A Safe and Fast Closed-Loop Start-Up Strategy for Triple-Active-Bridge Converters Under DC Microgrid Application

Triple active bridge (TAB) converters are widely adopted in dc microgrids, wherein the safe and fast start-up is a key operational requirement. Due to the integrated topology, it is difficult to establish an online and closed-loop start-up strategy to meet this requirement. A common approach is to operate the TAB converter as the dual active bridge (DAB) converter to simplify the start-up process, leading to insufficient output power and limited start-up speed. To address these issues, a closed-loop start-up strategy with dual single phase-shift (DSPS) modulation tailored for the TAB converter is proposed in this article. Major contributions include three aspects. First, a slope comparison method is proposed to quickly observe the system's maximum current point for safe operation. Second, a novel partial derivative tracing method is proposed to solve optimal phase-shift angles for online control. Finally, a safe, fast, and simplified closed-loop TAB start-up strategy based on DSPS control is developed, which maximizes output power while ensuring safe current limitation. The experimental results verify the effectiveness of the proposed strategy. With DSPS control, the start-up speed can be increased by 34% while maintaining controllable current stress compared to the direct application of the DAB start-up strategy.