Period doubling bifurcation in buck convertersis studied by using the harmonic balance method.A simple dynamic model of a buck converter in continuous conduction modeunder voltage mode or current mode controlis derived.This model consists of the feedback connection of a linear system and a nonlinear one.An exact harmonic balance analysis is usedto obtain a necessary and sufficient condition fora period doubling bifurcation to occur.If such a bifurcation occurs,the analysis also provides information on its exact location.Using the condition for bifurcation,a feedforward control is designed thateliminates a period doubling bifurcation.This results in a wider range of allowed source voltage,and also in improved output voltage regulation.