Design Of Charging And Management System For Energy Storage Lithium Battery

In recent years,lithium battery with its high energy density,long service life,low self-discharge rate,which is gradually replacing the battery,is widely used in electric vehicles,aerospace and other high-power energy storage field.In the charging process of energy-storage lithium battery,not only the charging speed and accuracy should be achieved,but also the efficiency of the charger is highly required.In addition,the series lithium battery module is prone to the problem of single inconsistent,need to rely on external circuit to achieve balance.In order to solve these problems,this paper designs a two-stage structure lithium battery charger for a bridgeless PFC circuit +LLC resonant converter,and a balance controller based on flyback transformer.The specific contents of the paper are as follows:Firstly,aiming at the complex nonlinear time-varying system such as lithium battery,the Thevenin equivalent circuit model was used to model the lithium battery,providing a basis for the design of the subsequent battery charging and management system.On the basis of studying the voltage,temperature and OCV-SOC curve of lithium battery,the model parameters were identified based on the recursive least square method with forgetting factor.After 57 iterations,the identified parameters could meet the accuracy requirements.Secondly,in order to reduce the switching loss in the charging process and improve the overall efficiency of the charger,a two-stage structure is adopted to design the charger for lithium battery.Compared with the traditional Boost-PFC circuit,the former AC/DC circuit is designed with the totem pole type bridgeless PFC circuit with lower loss,and the component parameters are calculated.The LLC resonant converter with good isolation,lower loss and wide output range is selected as the topological structure of the back-stage DC/DC circuit.Based on the study of the principle of the LLC circuit and the steady-state voltage gain,the conditions to realize the zero voltage conduction of the switch tube are analyzed,and the resonant element parameters are calculated.Then,according to the traditional CC-CV charging control strategy of lithium battery,the controller design of the front circuit and the rear circuit of the charger is carried out respectively.The working duty cycle ratio of PFC circuit is adjusted by single cycle control mode.The working frequency of LLC circuit is adjusted by PFM control mode,and the compensator is designed by PI network.Through the simulation experiment,the dynamic characteristic of the output is analyzed,and the reliability and rationality of the control method are verified.Finally,aiming at the voltage inconsistency phenomenon in the charging and discharging cycle of lithium battery module,the reason of this phenomenon is analyzed,and the flyback transformer with large equalization current and high equalization efficiency is selected to design the equalizer,and the equalization effect is verified by the simulation software.In addition,the module controller in the management system is designed,and the hardware circuit and software program are designed respectively for the voltage of single lithium battery,the voltage and current state of charger and the temperature of battery module,and the effectiveness and accuracy are verified by the simulation software.