Design Optimization of a High Torque Density Halbach Array Axial Flux Brushless Permanent Magnet Machines

Abstract

It has been a grand challenge to design the permanent magnet (PM) machine with high torque, high power density. Halbach array, axial flux PM machines arc the representative design for reaching the goal. With afore­mentioned methodologies, however, the cogging torque which proportionally increased with increasing torque density was a major drawback to the performance of the PM machines. Many previous studies have been investigated to reduce the cogging torque, but were limited on the radial flux PM machines and rotors designed with alternative polarity arrangement which has an identical topology as commercial motors. Due to the different topology and the backEMF shape, however, the conventional methodologies for cogging torque reduction are ineffectual to be applied on Halbach array axial flux PM machines, which has significantly high torque density. To address this drawback, this paper suggests an optimal design methodology to reduce cogging torque in Halbach array axial flux PM machine. The methodology was verified through a finite element analysis, and confirmed that the cogging torque, which accounted for 0.2927 Nm of the non-skewed PM machine, decreased to 0.0347 Nm, which corresponds to 88.15 %.