DOE Upping Investment in Advanced Power Electronics and Electric Machines Research

22 May 2009

In addition to increasing the overall budget, DOE is providing more funding to other segments within APEEM in FY2009. (Difference in pie chart size is representational, and not to scale.) Click to enlarge.

The US Department of Energy (DOE) increased the budget for Advanced Power Electronics and Electric Machines (APEEM) research to $17,358,000 in fiscal 2009, up 12% from the FY 2008 budget of $15,462,000. The APEEM effort comprises power electronics, electric machines, thermal control and integrated systems—components that are unique and critical to electric-drive or assisted vehicles.

All elements within the APEEM category must advance to achieve lower cost, smaller and lighter footprints, and higher efficiency to meet marketplace demands—and the DOE development targets—said Susan Rogers, who runs the APEEM programs within the DOE’s Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies program, at the DOE Merit Review meetings this week in Washington.

Generic electric traction drive components. Source: DOE. Click to enlarge.

APEEM systems are critical for the entire range of electrification applications, from conventional hybrids to full battery electric vehicles, albeit with different sizing. They are also an important cost component. Benchmarking work done by the DOE estimates that PEEM represents 54% of the cost distribution of the MY 2007 Camry electric traction drive system, with the battery accounting for 33% and the generator accounting for 13%. The distribution is also roughly the same for a Gen-II Prius.

The current basic DOE requirements are for 55kW peak for 18 sec; 30 kW continuous; 15 year life; and the ability to use 105 °C coolant or air. DOE has defined performance and cost targets in meeting those requirements. By 2020:

• Traction drive systems should cost $8/kW, be more than 94% efficient, and offer densities of 1.4 kW/kg and 4 kW/L.

• Power electronics must cost $3.3/kW, and support densities of 14.1 kW/kg and 13.4 kW/L.

• Motors must cost $4.7/kW, and offer densities of 1.6 kW/kg and 5.7 kW/L.

These targets, noted Ayman EL-Refaie from General Electric, who presented the status of that company’s work on an advanced IPM motor at the Merit Review, are extremely aggressive.

DOE APEEM targets. Source: DOE. Click to enlarge.

Power electronics. In FY09, the emphasis on power electronics research is the reduction of cost and volume; eliminating, for example, a separate boost converter and reducing capacitor size. The program is also seeking to enable high-temperature operation, and to work with charging systems for PHEVs.

Approaches include integrating multiple functionality into one inverter unit and minimizing capacitance need, while designing to use high-temp coolant, and develop high-temperature components (gate drives, capacitors).

Electric machines. DOE shifted from an initial focus on induction motors due to cost to IPM (interior permanent magnet) motors as volume constraints became a greater consideration. IPM motors offers higher power density and efficiency. Now PM cost and rare earth material supply uncertainty has resulted in a reexamination of IPM.

The emphasis in FY09 is to reduce the motor cost and integrate voltage boost—which also reduces PE cost. Approaches being explored are high-speed designs using no PM material, higher-performance IPM motors, and a magnet effort to reduce cost and improve temperature capability.

Thermal controls. The current emphasis is to enable increased power density and lower system cost; increase the rate of heat transfer; decrease thermal resistance; and evaluate the impacts on life and reliability early in the development process.

Approaches in FY09 include analysis of thermal stress and fatigue life of APEEM packages; characterization and development of advanced liquid cooling technologies; complete an assessment of state-of-the-art systems; and demonstrate advanced air-cooling heat transfer and system level performance.

Integrated systems. The current emphasis is to document the performance of current state-of-the-art PEEM systems (a Prius system) at end-of-life, and to develop an integrated traction drive system meeting 2010 targets—a project being led by General Motors.