Study On Equalization Topology And Equalization Strategy Of Electric Vehicle Series Battery Pack

In recent years,facing the increasingly serious environmental pollution and energy crisis,electric vehicle industry has become one of the key strategic emerging industries in China.However,due to the series battery pack inconsistency problem of electric vehicles,the performance of electric vehicles is seriously restricted.As an effective way to solve the series battery pack inconsistency problem,the equalization topology and equalization control strategy have been developed as one of the key technologies for automotive power batteries.In this paper,we take series-connected battery pack as the research object and conduct an in-depth study from two aspects of equalization topology and equalization control strategy.First,to address the shortcomings of the traditional DC-DC equalization topology with long equalization path and slow equalization speed,this paper proposes a multi-interleaved symmetric equalization topology based on Cuk circuit,and investigates the working principle and structural characteristics.It is suitable for the case where the number of single cells in a series battery pack is small.For the case of a large number of single cells in a series battery pack,this paper improves the topology and proposes an improved multi-interleaved symmetric equalization topology,which complements each other and can meet the equalization needs of different numbers of cells in a wide range.Then,the proposed equalization topology is combined with the correspondence between the equalization current and the duty cycle of the control signal based on the analysis of the working principle,and the improved most value method equalization control strategy and the improved mean value method equalization control strategy are proposed.The two equalization strategies are used in the charging and discharging operation state and the static operation state of the series-connected battery pack,respectively,to solve the "one high,many low","one low,many high" and "many high,many low" inconsistencies.In addition,the MATLAB/Simulink simulation platform was used to build and complete the comparative simulation of the equalization system.According to the simulation results,it can be seen that the charge state of the battery pack changes more in the same time during charging or discharging,and the equalization effect is better.In the static state,the time for the battery pack to reach the same equalization effect is reduced by 28% and 51.2%,42% and 60.3%,respectively,with faster equalization.Finally,the experimental platform of the equalization system is built using DSP as the main controller,and the improved multi-interleaved symmetric equalization topology and equalization strategy are experimentally verified using the experimental platform.The experimental results demonstrate that the proposed equalization topology and equalization control strategy can improve the inconsistency of the battery pack under different operating conditions and effectively improve the energy utilization of the battery pack.