Electric, hybrid, and fuel cell vehicles need electric drive system components that are lightweight, compact, durable, and efficient. Oak Ridge National Laboratory’s Power Electronics and Electric Machinery (PEEM) group is focused on developing revolutionary new power electronics, electric motor, and traction drive system technologies that will leapfrog current on-the-road technologies, leading to lower cost and better performance.
The PEEM Laboratory located at the National Transportation Research Center is a primary laboratory for DOE Vehicle Technologies Office electric drive technologies research and development. Current projects include benchmarking industry devices, developing new technologies for thermal management and packaging of power electronics, prototyping novel power electronics components, creating wireless charging systems for electric vehicles, extending power module operating range with wide bandgap materials, and designing new motors and digital controls that reduce or eliminate the use of rare earth materials. PEEM researchers use analysis, modeling, simulation, and unique, PEEM-developed equipment and capabilities to evaluate power electronics and electric machines.
Projects are funded primarily through the DOE Electric Drive Technologies program, with additional funding from the Advanced Research Projects Agency-Energy (ARPA-E) and industry partners. Researchers also work closely with industry through organizations such as U.S. DRIVE, which bring together government and automotive manufacturers.
PEEM staff members hold advanced degrees in physics and electrical and mechanical engineering. Collectively, they have been granted more than 50 patents and published more than 400 technical papers. Most are active members of professional societies such as the Institute of Electrical and Electronics Engineers, the Institution of Electrical Engineers, the American Society of Mechanical Engineers, and the Society of Automotive Engineers, and hold leadership positions in these organizations.
Building Better Components
Researchers are focused on developing lighter, smaller, more rugged, and more efficient components to control the flow of power in the electric vehicle drivetrain (e.g. chargers, inverters, and dc-dc converters). Using all–silicon carbide (SiC) semiconductors, PEEM staff are targeting reductions in onboard charger and dc-dc converter costs of 50% while maintaining efficiency and cutting component weight and volume in half.
PEEM engineers have developed all–silicon carbide (SiC) inverters with innovative high-temperature module and heat sink designs. For example, researchers leveraged ORNL capabilities in additive manufacturing to create a novel liquid-cooled all-SiC traction drive inverter, featuring 50% printed parts. The inverter has an optimized, 3-D printed heat sink, which allows for better heat transfer throughout the unit. Through additive manufacturing, researchers were able to place lower-temperature components close to the high-temperature devices, further decreasing the electrical losses and reducing the volume and mass of the package.
Wide Bandgap (WBG) Power Devices
WBG technology enables devices to perform more efficiently at a greater range of temperatures than conventional semiconductor materials. Specific advantages of WBG devices include: higher inherent reliability; higher overall efficiency; higher frequency operation; higher temperature capability and tolerance; lighter weight, enabling more compact systems; and higher power density.
ORNL collaborated with partners to build the industry’s first silicon insulated-gate bipolar transistor–SiC Schottky diode hybrid 55 kW inverter. The WBG SiC materials enable the inverter to perform with up to 30% efficiency improvement compared to an all-silicon module.
Device Evaluations
- 1200V, 35A SiC Diode
- 1200V, 100A SiC Diode
- 1200V, 33A SiC MOSFET
- 1200V, 6A SiC BJT
- 1200V, 8A JBS Diode
- 1200V, 30A JBS Diode
- 1200V, 100A JBS Diode
- 1200V, 50A SiC JFET
- 1200V, 100A SiC JFET
- 1200V, 100A SiC MOSFET
WBG device evaluation has been performed by ORNL in the WBG Data Analysis and Technology Assessment (DATA) facility for more than 10 years. Benchmarking evaluation and characterization are done at the bare die and packaging level and through device modeling. ORNL works collaboratively with device manufacturers from around the world to assist in moving WBG device technology forward.
Packaging
In the power device packaging laboratory, researchers are engaged in the development of advanced power electronics modules for electric vehicles. Research and development is targeted to achieve comprehensive improvements in efficiency, functionality, reliability and cost effectiveness of power electronics modules.
PEEM advances the electrical, thermal, and thermo-mechanical performance of power modules through structural optimization, materials development, and innovations in manufacturability. Current projects are focused on developing novel power packaging techniques that exploit the superior attributes of WBG semiconductor materials.
For example, researchers created a highly integrated power module package that features double-sided cooling and three-dimensional, planar power interconnection. These new packaging technologies have been demonstrated in the fabrication of all-SiC power modules that show improvements in efficiency, power density, system cost savings, and ease of manufacturability.
Wireless Charging
ORNL developed the world’s first high-power (20 kW) wireless charging system for passenger cars. The system achieved 90% efficiency at three times the rate of the plug-in systems commonly used for electric vehicles – transferring power from the ground coil to a coil on the vehicle across a 16 cm air gap. The laboratory demonstrated the technology incorporated into a Toyota RAV4 and used the same vehicle to show dynamic, in-motion wireless charging. ORNL has also demonstrated level 2 (6.6 kW) bidirectional wireless charging by sharing power between a printed utility vehicle and a printed building as part of the Additive Manufacturing Integrated Energy demonstration.
Electric Machines
Researchers are developing novel concepts and building new electric motors that reduce or eliminate the use of rare earth materials while maintaining high power density, specific power, and efficiency. Most electric and hybrid electric vehicles on the road today have motors that use rare earth permanent magnets. The US currently imports rare earth materials, so researchers are focusing on this area as a matter of national energy security.
The PEEM group uses sophisticated computer simulation to identify new motor designs that meet the performance parameters without employing rare earth materials. Researchers build the most promising prototypes and evaluate the motors using dynamometers and other testing capabilities.