This work derives the closed-loop input and output impedances of three
major types of DC-DC converters (Buck, Boost, and Buck-Boost) operating
in voltage or current mode control. First, it introduces the
small-signal converter model employed to derive the input and output
impedances. Next, it reviews open-loop impedances for use in simplifying
the expressions developed for closed-loop impedances. It then derives
the closed-loop impedances by closing the voltage or current loop
(depending on control method) in the converter model. Finally, The
validity of the impedances thus derived is verified by simulation.