About the Project

The electric drive system is the technology foundation for hybrid electric and fuel cell vehicles. NREL focuses on developing advanced power electronics and electric machinery technologies that improve and dramatically decrease vehicle systems costs, under DOE's Power Electronics and Electric Machines (PEEM) subactivity. NREL supports the PEEM project goals to ensure high reliability, efficiency, and ruggedness; and simultaneously reduce cost, weight, and volume for advanced vehicles. Key components for these vehicles include motors, inverters/ converters, sensors, control systems, and other interface electronics. The PEEM subactivity is under DOE's Vehicle Technologies Program.

NREL's diverse team of scientists and engineers focus on understanding and improving the way the various new components of tomorrow's automobiles and heavy trucks will function as a unified system to improve fuel efficiency. PEEM power electronics research includes fundamental R&D; development of an integrated chip controller (without external circuitry) to reduce cost; development of a bi-functional DC/DC converter to interconnect the fuel cell's high-voltage bus to the low-voltage bus for auxiliary loads; development of a lightweight, low-cost inverter to convert DC power from a fuel cell or battery to AC power for the electric motor; and research on capacitors as alternatives to inverters. Figure 1 shows the PEEM subactivities with the resulting outputs and the collaboration between this activity and others. NREL's key work in systems integration, thermal management, and capacitors is highlighted in red.

Power Electronics and Electric Machines to support FreedomCAR and 21st Century Truck

Figure 1. DOE's PEEM subactivities with the resulting outputs and the collaboration between this power electronics activity and others.

DOE, NREL, industry, and other national laboratories are working to design, develop, and demonstrate advanced power electronic components and systems that will overcome major technical barriers to the commercialization of hybrid, advanced internal combustion, and fuel cell power electronics technologies. NREL is taking the lead on thermal management and components and systems research, such as advanced capacitor technologies. Our engineers and scientists are developing new methods to cool and control the insulated gate biopolar transistors (IGBTs) and capacitors that are used inside motor controllers to improve power distribution. In addition, NREL is helping DOE guide the PEEM subactivity to reach its goals.

Goals, Technical Targets, and Barriers for Light-Duty Vehicles

Goals

NREL is working toward the PEEM goals to develop by 2010 an integrated electronics system that costs no more than $12/kW peak and can deliver at least 55 kW of power for 18 seconds and 30 kW of continuous power. Additionally, the propulsion system will have an operational lifetime of 15 years (a FreedomCAR Partnership goal).

Technical Targets

Technical targets for inverters and motors for a traction powertrain are shown in Table 1. The actual power rating (kW) and the cost ($) are highly dependent on a specific vehicle's electrical requirements. The greatest challenge is cost, which is intensified by the need to simultaneously increase performance and reduce size and weight. It is anticipated that efforts beyond 2006 will be focused on an integrated inverter/motor system. The trend toward an integrated system encompassing the motor, inverter, cooling system, and all interface connections is represented in the targets shown in Table 2.

Barriers

Barriers to achieving the technical targets include:

1. Cost. Materials, processing, and fabrication technologies for power electronics and electric machinery are currently too costly for automotive applications.
   
   
2. Volume and thermal management. Power electronics and electric machines are bulky and difficult to package for automotive applications. Current thermal management techniques are inadequate to dissipate heat in high-power density systems. Achieving cost goals is difficult because the components must be packaged and cooled effectively.
   
   
3. Weight. Current electric machinery and power electronics controllers are too heavy and require additional structural weight for support.
   
   
4. Reliability and ruggedness. Power electronics modules and motors that meet the requirements for size and weight are not rugged or reliable enough to operate in harsh environments (e.g., extreme temperatures, humidity, dirt) for 150,000 miles or 15 years. Also, the operating and shelf life of energy storage (or buss) capacitors is only 5 years under moderate conditions.

These barriers must be considered together; one cannot be resolved at the expense of another. Performance must be improved, costs decreased, and size and weight reduced simultaneously.

Overall Approach

The power electronics and electric machine effort focuses on R&D in key technologies to enable achievement of the technical targets of the FreedomCAR Partnership. The Vehicle Technologies Program partners with automobile component suppliers to develop advanced technologies suitable for introduction into the marketplace. This cooperation ensures that the technical attributes, automotive-scale manufacturing, and cost sensitivities are addressed in a timely fashion and that the resulting technologies reside with companies that are willing and able to supply derived products to the automobile companies. NREL and other laboratories, universities, and small businesses will focus high-risk enabling technology R&D on overcoming the critical technology barriers. This research is coordinated with the electrical and electronics FreedomCAR technical team.

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