Charging and discharging control of a hybrid battery energy storage system using different battery types in order to avoid degradation

Recently, there has been a rapid increase of renewable energy resources connected to power grids, so that power quality such as frequency variation has become a growing concern. Therefore, battery energy storage systems (BESSs) have been put into practical use to balance demand and supply power and to regulate the grid frequency. On the other hand, a service life of a batteries becomes shorter due to degradation as the number of charging and discharging cycles increases. This paper presents a hybrid battery energy storage system (HESS), where large energy batteries are used together with high power batteries. The system configuration and the control scheme of the HESS are then proposed for frequency regulation applications. Simulation results show that the proposed control scheme effectively prevent degradation of the HESS compared to a BESS using large energy batteries only.