Advancing Higher Speeds and New Techniques for EV Recharging

The ability to charge electric vehicles at a very fast rate is a key to electrifying mobility across the U.S. It’s a focus of the U.S. Dept. of Energy’s Extreme Fast Charger project, whose potential was demonstrated convincingly on a production GMC Hummer EV at the American Center for Mobility (ACM) in Ypsilanti, MI, last fall.

The Hummer EV observed by SAE Media featured an 800-volt electrical architecture — considered state-of-the-art for DC “extreme fast” charging. Both GM and Delta Electronics (Americas) Ltd., which provided the charging system, are partnering with DoE on the program. The results of the demonstration were “phenomenal,” said Jim Khoury, Senior Manager of Global Electrification at GM.

The parameters for the extreme fast charger were established in an earlier test that also involved a Hummer EV. That test, spanning nine minutes at 500 amps at an average 725 volts, yielded nearly 55 kWh before the EV’s battery started to limit the current.

“While other DC fast chargers can also charge at 500 amps, the power capability is lower, so it power-limits sooner in the charge cycle. Our power limit is 400 kW,” said Dr. Charles Zhu, VP of the Automotive Business Group for Delta Electronics, and the Principal Investigator for the DoE project. He said that generally, the Delta extreme fast charging system can deliver 66.7 kWh in 10 minutes.

Medium-Voltage Benefits

Delta Electronics developed the solid-state transformer (SST), power cabinet, and the charging stand/dispenser that are vital to the project. The SST converts the “medium voltage” (13,200V AC) into 1000V DC. The power cabinet uses the DC voltage to create a current source, providing up to 500 amps. The dispenser communicates with the vehicle and provides current to the battery pack.

Current-generation fast chargers are considered low-voltage. Tesla’s Supercharger, for example, runs at 480V. The move to medium voltage presented hurdles, explained Zhu. “Medium voltage can jump a wider gap because of its higher potential energy,” he said, noting special wire, materials, and designs were needed to accommodate the higher voltages. From a safety standpoint, the DoE-Delta extreme fast charger has a medium-voltage switch to isolate the system from the grid. A licensed electrician with proper personal protection equipment must close the switch.

“If something goes wrong, the ‘blast radius’ is about 30 ft [91.4 m], which is why all others must stand clear when the switch is actuated,” Zhu said.

There are strong reasons to opt for medium voltage, according to Zhu. “The advantages that we gain from pulling directly from medium voltage include higher efficiency, as a conventional transformer can be about 95 percent efficient,” he said. A conventional transformer needs to have energy pass through a conversion stage — another loss — to create the DC current needed to charge a vehicle battery, he added. The medium-voltage system provides an approximate 96.5 percent output and eliminates the conventional transformer from the charging process.

“13.8 kW medium voltage and charging current up to 500 amps are key features to enable energy efficient and highly scalable extreme fast charging,” Zhu said.

Michael Standing, Delta Electronics Program Manager for the extreme fast-charger system, said that eliminating a traditional transformer in favor of a power conversion via a solid-state transformer equates to about a 3 percent efficiency gain.

“When you’re talking about 400 kW, three percent starts to be significant. The losses go out in heat, and you pay for the electricity that you’re wasting,” Standing said, adding that the extreme fast-charging system would eventually be a less-expensive way to charge a vehicle.

Delta Electronics has multiple extreme fast-charger system patents relating to power-conversion topology and control. To reach production readiness, the system would need to undergo additional development, system integration, and testing. Regulatory certification also is required.

Charging On-the-Go

Then there’s the ultimate time-saver: charging without stopping at all. A roadway-embedded wireless charging network for EVs is coming to a stretch of urban highway in Detroit, marking a pilot-program first on a U.S. public road. “Our electric vehicle receiver units are modular and compatible with passenger vehicles and with light-, medium- and heavy-duty commercial vehicles,” said Oren Ezer, CEO of Electreon, based in Tel Aviv, Israel. Michigan is expected to operate the first electrified roadway in early 2025.

