This paper deals with voltage stability of DC power systems in More Electric Vehicles (MEVs) in presence of Constant Power Loads (CPLs). Large signal voltage stability is studied according to Lyapunov theory. Original analytical developments are presented to evaluate a Region of Asymptotic Stability (RAS) around a system's stable equilibrium point. Analytical forms are found, which show how the RAS boundaries vary as a function of the system's supply voltage, when the latter is floating. The validation has been carried out by means of the numerical continuation analysis. This result makes it possible to point out how supply voltage fluctuations can decrease the RAS, up to impairing voltage stability not only for large, but even in case of small perturbations.
