Semi-analytical model for triangular skewed permanent magnet axial flux machine

Various design techniques are available for cogging torque reduction of permanent magnet radial flux machines. Most of them are applicable for axial flux permanent magnet machines. Due to the manufacturing ease of magnet for axial machine, additional freedom of magnet shaping for cogging reduction can be exploited. To achieve the reduction of the cogging torque, the magnet pole is varied from inner radius to outer radius, which results a shape of triangular magnet. In this paper, semi-analytical analysis for field solution is developed. The field solution is achieved by combining multi slice method and sub domain magnetic field analysis approach. Four different types of semi closed slots viz. parallel slots with parallel openings, parallel slots with trapezoidal openings, trapezoidal slots with parallel openings, and trapezoidal slots with trapezoidal openings are used for cogging torque investigation. The analytically obtained solution is validated with finite element analysis (FEA). It is found that the influence of slot's opening shape dominates on shape of slots.