Research On Intelligent And Fast Charging Technique For Electric Vehicle Batteries

Utilization of electric automobiles have attracted extensive attention of worldwide due to the effect of energy crisis and environmental pressure. However, charging technology is one of the crucial factors that restrict the popularization of electric automobiles. Current charging methods, which do not strictly follow physical and chemical reaction laws of internal batteries, mostly have the problem of overcharging and gassing, which has great influence on the service life of storage battery and waste energy. Though the ideal charging curve theoretically is proposed by Marse Law, there are a large number of factors influencing storage battery charging. It is difficult to be expressed by mathematical model, to bring great difficulty in actual control. Polarization problem is the bottleneck for rapid charging of storage battery. Although it has been noted in existing researches that large current as well as short-time discharging can eliminate polarization problem in an effective manner, neither the current size nor the time for discharging has been presented. This dissertation mainly focus on intelligent and rapid charging of lead-acid batteries, used in electric automobiles, and propose the triple-feedback Fuzzy-PI charging control algorithm based on voltage, current and temperature, depolarization algorithm as well as the design of charging devices etc.First of all, the triple feedback Fuzzy-PI charge control algorithm was proposed which divided the whole charging process into three processes of pre-charging, intelligent fast charging and cut-off charging. During the pre-charging stage, whether the storage battery met the fast charging conditions was judged. If not, the small constant current was adopted to charge the storage battery until the fast charging conditions were met. During the intelligent fast charging stage, the real-time collection of voltage, current and temperature were firstly gathered and then the charging voltage by reasoning with the Fuzzy-PI controller was obtained. During the cut-off charging stage, the small current floating charge was employed until the storage battery reaches saturation.Secondly, for the discharge depolarization issue, this dissertation selected several single batteries with the similar charging parameters to form two reference groups. Firstly, the discharge time was set for the first group, the discharge current was changed and then the single-battery terminal voltage was compared after this process to get the optimum discharge current; secondly, the discharge current was set for the second group and the discharge time was changed to get the best discharge time; finally, the depolarization effects of the discharges of these two groups were compared and the best discharge depolarization program was got.Finally, based on the above-mentioned control thought, this dissertation established the object control model, designs the main circuit of charging and the control loop, calculated the key parameters in the main circuit and then verified the correctness of the design with the PSIM software.The experiment results of the single group of the storage battery show that the intelligent fast charging algorithm based on the triple feedback Fuzzy-PI can intelligently adjust the charging process according to the internal physical and chemical reaction principles of the storage battery. The depolarization algorithm timely and effectively gets rid of the polarization phenomenon in the charging process. The combination of these battery algorithms achieves the intelligent and fast charging for storage battery.