Speed Identification And Fractional-Order Sliding Mode Control Of A Bearingless Induction Motor

A bearingless induction motor(BIM)realizes rotor rotation and self-suspension through the combined action of two sets of windings in stator slots.The BIM does not need the support of traditional mechanical bearings,and breaks through the limit of the mechanical bearing on the critical speed.It has the advantages of no wear,no friction,no lubrication,simple structure and has a wide application prospect in the fields of high-speed and high-precision numerical control machine tool,semiconductor industry,life medicine and other fields.The suspension mechanism of BIM,the mathematical model,the speed sensorless control,the fractional sliding mode control and the digital control system are studied in this dissertation.The major work and achievements are as follows:(1)The research background and present situation of the bearingless motor are elaborated,and the development issues and application areas of the BIM are outlined.In addition,the research status of sliding mode variable structure,the generation and suppression of sliding mode jitter and the application of fractional calculus in sliding mode are introduced.Based on the establishment of the BIM mathematical model,a rotor magnetic field-oriented control system is designed to lay the foundation for the research of sliding mode observation and control.(2)Aiming at the low-cost and high-performance operation requirements of BIM,a speed sensorless control strategy with improved sliding mode observer and phase-locked loop is proposed.In order to reduce the high-frequency jitter,the switch function with double boundary layer is introduced into the sliding mode observer,and the equations of the observed rotor flux are established.Then,the high-precision phase tracking performance of the phase-locked loop is used to extract the speed information from the observed rotor flux to improve the accuracy of BIM speed self-detection.(3)In order to improve the anti-load disturbance ability of the BIM control system,a fractional-order sliding mode control strategy based on the improved load torque observer is proposed.The fractional-order integral operator of the speed error is introduced into the design of the sliding mode surface,and the fractional-order sliding mode controller is designed based on the BIM mathematical model.The proportional integral form is used instead of the integral form in the traditional reduced-order load observer to design the improved load torque observer.And the real-time observed load torque is introduced into the fractional-order controller,which effectively improves the anti-disturbance capability and dynamic response performance of the BIM speed control system.(4)The digital control system based on TMS320F2812 DSP is introduced in the terms of the hardware circuit and the software design.Experiments are carried out on the prototype,and its speed response,rotor radial displacement,and rotor motion trajectory are studied.The experimental results show that the designed system has excellent speed performance and stable suspension performance.