Electreon’s patented wireless in-road EV charging technology already is in use in various European demonstration projects, including a 0.7-mile (1.05 km) intercity toll road in Italy and a 1-mi (1.65 km) public road in Sweden. Sweden’s policymakers aim to have 1,243 miles (2,000 km) of electrified roadway in operation by 2030. Detroit’s electrified roadway will be near Michigan Central, a mobility-innovation district under development by Ford Motor Co.

“The wireless charging infrastructure will support a suite of use cases involving various vehicle types, including autonomous vehicles, and it will support partners, like Ford,” said Jim Buczkowski, the company’s Executive Director of Research and Advance Engineering.

Cloud-Based System Monitoring

The $1.9 million-plus Michigan project involves one lane of public roadway for a minimum of one mile (1.6 km). After the existing road surface is removed, rubber-coated copper coil segments will be buried 3.15 inches (8 cm) under a new road surface. “Non-electric vehicles are able to use the roadway as usual without any disruption,” said Dr. Stefan Tongur, Electreon’s VP.

The roadway’s coil segments transmit power to an EV undercarriage-mounted receiver via magnetic resonance induction as the EV moves or is parked directly above the coils. A power-management unit located either underground or above-ground near the roadside will transfer the energy from the electric grid to the roadway’s copper-coil infrastructure. “Cloud-based management software enables live monitoring and provides smart-charging insights,” Ezer explained.

Electreon’s technology solution has 19 patents covering various proprietary aspects, including the engineered system architecture and the communication mechanism between an EV fitted with a power receiver and the embedded roadway coils. “The intellectual property of our vehicle receivers will be released to OEMs for free,” Ezer promised.

Both the battery size and the number of receivers connected to an EV influence the charging time. “The driving speed has a negligible effect on the charging performance,” Ezer explained. He said to date, Electreon has tested its receivers up to a speed of 49.7 mph (80 kph). As an example, if a commercial truck with five receivers is traveling at 37 mph (60 kph), 37 miles (60 km) of electrified road is needed to fully charge the battery. If the vehicle is traveling at 12.4 mph (20 kph), 12.4 miles (20 km) of electrified road are needed to fully charge the battery.

Larger vehicles can support multiple Electreon receivers. For instance, Class 8 trucks can be fitted with up to seven undercarriage receivers. Buses could have three receivers, while passenger vans might have two receivers. “The number of receivers on an electric vehicle depends on the use case, the vehicle size, and the vehicle type,” Ezer said. Each Electreon receiver for heavy-duty EVs is capable of supplying up to 25 kW to the battery. Based on the power transfer rate requirements of light-duty passenger EVs, Electreon offers 7 kW and 11 kW receiver options.

Michele Mueller, MDOT Senior Project Manager for connected and automated vehicles, said that electrified roadways could accelerate the adoption of EVs by enabling continuous vehicle operation via safe and sustainable public street energy platforms. “A wireless in-road charging system will be revolutionary for EVs by potentially extending an EV’s battery charge without having to stop (and plug-in),” Mueller said. She added that electrified roadways also could reduce EV range anxiety.

Four-Season Testing

The Detroit demonstration project will provide a four-season venue to test hardware and performance objectives. Electreon’s Tongur said that based on findings from ongoing projects in Europe, weather won’t be an issue. “Since the (wireless) infrastructure lies beneath the roadway, the energy transfer is not affected by snow and ice. The road can be maintained — plowed, salted, etc. — as usual without affecting the coils beneath the asphalt,” Tongur said.

Wireless charging of EVs isn’t new to America, as the largest fleet of all-electric transit buses in the U.S. use a patented wireless charging system from Salt Lake City, Utah-based WAVE (Wireless Advanced Vehicle Electrification). Forty-eight of Southern California’s Antelope Valley Transit Authority’s 54 BYD-built buses are fitted with WAVE undercarriage receivers. Those WAVE-compatible electric buses use wireless charging depots located within a 100 square-mile (260 km) area.

This article was written by Kami Buchholz, an automotive journalist and longstanding contributor to the SAE Media Group, who specializes in a wide spectrum of technology coverage for the automotive and commercial-vehicle industries. For more information, visit here  .

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