High efficiency bi-directional DC-DC converter for charge balancing control of EV application-specific battery strings

This paper sets forth the design of a soft-switched bi-directional DC-DC converter for charge balancing control of Electric Vehicle (EV) application-specific Li-ion battery strings. A high efficiency phase shifted full bridge converter steps down the pack voltage in order to charge one cell at a time, while a push-pull converter boosts the voltage of one individual cell to meet the charging voltage of the entire string. The resonant converter is designed to achieve zero voltage switching (ZVS), whilst secondary synchronous rectification (SR) reduces even more the total power losses. The mathematical model is simulated and experimentally validated on a prototype board. Both simulation and real model measurements prove that the proposed topology attains a very high performance.