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Power Electronics

It’s Electric: Silicon Carbide Takes Army’s Vehicle Fleet Into The Future

Chris Noon
February 15, 2020
It famously took 1.21 gigawatts, roughly the capacity of a large nuclear power plant, to fire up the DeLorean time machine in the “Back to the Future” movies. Time travel might still be the stuff of science fiction but some of Dr. Emmett Brown’s technology wasn’t too far from reality. His attempts to channel the energy from a lightning bolt into the DeLorean’s flux capacitor, for example, were also a madcap introduction to power electronics, the systems that send electricity around in cars and many other machines and devices.
As cars are becoming increasingly electric, the importance of power electronics is also surging. Just ask Lauren Boteler, a technical expert at the Adelphi, Maryland-based United States Army Research Laboratory (ARL). She and her team are building resilient, lightweight and compact power electronics for the Army’s growing fleet of electric vehicles (EVs). And they’re getting some outside help: Last week, GE Research announced that its engineers would collaborate with the ARL to take the stalwart semiconductors in those EVs to the next level.

While Boteler is not working on souped-up DeLoreans, she does have a good idea of what tomorrow will bring. “The world is moving away from mechanical systems, and the same thing is happening in the military,” she says. “The U.S. Army’s vehicles are increasingly electrified, and we’re also seeing the growth of drive-by-wire systems,” she adds, referring to the systems that control the engine, handling and suspension of an EV via electronics, rather than doing it mechanically.

EVs might look similar to gas-guzzling cars but under the hood, it’s a different story. Instead of pistons and valves, EVs need a charger, batteries, an electric traction motor, a transmission kit, a circuit box holding the power electronics, and some sort of cooling system so they do not overheat.

The power electronics setup varies from vehicle to vehicle but most EVs have an inverter that converts the battery’s direct current (DC), which travels in one direction, into alternating current (AC), which periodically reverses, and is suitable for powering the vehicle’s electric motor. Then there are converters that maintain the DC, but lower the voltage from the battery to for auxiliary devices — in the U.S. Army’s case, active protection systems or laser-enhanced weaponry — or step it up to recharge the battery. “Power electronics basically change the flavor of the electricity in vehicles,” Boteler says. “The battery is one flavor of energy, but lasers and so on need another kind of flavor.”

The master caterers in electrical systems who can provide all of these flavors are semiconductors. Everyone knows about the silicon semiconductors in our phones and computers, but Darin Sharar, a thermal science engineer at the Army research laboratory, says silicon alone will not cut it for the U.S. Army’s EVs. “Silicon is great, apart from when you put a high current through it,” he says. “That’s why we’re interested in silicon carbide, which allows us to push the limits.”

 width= Above: GE Research announced that its engineers would collaborate with the United States Army Research Laboratory to take the stalwart silicon carbide chips in those electric vehicles to the next level. Image credit: Army. Top image: The problem is that SiC chips are hard to make, and that’s where engineers at GE Research come in. They’ve been working with the material for years and now are helping the Army shrink SiC chips in its vehicles, while simultaneously boosting their thermal limits. Image credit: GE Reports. 

The prized quality of silicon carbide (SiC) as a semiconductor is its wide “band gap,” a property that allows chips made from the material to efficiently handle higher voltages and temperatures.

Silicon carbide is more than just a cool customer. Boteler says a single silicon carbide device can do the job of numerous silicon devices working in parallel, which reduces the size and weight of the electrical apparatus in the U.S. Army’s EVs. That can boost the speed and mobility of the force’s trucks.

The problem is that SiC chips are hard to make, and that’s where engineers at GE Research come in. They’ve been working with the material for years and now are helping the Army shrink SiC chips in its vehicles, while simultaneously boosting their thermal limits.

GE’s focus will be the Package Integrated Cyclone Cooler (PICCO) project. Peter de Bock, a principal engineer for GE Research’s Thermosciences division and project leader, says PICCO will leverage cutting-edge additive manufacturing, or 3D-printing technology, to produce copper and ceramic parts that will “boost the thermal inertia” of the power electronics packages. Translation: This means that the material will be able to stay cool and maintain performance, even when ferrying and converting huge quantities of power.

“We want to ensure that the package, which receives a large pulse load, will not reach an extreme, high temperature,” Boteler says. The team of engineers will work to guarantee that even high-intensity, peak load conditions, such as when a vehicle is accelerating up a steep hill, will just be business as usual for the power electronics in the U.S. Army’s EVs. “We want a ‘steady-state’ solution that can handle those ‘5% of times’, 100% of the time,” Boteler says.

Boteler, de Bock and their teams say the co-design process, which allows Army and GE teams of mechanical, thermal and electronic engineers to work together, is highly efficient because their work and skills frequently overlap. “We can instantly share how an electrical circuit might be affected by heat or see how a design might need geometric flexibility or new material solutions,” says Boteler. “We’re not limited by a sequential, siloed approach.”

The project team is utilizing ParaPower, an open-source software tool developed by the Army research lab to collaborate with partners and accelerate the design process. “It’s a unique and generous initiative from the U.S. Army,” says de Bock. Adds Boteler: “We can instantly share how an electrical circuit might be affected by heat or see how a design might need geometric flexibility or new material solutions. We’re not limited by a sequential, siloed approach. It completely opens up the design space, allowing us to rethink everything.”

* This research was sponsored by the U.S. Army Research Laboratory's Sensors and Electron Devices Directorate (SEDD) and was accomplished under Cooperative Agreement Number W911NF1920276. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Army Research Laboratory's Sensors and Electron Devices Directorate (SEDD) or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.
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