An Optimized Topology for Next-to-Next Balancing of Series-Connected Lithium-ion Cells

Voltage balancing between series-connected cells of rechargeable lithium-ion batteries is important for battery life, autonomy, and safety. Active balancing is the designated choice for applications that are sensitive to energy losses and maximized autonomy. First, a well-known next-to-next balancing technique is presented and its design and operating limitations are analyzed. Then, the paper focuses on an evolution of the converter's architecture offering better performances while being more compact, requiring fewer and smaller filtering needs and still, being simple to implement. The experimental results of the balancing operation of a pack of eight cells connected in series show demonstrative and satisfactory results.