coming change in terrain, such as a hill, by building up speed ahead of time in the interest of expending the least amount of energy in climbing the hill rise. But predictive powertrain control is an order of magnitude more complicated when applied to hybrids because power splits between the internal combustion engine and the electrical portion of the vehicle.

"The battery services both propulsion and the electrical loads such as A/C, and that makes predictive management of the system very difficult," says Saltsman. Eaton already has predictive controls for conventional vehicles. Saltsman says it will try to extend this work to hybrids under the ARPA-E grant in an effort to orchestrate vehicle conditions in a way that will best utilize the battery.

Also part of the effort is the development of a flexible high-voltage dc architecture as part of the brain that handles accessory load management, Saltsman says.

The whole effort is expected to take three years. The project will culminate in a hardware-in-the-loop system to be built at NREL that will be demonstrated on hills there.

Eaton's announcement of the work can be found here:

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