Abstract: The two-stage AC-DC converter exhibits an inherent characteristic of instantaneous power fluctuation in the power factor correction (PFC) of the front stage, resulting in a double-frequency ripple in the bus voltage that adversely affects the output voltage quality of the rear CLLLC resonant converter. In order to address these challenges, a feedforward control method based on second-order generalized integral (SOGI) is proposed for variable gain bus voltage ripple compensation. SOGI is utilized to extract information regarding bus voltage ripple. By analyzing the relationship between quality factor Q and voltage gain as well as considering how bus voltage ripple impacts normalized frequency, we investigate its influence mechanism on output voltage of CLLLC resonant converter and derive a relationship between Q value and feedforward gain coefficient K_a. Through simulation optimization and data fitting, we obtain a curve representing the feedforward variable gain coefficient. Simulation and experimental results demonstrate that, compared to non-feedforward control methods, our proposed approach achieves superior suppression effect on output voltage ripple of CLLLC resonant converters with a reduction rate up to 72%, thus validating its effectiveness.