Droop K-Sharing Function for Energy Management of DC Microgrids

Slow dynamic response sources, such as fuel cells, are frequently used with faster units, such as batteries and ultracapacitors. In this context, this article gathers the advantages of two energy management techniques to propose the droop k-sharing function. In droop control, energy management is easily implemented using the virtual resistances concept, eliminating the need for fast communication links between the sources. The k-sharing function improves the performance of microgrids with slower sources assigning a preestablished dynamic behavior using a low-pass filter, while the storage unit absorbs the fast transients. Additionally, the k-sharing function also enables the storage unit to share power at a steady state. Therefore, the main advantage of the proposed energy management algorithm is that the control loops of each power source are not coupled to each other, which is accomplished by designing the k-sharing function similarly to the droop technique, eliminating the need for high-speed links of communication and improving the microgrid speed response during fast changes of load. The effectiveness of the proposed function and the theoretical analysis are evaluated using a dc microgrid composed of an H-1000 fuel cell manufactured by Horizon Fuel Cells and three Zippy Compact 5000 25 C Li-Ion batteries in series connection.