Research On Charge Equalization Of Power Lithium-ion Batteries

Under the background of energy saving and environment protection, in order to achieve the sustainable development, the research on energy-efficient and pollution-free electric vehicles (EV) becomes more and more important. At present, eclectic vehicles'research and development has been stepped into the early stage of industrialization while being still restricted by the traction of batteries'service life. EV's endurance mileage and dynamic performance is dependent on the traction of batteries which are taken as an important energy source. The initial differences among batteries which lead to un-uniformity after charging and discharging are the main reasons for the shortened life of batteries. Equalizing charge could solve the problem mentioned above.In this paper the lithium batteries were chosen as the object of study and its working performance analyzed. Based on state of charge (SOC) of batteries, an equalizing charge method was designed for lithium batteries, which means losing no energy. Taking SOC as the equalization standard, it could improve the efficiency of equalizing charge and avoid the lag of voltage balance. The major contents included in the paper were proposed as follows:Firstly, the un-information problem appeared in traction batteries was analyzed and the methods of equalizing charge presented at home and abroad researched. The deterioration of batteries'performance was due to the progress of charging and discharging. At the same time, the overcharge of single cell must be avoided.Secondly, with the depth research on lithium batteries, the equalization charge method based on SOC was designed and its principle and working process analyzed. The circuit design of the whole equalizing system was completed.Finally, in view of the existing battery models and SOC estimation strategy, the battery simulation model was established employing the methods of open circuit voltage detective and ampere hour meter with MATLAB. The equalizing charge strategy and controller based on fuzzy control theory were designed. The simulation results in different charging modes prove its good balance effect.