Mathematical Modeling of a Linear-Induction Motor Based on Detailed Equivalent Circuits

Abstract

Electric drives based on traction linear-induction motors are used in industry and city transport. The main advantages of this electric drive are unrestricted acceleration and vehicle climbing angles, as well as ecological cleanliness. The development of high-speed design and analysis software tools for linear electric motors is thus becoming quite timely. The use of the finite-element method for solving field problems in a three-dimensional setting and dynamic vehicle-operation regimes is time-consuming. It is proposed to use a detailed magnetic equivalent circuit of a linear-induction-motor longitudinal section with the introduction of the Bolton coefficient to correct for the transverse-edge effect in a solid secondary element. Model features based on multilayer magnetic equivalent circuits are shown, and the effect of the number of layers on the designed motor-traction force is evaluated. When selecting an appropriate pole pitch-to motor gap ratio, a two-level equivalent circuit turns out to be suitable. The secondary element is represented in the model as a set of rectangular rods connected in parallel. The influence of the calculation method of the secondary rods’ motional EMF on the motor-traction-force accuracy is shown. The greatest error is observed in a low-slip region (when the motor passes into a generative braking regime) and the simplest spatial derivative of the magnetic flux. When the derivative calculation formula becomes more complicated, the indicated error sharply decreases. Another way to reduce the calculation error of the motional EMF in the secondary element circuit is to increase the number of these circuits by decreasing the width of the elementary rod. The prominence of the detailed magnetic equivalent-circuit method and convenience of online viewing should be noted.