Flexible Control of Interlinking Converters for DC Microgrids Coupled to Smart AC Power Systems

This paper presents a multifunctional control system for interlinking converters interfacing microgrids and ac mains. Applicable standards pose power quality and grid-support function requirements for converters that interface energy resources of dc nature with an ac utility grid. At the same time, the forthcoming smart grid scenario calls for additional functionalities, enabling the effective integration of hybrid (i.e., dc or ac) microgrids, that are applicable to both grid-connected and islanded modes of operation. This requires novel interlinking converter controllers with extended flexibility. The control system described in this paper fulfills both connected and islanded operation needs and provides seamless transitions between the two modes. Such valuable functionalities are attained owing to an underlying, large-bandwidth, triple-loop control organization. The target converter is meant to be connected to a local dc subgrid at the dc side and to a local ac subgrid at the ac side. The controller manages the connection of the ac-side subgrid with the utility grid, ensuring a fast response control of the ac grid current. Therefore, it allows interfacing of renewable sources and loads, aggregated in dc and ac nanogrids or microgrids, with smart power systems, providing enhanced power quality, stability, and flexibility of operation.