What is the current component at the input of dc-dc converters?
Generally in DC-DC circuit models, the converter load is modeled as a current source (i2) with a resistance in parallel. This is to generalize the model as much as possible and to take into account not only the passive loads, but also the active loads such as batteries.

You can see i2 as current source in load side in the aforementioned paper (Fig. 5).