| Due to the dual pressure of resources and the environment,more and more countries have begun to research and develop electric vehicles to replace traditional vehicles.Lithium-ion batteries are considered to be the best energy choice for electric vehicles.Lithium batteries generate a lot of heat when they are working.Too low or too high temperature will affect the capacity and life of the battery.It has the best performance at 25 ?-40 ?.Under some extreme conditions,the maximum temperature difference between the surface and the core may reach 10 ?,which will cause the core temperature to reach a critical point earlier than the surface temperature,and eventually lead to thermal runaway and even explosion.Therefore,it is necessary to design an efficient battery thermal management temperature control system to track and control the core temperature of the battery,which is of great significance for improving the performance of the battery and ensuring battery safety.This article is based on air-cooled heat dissipation.The main research is as follows:Firstly,a multi-state reduced-order thermal model(Reduced order model,ROM)based on air cooling was established.By analyzing the heat generation characteristics of the battery core,the heat transfer characteristics between the battery core and the surface,the surface and air,a cell is simplified to three temperature states: the battery core temperature,the battery surface temperature,and the air temperature according to Newton's cooling law and Newman's heat generation theory.A battery pack ROM whose internal resistance changes with temperature is established.Then,the relationship between battery internal resistance and temperature was obtained by HPPC(Hybrid Pulse Power Characteristic)internal resistance test experiment,and the thermal parameters were identified by forgetting least square method.In ANSYS,a CFD model of the battery pack is simulated based on the structure of the battery,heat generation and dissipation characteristics.Firstly,the reliability of the CFD model is verified by comparing with the experimental correlation,and it is proved that the temperature obtained in the CFD model can represent the actual measured temperature.Then,the effectiveness of battery pack ROM is verified under NEDC(New European Driving Cycle)and US06(High Speed/Load Transient Control Cycle).The experimental results show that the battery pack ROM established in this paper can accurately simulate the actual temperature change of the battery pack.In practice,the core temperature of the battery is an unmeasured quantity,so the core temperature needs to be estimated before designing the battery pack temperature control system.In this paper,a Kalman filter is used to estimate the core temperature of the battery pack.A backstepping sliding mode controller(BSMC)was designed to adjust the temperature of the inlet air to cool down the battery pack.The backstepping control is highly robust and can handle precise model control problems.Sliding mode control can suppress disturbances and is not very sensitive to parameter changes.The battery temperature control system is subject to external disturbance of the load current and the parameters such as battery internal resistance are time-varying.Therefore,the advantages of sliding mode control and backstepping control are combined here,and the core temperature of lithium-ion battery is tracked by using BSMC.Under NEDC and US06,the core temperature of the battery pack estimated using the Kalman filter is verified by the core temperature obtained from the CFD model.Then the validity of the BSMC was verified by joint simulation with ANSYS and MATLAB.Finally,the core temperature tracking effects of the PID controller and the BSMC are compared respectively.The results show that the BSMC has better tracking control effect and small tracking error,temperature fluctuates little and it can also achieve a good control effect without adjusting the parameters when changing the conditions.In this study,a battery pack ROM with time-varying internal resistance was established by analyzing the heat generation and heat transfer characteristics of the battery.The thermal parameters in the battery pack ROM were identified by forgetting least squares method,and the model accuracy was verified by comparing with the CFD model.Then,based on the characteristics of interference and time-varying parameters,a BMS was proposed.Finally,the effectiveness of the temperature controller was verified by the joint simulation of ANSYS and MATLAB. |
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