Optimized structure 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 security. Active balancing is the designated choice for applications that are sensitive to energy losses. A well-known next-to-next balancing technique is presented and its design and operating limitations are analyzed. This paper then presents a new technique for next-to-next balancing that improves on the conventional technique by offering better performances while being simpler to implement. Experimental results show an important reduction of the size of the magnetic coupler while maintaining efficiency at a level above 90%.