Voltage quality comparison of DC microgrids for centralized and distributed secondary control approaches

Microgrids are considered as a platform for the use of distributed energy resources (DERs). The traditional AC distribution systems result in the emergence of AC grids. In order to reduce costs and losses and increase reliability, recently, DC distribution systems and subsequently DC microgrids have been considered. In this paper, the quality of DC voltages during the islanded mode is studied. In this mode, DERs are usually controlled by droop characteristics. In the use of the droop characteristics, the micro grid voltage deviation occurs from a nominal value. For voltage restoration, low band width communications as a part of secondary control are used. This control level, provides voltage restoration with one of two centralized and distributed approaches. In this paper, the voltage restoration with these two approaches is studied and analyzed, and then a comparison is presented. It is shown that for the centralized approach, the point of common coupling has desirable voltage quality and for the distributed approach, DERs buses have desirable voltage quality. For verification, the time domain simulation of a DC microgrid is used.