Investigation of Forces in Linear Induction Motor Under Different Slip Frequency for Low-Speed Maglev Application

The linear induction motor (LIM) applied in low-speed Maglev train produces not only the thrust force to drive the train, but also the normal force that affects the levitation system. Three finite element models are employed to investigate the influence of transverse edge effect, longitudinal end effect, transverse edge shape of secondary aluminum plate and its temperature, etc., on the force performance under different slip frequency. For the transverse edge effect, a precise correction factor is proved to be more suitable than the common Russell and Norsworthy's factor. An analytical method using an equivalent circuit model is improved based on an existing model for nonferromagnetic secondary LIM. The amendments account for the primary iron loss, the eddy current of secondary back iron, and the calculation of normal force. Based on this equivalent circuit model, the performance curves of thrust force, normal force, efficiency, and power factor against the train velocity are obtained for given slip frequency and thrust force. The influences of transverse edge, longitudinal end, and air gap length are also investigated. Analytically predicted results are validated by finite element models and measurements.