| Bearingless motor can produce magnetic levitation force on the basis of electromagnetic torque by synthetic magnetic field effect of two sets of winding in the stator slots,it integrates the function of rotation and levitation,individual component of radial support can be removed,so it has the advantages of no-friction,no-wear,no-lubrication,no-pollution etc.According to the structural characteristics of rotors,the bearingless motor can be divided into induction type,permanent magnet type and type switch resistance etc.Among them,the induction type bearingless motor(bearingless induction motor,BIM)has similar running characteristics to the induction motor,it has the advantages of simple rotor structure,uniform air gap magnetic field,high running reliability,low pulsation of the slot and wide range of weak magnetic regulation,It is easy to realize high speed,high precision and high power,and has wide industrial application prospect.In this paper,BIM is taken as research object,and aim at realization of 5 degree of freedom(5-DOF)precise levitation control of rotating rotor.So this paper study at critical technology of BIM,such as structure of electromechanical,analysis of magnetic field in air gap,multi variable decoupling in the magnetic field,the whole PID control and dual DSP digital control system etc,the details as following aspects.(1)Air gap magnetic field of BIM is generated by the current of the two sets of windings in the stator,torque and levitation windings,so electromagnetic torque and levitation force are very sensitive to the external load.Therefore,in order to realize precision control of BIM,it is key process to establish levitation force model in consideration of rotor eccentricity and external torque.Based on the forming principle of air gap magnetic field,the equation of electromagnetic torque is derived with magnetic circuit calculation method,further more,the model of levitation force is established,which considers rotor eccentricity and external torque,validity and correctness of model are verified by finite element simulation and experimental.(2)At present,researchs on BIM mainly focus on control method and control strategy of 2-DOF,it is far from the practical industry.In this paper,on the basis of the research of 2-dof BIM,A new structure of 5-DOF BIM is proposed,which is composed with two 2-DOF BIM and a axial magnetic bearings.it is not a simple assemble,the emphasis is on the precise coordinated control of torque and levitation.Therefore,according to the electromagnetic torque and levitation force mathematical model,the whole design scheme for 5-DOF BIM is offered,which can be taken as the basis for parametric design of electromechanica structure,finite element simulation and process design of control system.(3)Levitation control of BIM is a multi-input multi-output(MIMO)system,in order to realize multivariable decoupling of electromagnetic torque and levitation force,multi-components of levitation force,based on field-oriented control strategy,the electromagnetic torque vector control model is established,the magnetic field of levitation and torque can be decoupled according to different speed.Then,by using the method of coordinate transformation,the levitation force is decomposed into two components which are mutually perpendicular,so decoupling control of levitation force can be realized.The experimental results show that the multivariable decoupling control method can realize the stable levitation of BIM in rotating state.(4)when 5-DOF BIM is running,the motion pattern is complicated because of the rotor irregular eccentric state.Traditional decentralized PID control strategy controls 2-DOF BIM separatly according to the feedback of displacement sensor,so the integrity of rotor levitation control is separated.In this paper,the rotor is regarded as a rigid body,through mechanical dynamics analysis and modeling,the displacement feedback and levitation force of each 2-DOF BIM are transformed into the parameters of the rotor motion equation.so integral PID control for 5-DOF BIM levitation system can be realized.(5)5-DOF BIM control is a multi-signal output system,a single DSP control system is difficult to meet all the requirements because of limited number of interfaces.So,a dual DSP hardware control system based on dual port RAM is presented in this paper,the software program is worked out and the hardware experiment platform is constructed.The experimental results show that the software and hardware system can guarantee synchronization of data communication of each drive control unit.(6)Based on research above,experimental prototype and control system of 5-DOF BIM is developed:(1)Based on experiment of controllable levitation force measurement,the linear range of levitation force corresponding to levitation winding current is obtained account magnetic saturation,validity of levitation force model is verified.(2)Based on decoupling control experiment of levitation force,it is verified that the levitation force decoupling control can be realized by torque windings magnetic field oriented control strategy.(3)Based on the experiment of 5-DOF levitation,variation regularity of rotor levitation control precision is obtained at different speeds,the validity of the dual DSP hardware control system is verified.(4)Based on experiment of radial load impact to rotor,The whole PID control is proved to be better than decentralized PID control,which can effectively improve the radial displacement recovery ability of the rotor under the impact load. |
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