Passive balancing algorithm for charge equalization of series connected battery cells

The progressive cost reduction of Lithium-ion batteries drives an everyday larger number of applications to enjoy the advantages of this energy storage technology. At the same time, issues like safety and charge unbalance in batteries with series-connected cells may limit the full exploitation of the technology, as charge unbalance reduces the usable capacity of the battery. This work describes a passive cell equalization procedure executed by the Battery Management System that reaches the balance of the battery with negligible additional costs. It is based on an iterative algorithm that progressively reduces in small consecutive steps the charge levels of the most charged cells by activating bleeding resistors. The algorithm takes into account the inaccuracies of the measurement of the cell voltages, the maximum possible balancing power, and reduces the effect of the cell short-term relaxation phenomena. It is fully parametric and can be tailored to any kind of battery. The algorithm is experimentally validated with a 10-cell Li-ion battery and its functionality is successfully demonstrated.