Research On Hierarchical Equilibrium Control Of Lithium-Iron Phosphate Power Battery Pack Based On SOC

With the rapid development of new energy vehicles,the number of power batteries has also shown a rapid growth trend in recent years.The power battery’s open circuit voltage,working voltage,and State of Charge(SOC)are inconsistent under the influence of manufacturing and later use.These inconsistencies will cause the endurance of new energy vehicles to decline and affect the user’s experience.The equilibrium control can solve the problem of inconsistent battery parameters,and it is also the key technology to improve the endurance of new energy vehicles.The research takes SOC as an equilibrium variable and conducts a series of studies on the equilibrium control of Ferrous lithium-iron phosphate power batteries.SOC estimation is an important factor affecting the power battery’s equilibrium control effect.In this research,a linear dynamic battery model is established with the help of moving window technology and a partial least square regression method to estimate the SOC of the battery.The results are compared with the Extended Kalman Filter(EKF)method based on the second-order RC equivalent model.The results show that the linear dynamic battery model can automatically update the parameters,effectively improve the online estimation accuracy and calculation efficiency of SOC,and provide accurate variables for the following research on the equilibrium control of power battery packs.Due to the inconsistency of the power battery pack,the battery may be overcharged and over-discharged in the working process,which will reduce the cycle life of the power battery.Aiming at these problems,this research takes SOC as the evaluation index of battery inconsistency and designs a layered equilibrium circuit based on energy storage inductance and a multi-winding transformer.This circuit can balance the series-connected power batteries and avoid overcharge and over-discharge.To verify the effectiveness of the circuit,the simulation models of hierarchical equilibrium circuits and traditional single-layer equilibrium circuits are built respectively.The results show that the hierarchical equilibrium circuit has improved the equilibrium accuracy and speed.To further improve the equilibrium effect of the hierarchical equilibrium circuit,the research uses an equilibrium method based on credibility reasoning,which represents the overall energy state of the battery pack through the credibility of the unbalanced power battery pack.In this research,the reliability reasoning method is compared with the traditional threshold method through the simulation platform,and the feasibility and effectiveness of the equilibrium method are verified under various working conditions.This research proves that the hierarchical equilibrium scheme based on reliability reasoning can improve the equilibrium speed and the consistency of the battery pack compared with the traditional threshold method on the MATLAB/Simulink and ADVISOR platform.This system reduces the influence of SOC value on the equilibrium control,which can not be measured directly,thus making the equilibrium effect of the battery more obvious.