| This project is one part of the National Natural Science Foundation for young of‘Fundamental Research of a 3 Degree-of-Freedom Bearingless Permanent Magnet Motor with Axial Active Suspension(51007051)’. It is a comprehensive study on magnet field of bearingless permanent-magnet motors with rotor eccentricity based on analytical-perturbation method. Based on this, the optimization design of the motor is given.The suspension and rotation of bearingless permanent magnet motors are achieved through electromagnetic force. But rotor eccencitricity brings difficulty to the motor magnetic field analysis and operation control. The finite element method(FEM) can solve the problem of fiexed position of with rotor eccentricity exactly. But it is difficult to handle moving eccentricity in FEM. In this dissertation, the analytical-perturbation method is adopted to analyze the magnetic field of bearingless motors with rotor eccentricity. The magnetic vector potential is used as variable for considering the load of winding. The free eccentricity rotation is realized without meshing based on analytical-perturbation method. The magnetic field of surface-mounted and consequent-pole bearingless permanent-magnet motors is analyzed. The main works include the follows:Firstly, an exact analytical model is established for the mangnetic field of surface-mounted bearingless permanent-magnet motor with rotor eccentricity and no-eccentricity. The boundary conditions and general solutions are given. The coefficient matrixes are determined by the boundary conditions. The unbalanced magnetic pull and the levitation force are calculated. The solutions of the magnetic field have been verified by FEM. The cogging-torque and back electromotive force(EMF) are calculated. The result of the back EMF is verified by experiment.Secondly, the solution for the magnetic field of this type motor which has slots in both stator and rotor with rotor eccentricity is proposed. An exact analytical-perturbation model is set up for the consequent-pole bearingless permanent-magnet motor with both eccentricity and no-eccentricity. Two sets of coordinates are established. The eccentricity boundary condition which connects the two sets of coordinates is deduced. The magnetic field distribution is obtained. The results of the air-gap flux density are verified by FEM. The cogging-torque andback EMF are calculated, and the back EMF result is verified by experiment. The unbalanced magnetic pull and the levitation force with different eccentricity parameters are researched.Thirdly, Based on the above results surface-mounted and consequent-pole bearingless permanent-magnet motors are designed. According to the motors’ characteristics, the traditional design method is adopted for the first estimate of the motor, and then the study is focused on the suspersion performance which is affected by key dimensions of the motor. The suspersion performance of surface-mounted bearingless permanent-magnet motor is studied at different pole arc coefficient and slot opening width. The suspersion performance of consequent-pole bearingless permanent-magnet motor is studied at different permanent magnet thickness and slot opening width. At the end, the project of the motors is given by considering the influence of various parameters.Finally, the control system of bearingless permanent-magnet motor is built for experiment research, including surface-mounted and consequent-pole motor’s hardware and software control sytems. The relation of rotor eccentricity and levitation current is experimented. The static and adjust-speed suspersion performance of the motors is experimented. |
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