Current equalization of serially connected battery cells for a possible second life application

This article presents a method to control the current of each battery cell in a serially connected battery stack according to each cell capacity. With this method battery cells with different capacities and even battery cells with different chemistries can be serially connected. Therefore, significantly more energy can be extracted from the battery stack and a second-life-option for old batteries with a large capacity variation is possible. The required power converter structure as well as the calculation of the individual cell currents are presented. A simulation of the power converter is performed and validated by a prototype with twelve serially connected battery cells.