The free-piston Stirling power convertor is being considered as an advanced power-conversion technology for future deep-space missions requiring long-life radioisotope power systems. The NASA Glenn Research Center plays a critical role in developing advanced technologies to significantly improve the Stirling convertor. One of the key areas identified for technology development is the controller. The Glenn controller effort is focused on developing an active power factor correction (APFC) controller capable of dual-convertor operation. The APFC technology uses power electronics, which eliminates the tuning capacitors required for other control approaches, such as Zener-diode controllers. These capacitors add significant size, mass, and parts count to the system. Eliminating them will minimize volume and mass, which are critical parameters for space applications.
Dual-opposed SBIR EE–35 Stirling convertors.
Glenn’s in-house APFC controller development staff, in conjunction with engineers from Artic Slope Research Corporation (ASRC) and ZIN Technologies, began with a proof-of-concept unit designed to control a single Technology Demonstration Convertor from Infinia Corp. (Kennewick, WA). After successful operation of the APFC controller, modifications were made to include features such as startup capability and overload protection. The controller hardware and software were later tailored to operate EE–35 convertors and Advanced Stirling Convertors (ASCs) from Sunpower, Inc. (Athens, OH). Present-day development is focused on a third-generation prototype unit to validate the APFC controller as a viable control technology. The preceding photograph shows two EE–35 convertors in the dual-opposed configuration used for testing the APFC controller. The following photograph shows the third-generation prototype APFC control system.
Third-generation APFC controller prototype hardware.
High-power, synchronized operation of dual EE–35 convertors was achieved this year, along with successful startup of the convertors with the third-generation prototype module. These are significant steps in proving the APFC technology. Work will continue on the development and testing of a planned thermal vacuum unit, to be tested with ASCs in a thermal vacuum chamber.
Find out more about the research of Glenn’s Thermal Energy Conversion Branch: http://www.grc.nasa.gov/WWW/TECB/
Glenn contacts: Linda M. Taylor, 216–433–8478, Linda.M.Taylor@nasa.govLast updated: December 28, 2007
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