Electrical power system stability assurance for the International Space Station

The International Space Station (ISS) adopted a direct-current (DC) electrical power system (EPS). Switching mode DC power converters are playing a major role in power conversion, conditioning, and control. The stability of a switching mode converter has long been studied due to its negative input impedance at low frequencies. Integrated EPS stability will be assured by computer modeling, simulation, and analysis with one of the most advanced and accurate techniques developed academically. The impedance separation criteria and minimum phase margin criteria are used to check the entire system and individual load stability, in addition to the other requirements defined in the power quality specification. The modeling/simulation and testing are to be accomplished both at the individual load and element level. For modeling, the EPCE (electrical power consuming equipment) input filter model with a constant power load is used first for each EPCE for the system-level analysis; it is then replaced by the averaged Vorperian/Ridley model, when available, to finalize the analysis results. The EPCE large-signal model is used for the nonlinear time domain simulation and analysis. The small-signal model will be used for the linear system frequency domain analysis. The EPCE test measurement data is used to validate the accuracy of the EPCE model. The element-level test data is used to validate the accuracy of the element model and assure element-level interface stability. This paper documents the theoretical basis and the approach for the ISS EPS stability assurance for the secondary power circuits