Analytical modeling of cogging torque of single-phase brushless DC motor with gradient airgap structure

Accurate calculation of cogging torque is the basis for solving the dead point problem in the start-up of single-phase brushless DC motor. Aiming at the problem of cumbersome and time-consuming finite element modeling of single-phase brushless DC motor, an analytical model of the cogging torque of single-phase brushless DC motor with gradient airgap structure was established. Firstly, the analytical expression for the airgap flux density with the gradient airgap structure was derived. Then, the energy method was employed to derive the analytical expression for the cogging torque. Subsequently, the airgap flux density and the effective airgap length function were simplified and Fourier decomposed. Finally, the analytical model for the cogging torque was obtained. The analytical model of cogging torque was calculated by the adaptive multi-segment trapezoidal algorithm to avoid the problem of poor generalization and low prediction accuracy caused by the ambiguous physical meaning of the variables in the traditional model. The analytical results of the cogging torque under the gradient airgap structure were compared with the finite element results, and the over-zero offset angle and peak value were analyzed to verify correctness of the established analytical model of cogging torque. The analytical model can be solved quickly and accurately by computer programming, and the variables in the model are related to the motor structure with clear physical meanings, which makes it easy for the designers to search for the laws between the variables when optimizing the cogging torque. © 2024 Editorial Department of Electric Machines and Control. All rights reserved.