High efficiency switching sequence and enhanced dynamic regulation for DAB converters in solid-state transformers

This paper presents an advanced switching sequence based on boundary control for the Dual Active Bridge (DAB) DC-DC converter applied in a Solid-State Transformer (SST). The implementation of the switching sequence follows the recent advancements in curved switching surfaces for DAB converters - the Natural Switching Surface (NSS) - and contributes to higher efficiency and transient regulation. The proposed switching sequence improves the overall efficiency of the converter by ensuring soft switching transitions in the full operating range. Furthermore, it incorporates a fully controlled burst-mode switching sequence for light loading conditions to further extend the efficiency gains. Dynamic regulation, an important requirement in SST, is also addressed by the proposed boundary-based sequence. As a result, excellent dynamic response is obtained by taking advantage of all the possible switching structures of the converter. The analysis provides insight into the natural trajectories of the converter, which produce soft-switching transitions and enable the converter structures to achieve the target operating point directly. Simulation and experimental results are presented to validate the benefits of the switching sequence and illustrate the dynamic regulation.