In general, partial power of the parallel ac/dc converter is processed only once and transferred directly. In order to keep the output voltage constant, the switching duty ratio in the parallel converter must vary with the line phase. It means that the operating point of the parallel ac/dc converter changes with the variation of input voltage, which would be a challenge for controller design. In this paper, the dynamic modeling of a single-stage single-switch parallel boost-flyback-flyback converter is developed by the linearization of its large-signal equations. To overcome the modeling uncertainty due to the variation of operating point, the feedback controller is designed based on the boundary of the mode to obtain zero steady-state error, fast rise time, and heavily damping within input voltage range. Both the derived dynamic modeling and the designed voltage controller are demonstrated by the provided simulation and experiment results.