Study On Nonlinear Decoupling Control For 5 Degree-of-Free Bearingless Induction Motor

The bearingless motor is a new type of motor which hybridizes the motors and the magnetic bearings. It has been the focus of research work on high speed motors. As the bearingless motor is constructed with contact-free bearings, it works free of wear, frictionless, free of abrasion and without lubrication. With these advantages and other features, the bearingless machine motor demonstrates the potential applications in space technology, machine tools, high vacuum technology, biologic medicinal engineering, and ultra high-speed drives and so on. And the bearingless induction motor is one of the earliest motors on which are researched, because of its easy field weaken, simple structure, high reliability. This dissertation focuses on an innovated 5 degree-of- freedom bearingless induction motor.Firstly, an innovated 5 degree-of-freedom bearingless induction motor is proposed, which is composed of a 3 degree-of-freedom magnetic bearing and a 2 degree-of-freedom bearingless induction motor. Then the mechanical equations of magnetic bearing and bearingless induction motor are given. Also the state equations of the 5 degree-of- freedom bearingless induction motor are set up.Secondly, the reversibility of system based on the mechanical equations is discussed. Because the 5 degree-of-freedom bearingless induction motor is a multi-variable, nonlinear and strong-coupled system, a method based onα-th order inverse system theory is used in realizing dynamic decoupling control in motor system. Cascading theα-th order inverse system with the motor system, a pseudo-linear system is completed. So it is decoupled into two kinds of independent linear subsystems—radial displacement subsystems and torque subsystem, and then a linear close-loop adjustor is designed to control each of the subsystems. Instant ofα-th order inverse system theory, a method based on artificial neural networks (ANN) inverse system is used in realizing dynamic decoupling control in motor system. The simulation results have showed that the whole control system has good dynamic and static performance under load disturbance based on ANN inverse system method.Finally, the control structure based on digital signal processor (DSP) of 5 degree-of-freedom bearingless induction motor is discussed; the main hardware system is given too. The implementation of torque control system, radial displacement control subsystem and magnetic bearing control system based on the principles and the characteristics of the 5 degree-of-freedom bearingless induction motor are designed.