This paper deals with the modeling of nonlinear and time-varying dc-dc converters in linear parameter variant (LPV) form. Such LPV models are employed to derive synthesis conditions in order to obtain robust gain-scheduled controllers in a systematic form, thanks to a linear convex formulation. The proposed synthesis algorithm allows taking into account uncertainties of the system and common specifications of power converters, such as settling time, overshoot and disturbance rejection. The LPV formulation allows to obtain improved robustness and performance properties, as compared to previous time-invariant synthesis approaches. The results are verified by boost dc-dc converter simulations.