Active Battery Balancing for Battery Packs

In electric vehicle applications, it is necessary to use series strings of batteries since the required voltage is higher than the one that can be obtained from a single battery. Due to several factors, imbalance of batteries in these battery systems is usual and an important factor that has to be taken into account. Many balancing methods have been developed with a lot of different advantages, but all of them also have a lot of disadvantages such as complexity and/or high cost, which are the common problems that can be found in most of these equalization methods. In the present work, a low cost and very simple equalization method is proposed, in which a novel control is applied to a shunting transistor topology. It allows the transistors to regulate the amount of current that goes through each battery cell in the string depending on their State of Charge (SOC), during the charging process. This control ensures that the least charged cells to be charged faster, and the most charged ones to be charged more slowly. Design criteria are discussed and simulation results are carried out in a generic battery low power application which proves the control method. Fast equalization with a low complexity and cost is obtained