Design methodologies of modular active equalization circuits for lithium-ion battery packs

This dissertation deals with the maximization of the usable capacity of lithium-ion battery packs which present imbalances. The original contribute proposed regards the development of model-based design methodology for active balancing systems, which also include parasitic effects and control nonlinearities. In particular, two different active balancing circuits have been detailed analyzed. Through a multi-winding transformer architecture, a cells-to-cells self-balancing energy tranfer process have been modeled. Then, a proper design methodology have been developed and, subsequently, experimantally verified. Indeed, an experimental prototype have been designed and tested under different imbalance conditions by using a Hardware-in-the-loop approach. The same systematic approach have been adoptet for another active balancing circuit which include and inductor for the adjacent-cell-to-cell energy transfer. Unlike the other architecture, multi-inductor balancing circuit need a roper control of the duty cycle. On this basis a variable frequency control has been proposed for maximizing the mean balancing current of the cells. Numerical results show improvement in equalization time and energy efficiency.