Analytical Magnetic Field Calculation of Slotted Brushless Permanent-Magnet Machines With Surface Inset Magnets

This paper presents an analytical magnetic field calculation for slotted brushless permanent-magnet (PM) machines equipped with surface inset magnets. The analytical expressions can be used to calculate both open-circuit and armature reaction field distributions. Although the expressions can be used for brushless PM machines with any magnetization pattern, the results of the open-circuit magnetic field are presented for three different magnetization patterns: radial, parallel, and Halbach. Different winding structures, such as overlapping, nonoverlapping with all teeth wound and nonoverlapping with alternate teeth wound, can be considered to compute the armature reaction field distribution. The analytical expressions can be used for the surface inset magnet structure with airspace between the magnets and the iron interpoles but they cannot be used in the case of brushless machines with surface mounted magnets. The calculations account for slotting and slot-opening effects via the subdomain technique. The analytical results for a four-pole, six-slot brushless PM machine with three magnetization patterns and nonoverlapping winding are presented and evaluated by comparing them with those obtained from the finite element method.