Control of permanent magnet magnetization pattern and analysis on electric and dynamic characteristics of brushless DC motors.

摘要

The magnetization pattern studied in the present dissertation is named non-conventional magnetization because the magnetic orientation is not uniform over a magnet pole and each location in the magnet can have both radial and tangential components depending on the geometry of the magnetizing fixture. Actual magnet samples were prepared and magnetized in the magnetizing fixtures with different geometry. The prototype motors with these magnet samples were tested and huge improvement on motor performance was observed, which is due to the change in the magnetization pattern of the permanent magnet.; An analytical expression for the air gap flux density created by non-conventional magnetization pattern was developed and the results were compared with the FE results.; Since the importance of the magnetization pattern was known there have been efforts to build FE models to predict the magnetization pattern of a permanent magnet by simulating magnetizing process. The actual magnet samples were prepared which were magnetized in the magnetizing fixture under the same magnetizing conditions as those used in the FE models. The accuracy of the prediction was verified by measuring the BEMF profiles of the prototype motors.; Parametric study on magnetizing fixtures was made with focus on the effects of the permeability and electrical resistivity of steel on magnetization patterns. It was shown that the effect of the induced current must be included in the magnetization pattern prediction program to increase the accuracy of prediction. The results show that the permeability of steel affects not only the intensity of the magnetizing field set up by the applied current but also the induced current which comes from the time rate of change of the magnetic field passing through the conductor in the fixture.; The magnetization pattern of a permanent magnet in a brushless DC motor also affects the unbalanced magnetic forces acting on the rotor, which are sources of vibration. Two different magnetization patterns were implemented in a FE model to estimate the unbalanced magnetic forces. The unbalanced magnetic forces were computed for both static and dynamic eccentric cases and the results show that different magnetization patterns also produce different unbalanced magnetic forces in both static and dynamic eccentricity cases. (Abstract shortened by UMI.)