Simulation And Performance Control Analysis Of The Transcritical CO₂ Automotive Air Conditioning System

With the development of society and increasing daily life standard, the utilization of automobile becomes more and more widely. Security, comfort and economy efficiency are important evaluation indicators of the vehicle performance.On the basic premise of meeting comfort, the eliminating frost and fog function of automotive air condition could improve security; the researches on reasonable matching and optimization were benefit for economy efficiency. Therefore, the attention on automotive air condition was increasing as time goes by. With the approaching of deadline for the use of Freon products, researchers'attentions were transferred to the development of refrigeration system with environmental protection. Being as a kind of refrigerant, CO₂ became a major research focus on automotive air condition. The research on transcritical CO₂ automotive air conditioning system in this paper was necessary, and it also could provide certain reference value for future development of excellent performance automotive air conditioning system and research on other refrigeration systems.Based on thermodynamics method energy analysis, exergy analysis and entropy analysis about refrigeration cycle of transcritical CO₂ were proceeded in this paper. In order to obtain exergy loss distribution exergy loss of each component was derived in detail. A result was found in this research that in some cases exergy loss of gas cooler is most and thus gas cooler has greater energy-saving space. Under the guidance of the above-mentioned theory, using AMESim Software, physical model and semi-theoretical model of the transcritical CO₂ automotive air conditioning system was established and simulated. Moreover, the factors of influencing refrigeration were analyzed thoroughly. In virtue of capacity of AMESim Software, which could directly observe the changes of parts structure parameters and reflect the influence of working conditions on system performance, the purposes of model validation and system performance analysis were achieved. Comparative analysis between the model simulation data and the experimental data of literature showed that the transcritical CO₂ automotive air conditioning system model established in this paper is reasonable; Not only it can be used in parameters predicting and performance analysis on each steady state condition, but also response system dynamic performance more accurately. It provided guarantee for designing controller of tracking control target. Model analysis was proceeded in a variety of conditions. Through these analyses, the influence of three parameters, which contained gas cooler air inlet temperature, evaporator air inlet temperature and compressor speed on system characteristics was analyzed thoroughly. Based on the previous model analysis, according to relationship between the optimum high pressure and the maximum COP and relationship between the optimum high pressure and the ambient temperature, combining with experimental results discussed in the literature about influence of high pressure on COP in a variety of conditions, working conditions, control target and others of controller designed in this paper were put forward. In this study, influence of changes in ambient temperature on the optimum high pressure under certain compressor speed conditions was taken as the interference on system performance; high pressure was controlled by the controller to track its optimum value for ensuring the best performance of overall system.Both traditional PID controller and fuzzy PID controller designed in this paper could control high pressure to track its optimum value for achieving the purpose of system control in the case of disturbance. Choices of parameter ranges of proportional, integral and differential in fuzzy controller were based on parameters calibration of the traditional PID controller. Through the performance and the effects comparison of the two controllers, a conclusion was carried out that designing fuzzy PID controller based on traditional PID controller can improve the efficiency of parameters calibration of the fuzzy controller; compared with the traditional controller, fuzzy PID controller not only has great advantage in some control performance indicators, such as overshoot, settling time etc., but also can automatically adjust the parameters online and adapt to various working conditions of system.