Control Techniques With Low Computational Burden for a DAB-Based Two-Stage DC-DC EV Charging Converter System

Abstract

In the future, electric vehicle (EV) charging dc-dc converter systems are usually required for realizing bidirectional operation, electric isolation, and large voltage range, which can be realized at the dc stage. However, because of unavoidable reactive power, the typical bidirectional and isolated dc-dc converters, such as dual-active-bridge (DAB) dc-dc converters and LC-based resonant dc-dc converters, usually generate large current stress at wide-range voltage. Thus, the design cost for high-power applications will inevitably be expensive. Consequently, this article, combining a three-level buck-boost stage, adopts a DAB-based two-stage dc-dc converter with a low current stress. Then, the simple control schemes, including the soft start-up method, the linear current-control-based inner loop technique, and the soft shutdown method, are proposed for the charging of EV. Especially, based on the naturally transient behavior, the linear current-control-based inner loop technique is presented with low computational burden and without instability concern. The proposed linear technique can easily and steadily realize the charging requirements such as constant current, power, and voltage charging. Besides, the presented method has no current and voltage shoots during transient process, which can significantly enhance charging reliability. Moreover, the changing rate of a charging current can be consistent and controllable to fulfill batteries' charging requirement. Finally, experiment results are provided to verify the effectiveness of the proposed techniques.