Selecting Method for Number of Slots and Poles in Brushless Direct Current Motor

Abstract

Cogging torque is produced by the magnetic interaction between the stator core and the permanent magnet attached to the rotor. If we use the fractional slot winding, we can decrease cogging torque. In this paper, we propose a method to select number of poles and number of slots reasonably so as to satisfy the three technical requirements (the number of slots of unit winding per phase must be integer, the three-phase symmetric situation must be satisfied, the number of slots per pole per phase must be larger than 0.25.) and two economical requirements (coil pitch factor must be larger than 0.5, winding factor must be larger than 0.85.) of Brushless DC motor. We also propose a method to select a number of poles and a number of slots so that the goodness coefficient is small and the periodic coefficient is large to decrease cogging torque.