A Research On Active Equalization System Of LifeO₄Power Battery Pack

The development of electric vehicle is capable to improve the environmentquality. As a reliable power supply, the performance and costing of LiFePO4powerbattery pack will play a decisive role in the industrialization of the electric vehicle.During the course of work, the inequality of LiFePO4power battery will becomemore severe after several times of charging and discharging. If the inequality ofbatteries cannot be effective controlled, some of the batteries will be over-charged orover-discharged, which can damage batteries, then degrade the performance ofbattery pack and shortened the battery life significantly. Thus, that adds to the cost ofelectric vehicle, even cause the self-ignition accident of electric vehicle. So, it isimportant to study the equalization of power battery pack during charging cycle anddischarging cycle, and it will also play a decisive role in the industrialization of theelectric vehicle.To solve above questions, this thesis offers a research of improvement method toexisting LiFePO4power battery active equalization technology. In this research,author has made a reasonable goal, then proposes two active equalizations schemebased on DC-DC converter. Next, the theoretical research and analysis have beenshown in this thesis. Finally, both the simulation and the experiment have been givento verify the scheme.The most important work of this thesis can be divided into two parts. The firstpart is to select a high performance topology of active equalizer by analyzing existingstructures, as the base of this research. Part two is aims to solve the limitation ofexisting balancing control strategy, which can be realize by the proposed controlstrategies, such as frequency table look-up control strategy with voltage differencesand control strategy based on dynamic balanced point. Then, according to these twostrategies, the equalizer topology has been optimized separately, in order to satisfy theequalization methods. Finally, the simulation and experiment have been shown.The simulation result proves that both two control strategy can improve theperformance of active equalization of LiFePO4power battery pack. Compared withothers, equalization system with proposed scheme is more fast and efficient,especially the scheme with control strategy based on dynamic balanced point. Meanwhile, by using the combination of FPGA and MCU, the equalization systemwhich adopts layered structure can be realized in the application of large number ofcells.