An Active Fast Equalizer for Series-Connected Batteries with Adaptive Balancing Current Control

In this paper, an active fast equalizer for series-connected battery packs with adaptive balancing current control is proposed. The proposed equalizer can control and maintain the balance current as well as the operating mode to shorten the balance time and improve the balance efficiency. The realized isolated bidirectional equalizer not only can do a balance between any cell but also equalize multiple cells in the same balancing period. As the duty ratio of the main switch in conventional equalizers is kept constant during the equalization process, the voltage difference change in cells will cause balance current decrease and result in the extension of the balance time, especially in the later phase of balancing. To deal with this problem and take the battery nonlinearity and circuit parameter non-ideality into consideration, an adaptive balance current control based on fuzzy logic inference is addressed. Throughout the balancing process, the presented approach can modulate the duty ratio adaptively according to the variations of the cell and pack voltages to maintain the balance current. The balanced charge can be bi-directionally transferred between the battery and the battery pack. Experimental results and comparisons with those of obtaining from other counterparts are given and discussed to validate the feasibility, effectiveness, and performance improvement of the studied scheme.