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 ultra-capacitors. In this context, this paper 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 pre-established 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 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 25C Li-Ion batteries in series connection.