Electromagnetic Analysis Of Brushless Dc Permanent Magnet Motor

The DC brushless permanent motor is a new kind of motor, which finds its wide applications with development of the power electronics technology. Being keep good starting performance and speed regulation performance of the conventional DC motor, it avoids the noise and spark caused by the mechanical commutation. Because the DC brushless permanent motor is of obvious advantages in operating performance and particular structure, it is significant to perform research on the motor. Based on the known research experience, the analytical method and the finite element method are applied to calculate parameters and analyze operating performance of the DC brushless permanent motor. Therefore, the comparative ideal results are obtained.In process of parameter calculation and performance prediction of the DC brushless permanent motor, the mathematic model of permanent-magnets is set up and the expression for air-gap magnetic flux density is deduced under the uniform air-gap assumption. The relative permeance factor is yield by means of Schwarz-Christoffel transformation, which is the basis for calculating no-load air-gap magnetic flux density and back electromotive force in the DC brushless permanent motor with tooth-slot effect consideration. The analytical method is easy to use and clear for expression, but the calculation accuracy is affected by the assumptions that are made on the ideal model instead of the actual structure of the motor.The finite element method, based on actual model of the motor, can consider rotor and stator core's saturated magnetic property, stator slot shape and nonlinear demagnetize curve of the permanent magnet, consequently, it gives more accurate results than the analytical method. The permanent magnet and motor's models are established by the finite element method, which are used to calculate the air-gap magnetic density and the winding inductance of the DC brushless permanent motor. For calculating the back electromotive force, the border-sliding method is performed to avoid meshing the model each time and simplify the calculation process.Since the torque ripple is an inherent phenomenon in operating process of the DC brushless permanent motor, it is necessary to improve operating performance by decreasing or eliminating the torque ripple. Based on previous research results, the reasons to generate the torque ripple are detected and some formulas are deduced in detail. Several measures are put forward to decrease the torque ripple, which carry out analysis and calculation by the finite element method. The calculated results validate correctness of the presented methods.