SOC Estimation Of Power Lithium Batteries And Research On Battery Management System

Conventional fuel vehicles will cause pollution to the environment,and the fossil energy is decreasing and becoming depleted.,so electric vehicles instead of transmission fuel vehicles is a major trend in the development of the automotive industry.Battery management system is a hot and key technology in the research of electric vehicles.The main tasks of the BMS include the estimation of the state of charge,state of health and so on,the collection of information about the operating current,voltage,temperature,the balancing between different battery monomers,and the thermal management of the battery.In this paper,for the precise estimation of the SOC,the collection of battery operating information,and the balancing of different battery monomers,work has been done in the following areas:(1)Analyze the advantages and disadvantages of the electrochemical model,equivalent circuit model and black box model of the battery,and finally adopt the improved second order equivalent model,which is beneficial to the engineering application,and the accuracy of the model is high.On this basis,the off-line parameter identification based on HPPC experiment and the parameter identification based on forgetting factor recursive least square method are carried out in the second order equivalent model.(2)Two methods are used to estimate battery SOC,one is unscented Kalman filter,which mainly introduces the core UT transformation,the other is the optimal adaptive gain nonlinear observer,which is also the main innovation point in this paper.The observability of battery model,the design of observer,the proof of observer convergence and the optimization of observer gain using differential evolution algorithm are introduced,and SOC estimation experiments under two operating conditions are done.(3)BMS hardware and software design,using STM32F407VET6 and special battery monitoring chip LTC6804-2 design hardware circuit,mainly including battery voltage,temperature acquisition circuit,current acquisition circuit and battery external balancing circuit,and design the corresponding software program.Finally,the effectiveness and advancement of the proposed optimal adaptive gain nonlinear observer are proved by experiments,and the designed BMS are tested.The test results show that the BMS data acquisition accuracy is very high and can effectively improve the inconsistency of voltage between different battery monomers.