Electronics and Semiconductors

Toward Extreme Fast-Charging Stations for Electric Vehicles

17 October 2018
A concept illustration of how the extreme fast-charging system may look like. Source: Missouri S&T

Researchers at the Missouri University of Science and Technology (Missouri S&T) and three private companies are working together to develop fast-charging systems that would refuel electric vehicles (EVs) in the same amount of time it takes to fill up a conventional vehicle with gas.

Through a grant from the U.S. Department of Energy, over the next three years the engineers will develop a system that would be more user-friendly by reducing the time it takes to recharge an EV. Most electric chargers take anywhere from a few hours to overnight to fully charge; even Tesla’s Supercharger station takes up to an hour.

“The big problem with electric vehicles is range, and it’s not so much range as range anxiety. People are nervous about not being able to get where they’re going,” said Dr. Jonathan Kimball, Missouri S&T professor of electrical and computer engineering. “With a conventional vehicle, you pull up, get gas, and in 10 minutes you’re back on the road.”

Challenges to the System

One of the challenges to developing such a system is if the batteries used in EVs can withstand such speedy charges. Overcharging a lithium-ion battery could lead to overheating or even thermal runaway, or perhaps damage the battery and degrade its service life.

“At extreme fast charging rates, lithium-ion batteries can be damaged severely due to the limited energy transfer properties of the battery materials,” said Dr. Jonghyun Park, assistant professor of mechanical engineering at Missouri S&T. “This not only degrades battery performance, but also causes a short circuit that can lead to a safety issue.”

Researchers are looking into a model-based protocol for monitoring the battery’s charge and health status to determine if something is wrong.

A second challenge is pulling large amounts of electricity from the power grid. Researchers estimate it will take about 300 to 400 kW to recharge a car battery in about 10 minutes. Several cars charging simultaneously could draw more than 1 MW in power. In certain locations in the U.S., this amount of electricity could power hundreds of homes for an hour. Furthermore, the sudden, high current for fast charging would affect the power quality from the utility provider, affecting other customers that need power.

The engineers hope to lessen this impact on the electric grid by first connecting the battery and then ramping up to connecting directly to the 12 kV distribution network.

One of the companies involved in the project is Ameren, Missouri’s largest electric power provider. Ameren will look to demonstrate the charging stations' draw on the grid and then mitigate it by using an energy storage system to provide a buffer.

The final challenge is to connect directly to the medium-voltage distribution network and feed energy to the cars. A medium-voltage connection can reduce size and cost while increasing efficiency.

To contact the author of this article, email PBrown@globalspec.com

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