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A Blended Battery Pack for Cars

Combining different battery technologies could improve vehicle performance and reduce costs.
January 26, 2009

The race is on to find the ideal battery chemistry for plug-in hybrids and all-electric vehicles, but a startup in Indiana believes that a combination of different storage technologies might be the best way to improve vehicle performance and reduce cost. The company’s technology allows vehicles to run on a combination of fuel cells, ultracapacitors, and old-fashioned lead-acid batteries.

Smart switch: Indy Power Systems has developed the Multi-Flex Energy Management System, a laptop-size power converter. The system allows makers of plug-in electric vehicles to use a combination of power sources–including lead-acid and lithium-ion batteries and ultracapacitors–and optimizes the blend to increase battery life, improve performance, and reduce cost.

Noblesville-based Indy Power Systems has developed an energy management system for vehicles that can quickly switch between two or more energy sources, even when their voltages are different. “It’s basically a switch that directs energy in any amount and any direction,” says Steve Tolen, chief executive officer and founder of Indy Power, which operates out of Purdue Research Park. “The hardware handles the switching, and the software handles the timing and amounts.”

Tolen says that the power electronics package–called the Multi-Flex Energy Management System–is only slightly larger than a laptop computer. He describes it as a custom, software-controlled, DC-to-DC converter that’s bidirectional and variable.

“Imagine adding hot and cold water to a tub. We can add a variable amount of hot and a variable amount of cold in different volumes to match the outflow of the drain, which can also be variable,” Tolen explains. “In other words, the motor can ask for different amounts of current, and we can provide that, and in different ratios from the two (or more) power sources, regardless of the voltage of the power sources.”

For example, an electric vehicle could have both lead-acid and lithium-ion battery packs. Advanced lead-acid batteries may be cheaper, but they are also heavier and deteriorate more quickly if subjected to regular depletion and recharging. Lithium-ion batteries are generally more robust and lighter but are far more expensive. Combining the two means that you can use less of each. And just as important, says Tolen, the two chemistries can be balanced against each other to optimize performance. For example, the lithium-ion battery can be used to relieve stress on the lead-acid battery and extend its life, and vice versa.

Reza Iravani, a professor of electrical and computer engineering at the University of Toronto, says that Indy Power’s system is part of a trend toward greater emphasis on hybrid storage. For example, he says, Researchers in Australia have designed a car-battery system that combines lead-acid technology with supercapacitors, resulting in a fourfold increase in the life of the lead-acid batteries.

“The concept is being pursued by many different research groups,” says Iravani, who is working on a similar system that utilities could use to switch between energy-storage technologies and renewable energy sources, such as wind and solar. Iravani says that within five or six years, hybrid approaches will significantly improve the performance of energy-storage systems.

Indy Power has already demonstrated its technology in golf carts and is scaling up to highway-capable vehicles. A manufacturer approached the company just last week, says Tolen, to say that it was interested in combining two different lithium-ion chemistries and a lead-acid battery pack in a plug-in hybrid vehicle.

Indy’s system can also be customized with a simple software upgrade, says Tolen. He envisions a day when we can upgrade the performance of vehicles in much the way we add RAM to computers. “My wife never drives more than 20 miles a day, so I would probably put 100 percent lead acid in her vehicle. Some people might want to go 40 miles, so they’ll have five kilowatt-hours of lithium-ion batteries and maybe 15 kilowatt-hours of lead acid. It depends on preferences. We just need to change the paradigm of how we buy cars.”

The company has some technical veterans behind it. One of its directors is Bill Wylam, a former General Motors engineer who was responsible for the development of the propulsion system for GM’s EV1 electric car. Indy Power’s chief operating officer is Bob Galyen, who helped develop the battery pack for the EV1 prototype.

Tolen says that Indy Power has also been approached by utilities that would like to see the Multi-Flex system scaled up for grid-based applications. Iravani says that selling to the electricity sector will be more difficult given its aversion to risk, but he believes that the combination of power electronics and hybrid energy storage could increase grid reliability and allow utilities to use more renewable energy.

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