Influence of the Coil Pitch and the Slot/Pole Number Combination upon the Performance of Permanent Magnet Motors

This paper presents a mathematical investigation of the influence of the slot/pole number combination on the iron loss of permanent magnet (PM) motors. A simplified electromagnetic model of PM motors was used to develop a mathematical method of evaluating iron loss for any combination of slots and pole pairs. An investigation of the magnetomotive force distribution of stator teeth and its expression as a complex Fourier series expansion revealed that the coordinate system can be easily transformed, thereby enabling rotor iron loss to be calculated. A core factor was defined on the basis of the calculated iron losses and a map of slot/pole number combinations was created. Several promising combinations were selected from the map and their respective advantages and disadvantages were identified. A new promising combination was found featuring windings with a coil pitch of two slots. It is noteworthy that this slot/pole number combination has characteristics in-between concentrated windings and distributed windings.