Optimized Bidirectional On-Board Charger Using a Novel Unfolder-Dab Topology

Electric vehicles rely on on-board charger converters to create a bidirectional power link between the battery and the grid when fast dc charging infrastructure is not available. Power density, weight, efficiency, and cost are among the key challenges for these converters, which must operate under a wide range of input and output voltages, as well as in single and multi-phase configurations, leading to costly and suboptimal designs. In contrast to classical designs where a dedicate rectifier branch should be included to operate in single-phase, the proposed paper features a novel unfolder-DAB structure to avoid extra components for single-phase operation. The proposed structure allows single-phase current rectification by using middle point connection over the primary of the DAB converter used to 1) provide isolation, and 2) adapt battery voltage variations according to its SOC.As a result, and in contrast to classical implementations, all the power electronics are continuously used, independently of the grid configuration, yielding to a cost reduction and efficiency improvement.Besides in the proposed bidirectional charger, an inherent dc-link voltage balance is performed, removing additional balancing resistors or extra measurements. The proposed converter has been successfully tested using a 11 kW OBC prototype.