A Comprehensive Review of Cogging Torque Reduction Strategies in Axial-Field Flux-Switching Permanent-Magnet Machines

Axial-field flux-switching permanent-magnet machine (AFFSPMM) is an outstanding topology for sustainable applications. This structure encompasses several advantageous features, including compact volume, high power and torque density, worthy rigidity, and a separate assembly. These attributes have rendered this type of machine an optimal choice for the mentioned purpose as well as electric transportation. The use of a permanent magnet (PM) in this type of machine can lead to the production of cogging torque (COT), which is due to the saliency of the stator and rotor parts. This phenomenon has led to concerns among machine researchers and designers regarding the presence of noise, vibration, torque ripple, and speed fluctuations. This drawback can be mitigated either in design and structural considerations or in control and excitation methods. The complexity and commercial concerns are the main motives for focusing on the machine parts modification rather than the control aspects. In this paper, first, a brief statement of the design procedure, the essence of COT, and the problem statement are introduced. An in-depth review of various design strategies aimed at reducing COT is then presented. Consequently, a comprehensive comparison is presented, including an evaluation of the advantages, disadvantages, cost, complexity, and other relevant factors, to help researchers, designers, and manufacturers select the most appropriate strategies for each application considering the requirements. The review not only involves the key achievements of the topologies but also provides insight into the methodologies where the Finite Element Method (FEM) and experimental results authenticate the effectiveness. Indeed, the IEEE standard 1812-2023 considered to measure COT in both dynamic and static modes.