Design and Implementation of a Two-Stage Resonant Converter for Wide Output Range Operation

This article proposes and analyzes a two-stage isolated dc–dc converter for electric vehicle charging applications, where high efficiency over a wide range of battery voltages is required. It employs a first preregulation stage and a second half-bridge LLC stage, integrated with the first. The second stage is always operated at resonance, ensuring high efficiency. The first preregulation stage is responsible for the desired input-to-output voltage conversion ratio and the zero-voltage switching operation of all the switches. This allows low conversion losses even with voltages that may vary over a wide range. The article presents the conversion structure, the converter analysis, the design of the magnetic elements, and demonstrates the converter operation considering an experimental prototype interfacing a
${750\text{-}} \mathrm{V}$
dc-link with an output bus with nominal voltage range
${250} \mathrm{}$
–
${500}\, \mathrm{V}$
. The implemented module is rated
${5}\,\text{kW}$
and achieves a peak efficiency of
$\boldsymbol{98.0\%}$
at
${3\text{-}} \text{kW}$
output power.