Design and Simulation of an LLC Resonant DC-DC Converter for 400V/12V Power Conversion Applications

This thesis presents the design and simulation of a full-bridge LLC resonant DC-DC converter for 400 V/12 V power conversion at a rated output power of 1 kW. The work is motivated by the need for efficient, isolated, and high-power-density conversion in applications such as electric vehicles and data centres. The study first reviews the operating principles of the LLC resonant converter, including resonant-tank behavior, soft-switching operation, gain characteristics, and control methods. An analytical design procedure is then developed to determine the transformer turns ratio and resonant-tank parameters from the required input-voltage range and output specifications. The proposed converter is validated through open-loop and closed-loop simulations. A variable-frequency control scheme with PI regulation is implemented to maintain the 12 V output under input-voltage variations. Simulation results show that the designed converter achieves the required conversion and maintains stable operation over the specified 375-425 V input range, while delivering output power close to the rated value. These results confirm that the proposed LLC converter is a suitable solution for high-efficiency isolated DC-DC power conversion applications.