Global energy demands are surging, pushed by energy-intensive data centers powering artificial intelligence and increased manufacturing. How will the world meet these rising energy needs?
One answer is to get more use out of the energy we already produce and at a lower cost. In pursuit of this goal, NREL researchers have created a silicon-carbide-based power module — a physical housing for the power electronics that control the flow of electricity between systems — with never-before-seen efficiency, power density, and low-cost manufacturability.
The breakthrough, called NREL’s Ultra-Low Inductance Smart power module, is nicknamed ULIS. Powered by silicon carbide semiconductors, ULIS is capable of achieving five times greater energy density than predecessor designs in a smaller package, making it possible for manufacturers to build and power more efficient, compact, and lighter technologies. The 1200-volt, 400-amp power module is suitable for use in data centers, power grids, microreactors, and even heavy-duty vehicles such as next-generation aircraft and military vehicles.
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Principal Investigator Faisal Khan, NREL’s Chief Power Electronics Researcher.
Tech Briefs: What was the biggest technical challenge you faced while developing ULIS?
Khan: ULIS uses a non-orthodox fabrication process. A power module is a switching device; it has a top switch and a bottom switch, and we use commercially available dies. So, we did not follow the way other power modules are fabricated because other power modules are rectangular, they have specific current routing, the way the current flows in the inside the module. We didn't follow that because our first intent was to reduce the parasitic inductance so that we can switch faster. And we needed a flux cancellation technique, which means flux induced by the current. We needed to cancel it so that the effective inductance inside the module was low — or even if it is not low, but when you apply current, it acts like it's low.
That's why we had to design ULIS in a way which was non-conventional, non-orthodox, but it was not easy. It needed very, I would say, delicate machining. That was the biggest challenge for us.
Tech Briefs: Can you please explain in simple terms how ULIS works?
Khan: ULIS has three major innovations. The first one is ultralow inductance, meaning it has a certain number of devices that are connected in parallel and series — so four devices are connected in parallel at the top, four devices are connected in parallel at the bottom and these two groups are connected in series. Each device is rated at 100 amps, so the group of four in parallel is rated at 400 amps and each group is rated at 1.2 kilovolts. The way it works is, if you apply a gate signal to the top group, the top switch activates; if you apply a gate signal to the bottom group, the bottom switch activates.
We connected the dies at the top to the dies at the bottom such that the effects of the parasitic inductances cancel each other and the overall effective parasitic inductance is extremely low. For the best commercially available 400-amp, 1.2-kv module, the parasitic inductance is about six nanohenries, while for ULIS, it is close to 500-600 picohenries — a 10 to 11 times reduction.
How it works is very difficult to explain, but the overall concept is flux cancellation inside the power module. This is a patent-pending technique, and we are trying to find a vendor who would be interested in commercializing it.
The second innovation is our insulation layer. Every power module needs that because the dies on the top have to be insulated from the bottom. Commercially available modules use ceramic, which provides electrical insulation and is thermally conductive. Those are propertieswe need. The biggest drawback of ceramic is that it's expensive.. It is also very difficult to work on — you need very special machining to cut it. Our intent was to design a fabrication process where rapid prototyping is possible. So, instead of ceramics, we use Temprion, which is a polyamide film that you can cut. It provides the necessary electrical insulation, and at the same time it is thermally conductive. Although it is not as good as ceramic, the layer is so thin that there is no compromise in thermal conductivity. So rapid prototyping is possible.
Number three, ULIS can be wirelessly controlled. When a system has many power modules, it is very difficult to control each of them because there will be so many wires. So, in a complex system, where there are so many modules, if you can control them wirelessly and monitor them wirelessly, that's a great advantage.
Tech Briefs: You said that ULIS is patent-pending and you're looking to commercialize it. My question is: Where do you go from here? What are your next steps?
Khan: Yes. ULIS has gone through multiple iterations. The one we started with had a 700-picohenry inductance, and now it is less than 600 picohenries. Now we are trying to build a circuit around ULIS. So, it could be a big inverter, a big battery charger, or an AC-DC converter.
Last year, ULIS went to the R&D 100 competition, and we became one of the finalists — we became one of the top 158 projects. But, to be eligible to get the R&D 100 Award, you need to be in the top 100. Unfortunately, we couldn't get into the top a hundred.
This year, we are trying to go for it again because it's a full package. To be eligible with R&D 100, one of the key things is a licensed technology. So if we can license this technology, if we can show that a company has licensed this ULIS power module, that would make us very competitive for this award. So, we are going to build a system around ULIS and showcase that something built around it is very compact in volume and weight compared to commercially available solutions.
Transcript
00:00:01 How do we make vehicles, industrial machinery, energy storage, and aircraft more efficient, compact, safe, and affordable? We build a better power module. Power modules are essential parts of high-voltage modern electronics that convert energy from sources to destinations, like a vehicle battery to its motor. But modern power modules are limited by their size and parasitic inductance: a measure of energy wasted when modules convert electricity. Now NREL's new ULIS power module can power vehicles and other high-voltage electronics at a fraction of the size, cost, and parasitic inductance of its competitors. But that's not the only way ULIS bests the competition. It's also simpler, quicker to assemble, and more efficient. ULIS is modular, adaptable to serving a wide range of technologies and designs, and capable of
00:00:59 wirelessly monitoring a machine's health in real time to predict faults before they happen. Thanks to its unmatched power density, ULIS can unlock exciting new technologies like portable superfast EV chargers, miniature fusion reactors to support microgrids and data centers, and even advanced air mobility. ULIS’s power pack design can help build a safer, smarter, more efficient, and more affordable future of modern electronics. It's more power for less.
