Hybrid Energy Storage System Sizing for Smoothing Renewable Generation Intermittencies

This paper presents a strategy for sizing the capacity of a lead-acid battery and the capacitance of an ultracapacitor that compose a passive hybrid energy storage system, useful for smoothing grid power steps caused by renewable generation sources. This analysis is based on the electrical model of the battery/ultracapacitor association, determining the settling time and the instantaneous power ratio absorbed by each one when subjected to current step input. Based on this study, the storage elements were dimensioned. The smoothing capability obtained by the hybrid storage system is analyzed in a DC-bus, in which the power balance can be analyzed. It is connected to the hybrid storage system, using two cascaded bidirectional buck-boost converters, to the generation source, and to the grid, where the last two are considered current sources. The theoretical development was validated, and the power balance in this DC-bus was analyzed by computational simulations.