Design of a battery charger for the NASA EOS space platform

A battery charger design for the NASA Earth Observing System (EOS) space platform has been developed and tested. The authors discuss the design of the battery charger power state and its current and voltage control loops. In addition to restoring energy to the batteries, this charger regulates the spacecraft bus voltage during the posteclipse transition period. The battery charger design and analysis were facilitated by use of the pulse-width-modulated (PWM) switch model 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.