Charge equalisation for series-connected LiFePO4 battery strings

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.