Mitigation of cogging torque in transverse-flux permanent-magnet machines with flux concentrators by step skewing of stator pole

Abstract

The objective of this article is to study how the stator step skewing method can lead to the reduction of the cogging torque of a transverse-flux permanent-magnet (TFPM) machine with flux concentrators. Three structures are analysed and compared in terms of their influence of the skewed displacement on the cogging torque using the three-dimensional finite element method (3D-FEM). Thereafter, to validate the FEM results, cogging torque is calculated by applying a Schwarz-Christoffel (SC) conformal mapping. To apply this transformation, the 3D TFPM generator structure with axially magnetised permanent magnets (PMs) is converted into a 2D structure with radially magnetised PMs and the cogging torque of the machine is predicted using both the analytical method and 3D-FEM. The accuracy of the approach is demonstrated by the adequate agreement between the results obtained through this SC mapping and those of the 3D-FEM. In addition, two 100 W prototyped TFPM machines are designed, simulated, manufactured and tested to validate the effects of the step-skewed stator yoke on the predicted cogging torque and back-EMF. © The Institution of Engineering and Technology 2020