Research On Power Supply And Equalization Technology Of New Lithium-ion Battery System

Due to the different charging efficiency,discharging efficiency and decay rates of lithium-ion battery,the SOC(State of Charge)between cells may be unbalanced.Therefore,it is necessary to add a battery equalizer on the battery pack.The traditional passive equalization based on energy dissipation can not meet the safety and rapidity of the battery pack.Finding a better battery equalization method has become an urgent need in the field of battery energy storage.Aiming at the characteristics of lithium-ion battery system,this thesis designed a new lithium-ion battery system architecture to supply power and equalization,and proposed a control algorithm for this balanced structure to achieve rapid balance between cells.Aiming at the problem of slow balance and poor scalability of battery equalization system,this thesis proposed a modular balanced architecture based on energy control.Compared with the traditional active balanced structure based on energy transfer principle,the active balanced architecture based on energy control principle improves the balance speed and scalability of battery equalization system.In order to achieve the stability of battery equalization system,this thesis established a mathematical model.This thesis analyzed the connect characteristics of the cell equalization system,tested cycle HPPC(Hybrid Pulse Power Characteristic)for lithium-ion battery,and established the fist-order Thevenin circuit model of lithium-ion battery and the first-order small signal model of the equalization circuit respectively.The battery system model examined the stability of the system.Aiming at the active balance circuit structure based on energy control principle,this thesis proposed a two-stage modular balanced strategy.The first stage is the equalization algorithm of battery system,which adjusts the reference value of droop resistance and port voltage through the battery module SOC to realize the SOC balance among the modules.The second stage is the equalization algorithm of the battery module.Under the charging modes and the discharging modes,the energy distribution of the output port and the input port are adjusted to achieve the SOC balance among the cells.The two-stage balalcing strategy not only realizes the stable control of the battery system,but also realizes the rapid battery equalization between the battery.This thesis carried out the time-domain simulation of battery equalization system in MATLAB simulation software,build a hardware experimental platform of battery equalization system,and tested the circuit experiment.The simulation and experimental results show that this equalization method is feasible based on energy control principle,and compared with other equalization methods,this methods has a faster equalization rate.