Research On Speed Sensorless Control And Torque Expansion In Field-weakening Region For A Bearingless Induction Motor

With the increasing requirements of modern agricultural equipment and advanced manufacturing in terms of high speed and high accuracy,the original performance of traditional asynchronous motors will be changed.Operating efficiency will be reduced due to mechanical wear and liquid corrosion during high-speed operation.A bearingless induction motor(BL-IM)superimposes radial suspension force windings into the stator winding,which has the advantages of a uniform air gap,no lubrication,small torque pulsation,and long service life.It can achieve "selfsuspension" operation without friction and wear under high-speed operation and has broad application prospects in the fields of the semiconductor industry,flywheel energy storage,agricultural generators,and magnetic suspension centrifugal pumps.This dissertation is conducted research on the BL-IM mathematical model,speed sensorless operation,torque expansion in the field-weaking region and digital control systems.The main research results are as follows:1.Based on the research background,current status,and future domestic and foreign development trends of the BL-IM,the sensorless technology,torque improvement in the field-weakening region of the BL-IM are expounded,and the airgap magnetic field directional decoupling control is established by its operation principle and mathematical model,which has laid the foundation for the BL-IM efficient and steady operation.2.In order to realize the self-identification of the suspension rotor speed in the operation control of the bearingless induction motor(BL-IM),a speed sensorless control strategy of the speed adaptive flux observer is proposed.This strategy adopts the small signal linearization method to analyze the stability condition of the observer.Then,based on the construction of the full-order model of the controlled object,a feedback loop containing the measured object variable is designed to form a reducedorder speed observer to realize the self-identification of the motor speed.3.In order to realize the Maximum Torque Output(MTO)in the field-weakening region for the bearingless induction motor stator vector control,a flux feedforward control strategy was proposed.This strategy is based on the restrictions of the stator flux-oriented control and the dynamic characteristics of the current in the BL-IM field-weakening region,the field-weakening region could be divided into two parts.By this way,the optimal flux mathematical model of the motor can be obtained.Finally,the proposed flux feedforward control strategy in the field-weakening region can make the output torque be expanded significantly when the BL-IM runs beyond the rated speed.4.The experimental platform is constructed which is based on the digital signal processor.Experiments were conducted on the motor torque and suspension force,and the experimental waveforms were analyzed and compared.The experimental results indicate that the system can ensure the BL-IM operates stably and has good suspension characteristics.