Uncoupling Batteries From EPS Design — A Power System for the Modern Era

Space electrical power system (EPS) architectures have often been strongly tied to the voltage of the batteries they employ; the battery operating voltages often dictate the solar cell string lengths and the voltage of the primary buses used for power distribution throughout the spacecraft, as well as internal particulars. This paper presents an alternative space EPS architecture that is independent of battery voltage, and instead, simply treats the connected batteries as a source of power and energy which can be drawn from as desired, and recharged as required. This EPS architecture utilizes a ring bus topology, wherein energy sources feed power into the ring and energy sinks (aka loads) pull power from the ring. The resulting EPS is highly configurable and supports a wide range of spacecraft configurations, giving spacecraft designers considerably flexibility in both the design and mission stages. After a brief overview of some common space EPS architectures, we present Pumpkin's 200W-class TRL9 EPSM1 and its implementation. We illustrate a variety of possible configurations, and list the design freedoms that accompany them. We address efficiency issues and what drives overall system efficiency. We discuss real-world on-orbit performance and the use of configuration flexibility in certain scenarios.