A high efficiency equalizer based on forward converter for series connected battery string

In the series-connected lithium-ion battery string application for electric vehicles, equalizer is needed to enhance battery cycle life and maintain the stable performance. The equalizer is taken as an important part of battery management system (BMS), which detects the voltage of each cell to determine the control strategy for equalizer. How to improve the efficiency and reduce loss is always the problem to be solved. This paper proposes a high efficiency nondissipative equalizer for series-connected battery string, which uses forward converter to transfer energy from the highest voltage battery to the lowest voltage one. Current feedback is taken to maintain the stability of output current by adjusting the duty of Pulse Width Modulation (PWM) signal. The proposed equalizer has characteristics such as low loss, high efficiency and short equalization time. The operation principle of the proposed equalizer and design analysis is presented in this paper. Experimental results verify that the proposed equalization method has good cell balancing performance.