Research On Control Method Of Magnetic Bearing

The magnetic bearing is a device that is powered by an electromagnet or a permanent magnet to suspend the rotor.The rotor has no mechanical contact with the stator during the rotation of the rotor.It has the advantages of no friction,no lubrication,long service life,etc.Currently,it has been widely used in high-speed machine tools,flywheel energy storage,molecular pumps,etc.Unlike ordinary mechanical bearings,the rotor of a magnetic bearing system is suspended in space,so it is easily disturbed by the outside world and its own magnetic field,which causes the rotor to deviate from the center equilibrium position and even cause system failure.Under the conditions of constant speed and variable acceleration,the displacement of the rotor will change periodically due to the centrifugal force,and the unbalance vibration will occur at the same frequency as the speed.In order to solve the problems of the magnetic bearing system,this paper designs a better controller for the axial magnetic bearing and the radial magnetic bearing,and at the same time,under the premise of ensuring the stability of the system,in this paper,the method of suppressing the unbalance vibration in the process of its motion is studied.Firstly,the electromagnetic force of the rotor is analyzed,and the working principle of the magnetic suspension bearing-rotor system is expounded.Based on this,a mathematical model of the axial single-degree-of-freedom and radial four-degree-of-freedom of the magnetic bearing is established.The mathematical models of displacement sensors and power amplifiers are given.Then,combining the advantages of PID control and fuzzy control,the axial single-degree-of-freedom magnetic suspension bearing model is controlled by fuzzy PID control.Based on this improvement,the fuzzy controller outputs an adaptive expansion contraction factor,which makes the domain of the PID fuzzy controller adaptively change.The radial four-degree-of-freedom model is decoupled and decentralized controlled by H ?Controller,and the simulation analysis is carried out.Thirdly,the causes of unbalanced vibration during rotor motion are analyzed.The phase-variable peak of gain control method and the phase-variable automatic balance method are used to suppress the imbalance.The suppression principle of the two methods is described and analyzed.The effect of different filter parameters on the suppression effect is analyzed.The two methods are used to suppress the unbalanced vibration of the rotor at constant speed and constant acceleration,and the suppression performance is analyzed.Finally,a phase stabilization method is used to suppress the unbalance response by combining the phase-variable peak of gain control method with the phase-variable automatic balance method.The simulation results show that this method can achieve the same suppression effect as the former two methods.At the same time,it can avoid the problem that the first two methods need to perform switching control at low speed and high speed.