SOC Estimation And Charging And Discharging Balancing For Lithium-ion Battery Pack

In order to meet the challenges of energy and environment,and to accelerate the upgrading of traditional automobile industrial transformation,electric vehicle industry has become an important strategic emerging industry and taken larger roles in promoting the transformation of the economic development mode.As a key subsystem of electric vehicles,Battery management system provides reliable guarantee for safety driving by real-time monitoring and management of the power battery pack.One of the key technologies of the battery management system is to accurately estimate of the state of charge of the battery,which is the condition and fundamental for optimizing the energy management of electric vehicles.Another key technology for battery management is battery equalization technology,which improves energy inconsistency of the battery pack and is critical to increasing the usable capacity of the battery pack.In this paper,the charge state estimation and charge-discharge equalization technology of lithium-ion battery pack are studied.The modelling of lithium-ion battery based on the second RC equivalent circuit is firstly studied.After the parameters of the lithium-ion battery model is determined initially by the pulse discharge experiment method,multi-objective optimization was carried out to determine the optimal battery model parameters,which was verified through the Hybrid Pulse Power Characterization test method.An Improved adaptive extended Kalman filter for state of charge estimating is then proposed.The method adaptively adjusts the sliding window length based on the new rate adjustment factor,and automatically corrects the noise covariance matrix of the filter.The results of numerical simulation and experimental show that the proposed estimation method can accurately estimate state of charge of the lithium-ion battery pack,and has strong robustness.A charge-discharge equalization method based on average state of charge is presented in this paper at last.The balance circuit can be switched to charging condition,discharging or resting condition.The equalization strategy firstly evaluates the inconsistency of the battery pack based on the standard deviation of the state of charge.Under the charging condition,the battery sub-module with the state of charge higher than the average state of charge is discharged;under the discharging or resting condition,the battery sub-module with the state of charge lower than the average state of charge is charged.The results of numerical simulation and experimental show that the proposed equalization method can significantly improve the energy inconsistency.