Research On SOC Estimation And Equilibrium Technology Of Power Battery In Electric Vehicle

With the widespread use of electric vehicles,the role of battery management systems has become more prominent.As an important part of the battery management system,the estimation of the state of charge?SOC?of the power battery is affected by many factors,which makes the estimation accuracy lower,and the long-term usage of the battery will increase the battery inconsistency.Therefore,SOC estimation and battery equalization technology are becoming more and more important.In this paper,the characteristics of LiFePO₄ battery are analyzed,and the estimation of the state of charge and the equalization technology between batteries are mainly researched.After considering the accuracy and real-time of SOC estimation,the simplified electrochemical model is used as the battery model for SOC estimation.Then,the battery pack is discharged at different discharge rates.Finally,the parameters of the model are obtained by using the recursive least squares method and using the data obtained by the discharge to obtain the model parameters of the battery pack.In view of the large cumulative error of the traditional current integration method,the open circuit voltage method is only applicable to the SOC estimation under the condition of the battery standing.This paper uses the Extend Kalman Filter?EKF?to estimate the SOC and formulates the current integration method.making it as the equation of state for the EKF.The simulation results show that the proposed method can control the SOC estimation error within 6%,which has a good estimation effect,but the shortcoming is that the SOC estimation effect at the end of the discharge is poor.The self-Adaption Unscented Kalman Filter?AUKF?is used to estimate the SOC.The results show that the plateau and EKF have similar estimation effects,and the estimation effect at the end of the discharge is better than the EKF algorithm.The estimated error of the SOC is controlled within 4%.Aiming at the inconsistency of single cells in the battery pack,the improved buck-Boost circuit is used to equalize the four batteries,and the effectiveness of the method is verified by simulation.For the case of more single cells,this paper uses the hierarchical Buck-Boost circuit to simulate and analyze 8 batteries,and verifies the feasibility of the method.At the same time,for the problem of inconsistency of single cell in charging,this paper uses fuzzy control to control the switching tube of Buck-Boost charging equalization circuit,and changes the equalizing current by changing the duty cycle of the switching tube.The final result shows the inconsistency among the batteries is eliminated and the goal of balance is achieved.