Research On Direct Torque Control And Speed Sensorless For Bearingless Induction Motors Based On Sliding Mode Variable Structure

Bearingless motors have great utility value in precision machining,aseptic workshop,flywheel battery,aerospace,vacuum technology,life science and other fields due to the advantages of no friction,no need for lubrication,low noise and long life.Among the numerous types of bearingless motors,the bearingless induction motor(BIM)equipped with squirrel cage rotor possesses the qualities of low cost,simple structure,high mechanical strength and low cogging pulsating torque,which makes it suitable for the harsh environment,such as ultra-clean,vacuum and strong corrosion.Consequently,BIM is one of the research hotspots in the fields of special electric power transmission and bearingless motor.The operation principle and mathematical model of BIM,direct torque control(DTC)and suspension force control,speed sensorless technology and digital control system of BIM are studied in this paper with the support of the National Natural Science Foundation of China(51475214)and the Natural Science Foundation of Jiangsu(BK20141301).The detailed research contents are as follows:Firstly,the research background,present research situation,application fields and development prospects of BIM are introduced.Also,the research backgrounds of DTC and speed sensorless technology are summarized.On the base of analyzing the operation principle of BIM,the mathematical model of BIM is established.And then the traditional DTC system of BIM is constructed by applying traditional DTC method to the torque winding of BIM.Secondly,in order to solve the problems of the large torque ripple and unstable rotor suspension performance in traditional DTC for BIM,a novel method of DTC is proposed based on the sliding mode variable structure(SMVS).To improve the rotor suspension performance further,a SMVS controller is designed to replace the traditional PID controller of the suspension force closed-loop control.In addition,a speed estimation method based on sliding mode variable structure model reference adaptive system(SMVS-MRAS)is proposed to implement the operation of DTC system of BIM under speed sensorless condition.The control system of BIM based on proposed method is simulated and analyzed in Matlab/Simulink.Lastly,the digital control system of BIM is designed based on TMS320F2812 DSP and then the experimental research is carried out.The SMVS-DTC is adopted in the torque winding and the SMVS controller is applied to the suspension force winding.The experimental results indicate that the proposed SMVS-DTC method and the radial suspension force control method can effectively suppress the torque ripple and improve the rotor suspension performance of BIM.