• Why Amazon is investing in a startup that's shrinking the footprint of EV charging
  • Newsletter
  • Donate
Clean energy journalism for a cooler tomorrow

Why Amazon is investing in a startup that’s shrinking the footprint of EV charging

Resilient Power uses cutting-edge electronics to make heavy-duty EV charging cheaper, smaller and more flexible.
By Jeff St. John

  • Link copied to clipboard
Resilient Power’s solid-state transformer tech could make heavy-duty EV charging much cheaper and more flexible. (Resilient Power)

Electric vehicle chargers can’t just connect to the power grid willy-nilly. Converting the grid’s higher-voltage alternating current to the lower-voltage direct current that EV batteries can accept requires lots of equipment — step-down and step-up transformers, bidirectional inverters and power converters, switchgear and other devices — all configured to meet specific charging needs.

Add more vehicles or chargers and all that equipment must be reconfigured, costing more money and time. That could limit the flexibility of companies that plan to go big into EVs in the coming years — like, say, Amazon.

That’s why Amazon’s Climate Pledge Fund last week joined a $5 million seed round of investment in Resilient Power. The Atlanta, Georgia-based startup is working on solid-state transformers, which are devices that can combine all of a heavy-duty EV charging system’s power conversion steps in one unified, digitally controlled package.

Think of it as a bridge between the grid and individual chargers,” Matt Peterson, head of Amazon’s Climate Pledge Fund, said in an interview last week. Instead of the wound-up copper wire and ferrite-core transformers that have been used to convert grid power from one voltage to another since the days of George Westinghouse and Nikola Tesla, solid-state transformers are completely semiconductor-operated,” he said, manipulating the flow of power in much the same way that microprocessors control the flow of electrons representing data.

These types of power conversion technologies are already at the heart of EV drivetrains, solar inverters, variable frequency drives and other key pieces of the clean energy landscape. Unlike most of these systems, however, Resilient’s charging control hub can handle up to 1.5 megawatts of power, allowing it to be connected directly to higher-voltage power grids, rather than the lower-voltage power sources available within most buildings.

Using semiconductors instead of electromechanical gear allows Resilient to manage that power in about one-tenth the space of an equivalent system designed and built using transformers and other standard electronics hardware. The company’s system will be delivered in a pre-manufactured box, rather than being integrated on-site, allowing it to be installed in about one-tenth the time.

And because it can handle a number of different charging ports and configurations without adding or reconfiguring equipment, the Resilient system is far more adaptable to changing circumstances. These features could help reduce some of the bigger challenges of connecting lots of high-speed EV chargers in dense urban environments or at fleet charging depots.

This is the type of unit we believe is necessary to accelerate the adoption of electric vehicle charging infrastructure at scale,” Peterson said. Amazon has plans to build out a large EV fleet. It has invested billions of dollars in EV startup Rivian and expects to deploy 100,000 of that company’s electric vans by 2030.

We need to be really creative about how we’re thinking about placing these charging units,” he said. While Resilient’s systems are still in early development, we can work relatively quickly to take it to the next level” once the equipment is ready for deployment, he said.

Piecing together the power electronics for high-voltage EV charging

Resilient is far from the first company to explore solid-state transformers for high-voltage EV charging. Over the past decade or so, a host of semiconductor makers, electric power equipment manufacturers, university researchers and Department of Energy laboratories have been working with advanced semiconductors and digital power flow controls on similar goals.

This concept has been out there for a very long time,” said Sunil Chhaya, senior technical executive for EV integration with the utility-funded research organization Electric Power Research Institute. In fact, EPRI has been working on it for more than a decade, most recently in a DOE-funded project with global electronics equipment maker Eaton and EV fast-charging maker Tritium. Other DOE-backed projects include an extreme fast-charger being developed by Delta Electronics.

But there are some big challenges to adapting these technologies for use in high-voltage EV charging. One of the biggest has been coming up with a combination of semiconductors that can handle the high voltages involved without being overloaded or wasting too much energy in the power conversion process, Chhaya said.

Converting the up to 15,000-volt alternating current on the distribution grid to the 480-volt direct current required to charge EVs is a technically complex task, involving very high-frequency power switching and careful isolation at each stage of the process, he said.

