Research On AC Internal Heating Device Of Lithium-ion Battery

Lithium-ion batteries are widely used in electric vehicles because of the advantages such as high energy density and long life.However,the performance of lithium-ion batteries will be seriously degraded in low temperature environments.Therefore,the use of lithium-ion batteries in low-temperature environments must heat the batteries firstly.Compared with external heating strategy,internal heating is more flexible,with higher heating uniformity and heating efficiency.However,the existing AC internal heating device is generally a bulky and costly bipolar power supply,which reduces the engineering applicability of low-temperature heating.In view of the above problems,this paper carries out the design of the AC internal heating device.Two heating topologies without external power supply are proposed and designed.Based on the two heating topologies,an AC internal heating strategy based on optimal frequency is proposed.The specific research work is as follows:Firstly,using power electronics topology instead of bipolar power supply,two AC internal heating topologies without external power supply are proposed.In this paper,the modal analysis of the two heating topologies is carried out,and the output peak current and current frequency of the two heating topologies are derived.Secondly,in order to obtain the impedance characteristics of the experimental battery,a temperature-coupled PNGV model was used to model the experimental battery.This paper obtains the open circuit potential characteristics of the experimental battery at different temperatures and uses function to fit open circuit potential curve.Furthermore,the impedance characteristics of the experimental battery at different temperatures and different SOC are obtained by parameter identification.Next,combining the above two parts,the design of the AC internal heating device for the lithium-ion battery is carried out.The optimal heating current frequency based on the two heating topologies is derived respectively,and then the variable frequency heating strategy based on the optimal frequency is proposed.Two heating topologies were designed,including topological parameter index design and hardware circuit design.Finally,the correctness of the previous design and the effectiveness of the heating device are verified.A lithium-ion battery internal heating platform is built to verify the electrical effectiveness of the full-cycle Buck-Boost mutual heating topology.An experimental battery thermal resistance model is established,and the model is verified by combining the measured heating data of the mutual heating topology.Based on the experimental battery thermal resistance model,the heating effectiveness of the two heating topologies and the effectiveness of the variable frequency heating strategy based on the optimal heating frequency are verified.