Design of fast charging technique for electrical vehicle charging stations with grid-tied cascaded H-bridge multilevel converters

To compete with gas stations, electrical vehicle charging stations should be able to charge batteries as fast as possible. In this paper, a fast charging technique for a grid-tied, cascaded H-bridge (CHB) converter based charging station is developed. A controller is designed to achieve constant current-constant voltage (CC-CV) charging for all of the cells of the CHB converter. As proven in this paper, to achieve fast charging, the effects of internal resistance and polarization parameters of battery should be compensated. To reach this goal, the internal resistance and polarization parameters of battery are estimated based on the initial fast measurements before formal battery charging. The estimated parameters can increase the constant current charging duration for Li-Ion batteries so the charging speed is improved. Experiments are conducted on a charging station which is based on a 7-level grid-tied CHB converter to validate the proposed fast charging technique.