表貼式永磁直流無刷電動機的初步設計與齒槽轉矩研究

Abstract

直流無刷電動機（Brushless Direct Current Motor，BLDCM）由於具有體積小、 效率高、維護方便、以及調速性能好等諸多優點而越來越受到人們的關注。由於BLDCM採用永磁體勵磁，永磁體和有槽電樞鐵芯相互作用會產生齒槽轉矩。這是由於永磁電機本身的齒槽物理結構產生的一種轉矩，即使永磁電機的繞組不通電也會產生這種轉矩。齒槽轉矩會使電機出現轉矩波動，進而產生振動和雜訊，使電機不能平穩運行，影響電機的性能。因此，研究削弱BLDCM的齒槽轉矩的方法具有十分重要的意義。 本論文首先介紹了BLDCM的研究現狀，對現階段國內外有關齒槽轉矩削弱方法的研究現狀進行概述。詳細介紹了BLDCM的基本結構及工作原理，通過理論推導得到BLDCM的數學模型以及工作特性曲線。 然後，對齒槽轉矩產生的機理進行了圖解分析，並詳細介紹了齒槽轉矩的四種主要分析方法：磁通-磁動勢繪圖法、能量法、Maxwell張量法以及有限元分析法。其中重點介紹了基於能量法和傅立葉分解的齒槽轉矩運算式的推導過程。 其次，介紹了 BLDCM的常用設計方法等效磁路法，探討電機本體電磁參數設計流程，以電磁參數設計理論為基礎，設計了一台額定電壓 24V、額定功率 30W、額定轉速 1350rpm連續運行的 BLDCM，並用ANSYS Maxwell設計軟體驗證了設計結果的合理性。 再次，介紹電磁場分析常用的分析方法:有限元法，對ANSYS Maxwell有限元分析軟體進行簡要介紹。以基於能量法和傅立葉分解推導得到的齒槽轉矩運算式為基礎，首先從理論上探討定子槽口寬度，永磁體極弧係數，極數和槽數的配合等七個方面對電機齒槽轉矩的影響規律。然後把每一種方法應用到本文設計的12槽10極電機，利用ANSYS Maxwell軟體，進行了模擬，驗證了每一種方法的正確性。 最後，介紹了參數優化的重要方法遺傳演算法，並利用ANSYS Maxwell自有的遺傳演算法分析模組，進行了槽口寬度，極弧係數，磁極厚度組合參數優化，結果表明組合參數優化可以較大程度降低齒槽轉矩。

The Brushless Direct Current Motor(BLDCM) has attracted more and more attention because of its advantages such as small size, high efficiency, easy maintenance, and good speed performance. Because the BLDCM uses permanent magnet excitation, the interaction between the rotor magnets and the stator teeth of the machines will produce cogging torque. It is a kind of torque that is caused because of its own structure. It will be generated even when there is no armature current. Cogging torque will cause parasitic ripples which further leads to mechanical vibration and acoustic noise. In addition, it has a certain influence on the accuracy and performance of the speed control system and position control system. Therefore, it is of great significance to study methods to mitigate the cogging torque of BLDCM. Firstly, this thesis introduces the research status of BLDCM, and summarizes the current research situation of the cogging torque weakening method at home and abroad. The basic structure and operating principles of BLDCM are introduced in detail. The mathematical model and operating characteristic curve of the motor are obtained by theoretical deduction. Secondly, the mechanism of the generation of cogging torque is analyzed by diagrams, and four main analysis methods of cogging torque are introduced, they are Flux-MMF graph method, energy method, Maxwell tensor method and FEA method. The derivation of cogging torque expression based on energy method and Fourier transform is especially introduced. Thirdly, the principle and characteristic of equivalent magnetic circuit method is introduced. The design process of electromagnetic parameters of motor is studied. On the basis of the electromagnetic p arameters design theory of BLDCM, a continuous operation BLDCM, which rated power is 30W, rated voltage is 24V, rated speed is 1350rpm, is designed. The rationality of the design result is verified with the ANSYS Maxwell design software. Fourthly, the commonly used finite element method for electromagnetic field analysis is introduced, and the finite element analysis software ANSYS Maxwell is briefly introduced. Based on the expressions of the cogging torque deduced from the energy method and the Fourier transform. This paper first discusses the influence law of seven aspects including the stator slot width, permanent magnet pole arc coefficient, slots per pole in theory. Then each method is applied to the 12 slot 10 pole motor designed in this paper. The simulation is carried out by using ANSYS Maxwell software, and the correctness of each method is verified. Finally, an important parameter optimization method called genetic algorithm is introduced. Using ANSYS Maxwell genetic algorithm analysis module, the combination parameters of the slot width, pole arc coefficient and magnetic pole thickness is optimized. The results show that the combined parameter optimization can greatly reduce the cogging torque.