Distributed AC-DC Coupled Hierarchical Control for VSC-Based DC Microgrids

In this article, a distributed ac-dc coupled strategy for the hierarchical control of voltage source converter (VSC)-based dc microgrids is proposed. Unlike existing hierarchical control methods, this approach directly controls the ac inductor current (i(d)) of the VSC's inner loop in both primary and secondary layers to achieve proportional power sharing and voltage regulation. Specifically, an ac current-based i(d)-v(dc) droop method is used in the primary layer, without any external dc voltage/current control loops. In the secondary layer, an ac current-based compensator is used to adjust the average dc voltage and ensure accurate power sharing among sources. In the communication layer, the global average information is obtained by transferring only one variable. Furthermore, the steady-state, dynamic, small-signal stability, and large-signal stability performance are analyzed. A fresh insight into the effect of the droop gain on system large-signal stability is provided. Finally, the analytical results have been verified through experiments on a laboratory-scale dc MG.