An effective hybrid energy storage system based on battery-EDLC for distributed generation systems

All stand-alone distributed generation systems require an energy buffer to bridge the mismatch between available and required energy. The lead acid battery, which has a high energy density, is the most popular form of energy storage utilized. Nevertheless, it is impossible to supply the load with an instantaneous large power, due to its low power density. Accordingly, in this paper, a new hybrid energy storage system which is composed of battery and electrical double layer capacitor (EDLC) connected in parallel is established, it could make the best use of the characteristics of high energy density of battery and high power density, long circle life of EDLC. A buck and a bi-directional converter are also proposed to charge the battery and the EDLC with an additional function to stabilize the DC bus voltage. In comparison with the battery alone energy storage system, the proposed scheme can significantly improve the performance of the distributed generation system, enhance the energy using efficiency and reduce the battery capacity. Furthermore, the life of the battery can be lengthened for the reduced charging/recharging frequency of the battery when the generated power and the load power vary quickly. The high stability and high efficiency of the proposed system is verified through simulation and experiment results under various conditions.