Investigation of Additional Radial Air Gaps on Cogging Torque in Modular Permanent Magnet Machines Based on Taguchi Method

This paper investigates the influence of randomly distributed additional air gaps (AAGs) between stator teeth and back-iron on cogging torque in 12-slot/10-pole modular permanent magnet machines by using Taguchi method. It has been observed that with uniform AAGs, a maximum cogging torque exists, while non-uniform AAGs significantly affect cogging torque, particularly resulting in the worst-case scenario with the highest cogging torque due to random non-uniform AAG distributions. In comparing uniform and non-uniform AAGs, two key findings are: (a) main harmonic order of pole number of cogging torque in non-uniform AAGs is much lower than that of least common multiple of slot and pole numbers in uniform AAGs; (b) amplitude of cogging torque in non-uniform AAGs is much higher than that in uniform AAGs. Hence, special attention should be paid to controlling non-uniform AAGs in mass production. The correctness of the results is validated by experiments based on the prototype in mass production.