In this paper, two main kinds of the secondary, i.e., the solid and laminated back iron secondary, are applied in linear metro, as well as electromagnetic forces and secondary losses of the single-sided linear induction motor (SLIM) with different secondary are calculated by the finite-element method (FEM). First, in solving region, the fundamental equations of the magnetic field with eddy currents in the secondary are deduced, and specific boundary conditions for each part of SLIMs are given. Equations of the secondary loss and efficiency are presented. Second, 120-kW SLIMs with two types of the secondary for metro are calculated by the three-dimensional FEM, respectively. The efficiency and secondary loss are analyzed for different numbers of the lamination in the secondary back iron. The optimal number of the back iron lamination is then obtained. Third, considering the influence of the end and edge effect, the air gap flux density with different secondaries is calculated. Then, the thrust and vertical force are analyzed for SLIMs with two kinds of the secondary. Finally, numerical results of the efficiency, thrust, and vertical force, which are obtained from different secondaries, are experimentally validated by measurement on the test rig of the SLIM.

In order to improve the performance of linear induction motors for urban rail transit, the ladder-slit secondary is designed, and the performance of linear induction motors with the ladder-slit and flat-solid secondary is calculated and compared. First, for the ladder-slit secondary, the slot combination, widths of the secondary conductor, and side bar are designed. Second, the finite-element model of the linear induction motor with the ladder-slit secondary is developed, and the influence of vertical forces on widths of secondary conductors is presented. Third, the eddy current and the transversal air-gap flux density are compared when the ladder-slit and flat-solid secondaries are applied, respectively. Finally, experiments are carried out by test lines to validate the calculated results of the force and efficiency. It shows that the ladder-slit secondary can reduce the edge effect and improve the performance.

Propulsion, levitation, and guidance (PLG) are the main technologies of high-speed maglev system. A linear synchronous motor (LSM) integrated with PLG is presented, which can simultaneously realize the three functions of the maglev system by only one electromagnetic system. A novel bilateral Fourier decomposition method for analyzing the 3-D force characteristics of the LSM is proposed, which has the advantages of wider range of solutions, simpler formulation, shorter computation times, and satisfactory precision. First, the topological structure of the LSM is introduced, and the 3-D magnetic field generated by the secondary superconducting (SC) coil is calculated. Second, the primary current of the combined coil is decoupled into PLG current, and then, the analytical expressions of forces generated by three currents are obtained. Finally, the 3-D force characteristics of the LSM at different running speeds, different suspension heights, and lateral offset of the maglev are calculated, and the correctness of the theory is verified by the publicly measured data on the Yamanashi line. The results obtained by the bilateral Fourier decomposition method provide a certain reference value for the LSM integrated with PLG in the initial stage of electromagnetic design.

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.

Propulsion, levitation, and guidance (PLG) are the key technologies of high-speed maglev system. A linear synchronous motor (LSM) combined with PLG is presented, which can simultaneously realize the three functions of PLG. A novel analytical method for analyzing the 3-D electromagnetic forces of the LSM is proposed. First, the overall structure and operating principle of the high-speed maglev system are discussed. Second, the 3-D analytical model of the LSM is proposed, and the analytical expressions of propulsion force, levitation force, and guidance force are obtained according to the change in the system magnetic field energy during the operation of the maglev train. Finally, the 3-D force characteristics of LSM under different operating conditions of maglev train are calculated and simulated, and the correctness of the 3-D analytical model is verified by the publicly measured data on the Yamanashi line.

Electromagnetic characteristics of single-sided linear induction motors (SLIMs) will be changed when the primary is displaced sideways from the symmetrical position in the metro. The transverse force will be produced, and edge effect will increase. In order to reduce the influence of the transverse force on the stability of the vehicle guidance system, the construction of the ladder-slit secondary, which consists of the slit aluminum and solid back-iron plates, is proposed and analyzed. A 3-D finite-element model (FEM) of the linear induction motor with the ladder-slit secondary is developed. With the different transverse displacements, the air-gap flux density, eddy currents, and forces are calculated and compared with the linear induction motor with the flat-solid secondary. It shows that the ladder-slit secondary can reduce the transverse force and edge effect, as well as is a good method to achieve the transversal stabilization of the rail vehicle.