Study On System Design And Control Methods Of Hybrid Magnetic Bearing Momentum Flywheel

Magnetic bearing reaction and momentum flywheels are new types for attitude control system of space vehicles, which use magnetic bearings instead of conventional balling bearings. Magnetic bearings can offer many distinctive advantages: non-contact between stator and rotor, extremely low friction loss, vibration control, and high rotational speed. So the stabilization and pointing accuracy of the attitude control system could be improved greatly.The dissertation focuses on the hybrid magnetic bearing reaction and momentum flywheels with a permanent magnet excitation. The key technologies of magnetic bearing flywheels, such as the configuration analysis, the structure design and optimization, the relation between structure parameters and the control performance, rotor dynamic analysis, nonlinear control approaches, and experiment research are studied systematically. Some results attained are as follows.Firstly, in the configuration design of magnetic bearing reaction and momentum flywheels, based on widely studying the configurations of all kinds of magnetic bearings and considering the limitations and requirements of space environment, the hybrid magnetic bearing with a permanent magnet excitation is obtained. The prototypes of reaction and momentum flywheels are determined using the hybrid magnetic bearing.Concerning the structure design of hybrid magnetic bearings, an engineering design method for the hybrid magnetic bearing is developed according to the magnetic circuit theory. The structure parameters of permanent magnet and electric magnet are designed and analyzed. Based on the equivalent bias current, the linearization method of magnetic force for hybrid magnetic bearing is studied aimed at the application for the linear model of magnetic bearing control system. The linear structure parameter design method of magnetic bearings based on the stiffness is presented aimed at the importance of the stiffness of magnetic bearings. The control performance is considered in the approach and shows a good effect. The paper discusses the ferromagnetic resistance in the magnetic circuit calculation, the relation between structure parameters and the control properties, the response rate of electromagnetic coil current and the magnetic force. Some principles of the structure design are proposed to improve the system performance.Secondly, according to the magnetic circuit theory, the multi-objective optimization design of the mass and leakage flux coefficient of permanent magnetic circuit, the mass of electric magnetic circuit, and the negative stiffness of the hybrid magnetic bearing bring forward under the requirements of space application, with Evolutionary Algorithm and Simulated Annealing. The design optimization of the strength of the flywheels rotor is done.With the finite element method, the three dimensional magnetic field of the hybrid magnetic bearing is calculated and analyzed. The validity of the magnetic circuit design method is verified. Aimed at the eddy current losses, the structure of hybrid magnetic bearing is ameliorated and the magnetic field is also analyzed. Considering the strength of material of momentum flywheels at a high rotational speed, the stress and strain calculation is completed with the finite element method.On the part of motion analysis of the magnetic bearing reaction and momentum flywheels, the dynamic model and control system model are established. The stability analysis of motion and the critical rotational speed are investigated based on the motion equation of rigid magnetic bearing momentum flywheels. The coupled translation motion in two degree of freedom in momentum flywheel's radial direction is discussed.In the research of the control approach for magnetic bearing reaction and momentum flywheels, first the linear controller is designed and the magnetic bearing flywheels suspend steadily. To restrain the precession and nutation of high speed rotor, the cross feedback controller is completed. Second the nonlinear control methods are applied to the system. The traditional variable structure control (VSC) of hybrid magnetic bearing momentum flywheels are designed. And the simulation shows good dynamic response and stability. Then the whole sliding mode variable structure controller has been made for the momentum flywheels, which eliminates the reaching phase. The result shows better robustness compared with the traditional VSC.Finally, experiment research on the magnetic bearing momentum flywheels is done. Aimed at the structure parameters design and the control system, the analysis and test are carried through. The static suspension, dynamic suspension and decreasing speed experiments are studies. The prototypes of the magnetic bearing momentum flywheels achieve the expected performances such as the momentum, velocity, and damping moment.