Management of hybrid (AC-DC) micro-grids

The objective of this paper is to demonstrate the sharing of demanded power in a single-phase hybrid micro grid operating in autonomous island mode. We assume that we have DC power sources such as a photovoltaic array and wind turbine in the DC sub-grid that are tied to the AC sub-grid consisting of two uninterruptible power sources (UPS) through a bi-directional single phase inverter. Demand-droop control is used to manage power sharing between power sources in each sub-grid; however, managing the power flow through the entire grid is still a challenge. To overcome this we develop droop control strategies for each sub-grid, and droop control for the interfacing converter. Simulation results using MATLAB are used to demonstrate the performance of the power sharing methodology developed. Four different scenarios have been tested: (1) both sub-grids are heavy loaded, (2) both sub-grids have are lightly loaded, (3) a heavy DC load with a light AC load, and (4) a heavy AC load with a light DC load.