Research On Equalization Control Strategy And System Implementation Based On SOC For Battery Pack

With the continuous development of the world economy,the world's car ownership continues to increase,leading to further environmental pollution and energy crisis,so electric vehicles have become a research hotspot.The research focus of electric vehicles is on power batteries,and the power battery management system needs to provide a good power source for electric vehicles.The battery cells currently produced cannot meet the voltage and power requirements of electric vehicles.Therefore,a large number of cells are required to be connected in series and parallel to provide energy for electric vehicles,so that inconsistencies of cells will occur,affecting the capacity utilization of the battery pack.and the driving range of pure electric vehicles.Therefore,this paper focuses on the battery's inconsistency in battery cell equalization control research.Firstly,the battery production and later use are introduced,and the influencing factors of lithium-ion battery inconsistency are analyzed.The solution to the inconsistency between the monomers is described,and the importance of the equalization control system to improve the inconsistency is emphasized.Finally,the advantages and disadvantages of three equalization variables of open circuit voltage,battery capacity and state of charge(SOC)for battery equalization control are analyzed.Finally,SOC is selected as the control variable of battery pack equalization control system.Then,the metrics for the design of the battery equalization control circuit are introduced.According to the design standard of the equalization circuit,a bidirectional non-dissipative equalization circuit based on power inductor is built.The equalization principle of the equalization circuit is analyzed and the equalization current is calculated.In order to speed up the battery pack equalization control and improve the consistency of the battery pack,a two-stage bidirectional non-dissipative equalization circuit model based on power inductor is built to realize the modular design of the battery equalization circuit.Second,battery SOC estimation is performed to provide an accurate equalization variable for equalization control.Since the battery SOC cannot be directly measured,battery SOC estimation is required.The accuracy of the battery model is the basis of battery SOC estimation.In order to improve the accuracy of the battery model,a second-order RC equivalent circuit model considering temperature is designed.The battery model parameters are identified by least squares method and in Matlab/Simulink environment.The simulation model was built to verify the accuracy of the second-order RC battery model considering temperature.After considering the capacity attenuation during battery use,it will affect the battery SOC estimation.Therefore,the extended Kalman filter algorithm is used to realize the SOC estimation considering battery capacity attenuation.Finally,the accuracy of SOC estimation is analyzed to ensure accurate balance for battery balance.Finally,in order to effectively achieve the balance between the cells in the battery pack,a model predictive controller is designed to perform the equalization control of the battery pack,and the time efficiency and energy efficiency of the experimental simulation results are compared with the simulation results based on the fuzzy logic control.The experimental results show that the proposed two-way bidirectional non-dissipative equalization circuit and the model-based predictive control equalization method can not only improve the inconsistency of the battery pack,but also effectively reduce the energy consumption and time.