Study On Nonlinear Decoupling Control Strategy Of Bearingless Induction Motor

The bearingless induction motor, which combines characteristics of induction motor and magnetic bearings, can provide both torque and radial suspension forces. The potential value and the complex operation control has become a new research field of the high-speed AC drive. Because the bearingless induction motor is a nonlinear, multi-variable and strong-coupled system, this dissertation focuses on the nonlinear decoupling control of the motor supported by the National Natural Science Foundation under grant 60674095 and 61174055. The mathematical model of the bearingless induction motor, the rotor flux oriented control method for the torque windings and the nonlinear internal model control strategy based on inverse system theory are studied. Besides, the nonlinear decoupling control strategy based on support vector machine (SVM)α-th order inverse system is also proposed, and the digital control system of the bearingless induction motor is designed.The structure, implementation and the principle of the radial suspension force of the bearingless motor is introduced, the mathematical model of the suspension force and the rotation part of the motor is derived, and the motion equations are set up. By finite element simulation, the structure and performance of the bearingless motor are verified.To realize the decoupling control of electromagnetic torque and radial suspension force of the bearingless induction motor, the rotor flux oriented controller for the drive control system is utilized. However, in the control algorithm based on rotor flux orientation of torque windings, coupling still exists between the radial suspension forces. A novel rotor flux oriented control system is proposed in which the rotor currents generated by the suspension control windings are taken into account. So the improved rotor flux oriented control system has better suspension characteristic than the previous one.In this dissertation, a new internal model control (IMC) strategy based on inverse system theory is proposed to realize the dynamic decoupling control between torque and suspension force for bearingless induction motor. Inverse system method is used to decouple the original nonlinear system into four independent pseudo-linear subsystems, that is, two radial displacement subsystems, a speed subsystem and a rotor flux subsystem. Then, the internal model control method is introduced to the four pseudo-linear subsystems to ensure the robustness and anti-jamming ability of the closed-loop system.Since the accurate mathematical description of the bearingless induction motor is difficult to acquire, SVM regression method is used to identify the inverse model of the bearingless induction motor. By cascading the inverse model with the original one, the nonlinear bearingless induction motor system is decoupled. Then, linear control system techniques are applied to the linear subsystems to synthesize and simulation. The results show that the dynamic decoupling control among the speed subsystem and the rotor displacement subsystems can realized by SVMα-th order inverse system. Besides, the SVMα-th order inverse system has better robustness and higher tracking accuracy than the inverse system method.A digital control system for real-time control is designed on DSP (TMS320F2812) which includes hardware design and software programming. The hardware circuits are composed of the the main circuit, the drive circuit, the protection circuits, the test circuits, the fault signal processing circuit and so on. In the software part, based on rotor flux oriented control of the bearingless induction motor, the software architecture of the digital control system is given and the detailed flow charts of all program modules are introduced.