Boosting Thermal Management & Reliability of Vehicle Power Electronics

More and more electric cars are hitting
the road, translating into greater energy
efficiency and cleaner air. While the typical American spends more than $1,400 each year on gas to get from Point A to Point B, most electric car owners only pay about $540 per year to charge up. But electric car sticker prices can still be high, and performance doesn’t always match that of conventional gas-powered vehicles. Improving the performance of power electronic components will be critical if electric cars are to claim the 50% market share experts predict. Research at the National Renewable Energy Laboratory, or NREL, is helping boost the performance of these power electronics, while driving down size, weight, and cost. Electric vehicles rely heavily on power electronics, including inverters, converters, and chargers to control the flow of electricity between
the battery, the motor, and other powertrain components. In electric vehicles, these components need to operate at higher temperatures, voltages,
switching frequencies, and power conversion efficiencies. That’s where NREL’s thermal management and reliability research comes in. NREL’s thermal management strategies make it possible to develop smaller, higher performance
and more energy efficient power electronic components, like the wide-bandgap technology that is a strong interest for integration into future
electric vehicles. NREL’s wide-bandgap thermal management strategies led to the world’s first commercial high-temperature, high-power density automotive traction drive inverter, an innovation recognized with an R&D 100 Award. Thermal research at the package level focuses on die- and substrate-integrated cooling strategies and heat transfer enhancement technologies. System-level thermal research and analysis supports the development of thermal
management strategies for the entire power electronics system, with packaging
solutions that increase power density and reduce cost. NREL’s research on the reliability of new electronics packaging results in longer-lasting components
that operate more efficiently and dependably under higher temperatures. By pinpointing causes and locations of failure, such as separation, delamination,
and cracking, researchers can help industry partners design more reliable
components. Materials and designs are put through their paces as researchers age power electronics under accelerated thermal and humidity conditions. One body of work quantifies the aging of large-area bonded interface materials that adhere the insulating substrate within a power module to its base plate. NREL researchers focus on improving the bond strength and lifetime of these interface materials…and recently sintered silver, a potentially more reliable and
environmentally friendly alternative to traditional high-temperature soldering,
is given much attention. Using a variety of non-destructive techniques, such as acoustic microscopy, allows researchers to observe the development of voids,
cracks, or delamination within sample layers. Transducers generate ultrasound
with a frequency customized to each sample material, making it possible to
image an internal layer with maximum resolution. Periodic scans of a sample expose changes over time, revealing areas for attention. Mechanical evaluation of sintered silver is an important step in exploring the viability of this high-temperature alternative to traditional solders. After a stencil-printing process is used to produce samples with consistent bond
line thickness, researchers heat them up to 250 degrees Celsius to trigger the sintering process and synthesize a double-lap sample configuration with two interfaces of sintered silver for mechanical testing and measurement of changes in strain. Results are incorporated into constitutive models for use in finite element numerical modeling. After NREL completes this early-stage research, industry figures out how to incorporate the new technology
into cars coming off the assembly line. All of this power electronics research
and development is conducted with the goal of reducing component size and cost, while improving performance and reliability, which will make electric
cars more affordable and appealing to even more drivers. Learn more about NREL’s power electronics research and partnership opportunities on our website.