Energy is so very important to our future. Conserving it, harnessing it, using it responsibly, and becoming more aware of its impact are the keys to energy’s future.
The US Department of Energy (DOE) has issued certain energy targets, set to be achieved by 2020… but wouldn’t it be great if they were met even earlier? These standards set metrics which the energy industry must meet, including power density, specific power, and the efficiency of power inverters (devices that take batteries’ direct current and turn it into the alternating currents needed for electric motors). Power inverters are a significant technology, and their performance directly impacts that of the electric vehicles that use them. As electric vehicles (EVs) continue to become more prominent in the US car park, enhancements to their performance will receive special attention.
EVs rely especially on their power inverters, which have been called “the heart of an electric vehicle”. Madhu Chinthavali, who led the Power Electronics and Electric Machinery Group on this project, gave the inverter that designation, and it seems he has quite a lot to be proud of for his team’s work toward keeping that heart beating healthily.
Below are the DOE’s targets for 2020, compared against a prototype power inverter recently produced by researchers at the DOE’s Oak Ridge National Laboratory (ORNL). The ORNL prototype is very close to already meeting (or beating!) all of the target metrics. In addition, the prototype significantly reduced the weight and volume of a typical power inverter, contributing to larger vehicular lightweighting targets.
|Metric||DOE 2020 target||ORNL prototype|
|Power density||13.4 kW/L||13.33 kW/L|
|Specific Power||14.1 kW/kg||11.5 kW/kg|
How were these improvements achieved? What’s so special about this prototype?
The ORNL prototype was created using 3D printing and novel silicon carbide (SiC) wide band gap (WBG) semiconductors. Created under the auspices of a DOE-funded project, the two-year, $1.45-million endeavor integrates WBG technology with novel circuit forms and advanced packaging. These improvements combine together in a neat package that lowers production prices and waste volumes, increases performance efficiency, and raises power density.
This 30-kW prototype model is about 50 percent 3D printed, and following the success of this model, researchers are already working on the next version, which will further increase the use of 3D printed components and decrease weight and size of the unit.
“With additive manufacturing, complexity is basically free, so any shape or grouping of shapes can be imagined and modeled for performance,” Chinthavali said. “We’re very excited about where we see this research headed.”
The WBG technology is of particular importance as work continues. Heat transfer through the unit can be improved as the inverter’s heat sink is optimized, which can be achieved via 3D printing. Electrical losses can be reduced by additive manufacturing’s capability to allow lower-temperature components nearer to high-temperature devices.
“Wide band gap technology enables devices to perform more efficiently at a greater range of temperatures than conventional semiconductor materials,” said Chinthavali.
Further advantages of WBG, according to ORNL, include:
- higher inherent reliability
- higher overall efficiency
- higher frequency operation
- higher temperature capability and tolerance
- lighter weight, enabling more compact systems
- higher power density
The prototype lights the way for further improvements. Already, this iteration — with its liquid-cooled SiC traction drive inverter — has a confirmed almost-99 perecent efficiency, which beats the DOE’s 2020 target. By building next generations out of higher percentages of 3D printed parts, the next goal becomes an inverter only half the size of currently available models, and (eventually) four times the power density of this prototype.
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