Model-Free Energy Management System for Hybrid Alternating Current/Direct Current Microgrids

A hybrid ac/dc microgrid combines the benefits of ac and dc power systems. It provides high efficiency and is compatible with conventional ac distribution network. This article proposes a centralized energy management approach to perform coordinated control on a hybrid ac/dc microgrid as a single-controllable entity. The central controller relies on low-bandwidth communication channels and is aimed at achieving 1) proportional power sharing among energy storage units located in both dc and ac sides of the microgrid, 2) state-of-charge equalization of the energy storage units, 3) grid power flow control, 4) plug-and-play capability, and 5) operation in grid-connected and islanded modes through an interlinking utility interface converter. The state-of-charge equalization method guarantees uniform operation of the energy storage units during both charge and discharge modes considering typical operational transients. Finally, the proposed model-free approach is evaluated experimentally through a laboratory-scale hybrid ac/dc microgrid in different operational conditions in both grid-connected and islanded operating modes.