Charge equalisation for series-connected LiFePO4 battery strings

Abstract

LiFePO4 batteries are suitable for high power applications because of their advantages of large discharge current and high efficiency. Owing to the characteristics of LiFePO4 batteries, it may cause overcharge/over-discharge and reduce the cycle life of the battery when series-connected batteries are used. This study proposes a charge equaliser based on an interleaved active clamp flyback converter. The interleaved topology reduces the output ripple current. Therefore the rectifier diode conduction loss can be reduced. With a clamp capacitor and leakage inductance, the switches are turned on with zero-voltage switching while the voltage stress of switch is reduced. Furthermore, a constant switching frequency and duty ratio are designed to achieve a simple control for the proposed system. The simulations and experimental results are provided to verify the performance of the proposed charge equaliser.