US team hails EV fast charging technology breakthrough

An EV fast charger that is smaller than existing systems and wastes 60 per cent less power during charging has been developed in the US.

EV fast charging

Developed by researchers at North Carolina State University, the new solution is at least 10 times smaller than similar systems and is now being optimised to charge vehicles more quickly, while also charging multiple vehicles simultaneously. The new technology has been dubbed a medium voltage fast charger (MVFC).

According to NC State, conventional, 50kW chargers include a distribution transformer, which weighs 1000kg, and a separate fast charger unit, which weighs 200 to 600kg. To support the weight, this transformer-and-charger system usually needs to be installed on a concrete slab.

The transformer takes power from a utility medium-voltage line and steps down the voltage to 480V so that it that can be used by the fast charger. The fast charger takes the AC voltage and converts it to DC voltage that is compatible with the electric vehicle’s battery.

“Our 50-kW MVFC weighs only around 100 kilograms and can be wall-or pole-mounted,” said Srdjan Lukic, an associate professor of electrical engineering at NC State and one of the researchers who developed the technology. “The MVFC does the work of both the transformer and the fast charger, taking power directly from a medium-voltage utility line and converting it for use in an electric vehicle battery.

“This new approach offers four times more power from the same system footprint, reducing the system installation costs at the same time,” said Srdjan Srdic, a research professor at NC State who also worked on developing the technology.

The researchers were able to make the technology so much smaller, in part, because they used wide bandgap semiconductor devices. This also made the technology more energy efficient.

At present, the best transformer-and-charger stations are reported as having an efficiency of up to 93 per cent, meaning that at least seven per cent of the power is lost to heat during the charging process.

In testing, the prototype MVFC has a reported efficiency of at least 97.5 per cent, meaning an additional 4.5 per cent of the power is used to charge the vehicle, rather than being wasted as heat. This reduces operating costs, increasing revenue without increasing the cost to consumers.

“In other words, we were able to cut the wasted energy by more than 60 per cent,” Lukic said.

The current version of the MVFC charges at the same speed as existing charging stations. That’s because this iteration of the MVFC was designed to operate at 50kW, which is the power level of a typical fast charger.

However, the research team is in the process of building a next generation MVFC that handles much higher power, and is capable of charging more vehicles more quickly.

“We’ve had the more powerful, multi-vehicle MVFC in mind for some time, and recently received funding from the [US] Department of Energy to build a next-generation prototype,” said Lukic, who is the deputy director of the FREEDM Engineering Research Center at NC State.

In the multi-port station design, a utility line is connected directly to a solid-state transformer, (SST), which is a power-electronics-based smart transformer. The SST then feeds a local DC microgrid, with battery storage systems and multiple charging nodes that vehicles can plug into.

NC State said the multi-port MVFC will have a rating capacity of one megawatt, with each charging node capable of providing up to 350kW of power. The upgrade from 50kW to 350kW means that a vehicle can be charged up to seven times faster.

“We’re currently looking for industry partners to help us move from our fully functional prototypes to the marketplace,” added Lukic.

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