Improvement Of The Heating Performances Of AC/HP System For Electric Vehicle Under Low Temperature

Electric vehicle has become the focus of modern automotive industry,the main obstacles in promoting electric vehicle are the limited battery capacity and driving mileage.The application of the AC/HP(Air Conditioning/Heat Pump)system will greatly reduce the electric vehicle energy consumption,therefore,it is of great significance to the development of electric vehicles.Aimed to resolve the problems of the performance decline and the insufficient heating capacity under low ambient temperature,the operation characteristics and influence factors of the electric vehicle AC/HP system were comprehensively studied by means of experiment and simulation,respectively.The effective measures to improve the heating performance of the AC/HP system were explored in the ambient temperature range of-15℃~0.The main works in this paper are as follows:Applications of electric vehicle and its air conditioning system were reviewed and the structure characteristics,working principle and main parameters of the AC/HP system were investigated.Working fluids in the electric vehicle AC/HP system were determined(R134a、R407C and R410 A,respectively)considering the thermophysical properties,system operating characteristics,safety and other factors.Based on the ideal vapor-compression cycle,impacts of the refrigerants,condensation temperature,evaporation temperature,evaporator superheat degree and condenser subcooled degree on the heating performance of the AC/HP system were quantitatively analized under low ambient temperature.An electric vehicle AC/HP system with the functions of cooling/heating was developed,and the system heating performances under low ambient temperature were experimentally studied in an environmental chamber.Influences of the ambient temperature,compressor speed,displacement and refrigerant types on the AC/HP system and its main components were discussed and various parameters were regulated to improve the system heating capacity.On the basis of the above experiments,simulation model of the AC/HP system was established with AMESim,effects of the compressor speed,ambient temperature,air conditions of heat exchanger inlet,the system structure parameters(including the compressor displacement,hydraulic diameter of the heat exchanger pipe,the throttle cross-sectional area,etc.),appended condenser and refrigerant properties on the system heating performance under low temperature were quantitatively studied and the effective measures to improve the heating capacity were determined.The AC/HP system heating process under low temperature was also studied by using the method of exergy analysis.Variations of the system exergy efficiency and exergy loss of the main components were comprehensively analized,energy utilization levels of the AC/HP system were quantitatively evaluated and the inefficient components of the system were located.These works were helpful for the improvement of system structure and economic performance.Based on the co-simulation of AMESim and Simulink,the compressor speed and the throttle opening were regulated using the method of fuzzy control,respectively.In this way the heating capacity(electric vehicle cabin temperature)and the mass flow rate of the AC/HP system were effectively controlled.A fuzzy throttling control strategy aimed at condenser subcooled degree was proposed in the paper,the system heating capacity was increased by improving the condenser heat exchange.