The power electronics activity focuses on research and development (R&D) for flexible, integrated, modular power electronics for power conditioning and control, including a power switch stage capable of running a variety of motors and loads.
Efforts are underway to reduce overall system costs for these vehicles through the elimination of additional cooling loops to keep the power electronics within their safe operation ranges. These challenges are being met within the program through research in:
- Silicon carbide and Gallium Nitride semiconductors, which can be operated at much higher temperatures than current silicon semiconductors;
- Packaging innovations for higher temperature operation;
- Improved thermal control technologies; and
- Innovative power circuit topologies that minimize critical components unsuitable for operation in elevated temperatures
Capacitors account for a major fraction of the weight, volume, and cost of an inverter. Currently, polymer-film capacitors are used for automotive applications; but, in addition to being bulky, they cannot tolerate the high temperatures that are anticipated. Two promising alternatives are ceramic capacitors and improved film capacitors using new materials. Research to date has identified several candidate polymers with higher temperature capabilities, and research will continue on ceramic capacitors, which have the greatest potential for volume reduction and the ability to tolerate very high temperatures. The emphasis for ceramic capacitors will be on ensuring a benign failure mode, validating high temperature reliability, and lowering the cost.
Bidirectional voltage converters are needed to boost the voltage from the battery to a level acceptable for optimum performance of the motor. In addition, hybrid vehicles will require AC/DC converters to interconnect the high-voltage bus and the low-voltage bus for vehicle auxiliary loads. Technical issues to be addressed for both boost and buck converters include choice of topology, filtering requirements, switches, switching frequency, radio-frequency interference considerations, thermal management, and types of magnetic components. An inverter, which converts direct current (DC) power from a fuel cell or a battery to alternating current (AC) power for the motor is also needed. Cost, reliability, weight, and volume are critical factors.