ZCS bi-directional DC-to-DC converter application in battery equalization for electric vehicles

A systematic approach to the analysis and design of a soft-switching bi-directional dc-to-dc converter for the cell voltage balancing control of a battery powered electric vehicle is presented in this paper. The quasi-resonant converter circuits are designed to achieve the zero current switching (ZCS) for reducing the switching loss of bi-directional converters. Results indicate that the switching loss, switching waveform and EMI emission can be substantially improved by using the quasi-resonant ZCS (QRZCS) technology in the battery charging system with a battery equalizer. The validity of the battery equalization is further verified by using an experimental installation of a three-cell lithium-ion battery string. Simulation and experimental results show that the proposed battery equalization scheme can not only achieve the bi-directional battery equalization performance, but also can reduce the switching loss during the equalization period.