  Rapid developments in power distribution systems and renewable energy have
widened the applications of dc--dc buck--boost converters in dc voltage
regulation. Applications include vehicular power systems, renewable energy
sources that generate power at a low voltage, and dc microgrids. It is noted
that the cascade--connection of converters in these applications may cause
instability due to the fact that converters acting as loads have a constant
power load (CPL) behavior. In this paper, the output voltage regulation problem
of a buck--boost converter feeding a CPL is addressed. The construction of the
feedback controller is based on the interconnection and damping assignment
control technique. Additionally, an immersion and invariance parameter
estimator is proposed to compute online the extracted load power, which is
difficult to measure in practical applications. It is ensured through the
design that the desired operating point is (locally) asymptotically stable with
a guaranteed domain of attraction. The approach is validated via computer
simulations and experimental prototyping.
