A dual active bridge DC-DC converter with optimal DC-link voltage scaling and flyback mode for enhanced low-power operation in hybrid PV/storage systems

Today's PV micro-inverters (MIVs) provide a modular solution for generation, however the energy storage architectures remain centralized, requiring an additional bi-directional ac-dc converter, with complex cell balancing circuits. Distributing storage capacity within the smart PV panels allows power fluctuations to be locally buffered, while minimizing the need for additional power electronics and balancing circuits. The dual-active-bridge (DAB) topology, which is adopted in this paper, provides bi-directional power flow; however it generally suffers from poor efficiency at low power. It is shown that with a minor modification, the DAB can be operated as a two-transistor flyback converter for improved efficiency. In addition, the dc-link voltage can be dynamically adjusted for the best performance in DAB mode. The proposed control scheme is demonstrated on a 100 W prototype, with up to 8% increase in efficiency at low power.