Modeling And Control Of Automobile Waste Heat Driven Ejector Refrigeration System

Ejector pump technology research has been a hundred years of history. The ejector is to improve the fluid pressure without the direct consumption of mechanical energy equipment.The low-grade waste heat can be used as a driving energy in the steam jet refrigeration. Its structure is simple and reliable. The low running costs and environmental friendliness are widely used. Today automotive air conditioning system is still the main compression refrigeration. Jet refrigeration air conditioning of automotive waste heat driven research is mainly in the experimental and theoretical research. Currently researches on jet refrigeration system focused on the ejector design, testing and designing refrigerant operating parameters,the opening degree of the expansion valve of the injection fluid is controlled, and etc. Few studies are in the control field. Based on the above situation, the main research work and conclusions of this thesis are as follows.In this thesis, steam jet refrigeration work process of energy conversion is in-depth analyzed. With water vapor as the refrigerant medium, conservation and heat transfer theory, a key component of jet ejector refrigeration system of one-dimensional model is established based on energy balance principle.The cooling performance of ejector refrigeration system is mainly affected by the change of enthalpy of working steam and injection steam. In this thesis by solving the data model,using MATLAB R2014 a as the identification tool, the refrigeration system with injection fluid pressure of ejector as the input and the outlet pressure of ejector as output, the transfer function is established.Because that the compression ratio, injection fluid pressure of ejector as the input and the outlet pressure of ejector as the output, reflects the ability of ejector and performance of the ejector system. Based on the data model and combined with the operation parameters, PID controller is applied to control the compression ratio by controlling the opening degree of the expansion valve of the injection fluid. Furthermore, simulation result shows that any output pressure value between the 0.3Mpa~0.8Mpa can be stably tracked.Results also indicated that by using conventional PID control can achieve good controleffect, the controller has the advantages of fast response, small overshoot and anti-interference ability. It is suitable for automotive air-conditioning control.