Influence of Current Ripples in Cascaded Multilevel Topologies on the Aging of Lithium Batteries

Previous studies have proposed to use cascaded multilevel topologies in stationary battery energy storage systems (BESSs) or in BESSs of electric vehicles, due to the balancing capability or the high efficiency of these topologies. Because of the elimination of the direct current (dc) bus, the batteries in these topologies are expected to experience large current ripples. However, whether these current ripples can accelerate the aging of the batteries has not yet been dedicatedly investigated, although it is a determining factor for the feasibility of this category of topologies. Therefore, this article first summarizes the existing studies regarding the influence of current ripples on the aging of lithium batteries, which proves the necessity of an experimental investigation. Then, a long-term aging experiment on battery cells is conducted, in order to examine the influence of the current ripples in cascaded multilevel topologies. According to the experimental results and the conclusions in previous studies, the ripples in cascaded multilevel topologies generally have a negligible influence on the aging of batteries, except in certain scenarios. These scenarios can be identified by the three preconditions, first, current ripples must contain micro charge and discharge cycles; second, the microcycles are below 10 Hz; third, low frequency microcycles must contribute a large amount of charge throughput.