the cost of installed capacity is approximately $10 million per kW [1,2], and the running cost is approximately $50 per kW/hour [1]. Mass is another dominate factor in designing the power system as are costs of approximately $3000 per pound to launch a spacecraft [1], The high cost of launch and installed power capacity demands a low mass and highly efficient power distribution system. The power converters are integral parts of any spacecraft power system. The function of these converters is either to provide power for distribution, at a given frequency and voltage level of predefined characteristics, to several sub-power systems or to convert the distribution power to conditioned power as required by the load. The objective, therefore, is to design an end-to-end spacecraft power system which has the highest efficiency and the lowest mass. This paper presents the various power conversion techniques which shall be useful to enhance the performance of such a power system in future space applications. For high power conversion, resonant mode converters offer high efficiency, low mass and volume, less EMI, and high reliability. Therefore, various conversion techniques are investigated with respect to the resonant mode approach. Pulse width modulated DC/AC resonant inverter topologies are presented. The behaviour of parallel-resonant, series-parallel resonant and hybrid resonant inverters is analyzed and their performance characteristics are presented. A comparative discussion is given to help in the selection of a particular inverter topology for a given application. Constant frequency DC/DC resonant converters are described and their performance characteristics derived. Three resonant converter configurations—series, parallel, and series-parallel are compared. Two new Type-1 and Type-2 converters for AC/DC power conversion are presented. The transient and steady-state behaviours are described. Main features and limitations of these two converters are given. 2 Elements of Future Spacecraft Power Systems Future spacecraft power systems are required to provide high power levels (i.e. 30-300 kW) to consumer loads that demand various power types for their operation. The energy requirements of the consumer loads are mainly provided by photovoltaic generation with electro-chemical energy storage. The photovoltaic generation system usually provides the orbital average consumer load power demand and charge the energy storage system during insolation. The energy storage system provides the capability for consumer load average power requirements during eclipse. The peak power requirements of the consumer loads are provided by the energy storage system during both the eclipse and insolation periods when consumer load power demand exceeds the photovoltaic power generation capability. A block diagram of a typical future spacecraft Electrical Power System (EPS) is depicted in Fig. 1. The elements of the EPS, as shown in Fig. 1, consist of a power generation system, an energy storage system, power conversion and distribution system, and finally the consumer loads. The power generation system may make use of various state of the art technologies available today (i.e. solar arrays, solar dynamics systems, nuclear systems, etc.). The most experience with power generation systems is accumulated with photovoltaic (PV) generation systems and thus PV generation systems are more cost effective in space application.
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