Research On Active Equilibrium Strategy In Power Battery Charging

In recent years,the haze and other environmental issues profound impact on human life,travel as much as possible to use clean energy has become the consensus of the people of the world.The Tesla Inc,which founded in 2003 set off a boom in electric vehicle manufacturing.Vehicle power battery pack as a key component of electric vehicles,its performance directly affects the further popularization of new energy vehicles.In order to meet the electric car on the voltage,power and driving range requirements,vehicle power battery is generally multi-cell batteries in parallel into a battery module,a number of battery modules in series into a packet,multi-packet battery in series into a battery pack.But the cell battery in the manufacture,production,transportation,holding and the use of the process will have a slight difference,and with the accumulation of time,this difference will gradually increase,so that the entire group of batteries in the use of the process in the temperature,voltage,soc and internal resistance and other parameters of the imbalance,affecting the power battery charge and discharge efficiency and vehicle performance and safety.By studying the influence of the parameters of the battery on the charging efficiency,it is necessary to propose a suitable method of charging the battery.At the same time,to achieve the battery pack fast and good charging target,something should done,such as analyzes different equilibrium topologies,finds the appropriate topology with high equalization efficiency,simple control strategy and easy to coordinate with the charging process structure.Therefore,in this paper we intend to use the battery charging process optimization and battery active balance combined to eliminate the charging process of the battery within the group caused by the impact of imbalance.The main contents of this paper include the following aspects:(1)To study and compare the development of domestic and internationalcharging technology and balanced technology to understand the effect of different charging methods on the battery temperature,internal resistance,polarization and other parameters,and by analyzing the different balanced topology,such as the realization of cost,technical difficulty and so on,we have a better theoretical understanding of the equalization technology in the process of power battery charging.(2)To study the principle of electrochemical reaction of lithium iron phosphate battery,analysis the characteristics of the battery performance characteristics such as capacity,voltage SOC and internal resistance,and build the corresponding battery experiment on room temperature,constant temperature and other different temperature.To Analysis the experimental data,obtained the conclusion that the different temperatures on the battery has a significant impact on the various parameters.In this paper,we chose the model of dual RC equivalent circuit as the circuit model.The Ampere-hour integral method is used to estimate the battery soc.The parameters of the battery model are obtained by HPPC hybrid pulse test with different soc points.The dynamic simulation model of the battery is established and verified.(3)Through theoretical analysis and experimental verification,the advantages of charging time and charging efficiency are studied.On the basis of the theory of optimal charging of the battery,the multi-stage charging method is used to carry on the fast charging research to the power battery,The experimental results are analyzed and the charging time and charge capacity are taken into account,then we chose the optimal value of the five-stage charging current(1.9C,1.6C,1.2C,0.7C,0)(4)The process and the causes of the inconsistency of the single cell in the battery are explored.The existing passive equalization and the active equilibrium topology are analyzed,And by building the corresponding model in the simulation software,analyzes the equilibrium efficiency of centralized capacitor,concentrated inductance and bi-directional flyback transformer and shunt active,select the samemodule single cell using centralized inductive equilibrium,different modules of battery using parallel equalization.(5)Set up a fuzzy equalization control system control strategy,use the battery voltage,temperature and battery soc variable as a balanced control variable,and use the voltage difference and the average and the soc difference and the average as a balanced open sign,the output variable is balanced current and equalization time,and the simulation results show that the energy transfer efficiency of the battery is high,which can achieve faster and better charging.