The RMS current stress reduction technique in link capacitor of two-stage AC/DC converter

The RMS (Root Mean Square) current reduction technique for the link capacitor of two-stage PFC (power factor correction) AC/DC converter is proposed. Although there exist various factors for optimizing the link capacitor, the RMS current stress is one of the most important factors to determine the capacitor size. To reduce the RMS current of the link capacitor, the main concept of the proposed method is by adding the small C-L-L-C filter around the link capacitor. Namely, the front C-L filter and rear L-C filter of proposed C-L-L-C filter can effectively reduce the RMS currents entering into and coming out of the link capacitor by filtering out the switching current components, respectively. Especially, since the crossover frequency of proposed filter is very far from that of the PFC converter, the proposed filter has hardly any effect on the dynamics of the AC/DC converter and thus, makes it easy to design the overall system controller. To confirm the validity of proposed filter, the theoretical analysis, design considerations, and experimental verification are presented.