Experimental data for two different alternator configurations in a solar Brayton power system

A solar dynamic (SD) space power system has been under test at the NASA Lewis Research Center since 1994. The SD Ground Test Demonstration (GTD) system includes a solar concentrator, heat receiver with thermal energy storage, Brayton power conversion unit and radiator installed in a thermal-vacuum chamber with a solar simulator. The Brayton unit has been operated with two different turboalternator-compressor (TAC) assemblies, one which included a Rice-Lundell alternator and another which incorporated a permanent magnet (PM) alternator. The Rice alternator was part of the mini-Brayton rotating unit, designed and built during the 1970´s and refurbished for the GTD. The PM TAC was a development unit from the Joint US/Russian SD Flight Project. This paper highlights the operational differences (and similarities) between the Rice and PM TAC configurations including a comparative evaluation of startup characteristics and operating performance. The two alternator configurations were tested under similar thermal conditions, as an interchangeable component within the SD system. The electrical characteristics of the two units, however, dictated the use of significantly different power conditioning and control strategies. The electrical control architectures are described and compared. Test data are presented on TAC startup and system operating performance for both configurations