In addition to the inherent regulation of the solar cells, there are other characteristics which must be considered, such as the IR drop on conductors and protective equipment, variation in the photovoltaic cell output with solar intensity and the long term degradation of the cells' output. These various losses can all add and present a minimum voltage to the load. Figure 5-2 summarizes these losses. The impact of these losses on the solar cell source characteristics is indicated by Figure 5-3. 5.2 POWER SOURCE-CONVERTER INTERFACE The interface requirements for the solar array and converters was originally examined from the standpoint of obtaining a minimum output power variation over the 30 year operating life of the MPTS. A better criteria used here is to obtain maximum available power, which depends on the maximum current line. It must be remembered, however, that this maximum current line is a limitation of the solar cells when they are all involved as a group with all of the converters operating as a group. Current for an individual converter is not limited by the maximum current line. Figure 5-4 is a diagram depicting the volt-ampere characteristics of the klystron and the volt-ampere characteristics of the solar cells superimposed. The use of available power is given in Figure 5-5, where available power usage refers to the percentage of source power converted to rf compared to the maximum available for conversion at the particular operating voltage. Except for the case of constant current operation, where a 5 percent additional loss in efficiency occurs at minimum voltage, klystron efficiency is assumed to be constant. These results show little difference between constant current operation and no regulation. The implementation of the no-regulation technique is simpler and less complex. It is the recommended method of operating the klystron assuming accurate phase correction can be made in this mode as described in Section 4 (DC-RF Conversion).
RkJQdWJsaXNoZXIy MTU5NjU0Mg==