Research On Dynamic Characteristics Of Active Magnetic Bearing-Rotor System

Compared with traditional rolling bearings and journal bearings,active magnetic bearings have the advantages of no contact,no lubrication,no wear and so on.Moreover,the bearing force of the acive magnetic bearing is controllable,and the magnetic force can be applied to the rotor by designing the control strategy to realize active control of the vibration of the rotor system.Active magnetic bearing is a new type of support,and its support characteristics are closely related to its structural parameters and control parameters.The rotor systems supported by the active magnetic bearings have different dynamic characteristics in many respects than the rotor systems supported by the conventional mechanical bearings.In this paper,the dynamic characteristics of the active magnetic bearing-rotor system are discussed from three aspects:the vibration suppression of the unbalance,the rubbing fault and the influence of the seal airflow excitation.The main research contents are as follows:(1)The active magnetic bearing-rigid rotor system model is established,and the unbalance vibration of the rotor system is suppressed using the automatic balancing method.Firstly,considering the geometric relationship between electromagnetic bearing,sensor position and rotor centroid position,the dynamic equation of magnetic bearing-rigid rotor system is established.The parameters of the PID decentralized control system are then designed using an optimization method.Finally,the automatic balance control method is used to control the unbalanced vibration of the rigid rotor.Combined with the time domain diagram and the spectrogram,the control effects before and after the unbalanced vibration control are compared and analyzed from the two aspects of rotor vibration displacement and control current.It is found that the automatic balance control can reduce the vibration response of the rotor system and significantly reduce the control current.In addition,in order to solve the influence of the notch filter on the stability of the control system,the rotor system is controlled in stages over different speed ranges.Finally,through the adjustment of the phase compensation of the notch filter,the stable operation of the rotor system over the entire operating speed range is successfully achieved.The rotor system can be controlled in stages over different speed ranges.(2)The dynamic model of the rubbing fault of the magnetic bearing-rotor system is established.The nonlinear dynamic characteristics of the rotor system when the rotor and the protective bearing are rubbed are studied.Using the axial trajectory,time domain diagram,spectrogram,Poincare diagram and bifurcation diagram,the effects of rotational speed,unbalance excitation and electromagnetic bearing structural parameters on the dynamic characteristics of the rotor system are studied.It is found that when the rotor supported by the magnetic bearing rubs against the protective bearing,the rotor system exhibits very complex nonlinear dynamic characteristics such as periodicity,quasi-periodicity and chaos.Appropriately increasing the bias current of the magnetic bearing and reducing its initial clearance within a certain range helps to stabilize the faulty rotor system.(3)The magnetic bearing-seal-rotor system model is established.The effects of rotational speed,sealing parameters and electromagnetic bearing control parameters on the dynamic characteristics of the rotor system are studied.The dynamic model of the rotor system is established using the Mszynska sealing force model and the nonlinear magnetic force model.Combined with the spectrogram,waveform,axis traj ectory and bifurcation diagram,the effects of the rotational speed,sealing force parameters and magnetic bearing parameters on the rotor system under the seal airflow are analyzed.It is found that the influence of the rotational speed,the sealing pressure difference and the sealing gap on the magnetic bearing-seal-rotor system is obvious.At high speeds,the seal airflow force excites the low frequency components of the rotor system.With the increase of pressure difference and sealing gap,the amplitude of the lowfrequency component of the rotor vibration increases,and the rotor gradually enters the quasiperiodic motion from the stable periodic motion,and the stability of the rotor system deteriorates.The proportional coefficient and differential coefficient in the magnetic bearing PD control system have a great influence on the rotor system.The stability of the magnetic bearing-seal-rotor system can be improved by appropriately changing the parameters of the PD controller.