The state of charge balancing techniques for electrical vehicle charging stations with cascaded H-bridge multilevel converters

In this paper, two state-of-charge (SOC) balancing techniques are proposed for an electrical vehicle charging station which is based on a grid-tied cascaded H-bridge (CHB) multilevel converter. The first proposed technique uses the redundant states of the CHB converter to generate different AC voltages to balance the SOCs of the CHB cells. For the first proposed technique, the active power injected to the CHB converter is calculated and the optimal switching state that can regulate the SOCs of batteries is designed before switching transitions. In the second proposed technique, the information of AC input current is employed to design the switching states at each quarter of the period. As shown in this paper, the two proposed techniques can regulate the SOCs of the multilevel converter much faster than two conventional techniques in literature without increasing cost or complexity of the converter. This can increase the battery charging speed on the grid-tied converter. The experiments are conducted on a 7-level CHB converter to validate the two proposed techniques.