  In railway applications, it is common to use an LC filter connected between
the catenary and the input port of the main converter of the auxiliary and
traction systems. In addition, in the auxiliary systems, there is a converter
operating as a battery charger, which requires a very low ripple in the output
current and output voltage, so a postfilter may be placed at the output port of
the converter. This article proposes a step-by-step methodology to extend the
injected-absorbed-current (IAC) method in order to obtain transfer functions
that consider the effects of the input filter, output postfilter, and some
feedforward compensations. The proposed methodology allows reusing the
characteristic coefficients of the DC-DC converter model derived from the
existing IAC method. One of the advantages of the proposed methodology is that
the transfer functions obtained in this article are valid for cases where both,
one or none of the filters, are implemented. Finally, for the experimental
validation of the proposed methodology, the phase-shifted full-bridge converter
was selected as a convenient example. Furthermore, the experimental
measurements have been performed on two prototypes.
