Study On The Fuzzy Control Method For Magnetic Bearings

Magnetic bearings are novel supporting components, which are electrimechanical systems consisted of rotor, bearing and position controller. It has been attracting great attention because of the advantages of no mechanical touch, no frays and dispensing with lubricate compared with the traditional bearing. Magnetic bearings can work well only in the help of control system. So the performance of controller affects the dynamic performance of magnetic bearings and the control precision of the rotor directly.In this article, the reasonable mathematic model was built up based on the study of the single freedom magnetic bearings, and the model of the control system was given too. Basing on this, this paper analyses how the parameters of the PID controller affect the performance of the control system fist, then presents a variable parameters PID controller applied to the magnetic bearings system. The parameters turning principle of this controller are proposed. The control system is simulated with the Simulink of MATLAB; the parameters turning module and the nonlinear model of the magnetic bearings are realized by S-function.This article introduces the experimental system based on the digital control system of magnetic bearings, and discusses the function of the system's constituting parts, and then analyses the experimental data.The usual design of the magnetic controller always linearizes around the balance point and bases on the linear system theory to design the linear controller. But classical PID controller often can't overcome efficiently the effects of great changes of model parameters and nonlinear factors. In this paper the basic fuzzy controller is designed and the computer simulation on MATLAB is implemented. To improve the steady performance of the system, a fuzzy-PID combined controller is applied to the magnetic bearings system: applying fuzzy control in a large error range; applying classical PID control in a small error range. The simulation results show that this kind of control strategy can make the rotor of the magnetic bearings stabilize in a large range.How to choose the threshold is the key to design the fuzzy-PID controller. Too early switch can not present the advantage of fuzzy controller and even lead to integral saturation, while too late switch can not turn into PID control because of the static state error of fuzzy-PED control. At last, the choice principle of the threshold is analyzed and simulated.