Control Strategies of a DC Microgrid for Grid Connected and Islanded Operations

This paper proposes an algorithm for coordinated control of the distributed generators integrated to a dc microgrid (DCMG), in islanded and grid connected modes of operation. The proposed DCMG connects various types of nonconventional energy sources, storage system to the dc, and three-phase, as well as single-phase ac loads. A control strategy for three-phase voltage source inverter to integrate the three-phase load, as well as utility grid into the DCMG, under various operating scenarios, has also been proposed. The proposed control strategy uses a combination of the feed-back and feed-forward control loops. Dual proportional integral controllers for ac voltage regulation and inner current control have been suggested in two rotating direct- and quadrature- axis synchronous reference frames for controlling the respective positive and negative sequence components. Simulations are carried out to verify the robustness of the proposed algorithm and control strategy under different operating conditions including fault scenario and its effectiveness in maintaining the dc voltage of the microgrid.