Research On Nonlinear Decoupling Control Of The Bearingless Induction Motor

Bearingless motor has combined characteristics of motor and magnetic bearings. It is a new type motor which can implement electromagnet torque control and levitation force control all in the motor at the same time. The bearingless technology of motors has the hermits of compactness, high reliability, shortened shaft length and reduced system size, high speed or high power operations. At the same time it possibly inherently reduces cost and improves rotor dynamics. There are a lot of kinds of bearingless motors, among which the bearingless induction motor is one of the focuses of this research field at present due to its simple structure and high reliability. This dissertation focuses on the nonlinear decoupling control of the bearingless induction motor including accomplishment of bearingless induction motor system, single DSP controlling, the independent control of levitation system, the influence of induce current in squirrel cage caused by levitation control winding and the influence of rotor eccentricity. A control system of bearingless induction motor based on torque winding air gap field oriented vector control is accomplished. As the bearingless induction motor is a strongly coupled complicated nonlinear system, the decoupling control of electromagnet torque and radial levitation force is the base of the stable operation of bearingless motor. Based on the levitation principle of bearingless motor, the torque winding air gap field oriented vector control is utilized to realize the decoupling control of the nonlinear system even in the transient case. And aiming at squirrel cage bearingless induction motor, a control system is accomplished and tested on the test machine. The laboratory bearingless induction motor is successfully levitated for the first in our country and can be operated stable as well as transient conditions. The problems of complicated configuration and communication delay between the dual windings of bearingless induction motor result in the air gap flux error between dual windings and deteriorates the decoupling between torque control and levitation force control and the levitation characteristics of bearingless induction motor. The scheme of controlling dual windings of bearingless induction motor utilizing single DSP(TMS320f240) is proposed to overcome the air gap flux error between dual windings caused by communication delay between the dual windings. The hardware and software configurations of the control system are optimized. The independent control of torque winding and levitation control winding is an effective way of high speed operation for bearingless induction motors. Aiming at the complicated nonlinear system of bearingless induction motor which is strong coupled by torque winding flux, based on the independent control algorithm of the levitation system, the voltage-model method identifying the air gap flux of torque winding based on the inverter switching state and air gap flux model are proposed to realize the independent control of the levitation system. In such way, not only the high speed operation become possible, but also keeps the control project of the motor flexible. As an induction motor, it is inevitably for the levitation control winding of bearingless induction motor to induce current in the squirrel cage. It is the current loss of the levitation control winding. The current loss of the levitation control winding results in the air gap flux error of the levitation control winding and influences the decoupling of radial levitation control force. The air gap flux feedback control of the levitation control winding is proposed to eliminate the influence of induce current of squirrel cage caused by the levitation control winding. It is inevitable for bearingless induction motor to operation with rotor eccentricity. Not only the active control force, but the unbalance radial magnetic pull force caused by rotor eccentricity act on the rotor. Aiming at rotor eccentricity operation of bearingless induction motor, the force acting on rotor is analyzed and radial force...