Research On BMS Of Electric Vehicle Power Lithium Battery Energy Management System

In the 21st century,the global energy crisis and environmental pollution are becoming increasingly serious.It is an inevitable trend for new energy vehicles represented by electric vehicles to replace traditional fuel vehicles.Because of the advantages such as good acceleration performance,low driving noise and low pollutant emission,electric vehicles have become the new focus of the automotive industry and been widely concerned and favored.Power battery technology is one of the key factors restricting the development of new energy automobile industry.In order to ensure the safety,stability and long life of power battery,it is important to research the Battery Management System(BMS)for its monitoring,state estimation and management.The battery management system mainly includes: battery unit voltage acquisition,PACK total voltage acquisition,temperature acquisition,current acquisition,State of Charge(SOC)estimation,State of Power(SOP),State of Health(SOH),State of Function(SOF),battery equalization,insulation monitoring,high voltage interlock detection,battery overcharge protection,over discharge protection,over temperature protection,collision protection,Controller Area Network(CAN)communication,diagnostics,etc.The main research contents of this paper include the following aspects:Based on 40160 ternary lithium battery,the working principle and characteristics of lithium battery were analyzed.Comparing various battery equivalent models,the second-order RC battery equivalent circuit model was established.And parameters of the battery model were identified by HPPC(Hybrid Pulse Power Characteristic)experimentAiming at the problem of large error in lithium battery SOC estimation,the method that combines Ampere Hour integral method and Unscented Kalman Filter(UKF)was adopted after analyzing several common SOC estimation methods.The calculation process of UKF was deduced,and SOC was estimated by the battery equivalent circuit model.By analyzing several equalization control methods and topology circuits,this paper adopted battery SOC and cell voltage limiting based equalization control method and bidirectional synchronous fly-back topology circuit for the consistency problem of lithium battery.According to the functional requirements of the battery management system,the cell voltage sampling circuit was designed based on LTC6803 sampling chip,while the active balance circuit was designed based on LTC3300.The NTC(Negative Temperature Coefficient)thermistor and the Hall current sensor were used as temperature sensor and current measurement respectively.The hardware and software design were completed,which could realize the functions of voltage acquisition,current acquisition,temperature acquisition,SOC estimation,battery equalization,AC and DC charging,fault detection and protection.Experiments indicated that the error of the SOC estimation is less than 2%,the battery information collection accuracy meets the requirements,and the battery balance reaches the desired effect.