Keeping It Cool With Power Electronics and Electric Machines System Designs | News

Recent Advancements Shore Up New Research in Transportation and Manufacturing

NREL researcher Sreekant Narumanchi uses a liquid cooling loop to characterize reliability
of the NREL-designed dielectric fluid jet impingement cooling approach. Photo by Dennis Schroeder, NREL

Always with an eye toward the future, National Renewable Energy Laboratory (NREL)
researchers are  revolutionizing clean energy mobility beyond light-duty electric
vehicles (EVs) by building advanced power electronics systems that control the flow of electricity to propel large and advanced electric machines,
including those used in planes, trains, and heavy-duty transportation. With support
from the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E)
programs, NREL is partnering on new research projects in sustainable aviation, grid
storage, and energy-efficient computing.

“It’s an exciting time to be working in power electronics,” said NREL Senior Researcher
Sreekant Narumanchi. “These important partnerships are enabling us to develop the
most cutting-edge system designs to decrease costs, reduce component footprints, and
improve overall performance, reliability, and efficiency.”

Electrified mobility applications use power electronics, such as inverters, converters,
and chargers, to manage electricity flow between the battery, electric motor, and
other powertrain components. Depending on the application, systems must operate at
higher temperatures, voltages, switching frequencies, and power conversion efficiencies.
Advanced systems bring advanced challenges, but NREL researchers are pioneering new
power electronics and electric motor packaging, semiconductor electro-thermal designs,
and thermal management systems for transportation and manufacturing. NREL’s experimentation facilities offer world-class evaluation and measurement in heat transfer, reliability characterization,
package prototyping, and thermal and thermomechanical modeling.

State-of-the-Art Power Electronics and Electric Machines for Peak Performance

A woman operating lab equipment.

NREL researcher Emily Cousineau uses the Dual Column Tabletop Instron 5966 testing
system to measure mechanical and thermal properties of material layers. Photo by Dennis Schroeder, NREL

Power electronics are at the heart of power conversion in an electric-drive vehicle,
managing power flow between various components within the vehicle. Next-generation
power electronics and electric machine designs can improve the performance of EV powertrain
components and the digital technologies that make EVs safer and smarter. In larger
applications, such as heavy-duty equipment, the power electronics also require high-power
and high-temperature optimization.

As a leader in wide-bandgap (WBG) power electronics research, NREL evaluates and develops
electro-thermal semiconductor designs and packaging technologies that offer improved
reliability, power density, and efficiency. WBG devices, such as silicon carbide or
gallium nitride, offer lighter, more compact, and potentially robust alternatives
to traditional components. Continued research is helping highlight these advantages
and increase the adoption of WBG systems.

“Our team is collaborating with industry partners, such as General Electric, Cummins,
BorgWarner, and John Deere, to optimize the thermal performance of power-dense WBG
inverters and electric motors,” Narumanchi said. “The lighter overall weight, footprint,
and improved performance of these designs offer clear benefits to fuel efficiency
and operating costs for electrified mobility applications.”

NREL researchers rely on leading-edge modeling and characterization to perform reliability
evaluation and failure analysis of new power electronics designs. Advanced modeling
capabilities allow researchers to identify thermal bottlenecks and optimize the performance
of power electronics packaging. In addition, researchers leverage extensive characterization
through thermal, humidity, and vibration testing to better understand how stressors
affect emerging technologies. As a result, NREL-designed systems prioritize safety,
reliability, and efficiency for peak operating performance.  

Unparalleled Thermal Management and Cooling Capabilities

A man operating lab equipment.

NREL researcher Gilbert Moreno preparing experiments on the dielectric fluid loop
to evaluate heat transfer of electrical system component. Photo by Dennis Schroeder, NREL

Overheating can cause irreparable damage to power electronics and electric motors,
causing the system to slow down or malfunction. Advanced thermal management systems
are critical to the performance and safety of all electrified traction drive components,
including semiconductor power device, power modules, inverters, and electric motors.
NREL engineers are experts in system-level thermal management designs that incorporate
advanced heat transfer to regulate temperatures throughout the complete power electronics
and electric machine system. In addition, recent innovative cooling strategies, such
as jet impingement, push the boundaries of design for power electronics and electric

“Advanced cooling and thermal management systems optimize performance of electric
vehicles and advanced machines,” Narumanchi said. “These systems help keep temperatures
within operational limits, reduce the volume and weight of components, improve efficiency
of components, and increase efficiency and range of the vehicle. Ultimately, these
benefits contribute to reduced fuel consumption and greenhouse gas emissions.”

An ongoing ARPA-E collaboration with Stanford University is “Exploring the Limits of Cooling for Extreme Heat Flux Applications,” with improved chip thermal management for data centers and power electronics. Stanford
University researchers are developing a novel cooling technology, the Extreme Heat
Flux Micro- (EHFμ-) Cooler, supported by NREL’s experimental reliability evaluation
of the thermal management technologies. The EHFμ-Cooler significantly reduces device
temperature, resulting in heat flux dissipation over 1,000 W/cm2 to cool the device.

NREL’s thermal management research also includes two projects within the ARPA-E Aviation-class Synergistically Cooled Electric-motors with iNtegrated Drivers
(ASCEND) program
to support the development of innovative lightweight and ultra-efficient electric
motors, motor drives, and thermal management systems for sustainable aviation. The
first project, led by the General Electric Global Research Center, will design a 2-MW
fully integrated all-electric aircraft powertrain and demonstrate a 350-kW lab-scale
prototype to enable zero carbon emission narrow-body commercial aircraft with all-electric
propulsion. The second project, led by Marquette University, focuses specifically
on building a high-power-density motor for aviation propulsion. NREL’s support for
these projects includes thermal management modeling, analysis, and characterization
of the advanced cooling concepts and inverter components, alongside thermomechanical
design and techno-economic analysis for various power electronics, electric motor,
and integrated electric drive components.

Power Electronics Expertise for a Clean Energy Future

A man operating lab equipment.

NREL researcher Joshua Major operates the Accelerated Drive Cycle Platform featuring
a single-axis electrodynamic shaker and AGREE-style environmental chamber used to
perform reliability testing on system components. Photo by Dennis Schroeder, NREL

These existing partnerships barely scratch the surface of NREL’s advanced power electronics
and electric machines capabilities, and more exciting research is just beginning.
ARPA-E recently selected three new projects backed by NREL expertise:

  • Repurposing Infrastructure for Gravity Storage Using Underground Potential Energy, led by NREL, will use electromechanical system-level modeling to determine drivetrain
    component sizing to convert inactive oil and gas wells into energy storage devices.
  • Bringing Three-Dimensional Packaging and Thermal Management to Power Electronics,
    led by Synteris
    , will include NREL research to improve the thermal management, power density, performance,
    and lifetime of ceramic packaging for power electronic modules.
  • Substation in a Cable for Adaptable, Low-Cost Electrical Distribution (SCALED), led by Virginia Polytechnic Institute and State University, will include NREL thermal
    management research to develop compact, high-performance power electronics components
    in the context of grid applications.

As part of the ARPA-E OPEN 2021 program, these projects prioritize high-impact, high-risk
technologies that support novel approaches to clean energy challenges.

“Each of these projects involve exciting new collaborations with industry and university
partners—as well as collaborations across groups at NREL—to develop pioneering power
modules, packages, converters, and drivetrain components impacting multiple energy
efficiency and renewable energy applications,” Narumanchi said.

Learn more about NREL’s sustainable transportation and mobility and advanced manufacturing research.