Current Stress Optimized Strategy for the Dual-Active-Bridge Converter With Triple-Phase-Shift and Variable DC-Link Voltage Control

The dual-active-bridge (DAB)-based two-stage ac/dc converter is extensively applied in various scenarios, including electric vehicle chargers and solid-state transformers. In the two-stage ac/dc power converter, the dc-link voltage serves as the input voltage of the DAB converter and provides an additional control parameter affecting efficiency. Previous studies primarily focused either on variable dc-link voltage or on phase-shift degrees of freedom alone, neglecting the simultaneous use of both dc-link voltage and phase-shift for efficiency improvement. This article presents a current stress optimized strategy for the DAB converter with triple-phase-shift (TPS) and variable dc-link voltage control. First, the TPS modulation scheme and variable dc-link voltage range are introduced. Second, optimal dc-link voltage and phase-shift values are determined using analytical optimization algorithms. Based on these findings, a control scheme integrating the optimal variable dc-link voltage and phase-shift values is proposed. Furthermore, it is compared with conventional fixed dc-link voltage control to demonstrate improvements in zero-voltage switching range and peak current level. Finally, the effectiveness of the proposed strategy is verified through experiments on a two-stage ac/dc converter prototype, demonstrating its capability of significantly enhancing system efficiency across all power ranges.