A Comprehensive Time-domain-based Optimization of a High-Frequency LLC-based Li-ion Battery Charger

The LLC resonant converter, as a promising solution for battery charger applications, has the ability to adjust its output voltage during Constant Current and Constant Voltage modes in the charging profile. However, its operation mode changes as switching frequency changes. Therefore, for efficiency-oriented optimizations in battery charger applications, the one-pointed efficiency is not an appropriate objective. To this end, in this paper, a multi-pointed averaged efficiency is considered for optimization along with the transformer volume. Another factor of a proper design for a wide output range LLC is the converter peak voltage gain that is calculated based on an accurate method. The efficiency calculations are carried out by using time-domain-based analysis for every operation points. Regarding dead-time, a worst case is realized during the charging profile. At last, a 500W 400V:48V battery charger is designed with this procedure, and verified by simulation.