Research On Consistency Analysis Of Power Batteries And SOC Equalization Strategy

Because of the consistency problem,the capacity and service life of the battery pack is far less than that of the single cell,so the balanced management of the battery has important practical significance for the battery.The equalization technology of power battery for pure electric vehicle is studied in this paper.The main research work is as follows:(1)The performance of power lithium battery inconsistency was analyzed by identification method.The steps and methods of all the battery experiments in this paper were described in detail.Based on the equilibrium structure adopted in this paper,the DC / DC active equilibrium structure based on the switch array was determined.In addition,the equalization strategy based on external voltage equalization and SOC equalization were analyzed in detail.It was proposed to control the consistency of the battery pack based on the SOC equalization scheme.(2)On the problem of battery modeling and parameter identification,this paper gave a method,that the function between the OCV and the SOC could be got.And the state equation of the n-order RC model was deduced,and the specific method of the off-line parameter identification was given.The result showed that the model error was 32 mV.The FFRLS algorithm was used to realize the real-time identification of the battery parameters by On-line identification,and the specific on-line identification flow was given.The results show that the least squares algorithm could be obtained by using the forgetting factor real-time update,and the model was composed of the identification parameters.The output error could be controlled in reasonable range.(3)In estimating the state of charge of each cell,this paper discussed how the Kalman filter was applied to the equivalent circuit model and implementation steps.Two estimation methods,on-line estimation and off-line estimation were given for estimating the SOC of the battery.In the aspect of off-line estimation,the way of estimating the SOC based on the known battery model parameters was explained.The DST condition test and the UDDS condition test were used as the application case.In the case of the joint estimation of state and parameters,the method of AFFRLS and EKF filter algorithm was used.The final SOC estimation accuracy was less than 2%.(4)Aiming at the problem of equalization strategy based on SOC,a battery equilibrium simulation platform composed of six monomer models was proposed.The composition of the simulation platform was introduced in detail,and the DST condition and UDDS condition were used to verify the algorithm.The results met the requirements.The simulation strategy was divided into single channel and multi-channel equalization structure.The single channel adopted three equalization control strategies: the equilibrium based on the extreme value method,the equalization strategy based on the SOC mean value,and the combination of the extreme value and the mean method.Multi-channel was mainly used double-layer equalization logic,which can control the consistency of the SOC from different pack within a reasonable range.