Study On Control Strategy Of Bearingless Induction Motors

The bearingless motor which combines magnetic levitation bearings with the drive windings is a new type of motors. In recent years the research on it has become a focus in the domain of the AC drive with high and ultra high speed for its potential value and complex operation control. It winds magnetic levitation bearings with the drive windings by taking advantages of the similarity between the structure of magnetic bearing and that of the AC motor. Its rotor can rotate and be suspended simultaneously by changing and controlling the magnetic field distribution purposefully. The bearingless induction motors which have the advantage of simple structure and high reliability have been studied earlier and more than other types of bearingless motors.In this dissertation, the mathematical models of the bearingless induction motor are derived based on the anlysis of its basic principle. The study above lays the theoretical foundation on its suspension operation control. Two kinds of high performance vector control strategy including motor winding air-gap flux orientation and motor winding rotor flux orientation of the bearingless induction motor are proposed by introducing the magnetic field oriented control technology. On the basis of the comparative theoretical analysis, the respective advantages and disadvantages of those above are claritied. The control system models of those above are established in MATLAB/SIMULINK and comparative simulations are made under a wide range of operation conditions. In this desseration, a nonlinear control strategy based on motor winding stator flux orientation of the bearingless induction motor is proposed for the first time. Adaptive flux observer is designed to observe stator flux. The needed motor winding air-gap flux in radial levitation controller is obtained by motor winding stator flux and stator current. The control system above is simulated under a wide range of operation conditions. The validity of proposed control strategy is proved by simulation results. The influence and compensation of levitation controlled coupling are also studied. At last, the control strategy based on mutual model reference adaptive system(MRAS) is proposed, which will meet the need of speed sensorless operation for the bearingless induction motors. The prototype is successfully levitated under the condition of heavy load dirturbance and can be operated stable as well as transient conditions.