An Advanced Equivalent Circuit Model for Linear Induction Motors

In this paper, a distribution function to model the longitudinal end effect for the linear induction motors is developed to predict the variation of the air-gap flux distribution with the slip. The classic equivalent circuit model presented by Duncan is improved by taking the air-gap flux distribution function into account. First, the longitudinal air-gap flux and secondary demagnetizing current distribution function based on the travelling wave theory are proposed to describe the variation of the distributions. Second, an extra magnetizing branch, which takes the output power losses due to the longitudinal end effect into account, is connected in parallel with the existing magnetizing branch of the T-type circuit. Then, two coefficients used for correcting the magnetizing inductance and secondary resistance in the equivalent circuit are obtained. Third, the thrust and vertical force are calculated and compared with the existing model, as well as the efficiency and power factor in a range of rated speed is presented. Finally, these calculated results are validated by measurements on an experimental rig of the linear induction motor.