Research On A Bearingless Fixed-Pole Rotor Induction Motor And Its Repetitive Control

Electromagnetic forces in bearingless motors are used to replace the traditional mechanical bearings to support rotors.The combination of rotor suspension and rotation is realized by the torque field and suspension force field.In comparison with magnetic bearing motors,the bearingless motor fully improves the axial space utilization and electromagnetic utilization rate.Therefore,it is particularly suitable to operate for special application,such as superhigh-speed drives,high-speed flywheel storage system,high-speed molecular pump,sealed pump,and artificial heart pump.The bearingless induction motor(BIM)integrates the advantages of magnetic suspensions and the characteristics of induction motors.It possesses the unique and excellent quality of no friction and wear,no lubrication and sealing,easy to achieve high-speed and high-precision operation in bearingless motor,as well as small size,low noise,easy field weakening and high reliability in the traditional induction motors.The BIM has become one of the mainstream motors in the field of bearingless motor.A bearingless fixed-pole rotor induction motor(BFPRIM)is proposed in this dissertation to solve the problem thatAiming at the defects that the rotor current induced by suspension force winding magnetic field causes interference in suspension force and torque,a bearingless fixed-pole rotor induction motor(BFPRIM)is proposed in this dissertation.The operation mechanism,structure design,mathematical model,electromagnetic performance,compensation function design of repetitive control system,improved repetitive control and digital control system are deeply studied.The main contents of the dissertation and the achievement are as follows:(1)On the basis of reviewing the research background,current situation and application prospects of bearingless motors at home and abroad,a new BFPRIM structure is proposed and its mathematical model is established.The BFPRIM overcomes the shortcomings of the traditional squirrel cage BIM that the suspension force winding magnetic field induces electromotive force in the rotor producing current,which leads to the radial suspension force response delay and loss.The suspension precision is improved in the BFPRIM.The structure of the BFPRIM is designed and its operation principle is analyzed.The mathematical models of torque and radial suspension force of the BFPRIM are built.(2)The electromagnetic properties of the BFPRIM are analyzed.Based on transient finite element method,the 3D finite element analysis model of the BFPRIM is established.The electromagnetic parameters of BFPRIM such as air gap magnetic field,rotor current,radial suspension force and torque are calculated.The electromagnetic performance of the traditional BIM with the same stator size is compared by the finite element simulation.The research results show that the BFPRIM suspension force winding magnetic field does not induce current in the rotor,and the correctness of the BFPRIM structure and suspension mechanism is proved.(3)In order to improve the levitation accuracy,a BFPRIM repetitive control strategy is proposed on the basis of the air gap magnetic field oriented decoupling control.The repetitive controller is built based on the internal model function,periodic delay function and compensation function.The performance of the repetitive controller is analyzed in terms of stability,error convergence rate,steady-state error and disturbance suppression characteristics.The simplified model of the BFPRIM suspension control system is established.Combined with the BFPRIM dynamic control system model,the BFPRIM repetitive control system is designed.Based on the analysis of system stability,the compensation functions in high-,middle-and low-frequency band are designed.The research results prove that the accuracy of the BFPRIM suspension control system is effectively improved by the repetitive control strategy.(4)An improved repetitive control strategy of the BFPRIM is proposed.Classical repetitive control has strict requirements on the period of the external signal and the number of samples per period.Consequently,to further improve the performance of the repetitive controller,a fractional delay filter and a weight expansion module are added to optimize the internal model of the repeated controller.An improved repetitive controller is designed.Its stability criterion and robustness are studied,and the design method of the important parameters of the improved repetitive controller is given.The research results show that the improved repetitive controller further improves the rotor suspension accuracy and has good robustness.(5)The BFPRIM digital control system platform based on TMS320F28335 core processor is established.The power driving circuit and the detection circuit of the main parameters of the motor are designed,and the BFPRIM experimental prototype is processed.The BFPRIM experimental researches on suspension operation at different speeds,speed regulation and disturbance have been carried out.The experimental results show that BFPRIM can achieve stable suspension operation and has good anti-interference ability,which proves the effectiveness of the control system.