Design Of A 5-degree Bearingless Induction Motor And Control System

A 5-degree-of-freedom magnetic suspension motor system consists two components:a 3-degree-of-freedom magnetic bearing(MB) and a bearingless induction motor(BLM),which can achieve rotor suspension and produce torque to drive the load at the sime time.This system inherit all the strongpoints of the magnetic bearing motor system,such as no friction and abrasions,no lubrication and no sealing,high speed,high precision and long service life,etc,which have innovated the traditional supporting forms fundamentally.A novel AC-DC 3-degree of freedom hybrid magnetic bearing(HMB) incorporates the merits of three-phase AC exciting,permanent magnet flux biased and axial-radial combined control,it has compacter structure,lower manufacturing and operation costs,etc.And the bearingless induction motor,because of its simple structure,high reliability,air-gap uniform and easy field weaken,has more value of researchs and applications than other motors.For this dissertation detail contents as follows:Firstly,based on the analysis to all kinds of magnetic bearings' structures and magnetic circuits,an innovated structure of three degrees of freedom HMB is proposed.The flux path is calculated by using equivalent magnetic circuit,the formulas and mathematics models of the axial and radial magnetic suspension forces are deduced respectively.Nonlinearities of suspension forces and cross coupling between different degrees of freedom are studied further by calculating the suspension forces at different displacements and control currents to validate the feasibility of the mathematics models.The methods on parameter design and calculation of the novel HMB are presented,a prototype is designed too.The prototype is simulated to analyze the magnetic circuits by using finite element analysis software Asoft/Maxwell.The simulation results have verified the feasibility of the theory study,and some parameters have been optimized according to the simulation results too.Secondly,this dissertation exponds the principle of the bearingless induction motor,and gives the suspension models based on the magnetic force,and analysis of levitation force are presented in a bearingless induction motor.A prototype designed on the base of a traditional induction motor.And flux distributions and radial force of an the prototype is analyzed employing the Finite Element Method(FEM).Relationships between the radial force and radial force winding currents are influenced by magnetic saturation.It was shown that the generated radial force reaches its maximum value due to magnetic saturation.The mechanism of radial force is defined and the analyzed results will be applied to derive more precise radial force model.Finally,establish a experimental all-digital platform for the five degrees of freedom spension system,buildup a control system based on air-gap flux orientation,and the decentralization PID control is used to maintain equal air in the five degrees of freedom.The digital controller guarantees rotor suspension steadily,and the speed of rotor reaches 3000 rpm.