A Modularized Equalization Method Based on Magnetizing Energy for a Series-Connected Lithium-Ion Battery String

Abstract

A single charge equalizer using the multi-winding transformer (SCEMT) is useful for the precise and fast equalization. Since this type of equalizer requires voltage sensing circuits for each battery cell, the size and cost of the overall equalizer system increase. In this paper, a novel switching method, which does not require voltage sensing circuits, is proposed for the SCEMT. However, due to the problems related to the implementation of multiwinding in a single transformer, the SCEMT is definitely difficult to apply to long series-connected lithium-ion battery string. In order to overcome these drawbacks, a novel module charge equalizer based on the configuration of the SCEMT is developed. Unlike the conventional module charge equalizer using additional components, the proposed novel module charge equalizer utilizes the magnetizing energy of the multiwinding transformer for the equalization among modules. Therefore, proposed module charge equalizer does not suffer from the size, cost, and loss related to the modularization. The validity of the proposed module charge equalizer is verified through experimental results.