Balanced Battery Output Based On SOC And Redundant Cells Management

Lithium-ion battery has become the main choice for power batteries as its excellent performance.Power batteries need to determine their continue voyage course through the state of charge during operation.Because the state of charge of the battery is affected by various parameters,the accuracy of the existing estimation algorithms is not accurate enogh.So this paper proposes an improved algorithm to estimate the state of charge of the battery to improve the estimation accuracy.In actual application,the power battery pack is made up of multiple cells in series.Due to the differences in the parameters of the cells,the capacity of the battery pack is inconsistent.Therefore,based on a redundant equalization circuit,this paper improves the inconsistency of the battery pack to extend the discharge time.The specific research content is as follows:Firstly,the second-order RC(RC,Resistor-Capacitance Circuit)is used as the battery estimation model,and the relevant parameters of the battery model is identified.In order to estimate the state of charge of the battery,the existing estimation methods are introduced in detail.Aiming at the problem of low estimation accuracy of the existing algorithms,an improved algorithm using parameter iteration is proposed.In order to verify the superiority of the proposed improved algorithm,the experimental data of constant current charge and discharge were used to compare the existing estimation method and the proposed improved algorithm.Then,the improved algorithm was tested based on FUDS(FUDS,Federal Urban Driving Schedule)conditions.The experimental results show that the error of the improved algorithm is less than 3.5%,thus the correctness of the proposed algorithm is verified.Secondly,under large dispersion condition of the battery pack,analysis and simulation of capacitance type balance,inductance type balance,transformer type balance,redundant type balance is implemented,the results show that the redundant balance circuit has better balance performance.However,the switching times are also large,and the discharge time is shortened when the dispersion is further aggravated.In view of the above problems,this paper conducts in-depth research from the equilibrium control strategy and the topology.For the problem of large switching times,the balance strategy is improved,and the control strategy of the staged energy control method is proposed.When the dispersion of the battery pack is further aggravated,in order tosolve the issue that the redundant equalization circuit can't fully equalize the battery pack and cause the discharge time to become shorter,the balance topology is improved,and a redundant equalization with a DC-DC converter is proposed,to extend the discharge time.For verification,a simulation model is built.Finally,in order to verify the balance control strategy and the improved redundant balance circuit proposed in this paper,a corresponding experimental platform is built,and experiments are carried out under the premise of ensuring that the battery's initial state and load are consistent.Through the analysis of the experimental data,it can be seen that the staged energy control method can effectively reduce the number of switching times and improve the system stability.Meanwhile,the improved redundant balance structure can increase the discharge time by 9.5%.The experimental results verify the feasibility and accuracy of the proposed scheme.