Research On Robust Two-Degree-of-Freedom Control For A High Stiffness Magnetic Levitation Unit

Nowadays magnetic levitation has been paid more and more attention because of its many advantages such as frictionless, no wear, no need of lubrication, long life, no noise, low power consumption and so on. Therefore, magnetic suspension principle can be used to accomplish no friction drive, in order to improve the machining accuracy and efficiency. The performance of magnetic levitation mainly depends on the design of control system. Technology of robust two-degree-of-freedom control(2-DOF) not only can solve the conflict between disturbances rejection and tracking problems existed in traditional PID control, but also can insure the control system good stability under the condition of uncertainties at maximal range largest. Thus, H_∞control theory is explored to research robust 2-DOF control principle and its realization method. And disturbances rejection and tracking problems of magnetic levitation unit is solved mainly.Firstly, base on reading lots of related references, development status and prospects of magnetic levitation technology is overviewed; the applications in transportation and industry fields of magnetic levitation control technology is stated; magnetic levitation control methods are stated, and tradition control and modern control methods are classification and comparative analysis. Secondly, according to analysis of the magnetic levitation system working principle, the nonlinear mathematics model of the single magnetic levitation system(SMLS) is established; and linearized the model by using Taylor expansion. Studying the local linearized transfer function of single magnet levitation system, the stability, robustness and stiffness of system are analyzed. Thirdly, H_∞control theory is discussed in detail. Aiming at tracking, anti-disturbance and robustness performances of magnetic levitation system, the H_∞controller is designed by mixed sensitivity method. And simulation of the control system is made using MATLAB's Simulink. Finally, the robust 2-DOF control strategy based on mixed sensitivity problem is proposed to solve the problem existing traditional control strategy, that is, the conflict between tracking and robustness. And the robust 2-DOF control system of magnetic levitation unit is discussed in detail, and the robust 2-DOF controller is designed and simulink. The simulation results show that robust 2-DOF controller can ensure system has strong robustness to parameter variations; good performance to resist the load disturbance, fast response speed, high stiffness of suspension gas, and the control precision is improved effectively. The simulation results show that this controller has good control effect.