Soft Starting Strategy of Bidirectional LLC Resonant DC-DC Transformer Based on Phase-Shift Control

Bidirectional LLC resonant DC-DC transformer (DCT) has the advantages of LLC resonant converter in achieving high efficiency and high power density, which features soft switching regardless of the direction of the power flow. Due to the existence of large filter capacitor, the inrush current is inevitable in the starting process. A improved soft start control strategy based on phase shift control is proposed by the analysis of gain characteristics of LLC resonant DCT. It can charge output capacitor gradually, build up output voltage smoothly and eliminate the inrush current effectively. The performance of the proposed control scheme is verified by simulation and experimental results.