A Novel Technique on the Analytical Calculation of Open-Circuit Flux Density Distribution in Brushless Permanent-Magnet Motor

Both the cogging and electromagnetic torques depends on the shape of the flux density distribution in the airgap region. A two-dimensional (2-D) analytical method for predicting the open- circuit airgap field distribution in brushless permanent magnet motors, considering the direction of magnetization, i.e., radial or parallel, and the effect of real shape of stator slot-openings is presented in this paper. It involves the solution of the governing field equations in polar coordinates in airgap and magnet regions. This method uses a new 2-D relative permeance function. For the comparison purposes, a 2-D finite element (FE) analysis is used for the analysis of a fully-pitched, double-layer windings brushless permanent-magnet (PM) drive. The results obtained by this method are very close to those obtained by FE analysis especially at the corner tips of the tooth.