Research Of High-Speed PMBLDCM Based On Soft Magnetic Ferrite

With the development of high-speed bearings and motor control technique, the High-speed permanent-magnet motors, which have advantage of low rotor loss and high power density, have more and more extensive application, such as the numerically controlled high-speed drills, the milling equipments, the precision carving machines, the precision grinding machines, the machining centers and other high-speed mechanical situation, which improve the machining accuracy and the production efficiency. Therefore, the research of high-speed permanent-magnet motors have much theoretical and applied value.According to the summary of research status, structure type and design features in high-speed motors, firstly, this paper presents a novel high-speed PMBLDCM motor based on the soft magnetic ferrite. Considering the characters of high initial permeability, high resistivity and low loss for soft magnetic ferrite in the high-frequency alternating field, soft magnetic ferrite ring is used as stator core, rare earth PM ring serves as the rotor poles, and the slotless configuration with long effective air gap is adopted, the winding homogeneously distribute in long effective air gap. Thanks to slotless, the winding can have large electric loading, which can compensate the drawback of low magnetic loading in soft magnetic ferrite. The size matching design between the stator magnetic ring and the PM magnetic ring can make themselves work in their best operating points respectively, which ensure the high power density of motor. Secondly, according to the analysis of finite element method, the magnetic-field distribution is nonhomogeneous very much in long effective air gap of such motor. The winding induced electromotive force not only have something to do with magnitude of magnetic field, but also have something to do with the position of the winding conductor, therefore, the analytical calculation is introduced to deduce the calculated method of winding induced electromotive force. Finally, the results of magnetic field analysis, core loss analysis and the prototype test prove that the core loss can be greatly reduced, which verifies the high-speed PMBLDC motors based on soft magnetic ferrite is feasible.Based on the specific application, this paper designs the control system of high-speed PMBLDCM for the turbo molecular pump. Considering the characters of turbo molecular pump, this paper uses the special control chip of BLDCM (MC33035)and micro-controller (MCU) to implement the control system. The rapidity, high reliability of the MC33035 and the flexibility of MCU are combined to improve the credibility, stability and flexibility of control system. Based on the characters of high-speed and large-inertia in turbo molecular pump, this paper designs the soft start of motor. Rotor-position sensor signal is used to implement real-time revolution detection and display; digital PI regulators is adopted to realize the speed control of motors; current peak protection and busbar current average value clipping is used to realize over-current protection of motors. Finally, considering the specificities of large inertia and long-time stopping in turbo molecular pump, braking unit is designed, relative speed state in braking process of motor is used reasonably to realize triple-section braking of motor, which ensures the requirement of rapid braking and safety arrestment. This system has good man-machine interactive function; the motor controlling parameter can be real-time modified by the control panel, which can display motor running state.After the experiment of the prototype, the result prove the credibility and convenient operating of the control system. The motor starts smoothly, has wide speed range and high steady speed accuracy, braking process is quick and smooth, the control system contents the running characteristic of turbo molecular pump.