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Since the linear induction motor for urban transit usually works with a magnetically saturated secondary back-iron, this paper presents an analytical method to consider the nonlinear phenomena, e.g. ferromagnetic saturation and hysteresis. By solving for the qusi-3D field distribution in the air-gap and in the secondary plate, the magnetizing reactance and secondary impedance are determined. The saturable characteristics in the secondary back-iron, together with the hysteresis, the skin effect, the induced secondary eddy currents, and both transversal and longitudinal end effects are taken into account. Calculations for motoring and for generating operation under constant-current conditions are compared with experimental results, and good agreement is obtained. The analysis is valid over a wide range of operating conditions, and its calculation accuracy is distinctly better than those without considering the nonlinearity.

linear induction motors， saturation， hysteresis， 3D analytical method