In this paper we propose a sliding mode control scheme that allows robust control of the output voltage in a class of non-linear switched converters that includes the non-inverting buck-boost, the Watkins-Johnson and the inverse of Watkins-Johnson. Using a full-state reference profile-based sliding surface, periodic signals may be tracked by the output voltage under appropriate restrictions. Furthermore, semi-infinite programming techniques are used to minimize power loses while taking into account the existence of load perturbations. The procedure consists of choosing a reference signal for the inductor current with minimum root mean square, subject to the maintenance of sliding regime under possible load variation in a set with known bounds. Realistic simulation results show a highly robust performance in the presence of load disturbances.