Research On Simulation Of Carbon Dioxide Heat Pump Air Conditioner Heating Performance And Control Strategy For Electric Vehicles

With the development of the society,the demand for the good environment is increasing and the production of electric vehicles is increasing.At present,the PTC（positive temperature coefficient）is widely used in the electric vehicle air conditioning system,which leads to a large reduction in the range of the endurance.The heat pump air conditioning system（HPACs）is studied to reduce the energy consumption.Firstly,a heat pump air conditioning experimental system was designed to study the effects of R134a refrigerant’s mass charge on the HPACs under heating condition.The experimental results showed that the outlet pressure and temperature of the compressor increased when the mass charge increased,and the optimum mass charge of R134a was600g.The heating performance of R407C was the best among the R407C,R410A and R134a when the environmental temperature was below 10℃.The simulation model of HPACs was established by using AMESim software,and the accuracy of the model was checked by test data.A CO₂ HPACs was proposed,and a simulation model ofCO₂ HPACs was established.The results of the heat pump air conditioning model simulation study showed that the compressor outlet pressure increased with the increase of the compressor speed and then stabilized.The system transitioned from subcritical conditions to transcritical conditions.Under transcritical conditions,the maximum pressure of the system was 7.5MPa.Under subcritical conditions,there was an optimal high-pressure side pressure in the CO₂ HPACs,and the system can be operated under the optimal high-pressure side pressure by adjusting the cross-sectional area of the throttling tube.As the charge volume increased,the outlet pressure of compressor,the power consumption of compressor,and heating capacity increased firstly and then stabilized.The optimal mass charge is about400g.Comparing the structural parameters and performance parameters ofCO₂ and R134a HPACs,the results showed that the volume ofCO₂ HPACs was as large as the R134a system and did not occupy too much space in the vehicle.The heat production of theCO₂HPACs is far greater than the R134a system,and the COP of the two systems was not quitedifferent.In terms of heating,theCO₂ HPACs had a great advantage over the R134a system.Finally,a fuzzy controller was designed with the temperature difference and temperature difference rate as input and PWM（pulse width modulation）as the output.An electric vehicle HPACs with automatic control function was established based on the Simulink and AMESim.The simulation results showed that the fuzzy controller had good control effect and good response to external disturbances.At the same time,the heat pump system had good heating performance.