Research On Battery Management System Based On Modified Open Circuit Voltage-ampere Hour Integration Method

Be faced with the problems of urban traffic congestion and serious environmental pollution,in order to meet the needs of low-and middle-income people for short-range means of transportation and the demand for energy conservation and environmental protection of our country,conventional power batteries for electric two-wheelers are gradually being replaced by lithium-ion batteries with high energy density and long cycle life.During this process,the driving safety and battery life are not effectively guaranteed since the single safety protection method of the existing battery management system(BMS)of electric two-wheelers and the limited estimation accuracy of the state of charge(SOC).To this end,relying on the means of experimental testing and simulation,this thesis explored characteristic and SOC estimation of power battery,and completed the design and functional verification of the BMS with the help of software and instruments.The main work contents and conclusions are as follows:(1)Taking 18650 ternary lithium ion battery as the research object,the temperature characteristic test,rate characteristic test,aging characteristic test,open circuit voltage characteristic test and hybrid pulse power characteristic test were carried out.Based on the experimental data,the evolution of battery discharge capacity with ambient temperature,discharge ratio and aging degree,and the influence of ambient temperature on open circuit voltage(OCV)were analyzed.The results show that low temperature environment has a great influence on the discharge capacity.The discharge capacity at-20 ℃ is 76.87% of that at room temperature;The battery has excellent rate performance,and the high current discharge efficiency of 3.0c is 98.93%;During the first 300 cycles of the battery,the capacity attenuation rate is first fast and then slow.After more than 300 cycles,the capacity attenuation rate accelerates,and the capacity attenuation is as high as13.74% in the next 230 cycles;Under the same SOC condition,the OCV of battery increases with the decrease of ambient temperature.When SOC = 0,the OCV corresponding to 0 ℃,-10 ℃ and-20 ℃ increases by 10.77%,11.88% and 13.24%respectively compared with that corresponding to 25 ℃.(2)Based on the battery characteristic tests and analysis results,by establishing the dual input model of ambient temperature and open circuit voltage and deriving the formula of capacity correction coefficient,an SOC estimation strategy that is based on the modified open circuit voltage-ampere hour integration method(OCV-AH)was proposed.Experiments and simulations were carried out at ambient temperatures of 35 ℃,10 ℃,-5 ℃ and-15 ℃.The results show that the greater the temperature difference between ambient temperature and 25 ℃,the better the correction effect of modified OCVAH.The extended kalman filter(EKF)based on the second-order RC circuit model was designed as the control group.Experiments and simulations were carried out under the dynamic working conditions of urban dynamometer driving schedule(UDDS)at three ambient temperatures of-10 ℃,20 ℃ and 35 ℃.The results show that the SOC estimation of EKF in low temperature environment is poor,and the maximum error is greater than 17%,The modified OCV-AH can ensure that the maximum error is less than3% in a wide temperature range.(3)The functional requirements and master-slave structural framework of BMS were clarified according to the practical application.The hardware circuit and PCB design of the slave module with the battery management chip SH367309 as the core and the software design of the master module with the single chip microcomputer STM32 as the core were completed.Finally,taking 20 series of ternary lithium-ion battery packs as the test object,the data acquisition,balance management,safety protection and SOC estimation of BMS were verified.The results show that the designed BMS meets the requirements of electric two wheeled vehicle.