Study On Structure Design And Control Methods Of Permanent Magnet Biased Hybrid Magnetic Bearing

With the development of modern industry, a variety of demanding performance requirements of rotating machinery are putted forward. In the energy and chemical machinery, the rotation speed and accuracy require of the rotor are ever growing, and the gap of the rotor and stator as small as possible in pursuit of greater efficiency; while others work in extreme hot or cold environments of the war industry and aerospace field of rotating machinery, in addition requires the withstand the harsh environment test, the support controllability, security and reliability are often first considered.Therefore, the advantages of high speed, friction power consumption, and no lubrication and controllability of magnetic bearings which has become increasingly one of hot topics of the scientific and technological fields and the business community concern.High-performance magnetic bearings is a comprehensive high-tech engineering, which involved in mechanics, electromagnetics, electronics, rotor dynamics, control engineering and computer science and other subjects. At present, the magnetic bearings are basically the study on the electrical, while the mechanical parts are very few studied.In this paper, the structure and magnetic properties of mechanical parts of magnetic bearings were studied. According to the existent problems of modern magnetic bearing system, the permanent magnet biased hybrid magnetic bearing were designed by the magnetic field generated for permanent magnets to replace the static bias magnetic field generated for electromagnets, while the use of electromagnets as a regulation device of magnetic bearing. The primary contents and original contributions of this thesis are as follows:(1) In view of the problems of magnetic bearing, a hybrid active magnetic bearing system is proposed by a permanent magnet generate static bias magnetic field and electromagnets provide the control magnetic field. The new type structure of magnetic bearing is designed which is based on the original structure. The radial magnetic bearings and axial magnetic bearings are made into an organic whole by the structural optimization, which make the magnetic bearing performance improve significantly.(2) The structure and working principle of the permanent magnet biased hybrid magnetic bearing are introduced. On this basis, the equivalent magnetic circuit model of the magnetic bearings is established, and magnetic circuit is analyzed by superposition principle as well as the load capacity expression of the magnetic bearings was deduced. The design method and the operating characteristics of permanent magnet are introduced.(3) Using Ansoft software's Maxwell 2D eddy current solver and eddy axial magnetic field solver to solve the calculation of two—dimensional eddy current field for the magnetic bearing, magnetic density, magnetic flux density and other parameters are obtained when only permanent magnet and the load current, which provided reference for design of electromagnetic bearing. It also shows the use of laminated rotor power than using a small solid rotor, eddy current loss is small, so the superiority of the rotor lamination design feasible.(4) The force coupling and motion coupling of hybrid magnetic bearing are analyzed, which obtained the distribution of radial suspension force along the circumferential direction at different rotor angles and the distribution of force coupling of radial suspension force and axial suspension force, as well as the relationship of the current and the suspension force.(5) The system architecture and system parameters of magnetic bearing are described and the mathematical model of a single freedom degree and five freedom degrees of mechanical structure are analyzed, which provide the basis for control system design. The supporting system itself of magnetic bearings is unstable, it is necessary to achieve rotor stabilit suspension by feedback control. According to the structural characteristics of control system of hybrid magnetic bearing, PID control method has been improved by a non-linear compensation PID control and PID control based on genetic algorithms method, and a comparative study is carried out for them.(6) Designed controller of the system, selected PID control of a modern industrial control of the most commonly used form, and used MATLAB's Simulink Blockset to adjust PID control parameters. By comparing and analyzing to the step response, bearing rolling process and current waveform when the load change by the use of design of PID controller, nonlinear compensation PID controller and the PID controller based on genetic algorithms.