Design of Slotless BLDC Motor for Eliminating Cogging Torque

Design of a cogging torque free motor is presented in this paper. Cogging torque is a disturbing phenomenon in electrical machines that causes certain problems in performance of them. This unwanted component in output torque could be reduced or eliminated by some methods i.e. skewing the stator slot, skewing the permanent magnets (PMs) of rotor, employing fractional pitch winding and building slotless motor. In this paper, firstly these ethods are discussed and then the effect of skewing PMs is investigated which is distinguished by a design parameter i.e. offset. After that, slotless structure of a brushless DC motor (BLDC) is considered. In a slotless BLDC motor, cogging torque would be eliminated and there is no major component of cogging torque in slotless structure of a BLDC motor. These types of motors are very convenient due to excellent features such as zero-cogging torque, minimal vibration, high speed capability, excellent power-to-weight ratio, compact design, light weight and etc. At the end, finite element analysis (FEA) is employed to validate the topics.