Performance and Design Comparison of Coreless Axial Flux Permanent Magnet Machines With Different Typical Rotor Optimizations

In this article, two typical topology optimizations of rotors, improving pole embrace of surface PMs and employing Halbach array PMs, are applied in coreless axial flux permanent magnet (AFPM) machines with printed circuit board (PCB) stators to improve the air gap flux density. Firstly, the sensitivity analysis of geometrical parameters in these structures to the key electromagnetic design and performance are discussed, including rotor thickness, current density, back electromotive force (EMF) and torque characteristics, as well as winding eddy current loss. A hybrid calculation method of analytical expression and three-dimensional (3D) magnetostatic simulation is adopted to replace a portion of transient 3D finite element analysis (FEA). Then, a comprehensive comparison of several potential rotor topologies is performed. Based on the results, the optimization suggestions from various performance and design perspectives are given, e.g., the optimization of pole embrace may be more valuable than that of dual-segmented Halbach arrays due to an overall consideration of efficiency at high frequency, PM consumption, THD, and torque per unit PM mass. Finally, a prototype is manufactured and tested to validate the calculation results.