An analytical method for predicting cogging forces in linear induction motors

Cogging in a linear machine can be described as a

variation in the magnetic forces as the machine travels

along its linear uis. This effect can have a severe impact on

the overall precision and even stability of the linear uis. In

this paper an analytical method to predict the cogging

forces in Linear Induction Moton (LIMs) is presented. An

aecurate estimation of cogging is useful during the LIM

design stage to help millimize this performance limiting

factor. One common method used to predict cogging

torques in rotary induction moton is the tooth overlap

method. Due to the complexity of slot fringing effects in

slotted cores, and the fact that fringing effects significantly

influence the accuracy of this method, many researchers

alJo use Carter and Green coefficients to increase accuracy.

However, this approach does not accurately translate to the

linear motor case. In this paper an estimation of the

magnetic flux path (based on FEM simulations) is used,

along with the gradient ofthe magnetic energy stored in the

air gap, to predict the cogging forces in an LIM. The

aecuracy of this prediction method is also verified

experimentally through a cogging force analysis on a simple

one-tooth test-bed.