Resonant DC Transformer for Grid-Interactive Energy Efficient Buildings

Isolated active front-end (i-AFE) converters have gained importance in the last few years due to the emergence of dc applications that require isolation between the dc parts and ac utility grid. Examples of such applications include grid-interactive, or dc buildings, which, by standard, require galvanic isolation between ac and dc grids. The common approach to achieving isolation in i-AFE for grid-interactive buildings is the two-stage converters, which combine a non-isolated ac-dc stage with an isolated dc-dc stage that provides high-frequency isolation. Currently, the popular solution for the isolation stage is the dual-active bridge (DAB) converter. Even though it can provide better controllability than resonant topologies, it is less efficient at light load, where the dc buildings can operate for long periods. To address this topic, this paper evaluates a series-resonant converter (SRC) as an isolated stage for dc building applications. The SRC operates as a dc transformer (DCX) with a fixed voltage ratio (700/350 V). The design requirements were analyzed, and a 5-kW prototype was built and laboratory-tested to validate the presented analysis.