Research On Key Issues Of Dynamic Optimum Design Of Moving-magnet-iron Linear Compressor For Refrigerator

To meet the needs of energy saving and environmental protection, the linear compressor driven by linear oscillatory actuator becomes a current focus in research of next generation of compressor for household refrigerator. In accordance with the requirements and difficulties in design, various modern design theories and methods are adopted in the study of design and optimization of moving-magnet-iron linear compressor.Firstly, for the sake of easy manufacturing and reducing air gap reluctance, the structure of Redlich type linear oscillatory actuator is changed from typical moving magnet type to moving magnet-iron type. Based on the theory of dynamical analysis in electromechanical coupling system, the design scheme of dynamic optimum design of linear compressor is established, and the mathematical models are built according to the needs of research. In order to analyse the static characteristics of Redlich type linear oscillatory actuator, the magnetic circuit model and the3D finite element model in electromagnetic field are set up. In order to analyse the dynamic characteristics of linear compressor, the forced mechanism vibration model with double mass and double degree of freedom is established according to the compressor’s installment, and coupled with circuit system, the electromechanical coupling model is established. In order to optimize the structure of linear compressor, two kinds of global optimization model are established, which minimize the total cost of compressor and the volumes of parts respectively.The static characteristics of linear oscillatory actuator are analyzed qualitatively and quantitatively. By means of equivalent magnetic circuit method, some parameters, such as the flux linkage, electromagnetic force and inductor, are expressed as the functions of input current, moving part’s displacement and the linear oscillatory actuator’s structural parameters and material parameters, and then the static characteristics are qualitatively studied. By using3D finite element analysis, the electromagnetic field in actuator is analyzed, the flux linkage and electromagnetic force are quantitatively evaluated, and the results deduced by magnetic circuit method are corrected.The excitation loss proof of Nd-Fe-B permanent magnet in Redlich type linear oscillatory actuator in the condttioa of high temperature and alternating magnetic field is studied. The maximal demagnetizing working point of permanent magnet material is calculated, and the position of knee point at working temperature is deduced from the magnetic parameters at normal temperature, and then the determining formula of excitation loss is given, which is a necessary security constraint related to the optimization of linear compressor.By means of simulation approach combined with state-equation method and finite element analysis, the dynamic characteristics of linear compressor are studied. Various compressor running conditions are simulated, such as no load, load and striking cylinder. The voltage characteristic curves and frequency characteristic curves are drawn, and then the compressor’s performance and dynamic characteristics can be forecasted. Based on the frequency characteristic curves, the basic rules of improving performance by adjusting voltage frequency are determined. The influences of spring stiffness, mover’s quality, cylinder’s diameter and balance placement on compressor’s performance are discussed, and the references for structural optimization and improving performance are provided.According to needs of working performance and manufacturing cost, the structural optimization of linear compressor is carried out by using various modern design theories and methods. By means of dynamical analysis, the optimization model of linear oscillatory actuator is solved, and then the volumes of magnet and coil are minimized. By means of finite element analysis in electromagnetic field, the structure of iron core is optimized, and some suggests for material selection of permanent magnet bush are put forward. By means of structural finite element analysis and modal analysis, the spring support’s mechanical performance is analyzed, and the structure of spring support is optimized according to the analysis results.Finally, a prototype of linear compressor is made, and the experimental system of linear compressor is set up. With air as working fluid, the prototype’s performance is tested in different conditions, such as no load, load and with series capacitors. The results of experiment show that the specific power is within7～9kW/(m3/min) at the exhaust pressure of6bar, witch means that the compressor has good performance in energy consumption. The equivalent damping coefficient, which is a important dynamic parameter of the vibration model, is identified. Two different grade of Nd-Fe-B permanent magnet material are tested by experiment of excitation loss.