Cell voltage equalization using ZCS SC bidirectional converters

A quasi-resonant zero current switching (QR ZCS) switch-capacitor (SC) converter for the cell voltage balancing control of a series connected battery string is presented in this paper. The proposed cell voltage equalizers (CVE) are designed to operate in the discontinuous-current mode (DCM) to achieve zero-current switching (ZCS) for reducing the switching loss in the bi-directional DC/DC converters. Results indicate that the switching loss, conducted EMI emissions and equalization efficiency can be substantially improved using ZCS technology in the battery charging system with the CVE. The validity of the battery equalization is further verified using a three cells lithium-ion battery string installation. Simulation and experimental results show that the proposed battery equalization scheme can enhance the bi-directional battery equalization performance and also reduce the switching loss and conducted EMI emissions during the equalization period. Equalization efficiency above 90% can be achieved by the proposed QR ZCS battery equalizer under the specified cell equalization process.