Research On Energy Balance Control Strategy Of Battery Pack

With the rapid development of the era of intelligence,the automobile industry is expanding,and the problem of automobile exhaust pollution is being brought up.On the one hand,the government is constantly perfecting and tightening the exhaust emission standards.On the other hand,the electric vehicle technology is developing rapidly.In the development of electric vehicles,the battery management system is the "heart" of the car,which is the core technology.The maximum output power of an electric car can reach hundreds of kilowatts,so the voltage of battery pack is very high and it usually reaches several hundred volts.But because of the production process and safety problems,the voltage of a single battery is far lower than that,so the battery must be used in series.In a series battery pack,different batteries have different parameters due to the production conditions of the factory,and their self-discharge rate,internal resistance and capacity will always be different,which we call the inconsistency of the battery pack.Inconsistencies seriously affected the life of the battery,so battery equilibrium is one of the most core functions of battery management system,is also one of the most complex function.Firstly,this paper describes the development status and applications of the power battery pack.Based on the balancing factors of the battery pack,the reasons for the formation of the battery pack and the relevant solution are discussed.In this paper,the equivalent circuit model of various power cells was compared,Thevenin equivalent circuit model was selected for the analysis of battery state,and the estimation scheme of SOC was summarized.Secondly,this paper compares equilibrium strategies of two kinds of equilibrium topological circuits: passive equilibrium and active equilibrium.And we selecte Several typical topologies for presentation: resistance shunt equalization,switching capacitance equalization,switching inductance equalization,multi-transformer conversion equalization,single transformer transformation equalization,etc,mainly discuss the circuit structures,equilibrium strategies,application situations and advantages & disadvantages.Then,the multitransformer balance method is selected from several topology circuits introduced before,and the hardware debugging platform is further designed and implemented.According to the multitransformer equilibrium topology and lead-acid battery characteristics,we finally put forward a balanced control strategy whitch based on the combination of battery capacity and terminal voltage,and designed the algorithm.In this thesis,the design of the hardware platform and the equilibrium strategy are tested by experiment.First of all,we tested those modules: driver,DC-DC converter,voltage acquisition,485 communication,whitch mainly to ensure the safety of the experiment system,the feasibility and that the experimental data can be accurate enough to upload.Then,the equalization circuit uploads the battery voltages to MATLAB software,and the time-voltage curve of each battery is plotted to evaluate the performance of the equilibrium system.By comparing the equilibrium curve of the battery,it is fully explained that the balanced system and strategy designed in this paper can effectively achieve equilibrium and reduce the energy loss of the battery pack.