Performance estimation of a cell-to-cell-type active balancing circuit for lithium-ion battery systems

Active charge balancing is an approved technique to implement more energy-efficient and eco-friendly lithium-ion battery systems. The theoretical analysis presented in this paper provides a method to estimate the benefits of a cell-to-cell-type active charge balancing circuit in comparison to a passive balancing solution concerning energy savings and capacity gain. The calculation's variable parameters are the battery system configuration and the cell capacity distribution properties. Their validity is limited to applications with normally distributed cell capacities, limited maximum and minimum cell capacity and full cycle usage. The losses related to passive balancing in an nSmP battery system are calculated as well as the overall energy savings achievable with cell-to-cell based active balancing. The capacity gain factor of an actively balanced battery system related to a passive one is found to be in a range between 1.06 and 1.01 depending on the cell parameters and the system configuration. The derived formulas are verified by numeric simulations. Based on the results, several options are identified to increase the energy efficiency of conventional passive balancing systems. The findings can be used during the design process of new battery systems or to analyze and optimize any existing lithium-ion battery system.