Research On Key Technologies For The Management System Of Lithium-ion Power Battery

In recent years,China's Fuel-efficient vehicles and new energy automotive industry continues to develop rapidly.In 2016,the production and marketing of new energy vehicles exceeded 500,000 units,and China has been the world's largest market for two consecutive years.The power battery technology of one of the three key technologies for new energy vehicles(drive motor,power battery,vehicle electric control),battery management system is an indispensable part of it.Although the development of power battery management system has made great strides,but the market for the performance and safety of new energy vehicles also put forward more and more high requirements,and in recent years as more and more new energy vehicles into the market,due to the power battery system caused by the decline in car performance,battery fire explosion and other safety problems are also more prominent,it also shows that there are some key technical problems to be solved in the power battery management system,such as the accuracy of the state estimation of the battery,the equalization of the battery and the evaluation of the fault diagnosis,the potential failure risk and the measures to be taken in time.From the national 2016 issue of " Technology roadmap for energy saving and new energy vehicles " can be seen,the new energy vehicle power battery safety and reliability management theory is listed as one of the important core technologies in the future innovation and development.In this paper,the equivalent circuit modeling of lithium battery,the estimation technology of charge state,battery equalization technique and the electronic control design technology of management system are studied for the most widely used lithium-ion power Battery management system of hybrid electric vehicle and electric vehicle.To explore solutions to improve the performance and reliability of power battery packs,this includes the following:1)A modified second-order RC equivalent circuit model is proposed,based on the analysis of the existing lithium-ion battery model,This model facilitates the online computation of automotive-grade embedded processors.In the model parameter identification algorithm,according to the characteristic of the model function,the parameter identification of the static characteristic function of the model is carried out by the recursive damping least square method,and the identification of the parameters of the dynamic polarization characteristic of the battery is used to identify the model parameters by using the subspace system identification algorithm with small computational quantity and high identification precision.In order to verify the validity of the model,a lithium battery pulse charging and discharging experiment was designed,the simulation results of the experimental data and the battery equivalent circuit model were compared,and the results proved that the model can simulate the external characteristics of lithium battery,and the good model calculation precision lays a foundation for the subsequent state estimation of lithium batteries2)The current estimation theory of lithium battery charge state is compared,and the experimental platform of Li-Ni Co Mn lithium-ion battery is set up,and the mainstream Kalman filter Soc estimation method is described in detail.In this paper,a new algorithm based on iterative central differential Kalman filter for SOC estimation and weighted fusion with open-circuit voltage method is proposed,and the new weighted fusion algorithm is proved to have higher estimation precision.3)In view of the safe use of power battery,the maximum power estimation problem of the charge and discharge of the battery is studied,and the maximum estimation method based on the improved DP equivalent circuit model is put forward to control the battery's charge and discharge power in practical application,which can maximize the efficiency of the battery.It also protects the battery pack.4)For the equalization of the power battery pack,the paper compares the passive equilibrium method and various active equilibrium methods in the past.Because the double-tiered switch capacitor equalization method has a fast equilibrium speed,the advantages of simple control,but the conventional switch capacitor is easy to produce switching loss and electromagnetic interference,aiming at this problem,this paper proposes a lithium-ion power battery active equalization control method based on double-tiered quasiresonant switching capacitor,and uses soft switch technology to reduce the switching loss.This paper analyzes the problems that need to be considered in the practical application of the double-tiered quasiresonant switch capacitance equalization method,including the problems of equalization efficiency and parameter selection,and then simulates and analyzes the equilibrium circuit with the power simulation software.Then through the set up of the series battery equalization experimental platform,the paper gives the experimental verification of the theory,the simulation and experimental results verify the effectiveness of the equilibrium control method proposed in this thesis,and provide the effective basis and guarantee for the whole design of the power Lithium ion battery management system.5)Based on the study of the state estimation and equalization theory of lithium-ion batteries,a distributed software and hardware system for battery management is designed,and the scheme of design ideas is elaborated.Finally,the fault diagnosis and protection strategy of the power battery are studied,and the improved analytic hierarchy process is used to evaluate the status information of the BMS,and the system reliability risk of the battery is evaluated,which provides a quantitative basis for the protection strategy of the fault diagnosis system.