This year, the operating conditions of the Alternator Test Unit (ATU) were simulated, and its performance and interaction with various Lunar Surface Power System (LSPS) components were evaluated in the LSPS located at the NASA Glenn Research Center. Test results successfully demonstrated expected rectified user-load power quality during steady-state and transient conditions. They further demonstrated the ability of a high-power alternator control scheme based on parasitic loading of the alternator output to successfully regulate output bus voltage and alternator shaft speed. Information gained from this work could be used in the development and validation of analytical models used for performance prediction.
Overall schematic of the Lunar Power System Facility (LPSF).
Long description of figure 1.
The two primary objectives of the LSPS were to obtain test data to influence the power-conversion design and to assist in developing primary-power-quality specifications for an actual lunar fission surface power system. The main elements of the LSPS are a 50-kWe ATU, an alternator controller using a parasitic load, a main power distribution unit, and eight user loads. These elements are made of breadboard/brassboard components using readily available off-the-shelf hardware.
The ATU is the power supply for the LSPS. It is representative of the style of high-speed permanent magnet alternator that would be used on a Brayton power-conversion unit system. A variable-speed two-pole samarium cobalt permanent-magnet brushless motor drives the alternator in place of a Brayton cycle power system. The alternator is a six-pole permanent magnet alternator utilizing a Halbach array of samarium cobalt magnets. The ATU was operated at 35,000 rpm to a maximum of 50-kW three-phase power at 400-V rms line-to-line. A pressurized oil loop was used to lubricate and cool the individual shaft ball bearings and to cool the motor and alternator.
View of the ATU as installed in the LPSF at Glenn.
The alternator controller and parasitic load are designed to maintain a constant bus voltage and ATU shaft speed regardless of user loading. They do this by applying a parasitic load to the alternator output to maintain total load at the desired output voltage and speed. The alternator controller consists of two main circuits: (1) the power circuits including the parasitic load elements and (2) the sensing circuits and feedback control loops sending the control signals to the power circuits.
All user loads received direct-current (DC) power through transformers and 12-pulse rectification of the main three-phase alternating-current (AC) bus power. The alternator operated at a power factor of 0.97. The rectified direct-current voltage measured at the loads showed around 0.5-percent ripple. Switching user loads on and off had very minimal impact on the DC power quality at other user loads, the AC bus voltage, and alternator shaft speed.
Find out more about this research:
Glenn’s Thermal Energy Conversion Branch:
http://www.grc.nasa.gov/WWW/TECB/
Glenn’s Advanced Electrical Systems Branch:
http://www.grc.nasa.gov/WWW/5000/pep/electricsys/
Glenn contacts:
Arthur G. Birchenough, 216-433-6331, Arthur.G.Birchenough@nasa.gov
Lee S. Mason, 216-977-7106, Lee.S.Mason@nasa.gov
Analex Corporation contact:
David S. Hervol, 216-433-9624, David.S.Hervol@nasa.gov
Authors:
Arthur G. Birchenough and David S. Hervol
Headquarters program office:
Exploration Systems Mission Directorate
Programs/projects:
Prometheus Power and Propulsion Program, Fission Surface Power
Last updated: December 14, 2007
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216-433-8258
Point of contact for NASA Glenn's Research & Technology reports:
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216-433-2912
SGT, Inc.
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