A Natural Transient-Behavior-Based Control Theory for DAB-Based Two-Stage DC–DC Converter
Nie Hou, Yue Zhang, Yunwei Li
Abstract
Combining buck, boost, or buck-boost stages, the dual-active-bridge (DAB)-based two-stage dc–dc converter is regarded as a promising solution for high-power electric vehicle (EV) charging, where wide voltage range is required. However, the design of the control system becomes more complicated because of the power coupling between the two stages. Therefore, a natural transient-behavior-based control theory is proposed for simplifying the control system of the DAB-based two-stage dc–dc converter. Expect for the EV charging, this control theory can also be used for this two-stage converter connected to other high inertia loads, where the terminal voltage is changed slowly. Under the proposed method, the DAB stage is controlled as a step-change current source. Besides, the duty ratio of the buck, boost, or buck-boost stages, which can be directly calculated by the input and output voltage, is employed to match the middle dc-link voltage and the input voltage for DAB stage. Then the dynamic response for the input current of the buck, boost, or buck-boost stages is relied on their own natural transient behavior. Crucially, based on the transient analysis, the settling time of the buck, boost, or buck-boost stage can be determined for the step change, and the control period only needs to be larger than this settling time. Moreover, since the steady state can be obtained for each control period, a reliable control performance can be obtained without general stability analysis. Finally, experiment results are provided to verify the effectiveness of the proposed theory.