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.

-Active charge balancing is an approved technique to implement high performance lithium-ion battery systems. Enhanced balancing speeds and reduced balancing losses are feasible compared to passive balancing. The new architecture proposed in this paper overcomes several drawbacks of other active balancing methods. It consists of only 2 non-isolated DC/DC converters. In combination with a MOSFET switch matrix it is able to balance arbitrary cells of a battery system at high currents. Adjacent cells can be balanced simultaneously. For the given setting, numerical simulations show an overall balancing efficiency of approx. 92.5%, compared to 89.4% for a stack-tocell-to-stack method (St2C2St, bidirectional fly-back) at similar balancing times. The usable capacity increases from 97.1% in a passively balanced system to 99.5% for the new method.

This paper presents a theoretical analysis of the advantages of active charge balancing in lithium-ion battery systems and a comparison to passive balancing solutions. Universal equations to estimate the benefits of an actively balanced battery system concerning energy savings and lifetime extension are derived from basic statistics. The calculations depend only on the configuration and aging properties of the individual cells. Their validity is limited to applications with full cycle usage and cells whose capacity values are normally distributed. The losses due to passive balancing in an nSmP battery system are calculated as well as the overall energy savings when applying active balancing. Furthermore, the extension factor for the lifetime of an actively balanced battery system is found to be in a range between 1.23 and 1.02 depending on the system configuration and the cell parameter. Based on the results, several options are identified to increase the energy efficiency of conventional passive balancing systems.

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