Tom and Josh Keister, the father-and-son duo behind Resilient Power, say they’ve solved these problems through a distributed architecture that combines commonly available semiconductors. The technical term for the company’s approach is a cascaded H-bridge multilevel inverter,” Josh Keister, Resilient president, said in an interview last week.

We can harness the best of any transistors” that are now commercially available, he said, as opposed to systems that require high-power semiconductors that are still in development. 

Controlling high-voltage power flows through commercially available semiconductors requires a control system that can handle the super-fast switching operations involved, said Tom Keister, the company’s CEO. He worked on similar concepts at his previous position as head of power electronics R&D at Teco-Westinghouse Motor Company. Although his team went through quite a bit of variations, [they] still could not get the size down and the cost down.”

Resilient has finally succeeded in reducing both size and cost, he said. The company’s architecture also allows multiple EV charging ports to be powered through DC-to-DC converters linked via magnetic flux using a design principle known as galvanic isolation,” he added. This reduces the risk of surges and other incompatibilities that have limited solid-state transformers from being used at higher grid voltages, he said.

As for safety, Resilient has tested its system in overload and lightning-strike simulations with partners including DOE’s Savannah River National Laboratory and the National Renewable Energy Laboratory, which have also provided contracts and grants that made up a significant amount of the $3 million the company raised prior to its recent seed funding round.

(Resilient Power)

Solid-state transformers: The holy grail of a flexible grid? 

Resilient Power has four patents approved and three more pending for its approach to EV charging. But it has been exploring applications beyond EV charging since its 2015 founding, including a DOE project looking at the potential for solid-state power substation” technology that could provide bidirectional alternating current (AC) or direct current (DC) power flow control from one or more sources to one or more loads — regardless of voltage or frequency.”

Solid-state transformers (SSTs) have long been in development for grid applications like these, said Neal Dikeman, a partner at venture capital firm Energy Transition Ventures, which led the $5 million investment in Resilient along with Amazon and GS Futures, the corporate venture capital arm of South Korea-based GS Group. Various versions of solid-state power electronics are now serving roles on the power grid, he said, including the transmission grid tech of Smart Wires, a company he co-founded.

SSTs can change the world,” he said. The problem is, nobody’s gotten them to work at medium voltage,” as Resilient is now aiming to do. Other companies with similar power conversion technologies, such as Ideal Power, have limited themselves to lower-voltage applications.

Meanwhile, utilities tend to be slow-moving when it comes to introducing novel technologies into their mainstream grid operations, Dikeman said. But with massive growth plans ahead for electrifying transportation, EVs have now become the killer app for SSTs,” he said.

Not all EV charging applications are suited to the technology, he noted. But as EV charging needs grow to the scale where it will start to disrupt the power grid, approaches like Resilient’s can yield significant advantages in reduced cost and complexity.

Josh Keister estimated that his company’s approach could yield 40 percent savings over traditional approaches at charging loads of 1 megawatt, and it keeps going up from there.” It can also avoid the costs of engineering and construction to prepare sites for traditional equipment needed to support chargers, he noted.

Other containerized systems have been built to manage these heavy-duty charging loads — electric bus and drivetrain maker Proterra has a cargo-container-sized multiport charging system, for example — but Resilient’s system is about one-thirteenth the footprint” of Proterra’s system, Josh Keister said. Tesla’s urban charger system, on the other hand, manages to fit into a smaller footprint by providing one-fifth the power of its larger systems, which means they make you wait five times longer for charging in the city.”

EPRI’s Chhaya highlighted the flexibility benefits of the solid-state transformer approach to EV charging. Around the world, EV charging plazas are being planned for multi-megawatt-scale charging loads. Using solid-state power conversion systems allows a site to tap into the high-voltage and high-power capability without having to necessarily plan all the plaza at once,” he said. That way, every time you add more endpoints, you don’t have to mess with the entire design.”

The same flexibility can allow a much wider range of options for adding batteries, solar panels and other systems, as an increasing number of high-impact EV charging sites are doing, he said. You can almost have a microgrid in the middle there.”

Tom Keister sees great promise for solid-state transformers across the power grid. But right now, EVs are the top focus. Utilities are saying they need EVs. Commercial buildings, restaurants, manufacturers need EVs,” he said. We saw EVs as the pathway to a whole new world of microgrids.”

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.