Research And Design About Equalization System For Power LifePO₄ Batteries

As a result of fossil fuel exhaustion and environment deterioration, improving energy efficiency and exploiting new energy are drawing more and more attention from countries and areas all over the globe. New energy vehicles, as an essential part in energy transformation, is becoming a hot issue of all countries. Power LIFEPO4 battery shows a huge developing prospect for its outstanding performance in dynamic response and long circling life, though some proper management devices are needed for maintenance. And equalization control plays a crucial role in battery management because it directly relates to battery safety and work life.In order to realize a better equalization control of single cells in battery pack, according to its internal structure and operating principles, this paper has analyzed the features shown by power LIFEPO4 battery in temperature, charge-discharge and internal resistance, on the basis of experimental results of standard charge, standard discharge, discharge in different temperatures, HPPC(Hybrid Pulse Power Characteristic test). Experiments are carried out on the same shipment of power LIFEPO4 battery to calculate inconsistency in voltage, capacity, internal resistance during charging and discharging process, and combined with operation principles and characteristics of power LIFEPO4 battery, reasons accounting for this inconstancy and adverse effects caused on battery pack application are profoundly analyzed.Then a passive battery equalization system has been designed on the basis of LTC6804. The system can realize equalization by using resistance to exhaust energy in single cells with higher voltage, moreover we have built a passive equalization test platform, which has implemented tests as voltage accuracy, equalizing charge, equalizing discharge and equalizing temperature rise. Later, an analysis of operation principle of single-ended flyback circuit and its advantages in battery equalization was made before designing an unidirection active equalization system based on cooperation of LTC6804 and LT8584 which constitute single-ended flyback circuit to realize the energy transfer from cell to pack. Last, a bidirectional active equalization system based on cooperative operation of LTC6804 and LTC3300 was introduced, in which single-ended flyback circuit was ameliorated to synchronous flyback active circuit in order to realize independent bidirectional flow between cell and pack in each channel and it also showed favorable performance in equalization speed-lifting and loss reduction. On the basis of bidirectional active equalization system, a test platform was built to test characteristics of discharge equalization and temperature rise of the equalization system. Through all the data obtained from experiments, bidirectional active equalization system could improve the equalization speed effectively and decrease the energy loss compare to passive equalization system.