A Bearingless Induction Motor And Its Operation Control

A bearingless motor is a new type of motor which breaks through the traditional motor theory of keeping the balance of air-gap magnetic field to produce electromagnetic torque. Using the structure similarity between the magnetic bearing and motor’stator, the bearingless motor is embedded in two sets of different pole-pair windings to destroy the symmetry of air-gap magnetic field, and thus to produce electromagnetic torque and radial force so as to realize the functions of rotor suspension and rotation.Compared with other types of bearingless motors, the bearingless induction motor.(BIM), which not only contains the advantages of conventional induction motor, such as simple structure, low pulsating torque andeasy flux-weakening control, but also the virtues of magnetic bearing, such as no contact, no abrasion, no lubrication, no pollution and long service life, can make it popular in the special drive fields including high and ultra-high speed operation, vacuum, clean and corrosion environment, and promote the development of equipment toward high-grade, high-precision and sophisticated. Furthermore, the BIM has become one of the hot spots in the research fields of bearingless motors presently.Under the susports of the National Natural Science Foundation of China(61104016) and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (11KJB510002), in order to solve the application of BIM with high speed, high reliability and low cost in driving field, a comparative systematical and deep research of the BIM is made, including mechanical structures, mathematical model, electromagnetic analysis, decoupling control, speed-sensorless operation, and digital control system implementation and so on. The main contents of the dissertation and the achievement are as follows:1. The Maxwell force and Lorentz force in traditional motors are elaborated, and then the producing principle of radial suspension forces in the BIM is introduced. Based on the electromagnetic theory, the analytical expressions of the Lorentz force and Maxwell force with the eccentricity and non-eccentricity in the location of rotor are analysed and deduced. Through analyzing and comparing the performance characteristics of different BIM structures, the experimental mechanical structure system of BIM is designed.2. Based on the principle of virtual displacement, the mathematical models of BIM taking into account the rotor eccentricity are derived in detail, and their accuracy and precision are verified by the transient finite element method. This work lays the foundation for further suspension decoupling control of BIM.3. A novel decoupling control strategy based on least squares support vector machine(LSSVM) inverse are proposed for the2-degree-of-freedom and5-degree-of-freedom BIM, respectively, which are multi-variable, nonlinear and stongly coupled systems. Firstly, according to the reversibility analysis of original system, the inverse model of the2-degree-of-freedom BIM was approximated by LSSVM and connected with the original system to construct pseudo-linear system. The pseudo-linear system is equivalent to two independent linear displacement subsystems, a linear rotor speed subsystem and a linear magnetic flux linkage subsystem. And then the compound controller is designed. The simulation results show that this strategy has excellent decoupling effect and dynamic characteristics. Secondly, In view of the superiority of LSSVM inverse method, the inverse model of5-degree-of-freedom BIM is built using LSSVM which has a good fitting capability to high dimensional nonlinear functions with limited samples. In addition, the particle swarm optimization algorithm is used to optimize parameters of the LSSVM, which can improve the precision of the predictive model, and then the LSSVM inverse model is combined with the original system to constitute the pseudo linear system, and then PID closed-loop regulators are designed to realize the compound control for5-degree-of-freedom BIM. The dynamic decoupling control among the radial and axial displacements, speed and flux linkage are also achieved and the simulation researches verify the effectiveness of the proposed control strategy.4. Aiming at the need of speed sensorless operation for BIM, a novel rotor speed soft-sensing method based on LSSVM left inverse is proposed. Firstly, according to the inherent relationship among the variables of BIM, the speed subsystem consisting of rotor speed and stator currents of the torque winding is established and proved to be invertible. Secondly, the left inverse model was constructed using LSSVM, and then the obtained inverse model is combined with this subsystem, the rotor speed input of the subsystem is gained, i.e., the rotor speed is observed effectively. Finally, a vector control simulation platform of BIM is established to evaluate the proposed method. The simulation results demonstrates the proposed LSSVM left inverse method can accurately identify the speed parameter in a full speed operation region with good dynamic and static performance.5. According to the deficiency of single closed-loop control of the speed and radial displacement with the current regulated pulse width modulated (CRPWM) inverter in BIM control system, the vector control strategy based on the space vector pulse width modulation (SVPWM) is proposed. In order to improve the performance of the control system,the current closed-loops are adopted for both torque winding control and suspension force winding control. The hardware and software of digital control system are built with the core of digital signal processor TMS320F2812. And then, the experimental studies are carried out, and the experimental results verify that the stable suspension and operation of the BIM can be perfectly realized through the SVPWM control strategy.