Charge equalization for series connected battery strings

A simple technique that provides charge equalization for a series string of battery cells is presented. The advantages of accurate charge equalization are very substantial and include reduced damage to battery cells in the stack, and a dramatic increase in battery life. The basic technique utilizes a simple isolated DC/DC converter with a capacitive output filter along with a multi-winding coaxial winding transformer (CWT). The coaxial winding transformer is known for its low and controlled leakage inductance. The transformer leakage inductance is used as the main driving impedance to control the total charging current for the individual cells. The use of one low-power converter to obtain charge equalization for the entire battery string is very attractive and leads to a low cost implementation