The Magnetically Suspended Bearingless BLDC Motor And The Application On Computer Hard-Disk

Brushless DC motor is a new type of motor that gets much popularity in the past few years. It combines the characteristics of AC motor and DC motor. Therefore, it has excellent timing capability, high efficiency, simple configuration, reliable operation, and can be controlled and maintained easily. BLDC motor is broadly applied to industry. The bearings are the main problems to realize the high speed drive. The magnetic bearings provide the solution, and they are widely used in the high speed motors for the advantages of no contact, no lubrication, and no maintenance. However, the higher power consumption and considerable axial length result in decreased critical speeds and restrict microminiaturization of the motors at the high speed.The structure of the magnetic bearing is similar to that of the motors, and the combination of magnetic bearings and motors, which has the function of rotation and self-levitation with the aid of power electronics and microcomputer control, is highly desirable. Considered as a breakthrough in the field of high speed drives, this novel electrical machine named "bearingless motor" comes forth. The bearingless motor has many advantages over the traditional high speed motor with magnetic bearings. First of all, based on the magnetic field of the motor winding, the power consumption for levitation control decreases. Moreover, it has enabled compactness, high reliability, shortened shaft length and high speed or high power operations. For these reasons, the bearingless motor has widened the application of high speed drives, such as special motors in the areas of biotechnology, chemical, medical, semiconductor and miniature motors, etc. The combination of bearingless motors and brushless DC motors is valuable.In the dissertation, the analytical expression of the magnetic levitation force for the bearingless BLDC motor is proposed and it was verified by Ansoft/Maxwell, an electro-magnetic field analysis software. By studying the literature of foreign experts,the equivalence of the motor to two equivalent motors with different pole numbers is concluded. The decoupling between the torque and radial suspension force and the decoupling between the two parts of radial suspension force are realized by using the air-gap-flux oriented control method. The simulation of the bearingless BLDC motor, in which the result is logical, was completed by Matlab/Simulink. The motor model is established by Ansoft software. Finally, the motor in a type of computer hard disk is run by DSP controller.