Cogging torque in slotless permanent magnet machines

Abstract

Slotless permanent magnet machines theoretically do not produce any cogging torque, provided the stator inner surface reluctance remains unchanged. However, a cogging torque may occur due to a change in the electromagnetic design following material cost reduction in the manufacturing process. When the electromagnetic design is changed to reduce the waste in the manufacturing process (stamping of the laminations) by dividing the stator toroidal ferromagnetic core into two equal parts, gluing them together introduces a very small non magnetic gap between them, which affects the stored magnetic energy along the circumference and consequently gives rise to occurrence of a cogging torque. Using the finite element method its value is analyzed analytically and verified by a laboratory measurement. Results of our work, presented in this paper, will help scientists and engineers to understand and avoid the causes for the occurrence of the cogging torque in designing slotless permanent magnet machines, where the design itself is subjected to the manufacturing process.

Parametric Analysis for Performance Optimization of Line-Start Synchronous Motor with Interior Asymmetric Permanent Magnet Array Rotor Topology

“…In other analyzed operating points during motor acceleration, the demagnetization of magnets should not occur. The numerical model allows magnetic flux density distribution to be calculated in the motor cross-section by the aid of Finite Elements Method (FEM) thus allowing parts of the magnetic core with high flux density to be detected [22][23][24]. Another aspect of analysis of the models is the transient characteristics where the motor behavior in transient regimes such as start-up can be analyzed [25,26].…”

Optimization of cogging torque in outer rotor Permanent Magnet Synchronous Motors based on particle swarm algorithm

“…Effective reduction can be achieved through techniques like stator inclined slot and rotor inclined pole, once the pole-slot ratio is fixed, aiming to lessen torque ripple during operation [5] . However, these methods often demand high manufacturing precision, affecting large-scale applicability or adversely impacting motor performance and electromagnetic force balance, which outweigh their benefits [6][7][8][9][10] .…”