A Six-Degree-of-Freedom Trajectory-Switching Modulation Framework for Triple-Phase-Shift-Modulated Dual-Active-Bridge Converters

In order to effectively eliminate transient dc offsets in the high-frequency-link currents of non-resonant dual-active-bridge converter (NR-DABC), various optimized transient phase-shift modulation (OTPSM) strategies have been reported. Unfortunately, all previous modulation methods formulated for NR-DABC cannot be applied to suppress the transient beat-frequency oscillations in series-resonant DABC (SR-DABC). Recently, two novel OTPSM strategies have been studied to achieve transient oscillation-free dynamics in single-phase-shift (SPS) and triple-phase-shift (TPS) modulated SR-DABCs, respectively, but their effects on NR-DABC have not been comprehensively investigated. In addition, most existing OTPSM strategies developed for the SR-DABC are non-analytic and not suitable for practical use. To fill these research gaps, a more-general theoretical framework of OTPSM for SR-DABC's transient-performance improvement is established in this paper, and its effectiveness is verified by a newly derived six-degree-of-freedom (6DOF) trajectory-switching modulation (TSM) strategy, which is also compatible with NR-DABC. Furthermore, challenges in the development and use of OTPSM are analysed, and technical differences between the OTPSM strategies for NR-DABC and SR-DABC are summarized.