Research On The Reduction Method Of Thermal Model And Thermal Management Strategy Of Lithium-ion Battery Pack

Lithium-ion batteries are widely used because of a series of excellent properties.The performance,life span and safety of lithium-ion battery are closely related to the temperature of battery.The Battery Thermal Management System(BTMS)is needed to ensure the battery works within the proper temperature range in order to make full use of the battery's performance under the premise of thermal safety.Because the battery system is a complex distributed parameter systems,the change of temperature has a great deal of hysteresis.The battery system for temperature control is the key to prevent the temperature overshoot,which requires a strategy for temperature control of the battery to be compatible with the thermal model of the battery system,and the existing main problems of battery system thermal model is difficult to both accuracy and computational efficiency.Aiming at the above problems,this paper establishes an efficient battery thermal model,and based on this model,develops a temperature control strategy,and conducts experimental research in the simulation environment.Firstly,aiming at the problem of modal extraction for thermal model reduction of air-cooled battery system.By analyzing the electrochemical characteristics,heat generation characteristics and heat transfer characteristics of lithium ion battery,the related electrochemical parameters were identified by excitation response method,and the finite element simulation model of air-cooled battery system was established in COMSOL.Then,the finite element model was simulated under different working conditions,and the simulation results of temperature field and flow field were extracted to form the data space of the sample.In this sample space,POD modes of temperature field and flow field were extracted respectively by using eigenorthogonal decomposition(POD),and relevant modes with large feature proportion were screened.Secondly,aiming at the order reduction problem of the thermal model of air-cooled battery system,a battery thermal model which can give both accuracy and computational efficiency is established.Based on the POD mode of extracted flow field and temperature field,combined with the Galerkin projection,the Reduced Order Thermal Model(ROTM)of the air-cooled battery system is obtained by coupling the flow field and temperature field with the heat transfer coefficient.By comparing with the simulation results of the finite element model,it is shown that the reduced order thermal model has high precision and computational efficiency.Finally,aiming at the temperature control problem of battery system,the temperature control strategy is developed based on the reduced order thermal model.First of all,based on the principle of model predictive control,the overall scheme of temperature control of air-cooled battery system was developed based on the reduced order thermal model.Secondly,the reduced order thermal model oriented to temperature prediction control was derived,and the objective optimization function and parameter constraint conditions of temperature control were formulated,and the COMSOL and MATLAB joint simulation experiment platform was built.Finally,based on the platform,the temperature control effect of the air-cooled battery system is simulated under different control parameters,that is,the length of the predicted time domain is different from that of the control time domain.And compared with the simulation results of traditional PID control strategy.The experimental results show that the temperature control scheme designed in this paper can make the air cooled battery system work in a stable temperature range,and also can inhibit the system temperature overshoot.