For the long-primary double-sided linear induction motor (LP-DSLIM) excited by the symmetrical current, there are double slip frequency ripple in the thrust due to the dynamic longitudinal end effect. The expression of thrust ripple fluctuation caused by the dynamic longitudinal end effect are deduced firstly. Secondly, the method of suppressing the injected harmonic current is adopted, the expression of each part of thrust after injection are deduced and its characteristics are analyzed, from which the feasibility of this method to reduce the thrust ripple is illustrated. Finally, finite element simulation and experiment results indicate that the thrust ripple is significantly reduced after the injection of the harmonic current.

In order to improve the thrust density and efficiency of linear induction motors (LIM) in large load transport situations, a cross-shaped linear induction motors (CSLIM) structure is proposed in this paper. Firstly, for analyzing the characteristics of CSLIM, the magnetic field and electromagnetic thrust expression of long primary double-sided linear induction motors (LP-DSLIM) when considering the saturation of iron core are deduced, based on which the effect of iron saturation on electromagnetic thrust is analyzed. Secondary, the equivalent circuit of CSLIM is proposed and the effect of coupling on the electromagnetic thrust is analyzed. The results show that, the maximum electromagnetic thrust is reduced and the corresponding slip frequency is increased when iron saturation and coupling. For improving the problem of iron core saturation and coupling of CSLIM, a structure with square-type iron and lap winding is further proposed, and the rationality of CSLIM structure is verified by comparing the finite element simulation results of flux density on core, eddy current on secondary and the electromagnetic thrust.

For the permanent magnet linear synchronous motors (PMLSM) with high-speed and large-thrust under the periodic transient conditions, the corresponding length and cost requirements are large. This paper designs a toroidal long primary PMLSM. In order to analyze the characteristics of the motor, the expressions of the electromagnetic force and the air-gap magnetic flux density are derived, then the finite element comparison analysis is performed for the linear structure and the toroidal structure of the PMLSM. The results indicate that the space occupied by the toroidal structure is reduced greatly under the same performance index, the required power level has obvious advantages, and the acceleration and braking time are not limited by the stroke. The structure of toroidal PMLSM is further optimized so as to suppress the thrust fluctuation, the comparison of air-gap flux density and electromagnetic force finite element simulation results verifies the validity of the structural optimization.

In order to improve the thrust density and efficiency of linear induction motors (LIMs) in large load transport situations, a cross-shaped LIM (CSLIM) structure is proposed in this article. The equivalent circuit of CSLIM is built. Based on that, the electromagnetic thrust expressions are deduced, and the expressions for parameters of equivalent circuits are given. The relationship between the coupling characteristics of the secondary inductive eddy current and the condition of the motor is analyzed. Finally, the simulation results verify the validity and superiority of the proposed analysis.