Distributed Secondary Control for Current Sharing and Voltage Restoration in DC Microgrid

Direct current (DC) microgrid is being increasingly investigated in modern power grid. An important issue in DC microgrid operation is to ensure proper current sharing among converters. While this has been addressed through droop control, the resulting voltage deviation in DC bus has to be compensated. To solve this problem, a new distributed secondary control scheme is presented in this paper for both current sharing and voltage restoration. A key part of the presented scheme is the integration of a new parameter `virtual voltage drop' defined from droop gain and line resistance. Since the DC bus voltage is not required as a feedback signal, the proposed secondary control is simple and easy to design and implement. In addition, as the proposed scheme has no requirement for the loads, it can handle both resistance loads and constant power loads (CPLs). Simulations as well as experimental studies are carried out to demonstrate the effectiveness of the proposed scheme.