SECTION 5 POWER SOURCE INTERFACE AND DISTRIBUTION The power interface and distribution part of the study relates to the design of the equipment bringing the high voltage and high current power from the orbital power source, beginning at the brushes of the rotary joint of a solar oriented source, throughout the transmitting array to the dc-rf converters. It must provide switching capability, regulation of the power as required by the converters, and it must protect the MPTS against individual and localized failure modes, A solar photovoltaic power source was taken as the power source model because it is a leading candidate, is relatively well defined and presents a relatively difficult problem in regulation. The amplitron is to be operated in a constant current or constant phase regulation mode and the klystron is to be operated unregulated. A particular problem with the amplitron and solar cell power source combination is the high voltage as the system is started (such as following an eclipse), and it is recommended that this be solved by switches within the solar array that would bring up voltage in a programmed sequence. 5.1 POWER SOURCE CHARACTERISTICS Information on the solar cell characteristics has been obtained from a preliminary report in the solar photovoltaic array prepared by Spectro Lab, Inc. for the earlier SSPS Feasibility Study. Figure 5-1 presents the probable characteristics of a 1985 type solar photovoltaic array with no concentrators. This condition has been chosen as representing the most severe interface problems. Although the use of concentrators increases the current available from a given area of solar cells, there is no significant change in solar cell load characteristics. The following characteristics are evident: a. At the normal operating temperature of 300°K, the open circuit voltage is approximately 22 percent greater than the operating voltage. b. At colder solar cell temperature, the available voltage from the cell increases as the maximum current decreases. This characteristic presents a turn-on problem, particularly when the solar array emerges from an earth eclipse.
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