DC microgrids (MGs) have gained research interest during the recent years because of many potential advantages as compared to the ac system. To ensure reliable operation of a low-voltage dc MG as well as its intelligent operation with the other DC MGs, a hierarchical control is proposed in this paper. In this hierarchy, primary control level is used to regulate the common bus voltage inside each MG locally. A voltage secondary control (VSC) is designed to eliminate the dc bus voltage deviation produced by primary level while guarantees proper operation of tertiary level. This secondary control acts not only as a central controller for the each MG individually, but also as a decentralized controller when dc MGs are connected together. This way, VSC maintains the dc bus voltage around the voltage reference using an averaging method. This allows the power flow control to be achieved at the same time since it can be accomplished only at the cost of having the voltage deviation inside the system. Neighboring communication is employed to exchange the voltage output of MGs to the neighbors using low bandwidth communication (LBC) network. Finally, a power flow control (PFC) is proposed to control the tie-line current between the MGs. The effectiveness of the proposed scheme is verified through detailed hardware-in-the-loop (HIL) simulations.
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