System Operation and Energy Management of a Renewable Energy-Based DC Micro-Grid for High Penetration Depth Application

A renewable energy-based dc micro-grid with hybrid energy storage, consisting of battery and ultracapacitor, is investigated. To achieve high penetration depth of renewable sources into the utility grid, a novel system operation strategy and the corresponding energy management method is proposed. In the operation strategy, the ultracapacitor unit works as the sole voltage source of the micro-grid to support the dc link in both connected and islanding mode. The micro-grid is controlled to deliver/absorb predefined amount of power to/from the utility grid during connected mode and zero during islanding mode. This design will certainly simplify the power dispatching algorithm of the power system and increase the possibility of including large quantities of micro-grids into the utility grid. The energy management method is dedicated to conducting the net power of the micro-grid effectively. The net power is separated into high- and low-frequency components. The high-frequency power is suppressed by the ultracapacitor automatically and the low frequency power is shared by the battery and an adjustment unit. A small-scale dc micro-grid structure with a single dc link is considered for investigation. MATLAB/Simulink simulation results are presented to validate the proposed system operation strategy and the energy management method.