| With the increasing of energy consumption in the world,the air pollution is more and more serious,it is an important task to develop new energy vehicles for the development of modern industry.Among them,electric vehicles get concern because of its high efficiency,little pollution and other characteristics.Power battery pack is the only energy storage part of electric vehicles.When the performance of power battery pack drops to 80%,it will not be suitable to use in electric vehicles.Due to the advanced technology of power battery pack,the high safety and electrical properties is still maintained after retiring.It will cause tremendous waste if these power batteries are recycled.Therefore,li-ion power battery echelon utilization is considered.Due to the different self-discharge and environmental temperature,different single cell has different capacity,internal resistance and voltage,and there is some difference in the aging degree of each single cell.Therefore,it is essential to estimate the state of charge(SOC)and state of health(SOH)of the monomer battery in the electric vehicle li-ion power battery accurately for extending the li-ion power battery life and the battery echelon utilization.Firstly,the article conducts a study on the characteristic parameters of power battery pack,including the battery capacity,voltage and internal resistance.The method of characterizing the state of health of battery with ohmic resistance is proposed and the relation curve between battery capacity and ohmic resistance is established by accelerated ageing experiment.Through analyzing and comparing a variety of battery equivalent circuit model,the battery second-order Thevenin equivalent circuit model is selected because of its higher accuracy and simpler parameters.The open-circuit voltage and RC parameters of single cell were identified in different SOC through the battery charged and discharged experiments under two different conditions.The basic parameters of the battery model were obtained to estimate state of charge and health of the battery.In order to estimate the state of health of batteries accurately in time,this paper uses adaptive unscented Kalman filter(AUKF)to estimate the ohmic resistance and the state of charge accurately with UT transformation for two times.According to the function between the ohmic resistance and the state of health,the state of health can be estimated in real time.The battery charged and discharged experiments were done under two different conditions to verify the feasibility and accuracy of this method.Finally,through the estimation of SOH of the li-ion power battery pack and the monomer battery,positioning unqualified monomer battery,quantifying the battery intact rate,and formulating a clear solution for the electric vehicle li-ion power battery echelon utilization to maximize the resource utilization of waste power batteries. |
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