From voltage stiff to voltage weak DC distribution grid: Opportunities and challenges

This paper reviews the currently available dc micro-grids and dc grids. Currently, commonly existing and proposed dc microgrids are designed to provide sufficeint energy during system disturbance as in ac grid and, are mainly voltage stiff systems. It also compares the voltage stiff systems to a low energy system, which represents voltage weak dc system, from systems point of view. First, the definition of voltage weak dc systems is provided from a system perspective. Comparisons of both dc systems are reviewed on stability complexity, fault detection and isolation strategies and devices, and power management approaches. Various challenges and opportunities of voltage weak dc systems are briefly addressed. And also several architectures and topologies for voltage weak dc distribution systems are reviewed. Finally, this paper identifies a comparative advantage of such systems from a control, protection and system operation standpoints.