Research And Simulation Of The Control System For Bearingless PMSM

With the development of production and technology, high speed and high power electric machines are demanded urgently, especially in the applications of medical and biotechnical engineering, numerical control machine tools, compressor etc. But conventional motor can't meet the demands of high speed and high power. Magnetic bearings have been designed recently. Because magnetic bearings have some advantages: no contact, no lubrication, no wear etc. Therefore high speed and high power can be obtained. However in practice the size of magnetic bearings is often larger than the drive motor in high speed machines, which resulted in that the critical speed is decreased with the long shaft length. So high speed drive are difficult to realize. Due to these reasons, magnetic bearing functions are integrated into high speed motors. That is bearingless motors. Bearingless motors are rotational electric machines with shafts magnetically supported by electromagnetic forces with currents in both conventional motor stator windings and additional radial force windings in the same stators, therefore if the motor output powers are equal, the shaft length of a bearingless motor can be shorter than that of a conventional motor with magnetic bearings. High speed operations are simple and possible. Recently permanent magnet synchronous motors (PMSM) have wide attention due to developments of small magnets with strong magnetization and developments of mechanical configuration to hold magnets even though rotors are rotated at high speeds .Furthermore PMSM have the capability to achieve high power factor and high efficiency. So Bearingless PMSM has been widely studied. This dissertation is devoted to the control system, mainly in the fields of the hardware designs and the system simulations.Firstly, the fundamental principles of the bearingless and the radial suspension force are introduced. The mathematic model of radial suspension force and the PMSM are deduced. Then the relationships of currents and voltages in the radial force windings are derived analytically.Secondly, how to choose a feasible control strategy is discussed. And a control system based on rotor flux orientation is decided to be applied for the decoupling control of the electromagnet torque and radial suspension force. And the control system is simulated with Matlab Simulink toolbox. The simulation results show that the control system can ensure rotor suspend steadily, and reach the standard of good dynamic performance of the motor.Thirdly, a control circuit is designed, then some elementary testing have been completed .The testing waveforms from the experiments suggest the good performance of the control circuit.Finally, the digital controller used the TMS320LF2407 chip of TI company is introduced. And the digital control unit can produce three phase sine waves according to the demands of control system. At the same time some primary software flow charts are presented.This dissertation discussed the control system of Bearingless PMSM. Some valuable and significant conclusions are testified by the computer simulation, which found the basis of the project for the further studies.