Research On Active Control Technology Of Magnetic Bearing

Bearing is an inseparable part of machine tool control system,and it may be worn down due to its contact force and friction force produced by the direct contact of mating surfaces,thereby reducing the life of machine tool and bearing system.However,the magnetic levitation bearing realizes the suspension of the rotor through controllable magnetic force,which is capable of avoiding the mechanical wear caused by frequent frictions.In the meantime,such a mechanical wear can be actively suppressed by measuring the vibration deviation of the rotor in numerical controlled machining process.Magnetic levitation bearing has been widely applied in transportation,machinery industry and aerospace fields due to its advantages of frictionless,contactless and active control.Magnetic bearing system belongs to a typical mechatronics equipment by integrating the technologies of mechanics,control theory,electromagnetism and computer science,etc.Magnetic bearing system itself is an openloop and unstable complex system with the features of nonlinear and close coupling,which brings lot of difficulties to the design of controller,therefore,controller design has always been a hot spot and sticking point in related research.Taking the electromagnetic spindle installed on the vertical milling machine as the research object,this thesis conducts a close study on the performance characteristics of each component of the active magnetic bearing system,and obtain a mathematical model of single degree-of-freedom of magnetic bearing through mechanism modeling as well as the equivalent magnetic circuit method.Besides,it also linearizes the nonlinear mode.It further builds a radial four-degree-of-freedom mathematical model of magnetic bearings on this basis,and clarifies the coupling characteristics with or without asymmetry of rotating speed and structural parameters.In addition,it develops a feedforward decoupling controller to decouple the coupled system into four independent single-degree-of-freedom systems,by which significantly reducing the computational complexity of on-line identification of system parameters and facilitating the design of controller in the next step.A model reference adaptive method is specially designed for the decoupled single-degree-of-freedom system,thus forming a closed-loop magnetic levitation bearings control system.Compared with the traditional PID control method,the experiment proves that the model reference adaptive control method has achieved better transient performance as well as guaranteeing its control accuracy.Finally,this thesis presents a overall scheme of the digital integrated controller by adopting the core chip of TMS320F28377,meanwhile,it also gives a detailed description of the design of power supply module,displacement sampling circuit,current sampling circuit and current driving circuit,etc.The suspension and rotation experiments of active magnetic bearings are performed on the experimental platform,so as to verify the effectiveness of the designed control method and control system.This thesis is of far-reaching significance,since it lays a good foundation for the subsequent industrial application of magnetic bearing system embedded with active control in complex curved surface cutting and centrifugal pump vibration suppression.