Research And Implementation Of Active Equalization System For Ladder Utilization Of Lithium Ion Power Battery

With the popularization of pure electric vehicles,the disposal of decommissioned power batteries on electric vehicles has now become a research hotspot.However,for a echelon used battery pack,the inconsistency among the battery cells is much more serious than the new one.As a result,the highest priority is that the balanced system should be used to eliminate the inconsistency and increase the life of the battery cells.In this paper,after the grouping of the battery packs,a centralized single-core transformer is selected as the hardware topology,the hardware circuit of active balancing system which echelon used by lithium ion power battery is designed.Then based on terminal voltage,a three-phase bidirectional equilibrium strategy is proposed.Finally,the software design of the system is completed by the automatic generation of MATLAB code and the feasibility of the system is finally verified by bench experiments.This article concretely completes the following works:First of all,according to the the battery voltage,capacity,ohmic resistance and SOH value these four characteristics from national standard,analyzing experiment is carried out to get the characteristics of the lithium ion power battery which echelon used.According to the experimental results,the experimental battery pack was grouped and the grouped battery cells were regrouped according to the rules.Secondly,in this paper after analyzing and comparing the mainstream active equalized hardware topology,following aspects are considered as reference rules :equalization current size,balanced efficiency,equilibrium speed,control complexity,security,PCB size,and cost.So that the centralized single-core transformer-based hardware topology is chosen as the core to design a hardware circuit based on Freescale’s MC9S12XET256 as the main control chip.According to the designed schematic diagram,the PCB board is finally generated and tested.Again,this paper uses the terminal voltage of the battery cell as the equilibrium parameter,extracts and corrects the parameters,and determines the final equilibrium threshold based on the experiment.Based on the threshold,a three-phase balanced bidirectional equilibrium active equilibrium strategy is proposed.The Simulink of MATLAB is used to complete the establishment the models of equilibrium strategy,hardware and communication model.Based on the actual data collected,the correctness of the balance strategy was verified.Finally,complete the software integration according to the balance model with the driver code.After the code is generated automatically,it is downloaded to the hardware circuit.The physical verification of the system was carried out after setting up an experimental platform consisting of an equilibrium system,an acquisition system,a host computer,and a battery pack.Experiments show that the equalization system can complete the balance of the system.After the equalization,the pressure difference between the battery cells in the battery pack can be reduced to less than 100 mV.The average voltage difference between the battery cells and the battery pack can be reduced to less than 40 mV.The current during balancing work is maintained at about 3A.