Bs. Rahman et Dk. Lieu, OPTIMIZATION OF MAGNETIC-POLE GEOMETRY FOR FIELD HARMONIC CONTROL IN ELECTRIC MOTORS, Journal of vibration and acoustics, 116(2), 1994, pp. 173-178
A principal source of vibration in permanent magnet motors and generat
ors is the induced stress from the rotating permanent magnets. The har
monic content of this forcing function may excite resonant modes of vi
bration in the motor or surrounding structure. Thus attenuation of spe
cific harmonics is of considerable interest. This paper describes a me
thod for optimal shaping of the permanent magnets to eliminate one or
more of these harmonics. The analytical model for an optimized 4-pole
motor consisted of segmented PMs and a solid ring stator. The permanen
t magnets were modeled as a number of thin radially cut annular layers
with specific sector angles. Changing the shape of the PMs resulted i
n a different flux density field and thus a different frequency spectr
um of the forcing function. Attenuation of specified higher harmonics
could be achieved at the expense of increasing other harmonics. For a
4-pole motor, the optimization algorithm was fairly successful at elim
inating any one of the 8th, 12th or 16th harmonics. The algorithm used
was developed to solve combinatorial optimization problems, and drew
heavily upon principles from statistical mechanics. The final pole geo
metry is dependent upon the choice of the cost function used in the op
timization algorithm.