The Key Technologies And Experimental Investigation On The High Capacity Moving-magnet Linear Compressor

With the background of the national project on the Large Camera for Survey, a high capacity linear compressor driven by the moving-magnet linear oscillating motor was designed and developed based on the performance requirement of the high temperature and large cooling capacity pulse tube cryocoolerin this dissertation. The involved key technologies of the linear compressor were introduced. The coupling characteristics of the prototype with a coaxial pulse tube cryocooler were obtained as a result of theoretical and experimental research.The characteristics of magnetic circuit in C-type linear oscillating motor were investigated by analytical model. The expressions of motor force and coil inductance were obtained in term of energy with structural parameters of the motor. Finite element simulations were performed on the static characteristics of the motor. The optimized specifications of critical components including permanent magnet, excitation coil and magnetic yokes were obtained. The transient operating characteristics of motor were verified under specific load condition. The loss mechanism of the motor was studied by experiments.The dynamic model of linear compressor was built and the characteristics of piston were analyzed theoretically. The oscillatory characteristics of mass-spring-damper system were discussed in various damping condition. The mechanical damping coefficient was measured by experiment. The motion characteristics of piston were analyzed under resonant and nonresonantconditions. The influences of materials, wire-cut lines and structural dimensions on the axial and radial stiffness of flexure spring were studied analytically. In addition, the axial and radial stiffness, stress distribution and vibration modal of eccentric circular spiral and Archimedes spiralflexure springs were simulated by structural finite element software. The axial stiffness of the two kinds of flexure springs were measured by experiments and the relative error is within 2%。The thermodynamic process of the typical Stirling cryocooler and pulse tube cryocooler was analyzed using phase relation theory. The nonlinear characteristics of gas force in compressor chamber were studied and the nonlinear gas force was linearized as equivalent gas spring force and damping force by Fourier method. In analogy with transformer, the coupling mechanism of linear compressor and thermoacoustic refrigerator can be treated as electromagnetic mechanic and acoustic coupling field. Then the expressions of mechanical efficiency of the motor and PV power conversion efficiency of the compressor were deduced using the impedance relationship. The change of maximum PV power conversion efficiency with the impedance was obtained.According to the coupling characteristics of linear compressor and thermoacoustic refrigerator above, a user-defined script was developed based on ANSYS Maxwell software and a union numerical simulation platform was built to simulate the transient operation of linear compressorand was verified by experiments. The power factor of the motor was analyzed theoretically and some improvements were proposed. The resonant characteristics of the prototype were investigated with different charging pressures and the stiffness of flexure springs by experiment.The compressor weighs 8kg and the maximum input power exceeds 500 W. The measured specific magnetic force of the prototype is 13.9N/A and the transient average coil inductance is 17.27 mH. The operating frequency is 30.5Hz and the copper loss efficiency of the motor is 97.7% under no-load condition. The coaxial pulse tube cryocooler driven by the prototype can achieve 30 W cooling power at 170 K with 240 W input power. The two identical coaxial pulse tube cryocoolers in parallel driven by the prototype can achieve 50 W cooling power at 170 K with 405 W input power. In this case, the motor efficiency and PV power conversion efficiency are 76% and 45% respectively. The power factor increases to0.88 when anonpolarized capacitor is added into the motor in parallel. The current decreases by 25.7% compared to the no capacitor case and the motor efficiency increases to 88%. The high capacity pulse tube cryocooler driven by the prototype can achieve 30 W and 50 W cooling power at 170 K with 175 W and 320 W input power respectively. The motor efficiency reaches 83.5%.