A Two-Stage Twin-Bus Buck Converter for Battery Charging Applications

The paper describes and shows the operation of a two-stage isolated dc-dc converter for battery charging in electric-vehicle applications, where high efficiency is needed over a wide range of battery voltages. The proposed converter combines a first two-output isolation stage with CLLC resonant structure and a second two-input buck post-regulator. The post-regulator presents a twin-bus buck structure that allows low conversion losses even with output voltages that vary over a wide range, thanks to reduced voltage stresses across the switching devices. The isolation stage is constantly operated at resonance as a dual-output dc-transformer (DCX), thus ensuring high efficiency. The conversion structure, analysis, and design considerations are outlined considering an experimental prototype rated 10 kW, with input-bus voltage at 800-V and output-bus voltage ranging from 250 V to 500 V, which is suitable for electric-vehicles battery-charging applications.