This work develops a methodology to facilitate the optimum design of spacecraft power processing systems. Emphasis is placed on the battery charge and discharge systems. A comparison of several battery charge and discharge topologies is presented. Characteristics which effect the overall system performance are addressed including size, weight, efficiency, dynamic performance, electromagnetic interference, and reliability. A detailed comparison, using nonlinear design optimization techniques, is performed for three candidate topologies for application to the NASA Earth Observing System (EOS) satellite battery discharger. Experimental verification is provided. A novel zero-voltage-switching (ZVS) bidirectional converter topology is presented. A bidirectional battery charger / discharger has several advantages, including a potentially substantial system weight savings. However, it is shown that most of the advantages can not be realized unless zero-voltage-switching is incorporated. The design of a novel ZVS, multi-module, multi-phase, bidirectional converter with application to the NASA EOS satellite battery charger / discharger system is presented. The system not only yields high efficiency and light weight, but also possesses superior dynamic characteristics when compared to either a conventional bidirectional converter or separate charge and discharge converters. Design considerations for system control of the NASA EOS satellite are presented. A methodology is presented to insure system stability with an unknown complex load. / Ph. D.

Large-signal analysis of various spacecraft power systems is performed to predict the bus dynamics in various modes of operation. The large-signal trajectories of the system's operating point are analyzed employing qualitative graphical representation. The analyses are verified through simulation using EASY5 software. Small-signal dynamic characteristics of spacecraft battery charge converter systems are analyzed to facilitate the design of control loop for optimum performance and stability. Control-loop designs for the charge converters in bus voltage regulation mode, charge current regulation mode, and peak power tracking mode are discussed. / Ph. D.

A battery charger design for the NASA Earth Observing System (EOS) Space Platform has been developed and tested. This thesis discusses the design of the battery charger power stage and its current and voltage control loops. The charger was designed to minimize the mass and to maximize the efficiency. In addition to restoring energy to the batteries, this charger regulates the spacecraft bus voltage during the transition between eclipse and sunlight. The battery charger design and analysis was facilitated by use of the model for the pulse-width-modulated (PWM) switch and the new continuous-time model for current-mode control. Analyses of the battery charger small-signal behavior are compared to hardware measurements to verify modeling accuracy. / Master of Science

The integration of two Zero-Voltage-Switched Bidirectional Battery Charger Discharger (ZVS-BBCD) units into a space power system is shown. A robust design featuring: four interleaved phases, commandable charge rates, overcurrent protection, overvoltage protection, soft starting, reliable gate drive circuitry, high efficiency, and good dynamics is demonstrated. The ZVS-BBCD is compared to separate hard-switched multimodule charge and discharge units in weight and efficiency and is found to be significantly lighter with comparable losses. The ZVS-BBCD has similar characteristics in discharge and in charge bus regulation modes and allows the use of a common control design for both modes. The two ZVS-BBCDs are integrated into the NASA power system testbed built at the Virginia Power Electronics Center (VPEC) to test their dynamics. The result shows good characteristics including low bus impedance and fast transient response. / Master of Science