Dynamic Characteristics And Control Of Permanent Magnet Bias Bearing Based On Soft Magnetic Composite Materials

With the development of modern industry,magnetic bearings(MB)as a support with no mechanical contact,micro friction,and no wear can be used in extreme environments such as high vacuum and ultralow temperature because it does not need to be lubricated,sealed and can run in any medium.However,MB also have shortcomings such as limited carrying capacity due to saturation of magnetic materials and limited effective bandwidth due to limited driving power.In order to solve the problem of insufficient magnetic force and dynamic stiffness under high frequency conditions,this paper optimizes the existing MB structure by introducing soft magnetic composite materials(SMCs)with high resistivity for theoretical and simulation research and is carried out from the theory and simulation aspects.The main content and results are as follows:(1)A new type of permanent magnet bias thrust bearing(PMTB)structure made of SMCs was proposed,and the structure parameters for the bearing were optimized based on the adaptive particle swarm optimization(APSO).The dynamic flux distributions of PMTB at 50Hz and 1000Hz were obtained by finite element method(FEM).The equivalent reluctance models for the new type of PMTB considering the effect of eddy currents are derived,and the equivalent reluctance frequency responses of PMTB with different materials are analyzed.Based on the equivalent reluctance models,the dynamic force-current factor and force-displacement stiffness are given.The results show that the PMTB made of SMCs can provide more stable dynamic stiffness in the frequency range of 0-1000 Hz than magnetic thrust bearings(MTB),and its bandwidth gets to 1000Hz which is about 100 times as large as the PMTB made of traditional material.(2)In order to meet the requirements of lightweight power equipment and ensure the stability,dynamics and support characteristics of the system,a new type of three-degree-of-freedom axial-radial hybrid magnetic bearing(3-DOF ARHMB)with compact structure,short axial length and small volume is proposed.The axial direction adopts the PMTB made of SMCs.In the radial direction,the laminated structure is used to reduce the eddy current,and the Halbach array is introduced to strengthen the magnetic density of the radial air gap.Firstly,the dynamic magnetic flux distribution of the 3-DOF ARHMB is analyzed by the FEM,and the equivalent reluctance model with comprehensive consideration of eddy current effect and magnetic leakage effect is established,and then the frequency responses are analyzed.Secondly,a constraint model coupled with structural parameters,effective reluctance and magnetic leakage coefficient is established,and the optimal structural parameters of 3-DOF ARHMB were obtained by using APSO optimization algorithm.Finally,based on th e equivalent reluctance model,the axial and radial force-current stiffness and force-displacement stiffness are derived,and the dynamic characteristics of bearings with different structures and materials are compared and analyzed.The results show that the dynamic stiffness of the new 3-DOF ARHMB is about 6 times as large as that of PMTB,while the electromagnetic force of the new 3-DOF ARHMB is about 3 times as large as that of other 3-DOF magnetic bearings.The 3-DOF ARHMB made of SMCs has more stable dynamic stiffness,and its bandwidth gets to 1000Hz.Thus,it has better dynamic characteristics at higher frequency conditions,which is suitable for high-speed rotary support.(3)For the proposed new PMTB and 3-DOF ARHMB structures,the transfer function of the controlled system is deduced,and the control components are designed.Based on traditional PID control,two control strategies of nonlinear tuning PID and incomplete differential PID are adopted to simulate the magnetic levitation system,which avoids the artificial trial of control parameters and improves the anti-interference ability of the system.By analyzing the response results of the control system,it can be seen that the system has a fast response speed,short stabilization time,and the steady state error is approximately zero.Compared with the traditional PID control,it can effectively improve the control accuracy,enhance the dynamic control characteristics of the system,and have a good control effect.