Study On The Equalization Algorithm Of Power Battery Packs

As the source of power for new energy vehicles,the performance of power battery packs directly determines the output performance and driving range of new energy vehicles.In the use of electric vehicles,frequent switching of different working conditions results in the difference of charging and discharging time,current and heat in the battery pack.These factors aggravate the inconsistency of the battery pack,which will reduce the capacity and cycle life of the battery pack..The equalization system of power battery pack is an effective measure to improve the inconsistency of battery pack and a key technology to improve the capacity and prolong the life of battery pack.The main contents of this paper are as follows:(1)This paper analyzes the charging and discharging characteristics,temperature characteristics and the causes of the inconsistency of the Lithium iron phosphate power battery.The inconsistencies of the battery are shown from three aspects: open circuit voltage,working voltage and state of charge,it analyzes the influence of the inconsistency on the battery and the measures to improve the inconsistency of the battery.In this paper,SOC of the battery is selected as the evaluation criterion of the equilibrium control to improve the inconsistency of battery pack.(2)SOC estimation based on dynamic parameters of battery.Firstly,the secondorder RC equivalent circuit model of the battery is established,and the parameters of the battery model are identified by the forgetting factor recursive least square method.Next,the SOC of the battery is estimated by the dynamic parameters of the battery and the Extended Kalman Filter algorithm.Finally,the accuracy of SOC estimation method under constant current and pulse conditions is verified by MATLAB simulation,which provides an accurate evaluation index for balance control.(3)The double-layer bi-directional active equalization circuit based on energy storage inductor and multi winding transformer is designed to realize the equalization between the cell and battery pack in the module.The thesis completes the structural design,working principle analysis and calculation of related parameters of the bottom equalization circuit and the top equalization circuit,and the effectiveness of the equalization circuit is verified by simulation experiments in Simulink.This double-layer bi-directional equalization circuit based on the energy storage inductor and multiwinding transformer lays a good hardware foundation for the on-line battery equalization.(4)This paper presents an equilibrium control method based on fuzzy control algorithm.The fuzzy control algorithm takes the SOC of the battery as the equilibrium evaluation standard,which can adjust the size of the equilibrium current according to different input variables.In this paper,the fuzzy control algorithm is compared with the mean-difference algorithm.The two equalization algorithms are modeled and simulated in MATLAB,and the comparison and analysis are performed in terms of equalization time,equalization efficiency,and equalization effect.The simulation results show that the equalization based on the fuzzy control algorithm can effectively shorten the equalization time,reduce the energy consumption and have a better equalization effect.