Design And Analysis Of High-power Brushless DC Motors

With the dramatic improvement of power electronics, permanent-magnet materials, micro-processor, modern control theory, electrical machinery theory and other relational science and technology, the brushless dc motors (BDCM) has taken great development, and been applied in kinds of driven and servo-control system. The successful application in the drive system of capital ship in foreign countries has proved the feasibility of the high-power BDCM. In domestic, the medium or low power BDCM is manufactured on a large scale, while the development effort on the high-power BDCM drive is still preliminary. In this subject, two brushless dc motors were developed for the research and development of the high-power BDCM. The modeling and design analysis of the samples are presented in this paper. Firstly, considering the winding inductance, the model of a brushless dc motor with three-phase Y-connected windings in six-state operate mode was founded, based on the analysis of the phase commutation. And the relationship between the torque constant and back-EFM constant, the speed-torque characteristic and the armature equivalent resistance of brushless dc motors was researched by simulation technique. The existence of phase winding inductance has a great impact on them, accordingly it cann't be neglected in the design analysis of high-power brushless dc motors. As a special electromechanical integrated product, the design of BDCM cann't follows the conventional design method directly. Three methods of designing BDCM are summarized and compared with each other, and a field-circuit coupled method is brought forward, which uses the finite-element method (FEM) to get the parameters that the equivalent magnetic circuit method required for the accuracy in computing the no-load characteristic, and predicts load characteristic with FEM. Then, the computer aided design software is introduced. The field-circuit coupled method was employed to predict the performance of the samples, and the comparison with the experimental results validated the proposed method. At last, the armature-reaction of the samples is analyzed. The armature-reaction distorts the gap flux density distribution, and that distortion may result in magnetic saturation, so it plays a primary part in the effect on the performance of BDCM. Methods should be taken to weaken the q-axis armature reaction in the design of high-power BDCM.