Benchmark Report Hybrid Energy Storage Systems

PHEVs and BEVs make use of battery cells optimized for high energy rather than for high power. This means that the power abilities of these batteries are limited. In order to enhance their performance, a hybrid Rechargeable Energy Storage System (RESS) architecture can be used combining batteries with electrical-double layer capacitors (EDLCs). Such a hybridized architecture can be accomplished using passive or active systems. In this report, the characteristics of these topologies have been analyzed and compared based on a newly developed hybridization simulation tool for association of lithium-ion batteries and EDLCs. The analysis shows that the beneficial impact of the
EDLCs brings about enhanced battery performances in terms of energy efficiency and voltage drops, rather than extension of vehicle range. These issues have been particularly studied for the passive and active hybrid topologies. The classical passive and active topologies being expensive and less beneficial in term of cost, volume and weight, a new hybrid configuration based on the parallel combination of lithium-ion and EDLCs on cell level has been proposed in this article. This topology allows reducing cost, volume, and weight and system complexity in a significant way. Furthermore, a number of experimental setups have illustrated the power of the novel topology in terms of battery capacity increase and power capabilities during charging and discharging. Finally, a unique cycle life test campaign demonstrated that the lifetime of highly optimized lithium-ion batteries can be
extended up to 30%-40%.