Q:

What is the current component at the input of dc-dc converters?

The table below describles state space analysis in the field of power electronics. It is from a paper entitled "Signal Flow Graph in Loop Gain Analysis of
DC–DC PWM CCM Switching Converters by Wing-Hung Ki, Member, IEEE."
As shown in the picture, the input vector u(t) has the current component \$i_2\$. Unfortunately, the paper doesn't explain what it is. Could anyone clarify that?  For dc-dc converters such as buck, boost, buck-boost, the only input component that I know is \$V_g\$. So I have no idea what the input current \$i_2\$ is.

A:

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).

