Isolated Bidirectional Grid-Tied Three-Phase AC-DC Power Conversion Using Series-Resonant Converter Modules and a Three-Phase Unfolder

Power-bidirectional converters are used to integrate energy storage with both dc and ac distribution grids. A modular bidirectional dc-dc converter system consisting of multiple dual-bridge series resonant converter (DBSRC) modules can be reconfigured to extend the system operating range. This paper proposes a modular three-phase ac-dc converter system by adding a line-frequency unfolder to series-connected outputs of two DBSRC modules. The DBSRC modules are controlled to output time-varying currents, which are then reconstructed into sinusoidal ac currents by the unfolder. Compared with a conventional two-stage system with a dc-dc converter and a two-level voltage-source inverter, the DBSRC-unfolder system has smaller dc-link capacitance, negligible unfolder switching loss, reduced line filter size, and faster dynamic response. The system operation and performance are verified on a 1-kW experimental prototype.