A combinational power sharing strategy based on master-slave and droop methods for power-electronics-interfaced distributed generation units operating in a DC micro-grid

Renewable energy sources (RESs), distributed energy sources (DERs), and energy storage systems (ESSs) grid integration resulted in forming microgrid (MG) concept. Recently, DC microgrids (DC-MGs) have gained intensive attention compared to AC microgrids due to their high reliability and efficiency, easy interface with RESs and ESSs, and simple control. Proper power sharing is one of the most important challenges in islanding operation of DC-MGs. Power sharing methods are implemented in the islanded DC-MGs in order to share the load demand between DGs based on their capacity, and to maintain voltage in the desired range. In this paper, principles and flaws of droop and master-slave power sharing methods are individually discussed. Moreover, the proper voltage and current controller is designed for each distributed generation (DG) unit of DC-MG. In order to exploit positive features and mitigate negative effects of mentioned power sharing methods, a combinational master-slave and droop method is presented. Finally, various scenarios are carried out on a test DC-MG using Matlab/Simulink software in order to compare proposed power sharing method with droop and master-slave methods in the terms of their dynamic response, accuracy, and power sharing error.