Extension of the Injected-Absorbed-Current Method applied to DC-DC Converters with Input Filter, Output Post-filter and Feedforward Compensations

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.