Hierarchical Coordination of a Hybrid AC/DC SmartGrid with Central/Distributed Energy Storage

Abstract

This work describes a hybrid AC/DC Smart Grid distribution scheme installed at LEMUR microgrid laboratory. The control of the microgrid is carried out according to a hierarchical coordination considering the high level control. The configuration includes a microgrid ( G) connected to the main utility grid (MUG) by means of a solid state transformer (STT). The G is formed by several nanogrids (nGs). All (nGs) are based on four wire configurations, as they are usually employed in AC distribution systems. However, the scheme is considered as a hybrid Smart Grid because the connection among different nanogrids and with the SST are DC connections. The SST is also equipped with a third port connected to a central energy storage system (CESS). The coordination between the different involved in the systems: the installed dispersed generators at nanogrid level, the nanogrids, the SST and the CESS has been implemented using a bottom-up hierarchical approach. Several configurations at nanogrid and microgrid levels are shown and analyzed. For making the coordination of the different elements of the microgrid, a fast power flow alorithm for estimating the state of the microgrid in real time was developed. In this paper the proposed structure is described paying special attention to the power flow algorithm. The results obtained with the power flow algorithm in simulations were validated at laboratory level