Research On The Optimal Control Of Dual-active-bridge DC-DC Converter

Lightweight design is the key technology for the development of the high-speed train.In order to implement the lightweight of the high-speed train, the power electronic transformer traction becomes an advanced research hotspot. Thus, based on the application of this technology, this paper fouces on the research of the dual-active-bridge dc-dc converter that is one core component of the power electronic transformer traction.Firstly, this paper studies the typical phase-shift controls of the dual-active-bridge dc-dc converter, such as the single-phase-shift control, the extended-phase-shift control and the double-phase-shift control, and the power transmission characteristics of these phase-shift control are analyzed in detail. Then, in order to apply these phase-shift controls more conveniently, this paper proposes a unified-phase-shift control, and the equivalent conditions between this unified-phase-shift control and other typical phase-shift controls are also presented.In addition, the optimal controls of the current stress of the dual-active-bridge dc-dc converter are carried out aiming at reducing the power losses and boosting the efficiency of the dual-active-bridge dc-dc converter. In order to eliminate the dependence of the inductance that appears in the traditional current-stress-optimized schemes, this paper propose a novel current-stress-optimized scheme. Based on the novel scheme, these minimum current-stress controls of the extended-phase-shift control, the double-phase-shift control and the unified-phase-shift control are derived. Then, the comparative analysises of these optimal controls are also studied in this paper. Finally, the experimental results verify the dependence of the traditional current-stress-optimized schemes and the excellent optimal performances of unified-phase-shift with the current-stress-optimized scheme,which can significantly improve the efficiency of this converter.Moreover. In order to boost the dynamic performance of the dual-active-bridge dc-dc converter, this paper mainly research on the power-relating control, and analyze the inductance dependence of the traditional power-model control. Thus, based on the direct power control, this paper proposed a direct power control to eliminate the inductance dependence and improve the dynamic performances for this converter. However, the direct power control can only significantly change the dynaic performances when the input voltage of the dual-active-bridge dc-dc converter is changed. In order to enhance the robustness of this converter furtherly, this paper present a virtual-direct-power scheme by adding the feedback of the load current. Finanlly, the experimental results demonstrate the inductance dependence of the traditional power-model schemes and the excellent performance of the virtual-direct-power scheme.Eventually,because there are a few scheme to both inprove the efficiency and the dynamic performances of dual-active-bridge dc-dc converter, this paper combines the extended-phase-shift control and the direct-power control to proposed a extended-phase-shift with direct-power hybrid scheme. Then, in order to furtherly improve the behaviors of this converter,this paper proposes a unified-phase-shift with power-balancing scheme, and the inductance dependence of this method is also analyzed in detail, and then, a boundary control of the output voltage is presented to compensate the influens caused by the error value of inductance. Finally, experimental reaults verify that the extended-phase-shift with direct power control can effectively improve the efficiency and dynamic performances of this converter and the unified-phase-shift with power-balancing scheme can significantly boost the efficiency and dynamic performances of the dual-active-bridge dc-dc converter.