Power Electronics and Thermal Management

This is the March 2016 issue of the Transportation and Hydrogen Newsletter.

March 31, 2016

Photo of a man seated before a microphone and speaking.

NREL's Chris Gearhart provides congressional testimony on sustainable transportation.

U.S. Senate Hears of Role National Labs Play in Sustainable Transportation Innovation
On January 12, 2016, NREL's Chris Gearhart, director of the Transportation and Hydrogen Systems Center, provided testimony on new technologies in the automobile industry before the U.S. Senate Energy and Natural Resources Committee. Gearhart's statement stressed the role of innovation and technology, particularly the role of connected and autonomous vehicles, vehicle electrification and grid integration, hydrogen fuel cell technologies, and efficient internal combustion vehicles that operate on biofuels.

Watch the C-SPAN video of Gearhart's testimony.

Optical Thermal Characterization Enables High-Performance Electronics Applications

New vehicle electronics systems are being developed at a rapid pace, and NREL is examining strategies to remove excessive heat, which can degrade or damage components and devices. A unique laser-based transient thermoreflectance technique measures the thermal performance of materials and their interfaces that cannot be determined by conventional characterization methods. Critical experimental thermal-performance data obtained from this work will help make electronics components more efficient, less expensive, and higher performing.

Strategies Developed for Reducing Heating Loads, Increasing Driving Range of Electric Vehicles

The energy used to maintain cabin temperature at a comfortable level is a vehicle's largest ancillary energy load. This load significantly impacts fuel economy for conventional and hybrid vehicles, and it drastically reduces the driving range of all electric vehicles (EVs). Heating is more detrimental than cooling to EV range due to the low coefficient of performance or COP of electric heaters compared to air conditioners, and the higher temperature difference between the cabin interior and exterior in the winter. After conducting vehicle analysis and thermal modeling, NREL researchers documented several strategies that reduce heating loads in EVs and increase energy for vehicle propulsion.

Nanothermal Interface Materials: Researchers Develop and Characterize Promising New Materials

Conventional thermal interface materials (TIMs) can impede heat flow in packaged electronics systems due to their high thermal resistance, making it critical to develop and demonstrate TIMs with low thermal resistance and superior performance. The Department of Defense funded four institutions to use nanomaterials to synthesize high-performance TIMs. NREL participated by characterizing the thermal performance and reliability of the new TIMs. One company's TIM demonstrated outstanding thermal performance and reliability, thereby advancing the state of the art.

Simulation Tool Improved to Better Model Energy-Efficient Vehicle Heating/Cooling Systems

When in use, an electric vehicle's air conditioning and heating system is the largest auxiliary consumer of energy that would otherwise power the vehicle. NREL's MATLAB/Simulink thermal modeling framework, CoolSim, was recently enhanced to reduce researcher and computational efforts to analyze complex thermal management systems that can heat and cool an electric vehicle more efficiently. CoolSim's improved capabilities decrease the time and expense of simulating and evaluating these complex new systems.

Research Evaluates the Reliability of Emerging Bonded Interface Materials for Component Attachments

Conventional thermal interface materials (TIMs), such as greases and gels, have long caused reliability issues in automotive power electronics packages because TIMs can degrade when packages are subjected to thermal cycling and aging, resulting in increased thermal resistance and heating of the packages. Bonded interface materials (BIMs) have superior thermal performance and the potential to replace conventional TIMs, but pose their own reliability concerns due to the thermal stresses they can impart. NREL research is evaluating emerging BIMs, and results to date have identified BIMs with promising thermal performance and reliability.

Laminations for Electric Machines Characterized for Contact and Bulk Thermal Resistance

NREL researchers prepared and compiled data on the properties of stacked lamination materials commonly used in electric machines. The resulting evaluation methods and specialized data of particular interest to electric machine designers have been shared with industry and university researchers to support improved motor designs. Although the research focused on electric machines for electric-drive vehicle applications, the results are applicable to any electric machine where low thermal resistance and efficient heat removal are important for increasing machine performance and power density.

Researchers Successfully Develop and Demonstrate Techniques to Reduce Thermal Load of Rest Period Idling in Long-Haul Trucks

As a part of NREL's CoolCab project, researchers developed and demonstrated technology for reducing truck cab heating, ventilating, and air conditioning energy loads and fuel use while maintaining driver comfort when long-haul trucks are parked and idling during rest periods. In a recent study, NREL researchers collaborated with industry partners to develop and evaluate a thermal load reduction package that demonstrated an extraordinary 43% reduction in heating loads, as well as a 35.7% reduction in cooling.

Learn more about NREL's Power Electronics Thermal Management and Reliability and Vehicle Thermal Management RD&D.