Research On Magnetically Suspended Compound Molecule Pump And Its Control System For High Vacuum And Clean Environment

Shenguang III is a large engineering project under construction for laser-driveninertial confinement fusion (ICF), of which end optical components are used as theend equipment in laser path to perform functions, such as transforming frequency,separating harmonic and laser focusing etc. The critical component is crystal KDPlens which must work in closed vessel of high clean and vacuum with no oil andhydrocarbon. The normal requirement of vacuum degree is less than1×10-8Pa, evenbelow1×10-9Pa. In order to meet the strict requirement of high vacuum and clean,magnetically suspended compound molecule pump is studied in this dissertation.Turbine blade, multi-spiral groove traction structure and magnetic bearing systemwhich has such advantages as non-contact and no lubrication, are adopted to avoidthe pollution of oil and hydrocarbon. Additionally, the rigid critical speed higherthan normal work speed, the stability of wide rotational speed of rotator, the systemstability of gyroscopic effect in high speed, structural-mode and the suppression ofhigh order of torsion vibration mode, the vibration of system base andelectromagnetic noise are analyzed respectively. At last, the magnetically suspendedcompound molecule pump and its controller are developed, which lay a solidfoundation for the success of Shenguang III project.Based on the requirement of high vacuum for end optical component inShenguang III, the parameter of the magnetically suspended compound moleculepump is determined and the whole analysis is performed for overall structure. Thearguments of multilevel turbine blade and multispiral groove are designedindividually based on the mechanism of turbine blade and multispiral groove. Theflow pattern analysis of flow field is performed for multilevel turbine blade andmultispiral groove in Fluent software. The numerical simulation of flow law isanalyzed for bleed-off passage. The relationship between the geometrical parameterof multispiral groove traction structure and the performance of air exhaust is alsoanalyzed. These simulated results provide a foundation for designing and optimizingstructure. The magnetically suspended compound molecule pump with thesimulation of flow field is demonstrated to cut the price, which becomes asignificant approach for the design of structure.Based on the mechanism of magnetic bearing, the radial and axial magneticbearing physical construction of the magnetically suspended compound moleculepump is designed and improved. Based on the magnetically suspended compoundmolecule pump characteristics of the high speed, metabolic support stiffness andgyroscopic effect and infinitely thin blade, the blade rotor systematic model of the magnetically suspended compound molecule pump is established, which issupported by magnetic bearing. The modal analysis is performed for blade rotorusing the finite element software, thus the modal frequency and modal shape isobtained. Additionally, the phenomenon of frequency bifurcation of blade rotor inhigh speed is analyzed. These will provide a theoretical foundation for the design forcontroller.To control the magnetically suspended compound molecule pump blade rotor,discrete PID controller is investigated to meet the levitation stability and normalrotation for rigid rotor. The constraint of gyro effect is analyzed based on crossfeedback controller and the validity of the controller is demonstrated based on thesimulation using Matlab software. In order to avoid the vibration of structure modaland bending resistance high frequency mode, the notching filter is developed.Variable gain adaptive controller is designed to solve the problem of wideinsatiability of rotor and critical speed of superabundant stiffness for the normalrotational speed of blade rotor. Under the control toward vibration of samefrequency and support of magnetic levitation compound molecule pump andelectromagnetic noise, the non equilibrium compensation controller is developed.To verify the feasibilty and correctness of designed variable-gain adaptivecontroller and imbalance compensating controller, experiments including rotor staticsuspension, the constraint of gyroscopic effect, the compensation of control forimbalance, and high speed rotation are carried out. The result shows that themagnetically suspended compound molecule pump system can not only satisfyingthe requirement of surpassing the rigid critical speed of rotor, but also can overcomeinfluence of gyroscopic effect of rotor and restrain the flexible modal frequency ofrotor. At the same time the blade rotor of the magnetically suspended compoundmolecule pump can rotate around its principle inertia axis, thus the pedestalvibration and electromagnetic noise of the system can be decreased. The controlsystem can have great self-adaptability and robustness. The maximum radialvibration of the rotor is less than10μm on the rated speed which can achieve24000rpm. The rotor can rotate steadily on any frequency in the speed range of0~24000rpm. The experiment verified the validity and practicability of variable-gainadaptive controller and imbalance compensating controller, and verified indirectlythe validity and practicability of the magnetically suspended compound moleculepump system’s mechanical structure design and modal analysis. The experimentaccumulated the experience of design, test and operate for the magneticallysuspended compound molecule pump system. The performance of rotor speed, rotorvibration and stability of the magnetically suspended compound molecule pump isable to satisfy the circumstance of high vacuum and clean for the end opticalcomponent module in shenguang III. And the overall performance of this pump is in the domestic leading level.