Analytical study on the cogging torque in surface-mounted PM machines; effect of armature notches and PM segments

This paper presents the cogging torque calculation in radial-flux surface-mounted permanent-magnet machines based on energy approach, air-gap flux density and permeance functions. Magnet segmentation and teeth notching are two important techniques in reducing the cogging torque, so in this paper an analytical approach is investigated to model these effects on the produced cogging torque. This approach employs new methods to model the teeth notch and PM segments based on Fourier expansion and simplified flux distribution. The analysis results and comparisons verify the validity of the model that has advantages in sensitivity analysis and structure optimizations of surface-mounted permanent-magnet machines from the aspect of cogging torque. This model could be extended for other types of PM electrical machines.