Research Of Robust Control Of Magnetic Levitation Ball System

Maglev levitation technology makes the objects suspending by magnetic forceovercoming gravity. Magnetic system has no friction and no contact, so there is a goodapplication prospect. The structure of magnetic levitation ball system is relatively simple,and the research results can be directly applied to multi-degree-of-freedom magneticlevitation system. Moreover, the open-loop instability and nonlinear of magnetic levitationball system increase the difficulty of the control, and it can be used to verify various typesof control algorithms. Therefore, the research for magnetic levitation system has animportant theoretical and practical significance.The theory and experiment of magnetic levitation ball system are investigated in thispaper. The structure and principle of magnetic levitation ball system are introduced, and anexperimental bench is designed based on the operating principle of magnetic levitationsystem. The mathematical model of this system is established based on theelectromagnetism equations, electrical equation balance equation and kinetic equations.The model is linearization processed at the balance point, and the transfer function of thesystem is obtained by the Laplace transform. The open loop transfer function of the systemhas a positive pole, so the magnetic levitation ball system is unstable. In order to achievethe stable control of the system, the closed-loop feedback control of position is adopt.Because of the uncertainty and external perturbations, the model of this system is uncertain,and the robust control is studied. The H mixed sensitivity controller is designed bychoosing the weighted function. The order of the controller is reduced in order toimplement. At last, a digital control system is designed based on XE164FN to controlmagnetic levitation system. The control of the ball is realized, and the experimental resultsare analyzed in detail and show that the designed controller is feasible.The integrated design of actuator/sensor of magnetic levitation ball system isdiscussed in this paper. Because of the presence of the position sensor, the dynamicperformance and the reliability of the system are reduced. The sensitivity operating pointand resolution of the sensor can be impacted by the external environment, and this resultsthe poor robustness of the system. The integrated design can reduce the size of the system,improve the reliability of the system, and reduce the cost of the system. The difficulty ofthe integrated design is estimation of position. The principle of sensor-less estimation method is researched that the coil inductance relates to the air gap and the inductance canbe estimated by the current and voltage of the coil. The key of position estimation is toproduce a continuous disturbance of current in the coil. In this paper, the switching ripplegenerated in the PWM bridge circuit is used to estimate the position. A position estimatorfor magnetic levitation ball system is designed based on least squares identificationaccording to Faraday’s law of electromagnetic induction and the relates of voltage andcurrent. The experimental results certify the practical feasibility of the method of positionestimation based on least squares identification.