It is important that the end to end efficiency (^=^1 ■ ^2'^3' 'k' ^5) of the EPS be maximized in order to make maximum use of operated energy. Depending on the power level and the type of consumer loads, certain elements (main converter, secondary converter, secondary power distribution) of the EPS may not be required. The end to end efficiency of the EPS therefore becomes ^=^2'^5- However, not all future spacecraft consumer load requirements may be met simultaneously by removing certain elements of the EPS. Space Station Program (SSP) is an example for a very near future spacecraft that includes almost all the elements shown in Fig. 1 in order to meet the requirements of all consumer loads. The distributed nature and the power quality requirements of the consumer loads dictate the need for the EPS elements as depicted in Fig. 1 and thus the end to end power distribution efficiency. It is important that, during any power conversion process through various converters, conversion to the required power and voltage level should be achieved with the highest efficiency and the lowest mass. Inefficiency reflects itself as an additional mass on the spacecraft due to the need for rejecting the dissipated heat to space by radiators—or some form of an active cooling system. 2.2 Mass Overall spacecraft mass is an important factor that needs to be minimized. The lower the mass of the spacecraft, for a given power generation and distribution, the lower the cost of launching and maintaining the spacecraft in orbit. It is, therefore, mandatory to design a spacecraft with the minimum possible mass that meets the requirements of the spacecraft. Unfortunately, the mass of the elements of the spacecraft increase with an increase in the efficiency of the power distribution and conversion components. An optimum power distribution mass and efficiency will need to be determined. 3 DC/AC Inverter Systems This section presents high frequency DC/AC inverter systems. In advanced high power space systems these inverters are employed to convert the available DC voltage from solar arrays and batteries to high frequency AC voltage for an efficient and mass effective primary power distribution system [2,3]. Design driving factors are first introduced and then on the basis of main requirements, an optimum class of inverter circuit is selected. Basic control techniques of DC/AC inverters are described. Main inverter topologies and their performance are described. Finally, a discussion leading to the selection of a particular inverter topology for given load conditions is presented. 3.1 Design Driving Factors Figure 2 shows the design driving factors for DC/AC inverters. The characteristics of input DC voltage and output AC voltage determines the complexity of design. The following output voltage characteristics are normally required in the design of most inverters: (1) Tightly regulated output voltage from full-load to no-load.
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