Study On SOC Estimation Of Lithium Ion Battery And Equalization Technique Of Battery Pack

Electric vehicle has been greatly developed because of the need to solve environmental pollution and energy crisis.The important things for the development of electric vehicle are to prolong the endurance mileage and reduce costs.The key to solving these two problems lies in the battery system.Due to the limitation of current battery manufacturing technology,the performance of battery must depend on battery management system.The gordian technique of battery management system are state of charge(SOC)estimation and equalization technique of battery pack.It is also the main research content of this paper.Some common methods of SOC estimation and equalization technique of battery pack are introduced and analyzed in this paper.On this basis,some improvements and innovations have been made and some achievements have been made.In SOC estimation,a joint estimation algorithm is proposed in this paper.First,this algorithm is to determine the initial value of the SOC by open circuit voltage method.Then,the modified ampere-hour integral method is used for online estimation.The modified ampere-hour integral method is obtained by modifying the actual capacity of the battery through its health state and temperature.Finally,the off-line data are used to is segmented reduce the cumulative error of the modified ampere-hour integral method.Simulation results show the joint estimation algorithm reduces the cumulative error of traditional ampere-hour integral method.And,it can determine the initial value of SOC and has higher estimated accuracy.In equalization technique of battery pack,two new equalization circuits are proposed based on the analysis of a bidirectional non-dissipative equalization circuit based on storage inductor.Two circuits are bidirectional lossless equalization circuit is constrained by multiple conditions for a small number of batteries in series and bidirectional lossless equalization circuit is constrained by multiple conditions for a large number of batteries in series.Compared to bidirectional non-dissipative equalization circuit based on storage inductor,they have less equalization time when the distance between the target cells requiring energy transfer is long.And in other states of the same disequilibrium,It takes less equalization time and the consistency of every battery cell is better after equalization by using these two equalization circuits.The effectiveness and advantages of two new equalization circuits are verified by simulation and experiment.The study on the SOC estimation and equalization technique of battery pack is beneficial to improve the overall performance of electric vehicles and reduce the cost of electric vehicles.It also has great theoretical significance and practical value for the development of electric vehicles and energy conservation and environmental protection.Figure[97] table[1] reference[71]...