Research On Alternate Balance Control System Of Li-ion Battery For Electric Vehicle

With the energy demand increasing and environment deteriorating,electronic vehicles will become the dominate player in the vehicle market.As the key power source of electric vehicles,the inconsistency of state of charge between lithium-ion batteries is increasing while being used,which directly affects the cruising range of electric vehicles.Therefore,the battery balance control system has become a hot research topic in the field of electric vehicles.In this paper,the 18650 ternary lithium battery is taken as the research object,and the following research is carried out:Firstly,the extended Kalman filter algorithm is used to estimate the SOC for the battery.The second-order RC circuit model has been built,and the experiment of HPPC has been conducted to identify the battery parameters.The accuracy of the circuit model had been verified by the simulation in MATLAB/Simulink.Under the condition of 1C discharge rate and 1C,1/3C discharge rate,the working voltage data obtained by the circuit model is compared with the experimental data,and the error value is within 0.05V,verifying the validity of the circuit model.Under the condition of DC discharge and intermittent discharge,the programming simulations are carried out in MATLAB to estimate the SOC.Finally,the value of SOC is compared with experimental data,and the error value is controlled at about 3%,which verify the feasibility of the extended Kalman filter algorithm.Then,the short-circuit balanced topology and its control strategies are proposed.Taking SOC as the balance variable,the alternate recombination between different batteries is realized through turning on and off the relays to form a battery group in series,and charging and discharging experiments of the battery group are conducted to achieve the balance of SOC of all batteries.The simulations of corresponding charge and discharge are conducted to verify the feasibility of this system.The simulation results show that under normal working conditions,the inconsistency of single cells during charging and discharging is controlled within 1.556%;under fault working conditions,the battery pack can still be selectively discharged until the battery pack does not meet the discharge requirements.Finally,an experimental platform of alternate balance control system is built,and the experiment of voltage collection,SOC estimation and charging and discharging experiments under different working conditions are carried out.The experiment results show that the trend of change between the value of collected voltage and estimated SOC by the system are the same with the real value,which shows the methods adopted are feasible.In the discharge experiment,the delay time is shortened from 20s to 10s,the inconsistency was reduced to 1.27%under normal operating conditions,which can obviously improve the balance effect of this system.The experimental results are consistent with the simulation results,proving the effectiveness of the system proposed for battery balancing control.