Experimental Study And Simulation Analysis Of Electric Vehicle Thermal Management System Based On Heat Pump

As a kind of new energy vehicles,the electric vehicle with the characters of no emission pollution,high efficiency,and low noise,is the ideal development direction of new energy vehicles in the future.However,cabin thermal comfort and heat dissipation in power modules are two key factors that restrict the electric vehicle development.Compared with traditional internal combustion vehicles,there is no engine waste heat for electric vehicle to heat the cabin.In particular,using PTC(Positive Temperature Coefficient,PTC)heater to achieve cabin thermal comfort will seriously affect the driving range of electric vehicle.During the vehicle operation process,the electric motor and the battery would generate large quantity of waste heat.Without the reasonable cooling system,the efficiency and the driving range would be reduced when power modules are out of the proper temperature range.Therefore,it is necessary to develop the thermal management system combining heat pump system and power module cooling system.The thermal management system that can not only satisfy the cabin thermal comfort but also guarantee the power module operating temperature range is an inevitable trend in the electric vehicle development.The thermal management system based on heat pump system,motor cooling system and battery cooling system for electric vehicle was proposed in this thesis.The experimental setup was built for the designed system.Through the combination of experimental study and theoretical research,the performance under different operation conditions for electric vehicle thermal management system was analyzed.The main research results and contents of this thesis are as follows:1.An electric vehicle thermal management system based on heat pump was designed,which included motor cooling module and battery cooling module.The experimental setup was built up,which can test the system performance with the variation of compressor speed,environmental temperature,air speed,electronic expansion valve and different waste heat.2.The refrigerant charge experiment was conducted and the optimum refrigerant charge was determined as 400 g.The performance of thermal management system was tested under different working conditions.The heating performance was compared with air source heat pump system.The results showed that the electric vehicle thermal management system can achieve best COP(Coefficient of Performance,COP)with “the optimum superheat”.As for the cooling mode,the range of “the optimum superheat” was 21~28℃,while the range of “the optimum superheat” was 5~10℃ for heating mode.The vehicle speed had a more obvious influence on system cooling performance.The higher the vehicle speed was,the lower the condensing pressure was,which was in favor of cooling capacity increase.The cooling COP was reduced by 16.1%~27.5% when the battery cooling circuit was turned on.The thermal management system can keep the battery safety working temperature range(24.1℃~38.8℃).Compared with the air source heat pump system,when the environmental temperature was-7℃,the heating capacity was increased by 22.1%~27.5% and COP was increased by 19%~21.3% with the waste heat of 500 W.The heating capacity was increased by 47%~50.5% and COP was increased by 26.6%~29.3% with the waste heat of 1000 W.3.The precision of three classic flow boiling heat transfer correlations for mini channel,namely on behalf of superposition model(B_Correlation),selection model(KB_Correlation)and fitting model(SM_Correlation)were analyzed.Considering the predication precision,a new correlation was proposed.The mean relative error was 7.9%,which laid a foundation for the simulation model of the mini channel parallel flow evaporator in electric vehicles.4.The thermal management system simulation model was developed based on the combination of ANN(Artificial Neural Network,ANN)model and theoretical model.The simulation model was validated with experimental data,which gave the mean relative error of 8.5%,10.3% and 7.6% in cooling/heating capacity,power consumption and COP prediction,respectively.The results demonstrated that the model can predict the thermal management system with high accuracy.5.The secondary development of vehicle simulation software ADVISOR(AdvanceD VehIcle SimulatOR,ADVISOR)was conducted.To fulfil the joint simulation,the thermal management system simulation model and fuzzy control module for electric vehicle were embedded in ADVISOR.Under the UDDS(Urban Dynamometer Driving Schedule,UDDS)driving cycle,the effect of the cooling/heating motor heat recovery on the performance of thermal management system was analyzed in this thesis.The economic indexes were compared under different working modes.The results demonstrated that the thermal management system can provide suitable temperature for power units.For summer cooling mode,electric vehicle hundred kilometer energy consumption was improved by 19.1%~25.3 compared with none air conditioning and the driving range was reduced by 15.5%~28.7%.The hundred kilometer energy consumption was increased by 5.5%~12.3% when the battery cooling turned on and the driving range was decreased by 6.5%~11.3% accordingly.The cooling COP was decreased by 16%~23.8%.Particularly,for winter heating mode,compared with the PTC heater,the electric vehicles hundred kilometer energy consumption can be reduced as much as 16.4%~23.7%,and the driving range can be increased by 19.6%~31.1% with the thermal management system.The heating COP of thermal management system was improved by 33.8%~48.6% compared with single air source heat pump system.