Research On Active Balancing Strategy For Electric Vehicle’s Power Battery Package

Multistage power batteries are often used in electric vehicles to supply the energy.However,due to the temperature and manufacturing process of single batteries,the battery’s capacity will become inconsistent,which leads to some problems such as the overcharge and the over-discharge of batteries.Then,a threat to the performance and security of electric vehicles will be posed because of these problems.In order to ensure the power batteries can work safely and effectively,it is necessary to add the equalization circuit to it and match the corresponding control strategy.Nevertheless,existing balancing strategies generally have the defects of slow balancing speed and high energy consumption.Based on the above problems,the electric vehicle power battery pack is chosen as the research object,and the research will focus on the balancing strategy of power battery.The main research contents are as follows:(1)The lithium-ion battery used in electric vehicles is chosen as the research object,and the basic working principle and the internal characteristics are explored in depth.In addition,the overcharge and over-discharge process of lithium-ion batteries is measured through the battery testing equipment.Furthermore,the mechanism of lithium-ion battery’s overcharge and over-discharge is analyzed,and the harmfulness of battery pack’s imbalance is discussed.(2)The structure of electric vehicle battery pack is analyzed,and the necessity of balance under different connection modes is illustrated.After that,the inconsistency factors and unbalanced state of the battery pack are discussed,and the mathematical model of the unbalanced degree of the battery pack is established.Moreover,the dissipative passive balancing strategy and the non-dissipative active balancing strategy are analyzed and several common balancing strategies of power battery pack are introduced in detail.Then,the advantages and disadvantages of various methods are compared to seek the improvement space of the control strategy and topology structure in the existing active balancing scheme.(3)Because of the problems of low transfer efficiency,long transfer time and complicated circuit of current strategy,a new active balancing strategy called two-circuit interleaved parallel architecture for battery charge equalization(TIPAE)is proposed,which is based on the inductive parallel architecture equalization strategy(PAE)and the two-circuit interleaved architecture equalization strategy(TIAE).Besides,the related contents such as thetopology structure,control strategy and circuit element parameters are studied and calculated.The theory shows that the balancing scheme can effectively improve the balancing efficiency of battery packs.(4)The simulation circuit is built through the Simscape library in the Simulink platform,the control algorithm is written,and various balancing schemes are simulated.After that,the simulation tests of various balancing schemes are carried out under three conditions include idle,charging and discharging.The simulation results show that the new balancing strategy proposed in this paper has higher speed and lower energy loss than the traditional balancing strategy,and can effectively reduce the impact on battery health and safe operation of electric vehicles due to the inconsistency of the battery series.