An Investigation on Asymmetry Effects in Linear Induction Machines

Linear Induction Machines (LIM) present advantages in a broad range of applications such as military, transportation, and automotive products. The asymmetry effects influence the performance of LIM under motoring and generating conditions significantly. This means that one can not use the force characteristic under motoring to predict the performance under generating mode of operation. This must be taken into account in the control scheme of LIM. The present electromagnetic investigation shows that under field oriented control, Iq (quadrature axis current) illustrates asymmetric magnetization response. Furthermore, the asymmetric magnetization performance can cause asymmetric thrust force and normal force characteristics. However, Id (direct axis current) displays a symmetric response. Furthermore, the origin of the asymmetry effects is explained using the spatial distribution of the magnetomotive force which is influenced by relative positioning of three phase excitation windings during motoring and generating.